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Signatures of a Concentration‐Dependent Flory χ Parameter: Swelling and Collapse of Coils and Brushes
Author(s) -
Baulin Vladimir A.,
Halperin Avi
Publication year - 2003
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/mats.200350014
Subject(s) - swelling , flory–huggins solution theory , polymer , gaussian , thermodynamics , planar , phase transition , materials science , phase (matter) , brush , solvent , statistical physics , polymer chemistry , condensed matter physics , physics , chemistry , computational chemistry , quantum mechanics , composite material , organic chemistry , computer science , computer graphics (images)
The quality of solvents of polymers is often described in terms of the Flory χ parameter typically assumed to depend only on the temperature, T . In certain polymer‐solvent systems fitting the experimental data enforces the replacement of ( χ T ) by a concentration‐dependent χ eff . In turn, this modifies the swelling and collapse behavior. These effects are studied, in the framework of a mean‐field theory, for isolated coils and for planar brushes. The ϕ dependence of χ eff gives rise to three main consequences: (i) shift in the cross‐over between Gaussian and self‐avoidance regimes; (ii) a possibility of first‐order collapse transition for isolated flexible coils; (iii) the possibility of a first‐order phase transition leading to a vertical phase separation within the brush. The discussion relates these effects directly to thermodynamic measurements and does not involve a specific microscopic model. The implementation for the case of poly( N ‐isopropylamide) (PNIPAM) brushes is discussed.ϕ vs. z plots, for brushes with N = 300, σ / a 2 = 18 ( σ / R F 2 = 0.019) characterized by different χ eff .