title: pH-responsive core-shell particles and hollow spheres attained by macromolecular self-assembly.
abstract: According to our "block-copolymer-free" strategy for self-assembly of polymers, noncovalently connected micelles (NCCM) with poly(epsilon-caprolactone) (PCL) as the core and poly(acrylic acid) (PAA) as the shell in aqueous solutions were attained due to specific interactions between the component polymers. The micellar structure was then locked in by the reaction of PAA with diamine. Afterward, hollow spheres based on PAA network were obtained by either core degradation with lipase or core dissolution with dimethylformamide of the cross-linked micelles. The cavitation process was monitored by dynamic light scattering, which indicated a mass decrease and size expansion. The hollow structure is confirmed by transmission electron microscopy observations. The resultant hollow spheres are pH- and salt-responsive: there is a substantial volume increase when pH changes from acid to base, and vice versa. The volume change takes place dramatically over the pH-range from 5.8 to 7.5. Furthermore, this volume-pH-dependence is found to be completely reversible provided the effect of ionic strength is excluded. The volume change can be adjusted by changing the shell thickness and the cross-linking degree of the hollow spheres. The salt effect on the hollow sphere size depends on pH: with increasing salt concentration the size shows an increase, a decrease, and a little change in acidic, basic, and neutral media, respectively.
authors.affiliation: Department of Macromolecular Science and The Key Laboratory of Molecular Engineering of Polymers, Ministry of Education of China, Fudan University, Shanghai 200433, China.
authors.forename: Youwei
authors.initials: Y
authors.lastname: Zhang
authors.forename: Ming
authors.initials: M
authors.lastname: Jiang
authors.forename: Jiongxin
authors.initials: J
authors.lastname: Zhao
authors.forename: Zhouxi
authors.initials: Z
authors.lastname: Wang
authors.forename: Hongjing
authors.initials: H
authors.lastname: Dou
authors.forename: Daoyong
authors.initials: D
authors.lastname: Chen