Shape Of Microgels Research Articles

Magnetically Actuable Complex‐Shaped Microgels for Spatio‐Temporal Flow Control

AbstractComplex‐shaped microgels are promising building blocks for soft metamaterials. Their active and remote orientational control provides significant potential in architecting them in time and space. This work describes the use of magnetically actuable microgels of complex shape for spatio‐temporal flow control and showcases the concept for microfluidic impellers. First, the fabrication of complex‐shaped magnetically actuable poly(ethylene glycol) diacrylate based microgels via stop‐flow lithography is presented. The microgels comprise a pre‐programmed magnetic moment set by pre‐aligned maghemite nanospindles during the fabrication step. This feature allows the microgels to be positioned in a static magnetic field and rotate under application of a rotating external field. The dependence of the magnetic field rotation rate and strength, maghemite content, and microgel shape on the magnetic response of the microgels is comprehensively quantified. Finally, the magnetic complex‐shaped microgels are integrated as actuable impellers in a microfluidic chip. The microgels are positioned in space by polymerizing them around fixed poly(dimethylsiloxane) (PDMS) pillars. Free rotation around the PDMS pillar is achieved due to the oxygen inhibition layer at the chip and pillar surface. The versatility of the fabrication methodology is showcased by the investigation of in‐chip mixing in a microfluidic device consisting of soft responsive impellers.

FUNDAMENTAL PRINCIPLES OF MICROGEL SYNTHESIS BY INVERSE EMULSION METHOD

Microgels represent a unique class of compounds that combine the properties of such classes of compounds as colloids, macromolecules and surfactants in a unique way. Microgels are widely used for wastewater treatment, as drug delivery systems, for drying biodiesel, in tissue regeneration and implantation, in chromatography, etc. At this point, such methods of microgel synthesis as the precipitation method, suspension polymerisation and the emulsion method have been developed, which have become traditional in the synthesis of microgels. This publication reviews the inverse emulsion method for microgel synthesis based on polyacrylamide and its derivatives. This method was chosen due to a number of advantages, such as a high degree of monomer conversion, the ability to control the granulometric composition of gel particles during synthesis, a simplified drying procedure for the finished product, etc. The article describes the synthesis features that affect the size and shape of microgels, describes the main factors to consider when planning an inverse emulsion synthesis; shows the difference between macroemulsion, nanoemulsion and microemulsion. The article also presents some aspects of the synthesis of microgel based on acrylamide and its derivatives: the main free-radical initiators are listed; monomers that affect microgel properties are described. This review may be of interest to specialists who are just starting research in this field. Based on this publication, the reader will be able to plan and conduct an experiment on the synthesis of polyacrylamide-based microgels by the inverse emulsion method. For citation: Burin D.A., Rozhkova Yu.A., Kazantsev A.L. Fundamental principles of microgel synthesis by inverse emulsion method. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 3. P. 6-17. DOI: 10.6060/ivkkt.20236603.6732.

Novel Insights on the Three-dimensional Shape of Microgels at Fluid Interfaces

Mechanically soft colloids (microgels) adsorbed at the interface between two fluids offer superior advantages over hard counterparts for a variety of applications ranging from foams/emulsion stabilization to the assembly of two-dimensional (2D) materials. Particle deformability and compressibility impart additional responses to microgel-laden interfaces that can be controlled on-demand by varying single-particle properties (e.g. crosslinking content and polymer density profile) and/or external parameters (e.g. interfacial compression and tension, temperature, oil polarity). In order to understand how single-particle softness influences the resulting material properties, a detailed quantification of the microgel’s 3D conformation when confined at the fluid interface is of utmost importance. This article describes how different methodologies can be used to visualize, and in some case quantify, the conformation of adsorbed microgels, putting particular emphasis on the multiple advantages offered by in situ atomic force microscopy imaging at the fluid interface. The influence of the internal particle architecture, as well as that of temperature, interfacial tension and solubility in the organic phase, will be discussed. Finally, some perspectives on how softness can be exploited to tune the structural and mechanical properties of microgel monolayers will be provided.

Anisotropic Responsive Microgels Based on the Cholesteric Phase of Chitin Nanocrystals.

Anisotropic stimuli-responsive microgels based upon the cholesteric phase of chitin nanocrystals and N-isopropylacrylamide were designed and synthesized. The cholesteric structure was interrogated, and the texture was shown to directly influence the microgel shape and anisotropy. Changes in the microgel volume led to changes in the texture, where microgels comprising up to six bands exhibited a twisted bipolar texture, while those with greater volumes displayed a concentric-packing structure. As designed, the imprinted cholesteric phase induced an asymmetric response to temperature, leading to a change in shape and optical properties. Furthermore, the cholesteric structure is able to deform, facilitating transport into a small channel. Access to synthetic structures having a self-assembled twisted texture derived from cholesterics embedded within a polymer matrix will provide guidelines for designing biopolymer composites with programmable motion.

