We present a neutron-scattering study of depletion interactions in a mixture of a hard-sphere-like colloid and a nonadsorbing polymer. By matching the scattering length density of the solvent with that of the polymer, we measured the partial structure factor S c (Q) for the colloidal particles. It is found that the measured S c (Q) for different colloid and polymer concentrations can be well described by an effective interaction potential U(r) for the polymer-induced depletion attraction between the colloidal particles. The magnitude of the attraction is found to increase linearly with the polymer concentration, but it levels off at higher polymer concentrations. This reduction in the depletion attraction presumably arises from the polymer-polymer interactions. The experiment demonstrates the effectiveness of using a nonadsorbing polymer to control the magnitude as well as the range of the interaction between the colloidal particles.

The morphologies of thin, substrate‐free block copolymer films have been examined by cross‐sectional TEM. Two poly(styrene‐b‐butadiene) diblock copolymers were studied: one that forms PS cylinders and the other that forms PB cylinders in the bulk. Films were annealed while supported by metal TEM grids, embedded, and ultramicrotomed in crosssection. We find that at the metal support the film forms a meniscus‐like region, or Plateau border, which exhibits the bulk morphology. Away from the border, the film thickness decreases and regions of terraced in‐plane cylinder domains occur until a minimum thickness is reached. The minimum thickness region of the PB majority copolymer in cross‐section shows a PS interlayer penetrated by a hexagonal array of circular PB channels that connect upper and lower PB surface layers, and a total thickness of 25–27 nm. The minimum thickness region of the PS majority copolymer in plan view shows no image contrast, but in cross‐section reveals a continuous PS interlayer covered by layers of PB, and a total thickness of 20 nm. Comparisons with the chain dimensions suggest a bilayer arrangement for both morphologies with strongly perturbed chain conformations in the surface layers. © 1996 John Wiley & Sons, Inc.

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We report a light scattering study of the adsorption of end-functionalized polymers on colloidal spheres. A light scattering method is developed to measure the amount of polymer molecules adsorbed on the colloidal surfaces. The experiment reveals that only a fraction of the end-functionalized polymers is adsorbed on the colloidal surface. The results for the end-functionalized polymers are compared with those for the unfunctionalized polymer. It is found that the interaction between the colloid and the unfunctionalized polymer is repulsive, which introduces a depletion attraction between the colloidal particles. The functional end groups are found to interact attractively with the polar cores of the colloidal particles. The adsorption energy between the functional group and the colloidal surface is estimated to be ~4kaT. The experiment shows that the presence of the adsorbed polymer on the colloidal surfaces greatly reduces the depletion attraction between the colloidal particles and, therefore, enhances the stability of the colloid-polymer mixture.

The use of X-ray and neutron reflectivity measurements to determine the density profile across and interface or across thin films has become increasingly popular over the last few years. However, in general convenient model-independent methods of inverting the reflectivity profiles to obtain the density profile have been missing. We present here one such approach using the method of anomalous reflectivity from the substrate and demonstrate its applicability in the case of an organic thin film.