Preparation of tough, thermally stable, and water-resistant double-network ion gels consisting of silica nanoparticles/poly(ionic liquid)s through photopolymerisation of an ionic monomer and subsequent solvent removal

We report the preparation of tough, thermally stable, and water-resistant double-network (DN) ion gels, which consist of a partially-clustered silica nanoparticle network and poly(ionic liquid) (PIL) network holding an ionic liquid. Silica nanoparticles/poly([Evim][Tf2N]) DN ion gels are prepared by photo-induced radical polymerisation of [Evim][Tf2N] in a mixture containing silica nanoparticles, [Bmim][Tf2N], ionic liquid based cross-linker [(VIM)2C4][Tf2N]2, and ethyl acetate, followed by subsequent solvent evaporation. Tensile strength measurements show that the mechanical properties of the PIL DN ion gels were higher than those of the PIL single-network (SN) ion gel. A rheological study indicates that an enhancement in mechanical strength of the PIL DN ion gels can be achieved when silica nanoparticles form partial clusters in [Bmim][Tf2N]. The cyclic stress–strain measurement of the PIL DN ion gels shows hysteresis loops, suggesting that the silica nanoparticle clusters rupture and dissipate the loading energy when the PIL DN ion gels undergo a large deformation. The fracture strength and Young's modulus of the PIL DN ion gels increase as the diameter of the silica nanoparticles is decreased. Thermogravimetric analysis measurement shows that the PIL DN ion gel has a high decomposition temperature of approximately 400 °C. Moreover, the swelling test shows that the PIL DN ion gel possesses an excellent water-resistant property because of the hydrophobic nature of the PIL backbone. We believe that such tough, thermally stable, and water-resistant PIL DN ion gels can be used as carbon dioxide separation membranes, sensors, and actuators for soft robotics

Monodisperse polylactide microcapsules with a single aqueous core prepared via spontaneous emulsification and solvent diffusion

A simple approach to preparing monodisperse poly(D,L-lactide) (PDLLA) microcapsules with a single aqueous core is developed. The method is based on automatic water-in-oil-in-water double emulsion formation from oil-in-water single emulsion via spontaneous emulsification which voluntarily disperses part of continuous aqueous phase into the dispersed oil phase dissolving oil-soluble amphiphilic diblock copolymer, poly(D,L-lactide)-b-poly(2-dimethylaminoethyl methacylate)(PDLLA-b-PDMAEMA), followed by coalescence of tiny water droplets within the polymer droplets, coupled with quick precipitation of polymers by diluting the emulsion with water. In this study, we have investigated the effect of PDLLA to PDLLA-b-PDMAEMA ratios and flow rates of each solution during preparing the emulsion on the final morphology and the size of the microcapsules. It was found that the polymer blend ratio played a crucial role in determining internal structure of the microcapsules. The microcapsules size decreased with the increment of the flow rate ratios of the continuous phase to the dispersed phase and eventually reached 10 μm, while maintaining narrow size distribution. In addition, we have demonstrated that the microcapsules can encapsulate both hydrophilic and hydrophobic compounds during the formation

Continuous fabrication of monodisperse polylactide microspheres by droplet-to-particle technology using microfluidic emulsification and emulsion–solvent diffusion

Monodisperse polylactide (PLA) microspheres were continuously fabricated by microfluidic emulsification and subsequent dilution in water. The diameter was precisely tuned from 6 to 50 μm by changing the flow rate of the fluids in microfluidics or the PLA concentration in the dispersed phase. The use of amphiphilic oil-soluble poly(ethylene glycol)-b-polylactide (o-PEG–PLA) as a matrix resulted in a highly porous microsphere morphology, and the porosity was controlled by blending PLA. Therefore, monodisperse PLA microspheres with the predetermined surface porosity were continuously produced by just enough reagents and energy

Microfluidic Formation of Hydrogel Microcapsules with a Single Aqueous Core by

We report a simple process to fabricate monodisperse tetra-arm poly(ethylene glycol) (tetra-PEG) hydrogel microcapsules with an aqueous core and a semipermeable hydrogel shell through the formation of aqueous two-phase system (ATPS) droplets consisting of a dextran-rich core and a tetra-PEG macromonomer-rich shell, followed by a spontaneous cross-end coupling reaction of tetra-PEG macromonomers in the shell. Different from conventional techniques, this process enables for the continuous production of hydrogel microcapsules from water-in-oil emulsion droplets under mild conditions in the absence of radical initiators and external stimuli such as heating and ultraviolet light irradiation. We find that rapid cross-end coupling reaction of tetra-PEG macromonomers in ATPS droplets in the range of pH from 7.4 to 7.8 gives hydrogel microcapsules with a kinetically arrested core–shell structure. The diameter and core–shell ratio of the microcapsules can be easily controlled by adjusting flow rates and ATPS compositions. On the other hand, the slow cross-end coupling reaction of tetra-PEG macromonomers in ATPS droplets at pH 7.0 and lower induces structural change from core–shell to Janus during the reaction, which eventually forms hydrogel microparticles with a thermodynamically stable crescent structure. We believe that these hydrogel microparticles with controlled structures can be used in biomedical fields such as cell encapsulation, biosensors, and drug delivery carriers for sensitive biomolecules

Design of Clickable Ionic Liquid Monomers to Enhance Ionic Conductivity for Main-Chain 1,2,3-Triazolium-Based Poly(Ionic Liquid)s

