Kinetic glass transition in a copolymer micellar system with temperature-dependent short-range attractive interaction

We discuss in this paper the interaction and phase behavior of a micellar system formed by Pluronic L64 tri-block co-polymer (PEO₁₃PPO₃₀PEO₁₃) in heavy water at high concentrations, based on analyses of three sets of experimental data: small-angle neutron scattering (SANS), photon correlation spectroscopy (PCS) and zero-shear viscosity. This micellar system shows an inverted binodal line with a lower critical consolute point and a percolation line at moderate concentrations [1,2]. As one approaches the binodal line at constant weight fraction of the copolymer, the aggregation number and the stickiness parameter increase. In particular, at weight fraction of 5%, the stickiness parameter approaches critical value 10.2 at T=330.9 K. Near the critical point, micelles stay spherical but interact strongly with each other by a short range, temperature dependent attraction [3]. The frequency- dependent complex moduli G' (ω) and G' ' (ω) jump abruptly two orders of magnitude upon crossing the temperature- and concentration-dependent percolation line [1,4], showing that the short-range attraction leads to formation of polydispersed fractal aggregates of micelles at percolation. We observe dramatic modifications in shear moduli as the KGT line is approached [4]. We then describe the recently found re-entrant kinetic glass transition (KGT) lines and the logarithmic time dependence of the density-density correlation function in this system at high concentrations [5,6]. Finally, we show an experimental evidence of the repulsive glass-toattractive glass transition predicted by mode coupling theory for a system with a short-range attraction in terms of scaling plots of SANS intensity distributions at the transition [6].