Journal
SOFT MATTER
Volume 8, Issue 35, Pages 9127-9131Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c2sm25963j
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Funding
- National Science Foundation of China [21074123, 91027024, 50973101, 20974107]
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Laser-trapping Raman spectroscopy (LTRS) is adopted to detect the photo-induced isomerization of azobenzene in the cross-linked membrane of a single vesicle, which is self-assembled first by an amphiphilic copolymer, poly(N-isopropylacrylamide)-block-poly{6-[4-(4-pyridyazo)phenoxy] hexylmethacrylate} (PNIPAM-b-PAzPy6), and then cross-linked by reaction between 1,3-dibromopropane and pyridine groups in the copolymer chain. A series of polymer vesicles with different cross-linking degrees were made to meet the need of vesicles with different softness during this research work. Vesicles with 0.0% and 18.7% cross-linking degrees have characteristic photo-induced swelling-shrinking, others with higher cross-linking degrees do not. The isomerization of azobenzene is observed in situ by LTRS along with photo-induced swelling of single vesicles with different cross-linking degrees. Results from analysis of the obtained Raman spectra show that photo-induced isomerization of azobenzene is a trigger of the photo-induced swelling process and the swelling degree is mainly dependent on the degree of cross-linking, namely, the softness of the polymer vesicle. The former result is different from that obtained by analysis of UV-Vis spectroscopy for vesicle solutions and shows that photo-induced swelling-shrinking vesicles can be constructed by amphiphilic copolymers bearing azobenzene units in the minority.
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