Hydrophobic and Elastic Forces Experienced by a Series of Pyrene End-Labeled Poly(ethylene oxide)s Interacting with Sodium Dodecyl Sulfate Micelles

Abstract

A series of pyrene end-labeled poly(ethylene oxide)s (Py2-PEO(x) with x equal to 2, 3.4, 5, 6, 7.8, and 10 kg mol–1) were synthesized, and their interactions with SDS micelles were characterized by steady-state and time-resolved fluorescence. Pyrene excimer formation (PEF) indicated that both pyrenyl ends were located in the same SDS micelle whereas the absence of PEF reflected bridging of two SDS micelles by a Py2-PEO molecule having its pyrenyl end groups in separate micelles. PEF efficiency was characterized from the excimer-to-monomer fluorescence intensity ratio (IE/IM) which was determined as a function of PEO chain length and salt concentration. More detailed information about the PEF process was obtained by fitting the monomer and excimer fluorescence decays globally according to the model free analysis (MFA). MFA yielded the average rate constant ⟨k⟩ of PEF and the molar fraction (ffree) of pyrenyl labels that did not form excimer, thus reflecting the extent of bridging undergone by the Py2-PEO c...