Unlocking Chain Exchange in Highly Amphiphilic Block Polymer Micellar Systems: Influence of Agitation

Abstract

Chain exchange between block polymer micelles in highly selective solvents, such as water, is well-known to be arrested under quiescent conditions, yet this work demonstrates that simple agitation methods can induce rapid chain exchange in these solvents. Aqueous solutions containing either pure poly(butadiene-b-ethylene oxide) or pure poly(butadiene-b-ethylene oxide-d4) micelles were combined and then subjected to agitation by vortex mixing, concentric cylinder Couette flow, or nitrogen gas sparging. Subsequently, the extent of chain exchange between micelles was quantified using small angle neutron scattering. Rapid vortex mixing induced chain exchange within minutes, as evidenced by a monotonic decrease in scattered intensity, whereas Couette flow and sparging did not lead to measurable chain exchange over the examined time scale of hours. The linear kinetics with respect to agitation time suggested a surface-limited exchange process at the air–water interface. These findings demonstrate the strong influence of processing conditions on block polymer solution assemblies.

Cavitation-enabled rapid and tunable evolution of high-χN micelles as templates for ordered mesoporous oxides

“…16 The use of kinetic entrapment to prevent micelles from responding to changing solutions conditions is crucial to decouple the resulting pore size from an adjustable wall thickness. 27 Here we note that chain exchange is a much faster processes than micelle size equilibration. 16 Block copolymer micelles generally evolve through singlechain exchange, micelle fusion/fission or combination of these processes.…”

“…16 Block copolymer micelles generally evolve through singlechain exchange, micelle fusion/fission or combination of these processes. 27 The strong dependence of exchange rate on agitation was recently shown to be a novel method to tune micelle size distributions and then kinetically trap persistent micelles under high-χN conditions. For single-chain exchange, there is a double exponential rate dependence on χN, where χ is between the solvent and the solvophobic block and N is the solvophobic block length.…”

Ordered Mesoporous to Macroporous Oxides with Tunable Isomorphic Architectures: Solution Criteria for Persistent Micelle Templates

“…Considering the large molar masses and kinetically challenging conditions used here, one should not expect the micelles to fully equilibrate on a laboratory time scale. 99 The effect of the vortexing time and the enthalpic barrier to reorganization (final water content) were studied using P3 ( Figure S8). As expected, the average micelle diameters monotonically increased with increasing the final water content in the coassemble solutions ( Figure S8 a-c).…”

Elucidating the Molecular Processes for Creating Large or Bimodal Soft Nanoparticles from Block Copolymers via Blending

“…Before mixing, the ­concentrations for both PS(252K)‐b‐P4VP(43K) and PS(110K)‐b‐P4VP(107K) in DMF solution are 0.1 wt%. The water content in solution is about 5 wt% after exposing the solution to air for 36 h. By this method, we avoid external agitation effect on the micelle formation . Surprisingly, after about 36 h of exposure, we obtained significantly larger mixed micelles with a narrow size distribution as shown in Figure : The Z ‐average from DLS measurements is approximately 700 nm [540 nm for pure PS(110K)‐b‐P4VP(107K) and 330 nm for PS(252K)‐b‐P4VP(43K), respectively] and the dry micelle size obtained via TEM is about 100 nm [65.7 ± 4.9 nm for pure PS(110K)‐b‐P4VP(107K) and 73.8 ± 6.0 nm for PS(252K)‐b‐P4VP(43K) respectively].…”