Surface segregation driven by molecular architecture asymmetry in polymer blends

The contributions of chain ends and branch points to surface segregation of long-branched chains in blends with linear chains have been studied using neutron reflectometry and surface-enhanced Raman spectroscopy for a series of novel, well-defined polystyrenes. A linear response theory accounting for the number and type of branch points and chain ends is consistent with surface excesses and composition profile decay lengths, and allows the first determination of branch point potentials. Surface excess is determined primarily by chain ends with branch points playing a secondary role.

Figure 1

Structures of the branched polystyrenes and abbreviated names. In group 1 the number of ends was fixed at 6 and the number of branch points varied from 1 to 4. In group 2 the number of ends varied from 6 to 13 and the number of branch points fixed at 4.

Figure 2

Neutron reflectivity as a function of scattering wave vector, $q$, for a blend of 20 vol % 6-end PS with linear d-PS after annealing 12 h at $180°\mathrm{C}$. The solid line represents the reflectivity calculated from the model concentration depth profile shown in the inset.

Figure 3

SERS spectra for annealed blend films: (1) L-$\mathrm{hPS}/\mathrm{dPS}$ blend, (2) 6-$\text{star}/\mathrm{dPS}$, (3) 6-pom, (4) 6-$\text{branch}/\mathrm{dPS}$, (5) 9-$\text{branch}/\mathrm{dPS}$, and (6) 13-$\text{branch}/\mathrm{dPS}$.