Surface Enrichment in a Miscible Polymer Blend:  An Experimental Test of Self-Consistent Field and Long-Wavelength Approximation Models

Abstract

Neutron reflectivity (NR) and low-energy forward recoil spectrometry (LE-FRES) were used to study surface enrichment in miscible blends of deuterated polystyrene, d-PS, and poly(styrene-co-4-bromostyrene), PBr0.049S, having a 0.049 mole fraction of 4-bromostyrene units. The d-PS component was found to segregate preferentially to the polymer blend/air interface, whereas no enrichment of either component was detected at the polymer blend/silicon interface. The experimental values of the surface concentration, φ 1, and the surface excess, z*, of d-PS were interpreted using both the theory of Schmidt and Binder (SB) (J. Phys. II (Paris) 1985, 46, 1631) and the self-consistent field (SCF) approach of Genzer et al. (Phys. Rev. E 1994, 50, 2373). Although both SB and SCF models were found to be in good qualitative agreement with the experimentally measured values of φ 1 and z*, we demonstrate that the latter proves to be in better quantitative agreement with the experimental results. Moreover, a comparison of the SB and SCF volume fraction profiles of d-PS revealed that the SCF model described more accurately the experimental profile. We also demonstrated that adding long-range interactions to the surface potential in the SCF model produced just minor changes in the shape of the d-PS profile near the surface.

Analytic theory of surface segregation in compressible polymer blends

“…A possible contribution to this near surface density flattening could arise from the competition between density variations proximate to the surface and from disparities in the surface free energy parameters f s,i driving the surface segregation, a mechanism requiring a ''compressible'' theory. However, as noted by Genzer et al, 18 other complexities may arise due to compositional fluctuations emerging from the statistical copolymer character of the system studied by Norton et al…”

Surface segregation driven by molecular architecture asymmetry in polymer blends

“…The structure resulting from selfassembly often depends on a balance of enthalpic and entropic forces. Conventionally, the preferential segregation of one polymer to the surface of a polymer blend is driven by the bulk tendency to demix, generally associated with differences in the repeat chemistry of the two polymers [1][2][3][4][5][6][7]. However, surface segregation can occur in a blend of polymers having the same repeat chemistry due only to differences in chain sizes [8][9][10][11][12] or molecular architecture [13][14][15].…”

Effect of molecular weight and substrate on silicone segregation from UV resin at plasma polymerized mold interface

“…The concentration profile of a segregating mixture near a surface/interface has been widely investigated 4–8. However, most research focuses on the segregation in high‐molecular‐weight polymeric blends cast by solvents or in melt form.…”