Two Block Copolymers Form Micelles And Vesicles

Self-assembly of copolymer is one of the hottest subjects in polymer science now. Due to the potential applications of block copolymer in many fields, it has been received increasing attention.In this paper, self-assembly of three types of diblock copolymers, poly(styrene)-b-poly(ethylene)(PS-b-PE),poly(n-hexylisocyanate)-b-poly(ethylene glycol) (PHIC-b-PEG) and poly(oxyethylene) cholesterol ether (CS-b-EO), into micelles or vesicles in organic and aqueous solutions was studied with TEM, AFM, POM.For PS-b-PE, the influence of length of PS and PE blocks on formation of micelles was studied. It is found that spherical micelles are formed when PS block is longer in which the coronal extending free energy plays a dominant role, while 'broken flower' micelles are formed when PE block is longer in which the core crystal energy dominant. As for PHIC-b-PEG, the influence of temperature on the shape of micelles in toluene solution was investigated. It is observed that PEG₁₂-b-PHIC₃₀ forms spherical micelles in the range of studied temperatures (10℃, 50℃, 80℃) but PEG₁₂-b-PHIC₅₀ forms cylindrical micelles at 10℃, which transform into spherical ones at raised temperatures. Finally, we studied the self-assembly of CS-b-EO_n (n=5, 10, 15, 20, 24, 30) in aqueous solution. It is found that only CS-b-EO₅ can form vesicles but the others can not form vesicles.