Past Seminars Seminários Já Decorridos 2010

The Beauty of Liquid Crystalline Cellulosic Defects

By: Helena Godinho
From: Univ. Nova Lisboa
At: Complexo Interdisciplinar, Anfiteatro
[2010-01-13] 12:00

Cellulose, along with polypeptides and DNA, belongs to a family of organic molecules that can form cholesteric liquid crystalline (LC) phases, where the direction of preferential molecular alignment rotates in a helical pattern. Nano and microfibers electrospun from liquid crystalline cellulosic solutions were found to curl and twist which were understood on the basis of a model proposed by Goriely. This model assumes that tendrils of climbing plants such as passiflora edulis, behave as a slender elastic rod with intrinsic curvature and torsion. Since both these requirements seem to be fulfilled by most of electrospun cellulosic microfibers it was conjectured that the mechanism leading to their curling and twisting was the same as governs these phenomena in climbing plants. The physical basis for the intrinsic curvature of our fibers was attributed to the double core structure revealed by mechanical testing and SEM and also to the processing conditions of the material although the study of cellulosic precursor solutions flow was required in order to confirm the origin of the intrinsic curvature of the fibers. In this work we give evidence that the liquid crystalline phase rheological properties seem to be one of the factors that are at the origin of the formation of helices and spirals in cellulosic fibers. The role of the defects generated during the manufacture of the fibers is also discussed in the framework of previous work developed for cellulosic liquid crystalline phases.