The surface properties of symmetric microphase separated diblock copolymers of polystyrene (PS) and polymethylmethacrylate (PMMA) were investigated using X-ray photoelectron spectroscopy (XPS), the specular reflectivity of neutrons and secondary ion mass spectrometry (SIMS). PS, the lower surface energy component, exhibited a preferential affinity for the free surface. For copolymers that are far from the bulk microphase separation transition (MST), the surface consists of a layer of pure PS. When the system is close to the MST the surface is a mixture of PS and PMMA. The PS surface excess can be described bya N-1/2 dependence, where N is the number of segments that comprise the copolymer chain. It is shown that the surface undergoes an ordering transition at a temperature T2 that is above that of the bulk MST. The ordering of the bulk lamellar morphology is induced by an ordering at the surface. This is analogous to the ferromagnetic order observed in systems such as Gd at temperatures above the bulk Curie temperature. The results here are discussed in light of previous work on copolymer surfaces and in light of mean field theory.
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The angle resolved measurements of these samples made by the slow solvent evaporation process showed variations only for the shortest copolymer system, the PMMA fraction varied from 0.25 to 0.18 in going from 90° to 20°.
The angle resolved measurements showed variations only for the shortest copolymer system, the PMMA fraction varied from 0.22 to 0.17 in going from 90° to 20°.
Many of the films, particularly the high N systems, that were not annealed long enough yielded values of ψ1 that were closer to 0.5. After longer anneals they reached their equilibrium values.As N increased the time required to reach equilibrium increased appreciaby.
This work was supported in part by U. S. DOE under Contract DE-AC046-DP00789
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Green, P.F., Christensen, T.M., Russell, T.P. et al. Diblock Copolymers at Surfaces. MRS Online Proceedings Library 171, 317–327 (1989). https://doi.org/10.1557/PROC-171-317