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Symmetric, diblock copolymers confined between two solid surfaces were studied by neutron reflectivity. A multilayered morphology with an integral number of layers oriented parallel to the solid interfaces was found in all cases. The period of the confined multilayers deviated from the bulk period in a cyclic manner as a function of the confined film thickness. A first-order transition occurred between the expanded and contracted states of the copolymer chains. The data suggest that the deviation of the period from the bulk value decreases with increasing separation distance.PACS numbers: 61.41.+e, 61.12.Ex, 68.55.3k Symmetric, diblock copolymers are polymer chains comprised of two chemically distinct polymer chains covalently bonded together at one end where the volume fraction of each constituent is 0.5. In the bulk, copolymers above a critical molecular weight microphase separate [I] into lamellar microdomains having a period commensurate with the size of the copolymer chain, i.e. , on the size scale of hundreds of angstroms. However, in the vicinity of a surface, the specific interactions of the segments of each block with the surface force an orientation of the lamellar microdomains parallel to the surface with a period equal to the bulk value, Lrt [2-6]. The formation of such oriented multilayers, coupled with the high resolution of neutron reflectivity, has provided a route for quantitatively characterizing the morphology of ordered copolymer systems [5]. More generally, these self-assembled multilayers have proven to be ideal models for the investigation of such phenomena as two-dimensional coarsening processes [7][8][9] and finite size scaling effects on phase transitions [10,11]. Typically, copolymer films are prepared on a solid substrate leaving the polymer surface unconstrained. At equilibrium, the total film thickness at any point has been shown to be given by nLO, if the segments of one block segregate preferentially to both the air and substrate interfaces [3,6, 12], or by (n+ 2 )La, if one block segregates to the substrate interface and the other to the free surface [2]. Here, n is an integer. If the initial film thickness t does not conform to this condition, then the constraint is met by the formation of steps on the free surface with a height of Lo and a surface coverage commensurate with the relation of t to nLO or (n+ -, ' )Lo, respectively. In this work the first experimental studies on thin films of diblock copolymers confined between two flat rigid surfaces are reported. Replacing the free surface with another solid surface suppresses the surface topography and elirninates this route for meeting the thickness constraint.Consequently, the copolymer is forced from its bulk equilibrium morphology into a frustrated state. Theoretically this problem has been studied by several groups resulting in conIIicting predictions. Shull [13],from self-consistent field calculations, predicts that the copolymer period will either increase or decrease to accommodate the thickness constraint. Simulations...

We have used neutron reflection to study, for the first time, the structure of a surfactant layer adsorbed at the hydrophobic solid/water interface. Isotopic labeling of the water and of the hydrophobic selfassembled layer of octadecyltrichlorosilane (OTS) was first used to characterize protonated and deuteriated hydrophobic layers on the silicon oxide on the (111) face of silicon. This is the first time the structure and composition of such layers has been examined under water. Some water penetration into both the silicon oxide layer and the hydrophobic layer was observed. In the former case this is attributed to roughness of the oxide layer and in the latter to imperfections in the OTS layer. The thickness of the OTS layer was found to be 24 ( 2 Å, in agreement with other measurements in air. The adsorption isotherm of the surfactant tetraethylene glycol monododecyl ether (C 12E4) was measured using two independent measurements (different isotopic compositions) on the deuteriated OTS layer. The surfactant was found to reach a constant excess at the critical micelle concentration (cmc) very similar to that at the air/water interface, i.e., an area per molecule of about 50 Å 2 . The thickness of the surfactant layer was also found to be similar to that at the air/water interface and decreased rapidly with decreasing coverage. Estimates of the angle of tilt of the surfactant molecules from the surface normal were 53 ( 10°and 75 ( 10°at the highest and lowest coverages, respectively. Isotopic labeling of the two halves of the surfactant molecule was used to show that the molecule is partially oriented with the ethylene glycol groups pointing outward toward the aqueous solution. At the cmc the thicknesses of the two halves of the surfactant molecule were both found to be 10 ( 2 Å, to be compared with fully extended chain lengths of 16.9 (alkyl chain) and 14.2 Å (ethylene glycol chain). Some penetration of the OTS layer by the surfactant was observed at the highest surfactant coverages.

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We study the reversible aggregation of polystyrene latex spheres (PLS) in one phase mixtures of 2,6 lutidine plus water at temperatures and solvent compositions near the solvent mixture's critical point. The aggregation occurs only on the side of the critical composition rich in the liquid component which is nonpreferred when the system is in the solvent s two-phase region. The liquid that is preferred can be changed by changing the surface charge density of the PLS. The aggregation region extends to temperatures well beyond the wetting temperature, and dynamic light scattering shows no evidence of a thick layer building up on individual particles before they join aggregates.