Structure and Interfacial Energy Control by Semifluorinated Polymers, as a Mechanistic Tool to Orient Liquid Crystals

Clemson University, Clemson SC

Investigators

Abstract

This award seeks to develop the relationship between the molecular structure of a novel class of semifluorinated polymers, and their interfacial structure and energies. Long term it seeks to test the potential of these polymers as support layers to orient liquid crystal thin films. This will be attained using a novel fluoropolymer with a mesogenic group (i.e. liquid crystal molecule), beta-methylstilbene on its backbone bridged by a perfluorocyclobutyl ring (PFCB). The bridging groups are used to control the surface energy and flexibility of the polymer. Atomic Force Microscopy (AFM), polarized optical microscopy, contact angle measurements, and X-ray/neutron scattering and reflectivity will be used. For any liquid crystal based device, the liquid crystal molecules have to be aligned by the surface, however, the have to respond quickly, without any memory effects to an external stimuli. A delicate balance between two opposing factors, surface orientation and weak azimuthal anchoring is requires. The significance of the problem is manifested in the large number of studies, which address the issue. In the last 10 years fluorine has been introduced as a modifier for the surface anchoring. In the present study we propose to utilize the chemical structure of a polymer confined to construct orienting layers. Their surface interactions will depend solely on the nature of the polymer with no further external treatments. The design of the polymer includes incorporating a mesogenic group, or similar chemical backbone, which are expected to serve as a "nucleation site" for inducing ordering, bridged by a group that can modify the surface energy of the polymer to alter the anchoring energy. Standard techniques including differential scanning calorimetry X-ray scattering NMR and polarized optical microscopy will be utilized to characterize the bulk properties of the newly synthesized polymers. Films will then be cast on different supports and will be studied by atomic force Microscopy polarized optical microscopy, contact angle measurements, and X-ray/neutron scattering and reflectivity, to study their structure and surface energies. Following the formation of the energy controlled interfaces; composites with well-characterized liquid crystalline molecules will be formed. The orientation of the LC cast on the polymer layers and its response to electrical stimuli will be studied. The significance of the proposed research lies in the basic understanding of interfacial characteristics of polymers and its correlation with interfacial alignment of liquid crystals leading to far-reaching technological applications, ranging from new fast responding LC devices, to optical wave-guides and new fiber optics.