Characterization of Heterocoagulation with Oppositely Charged Polymer Colloid Particles through Online Tracking of Light Transmittance

What is the role of PEO chains in the assembly of core-corona supraparticles in aqueous dispersions?

Hypothesis The assembly of core-corona supraparticles in aqueous dispersions has been regularly assisted by auxiliary monomers/oligomers which modify the individual particles with, e.g., surface grafting of polyethylene oxide (PEO) chains or other hydrophilic monomers. However, this modification complicates the preparation and purification procedures and increases potential upscaling efforts. Hybrid polymer-silica core-corona supracolloids could be more simply assembled if the PEO chains from surfactants, typically used by default as polymer stabilizers, concomitantly act as assembly promotors. The supracolloids assembly could therefore be more easily achieved without requiring particles functionalization or post-purification steps. Methods The self-assembly of supracolloidal particles prepared with PEO-surfactant stabilized (Triton X-405) and/or PEO-grafted polymer particles is compared to differentiate the roles of the PEO chains in the assembly of core-corona supraparticles. Using time-resolved dynamic light scattering (DLS) and cryogenic transmission electron microscopy(cryo-TEM), the effect of concentration of PEO chains (from surfactant) on the kinetics and dynamics of supracolloids assembly is investigated. Self-consistent field (SCF) lattice theory was used to numerically study the distribution of PEO chains at the interfaces present in the supracolloidal dispersions. Findings The PEO based surfactant can be used as assembly promoter of core-corona hybrid supracolloids due to its amphiphilic nature and via establishing hydrophobic interactions. The concentration of the PEO surfactant, and especially the PEO chains distribution over the different interfaces, crucially affect the supracolloids assembly. A simplified pathway for preparing hybrid supracolloidal particles with a well-controlled corona coverage over polymer cores is presented.

Raspberry-Shaped Microgels Assembled at the Oil-Water Interface by Heterocoagulation of Complementary Microgels

Raspberry-shaped particles have attracted increasing interest due to their tunable surface morphologies and physicochemical properties. A variety of covalent and noncovalent strategies have been developed for the fabrication of raspberry-shaped particles. However, most of these strategies are complex or require precise control of solution conditions. In this work, we develop a direct approach for the fabrication of noncovalent raspberry-shaped microgels. Our strategy works through the electrostatically driven heterocoagulation of binary microgels with complementary functional groups at the oil-water interface. By introducing hexanoic acid (HA) into the oil phase, stable inverse water-in-oil (w/o) Pickering emulsions could be stabilized solely by HA-swollen microgels or self-assembled raspberry-shaped microgels. Furthermore, the formation mechanism and the interfacial properties of interfaces laden with raspberry-shaped microgels were investigated. The results indicate that HA can effectively improve the hydrophobicity and interfacial activity of microgels. In addition, raspberry-shaped microgels achieve high coverage on the droplet surface, resulting in the elastic interface and excellent stability of emulsions. We envision that these results will not only fill a knowledge gap in the field of soft matter interfacial self-assembly, but also will shed light on the rational design of raspberry-shaped soft colloids and the on-demand control of interfacial rheology. In addition, we expect that our results will contribute to wider applications of microgel-stabilized emulsions, including cascade catalysis, microreactor, and in vivo drug delivery.

Tailoring Disorder and Quality of Photonic Glass Templates for Structural Coloration by Particle Charge Interactions

To obtain high-quality homogeneous photonic glass-based structural color films over large areas, it is essential to precisely control the degree of disorder of the spherical particles used and reduce the crack density within the films as much as possible. To tailor the disorder and quality of photonic glasses, a heteroaggregation-based process was developed by employing two oppositely charged equal-sized polystyrene (PS) particle types. The influence of the particle size ratio on the extent of heteroaggregation in the suspension mixes is investigated and correlated with both the morphology and the resultant optical properties of the films. The results show that the oppositely charged particle size ratio within the mix greatly influences the assembled structure in the films, affecting their roughness, crack density, and the coffee-ring formation. To better differentiate the morphology of the films, scanning electron microscopy images of the microstructures were classified by a supervised training of a deep convolutional neural network model to find distinctions that are inaccessible by conventional image analysis methods. Selected compositions were then infiltrated with TiO₂ via atomic layer deposition, and after removal of the PS spheres, surface-templated inverse photonic glasses were obtained. Different color impressions and optical properties were obtained depending on the heteroaggregation level and thus the quality of the resultant films. The best results regarding the stability of the films and suppression of coffee-ring formation are obtained with a 35 wt % positively charged over negatively charged particle mix, which yielded enhanced structural coloration associated with improved film quality, tailored by the heteroaggregation fabrication process.

Synthetic strategies for raspberry-like polymer composite particles

The strategies used for the preparation of raspberry-like polymer composite particles are summarized comprehensively.