Molecular Mechanisms of Sorbed Ion Effects during Boehmite Particle Aggregation

Classical theories of particle aggregation, such as Derjaguin-Landau-Verwey-Overbeek (DLVO), do not explain recent observations of ion-specific effects or the complex concentration dependence for aggregation. Thus, here, we probe the molecular mechanisms by which selected alkali nitrate ions (Na+, K+, and NO3-) influence aggregation of the mineral boehmite (γ-AlOOH) nanoparticles. Nanoparticle aggregation was analyzed using classical molecular dynamics (CMD) simulations coupled with the metadynamics rare event approach for stoichiometric surface terminations of two boehmite crystal faces. Calculated free energy landscapes reveal how electrolyte ions alter aggregation on different crystal faces relative to pure water. Consistent with experimental observations, we find that adding an electrolyte significantly reduces the energy barrier for particle aggregation (∼3-4×). However, in this work, we show this is due to the ions disrupting interstitial water networks, and that aggregation between stoichiometric (010) basal-basal surfaces is more favorable than between (001) edge-edge surfaces (∼5-6×) due to the higher interfacial water densities on edge surfaces. The interfacial distances in the interlayer between aggregated particles with electrolytes (∼5-10 Å) are larger than those in pure water (a few Ångströms). Together, aggregation/disaggregation in salt solutions is predicted to be more reversible due to these lower energy barriers, but there is uncertainty on the magnitudes of the energies that lead to aggregation at the molecular scale. By analyzing the peak water densities of the first monolayer of interstitial water as a proxy for solvent ordering, we find that the extent of solvent ordering likely determines the structures of aggregated states as well as the energy barriers to move between them. The results suggest a path for developing a molecular-level basis to predict the synergies between ions and crystal faces that facilitate aggregation under given solution conditions. Such fundamental understanding could be applied extensively to the aggregation and precipitation utilization in the biological, pharmaceutical, materials design, environmental remediation, and geological regimes.

Towards predictive control of reversible nanoparticle assembly with solid-binding proteins

Although a broad range of ligand-functionalized nanoparticles and physico-chemical triggers have been exploited to create stimuli-responsive colloidal systems, little attention has been paid to the reversible assembly of unmodified nanoparticles with non-covalently bound proteins. Previously, we reported that a derivative of green fluorescent protein engineered with oppositely located silica-binding peptides mediates the repeated assembly and disassembly of 10-nm silica nanoparticles when pH is toggled between 7.5 and 8.5. We captured the subtle interplay between interparticle electrostatic repulsion and their protein-mediated short-range attraction with a multiscale model energetically benchmarked to collective system behavior captured by scattering experiments. Here, we show that both solution conditions (pH and ionic strength) and protein engineering (sequence and position of engineered silica-binding peptides) provide pathways for reversible control over growth and fragmentation, leading to clusters ranging in size from 25 nm protein-coated particles to micrometer-size aggregate. We further find that the higher electrolyte environment associated with successive cycles of base addition eventually eliminates reversibility. Our model accurately predicts these multiple length scales phenomena. The underpinning concepts provide design principles for the dynamic control of other protein- and particle-based nanocomposites.

Influence of Concentration Gradients on Electroconvection at a Cation-Exchange Membrane Surface

Membrane-based systems, such as electrodialysis, play an important role in desalination and industrial separation processes. Electrodialysis uses alternating anion- and cation-exchange membranes with a perpendicular electric field to generate concentrated and diluate streams from a feed solution. It is known that under overlimiting current conditions, reduced charge and mass transfer at the membrane interface leads to regions of high ion depletion generating instability and vortices termed electroconvection. While electroconvective mixing is known to directly impact the separation efficiency of electrodialysis, the influence of ion concentration gradients across the membrane experienced in a functional electrodialysis system is not known. Here, we report the influence of ion concentration gradients across a cation exchange membrane (Nafion) that is both aligned with and opposed to the applied electric field. Experiments were conducted by coflowing NaCl solutions of different concentrations (0.1-100 mM) on each side of the membrane, and electroconvection was visualized with a fluorescence dye (Rhodamine 6G). We obtained concentration profiles from fluorescence image data and systematically measured the thickness of the depletion boundary layer dBL under different conditions. We found smaller dBL values at a higher flow rate both with and without concentration gradients. Our results show that electroconvection is enhanced when the electric field is opposite to the direction of the concentration gradient.

Effects of particle shape and surface roughness on van der Waals interactions and coupling to dynamics in nanocrystals

The van der Waals interaction between colloids and nanoparticles is one of the key components to understanding particle aggregation, attachment, and assembly. While the ubiquity of anisotropic particle shapes and surface roughness is well-recognized in nanocrystalline materials, the effects of both on van der Waals forces and torques have not been adequately investigated. In this study, we develop a numerical scheme to determine the van der Waals forces and torques between cubic particles with multiple configurations and relative orientations. Our results show that the van der Waals torque due to anisotropic particle shapes is appreciable at nearly all configurations and mutual angles, outcompeting Brownian torque for various materials systems and conditions. Surface roughness enhances this particle shape effect, resulting in stronger van der Waals interactions ascribed to protrusions on the surfaces. Moreover, a scaling analysis indicates that the surface roughness alters the separation dependence of the van der Waals force and, more importantly, significantly influences the dynamics of two approaching particles. Our results clearly demonstrate that surface roughness and anisotropic shape play a crucial role in the energetics and kinetics of various particle-scale and emergent phenomena, such as crystal growth by oriented attachment, nanomaterials synthesis and assembly, mud flow rheology, as well as the deposition of natural nanocrystals within the subsurface.

Tracking nitrite's deviation from Stokes-Einstein predictions with pulsed field gradient 15N NMR spectroscopy

Predicting the behavior of oxyanions in radioactive waste stored at the Department of Energy legacy nuclear sites requires the development of novel analytical methods. This work demonstrates 15N pulsed field gradient nuclear magnetic resonance spectroscopy to quantify the diffusivity of nitrite. Experimental results, supported by molecular dynamics simulations, indicate that the diffusivity of free hydrated nitrite exceeds that of free hydrated sodium despite the greater hydrodynamic radius of nitrite. Investigations are underway to understand how the compositional and dynamical heterogeneities of the ion networks at high concentrations affect rheological and transport properties.

