Neutron Reflection Study of Surface Enrichment in an Isotopic Polymer Blend
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NEUTRON REFLECTION STUDY OF SURFACE ENRICHMENT IN AN ISOTOPIC POLYMER BLEND
R.A.L. JONES*, L.J. NORTON**, E.J. KRAMER**,R.J. COMPOSTOt, R.S. STEINt,T.P. RUSSELLtt, G.P. FELCHERt, A. MANSOURt and A. KARIMt *Present address: Cavendish Laboratory, Cambridge University, Madingley Road, Cambridge, CB3 0HZ, UK "**Materials Science and Engineering, Cornell University, Ithaca, NY 14850 tDepartment of Polymer Science and Engineering, University of Massachusetts, Amherst, MA 01003 ttIBM Almaden Research Center, San Jose, CA 95120 *Materials Science Division, Argonne National Laboratory, Argonne, IL 60439-4814
We have measured neutron reflectivities from the surface of films of
deuterated polystyrene (d-PS) and protonated polystyrene (PS) blends before and after annealing, and used the results to determine the concentration versus depth profile of the films. After annealing, the surface is enriched in d-PS, with a surface excess proportional to the bulk concentration of dPS, in agreement with previous measurements using forward recoil spectrometry[l]. The decay of the enhanced concentration into the bulk occurs over a length approximately equal to the bulk correlation length (-200 A), in close agreement with that predicted by current mean-field theory[2]. However, the agreement between the experimental reflectivity curves and the fitted curves is not completely adequate. Figure 1, a plot of k 4 R against k, demonstrates this point for a 15% d-PS sample. The dashed line is the best fit assuming the mean field profile. The inset shows the corresponding concentration profile and a trial profile, solid line, which fits the data much better. The small deviation between the theoretical and trial profiles may be due to the assumption of the theory that surface interactions leading to enrichment is short ranged.
Mat. Res. Soc. Symp. Proc. Vol. 171. t1990 Materials Research Society
336
Figure 1 -9
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1. R.A.L. Jones, E.J. Kramer, M.H. Rafailovich, J. Sokolov, S.A. Schwarz, Phys. Rev. Let. 62, 280 (1989). 2. I. Schmidt and K. Binder, J. Physique 46, 1631 (1985). 3. R.A.L. Jones, L.J. Norton, E.J. Kramer, R.J. Composto, R.S. Stein, T.P. Russell, A. Mansour, A. Karim, G.P. Felcher, M.H. Rafailovich, J. Sokolov, X. Zhao, S.A. Schwarz, submitted for puplication.
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