Hydrophobic Monomers Recognize Microenvironments in Hydrogel Microspheres during Free-Radical-Seeded Emulsion Polymerization

Double-emulsion synthesis of reactive epoxy nanospheres for advanced lithium-ion battery binders

The rapid advancement of electric vehicles imposes significant challenges on lithium-ion battery (LIBs) technology. Polymer binders offer a promising low-cost solution. However, for anode materials, the conventional styrene butadiene latex/carboxymethyl cellulose (SBR/CMC) binders exhibit inherent issues, including binder flotation during solvent evaporation and undesired film formation on anode surfaces. Herein, ultra-small reactive epoxy nanospheres (EPS, 70 nm) were successfully synthesized using a customized double emulsion (DE) demulsification method. The structural design of the internal water phase, two consecutive emulsifications and an innovative phase inversion strategy are crucial to achieve ultra-small particle size. By eliminating the binder migration phenomenon and establishing a covalent cross-linked network within the electrode, the EPS bonded electrode achieved a peel strength of 7.03 N cm-1, surpassing the 4.53 N cm-1 observed in the SBR bonded electrode. Furthermore, EPS can optimize the electrode pore structure and increase the electrode's wettability to the electrolyte, thereby improving the electrode rate performance. At a current density of 10C, the EPS bonded electrode achieved a capacity retention of 50.4 %, which is much higher than that of the SBR bonded electrode (21.2 %). Consequently, reactive EPS presents an effective way to enhance the overall performance of LIBs through the strategic design of polymer binders.

Direct Imaging of the Organic-Inorganic Interfacial Transformation

The organic-inorganic interfacial nanostructures between fillers and the matrix play a crucial role in the performance of polymer composites. Here we propose an in situ cryogenic transmission electron microscope technique (cryo-TEM) approach to directly observe the organic-inorganic interfacial transformation in a toluene diisocyanate (TDI)-based polyurethane composite during its synthesis process. Elliptical protrusions growing radially outward from the filler surface, which serve as the critical intermediate nanostructures of the interface layer, are observed by in situ cryo-TEM, indicating that the interface layer is formed through a curing reaction of the prepolymer molecules anchored on the filler surface. Both decreasing filler sizes and adding coupling agents can enhance the interfacial interactions. The addition of 0.05 wt % coupling agent increases the interface thickness from 83.93 to 129.31 nm and improves the fracture toughness of the composite by 75.1%. These findings provide new insights for rationally designing interfacial nanostructures and high-performance polymer composites.

Interfacial Electrokinetic Phenomena of Thermoresponsive Microgels with a Spatial Gradient of Charged Groups

When functional microgels are synthesized via radical copolymerization, spatial gradients of functional groups often form due to a difference in reactivity ratios between monomer and comonomer. In this study, we systematically investigated the effect of a decreasing gradient of charged groups from the core to the shell of microgels on their surface properties, which are crucial for colloidal particles, through the analysis of interfacial electrokinetic phenomena using Ohshima's equation. A series of electrophoretic analyses combined with dynamic light scattering revealed that the surface of the microgels undergoes a multistep collapse during the particle-size reduction due to dehydration upon increasing the temperature. Furthermore, the more complicated hierarchical gradient of charged groups within the microgels was elucidated by quantitatively evaluating changes in surface properties during precipitation polymerization based on interfacial electrokinetic phenomena.

Nanogels with tailored hydrophobicity and their behavior at air/water interfaces

The interfacial behavior of micro-/nanogels is governed to a large extent by the hydrophobicity of their polymeric network. Prevailing studies to examine this influence mostly rely on external stimuli like temperature or pH to modulate the particle hydrophobicity. Here, a sudden transition between hydrophilic and hydrophobic state prevents systematic and gradual modulation of hydrophobicity. This limits detailed correlations between interfacial behavior and network hydrophobicity. To address this challenge, we introduce a nanogel platform that allows accurate tuning of hydrophobicity on a molecular level. For this, via post-functionalization of active ester-based particles, we prepare poly(N-(2-hydroxypropyl)methacrylamide) (PHPMA) nanogels as a hydrophilic benchmark and introduce gradually varied amounts of hydrophobic propyl or dodecyl moieties to increase the nanogel hydrophobicity. We study the deformation and arrangement of these particles at an air/water interface and correlate the results with quantitative measures for nanogel hydrophobicity. We observe that increasing hydrophobicity of nanogels, either by increasing the hydrophobic moiety ratio or the alkyl chain length, leads to decreased particle deformability and aggregation of an interfacially-adsorbed monolayer. Contrary to what may be intuitively assumed, these changes are not gradual, but rather occur suddenly above a threshold in hydrophobicity. Our study further shows that the effect of hydrophobicity affects the nanogel properties differently in bulk and when adsorbed at liquid interfaces. Thus, this study establishes the transition of interfacial behavior between soft gel-like particles to a solid spherical morphology triggered by the increase in hydrophobicity.