Patient-Specific Deep Learning Model for Clinical Target Volume Delineation on Daily CBCT of Breast Cancer Patients based on Intentional Deep Overfit Learning (IDOL) Framework

PURPOSE/OBJECTIVE(S)

Increasingly complex target volumes and the use of modern irradiation techniques emphasize the importance of daily image guidance more than ever. Significant progress has been made in adjuvant breast cancer radiotherapy (RT) and the need for optimized image guidance is growing. Furthermore, the position of the breast during RT after breast-conserving surgery is highly variable than expected. In this context, cone beam computed tomography (CBCT) is a very effective tool enabling prompt and accurate adaptive radiation therapy (ART). In this study, we aim to develop a deep learning (DL)-based algorithm to segment clinical target volume (CTV) from daily CBCT scans. Also, we validate the optimization of further learning when applying the Intentional Deep Overfit Learning (IDOL) framework.

MATERIALS/METHODS

A total of 240 different CBCT scans obtained from 100 breast cancer patients were used for this study. CTV was defined as whole breast plus margin in all patients. The workflow consists of two training stages: (1) training a novel 'generalized' DL model (Swin_UNETR) to identify and delineate breast CTV on CBCT scans using 90 breast cancer patient cases (2) applying an 'intentional overfitting' to the 'generalized' DL model to generate a 'patient-specific' model using the remaining 10 breast cancer patients. In this study, for the intentionally overfitting stage, we additionally trained with CBCT scans from the patient's 1st fraction to the 14th fractions cases. The results of the proposed method were compared quantitatively with the expert's contours on 1st-15th fractions CBCT scans using Dice Similarity Coefficient (DSC).

RESULTS

The average DSC between the 'generalized' DL model-based breast CTV contours and reference contours for the patient's 15th fraction was 0.9672. When implementing the IDOL framework with the CBCT scan obtained during the patient's 1st treatment, the average DSC was improved to 0.9809. When additional CBCT scans taken during each of the 1st to 6th fractions were used for training, the average DSC could be most effectively raised to 0.9835. The p-value comparison between the 'generalized' DL model and the 1st fraction was found to be 3.62E-04, while the comparison with the 6th fractions resulted in a p-value of 8.36E-05. The average time required for IDOL training using one CBCT scan and six CBCT scans was 107 seconds and 127 seconds, respectively.

CONCLUSION

In this study, we developed a patient-specific DL-based training algorithm to segment CTV in CBCT scans for breast cancer patients. The performance improvement was relatively significant and was confirmed that using continual DL with additional CBCT scans, which are taken every day, can be more accurate and efficient than drawing breast CTV using a general model. Our novel patient-specific model can be effectively applied to various ARTs by not only reducing labor and time but also increasing accuracy.

Predicting Outcomes of Nanoparticle Attachment by Connecting Atomistic, Interfacial, Particle, and Aggregate Scales

Predicting nanoparticle aggregation and attachment phenomena requires a rigorous understanding of the interplay among crystal structure, particle morphology, surface chemistry, solution conditions, and interparticle forces, yet no comprehensive picture exists. We used an integrated suite of experimental, theoretical, and simulation methods to resolve the effect of solution pH on the aggregation of boehmite nanoplatelets, a case study with important implications for the environmental management of legacy nuclear waste. Real-time observations showed that the particles attach preferentially along the (010) planes at pH 8.5 and the (101) planes at pH 11. To rationalize these results, we established the connection between key physicochemical phenomena across the relevant length scales. Starting from molecular-scale simulations of surface hydroxyl reactivity, we developed an interfacial-scale model of the corresponding electrostatic potentials, with subsequent particle-scale calculations of the resulting driving forces allowing successful prediction of the attachment modes. Finally, we scaled these phenomena to understand the collective structure at the aggregate-scale. Our results indicate that facet-specific differences in surface chemistry produce heterogeneous surface charge distributions that are coupled to particle anisotropy and shape-dependent hydrodynamic forces, to play a key role in controlling aggregation behavior.

The Role of Ion Rotation in Ion Mobility: Ultrahigh-Precision Prediction of Ion Mobility Dependence on Ion Mass Distribution and Translational to Rotational Energy Transfer

The role of ion rotation in determining ion mobilities is explored using the subtle gas phase ion mobility shifts based on differences in ion mass distributions between isotopomer ions that have been observed with ion mobility spectrometry (IMS) measurements. These mobility shifts become apparent for IMS resolving powers on the order of ∼1500 where relative mobilities (or alternatively momentum transfer collision cross sections; Ω) can be measured with a precision of ∼10 ppm. The isotopomer ions have identical structures and masses, differing only in their internal mass distributions, and their Ω differences cannot be predicted by widely used computational approaches, which ignore the dependence of Ω on the ion's rotational properties. Here, we investigate the rotational dependence of Ω, which includes changes to its collision frequency due to thermal rotation as well as the coupling of translational to rotational energy transfer. We show that differences in rotational energy transfer during ion-molecule collisions provide the major contribution to isotopomer ion separations, with only a minor contribution due to an increase in collision frequency due to ion rotation. Modeling including these factors allowed for differences in Ω to be calculated that precisely mirror the experimental separations. These findings also highlight the promise of pairing high-resolution IMS measurements with theory and computation for improved elucidation of subtle structural differences between ions.

Nanoparticle Assembly and Oriented Attachment: Correlating Controlling Factors to the Resulting Structures

Nanoparticle assembly and attachment are common pathways of crystal growth by which particles organize into larger scale materials with hierarchical structure and long-range order. In particular, oriented attachment (OA), which is a special type of particle assembly, has attracted great attention in recent years because of the wide range of material structures that result from this process, such as one-dimensional (1D) nanowires, two-dimensional (2D) sheets, three-dimensional (3D) branched structures, twinned crystals, defects, etc. Utilizing in situ transmission electron microscopy techniques, researchers observed orientation-specific forces that act over short distances (∼1 nm) from the particle surfaces and drive the OA process. Integrating recently developed 3D fast force mapping via atomic force microscopy with theories and simulations, researchers have resolved the near-surface solution structure, the molecular details of charge states at particle/fluid interfaces, inhomogeneity of surface charges, and dielectric/magnetic properties of particles that influence short- and long-range forces, such as electrostatic, van der Waals, hydration, and dipole-dipole forces. In this review, we discuss the fundamental principles for understanding particle assembly and attachment processes, and the controlling factors and resulting structures. We review recent progress in the field via examples of both experiments and modeling, and discuss current developments and the future outlook.

