Crystallization and Phase Behavior in Block Copolymer Solution:An in Situ Small Angle X-ray Scattering Study

Amphiphilic diblock copolymers self-assemble into a variety of micellar structures with diverse shapes in selective solvents. Here, we study the concentration and temperature dependence of the packing structure of spherical micelles of a polyisoprene-b-poly(2- vinylpyridine)(PI-b-P2VP) diblock copolymer in toluene using synchrotron radiation small angle X-ray scattering (SR-SAXS) and atomic force microscopy (AFM) techniques. Randomly packed spherical micelles are detected in dilute solutions, while in concentrated solutions, face-centered cubic (FCC), body-centered cubic (BCC) mixed crystal structures, and pure BCC crystal structures are observed with an increase in concentration. In situ SAXS experiments on the FCC/BCC mixed crystal structures reveal a novel FCC/BCC → BCC → Disorder → BCC phase behavior during the thermal annealing process. These results demonstrated that the BCC phase is apparently more stable than the FCC phase in the current sphere-packing system and FCC/BCC is a metastable state. The incompatibility of the PI and P2VP blocks decreases at a higher temperature and renders the variation of domain spacing.

Amphiphilic diblock copolymers self-assemble into a variety of micellar structures with diverse shapes in selective solvents.Here,we study the concentration and temperature dependence of the packing structure of spherical micelles of a polyisoprene-Zb-poly(2-vinylpyridine)(PI-Zb-P2VP) diblock copolymer in toluene using synchrotron radiation small angle X-ray scattering (SR-SAXS) and atomic force microscopy (AFM) techniques.Randomly packed spherical micelles are detected in dilute solutions,while in concentrated solutions,face-centered cubic (FCC),body-centered cubic (BCC) mixed crystal structures,and pure BCC crystal structures are observed with an increase in concentration.In situ SAXS experiments on the FCC/BCC mixed crystal structures reveal a novel FCC/BCC→BCC→Disorder→BCC phase behavior during the thermal annealing process.These results demonstrated that the BCC phase is apparently more stable than the FCC phase in the current sphere-packing system and FCC/BCC is a metastable state.The incompatibility of the PI and P2VP blocks decreases at a higher temperature and renders the variation of domain spacing.