Chen Jianqiang, Zhu Chenyang, Yang Zhen, Wang Ping, Yue Yiying, Kitaoka Takuya
Laboratory of Advanced Environmental & Energy Storage Materials, Department of Environment Engineering, Nanjing Forestry University , 159 Longpan Road, Nanjing 210037, P. R. China.
School of Chemistry and Materials Science, Jiangsu Provincial Key Laboratory of Material Cycling and Pollution Control, Nanjing Normal University , 1 Wenyuan Road, Nanjing 210023, P. R. China.
Langmuir. 2018 Jan 9;34(1):273-283. doi: 10.1021/acs.langmuir.7b03490. Epub 2017 Dec 21.
Lack of deep understanding of nanoparticle (NP) actions at oil/water interface set an obstacle to practical applications of Pickering emulsions. Fluorescence labels fabricated by incorporation of carbon dots (CDs) into poly(N-isopropylacrylamide) (PNIPAM) matrix can not only mark the action of PNIPAM-based NPs in the interface but also reflect the colloidal morphologies of PNIPAM. In this work, we employed coaxial electrospraying for fabricating core-shell nanospheres of cellulose acetate encapsulated by PNIPAM, and facile incorporation of CDs in PNIPAM shells was achieved simultaneously. The coaxial electrosprayed NPs (CENPs) with temperature-dependent wettability can stabilize heptane and toluene in water at 25 °C, respectively, and reversible emulsion break can be triggered by temperature adjustment around the low critical solution temperature (LCST). Remarkably, CENP/CD composites exhibited a fluorescence "on-off" behavior because of the volume phase transition of the PNIPAM shell. CENP/CD composites in Pickering emulsions clearly elucidated the motions of CENPs in response to temperature changes. At temperatures below the LCST, the CENP concentration played an important role in surface coverage of oil droplets. Specifically, the CENP concentration above the minimum concentration for complete emulsification of oil phase led to high surface coverage and two-domain adsorption of CENPs at the interface including primary monolayer anchoring of CENPs on droplets surrounded by interconnected CENP networks, which contributed to the superior stability of the emulsions. Moreover, CENP/CD composites can be recycled with well-preserved core-shell structure and stable fluorescent properties, which offers their great potential applications in sensors and imaging.
对纳米颗粒（NP）在油/水界面作用的深入理解不足，为皮克林乳液的实际应用设置了障碍。通过将碳点（CDs）掺入聚（N-异丙基丙烯酰胺）（PNIPAM）基质中制备的荧光标记物，不仅可以标记基于PNIPAM的纳米颗粒在界面的作用，还能反映PNIPAM的胶体形态。在本工作中，我们采用同轴电喷雾法制备了被PNIPAM包裹的醋酸纤维素核壳纳米球，并同时实现了将CDs轻松掺入PNIPAM壳层中。具有温度依赖性润湿性的同轴电喷雾纳米颗粒（CENPs）在25℃时可分别稳定庚烷和甲苯在水中的乳液，并且通过在低临界溶液温度（LCST）附近调节温度可引发可逆的乳液破乳。值得注意的是，由于PNIPAM壳层的体积相变，CENP/CD复合材料表现出荧光“开-关”行为。皮克林乳液中的CENP/CD复合材料清楚地阐明了CENPs响应温度变化的运动情况。在低于LCST的温度下，CENP浓度对油滴的表面覆盖率起着重要作用。具体而言，高于油相完全乳化所需最低浓度的CENP浓度会导致高表面覆盖率以及CENPs在界面的双域吸附，包括CENPs在由相互连接的CENP网络包围的液滴上的初级单层锚定，这有助于乳液具有优异的稳定性。此外，CENP/CD复合材料可以回收利用，其核壳结构和稳定的荧光特性得以良好保留，这为它们在传感器和成像领域提供了巨大的潜在应用价值。
