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Advisor(s)
Abstract(s)
A celulose é o polímero renovável mais abundante do mundo. É conhecido pela sua excelente biocompatibilidade,
propriedades térmicas e mecânicas. A celulose assim como os polipéptideos e o ADN, pertence a uma família de moléculas
orgânicas que dão origem à formação de fases líquidas cristalinas (LCs) colestéricas. A Passiflora Edulis, tal como outras
plantas trepadeiras, possui longas e flexíveis gavinhas que permitem à planta encontrar um suporte para se fixar. As gavinhas
podem assumir a forma de espirais ou de hélices consoante sejam sustentadas por apenas uma ou por ambas as extremidades.
As hélices apresentam muitas vezes duas porções helicoidais, uma esquerda e outra direita, separadas por um segmento recto
denominado perversão. Este comportamento é consequência da curvatura intrínseca das gavinhas produzidas pela planta
trepadeira. O mesmo comportamento pode ser observado em micro e nanofibras celulósicas fabricadas a partir de soluções
líquido-cristalinas, numa escala três a quatro ordens de grandeza inferior à das gavinhas. Este facto sugere que o modelo
físico utilizado tenha invariância de escala.
Neste trabalho é feito o estudo de fibras e jactos que imitam as estruturas helicoidais apresentadas pelas gavinhas das plantas
trepadeiras. As fibras e jactos são produzidos a partir de soluções líquidas cristalinas celulósicas. De modo a determinar as
características morfológicas e estruturais, que contribuem para a curvatura das fibras, foram utilizadas técnicas de imagem
por ressonância magnética (MRI), microscopia óptica com luz polarisada (MOP), microscopia electrónica de varrimento
(SEM) e microscopia de força atómica (AFM) . A variação da forma das estruturas helicoidais com a temperatura parece ser
relevante para o fabrico de membranas não tecidas para aplicação em sensores termo-mecânicos.
Cellulose, the main constituent of plant cell walls, is an abundant and renewable resource found in most parts of the world. It is known for its excellent biocompatibility, thermal and mechanical properties. Cellulose along with polypeptides and DNA, belongs to a family of organic molecules that can form cholesteric liquid crystalline (LC) phases. Passiflora edulis, like other climbing plants, possesses long, tender, soft, curly and flexible organs called tendrils whose circumnutation allows the plant to find support. Tendrils curl into spirals or twist into a helix, often of one handedness over half of its length and of the opposite handedness over the other half, the two halves being connected by a short straight section – a perversion, depending on whether they are supported at just one end or supported at both ends, respectively. This is a consequence of an intrinsic curvature of the tendrils. Precisely the same behaviour can be observed in cellulosic fibers produced from liquid crystalline solutions, albeit on a length scale of microns and nanometers, i.e., three to four orders of magnitude smaller than in Passiflora edulis. This suggests that the same basic, coarse-grained physical model is applicable across a range of length scales. In this paper we report on those liquid crystalline cellulosic fibers and jets, which mimic the shapes of helical tendril structures. Liquid crystalline and isotropic cellulosic precursor solutions of curved and straight fibers are examined using nuclear magnetic resonance imaging (MRI), polarizing optical microscopy (POM), scanning electronic microscopy (SEM) and atomic force microscopy (AFM) techniques to determine morphological and structural features contributing to fiber curvature. We also highlight the critical dependence of the helical structures on temperature, which offers a potential for direct fabrication of biocompatible tunable high-surface area non woven mats with mechanical adaptability.
Cellulose, the main constituent of plant cell walls, is an abundant and renewable resource found in most parts of the world. It is known for its excellent biocompatibility, thermal and mechanical properties. Cellulose along with polypeptides and DNA, belongs to a family of organic molecules that can form cholesteric liquid crystalline (LC) phases. Passiflora edulis, like other climbing plants, possesses long, tender, soft, curly and flexible organs called tendrils whose circumnutation allows the plant to find support. Tendrils curl into spirals or twist into a helix, often of one handedness over half of its length and of the opposite handedness over the other half, the two halves being connected by a short straight section – a perversion, depending on whether they are supported at just one end or supported at both ends, respectively. This is a consequence of an intrinsic curvature of the tendrils. Precisely the same behaviour can be observed in cellulosic fibers produced from liquid crystalline solutions, albeit on a length scale of microns and nanometers, i.e., three to four orders of magnitude smaller than in Passiflora edulis. This suggests that the same basic, coarse-grained physical model is applicable across a range of length scales. In this paper we report on those liquid crystalline cellulosic fibers and jets, which mimic the shapes of helical tendril structures. Liquid crystalline and isotropic cellulosic precursor solutions of curved and straight fibers are examined using nuclear magnetic resonance imaging (MRI), polarizing optical microscopy (POM), scanning electronic microscopy (SEM) and atomic force microscopy (AFM) techniques to determine morphological and structural features contributing to fiber curvature. We also highlight the critical dependence of the helical structures on temperature, which offers a potential for direct fabrication of biocompatible tunable high-surface area non woven mats with mechanical adaptability.
Description
Keywords
Celulose Cristais Líquidos Espirais Hélices Cellulose Liquid Crystals Spirals Helices
Citation
CANEJO, J. P.; BROGUEIRA, P.;TEIXEIRA, P. I. C.; FEIO, G.; TERENTJEV, E. M.; GODINHO, M. H. - Hélices e Espirais em Micro e Nanofibras Celulósicas. Ciência & Tecnologia dos Materiais. ISSN 0870-8312. Vol. 23, nr. 3-4 (2011), p. 34-41.