The Impact of Nonpolymerizable Swelling Agents On The Synthesis of Particles With Combined Geometric, Interfacial, and Compositional Anisotropy

Reconfigurable homochiral colloidal clusters assembled under orthogonally applied electric and magnetic fields

Chiral structures assembled from colloids are of great interest for applications in metamaterials and micromachines. However, similar to their molecular counterparts, these assemblies often result in racemic mixtures. Achieving homochirality by breaking the symmetry remains a significant challenge. Here, we report an approach to obtain single-handed clusters from colloidal dimers using orthogonal electric and magnetic fields. Applying an alternating-current electric field perpendicular to the substrate generates a mixture of chiral clusters with both handedness. However, symmetry is broken by superimposing a planar rotating magnetic field, favoring one chirality over the other. The cluster's chirality can be precisely controlled in situ by adjusting the magnetic field's direction and strength, as well as the electric field frequency. Remarkably, this method also induces uniform chirality in initially achiral clusters when exposed solely to the electric field. Both experimental and numerical analyses reveal that the stability of specific handedness depends on the competition between forces and torques generated by the magnetic field, electric field, and electrohydrodynamic flow. Furthermore, we propose a strategy for producing colloidal clusters with uniform sizes and single-handedness through dynamic tuning of the electric and magnetic fields. This work not only demonstrates the potential of integrating external fields but also provides a viable way to create reconfigurable chiral colloidal structures.

Synthesis of dimpled polymer particles and polymer particles with protrusions - Past, present, and future

Since the development of emulsion polymerization techniques, polymer particles have become the epitome of standard colloids due to the exceptional control over size, size distribution, and composition the synthesis methods allow reaching. The exploration of different variations of the synthesis methods has led to the discovery of more advanced techniques, enabling control over their composition and shape. Many early investigations focused on forming particles with protrusions (with one protrusion, called dumbbell particles) and particles with concavities, also called dimpled particles. This paper reviews the literature covering the synthesis, functionalization, and applications of both types of particles. The focus has been on the rationalization of the various approaches used to prepare such particles and on the discussion of the mechanisms of formation not just from the experimental viewpoint but also from the standpoint of thermodynamics. The primary motivation to combine in a single review the preparation of both types of particles has been the observation of similarities among some of the methods developed to prepare dimpled particles, which sometimes include the formation of particles with protrusions and vice versa. The most common applications of these particles have been discussed as well. By looking at the different approaches developed in the literature under one general perspective, we hope to stimulate a more ample use of these particles and promote the development of even more effective synthetic protocols.

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.

Multicolor Electrochromic Dye-Doped Liquid Crystal Yolk-Shell Microcapsules

A new system of yolk-shell microcapsules containing two types of dye-doped liquid crystals was prepared via seed emulsion polymerization in which the synthetic process was mimicking plant respiration. The resulting system demonstrated reversible low voltage-driven switching between multispectral colored and transparent states. Moreover, wearable multicolor electrochromic fibers based on calcium alginate were produced via wet spinning to expand the application of yolk-shell dye-doped liquid crystal microcapsules. In addition to its long-term optical stability, the proposed cells and fibers also have satisfactory driving voltage values of color change (4.8 and 9.0 V), which are far lower than the human body safety voltage (12 V). We believe that the prepared microcapsules and fibers are potentially widely applicable in smart windows, electronic paper, and military camouflage clothing.

Bifunctional Janus Spheres with Chemically Orthogonal Patches

Bifunctional Janus particles with patches carrying orthogonal surface functionalities that can be independently modified are widely seen as promising building blocks for the bottom-up assembly of functional materials due to their full compositional and geometrical programmability. However, synthesis of these colloids remains an elusive task as current scalable procedures are generally limited to monofunctional particles only. Herein, a scalable bulk wet-chemical synthetic method for fabricating bifunctional Janus particles following a two-step dispersion polymerization is developed. Patch formation on these colloids is driven by the spontaneous phase separation between a brominated outer shell and poly(propargyl acrylate) (p(PA)), formed after the seed particles were swollen with the corresponding monomer. The size ratio between the two patches is readily tunable by controlling the volumetric ratio between the feeding monomers. The distinct patches of these Janus particles carry chemical handles facilitating independent and orthogonal surface modification using Atom Transfer Radical Polymerization (ATRP) and thiol-yne Click chemistry for the brominated and alkyne-containing patches, respectively. The presented route toward bifunctional patchy spheres provides a versatile starting point for the development of bifunctional colloidal particles with tailored directional properties.

