Small-Angle Neutron Scattering from Peptide Nematic Fluids and Hydrogels under Shear

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• 作者：Peter J. Mawer ; Thomas A. Waigh ; Richard Harding ; Tom C. B. McLeish ; Stephen M. King ; Mark Bell ; and Neville Boden
• 刊名：Langmuir
• 出版年：2003
• 出版时间：June 10, 2003
• 年：2003
• 卷：19
• 期：12
• 页码：4940 - 4949
• 全文大小：393K
• 年卷期：v.19,no.12(June 10, 2003)
• ISSN：1520-5827

文摘

Small-angle neutron scattering has been used to study the mesoscopic structure responsible for thenonlinear rheology of aqueous dispersions of self-assembling peptide fibrils (nematic-fluid states) andfibrillar networks (nematic hydrogels). The orientation of the nematic director has been studied as afunction of the shear rate (0-500 s^-1) in both gel and fluid phases. The powder-averaged scattering datafrom the fluid nematic phase has been modeled using a Kratky-Porod wormlike chain and the cross-sectional area (a stack of 8-10 tapes) of the self-assembled fibrils measured under flow in the directionof the velocity gradient. A separate observation of the aggregate structure in both the fluid and the gelstates was possible in the tangential-velocity direction. An apparent increase in the diameter of the fibrilsupon gelation is, in view of the electron micrographs, attributed to fiber formation by the entwining of pairsof fibrils: it is estimated that approximately 10% of the total contour length of the fibrils participates inthese fiberlike junctions. The stress-controlled nonlinear rheology has also been studied, and the nematicfluids were found to display Type I shear thinning behavior, typical of liquid-crystalline polymers. Stressrelaxation in the form of a loss of orientation only occurred at high concentrations (6 mM) in nematic gels.Furthermore, the gels were observed to display Lozenge shaped scattering at intermediate shear rates,indicative of mobile oriented fibrils in an unoriented network.