SimELIT: A Novel GUI-Based Comprehensive Ion Trajectory Simulation Software for Mass Spectrometry

Ion trajectory simulation in mass spectrometry systems from injection to detection is technically challenging but very important for better understanding the ion dynamics in instrument development. Here, we present SimELIT (Simulator of Eulerian and Lagrangian Ion Trajectories), a novel ion trajectory simulation platform. SimELIT is built upon a suite of multiphysics solvers compiled into OpenFOAM (an open-source numerical solver library particularly used for computational mechanics), with a simple web-based graphical user interface (GUI) allowing users to define the details of OpenFOAM cases and run simulations. SimELIT is a modular program and can provide extensions of physics (e.g., gas flows, electrodynamic fields) and thus enable ion trajectory simulations from the ion source to detector. The current version (SimELIT) provides two numerical solvers for ion trajectory simulations─(1) a Lagrangian particle tracker in vacuum and (2) a Eulerian ion density solver in background gas in the presence of electric fields. Here, we describe the architecture of SimELIT, including its use of Docker and the React Framework, and demonstrate the computation of ion trajectories of multiple m/z values in a static/linear voltage drop in vacuum (across a 1 m long flight tube). Further, the drift motion of ions under 1 Torr pressure conditions in a static background (N₂) gas through a 20 V/cm static electric field is shown. The results produced from SimELIT were compared with SIMION and theoretical estimates. In addition, we report the computation of ion trajectories in electrodynamic fields within a planar FAIMS device operating at atmospheric pressure.

Radiolysis and Radiation-Driven Dynamics of Boehmite Dissolution Observed by In Situ Liquid-Phase TEM

Over the last several decades, there have been several studies examining the radiation stability of boehmite and other aluminum oxyhydroxides, yet less is known about the impact of radiation on boehmite dissolution. Here, we investigate radiation effects on the dissolution behavior of boehmite by employing liquid-phase transmission electron microscopy (LPTEM) and varying the electron flux on the samples consisting of either single nanoplatelets or aggregated stacks. We show that boehmite nanoplatelets projected along the [010] direction exhibit uniform dissolution with a strong dependence on the electron dose rate. For nanoplatelets that have undergone oriented aggregation, we show that the dissolution occurs preferentially at the particles at the ends of the stacks that are more accessible to bulk solution than at the others inside the aggregate. In addition, at higher dose rates, electrostatic repulsion and knock-on damage from the electron beam causes delamination of the stacks and dissolution at the interfaces between particles in the aggregate, indicating that there is a threshold dose rate for electron-beam enhancement of dissolution of boehmite aggregates.

Predictive Theoretical Framework for Dynamic Control of Bioinspired Hybrid Nanoparticle Self-Assembly

At-will tailoring of the formation and reconfiguration of hierarchical structures is a key goal of modern nanomaterial design. Bioinspired systems comprising biomacromolecules and inorganic nanoparticles have potential for new functional material structures. Yet, consequential challenges remain because we lack a detailed understanding of the temporal and spatial interplay between participants when it is mediated by fundamental physicochemical interactions over a wide range of scales. Motivated by a system in which silica nanoparticles are reversibly and repeatedly assembled using a homobifunctional solid-binding protein and single-unit pH changes under near-neutral solution conditions, we develop a theoretical framework where interactions at the molecular and macroscopic scales are rigorously coupled based on colloidal theory and atomistic molecular dynamics simulations. We integrate these interactions into a predictive coarse-grained model that captures the pH-dependent reversibility and accurately matches small-angle X-ray scattering experiments at collective scales. The framework lays a foundation to connect microscopic details with the macroscopic behavior of complex bioinspired material systems and to control their behavior through an understanding of both equilibrium and nonequilibrium characteristics.

27 Al NMR diffusometry of Al13 Keggin nanoclusters

Although nanometer-sized aluminum hydroxide clusters (i.e., ϵ-Al₁₃ , [Al₁₃ O₄ (OH)₂₄ (H₂ O)₁₂ ]⁷⁺ ) command a central role in aluminum ion speciation and transformations between minerals, measurement of their translational diffusion is often limited to indirect methods. Here, ²⁷ Al pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has been applied to the AlO₄ core of the ϵ-Al₁₃ cluster with complementary theoretical simulations of the diffusion coefficient and corresponding hydrodynamic radii from a boundary element-based calculation. The tetrahedral AlO₄ center of the ϵ-Al₁₃ cluster is symmetric and exhibits only weak quadrupolar coupling, which results in favorable T₁ and T₂ ²⁷ Al NMR relaxation coefficients for ²⁷ Al PFGSTE NMR studies. Stokes-Einstein relationship was used to relate the ²⁷ Al diffusion coefficient of the ϵ-Al₁₃ cluster to the hydrodynamic radius for comparison with theoretical simulations, dynamic light scattering from literature, and previously published ¹ H PFGSTE NMR studies of chelated Keggin clusters. This first-of-its-kind observation proves that ²⁷ Al PFGSTE NMR diffusometry can probe symmetric Al environments in polynuclear clusters of greater molecular weight than previously considered.

Assembly-based pathways of crystallization

Solution crystallization of materials ranging from simple salts to complex supramolecular assemblies has long been viewed through the lens of classical nucleation and growth theories in which monomeric building blocks...

Shear stress dependence of force networks in 3D dense suspensions

The geometric organization and force networks of 3D dense suspensions that exhibit both shear thinning and thickening have been examined as a function of varying strength of interparticle attractive interactions using lubrication flow discrete element simulations. Significant rearrangement of the geometric topology does not occur at either the local or global scale as these systems transition across the shear thinning and shear thickening regimes. In contrast, massive rearrangements in the balance of attractive, lubrication, and contact forces are observed with interesting behavior of network growth and competition. In agreement with prior work, in shear thinning regions the attractive force is dominant, however as the shear thickening region is approached there is growth of lubrication forces. Lubrication forces oppose the attraction forces, but as viscosity continues to increase under increasing shear stress, the lubrication forces are dominated by contact forces that also resist attraction. Contact forces are the dominant interactions during shear thickening and are an order of magnitude higher than their values in the shear-thinning regime. At high attractive interaction strength, contact networks can form even under shear thinning conditions, however high shear stress is still required before contact networks become the driving mechanism of shear thickening. Analysis of the contact force network during shear thickening generally indicates a uniformly spreading network that rapidly forms across empty domains; however the growth patterns exhibit structure that is significantly dependent upon the strength of interparticle interactions, indicating subtle variations in the mechanism of shear thickening.

