Criteria for formation and flocculation of micelles from pure graft copolymers were investigated in single selective solvents by turbidimetry with the use of two series of graft copolymers from poly(vinyl acetate) (PVAC), i.e., PVAC–styrene graft copolymers with one branch and PVAC–methyl methacrylate graft copolymers with one and several branches. These graft copolymers could be completely coagulated through two processes in the selective solvents which had widely different ? temperatures. The first process is the formation of micelles. One sequence, i.e., either backbone or branch of the graft copolymers, becomes desolvated under conditions similar to those for the corresponding homopolymer. This results in formation of the core of the micelle, the other soluble sequence extending from the surface of the core into the solvent phase. As the soluble chains cover the micelle core, no macroscopic phase separation occurs, but a stable dispersion is formed. The second process is that the micelle becomes too unstable to exist as dispersed when the solvency of the medium for the soluble sequence decreases to a certain degree. As a result, flocculation of the micelle finally takes place. 相似文献
Summary: Dissipative particle dynamics simulations are performed on the distributions of two agents in a core‐shell‐corona multicompartment micelle. The simulated results show that when the agents are weakly hydrophobic, their distributions in the multicompartment micelle are largely affected by the interactions between the agents and the blocks; while for strongly hydrophobic agents, the self‐assembly of solubilized species in the micelle is also affected largely by the interactions between the species. This work confirms that a multicompartment micelle can store two agents within separate nanoscopic compartments simultaneously, and shows that the distributions of the agents can be tailored easily by changing the interactions presented. This provides molecular‐level information that is useful for the future rational design of new micellar systems with tailored properties.
Simulated cross sections of the multicompartment micelles with strongly hydrophobic solubilized agents (the solvent and block A are omitted for clarity, block B is dark gray, block C is light gray, agent P is white, and agent Q is black). 相似文献
The authors propose a mean-field model to explore the equilibrium coupling between micelle aggregation and lattice choice in neutral copolymer and selective solvent mixtures. They find both thermotropic and lyotropic transitions from face-centered cubic to body-centered cubic ordered phases of spherical micelles, in agreement with experimental observations of these systems over a broad range of conditions. The stability of the nonclosed packed phase can be attributed to two physical mechanisms: the large entropy of lattice phonons near crystal melting and the preference of the intermicelle repulsions for the body-centered cubic structure when the lattice becomes sufficiently dense at higher solution concentrations. Both mechanisms are controlled by the decrease of micelle aggregation and subsequent increase of lattice density as solvent selectivity is reduced. These results shed new light on the relationship between micelle structure--"crewcut" or "hairy"--and long-range order in micelle solutions. 相似文献
