A Versatile Synthesis Platform To Prepare Uniform, Highly Functional Microgels via Click-Type Functionalization of Latex Particles

Swelling and Collapse of Cylindrical Polyelectrolyte Microgels

In this study, we propose computer simulations of charged cylindrical microgels. The effects of cross-linking density, aspect ratio, and fraction of charged groups on the microgel swelling and collapse with a variation in the solvent quality were studied. The results were compared with those obtained for equivalent neutral cylindrical microgels. The study demonstrated that microgels' degree of swelling strongly depends on the fraction of charged groups. Polyelectrolyte microgels under adequate solvent conditions are characterized by a larger length and thickness than their neutral analogues: the higher the fraction of charged groups, the longer their length and greater their thickness. Microgels' collapse upon solvent quality decline is characterized by a decrease in length and non-monotonous behavior of its thickness. First, the thickness decreases due to the attraction of monomer units (beads) upon collapse. The further thickness increase is related to the surface tension, which tends to reduce the anisotropy of collapsed objects (the minimum surface energy is known to be achieved for the spherical objects). This reduction is opposed by the network elasticity. The microgels with a low cross-linking density and/or a low enough aspect ratio reveal a cylinder-to-sphere collapse. Otherwise, the cylindrical shape is preserved in the course of the collapse. Aspect ratio as a function of the solvent quality (interaction parameter) demonstrates the maximum, which is solely due to the electrostatics. Finally, we plotted radial concentration profiles for network segments, their charged groups, and counterions.

A new look at effective interactions between microgel particles

Thermoresponsive microgels find widespread use as colloidal model systems, because their temperature-dependent size allows facile tuning of their volume fraction in situ. However, an interaction potential unifying their behavior across the entire phase diagram is sorely lacking. Here we investigate microgel suspensions in the fluid regime at different volume fractions and temperatures, and in the presence of another population of small microgels, combining confocal microscopy experiments and numerical simulations. We find that effective interactions between microgels are clearly temperature dependent. In addition, microgel mixtures possess an enhanced stability compared to hard colloid mixtures - a property not predicted by a simple Hertzian model. Based on numerical calculations we propose a multi-Hertzian model, which reproduces the experimental behavior for all studied conditions. Our findings highlight that effective interactions between microgels are much more complex than usually assumed, displaying a crucial dependence on temperature and on the internal core-corona architecture of the particles.

A versatile synthetic platform for amphiphilic nanogels with tunable hydrophobicity

Functionalization of reactive precursor particles allows the preparation of amphiphilic nanogel libraries with tunable network hydrophobicity and comparable colloidal features.

Polyacid microgels with adaptive hydrophobic pockets and ampholytic character: synthesis, solution properties and insights into internal nanostructure by cryogenic-TEM

Microgels with internal and reconfigurable complex nanostructure are emerging as possible adaptive particles, yet they remain challenging to design synthetically. Here, we report the synthesis of highly charged poly(methacrylic acid) (PMAA) microgels incorporating permanent (poly(methyl methacrylate) (PMMA)) and switchable hydrophobic pockets (poly(N,N'-diethylaminoethyl methacrylate) (PDEAEMA)) via emulsion polymerization. We demonstrate detailed tuning of the size, crosslinking density and tailored incorporation of functional comonomers into the polyacid microgels. Analysis via cryo-TEM and pyrene probe measurements reveal switchable hydrophobic pockets inside the microgels as a function of pH. The particles show a rich diversity of internal phase-segregation, that adapts to the surrounding conditions. Large amounts of hydrophobic pockets even lead to hydrophobic bridging between particles. The study shows ways towards tailored polyelectrolyte microgels with narrow dispersity, high charge density, as well as tailored and reconfigurable hydrophobic compartments and interactions.

A robust platform for functional microgels via thiol-ene achemistry with reactive polyether-based nanoparticles

We herein report the development of crosslinked polyether particles as a reactive platform for the preparation of functional microgels. Thiol-ene crosslinking of poly(allyl glycidyl ether) in miniemulsion droplets - stabilized by a surface active, bio-compatible polyethylene glycol block copolymer - resulted in colloidal gels with a PEG corona and an inner polymeric network containing reactive allyl units. The stability of the allyl groups allows the microgels to be purified and stored before a second, subsequent thiol-ene functionalization step allows a wide variety of pH- and chemically-responsive groups to be introduced into the nanoparticles. The facile nature of this synthetic platform enables the preparation of microgel libraries that are responsive to different triggers but are characterized by the same size distribution, surface functionality, and crosslinking density. In addition, the utilization of a crosslinker containing cleavable ester groups renders the resulting hydrogel particles degradable at elevated pH or in the presence of esterase under physiological conditions.

Combining the incompatible: Block copolymers consecutively displaying activated esters and amines and their use as protein-repellent surface modifiers with multivalent biorecognition

We present the facile synthesis and orthogonal functionalization of diblock copolymers consisting of two incompatible segments, i.e. primary amines and activated esters, and demonstrate their use as protein-repellent brush layers with multivalent biorecognition.

Strong anionic polyelectrolyte microgels

We report a facile synthesis of highly uniform poly(styrene sulfonic acid) microgels, which carry a strong polyelectrolyte group at every repeating unit.