Visualizing Solution Structure at Solid-Liquid Interfaces using Three-Dimensional Fast Force Mapping

Amongst the challenges for a variety of research fields are the visualization of solid-liquid interfaces and understanding how they are affected by the solution conditions such as ion concentrations, pH, ligands, and trace additives, as well as the underlying crystallography and chemistry. In this context, three-dimensional fast force mapping (3D FFM) has emerged as a promising tool for investigating solution structure at interfaces. This capability is based on atomic force microscopy (AFM) and allows the direct visualization of interfacial regions in three spatial dimensions with sub-nanometer resolution. Here we provide a detailed description of the experimental protocol for acquiring 3D FFM data. The main considerations for optimizing the operating parameters depending on the sample and application are discussed. Moreover, the basic methods for data processing and analysis are discussed, including the transformation of the measured instrument observables into tip-sample force maps that can be linked to the local solution structure. Finally, we shed light on some of the outstanding questions related to 3D FFM data interpretation and how this technique can become a central tool in the repertoire of surface science.

The use of instant messaging in clinical data sharing: the EHRA SMS survey

Funding Acknowledgements

Type of funding sources: None.

Background

Nowadays, instant messaging (IM) provides fast and widespread communication. These platforms and apps enable the physicians to quickly share and send clinical data to their peers, to send information to their patients regarding their illnesses and to be reached for counselling and advise. Nevertheless, the use of IM has never been assessed in the cardiology community up until now.

Purpose

To assess the habits of cardiologists related to modern communication tools, their primary and secondary uses in clinical practice and the potential differences and preferences between different media in terms of ease of access, usefulness and trustworthiness.

Methods

An online survey was promoted by the EHRA e-Communication Committee and the EHRA Scientific Initiative Committee during the ESC Digital Health Week. All cardiologists were invited to participate via Twitter, LinkedIn, Facebook and other dedicated channels. The survey consisted of 22 questions and was made anonymous. The questions were made on an individual-basis and collected on SurveyMonkey.

Results

287 physicians from 33 countries responded to the survey. The mean age of the respondents was 43.4 ± 11.5 years, and 74.8% of them were male. 88.3% of all respondents routinely sends and 90.3% receives clinical data through IM. IM is used at least once a week (36.4%) or even once or more a day (40.4%) for sharing clinical data. WhatsApp is the most used IM app to share clinical data (79.4%). On a scale of 1 to 5, IM was second only to face-to-face contact (average 4.46) as the preferred method for sharing clinical data (average 3.69) and was considered better than phone calls (average 3.34) and e-mails (average 3.21). Twelve-lead ECGs (88.6%), medical history (61.4%) and echo loops (55.7%) are the data shared most often. Among potential pros of IM, the respondents listed being a fast way of communication (82.0%) and making it easy to contact colleagues (76.7%), while privacy issues regarding IM apps providers (62.7%) and other colleagues (45.6%) were commonly perceived as drawbacks. Only 57.4% of all respondents anonymize clinical data before sharing them through IM, and only 44.0% of the data received are reported to be anonymized. Of note, 29.3% of the respondents were not aware of the European General Data Protection Regulation (GDPR) on data protection at the time of the survey, and 29.8% do not know if their institution has a specific policy regarding the use of IM for professional use.

Conclusions

IM apps are used by cardiologists worldwide to share and discuss clinical data and are preferred to many other methods of data sharing, being second only to face-to-face contact. IM are often used and to share many different types of clinical data, being perceived as a fast and easy way of communication. Cardiologists should be sensitised to appropriate use of IM in accordance to GDPR and local policies in order to prevent legal and privacy issues.

Transport of Colloidal Particles in Microscopic Porous Medium Analogues with Surface Charge Heterogeneity: Experiments and the Fundamental Role of Single-Bead Deposition

Understanding colloid transport in subsurface environments is challenging because of complex interactions among colloids, groundwater, and porous media over several length scales. Here, we report a versatile method to assemble bead-based microfluidic porous media analogues with chemical heterogeneities of different configurations. We further study the transport of colloidal particles through a family of porous media analogues that are randomly packed with oppositely charged beads with different mixing ratios. We recorded the dynamics of colloidal particle deposition at the level of single grains. From these, the maximum surface coverage (θ_max = 0.051) was measured directly. The surface-blocking function and the deposition coefficient (k_pore = 3.56 s^-1) were obtained. Using these pore-scale parameters, the transport of colloidal particles was modeled using a one-dimensional advection-dispersion-deposition equation under the assumption of irreversible adsorption between oppositely charged beads and colloids, showing very good agreement with experimental breakthrough curves and retention profiles at the scale of the entire porous medium analogue. This work presents a new approach to fabricate chemically heterogeneous porous media in a microfluidic device that enables the direct measurement of pore-scale colloidal deposition. Compared with the conventional curve-fitting method for deposition constant, our approach allows quantitative prediction of colloidal breakthrough and retention via coupling of direct pore-scale measurements and an advection-dispersion-deposition model.

Correlation function approach for diffusion in confined geometries

This paper describes a formalism for extracting spatially varying transport coefficients from simulations of a molecular fluid in a nanochannel. This approach is applied to self-diffusion of a Lennard-Jones fluid confined between two parallel surfaces. A numerical grid is laid over the domain confining the fluid, and fluid properties are projected onto the grid cells. The time correlation functions between properties in different grid cells are calculated and can be used as the basis for a fitting procedure for extracting spatially varying diffusion coefficients from the simulation. Results for the Lennard-Jones system show that transport behavior varies sharply near the liquid-solid boundary and that the changes depend on the details of the liquid-solid interaction. A quantitative difference between the reduced and detailed models is discussed. It is found that the difference could be associated with assumptions about the form of the transport equations at molecular scales in lieu of problems with the method itself. The study suggests that this approach to fitting molecular simulations to continuum equations may guide the development of appropriate coarse-grained equations to model transport phenomena at nanometer scales.

Connecting particle interactions to agglomerate morphology and rheology of boehmite nanocrystal suspensions

HYPOTHESIS

The rheology of complex suspensions, such as nuclear waste slurries at the Hanford and Savannah River sites, imposes significant challenges on industrial-scale processing. Investigating the rheology and connecting it to the agglomerate morphology and underlying particle interactions in slurries will provide important fundamental knowledge, as well as prescriptive data for practical applications. Here, we use suspensions of nano-scale aluminum oxyhydroxide minerals in the form of boehmite as an analog of the radioactive waste slurry to investigate the correlation between particle interactions, agglomerate morphology, and slurry rheology.

EXPERIMENTS

A combination of Couette rheometry and small-angle scattering techniques (independently and simultaneously) were used to understand how agglomerate structure of slurry changes under flow and how these structural changes manifest themselves in the bulk rheology of the suspensions.

