Liquid Crystal-Templated Porous Microparticles via Photopolymerization of Temperature-Induced Droplets in a Binary Liquid Mixture

Abstract

Porous polymeric microspheres are an emerging class of materials, offering stimuli-responsive cargo uptake and release. Herein, we describe a new approach to fabricate porous microspheres based on temperature-induced droplet formation and light-induced polymerization. Microparticles were prepared by exploiting the partial miscibility of a thermotropic liquid crystal (LC) mixture composed of 4-cyano-4′-pentylbiphenyl (5CB, unreactive mesogens) with 2-methyl-1,4-phenylene bis4-[3-(acryloyloxy)­propoxy] benzoate (RM257, reactive mesogens) in methanol (MeOH). Isotropic 5CB/RM257-rich droplets were generated by cooling below the binodal curve (20 °C), and the isotropic-to-nematic transition occurred after cooling below 0 °C. The resulting 5CB/RM257-rich droplets with radial configuration were subsequently polymerized under UV light, resulting in nematic microparticles. Upon heating the mixture, the 5CB mesogens underwent a nematic–isotropic transition and eventually became homogeneous with MeOH, while the polymerized RM257 preserved its radial configuration. Repeated cycles of cooling and heating resulted in swelling and shrinking of the porous microparticles. The use of a reversible materials templating approach to obtain porous microparticles provides new insights into binary liquid manipulation and potential for microparticle production.

Emergent Properties from Three-Dimensional Assemblies of (Nano)particles in Confined Spaces

“…However, the generation of high surface area superstructures, such as porous superparticles, enables important advantages such as sequestration, storage, and directed release of cargo, as well as increasing the reactivity of the superparticle for chemical reactions taking place on its surface . Over the past few years, a number of strategies have emerged to generate porous, high-surface area superparticles. − …”

Exploiting Molecular Orders at the Interface of Microdroplets for Intelligent Materials

“…5CB molecules can coalign with RMs and LCOs inside microdroplets after the removal of organic solvent. 37,38 With PVA dispersed in water to offer planar anchoring, the microdroplets are formed with a bipolar configuration, where 5CB lowers the precursor viscosity of the organic phase and improves the surface anchoring strength. 39 After photopolymerization under UV light and the extraction of 5CB by organic solvent ethanol, spindle-shaped LCE microparticles are obtained, as a result of twisting of the director field and anisotropic shrinkage within the particle.…”

“…LCE microparticles with uniform size are produced via a microfluidic device, where nonreactive mesogenic 5CB and magnetic nanoparticles can be introduced (Figure a). 5CB molecules can coalign with RMs and LCOs inside microdroplets after the removal of organic solvent. , With PVA dispersed in water to offer planar anchoring, the microdroplets are formed with a bipolar configuration, where 5CB lowers the precursor viscosity of the organic phase and improves the surface anchoring strength . After photopolymerization under UV light and the extraction of 5CB by organic solvent ethanol, spindle-shaped LCE microparticles are obtained, as a result of twisting of the director field and anisotropic shrinkage within the particle. , The morphology of the microparticles can be tuned by varying the fraction of 5CB and the molar ratio of LCOs to RMs in the precursors.…”

Progress in Fabrication and Applications of Cholesteric Liquid Crystal Microcapsules

“…In addition, depending on the solvent quality and temperature, the prepared LC solid shells exhibited good swelling/shrinkage properties, which could be further used to encapsulate/release material in/out of the core of the LC solid shells, as demonstrated by encapsulating/releasing rhodamine 6G in/from the core (Figure 8D). Similarly, Guldin et al [115] synthesized polymeric porous microcapsules from phase separation of LC mixtures (5CB/RM257) by heating and cooling. Cooling makes the LC mixtures exhibited radial configuration, while RM257 was polymerized under UV (365 nm) irradiation, and heating after polymerization led to a reduction of 5CB and eventual escaped from the polymerized microparticle.…”