One-pot synthesis of micron partly hollow anisotropic dumbbell shaped silica core-shell particles

A facile method is described to prepare micron partly hollow dumbbell silica particles in a single step. The obtained particles consist of a large dense part and a small hollow lobe. The spherical dense core as well as the hollow lobe are covered by mesoporous channels. In the case of the smaller lobe these channels are responsible for the permeability of the shell which was demonstrated by confocal imaging and spectroscopy.

Preparation of morphology-controllable PGMA-DVB microspheres by introducing Span 80 into seed emulsion polymerization

Microporous, hollow, or macroporous polymer spheres were prepared by a seed emulsion polymerisation method. Different from the conventional seeded emulsion polymerization, the sorbitan monooleate (Span 80) was added to the seeded emulsion polymerization. In this study, the monodisperse PS seeds prepared by dispersion polymerization were swelled by dibutyl phthalate (DBP), glycidyl methacrylate (GMA), divinylbenzene (DVB) and Span 80 successively. The effect of the amount of Span 80 on the morphology of microspheres was investigated. As different amount of Span 80 was added to the mixture, the poly(glycidyl methacrylate-divinylbenzene) (PGMA-DVB) microspheres showed a variety of morphologies containing microporous, hollow, and macroporous structure. In addition, uniform hollow particles with different pore size can be obtained through adjusting the amount of Span 80.

The obtained PGMA-DVB microspheres showed a variety of morphologies by adjusting the amount of Span 80 in the seeded emulsion polymerization.

Combined chain- and step-growth dispersion polymerization toward PSt particles with soft, clickable patches

Particles with a hard body and soft, clickable dimple- or bulge-patches are prepared by simple combined chain- and step-growth dispersion polymerization.

Intriguing Morphology Evolution from Noncrosslinked Poly(tert-butyl acrylate) Seeds with Polar Functional Groups in Soap-Free Emulsion Polymerization of Styrene

Herein, we demonstrate a facile approach to prepare anisotropic poly(tert-butyl acrylate)/polystyrene (PtBA/PS) composite particles with controllable morphologies by soap-free seeded emulsion polymerization (SSEP). In the first step, noncrosslinked PtBA seeds with self-stabilizing polar functional groups (e.g., ester groups and radicals) are synthesized by soap-free emulsion polymerization. During the subsequent SSEP of styrene (St), PS bulges are nucleated on the PtBA seeds due to the microphase separation confined in the latex particles. The morphology evolution of PtBA/PS composite particles is tailored by varying the monomer/seed feed ratio, polymerization time, and polymerization temperature. Many intriguing morphologies, including hamburger-like, litchi-like, mushroom-like, strawberry-like, bowl-like, and snowman-like, have been acquired for PtBA/PS composite particles. The polar groups on the PtBA seed surface greatly influence the formation and further merging of PS/St bulges during the polymerization. A possible formation mechanism is proposed on the basis of experimental results. These complex composite particles are promising for applications in superhydrophobic coatings.

Localization of Polystyrene Particles on the Surface of Poly(N-isopropylacrylamide-co-methacrylic acid) Microgels Prepared by Seeded Emulsion Polymerization of Styrene

Composite microgels with polystyrene nanoparticles were synthesized by seeded emulsion polymerization of styrene in the presence of pH- and temperature-responsive poly(N-isopropylacrylamide-co-methacrylic acid) microgels as seeds. In particular, the core microgels maintained their swelled state as the pH was increased to 10 during seeded emulsion polymerization conducted at an elevated temperature. Furthermore, we tuned the swelling degree of the core microgels at pH 10 by changing the amount of methacrylic acid incorporated during the synthesis of the core microgels. Unlike deswollen microgels, during the seeded emulsion polymerization, the swollen microgels were covered with a monolayer of non-close-packed polystyrene particles on their surface, as confirmed by electron microscopy. A possible mechanism for the seeded emulsion polymerization of styrene in the presence of swollen microgels under alkaline conditions is proposed.

Impressed pressure-facilitated seeded emulsion polymerization: design of fast swelling strategies for massive fabrication of patchy microparticles

High-pressure and ultrasound swelling polymerization promote the fast and large-scale fabrication of patchy particles for potential applications.

Control of cross-linking and reactions in one-step dispersion polymerization toward particles with combined anisotropies

Particles with a combination of anisotropies in morphology, surface roughness, structure and composition are synthesized by one-step dispersion polymerization.