FINDINGS

Our experiments show that the boehmite slurries are thixotropic, with the rheology and structure of the suspensions changing with increasing exposure to flow. In the slurries, particle agglomerates begin as loose, system-spanning clusters, but exposure to moderate shear rates causes the agglomerates to irreversibly consolidate into denser clusters of finite size. The structural changes directly influence the rheological properties of the slurries such as viscosity and viscoelasticity. Our study shows that solution pH affects the amount of structural rearrangement and the kinetics of the rearrangement process, with an increase in pH leading to faster and more dramatic changes in bulk rheology, which can be understood via correlations between particle interactions and the strength of particle network. Nearly identical structural changes were also observed in Poiseuille flow geometries, implying that the observed changes are relevant in pipe flow as well.

In situ liquid SEM imaging analysis revealing particle dispersity in aqueous solutions

A quantitative description on dispersity of boehmite (γ-AlOOH) particles, a key component for waste slurry at Hanford sites, can provide useful knowledge for understanding various physicochemical nature of the waste. In situ liquid scanning electron microscopy (SEM) was used to evaluate the dispersity of particles in aqueous conditions using a microfluidic sample holder, System for Analysis at Liquid Vacuum Interface (SALVI). Secondary electron (SE) images and image analyses were performed to determine particle centroid locations and the distance to the nearest neighbour particle centroid, providing reliable rescaled interparticle distances as a function of ionic strength in acidic and basic conditions. Our finding of the particle dispersity is consistent with physical insights from corresponding particle interactions under physicochemical conditions, demonstrating delicate changes in dispersity of boehmite particles based on novel in situ liquid SEM imaging and analysis. LAY DESCRIPTION: In situ liquid scanning electron microscopy (SEM) was used to determine the interparticle distance of boehmite (γ-AlOOH) particles, a key component for waste slurry at Hanford sites. This type of quantitative measurement is important to understand various physicochemical nature of the radiological waste containing boehmite. In situ liquid SEM was enabled by a unique vacuum compatible microfluidic cell, System for Analysis at Liquid Vacuum Interface (SALVI). We collected secondary electron (SE) images and performed image analyses to determine particle centroid locations and the distance to the nearest neighbour particle centroid to arrive at the interparticle distances in acidic and basic conditions. Our results show that delicate changes occur among boehmite particles under different pH conditions using novel in situ SEM imaging.

Unexpected conformational behavior of poly(poly(ethylene glycol) methacrylate)-poly(propylene carbonate)-poly(poly(ethylene glycol) methacrylate) (PPEGMA-PPC-PPEGMA) amphiphilic block copolymers in micellar solution and at the air-water interface

HYPOTHESIS

This paper investigates the self-assembly behavior of a new amphiphilic block copolymer, PPEGMA-PPC-PPEGMA, in dilute aqueous solution and at the air-water interface. In PPEGMA-PPC-PPEGMA, the hydrophilic PEG moieties exist as side chains attached to the PMA backbone. Because of this unique non-linear architecture, the morphological and conformational properties of self-assembled PPEGMA-PPC-PPEGMA polymers are expected to be different from those of conventional linear PEG-based polymer surfactants.

EXPERIMENTS

For this study, three PPEGMA-PPC-PPEGMA samples having an identical PPC molecular weight (5.6 kDa) and different PPEGMA molecular weights (7.2, 2.8 and 2.1 kDa on either side) (named "G7C6G7", "G3C5G3", and "G2C6G2", respectively) were synthesized. The micellar self-assembly behaviors of these materials were investigated by cryo-TEM, rheology, DLS, and visual observation. Langmuir monolayers of these materials were characterized by surface mechanical testing.

FINDINGS

PPEGMA-PPC-PPEGMA micelles were found to have a spherical geometry, irrespective of copolymer composition. Interestingly, G2C6G2 and G3C6G3 micelles formed weakly-bound clusters, whereas G7C6G7 micelles predominantly existed as isolated micelles. Detailed analysis suggests that this unexpected trend in micelle morphology originates from the fact that the PPEGMA blocks are only partially hydrated at aqueous interfaces. Detailed features of the surface pressure-area isotherms obtained from Langmuir PPEG-PPC-PPEGMA monolayers further supported this notion.

Effects of catalyst droplets on wire growth and the resulting branched structures during VLS growth

The vapor-liquid-solid (VLS) method is vastly employed to grow hierarchical structures with unique properties. However, key questions remain, such as what controls the branched structures and what the roles of the catalyst droplet size are during the growth. Here, an in-depth understanding of the kinetics of the nucleation, growth, and subsequent coalescence processes of Bi liquid catalyst droplets is provided by direct observation of PbSe branched wire growth in an environmental transmission electron microscope. This brings a kinetic control of the branch density by varying the parameters, such as temperature. In addition, the dependence of the wire growth rate on the catalyst droplet size is revealed, i.e., the smaller the catalyst size the larger the wire growth rate, unlike the wire growth controlled by the Gibbs-Thomson effect, possibly due to different mass transport pathways and atomic surface diffusion. These results extend the fundamental understanding of the VLS growth mechanism of branched structures and benefit the structure design of hierarchical materials with tailored properties.

Connecting energetics to dynamics in particle growth by oriented attachment using real-time observations

The interplay between crystal and solvent structure, interparticle forces and ensemble particle response dynamics governs the process of crystallization by oriented attachment (OA), yet a quantitative understanding is lacking. Using ZnO as a model system, we combine in situ TEM observations of single particle and ensemble assembly dynamics with simulations of interparticle forces and responses to relate experimentally derived interparticle potentials to the underlying interactions. We show that OA is driven by forces and torques due to a combination of electrostatic ion-solvent correlations and dipolar interactions that act at separations well beyond 5 nm. Importantly, coalignment is achieved before particles reach separations at which strong attractions drive the final jump to contact. The observed barrier to attachment is negligible, while dissipative factors in the quasi-2D confinement of the TEM fluid cell lead to abnormal diffusivities with timescales for rotation much less than for translation, thus enabling OA to dominate.

Roles of notch signaling pathway and endothelial-mesenchymal transition in vascular endothelial dysfunction and atherosclerosis

OBJECTIVE

To investigate the role of the Notch signaling pathway on the endothelial-mesenchymal transition (EndMT) during vascular endothelial dysfunction and atherosclerosis.

