Schizophrenic core-shell microgels: thermoregulated core and shell swelling/collapse by combining UCST and LCST phase transitions.
Schizophrenic core-shell microgels: thermoregulated core and shell swelling/collapse by combining UCST and LCST phase transitions.
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DOI：
10.1021/la500133y
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发表时间：
2014-02
期刊：
影响因子：
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通讯作者：
Jun Yin;Jinming Hu;Guoying Zhang;Shiyong Liu
中科院分区：
文献类型：
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作者：
Jun Yin;Jinming Hu;Guoying Zhang;Shiyong Liu
采用种子乳液聚合法制备了具有pH和温度响应性的微交联聚（2-乙烯基吡啶）-聚（N-异丙基丙烯酰胺）（P2 VP-PNIPAM）核壳微凝胶。在酸性条件下，带负电的2，6-萘二磺酸钠（2，6-NDS）通过静电吸引作用内化到内核中，形成（P2 VPH（+）/SO 3（2-））超分子复合物。通过激光光散射和紫外-可见光谱研究了（P2 VPH（+）/SO 3（2-））-PNIPAM核壳微凝胶的温敏特性，发现在20-55 °C范围内，该微凝胶具有上临界溶解温度（UCST）和下临界溶解温度（LCST）的综合特性。UCST的性能是由P2 VPH（+）和2，6-NDS在高温下的静电吸引相互作用的折衷引起的，而随后的LCST转变与PNIPAM壳的热诱导坍塌相关。通过静态荧光光谱法监测2，6-NDS的控制释放随温度的变化。此外，停流配备了一个温度跳跃附件，然后被用来评估的动态过程，提出了毫秒的特征弛豫时间的2，6-NDS扩散过程。有趣的是，特征弛豫时间是独立的壳交联密度，而它是显着的壳厚度的影响。我们相信，这些具有热可调体积相变的双重温敏核壳微凝胶可能预示着在聚合物科学和材料领域的有前途的应用，特别是温度触发释放。
A variety of slightly cross-linked poly(2-vinylpyridine)-poly(N-isopropylacrylamide) (P2VP-PNIPAM) core-shell microgels with pH- and temperature-responsive characteristic were prepared via seeded emulsion polymerization. Negatively charged sodium 2,6-naphthalenedisulfonate (2,6-NDS) could be internalized into the inner core, followed by formation of (P2VPH(+)/SO3(2-)) supramolecular complex through the electrostatic attractive interaction in acid condition. The thermoresponsive characteristic feature of the (P2VPH(+)/SO3(2-))-PNIPAM core-shell microgels was investigated by laser light scattering and UV-vis measurement, revealing an integration of upper critical solution temperature (UCST) and lower critical solution temperature (LCST) behaviors in the temperature range of 20-55 °C. The UCST performance arised from the compromised electrostatic attractive interaction between P2VPH(+) and 2,6-NDS at elevated temperatures, while the subsequent LCST transition is correlated to the thermo-induced collapse of PNIPAM shells. The controlled release of 2,6-NDS was monitored by static fluorescence spectra as a function of temperature change. Moreover, stopped-flow equipped with a temperature-jump accessory was then employed to assess the dynamic process, suggesting a millisecond characteristic relaxation time of the 2,6-NDS diffusion process. Interestingly, the characteristic relaxation time is independent of the shell cross-link density, whereas it was significantly affected by shell thickness. We believe that these dual thermoresponsive core-shell microgels with thermotunable volume phase transition may augur promising applications in the fields of polymer science and materials, particularly for temperature-triggered release.