Polystyrene‐block‐Polyisoprene Diblock‐Copolymer Micelles: Coupled Pressure and Temperature Effects

Abstract

The structural changes of diblock‐copolymer micelles under pressures from 200 to 16 000 psi are investigated using small‐angle neutron scattering (SANS). Asymmetric polystyrene‐block‐polyisoprene (PS–PI) diblock copolymers are dissolved in decane, a selective solvent for PI, to form spherical micelles with a core of PS and a corona of PI. The micellar solutions are put under pressure at temperatures of 25 to 60 °C. At room temperature, elevating the pressure from 200 to 16 000 psi has no effect on the size of the micelles. While the micellar solutions remain stable, instantaneous association of micelles is detected. In contrast to micelles at atmospheric pressure, increasing the temperature at elevated pressures does not lead to dissociation of micelles; instead, the micelles aggregate and evolve into sheet‐like structures, reminiscent of a macroscopic phase separation. Furthermore, higher pressures lead to a smaller temperature range in which shape transitions take place.

Influence of hydrophilic block length on the aggregation properties of polyglycidol–polystyrene–polyglycidol copolymers

“…Aggregates of PEO–PPO–PEO triblock copolymers in water and water/ethanol solution studied by Soni et al 67 evidenced one peak at 0.70 1 Å −1 which was correlated to PPO core. The self-assembly under wide range of pressures and various temperatures of polystyrene- b -polyisoprene diblock copolymer in decane were studied by Cheng et al 68 Obtained patterns indicate spherical core of PS with diameter around 120 Å. Akiba et al , 69 studied partially benzyl-esterified poly(ethylene glycol)- b -poly(aspartic acid) diblock copolymer in water using SAXS. Peaks observed on diffractograms for this copolymer suspension have been assigned to micelles dense cores.…”

Self-Assembly of Block and Graft Copolymers in Organic Solvents: An Overview of Recent Advances

“…Later on, Cheng et al [ 40 ] studied the morphological changes of non-functionalized PS- b -PI copolymer in n -decane as a function of temperature and pressure using small-angle neutron spectroscopy (SANS). According to the authors, the increase in pressure from 200 to 16,000 psi, at room temperature, had no effect on the micellar characteristics ( N agg , R g , and R core ), but led to the formation of micellar agglomerates.…”