MATERIALS AND METHODS

Human coronary artery endothelial cells (HCAEC) were treated with the exogenous Notch homolog 1 (Notch1) factor to activate the Notch1 pathway, and cells were then observed under the microscope for morphologic changes. Changes in the expression of related proteins were detected by Western blot. In vivo experiments were performed using 18 Sprague Dawley® (SD) rats, and GSI factor was used to specifically inhibit Notch pathway activation. Rats were used and randomly divided into three groups: normal diet (ND) group, high-fat diet (HFD) group, and high-fat diet + GSI (HFD+GSI) group, 6 rats in each group. Hematoxylin and eosin (H&E) staining was used to examine the cardiac aortic morphology of the rats in each treatment group. Real-time polymerase chain reaction (RT-PCR) and Western blot were used to detect the expression of Notch1, Hes1, VE-cadherin and α-SMA in the aortic tissues of rats in each group at mRNA and protein levels, respectively.

RESULTS

After HCAECs were treated with Notch1, endothelial protein levels of VE-cadherin were significantly decreased and levels of the interstitial protein α-SMA were significantly increased. In the animal model, the rats fed with high-fat diet for two months presented obvious atherosclerosis spots in their aorta, but those fed with the same diet and treated with GSI inhibitor of Notch pathway showed significantly fewer atherosclerosis signs. Compared with ND group, mRNA and protein expression levels of Notch1, Hes1 and α-SMA were significantly increased, and the expression levels of endothelial marker VE-cadherin were significantly decreased in aortas of rats in HFD group. Compared with the rats in HFD group, the rats in HFD+GSI group showed significantly reduced expression levels of Notch1, Hes1 and α-SMA.

CONCLUSIONS

The activation of Notch signaling pathway can induce the EndMT progression and promote the development of atherosclerotic lesions.

Interplay between Short- and Long-Ranged Forces Leading to the Formation of Ag Nanoparticle Superlattice

Nanoparticle (NP) superlattices have attracted increasing attention due to their unique physicochemical properties. However, key questions persist regarding the correlation between short- and long-range driving forces for nanoparticle assembly and resultant capability to predict the transient and final superlattice structure. Here the self-assembly of Ag NPs in aqueous solutions is investigated by employing in situ liquid cell transmission electron microscopy, combined with atomic force microscopy-based force measurements, and theoretical calculations. Despite the NPs exhibiting instantaneous Brownian motion, it is found that the dynamic behavior of NPs is correlated with the van der Waals force, sometimes unexpectedly over relatively large particle separations. After the NPs assemble into clusters, a delicate balance between the hydration and van der Waals forces results in a distinct distribution of particle separation, which is ascribed to layers of hydrated ions adsorbed on the NP surface. The study demonstrates pivotal roles of the complicated correlation between interparticle forces; potentially enabling the control of particle separation, which is critical for tailoring the properties of NP superlattices.

In situ characterization of kinetics and mass transport of PbSe nanowire growth via LS and VLS mechanisms

We grew binary PbSe nanowires in an in situ gas-heating cell in a transmission electron microscope and elucidated species dependent mass transport pathways and key correlations among supersaturation, nucleation, and growth kinetics, thereby enabling morphological and compositional control of nanowires with tailored properties.

From Yielding to Shear Jamming in a Cohesive Frictional Suspension

Simulations are used to study the steady shear rheology of dense suspensions of frictional particles exhibiting discontinuous shear thickening and shear jamming, in which finite-range cohesive interactions result in a yield stress. We develop a constitutive model that combines yielding behavior and shear thinning at low stress with the frictional shear thickening at high stresses, in good agreement with the simulation results. This work shows that there is a distinct difference between solids below the yield stress and in the shear-jammed state, as the two occur at widely separated stress levels, with an intermediate region of stress in which the material is flowable.

Global topology of contact force networks: Insight into shear thickening suspensions

Highly concentrated particle suspensions (also called slurries) can undergo a sharp increase in viscosity, or shear thickening, under applied stress. Understanding the fundamental features leading to such rheological change is crucial to optimize flow conditions or to design flow modifiers for slurry processing. While local changes to the particle environment under applied shear can be related to changes in viscosity, there is a broader need to connect the shear thickening transition to the fundamental organization of particle-interaction forces which lead to long-range organization. In particular, at a high volume fraction of particles, recent evidence indicates frictional forces between contacting particles is of importance. Herein, the network of frictional contact forces is analyzed within simulated two-dimensional shear thickening suspensions. Two topological metrics are studied to characterize the response of the contact force network (CFN) under varying applied shear stress. The metrics, geodesic index and the void parameter, reflect complementary aspects of the CFN: One is the connectedness of the contact network and the second is the distribution of spatial areas devoid of particle-particle contacts. Considered in relation to the variation of the viscosity, the topological metrics show that the network grows homogeneously at large scales but with many local regions devoid of contacts, indicating clearly the role of CFN growth in causing the large change in the rheological response at the shear thickening transition.

Abstract P4-10-11: Pregnancy-associated breast cancer in a contemporary cohort of newly diagnosed women

Introduction: Pregnancy-associated breast cancer (PABC) refers to breast cancer (BC) diagnosed during pregnancy, lactation, or in the postpartum period. There is evidence that PABC is associated with a poorer prognosis, and that the development of the disease is influenced by the unique hormonal milieu of pregnancy. The purpose of this study was to investigate the clinicopathologic characteristics associated with PABC in a contemporary cohort of women with newly diagnosed BC.

Methods: Our institutional Breast Cancer Database was queried for women diagnosed with breast cancer between 2010-17 who had at least one full term pregnancy (FTP). Variables of interest included patient demographics and clinical and tumor characteristics. PABC was defined as breast cancer diagnosed within 24 months of delivery. Statistical analyses included Pearson's chi-square and logistic regression.

Results: Out of a total of 1934 women, 42 (2.2%) had PABC. Median follow up in the total cohort was 4.5 years. After adjusting for age at diagnosis, PABC was associated with older age at first FTP, ethnic minority status, BRCA mutation carriers, presentation with a palpable mass, higher histologic grade, and ER-negative and triple negative receptor status. Variables that were not significantly different between PABC and non-PABC cases included tumor histology, multifocality, presence of lymphovascular invasion, and family history of breast cancer.

Table:Selected Characteristics of Women with PABCVariableNon-PABC (n=1892)PABC (n=42)P-value*Age at first full term pregnancy  <0.001<35 years1610 (85%)28 (66.7%) ≥35 years277 (15%)14 (33.3%) Race  0.001White1397 (73.8%)23 (54.8%) Black181 (9.6%)8 (19%) Asian175 (9.2%)10 (23.8%) Hispanic131 (6.9%)1 (2.4%) Other8 (0.4%)0 (0%) BRCA 1,2 Positive56 (3%)9 (21.4%)<0.001Method of Presentation  0.002Breast Exam579 (30.6%)30 (71.4%) Mammography1137 (60.1%)10 (23.8%) Ultrasound87 (1.6%)2 (4.8%) MRI67 (3.5%)0 (0%) Other22 (1.2%)0 (0%) Invasive Grade  0.014Low213 (15%)0 (0%) Intermediate763 (53.8%)12 (37.5%) High442 (31.2%)20 (62.5%) Estrogen Receptor  0.034Positive1572 (83.9%)29 (69%) Negative301 (16.1%)13 (31%) Triple Negative135 (7.1%)7 (16.7%)0.041*P-values are age-adjusted.

