Institut des Molécules et Matériaux du Mans (IMMM), UMR 6283 CNRS - Le Mans Université, 1, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France.
Univ. Bordeaux, CNRS, Bordeaux INP, ISM, UMR 5255, F-33400 Talence, France.
J Colloid Interface Sci. 2022 Feb 15;608(Pt 2):1191-1201. doi: 10.1016/j.jcis.2021.10.074. Epub 2021 Oct 16.
Stabilization of water-in-water (W/W) emulsions resulting from the separation of polymeric phases such as dextran (DEX) and poly(ethyleneoxide) (PEO) is highly challenging, because of the very low interfacial tensions between the two phases and because of the interface thickness extending over several nanometers. In the present work, we present a new type of stabilizers, based on bis-hydrophilic, thermoresponsive microgels, incorporating in the same structure poly(N-isopropylacrylamide) (pNIPAM) chains having an affinity for the PEO phase and dextran moieties. We hypothesize that these particles allow better control of the stability of the W/W emulsions.
The microgels were synthesized by copolymerizing the NIPAM monomer with a multifunctional methacrylated dextran. They were characterized by dynamic light scattering, zeta potential measurements and nuclear magnetic resonance as a function of temperature. Microgels with different compositions were tested as stabilizers of droplets of the PEO phase dispersed in the DEX phase (P/D) or vice-versa (D/P), at different concentrations and temperatures.
Only microgels with the highest DEX content revealed excellent stabilizing properties for the emulsions by adsorbing at the droplet surface, thus demonstrating the fundamental role of bis-hydrophilicity. At room temperature, both pNIPAM and DEX chains were swollen by water and stabilized better D/P emulsions. However, above the volume phase transition temperature (VPTT ≈ 32 °C) of pNIPAM the microgels shrunk and stabilized better P/D emulsions. At all temperatures, excess microgels partitioned more to the PEO phase. The change in structure and interparticle interaction induced by heating can be exploited to control the W/W emulsion stability.
由于葡聚糖 (DEX) 和聚氧乙烯 (PEO) 等聚合物相之间的界面张力非常低，并且界面厚度延伸到几个纳米，因此，水包水 (W/W) 乳液的分离导致其稳定化极具挑战性。在本工作中，我们提出了一种基于双亲水响应性微凝胶的新型稳定剂，该微凝胶在同一结构中包含对 PEO 相具有亲和力的聚 N-异丙基丙烯酰胺 (pNIPAM) 链和葡聚糖部分。我们假设这些颗粒可以更好地控制 W/W 乳液的稳定性。
通过将 NIPAM 单体与多功能甲基丙烯酰化葡聚糖共聚合成微凝胶。通过动态光散射、zeta 电位测量和核磁共振技术随温度进行了表征。测试了具有不同组成的微凝胶，作为 PEO 相分散在 DEX 相中的液滴 (P/D) 或反之亦然 (D/P) 的稳定剂，浓度和温度不同。
只有具有最高 DEX 含量的微凝胶通过吸附在液滴表面显示出对乳液的优异稳定性能，从而证明了双亲水特性的基本作用。在室温下，pNIPAM 和 DEX 链都被水溶胀，并且更好地稳定了 D/P 乳液。然而，在 pNIPAM 的体积相转变温度 (VPTT≈32°C) 以上，微凝胶收缩并更好地稳定了 P/D 乳液。在所有温度下，过量的微凝胶更多地分配到 PEO 相。通过加热引起的结构和颗粒间相互作用的变化可用于控制 W/W 乳液稳定性。
