Hamley Ian W, Krysmann Marta J, Newby Gemma E, Castelletto Valeria, Noirez Laurence
Department of Chemistry, University of Reading, Whiteknights, Reading, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2008 Jun;77(6 Pt 1):062901. doi: 10.1103/PhysRevE.77.062901. Epub 2008 Jun 18.
The orientational ordering of the nematic phase of a polyethylene glycol (PEG)-peptide block copolymer in aqueous solution is probed by small-angle neutron scattering (SANS), with the sample subjected to steady shear in a Couette cell. The PEG-peptide conjugate forms fibrils that behave as semiflexible rodlike chains. The orientational order parameters P2 and P4 are obtained by modeling the data using a series expansion approach to the form factor of uniform cylinders. The method used is independent of assumptions on the form of the singlet orientational distribution function. Good agreement with the anisotropic two-dimensional SANS patterns is obtained. The results show shear alignment starting at very low shear rates, and the orientational order parameters reach a plateau at higher shear rates with a pseudologarithmic dependence on shear rate. The most probable distribution functions correspond to fibrils parallel to the flow direction under shear, but a sample at rest shows a bimodal distribution with some of the rodlike peptide fibrils oriented perpendicular to the flow direction.
通过小角中子散射（SANS）研究了聚乙二醇（PEG）-肽嵌段共聚物在水溶液中的向列相取向有序性，样品在库埃特池中受到稳定剪切作用。PEG-肽共轭物形成的原纤维表现为半柔性的棒状链。通过使用均匀圆柱体形状因子的级数展开方法对数据进行建模，获得了取向序参数P2和P4。所采用的方法与单重态取向分布函数的形式假设无关。与各向异性二维SANS图案取得了良好的一致性。结果表明，在非常低的剪切速率下就开始出现剪切取向，并且取向序参数在较高剪切速率下达到平稳状态，且对剪切速率呈假对数依赖性。最可能的分布函数对应于剪切作用下与流动方向平行的原纤维，但静止的样品显示出双峰分布，其中一些棒状肽原纤维垂直于流动方向取向。
