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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...

. 1990. Thermal diffuse x-ray-scattering studies of the water-vapor interface. Physical Review A 41(10): 5687-5690.Published Version

We have explored the use of chain end segregation as a means of controlling the properties of a polymer surface. Thin film blends of homopolystyrene (PS) and PS synthesized with low-energy oligotetrafluoroethylene chain ends (PS-TFE) were studied using neutron reflectivity. The fraction of PS-TFE that localizes near the surface was found to increase as a function of its concentration in the blend. Contact angle measurements indicate corresponding reductions in the surface tension due to the surface localization of the TFE chain ends. For a 10% blend of 6000 mol wt PS-TFE in 3 × 105 mol wt PS, the surface coverage of fluorocarbon ends was found to be >20%. A free energy model of the blends gives good qualitative agreement with the experimental results.

Neutron reflectivity has been used to study the organization of self-assembled multilayers of sulfonated polyaniline and polyallylamine. Films were prepared by the sequential adsorption of polycations and polyanions from dilute aqueous solutions. Scattering contrast was achieved by selective deuteration of the blocks of bilayers at varying intervals along the film. The multilayer structure was found to be preserved over 40 bilayer depositions, but with an internal organization which decays monotonically away from the substrate. These results suggest that the observed interfacial widths are primarily due to the accumulation of defects as the bilayers are deposited.

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