A Continuous Gradient Colloidal Glass

Advanced Tuneable Micronanoplatforms for Sensitive and Selective Multiplexed Spectroscopic Sensing via Electro-Hydrodynamic Surface Molecular Lithography

Micro- and nanopatterning of materials, one of the cornerstones of emerging technologies, has transformed research capabilities in lab-on-a-chip diagnostics. Herein, a micro- and nanolithographic method is developed, enabling structuring materials at the submicron scale, which can, in turn, accelerate the development of miniaturized platform technologies and biomedical sensors. Underpinning it is the advanced electro-hydrodynamic surface molecular lithography, via inducing interfacial instabilities produces micro- and nanostructured substrates, uniquely integrated with synthetic surface recognition. This approach enables the manufacture of design patterns with tuneable feature sizes, which are functionalized via synthetic nanochemistry for highly sensitive, selective, rapid molecular sensing. The development of a high-precision piezoelectric lithographic rig enables reproducible substrate fabrication with optimum signal enhancement optimized for functionalization with capture molecules on each micro- and nanostructured array. This facilitates spatial separation, which during the spectroscopic sensing, enables multiplexed measurement of target molecules, establishing the detection at minute concentrations. Subsequently, this nano-plasmonic lab-on-a-chip combined with the unconventional computational classification algorithm and surface enhanced Raman spectroscopy, aimed to address the challenges associated with timely point-of-care detection of disease-indicative biomarkers, is utilized in validation assay for multiplex detection of traumatic brain injury indicative glycan biomarkers, demonstrating straightforward and cost-effective micro- and nanoplatforms for accurate detection.

Optical properties of particle dispersed coatings with gradient distribution

Particle dispersed coatings with gradient distributions, resulting from either gravity or artificial control, are frequently encountered in practical applications. However, most current studies investigating the optical properties of coatings use the uniform model (uniform single layer assumption), overlooking the gradient distribution effects. Given the pervasiveness of gradient distributions and the widespread use of the uniform model, it is imperative to evaluate applicability conditions of the uniform model in practical applications. In this work, we comprehensively investigate the quantitative performance of the uniform model in predicting the infrared optical properties of coatings with gradient distributions of particle volume fraction using the superposition T-matrix method. The results show that the gradient distribution of particle volume fraction has a limited impact on the emissivity properties of T i O 2-PDMS coatings in the midwavelength-infrared (MWIR) and long-wavelength-infrared (LWIR) bands, which validates the uniform model for the gradient coatings with weakly scattering dielectric particles. However, the uniform model can yield significant inaccuracies in estimating the emissivity properties of Al-PDMS coatings with gradient distributions in the MWIR and LWIR bands. To accurately estimate the emissivity of such gradient coatings with the scattering metallic particles, meticulous modeling of the particle volume fraction distribution is essential.

Entropy production and collective excitations of crystals out of equilibrium: The concept of entropons

We study the collective vibrational excitations of crystals under out-of-equilibrium steady conditions that give rise to entropy production. Their excitation spectrum comprises equilibriumlike phonons of thermal origin and additional collective excitations called entropons because each of them represents a mode of spectral entropy production. Entropons coexist with phonons and dominate them when the system is far from equilibrium while they are negligible in near-equilibrium regimes. The concept of entropons has been recently introduced and verified in a special case of crystals formed by self-propelled particles. Here we show that entropons exist in a broader class of active crystals that are intrinsically out of equilibrium and characterized by the lack of detailed balance. After a general derivation, several explicit examples are discussed, including crystals consisting of particles with alignment interactions and frictional contact forces.

One Step Closer to Coatings Applications Utilizing Self-Stratification: Effect of Rheology Modifiers

Self-stratification of model blends of colloidal spheres has recently been demonstrated as a method to form multifunctional coatings in a single pass. However, practical coating formulations are complex fluids with upward of 15 components. Here, we investigate the influence of three different rheology modifiers (RMs) on the stratification of a 10 wt % 7:3 w:w blend of 270 and 96 nm anionic latex particles that do not stratify without RM. However, addition of a high molar mass polysaccharide thickener, xanthan gum, raises the viscosity and corresponding Péclet number enough to achieve small-on-top stratification as demonstrated by atomic force microscopy (AFM) measurements. Importantly, this was possible due to minimal particle-rheology modifier interactions, as demonstrated by the bulk rheology. In contrast, Carbopol 940, a microgel-based RM, was unable to achieve small-on-top stratification despite a comparable increase in viscosity. Instead, pH-dependent interactions with latex particles lead to either laterally segregated structures at pH 3 or a surface enrichment of large particles at pH 8. Strong RM-particle interactions are also observed when the triblock associative RM HEUR10kC12 is used. Here, small-on-top, large-enhanced, and randomly mixed structures were observed at respectively 0.01, 0.1, and 1 wt % HEUR10kC12. Combining rheology, dynamic light scattering, and AFM results allows the mechanisms behind the nonmonotonic stratification in the presence of associative RMs to be elucidated. Our results highlight that stratification can be predicted and controlled for RMs with weak particle interactions, while a strong RM-particle interaction may afford a wider range of stratified structures. This takes a step toward successfully harnessing stratification in coatings formulations.

Quantitative Optical and Structural Comparison of 3D and (2+1)D Colloidal Photonic Crystals

Colloidal crystals are excellent model systems to study self-assembly and structural coloration because their periodicities coincide with the wavelength range of visible light. Different assembly methods inherently introduce characteristic defects and irregularities, even with nearly monodisperse colloidal particles. Here, we investigate how these imperfections influence the structural coloration by comparing two techniques to obtain colloidal crystals. 3D colloidal crystals produced by convective assembly are well-ordered and periodically arranged but show microscopic cracks. (2+1)D colloidal crystals fabricated by stacking individual monolayers show a decreased hexagonal order and limited crystal registration between single monolayers in the z-direction. We investigate the optical properties of both systems by comparing identical numbers of layers using correlative microspectroscopy. These measurements show that the less ordered (2+1)D colloidal crystals exhibit higher reflected light intensities. Macroscopic reflection integrating all angles shows that the reflected light intensity levels out with an increasing number of layers, whereas incoherent scattering increases. Although both types of colloidal crystal show similar angle-dependent color shifts in specular reflection, the less-ordered structure of the (2+1)D colloidal crystal scatters light within a larger angular range under diffusive illumination. Our results suggest that structural coloration is surprisingly robust toward local defects and irregularities.