Conclusions: The association of PABC with ethnic minority status in our cohort is interesting and may be reflected in the increased proportion of triple negative breast cancers in the PABC group. In our contemporary cohort, PABC was associated with older age at first FTP. As more women delay childbearing, risk for PABC may increase. Our findings suggest that women who become pregnant at older ages should be followed carefully during pregnancy and in the postpartum period, especially if they are BRCA mutation carriers. The optimal approach for monitoring older women during pregnancy and the postpartum period is unclear. Clinical breast exam may play an important role, especially for those women known to be at increased risk for breast cancer.

Citation Format: Gooch JC, Chun J, Jubas T, Guth A, Schnabel F. Pregnancy-associated breast cancer in a contemporary cohort of newly diagnosed women [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-10-11.

Abstract P4-10-07: Breastfeeding experience among breast cancer patients in the modern era

Introduction: In recent years, the uptake of breastfeeding has become more common as it is regarded as healthy and beneficial for both mother and infant. The process of parturition and lactation plays a role in the normal differentiation and development of breast tissue, and multiparity has been associated with a decreased risk for breast cancer. The current study sought to describe the breastfeeding experience of a modern cohort of women with newly diagnosed BC, and to examine the clinicopathologic characteristics of their disease.

Methods: A retrospective review of our institutional Breast Cancer Database from 2009-2017 was performed to identify women with at least one full term pregnancy (FTP). Clinicopathologic and demographic information was recorded, including breastfeeding experience and cumulative duration of nursing. Women were grouped by self-reported breastfeeding experience and duration of breastfeeding for analysis. Pearson's chi-square tests were performed.

Results: Of 1919 patients, 1053 (54.9%) reporting breastfeeding. Breastfeeding increased from a low of 30.4% among women with first FTP (FFTP) in the 1950's to 84.6% with FFTP in the 2010's. There were no significant differences between those who did and did not breast feed with regards to race, family history, BRCA status, pathologic stage, grade, tumor histology, lymphovascular invasion (LVI), multifocality, tumor size or receptor status. When stratified by duration of breastfeeding, the most striking finding was that women who breastfed for >12 months were more likely to have tumors associated with LVI (p = 0.028).

Table– Breastfeeding Experience Among Parous Women with Breast CancerVariableNo Breastfeeding (n=866)Breastfeeding (n=1053)p-valueRace  0.432White648 (74.8%)767 (72.8%) Black73 (8.5%)112 (10.6%) Asian78 (9%)102 (9.7%) Hispanic64 (7.4%)67 (6.4%) Other3 (0.3%)5 (0.5%) Family history272 (31.4%)311 (29.6%)0.397BRCA 1,2 positive23 (2.7%)42 (4.0%)0.108Final Pathology Stage  0.2240190 (21.9%)222 (21.1%) I426 (49.2%)507 (48.1%) II197 (22.8%)229 (21.7%) III40 (4.6%)63 (6.0%) IV1 (0.1%)3 (0.3%) No residual (neoadjuvant)12 (1.4%)29 (34.1%) Invasive Grade  0.127Low92 (14.1%)120 (15.3%) Intermediate371 (56.7%)398 (50.6%) High191 (29.2%)268 (34.1%) Histology  0.130DCIS189 (21.8%)223 (21.2%) IDC531 (61.3%)688 (65.3%) ILC113 (13.1%)99 (9.4%) Other33 (3.8%)43 (4.1%) LVI127 (14.7%)174 (16.5%) Multifocality147 (17%)183 (17.4%) Median tumor size (cm; range)1.4 (0-9.5)1.3 (0-12.5)0.489Estrogen Receptor  0.206Positive726 (84.7%)861 (82.6%) Negative131 (15.3%)182 (17.4%) Progesterone Receptor  0.275Positive621 (72.5%)732 (70.2%) Negative236 (27.5%)311 (29.8%) HER2/neu Receptor  0.068Positive78 (12%)121 (15.4%) Negative571 (88%)667 (84.6%) 

Conclusions: Breastfeeding experience was not generally associated with significant differences in tumor or patient characteristics. However, breastfeeding for longer than 12 months was associated with LVI. It is possible that changes in the breast tissue that occur during the process of pregnancy and prolonged lactation may influence future tumor development. These findings are hypothesis generating and suggest that the relationship of prolonged breastfeeding and breast cancer development should be investigated further.

Citation Format: Gooch JC, Chun J, Jubas T, Guth A, Schnabel F. Breastfeeding experience among breast cancer patients in the modern era [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-10-07.

Abstract P5-02-01: The relationship of breast density in mammography and magnetic resonance imaging (MRI) in women with triple negative breast cancer (TNBC)

Introduction:

TNBC represent 10%–20% of invasive breast cancers. Previous studies showed that TNBC usually present with benign features on mammography, ultrasound and MRI. However, there is a dearth of information on the relationship of mammographic breast density (MBD), background parenchymal enhancement (BPE) and fibroglandular tissue (FGT) on MRI with TNBC. The purpose of this study was to evaluate the relationship between BD, BPE, and FGT in women with TNBC compared to non-TNBC in a contemporary cohort of women with breast cancer.

Methods:

The Institutional Breast Cancer Database was queried for women who had invasive breast cancer and underwent mammography and MRI between (2010-2017). Variables of interest included clinical, pathologic, and imaging characteristics. Statistical analyses included Pearson's Chi Square and logistic regression.

Results:

Of 2224 women, 210 (9%) had TNBC. The median age was 59 years (22-95) and median follow up was 4 years. When we looked at the clinical characteristics of women with TNBC compared to non-TNBC, race, BRCA1,2 status, method of presentation, palpability, histology, grade, and Ki67 were statistically different (Table 1). When we looked at the correlation of MBD, FGT, and BPE for women with TNBC, MBD was correlated with FGT (r=0.64) but weakly correlated with BPE (r=0.22). We found a significant association of low BPE and TNBC compared to the non-TNBCs (p=0.021) (Table 1). In a short period of time, only 8 women with TNBC had a recurrence with no significant association with MBD, BPE, or FGT (Table 1).

