Observation of Liquid-to-Glass and Glass-to-Glass Transitions in L64/D_2O Triblock Copolymer Micellar System

摘要

We report photon correlation spectroscopy (PCS), low shear viscosity and small angle neutron scattering (SANS) studies of a Pluronic L64 micellar system in aqueous solutions at high polymer concentrations (wt%), 35.0% < c < 54.4%, in a temperature range where a kinetic glass transition (KGT) has been observed. We analyze SANS intensity distributions in the liquid state assuming that the micelles are spherical and interact among themselves via an effective pair-potential consisting of a hard core plus a narrow attractive square-well, the depth of which is temperature dependent. Comparison of the potential parameters so obtained with the phase diagram predicted recently by mode coupling theory (MCT) allows us to verify the existence of the so-called "liquid to attractive glass" KGT line. We then use scaling plots of SANS intensity distributions to show the existence of another branch of the KGT line where transitions from a repulsive glass to an attractive glass occur. In particular, we show an evidence of the existence of the so-called A_3 singularity end point where two glasses become identical in local structure [Sow-Hsin Chen, Wei-Ren Chen, Francesco Mallamace, "The glass-glass transition and its end point in a co-polymer micellar system", to be published].