Controlled Shape Transformation and Loading Release of Smart Hemispherical Hybrid Microgels Triggered by ‘Inner Engines’

AbstractThe dynamic controlling and changing the shape of microgels, especially the anisotropic change, remains a challenge for the construction of advanced smart materials. To this end, the fabrication of hemispherical hybrid microgels (HHMs) with Au nanorods(AuNRs)‐based vesicles was demonstrated, with the thermo‐ and NIR light‐triggered anisotropic shape transformation and controlled release induced by ‘inner engines’. AuNRs‐based vesicles acting as ‘inner engines’ were first fabricated by the self‐assembly of thiol‐terminated block copolymers modified AuNRs, with the absorbance of NIR light (808 nm), thus generating heat in the system; second, poly(N‐isopropyl acrylamide) (pNIPAM)‐based HHMs containing AuNRs‐based vesicles were synthesized by the assistance of both microfluidics and photopolymerization. Importantly, uneven heat generated by the gradationally distributed AuNRs‐based vesicles in the hybrid microgels could cause an anisotropic shape change from hemispherical to mushroom‐like shape via external stimuli, with good reversibility and reproducibility. Based on this, the controlled release of loadings (e. g. Rhodamine B (RhB)) inside the engines of the microgels can be realized by combining NIR light irradiation and the shape transformation. Thus, HHMs with AuNRs‐vesicle‐based engines provide a novel platform for the investigation of drug release, artificial actuators, and micromotors.

Effect of micro-gel shape and concentration on sensory perception of micro-gels-enriched stirred yoghurts

Protein-enriched micro-gels of different morphologies were incorporated into stirred yoghurts. Resulting sensory and rheological properties were investigated. An experimental design was defined with two factors (micro-gel shape and concentration). Four different shapes were designed and three micro-gel concentrations were used (2.5, 5, 10 wt%). A Flash profile with experienced assessors was performed in combination with instrumental measurements in an attempt to relate the added micro-gel shape and concentration to sensory perception. The most important attributes to explain the texture of the micro-gels-enriched stirred yoghurts were consistency and graininess, which could then be associated to structural parameters. It has been shown that an increase in particle lengths and widths gave rise to a visual or mouthfeel grainy perception whereas the presence of entangled micro-gels contributed to instrumental and sensory consistency. Therefore, the sensory properties of micro-gels-enriched stirred yoghurts could clearly be distinguished depending on the characteristics of the added particles.

Fabrication of shape controllable Janus alginate/pNIPAAm microgels via microfluidics technique and off-chip ionic cross-linking.

A novel method to fabricate shape controllable alginate/pNIPAAm complex microgels is reported. Monodisperse alginate/pNIPAAm droplets are created via microfluidics and cross-linked in different concentrations of hot glycerol/barium acetate water solutions. By changing the initial droplet size and glycerol concentration of the collecting solution, the resultant microgel shape and surface details can be systematically tuned. High-speed imaging is used to visualize and explain the microgel formation process.

Poly(N-isopropylacrylamide) microgels at the oil–water interface: adsorption kinetics

Understanding the adsorption behaviors of soft poly(N-isopropylacrylamide) (PNIPAM) microgels to the oil–water interface has become increasingly important both in terms of fundamental science and applications of microgels as multi-stimuli responsive emulsion stabilizers. In the present work, we used pendant drop tensiometry to trace the evolution of oil–water interfacial tensions. We investigated two PNIPAM microgels with different cross-link density as well as poly(styrene-co-NIPAM) particles. We found that the adsorption of microgels from the aqueous phase to the oil–water interface is dominated by two steps. Microgels first diffuse to the oil–water interface and this diffusion process depends on microgel concentration in the bulk phase. The second process involves the deformation and spreading of microgels at the interface. The second process depends strongly on microgel deformability. The behavior of the different microgel systems is compared with conventional Pickering stabilizers and proteins. Our results demonstrate that the softness of the microgels dominates their properties at the oil–water interface. The change of microgel shape at the interface resembles the unfolding transitions observed with proteins. On the other hand, microgels are distinctly different from conventional, rigid Pickering stabilizers.

Dispersion Polymerization of Microgel in Aqueous Solution of Ammonium Sulfate and its Oil Displacement Efficiency Study

Microgel can be used as a novel deep profile control (conformance control) agent in the aspect of EOR(Enhanced oil recovery) in mature oil field development. Dispersion polymerization of microgel has been successfully carried out in aqueous AS (ammonium sulfate) media by using AM (acrylamide), PEG 200 DA (Poly(ethylene glycol(200) diacrylate)), PVP (Poly(vinyl pyrrolidone)), V-50(2,2’-azobis(2-amidino-propane) dihydrochloride), as the monomer, cross-linker, stabilizer and initiator, respectively. The effect of ammonium sulfate and Poly(vinyl pyrrolidone) concentrations are strongly on microgels successfully polymerization. POM（polarization microscope） and SEM （scanning electron microscope）results show that the shape of microgels is in oval or nonspherical state. The surface structure of microgel is rather accidented full of mesoporous. Addition of inorganic salts interacting with poly(acrylamide) microgel can affect its micromorphology and results in the appearance of single crystal clusters. Sand pack flowing experiment shows that the microgel has perfect propagating property during the process of injection and can achieve a high oil recovery efficiency of 23.4% by the total of 0.4 PV microgel solution injection.