Liquid crystals (LCs) are unique states of matter displaying the long-range order of crystalline materials while maintaining the flow properties of a liquid. The optical properties of LCs are significantly affected by their alignment and, therefore, methods to manipulate the alignment  of LCs are of interest. Alignment in confined structures is strongly affected by surface interactions that can lead to unique LC phases. Confinement effects can result in frustrated structures that are distinct from the mesophase, even when in thermodynamically stable states. In this work, electrospinning is used to confine a cholesteric LC in micro- and nano- scale geometries. Encapsulation in such small structures is of interest because, at this scale, surface interactions begin to play an increasingly important role in determining the geometric shape, size, and molecular director of the LC mesophase. In this work, we explore the effects of confinement on a chiral nematic LC within micro-scale polymeric cylindrical cavities. Coaxial electrospinning is used to fabricate a distribution of nanofibers consisting of a polyvinylpyrrolidone (PVP) polymer sheath and a chiral LC core made up of 4-Cyano-4'-pentylbiphenyl (5CB) with various concentrations of a chiral dopant, CB15. The effects of the cholesteric pitch and fiber diameter on the orientation of the LC, topological textures, and the chiral nematic to isotropic phase transition temperature, is investigated. Fiber samples are analyzed using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM).

Confinement-sensitive cholesteric liquid crystals in electrospun nanofibers

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