The name is absent

ditions. In a good solvent the brush is extended and follows a parabolic profile.
However, as the solvent quality decreases the brush height decreases and the profiles
become flatter than a parabola and almost step-like.

SCFT predicts that the scaling variable for average brush height changes with the
solvent quality [227]. For good solvent, < z >~ N_g∕y_g³∖ for theta solvent, < z >~
N_gp^x_g²∙, and for poor solvent, < z >~ N_gp_g. Figures 6.3b, 6.4a and 6.4b show that
modified iSAFT agrees with these scaling relations. It should be noted that for all
the cases studied here, N_g and p_g are chosen such that chains strongly overlap; i.e.
P_g » p_g, where p_g is the overlap threshold, p*_g scales as ~ N~^a, where a = 6/5 for
good solvent, 1 for a theta solvent and 2/3 for a poor solvent.

6.3.2 Structure of polymer brushes in the presence of an ex-
plicit solvent

Molecular Dynamics simulation for polymer brushes in the presence of free poly-
mer have been done by Grest [231]. The calculations were done for free polymers
with a small number of segments (Nf = 2, 5 and 10). Both the tethered and the free
chains were purely repulsive. To study the effect of explicit solvent on the structure
of the polymer brush, the overall density of the monomers in the system was fixed at
pσ³ = 0.85.

The structure of both the polymer brush and the free polymer are calculated using
modified iSAFT. The number of segments in the tethered chain are fixed to N_g — 100

161

<<   170   171   172   173   174   175   176   >>

More intriguing information