An overview of an important aspect of SANS research on charged colloidal suspensions is presented. These systems are characterized by pronounced interparticle correlations resulting from a strong and long-range double-layer interaction between macroions (i.e. the charged colloidal particles). Emphasis is laid on the use of simple statistical mechanical models, which are applicable in treating SANS data, that take into account the double-layer interaction. Examples are taken from work on dense protein solutions, ionic micellar solutions and protein-detergent complexes in aqueous solutions. Spherical and rod-like particles are considered. Polydispersity effects are taken into account whenever possible. In the case of rod-like systems, alignment by a shear gradient and the consequent analysis of two-dimensional SANS intensity distributions are briefly discussed.

The small-angle neutron scattering (SANS) technique was used to study the structure and interaction between micellar aggregates formed from an anionic surfactant, sodium dodecyl-o-xylenesulfonate, in aqueous solutions. In the range of monomer concentrations studied, namely, from 0.25 to 5 wt %, the intermicellar interaction was significant and the nonideality effect needs to be explicitly taken into account in the data analysis. The basic structural parameters of the micelle were determined at a low concentration by a contrast variation method at finite Q (Q is the magnitude of the scattering vector). The same set of basic parameters were then used as the input to study the growth and interaction of the micelles at higher concentrations and at different temperatures. The minimum micellar aggregate near cmc is found to be spherical with an aggregation number of 30. The aggregation number increases steadily at higher concentrations and the shape of the aggregates become prolate spheroidal. The interparticle structure factor was computed by solving a primitive model two-component Coulomb fluid in a mean spherical approximation. The effective charge of the micelle extracted from SANS experiment can be interpreted as the dressed charge we discussed in our previous paper.

We present the analysis of a series of small-angle neutron scattering data of a comb-shaped copolymer, poly( 1-octadecene-co-(maleic anhydride)), dissolved a t various concentrations in D20 a t room temperature. The results show a t full ionization the copolymers self-associate to form cylindrical micelles with a radius of 27 A and a length of 99 A. At low concentrations, the number of repeating units of the copolymer per micelle is determined to be 233 A 5 and the hydration number per hydrophilic head group equals 10. The number of repeating units gradually decreases to 98 with concomitant increase in the hydration number to 30 at 20 wt % solution. This indicates that the system tends to lower its free energy by decreasing the aggregation number of micelles at higher concentrations.ABSTRACT Lattice models for the prediction of conformational characteristics and thermodynamic properties at bulk polymer/solid and bulk polymer/gas interfaces are critically examined. Existing models are shown to fall into two broad categories: bond models, in which the probability of a chain conformation is expressed as a product of bond transition probabilities, and site models, in which the probability of a conformation is proportional to a product of probabilities characteristic of the sites occupied by successive chain segments. A general mathematical formulation is developed for bond models, which includes Dill and Flory's model of liquid bilayer membranes and Helfand's model of a pure homopolymer at an interface as special cases.The key assumptions, leading to closure of the bond model equations in each of these two cases, are elucidated.