Micellization and Phase Separation for Triblock Copolymer 17R4 in H₂O and in D₂O

Abstract

The reverse Pluronic triblock copolymer 17R4 is formed from poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO): PPO(14)-PEO(24)-PPO(14), where the subscripts denote the number of monomers in each block. In water, 17R4 shows both a transition to aggregated micellar species at lower temperatures and a separation into copolymer-rich and copolymer-poor liquid phases at higher temperatures. For 17R4 in H(2)O and in D(2)O, we have determined (1) the phase boundaries corresponding to the micellization line, (2) the cloud point curves marking the onset of phase separation at various compositions, and (3) the coexistence curves for the phase separation (the compositions of coexisting phases). In both H(2)O and in D(2)O, 17R4 exhibits coexistence curves with lower consolute temperatures and compositions that differ from the minima in the cloud point curves; we take this as an indication of the polydispersity of the micellar species. The coexistence curves for compositions near the critical composition are described well by an Ising model. For 17R4 in both H(2)O and D(2)O, the critical composition is 0.22 ± 0.01 in volume fraction. The critical temperatures differ: 44.8 °C in H(2)O and 43.6 °C in D(2)O. The cloud point curve for the 17R4/D(2)O is as much as 9 °C lower than in H(2)O.

Glycine elicited self-assembly of amphiphilic star block copolymers with contradistinct hydrophobicities

“…2(c) and 2(d) respectively. It was established that ∆H and CMT are significantly affected by replacing H2O by D2O [62,63]. However, in the present case, no significant change was observed on the CMTs of both the copolymers by replacing water with D2O.…”

Self-assembly of the triblock copolymer 17R4 poly(propylene oxide)14–poly(ethylene oxide)24–poly(propylene oxide)14 in D2O

“…While we did not deliberately investigate the formation of the film when samples were in regions II and III, we never observed the film except in region I. This surface film has not been studied in 17R4 in H 2 O [1]. Zhou and Chu [2] reported cloudiness in 17R4/H 2 O and found that it was eliminated by filtering the samples.…”

“…Thus the end blocks are hydrophobic and the center block is hydrophilic, allowing for possibilities of self-assembly in water. The phase diagrams of 17R4 in H 2 O and in D 2 O [1,2] show micellization lines intersecting liquid-liquid phase separations with lower critical solution points. In Fig.…”

“…The 17R4 sample, PPO 14 -PEO 24 -PPO 14 , was the same material used by Huff et al [1]. The manufacturer BASF Corporation reported an average molecular mass of 2650 g/mol and a mass density (q) of 1.048 g/mL.…”

“…1 is a ''cloud point curve'' drawn from the appearance either of cloudiness indicating the incipient phase separation or of an actual second phase. Because of the polydispersity of the copolymer solute, the cloud point curve is not the same as a true coexistence curve [1,4].…”