Micellar Solutions of Associative Triblock Copolymers:  Entropic Attraction and Gas−Liquid Transition

Abstract

We report the first clear observations of an entropy-driven phase transition between a dilute micellar “gas” and a disordered but highly associated micellar “liquid” realized with aqueous solutions of poly(ethylene oxide) chains fully end-capped with C16 and C18 hydrophobes. Dynamic light scattering and capillary viscometry determine the radii and aggregation numbers of the micelles and, together with the coexisting concentrations, permit estimates of the strength of the entropic attraction through the adhesive hard-sphere model. The behavior is qualitatively consistent with expectations for the entropy gain from the exchange of end blocks between cores of flowerlike micelles consisting of associative triblock copolymers.

A Molecular Picture for the Thermo-Reversibility of Gels Formed by Isophthalic Acid-Ended Telechelic Polymers

“…The micelle-micelle interaction is strong enough for the solution to phase separate [5,6]. This interaction energy only depends on the aggregation number of end groups, p, with larger p values indicating stronger interactions and p is invariant in T [5,6]. Our system differs from the interacting micelle theory in two ways: 1) lack of phase separation and 2) SANS shows the cluster size decreases for T above 30 C.…”

“…In addition, the interacting micelle theory assumes that micelles have an entropic attraction to each other: isolated micelles consist solely of loops while micelle interaction leads to an increase in conformations due to the exchange of end blocks between cores of micelles. The micelle-micelle interaction is strong enough for the solution to phase separate [5,6]. This interaction energy only depends on the aggregation number of end groups, p, with larger p values indicating stronger interactions and p is invariant in T [5,6].…”

“…As shown in Figure 3, the cluster size is dependent on temperature ( Figure 3A), but not on concentration ( Figure 3B bottom). According to the interacting micelle theory [5,6] the cluster size depends on the micelle-micelle interaction energy, and hence, the aggregation number of end groups, thus a decrease in cluster size suggests a decrease in aggregation number with increasing T above 30 C.…”

“…Transient network theory, from the kinetic theory of rubber elasticity, suggests that the elastic modulus is proportional to the number of elastically active bridges [2][3][4]. Another branch of theory, which we will refer to as 'interacting micelle theory', postulates that the dynamic of the system is determined by the interaction between micelles: micelles attract due to the entropy gain from the exchange of end blocks between cores of flower-like micelles [5,6]. Both theories assume that the aggregation number of end groups within a micelle core doesn't change with temperature, which is in agreement with the experimental data showing no temperature-dependent topological change.…”

Effect of Nonlinearity Strength in Chain Tension on Shear-Thickening of Associating Polymer Networks

“…1) A typical example of associating polymers is telechelic poly(ethylene oxide) (referred to as PEO hereafter) carrying short hydrophobic end chains at both its ends. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Aqueous solutions of telechelic PEO exhibit shear thickening followed by thinning under certain conditions: 2,3,6,8,[11][12][13]15,16,18) the stationary shear viscosity increases with the shear rate, attains a maximum at a moderate shear rate, and then decreases at a higher shear rate.…”