Machine-learning-assisted prediction of the size of microgels prepared by aqueous precipitation polymerization

The size of soft colloids (microgels) is essential; however, control over their size has typically been established empirically. Herein, we report a linear-regression model that can predict microgel size using a machine learning method, sparse modeling for small data, which enables the determination of the synthesis conditions for target-sized microgels.

Multi-layer core/shell microgels with internal complexity and their nanocomposites

In this study, we show that core/shell (CS) microgels with multiple layers can be created via a one-pot precipitation polymerization, in which monomers are added to the reaction flask multiple times once most of the previous monomer has been consumed. The complex internal structures of the microgels were examined using a combination of scattering and microscopy techniques.

Pre- and post-functionalization of thermoresponsive cationic microgels with ionic liquid moieties carrying different counterions

We investigate the effect of different anions on the temperature-dependent solution properties of poly(N-vinylcaprolactam) microgels carrying alkylated ionic liquid vinylimidazolium moieties synthesized by a pre- and post-functionalization approach.

Clarification of Surface Deswelling of Thermoresponsive Microgels by Electrophoresis

Although many investigations of thermoresponsive microgels have been reported, their surface properties, which are crucial in colloid science, are still not fully understood. In this study, microgels with surface-localized charged groups were synthesized by precipitation polymerization, and their electrophoretic behaviors were analyzed using a modified version of Ohshima's equation to obtain two surface properties of the soft particles: the softness parameter and the surface charge density. This systematic evaluation allows us to discuss the thermoresponsiveness of the overall microgels and their surfaces separately. Furthermore, the validity of the surface properties obtained from electrophoresis was verified by comparing them with the results of seeded emulsion polymerization in the presence of the microgels and the force-indentation curves obtained via high-speed atomic force microscopy (HS-AFM).

Durable gelfoams stabilized by compressible nanocomposite microgels

Compressible nanocomposite microgels can stabilize the air/water interfaces of gas bubbles for several months, which affords durable gelfoams.

Engineering hybrid microgels as particulate emulsifiers for reversible Pickering emulsions

Thermo-responsive microgels are unique stabilizers for stimuli-sensitive Pickering emulsions that can be switched between the state of emulsification and demulsification by changing the temperature. However, directly temperature-triggering the phase inversion of microgel-stabilized emulsions remains a great challenge. Here, a hybrid poly(N-isopropylacrylamide)-based microgel has now been successfully fabricated with tunable wettability from hydrophilicity to hydrophobicity in a controlled manner. Engineered microgels are synthesized from an inverse emulsion stabilized with hydrophobic silica nanoparticles, and the swelling-induced feature can make the resultant microgel behave like either hydrophilic or hydrophobic colloids. Remarkably, the phase inversion of such microgel-stabilized Pickering emulsions can be in situ regulated by temperature change. Moreover, the engineered microgels were capable of stabilizing water-in-oil Pickering emulsions and encapsulation of enzymes for interfacial bio-catalysis, as well as rapid cargo release triggered by phase inversion.

DNA introduces an independent temperature responsiveness to thermosensitive microgels and enables switchable plasmon coupling as well as controlled uptake and release

A novel DNA-microgel hybrid system with dual thermal responsiveness is introduced uitilizing covalent coupling of single stranded DNA (ssDNA) to thermoresponsive microgels (μGs). The spatial distribution of the coupling sites for the ssDNA was characterized with 3D superresolution fluorescence microscopy. The DNA-functionalized μGs remain thermoresponsive and can take up dye-labeled complementary ssDNA, which can be released again by overcoming the dehybridization temperature of the DNA independently of the volume phase transition (VPT) of the μGs. The same holds for nano-objects represented by plasmonic gold nanoparticles (AuNPs), the penetration depth of which was visualized via TEM tomography and 3D reconstruction and which show enhanced plasmonic coupling in the collapsed state of the μG and thus gets switchable. In contrast, if ssDNA was taken up just by non-specific interactions, i.e. into non-functionalized μGs, its release is temperature-independent and can only be induced by increasing the salt concentration. Thus, the incorporated ssDNA represents highly selectice binding sites determined by their base number and sequence, which makes the VPT, beeing determined by the μG composition, and the reversible uptake and release enabled through programmable DNA hybridization are independent features. The combination with the typically high biocompatibility and the retained swellability and permeability hold promise for new fundamental insights as well as for potential applications in biological environments.

Novel D–π-A and A–π-D–π-A three-component photoinitiating systems based on carbazole/triphenylamino based chalcones and application in 3D and 4D printing

A series of carbazole or triphenylamine based mono-chalcones, displaying either D–π-A or A–π-D–π-A architecture have been designed as photoinitiators for 3D and 4D printing.