Coil−Globule Transition of Poly(N-isopropylacrylamide):  A Study of Polymer−Surfactant Association

• Published in: Macromolecules Vol. 29; no. 11; pp. 4019 - 4028
• Main Authors: Walter, R, Rička, J, Quellet, Ch, Nyffenegger, R, Binkert, Th
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 20.05.1996
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties; Collapse; Intermolecular interaction; Anionic surfactant; Temperature effect; Aqueous solution; Experimental study; Acrylamide derivative polymer; Conformational transition
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma951529x

Time-resolved fluorescence depolarization is applied to investigate the association of sodium n-dodecyl sulfate (SDS) micelles with poly(N-isopropylacrylamide) in aqueous solutions using an amphiphilic fluorescent probe (3-perylenedodecanoic acid) which is incorporated into the SDS micelles. First, the effect of the surfactant concentration was measured:  in the presence of the polymer, above the critical aggregation concentration (CAC) of SDS, the rotational relaxation of the probe exhibits a slow and a fast component. The relaxation time of the fast component is the same as in a polymer-free solution above the CMC of SDS where, however, only one component is observed. The slower relaxation time is attributed to polymer-bound micelles which incorporate polymer segments into their core. Second, the effect of the temperature induced coil−globule transition is investigated:  in the course of the transition the rotational motion slows down almost 10-fold, indicating that the probe remains firmly associated with the polymer even in its dense globular state.