The presence of surfactants in large micelles gives rise to broad n.ni.r. resonances because of the long correlation time for diffusion around the micelle. This has been used to investigate the structure of surfactant aggregates in systems where other evidence indicates that large micelles occur.For polyethylene oxide surfactants at the cloud point, the surfactant micelles are small and the large units are formed by secondary aggregation of small micelles. For sodium dodecylsulphate with added salt, octanol or other surfactants, large micelles are formed. The changes in micelle size indicated by changes in n.m.r. linewidths are in agreement with changes measured by the quasielastic light scattering technique.

Constant and oscillatory Couette shear flow have been used in combination with small-angle neutron scattering to observe the shear-induced ordering in concentrated surfactant micellar phases. For the lamellar phase of hexaethylene glycol monohexadecyl ether, C16E6, two distinct lamellae orientations have been identified. At low shear gradients the lamellae are ordered parallel to the flow-vorticity plane, whereas at higher shear gradients the lamellae order parallel to the flow-shear gradient plane, corresponding to a rotation through 90 ° of the axis of orientation. At intermediate values of constant shear and for oscillatory shear, both lamellae orientations are simultaneously observed for the first time in a surfactant lamellar phase. For the lamellar phase, a dispersion of the binary surfactant mixtures of dioleyl cationic and 2-ethyl hexaglycerol monoether surfactants, a high degree of alignment, in the direction parallel to the flow-vorticity plane, is observed at zero and low shear. With time, during the application of a shear gradient of 25 s-i, the lamellar phase transforms to a highly ordered solution of monodisperse multilamellar vesicles.

A wide range of rod-like micellar solutions, aligned by couette shear flow, have been investigated by small-angle neutron scattering, SANS. The data are consistent with a previously reported theoretical interpretation, and rod dimensions are obtained from the theoretical fits. Scattering effects attributed to rod flexibility are presented and interpreted in terms of a simple model. The shear gradient dependence of the rotational diffusion coefficient due to entanglement of the rods is observed. In the limit of high shear the dilute rotational diffusion coefficient is recovered.

An L-carrageenan has been selectively cleaved a t the galactose 6-sulphate kink points to give short chain segments which do not gel but which give the optical rotation-temperature curve characteristic of gelation. This optical rotation change has previously been attributed to a helix to coil transition. The molecular weight changes with temperature of these i-carrageenan segments have been measured by light scattering and osmometry and it has been found that the optical rotation shift is paralleled by a dimerisation thus confirming the hypothesis of a coil to double helix transition. Light scattering shows behaviour typical of concentration dependent aggregation in both states, but this is not detected by osrnometry.THE carrageenans are sulphated galactans found only in red seaweeds and are built up from residues having the galacto-configuration linked alternatively a-( 1 __t 3) and p-(1 -4).lThe most important gel forming polysaccharides in the carrageenan series are K (I) and i(11) in which ( 13) linked P-~-galactose-4-sulphate residues and (1 + 4) linked 3,6-anhydro-a-~-galactose (or its 2-sulphate) residues alternate. These polysaccharides are of the masked repeating type and there is some formal replacement of the 4-linked anhydride units by galactose-6-sulphate and 2,6-di~ulphate.~s~There is good evidence from X-ray diffraction studies on oriented fibres that K-and L-carrageenans exist as double helices in the solid state? It has been suggested that the formation of gels when dilute aqueous solutions of these carrageenans are cooled is due to association of chain segments into double helices which

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