Table 1.Imaging Characteristics among TNBC compared to non-TNBCVariableTNBC (N=210)%Non-TNBC (N=2014)%P-valueRace    0.001White13665153376 Black35171749 Hispanic1261156 Asian23111739 Other42191 BRCA1/2    <0.001Positive3025425 Negative897579195 Method of Presentation    <0.001Breast exam1125475738 Mammography7737105753 Ultrasound731106 MRI126553 Palpable    <0.001Yes1185783342 No9144115258 Histology    <0.001DCIS with Microinvasion21382 IDC19693159079 ILC5226913 Invasive Other731176 Invasive Grade    <0.001Grade 11131016 Grade 22714111858 Grade 31688650126 ER    <0.001Positive00189194 Negative2101001226 PR    <0.001Positive00160080 Negative21010041221 Ki67    <0.001Median (range)60 (0-99) 10 (0-99)  Mammographic Density    0.165Less dense82417846 More dense11959103454 MRI BPE    0.021Low BPE707655564 High BPE222431236 MRI FGT    0.370Less dense475440449 More dense404642151 

Conclusions:

In our study population, MBD and FGT did not differ between patients with TNBC compared to non-TNBC. Interestingly, we found a higher proportion of women with lower BPE in the TNBC compared to the non-TNBC group. BPE refers to the amount of enhancing fibroglandular tissue and has been demonstrated to reflect variations in estrogen-mediated vascular permeability. Lower BPE in TNBC may reflect the fact that these tumors are not hormonally sensitive. This may also have implications for radiogenomics, which aims to correlate imaging characteristics with gene expression and genome-related characteristics in tumor biology. Further studies are warranted in looking at these imaging biomarkers and TNBC.

Citation Format: Chun J, Schnabel F, Gooch J, Lee J, Jubas T, Goodgal J, Guth A, Moy L. The relationship of breast density in mammography and magnetic resonance imaging (MRI) in women with triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-02-01.

Effects of Ionic Strength, Salt, and pH on Aggregation of Boehmite Nanocrystals: Tumbler Small-Angle Neutron and X-ray Scattering and Imaging Analysis

The US government currently spends significant resources managing the legacies of the Cold War, including 300 million liters of highly radioactive wastes stored in hundreds of tanks at the Hanford (WA) and Savannah River (SC) sites. The materials in these tanks consist of highly radioactive slurries and sludges at very high pH and salt concentrations. The solid particles primarily consist of aluminum hydroxides and oxyhydroxides (gibbsite and boehmite), although many other materials are present. These form complex aggregates that dramatically affect the rheology of the solutions and, therefore, efforts to recover and treat these wastes. In this paper, we have used a combination of transmission and cryo-transmission electron microscopy, dynamic light scattering, and X-ray and neutron small and ultrasmall-angle scattering to study the aggregation of synthetic nanoboehmite particles at pH 9 (approximately the point of zero charge) and 12, and sodium nitrate and calcium nitrate concentrations up to 1 m. Although the initial particles form individual rhombohedral platelets, once placed in solution they quickly form well-bonded stacks, primary aggregates, up to ∼1500 Å long. These are more prevalent at pH = 12. Addition of calcium nitrate or sodium nitrate has a similar effect as lowering pH, but approximately 100 times less calcium than sodium is needed to observe this effect. These aggregates have fractal dimension between 2.5 and 2.6 that are relatively unaffected by salt concentration for calcium nitrate at high pH. Larger aggregates (>∼4000 Å) are also formed, but their size distributions are discrete rather than continuous. The fractal dimensions of these aggregates are strongly pH-dependent, but only become dependent on solute at high concentrations.

Mechanistic Understanding of the Growth Kinetics and Dynamics of Nanoparticle Superlattices by Coupling Interparticle Forces from Real-Time Measurements

Superlattice structures formed by nanoparticle (NP) self-assembly have attracted increasing attention due to their potential as a class of nanomaterials with enhanced physicochemical properties tailored by the assembly structure. However, many key questions remain regarding the correlation between the dynamics of individual NPs and emerging superlattice patterns. Here we investigated the self-assembly of gold NPs by employing in situ transmission electron microscopy equipped with direct detection camera capabilities, which enabled us to track the rapid motion of individual nanoparticles in real time. By calculating the contributions of Brownian, van der Waals, hydrodynamic, and steric hindrance forces, we obtained a quantitative evaluation of the competitive interactions that drive the assembly process. Such competition between forces over various separations is critical for the kinetics of cluster growth, leading to the superlattice formation. Brownian motion resulted in the formation of small-sized clusters, whose growth dynamics was characterized as reaction-limited aggregation. Subsequently, at relative short-range particle separations, van der Waals force overrode the Brownian force and dominantly drove the assembly process. When the particles were in close proximity, a delicate balance between van der Waals and steric hindrance forces led to an unexpected dynamic nature of the assembled superlattice. Our study provides a fundamental understanding of coupling energetics and dynamics of NPs involved in the assembly process, enabling the control and design of the structure of nanoparticle superlattices.

Impact of Solution Chemistry and Particle Anisotropy on the Collective Dynamics of Oriented Aggregation

Although oriented aggregation of particles is a widely recognized mechanism of crystal growth, the impact of many fundamental parameters, such as crystallographically distinct interfacial structures, solution composition, and nanoparticle morphology, on the governing mechanisms and assembly kinetics are largely unexplored. Thus, the collective dynamics of systems exhibiting OA has not been predicted. In this context, we investigated the structure and dynamics of boehmite aggregation as a function of solution pH and ionic strength. Cryogenic transmission electron microscopy shows that boehmite nanoplatelets assemble by oriented attachment on (010) planes. The coagulation rate constants obtained from dynamic light scattering during the early stages of aggregation span 7 orders of magnitude and cross both the reaction-limited and diffusion-limited regimes. Combining a simple scaling analysis with calculations for stability ratios and rotational/translational diffusivities of irregular particle shapes, the effects of orientation for irregular-shaped particles on the early stages of aggregation are understood via angular dependencies of van der Waals, electrostatic, and hydrodynamic interactions. Using Monte Carlo simulations, we found that a simple geometric parameter, namely, the contact area between two attaching nanoplatelets, presents a useful tool for correlating nanoparticle morphologies to the emerging larger-scale aggregates, hence explaining the unusually high fractal dimensions measured for boehmite aggregates. Our findings on nanocrystal transport and interactions provide insights toward the predictive understanding of nanoparticle growth, assembly, and aggregation, which will address critical challenges in developing synthesis strategies for nanostructured materials, understanding the evolution of geochemical reservoirs, and addressing many environmental problems.