A series of clickable alpha-azide-omega-alkyne ionic liquid (IL) monomers with an ethylene oxide spacer were developed and applied to the synthesis of 1,2,3-triazolium-based poly(ionic liquid)s (TPILs) with high ionic conductivities via one-step thermal azide-alkyne cycloaddition click chemistry. Subsequently, the number of IL moieties in the resultant TPILs was further increased by N-alkylation of the 1,2,3-triazole-based backbones of the TPILs with a quarternizing reagent. This strategy affords the preparation of TPILs having either one or two 1,2,3-triazolium cations with bis(trifluoromethylsulfonyl)imide anions in a monomer unit. Synthesis of the TPILs was confirmed by H-1 and C-13 NMR spectroscopy and gel permeation chromatography. The effects of the length of the ethylene oxide spacer and the number of IL moieties in the IL monomer unit on the physicochemical properties of the TPILs were characterized by differential scanning calorimetry, thermogravimetric analysis, and impedance spectroscopy. The introduction of a longer ethylene oxide spacer or an increase in the number of IL moieties in the monomer unit resulted in TPILs with lower glass-transition temperatures and higher ionic conductivities. The highest ionic conductivity achieved in this study was 2.0 x 10(-5) S cm(-1) at 30 degrees C. These results suggest that the design of the IL monomer provides the resultant polymer with high chain flexibility and a high IL density, and so it is effective for preparing TPILs with high ionic conductivities

Flow synthesis of monodisperse micron-sized polymer particles by heterogeneous polymerization using a water-in-oil slug flow with a non-ionic surfactant

Flow synthesis of poly(methyl methacrylate) particles was performed by heterogeneous polymerization of methyl methacrylate using a water-in-oil (W/O) slug flow with or without a non-ionic surfactant in the continuous organic phase. It was found that undesired phenomena in this polymerization system, clogging of the channel and broadening particle size distribution, can occur when growing polymer particles adsorb to the W/O interface during polymerization, and that the addition of non-ionic surfactant to the continuous organic phase prevents the particles from adsorption to the W/O interface and gives monodisperse polymer particles. In addition, it was shown that as the initiator concentration increases, the particle diameter becomes larger, resulting in monodisperse micron-sized polymer particles with 100% monomer conversion at a 120-min reaction time. These results indicated that the heterogeneous polymerization process using a W/O slug flow can be a promising way to continuously prepare monodisperse polymer particles with micron sizes in a short reaction time

Microfluidic Fabrication of Monodisperse Polylactide Microcapsules with Tunable Structures through Rapid Precipitation

We describe a versatile and facile route to the continuous production of monodisperse polylactide (PLA) microcapsules with controllable structures. With the combination of microfluidic emulsification, solvent diffusion, and internal phase separation, uniform PLA microcapsules with a perfluorooctyl bromide (PFOB) core were successfully obtained by simply diluting monodisperse ethyl acetate (EA)-in-water emulsion with pure water. Rapid extraction of EA from the droplets into the aqueous phase enabled the solidification of the polymer droplets in a nonequilibrium state during internal phase separation between a concentrated PLA/EA phase and a PFOB phase. Higher-molecular-weight PLA generated structural complexity of the microcapsules, yielding core–shell microcapsules with covered with small PFOB droplets. Removal of the PFOB via freeze drying gave hollow microcapsules with dimpled surfaces. The core–shell ratios and the diameter of these microcapsules could be finely tuned by just adjusting the concentration of PFOB and flow rates on emulsification, respectively. These biocompatible microcapsules with controllable size and structures are potentially applicable in biomedical fields such as drug delivery carriers of many functional molecules

Controlled mechanical properties of poly(ionic liquid)-based hydrophobic ion gels by the introduction of alumina nanoparticles with different shapes

Ionic–liquid gels, also known as ion gels, have gained considerable attention due to their high ionic conductivity and CO2 absorption capacity. However, their low mechanical strength has hindered their practical applications. A potential solution to this challenge is the incorporation of particles, such as silica nanoparticles, TiO2 nanoparticles, and metal–organic frameworks (MOFs) into ion gels. Comparative studies on the effect of particles with different shapes are still in progress. This study investigated the effect of the shape of particles introduced into ion gels on their mechanical properties. Consequently, alumina/poly(ionic liquid) (PIL) double-network (DN) ion gels consisting of clustered alumina nanoparticles with various shapes (either spherical or rod-shaped) and a chemically crosslinked poly[1-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide] (PC2im-TFSI, PIL) network were prepared. The results revealed that the mechanical strengths of the alumina/PIL DN ion gels were superior to those of PIL single-network ion gels without particles. Notably, the fracture energies of the rod-shaped alumina/PIL DN ion gels were approximately 2.6 times higher than those of the spherical alumina/PIL DN ion gels. Cyclic tensile tests were performed, and the results indicate that the loading energy on the ion gel was dissipated through the fracture of the alumina network. TEM observation suggests that the variation in the mechanical strength depending on the shape can be attributed to differences in the aggregation structure of the alumina particles, thus indicating the possibility of tuning the mechanical strength of ion gels by altering not only particle kinds but its shape

One-pot synthesis of poly(ionic liquid)s with 1,2,3-triazolium-based backbones via clickable ionic liquid monomers

Clickable α-azide-ω-alkyne ionic liquid monomers were developed and subsequently applied to the one-pot synthesis of ionically conducting poly(ionic liquid)s with 1,2,3-triazolium-based backbones through a click chemistry strategy. This approach does not require the use of solvents, polymerisation mediators, or catalysts. The obtained poly(ionic liquid)s were characterized by NMR, differential scanning calorimetry, thermogravimetric analysis, and impedance spectroscopy analysis. Moreover, these poly(ionic liquid)s were cross-linked via N-alkylation with a dianion quarternizing agent to achieve enhanced ionic conductivity and mechanical strength. The resulting free-standing films showed a Young's modulus up to 4.8 MPa and ionic conductivities up to 4.60 × 10−8 S cm−1 at 30 °C. This facile synthetic strategy has the potential to expand the availability of poly(ionic liquid)s and promote the development of functional materials