Chains end-grafted in a theta-solvent and polymer melts: comparison of force-distance profiles

Citation
Llj. Cai et S. Granick, Chains end-grafted in a theta-solvent and polymer melts: comparison of force-distance profiles, ADV COLL IN, 94(1-3), 2001, pp. 135-150
Citations number
24
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
ADVANCES IN COLLOID AND INTERFACE SCIENCE
ISSN journal
00018686 → ACNP
Volume
94
Issue
1-3
Year of publication
2001
Pages
135 - 150
Database
ISI
SICI code
0001-8686(20011115)94:1-3<135:CEIATA>2.0.ZU;2-S
Abstract
We find an unexpected analogy between polymer melts compressed between stro ngly-attractive solid surfaces, and end-attached polymers in near-theta-sol vent. End-grafted polystyrene (PS) chains with various graft density were p roduced by immersing mica, coated with adsorbed diblock copolymers of PS/PV P, PS/polyvinylpyiridine, into trans-decalin at 24 degreesC (this solvent i s a near-theta-solvent for PS but a non-solvent for PVP), and the force-dis tance relations were measured using a surface forces apparatus. The end-gra fted PS chains repelled one another in spite of the theta-solvent situation . Repulsive forces began at a thickness, per adsorbed layer, equivalent to 4-5 times the unperturbed radius of gyration of the PS chain. These cases o f symmetrically-opposed PS layers are compared to the asymmetric case (PS o n one mica surface, the other mica surface bare) and to the case of adsorbe d PS homopolymer. Force-distance profiles in the presence of unattached PS homopolymer in solution at concentration c* (the overlap concentration) dis played repulsion beginning at considerably larger separation than in the pr esence of pure solvent. Finally, we compare to confined melts of linear pol ydimethylsiloxane (PDMS), cyclic PDMS and a linear perfluoropolyether (Demn um). For these cases of polymer melts confined between adsorbing surfaces, force-distance relations, could be described by the same functional relatio ns as for end-attached chains in near-theta-solvent. (C) 2001 Elsevier Scie nce B.V. All rights reserved.