Pre-submission Thesis Presentation

The molecular self-organisation and the emergent physical properties of materials under different external conditions is an active field of research in soft condensed matter science. The supramolecular order leading to various advanced functional materials has attracted much attention due to their technological applications as well as for fundamental understanding of their properties. In this thesis, two different types of soft materials which exhibit self-assembled structures have been studied experimentally. The first system studied is a calamatic liquid crystal compound (8OCB) consisting of highly polar rod-like molecules. This compound is known to exhibit three different metastable crystal phases and a stable solid phase on crytalisation from its solution. In this thesis, we study the crystal polymorphs of 8OCB liquid crystal formed from its supercooled smectic phase. Two different solid phases of this compound are often found to form during cooling from its melt. One of them is identified as a metastable crystal state known as long parallelepiped (PP) phase and the other one is stable commercial power (CP) phase. The CP phase is found to be heterogeneous in nature and exhibits a coexistence of fibrillar nano-crystallites embedded in a solid amorphous state. It is found that CP phase exhibits banded or non-banded spherulitic growth on sufficient supercooling from its melt. In quasi-two-dimensional geometry, the banded spherulitic domain with a circular boundary shows concentric colour bands between crossed polarisers. We have found that the concentric bands are formed due to the periodic variation of composition of fibrillar crystallites and amorphous phase along the radial direction of the domain. This variation changes the effective birefringence of the sample giving rise to the concentric colour bands between crossed polarisers.

      The second system studied in this thesis is the starch films formed on drying gelatinized potato starch solution droplets on a flat substrate. Starch apart from being the most consumable carbohydrate is also the source of one of the largest polymer found in nature. The circular starch films are studied using a variety of experimental techniques. Our experimental results show that the starch films formed on drying of gelatinized starch solution droplets are optically biaxial except at its center where it is optically uniaxial having an optic axis normal to the film. In the biaxial part of the circular film, the three principal indices α, β and γ are found along its normal, radial and azimuthal directions respectively. The starch films are found to be optically negative in both of its uniaxial and biaxial parts.