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Liquid crystalline materials

Liquid crystalline materials
This is an image of cellulose nanocrystals

The liquid crystalline state is a fundamental state of matter that combines mobility with structure. Biological membranes function in this state, which is thus essential to life itself. It is achieved by the self-assembly of molecules in particular ways, and is therefore a basic design element for obtaining materials with specific structures and properties. The CSACS research projects in this area reflect the creativity with which liquid crystallinity can be exploited to develop new and useful materials.

Projects

Liquid Crystal Gels

Liquid crystal gels are low-molar-mass liquid crystals whose long-range orientation or textures are stabilized by a polymer network. Generally, the network is covalent since it is formed by polymerization of a reactive monomer dissolved in the liquid crystal host. The use of non-covalent, self-assembled networks is being explored for making liquid crystal gels, which when functionalized with photoresponsive groups, will create dynamic functional materials that have potential applications in display technologies. We explore the reversible trans-cis photoisomerization of azobenzene to add new functionalities to these materials. In particular, we are interested in using them as optical materials to record diffraction gratings that can be controlled either by an electric field or light.

Liquid Crystals as Molding Tools in Self-Assembly: One- and Two- Dimensional SiO2

This project extends the current work of Harrod on the synthesis of a new class of self-assembling cationic, liquid crystalline surfactants to investigate their ability to encapsulate double-stranded DNA fragments. Sleiman is experienced in the synthesis of DNA oligomers and their application to the synthesis of hybrid inorganic/organic materials. Our mutual experience in using physico-chemical techniques for the characterization of "soft" materials.

Liquid Crystal Polymers

Novel LC polymers are synthesized by classical and supramolecular chemistry. Supramolecular chemistry is a recent design approach that can combine small molecule and polymer properties, as well as allow facile tailoring of the material properties. Thus, complementary polymers and mesogens are self-assembled through non-covalent interactions (ionic, hydrogen-bonding, coordination). The use of block copolymers leads to hierarchical structures, combining the (block copolymer) mesoscale and (liquid crystal) nanoscale, that begin to resemble nature's structures. Stimuli-sensitive mesogens are chosen to generate intelligent materials for specific applications (for example, optical). These materials are being investigated in the bulk, and as thin and ultra-thin films. Theory and computational modeling aid in understanding the various self-assembling processes involved.

Liquid Crystalline Suspensions

Under suitable conditions, rod-like colloidal particles can form liquid crystalline suspensions. When nanocrystals of cellulose are dispersed in water, they self-order to form chiral nematic phases with interesting physical and optical properties. Surface orientation of the nanocrystals, film roughness and stability to solvent were compared for the two multilayer preparation methods. Ionically crosslinked dip-coated films were stable in water whereas physisorbed spin-coated films re-dispersed in solvent. Attempts were made to induce alignment of the cellulose nanocrystals by varying the substrate, substrate pre-treatment, cellulose concentration and by applying a magnetic field.