Atomic Force Microscopy Study for Supermolecular Microstructures in Side-Chain Liquid Crystalline Polymer Films

Abstract

Atomic force microscopy (AFM) is employed to study the supermolecular microstructures of disclinations and inversion walls in thin films of a smectic side-chain liquid crystalline polymer. Two-dimensional nanostripes are formed in thin films when the material enters the smectic phase. A possible mechanism for their formation is also suggested. The stripes run parallel to the local director and thus decorate the overall patterns of nematic director around the disclinations and inversion walls. Three patterns involving radial, spiral, and circular supermolecular microstructures of a positive disclination with s = +1 and one hyperbolic pattern of a negative disclination with s = -1 are observed. The cores of all these microstructures exhibit circular dark centers in AFM height images. It is found that the specific configurations of a pair of (+1, -1) disclinations form during the late stage of annihilation and inversion walls always separate a pair of (+1, +1) disclinations. The analysis on the director fields around disclinations and inversion walls shows that the bend and splay elastic constants are of the same order of magnitude in the side-chain liquid crystalline polymer.

Optical Microscopy Study for Director Patterns around Disclinations in Side-Chain Liquid Crystalline Polymer Films

“…This is expected since the precise nature of defects observed in the planar films will depend on the detailed balancing of distortion of defects in the bulk elastic energy, and surface anchoring energy. , For a thin film, the surface anchoring energy due to confined environments, and the strong interaction between LC molecules and substrate, dominates over the bulk elastic energy. In our previous work, we employed TEM and AFM to prove that the center of the integer disclination is lower than the surrounding material and the mesogenic groups are tilting out of the film plane. − In such a geometric confined environment, the integer disclinations may be stabilized by “escaping core”, as shown in Figure a. Increasing the film thickness makes the bulk elastic energy become dominant.…”

“…The orientational properties are carried by the short mesogenic side chains, and the nature of the order parameter is then similar to the small molecule LCs . There are many theoretical and experimental indications that the values of elastic constants in side-chain liquid crystalline polymers are close to those in analogous small molecule LCs. , Recently, we reported the observation of two-dimensional stripes in thin films of a side-chain polymer using transmission electron microscopy (TEM) and atomic force microscopy (AFM). − When the samples were cooled to the smectic phase, after a holding period in the nematic phase, a characteristic pattern of stripes developed. The orientation of stripes, along the local director, was demonstrated by correlating the direction of the stripes with electron diffraction patterns.…”

“…11,12 Recently, we reported the observation of two-dimensional stripes in thin films of a side-chain polymer using transmission electron microscopy (TEM) and atomic force microscopy (AFM). [13][14][15] When the samples were cooled to the smectic phase, after a holding period in the nematic phase, a characteristic pattern of stripes developed. The orientation of stripes, along the local director, was demonstrated by correlating the direction of the stripes with electron diffraction patterns.…”

Epoxy nanocomposites filled with thermotropic liquid crystalline epoxy grafted graphene oxide

“…The condensate of epoxy liquid crystal has excellent mechanical, thermal, electrical, optical and other aspects of performance. 34,35 Zhang et al 36 and Han et al 37 reported the combination of carbon nanotubes (CNTs) and thermotropic liquid crystals (TLCs), it not only provides a useful way to align CNTs, but also dramatically enhances the TLC performance especially in the liquid crystal display technology. Biswas et al 38 and Zhao et al 39 reported the nanocomposite was prepared with exfoliated graphene nanoplatelets (GnP) and liquid crystalline polymer to achieve both high mechanical modulus and electrical conductivity.…”

Thermal and phase transformation behavior of epoxy‐functional graphene oxide/liquid crystalline epoxy composite

“…Lee et al reported that curing of LCE was accelerated by alignment of LCE on CF and anisotropic orientation of LCE enhanced dynamic modulus of CF‐reinforced LCE composites. Zhang et al and Han et al provided a useful method to align CNTs in thermosetting liquid crystalline (LC) polymer to enhance the liquid crystal display technology.…”