Vesicles made of PS-PI cyclic diblock copolymers: In situ freeze-drying cryo-TEM and dynamic light scattering experiments

Abstract

We have studied the morphology of self-assembled micelles made of linear and cyclic poly(styrene-b-isoprene) PS-b-PI block copolymers dispersed in selective solvents of the PI block (n-heptane, n-decane). Up to a copolymer concentration of 5 mg mL⁻¹, the micelles made from linear block copolymer chains adopt a spherical shape. Those arising from cyclic copolymer chains having exactly the same molar mass and volume fraction self-assemble into (i) planar sunflower-shaped particles at low concentration (c < 0.1 mg mL⁻¹), (ii) giant wormlike micelles at intermediate concentration (0.1 mg mL⁻¹ < c < 2 mg mL⁻¹) and (iii) vesicles at higher concentration (2 mg mL⁻¹ < c < 5 mg mL⁻¹). Those results were obtained using dynamic light scattering and in situ freeze-drying cryo-transmission electron microscopy. In this contribution, we discuss the effects of concentration and temperature on the morphology of the self-assembled particles made from both linear and cyclic PS–PI copolymers, and highlight the surprising vesicle formation in cyclic block copolymer solutions.