Block copolymer micelle solutions: 2. An intrinsic excimer fluorescence study

Abstract

We have utilized photostationary and transient excimer fluorescence to extend our study of the concentration dependence of PSPEP in heptane, given in the previous paper. The concentration dependence of photostationary observables, namely the excimer-to-monomer intensity ratio I D I M , the excimer bandwidth Δv D, 1 2 and the excimer band maximum position v D, can be explained in terms of the variation of solvent content in the core. Using a three-dimensional energy migration lattice model developed previously by Gelles and Frank in 1983 for studying miscible blends of polystyrene (PS) and poly(vinyl methyl ether), we have estimated the volume fraction of PS in the core as a function of concentration. In addition, both photostationary and transient results indicate that the free chain-micelle equilibrium is changed in favour of more free chains above 0.5% for the heptane solution and above 0.25% for the dodecane solution. The amount of free chains in the dispersed phase could also be estimated from the lattice model by a lever-rule approach. The critical micelle temperature (c.m.t.) can be measured by monitoring the changes of the excimer bandwidth at elevated temperatures. At temperatures below the c.m.t., two different transitions, in the form of small increases in I D I M , were observed, and have been attributed to the solvation of the micelle core and the disordering of the core-corona interface.