Associating polymers: Equilibrium and linear viscoelasticity

Abstract

A theory for the equilibrium and dynamic properties of a solution of telechelic polymers in the limit of high aggregation number is presented. It is shown that (1) the micelles formed by telechelic chains (flowers) in a dilute solution strongly attract each other, (2) at some concentration * the flowers form a reversible gel where they Eire connected by multiple bridges, (3) the dynamics of individual micelles in the gel is governed by the bridge/loop exchange rate and by the effective barrier associated with the hopping of a micelle to a new position; this barrier is determined by the energy Eissociated to a deformation/ compression of a micelle, (4) the viscosity is changing exponentially in the region > * (it is increasing in the vicinity of *); however, it can decrease (with ) in a limited concentration range above *.

Celebrating Soft Matter's 10th Anniversary: Chain configuration and rate-dependent mechanical properties in transient networks

“…23 When a chain is pulled out of a junction, the chain has a nite time on the order of its relaxation time aer which it no longer remembers the stress. 23 These ideas have been applied to multiple other systems in order to take into account the effects of network topology, 24 multifunctional stickers, 25 non-telechelic associations, 26 and the presence of intrachain associations 27 on the free energy of a system. All of the aforementioned theories utilize system thermodynamics to determine gel mechanical properties.…”

Phase behavior and viscoelastic properties of entangled block copolymer gels

“…[1][2][3][4][5][6][7] For example, asymmetric AB diblock copolymers, where A is the minority component, readily form spherical micelles in a nonsolvent for the A block [ Fig. 1(a)].…”

“…The interaction between micelles depends on the temperature, solvent quality, and architecture of the block copolymer. Although two diblock micelles in a good solvent always repel each other, 5 the bridging of triblock chains between micelles generates an entropic attraction. 2,[5][6][7] In a midblock-selective solvent, asymmetric ABA triblocks are tethered at both ends, yielding two possible conformations for the midblock: a loop conformation, in which both ends are attached to the same core, and a bridge conformation, in which the end blocks are attached to different cores 2,4 [ Fig.…”

“…1(c)] show no attraction. In this case, the system will behave essentially as a com-parable solution of an AB diblock with half the triblock molecular weight; 5 that is, we can conceptually form a loop by connecting the B ends of two diblock chains anchored in the same micelle, neglecting the small free-energy penalty to fold back the triblock loop. 2,4 However, when the loop/ bridge ratio is small or moderate [ Fig.…”

“…1(b)], the bridging chains produce an association, which can lead to phase-separated solutions at low polymer contents 2,4 and physical networks at high polymer contents. [5][6][7][8][9][10][11][12][13][14] Watanabe and coworkers 9,10 conducted extensive investigations of styrene-isoprene-styrene (SIS) triblocks in the midblock-selective solvent tetradecane at various polymer concentrations. The fraction of bridges was directly determined by an elegant dielectric technique and was shown to decrease as the triblock was diluted.…”