Haney Bobby, Werner Jörg G, Weitz David A, Ramakrishnan Subramanian
Department of Chemical and Biomedical Engineering, FAMU-FSU Engineering, Tallahassee, Florida 32310, USA.
Department of Mechanical Engineering and Division of Materials Science and Engineering, Boston University, Boston, Massachusetts 02215, USA and John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
Soft Matter. 2020 Apr 15;16(15):3613-3620. doi: 10.1039/d0sm00255k.
Although the utilization of rigid particles can afford stable emulsions, some applications require eventual emulsion destabilization to release contents captured in the particle-covered droplet. This destabilizing effect is achieved when using stabilizers that respond to controlled changes in environment. Microgels can be synthesized as stimuli responsive polymeric gel networks that adsorb to oil/water interfaces and stabilize emulsions. These particles are commonly hydrogels that swell and collapse in water in response to environmental changes. However, amphiphilic functionality is desired to enhance the adsorption abilities of these hydrogels while maintaining their stimuli responsivity. Microfluidic techniques are used to synthesize Janus microgels with two opposing stimuli responsive hemispheres. The particles have a temperature responsive domain connected to a pH responsive network where each side changes its hydrophilicity in response to a change in temperature or pH, respectively. The Janus microgels are amphiphilic in acidic conditions at 19 °C and alkaline conditions at 40 °C, while the opposite conditions cause a reduction of the amphiphilicity. By stabilizing emulsions with these dual responsive microgels, "smart" droplets that respond to environmental cues are formed. Emulsion droplets remain stable with smaller diameters when aqueous solution conditions favor amphiphilic particles yet, coalesce to larger droplets upon changing pH or temperature. These responsive Janus microgels represent the advancing technology of responsive droplets and demonstrate the applicability of microgels as emulsion stabilizers.
尽管使用刚性颗粒能够形成稳定的乳液，但某些应用需要乳液最终破乳，以释放包裹在颗粒覆盖液滴中的物质。当使用对环境的可控变化有响应的稳定剂时，就能实现这种破乳效果。微凝胶可被合成成为对刺激有响应的聚合物凝胶网络，吸附于油/水界面并使乳液稳定。这些颗粒通常是水凝胶，会根据环境变化在水中溶胀和收缩。然而，需要两亲性功能来增强这些水凝胶的吸附能力，同时保持其对刺激的响应性。微流控技术用于合成具有两个相对的对刺激有响应半球的Janus微凝胶。这些颗粒具有一个与pH响应网络相连的温度响应域，每一侧分别根据温度或pH的变化改变其亲水性。Janus微凝胶在19℃的酸性条件和40℃的碱性条件下具有两亲性，而相反的条件会导致两亲性降低。通过用这些双响应微凝胶稳定乳液，形成了对环境线索有响应的“智能”液滴。当水溶液条件有利于两亲性颗粒时，乳液液滴以较小的直径保持稳定，然而，在改变pH或温度时会聚结成更大的液滴。这些响应性Janus微凝胶代表了响应性液滴的先进技术，并证明了微凝胶作为乳液稳定剂的适用性。
