Orientational Ordering in the Nematic Phase of a PEG-Peptide Conjugate in Aqueous Solution

PMID: 18643322 PMID Help

Authors: M. J. Krysmann (University of Reading) , Valeria Castelletto (University of Reading) , Ian Hamley (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Review E , VOL 77 , PAGES 062901

State: Published (Approved)
Published: June 2008

Abstract: 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.

Subject Areas: Chemistry, Materials

Instruments: NONE-No attached Diamond beamline

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