Dupont Audrey, Eastoe Julian, Martin Laura, Steytler David C, Heenan Richard K, Guittard Frederic, Taffin de Givenchy Elisabeth
School of Chemistry, University of Bristol, Bristol, BS8 1TS United Kingdom.
Langmuir. 2004 Nov 9;20(23):9960-7. doi: 10.1021/la0483820.
Hybrid fluorocarbon-hydrocarbon (F-H) sulfate surfactants are shown to be efficient stabilizers in water-in-CO2 (w/c) microemulsions. The chain structure and F-H ratio affect the regions of P-T phase stability and aggregation structure in these w/c phases. High-pressure near-infrared spectroscopy and small-angle neutron scattering measurements of microemulsified water provide evidence for the stabilization of w/c microemulsion droplets. The relative lengths of the two chains were found to influence the favored aggregation structure: for symmetric chain surfactants (F8H8, F7H7) spherical reverse micelles are present, but for asymmetric chain surfactants (F7H4, F8H4) extended cylinder aggregates form. These changes in aggregation are consistent with different surfactant packing parameters owing to the controlled variations in molecular structure. Furthermore, the general order of w/c phase transition pressures (F8H8 < F7H7 and F8H4 < F7H4) is in line with estimations of surfactant fractional free volume, as proposed by Johnston et al. (J. Phys. Chem. B 2004, 108, 1962-1966). Studies of adsorption at the poly(dimethylsiloxane)-water interface are shown to be valuable for assessing the CO2-philicity of new surfactants. All in all, the symmetric F8H8 and F7H7 analogues are seen to be the most efficient compounds from this class for applications in CO2.
混合氟碳 - 烃（F - H）硫酸盐表面活性剂被证明是二氧化碳包水（w/c）微乳液中的高效稳定剂。链结构和F - H比例会影响这些w/c相中的P - T相稳定性区域和聚集结构。对微乳化水进行的高压近红外光谱和小角中子散射测量为w/c微乳液滴的稳定性提供了证据。发现两条链的相对长度会影响偏好的聚集结构：对于对称链表面活性剂（F8H8、F7H7），存在球形反胶束，但对于不对称链表面活性剂（F7H4、F8H4），会形成延伸的圆柱状聚集体。由于分子结构的可控变化，这些聚集变化与不同的表面活性剂堆积参数一致。此外，w/c相转变压力的一般顺序（F8H8 < F7H7和F8H4 < F7H4）与Johnston等人（《物理化学杂志B》2004年，108卷，1962 - 1966页）提出的表面活性剂分数自由体积估计一致。对聚（二甲基硅氧烷） - 水界面吸附的研究表明，对于评估新型表面活性剂的亲二氧化碳性很有价值。总而言之，在二氧化碳应用方面，对称的F8H8和F7H7类似物被认为是这类化合物中最有效的。
