Cellulosic Spirals and Helices
Godinho, M.H.1, Canejo, J.P.1, Borges, J.P.1 and Teixeira, P.I.2
1 Faculdade de Cięncias e Tecnologia - Universidade Nova de Lisboa, Portugal; 2 Instituto Superior de Engenharia de Lisboa - IPL, Portugal
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 . Recently it was found that helical micro and nano helices can be obtained from cellulose liquid crystalline phases by the electrospinning technique . The twisting is on a supramolecular scale, and similar to what has been seen in other systems such as amyloid (polypeptide) nanofibrils  and cellulose from Micrasterias denticulate . In fact, cellulose acetate was the first fiber reported to have been electrospun and is the most popular cellulosic material for electrospinning today. The fibre diameter can be significantly reduced from micrometres to a few nanometres using this technique, and suspended fibres with helical structures can also be prepared by careful choice of target. In this work we show that nano and microfibers electrospun from liquid crystalline cellulosic solutions will curl into spirals if they are supported at just one end, or, if they are supported at both ends, a helix hand reversal can be found - the spontaneous switching of a helical structure of one handedness to its mirror image. This same behaviour is known to be exhibited by the tendrils of climbing plants such as Passiflora edulis, three to four orders of magnitude larger than our fibres . The results obtained will be discussed in the framework of a model proposed by Goriely et al. .
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