Adsorption from polymer mixtures. The effect of molecular mass

Interaction of Solid Surfaces Across Binary Mixtures of Polymer Melts

“…This effect is stronger for long chains, which should lead to a depletion of long chains and an enrichment of short chains. [1][2][3][4][5] This prediction was confirmed for example by measuring the surface tension of polymers of different molecular weights. The surface tension increases with increasing molecular weight.…”

“…Polymer chains at a solid interface suffer from a loss of configurational entropy and they avoid the interface. This effect is stronger for long chains, which should lead to a depletion of long chains and an enrichment of short chains. − This prediction was confirmed for example by measuring the surface tension of polymers of different molecular weights. The surface tension increases with increasing molecular weight. − Direct evidence of the enrichment of short chains at a free polymer surface was obtained by neutron reflectivity measurements of blends of hydrated and deuterated polystyrene near the air surface , by surface-enhanced Raman spectroscopy and by secondary ion mass spectrometry …”

“…To estimate the degree of surface segregation, we used an equation derived by the numerical self-consistent field model of Scheutjens and Fleer and an analytical approximation. 4,5 For bimodal weight distributions, the entropically driven surface excess of the short-chain polymer of molar mass M s in a mixture with an average molar mass M h (both weight molar masses) and a bulk volume fraction is …”

“…(2) Even a small amount of short chains could hinder the formation of an immobilized layer. To estimate the degree of surface segregation, we used an equation derived by the numerical self-consistent field model of Scheutjens and Fleer and an analytical approximation. , For bimodal weight distributions, the entropically driven surface excess of the short-chain polymer of molar mass M s in a mixture with an average molar mass M̄ (both weight molar masses) and a bulk volume fraction φ is For mixtures of 5.9 and 19 kDa PDMS, the local volume fraction at the surface, Γ + φ, is at most 5.6% higher than the bulk volume fraction (Figure B,C). Thus, surface segregation alone cannot explain the change from repulsion to attraction at φ = 0.1−0.2, and we believe that the presence of short chains hinders the formation of an immobilized layer.…”