Glass transition behavior of perpendicularly aligned thermotropic liquid crystalline phases consisting of long-chain trehalose lipids

Abstract

The glass-forming ability of amphiphilic lipids has attracted attention owing to their specific potent applications. In this study, we used an aligned thermotropic liquid crystalline (LC) film made from a long-chain trehalose lipids (LTLs) and used the 2θ/ω scan analysis of the X-ray measurement to gain some insights into the glass transition behavior of glycolipids. A highly perpendicularly aligned single crystal-like film, in which the film thickness corresponds closely to the correlation length of the fluid lamellar (Lα) LC phase, was obtained after thermal annealing under reduced pressure. The temperature-dependence changes in the bilayer length of various LTL nanofilms, together with LTL powder samples, and film thickness of various LTL films were analyzed. As a result, the glass transition temperature (Tg) of LTL was successfully determined. Tg was the temperature at which the disappearance of the difference in the degree of structural relaxation occurred for the different cooling rates or the point of intersection of two extrapolated linear graphs with different thermal expanding properties. The longest bilayer length was observed at around Tg. Importantly, the layer number above Tg increased because of the development of thermal motion parallel to the film and subsequent rearrangement, whereas it was constant below Tg, persisting the layer structure due to the frozen state of sugar moiety. The experimental evidence suggested a unique feature of one glycolipid layer accompanying the glass transition for the Lα LC phase consisting of a long-chain glycolipid.