Synthesis of Optically Complex, Porous, and Anisometric Polymeric Microparticles by Templating from Liquid Crystalline Droplets

Abstract

It is demonstrated that aqueous dispersions of micrometer-sized liquid crystal (LC) droplets provide the basis of a general and facile methodology for the templated synthesis of spherical and nonspherical polymeric microparticles with complex internal structure and porosity. Specifi cally, nematic droplets of reactive (RM257)/nonreactive mesogens with distinct internal confi gurations are prepared using a range of approaches, the reactive mesogens are photopolymerized, and then the nonreactive mesogens are extracted to yield polymeric particles. It is found that LC droplets exhibiting bipolar, radial, axial or preradial confi gurations template the formation of spindleshaped, spherical, spherocylindrical or tear-shaped polymeric microparticles, respectively. Each type of microparticle exhibits distinct optical signatures indicating the presence of an internal LC-templated, anisotropic polymer network. In addition, by using a microfl uidic system to generate monodisperse LC droplets containing 10%-40% wt/wt of RM257, spindle-shaped microparticles with tailored aspect ratios ranging from 2.4 to 1.2 are formed. The mass density of spherical microparticles templated from radial LC droplets can be tuned to range from 0.2 to 0.6 g cm −3 , revealing the introduction of porosity (confi rmed by electron microscopy) with a volume-average pore diameter of 39 ± 16 nm (obtained from nitrogen sorption isotherms).

Liquid Crystal Templates Combined with Photolithography Enable Synthesis of Chiral Twisted Polymeric Microparticles

“…The shrinkage perpendicular to the nematic director was linearly dependent on the reactive mesogen content whereas it was almost independent of the reactive mesogen content along the nematic director similar to the previous studies . This difference in the shrinkage of the microparticles along and perpendicular to the nematic director resulted in a linear concentration dependency of the aspect ratio of the microparticles maintained after the extraction of the unreacted mesogens, consistent with the past studies on the LC emulsion polymerization . However, the extent of the shrinkage we observed in this study was slightly higher than that observed in past studies .…”

“…Figure C shows the shrinkage percentage of the microparticles along and perpendicular to the nematic director as a function of the reactive mesogen content. The shrinkage perpendicular to the nematic director was linearly dependent on the reactive mesogen content whereas it was almost independent of the reactive mesogen content along the nematic director similar to the previous studies . This difference in the shrinkage of the microparticles along and perpendicular to the nematic director resulted in a linear concentration dependency of the aspect ratio of the microparticles maintained after the extraction of the unreacted mesogens, consistent with the past studies on the LC emulsion polymerization .…”

“…LCs, due to their mesoscale ordering and fluidic properties, have been shown to be useful in the templated synthesis of polymeric materials . Past studies have shown multiple routes toward the synthesis of polymeric materials using liquid crystalline environments.…”

Optical properties of composite heterophase objects with liquid crystal material for different display applications

“…Firstly, the phase difference parameter Φ introduced in was calculated: Φ(θ( z )) = ΔΦ(θ( z ))/ΔΦ max (θ 0 ), where ΔΦ is the phase retardation difference and θ( z ) is the LC director distribution. ΔΦ(θ( z )) is described by the formula as follows: …”

“…There are porous systems made of polymers or solid crystals with the LC incorporated into the pores or confined space: polymer dispersed liquid crystals (PDLC), polymer stabilzed liquid crystals, fibers, porous silicon, or porous anodized aluminum oxide . Recently, many developments are described with mesogens comprising microparticles and nanoparticles for reduction of operation voltage or switching time . Such particles can have different shape: almost spherical, elongated like nanowires or disc‐like.…”