Sagisaka Masanobu, Ono Shinji, James Craig, Yoshizawa Atsushi, Mohamed Azmi, Guittard Frédéric, Rogers Sarah E, Heenan Richard K, Yan Ci, Eastoe Julian
†Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan.
∥Univ. Nice Sophia-Antipolis, CNRS, Equipe Surfaces et Interfaces, Parc Valrose, 06100 Nice, France.
Langmuir. 2015 Jul 14;31(27):7479-87. doi: 10.1021/acs.langmuir.5b01737. Epub 2015 Jun 30.
Hybrid surfactants containing both fluorocarbon (FC) and hydrocarbon (HC) chains have recently been shown to solubilize water and form elongated reversed micelles in supercritical CO2. To clarify the most effective FC and HC chain lengths, the aggregation behavior and interfacial properties of hybrid surfactants FCm-HCn (FC length m/HC length n = 4/2, 4/4, 6/2, 6/4, 6/5, 6/6, and 6/8) were examined in W/CO2 mixtures as functions of pressure, temperature, and water-to-surfactant molar ratio (W0). The solubilizing power of hybrid surfactants for W/CO2 microemulsions was strongly affected by not only the FC length but also by that of the HC. Although the surfactants having short FC and/or HC tails (namely, m/n = 4/2, 4/4, and 6/2) did not dissolve in supercritical CO2 (even at ∼17 mM, ≤400 bar, temperature ≤ 75 °C, and W0 = 0-40), the other hybrid surfactants were able to yield transparent single-phase W/CO2 mixtures identified as microemulsions. The solubilizing power of FC6-HCm surfactants reached a maximum (W0 ∼ 80 at 45 °C and 350 bar) with a hydrocarbon length, m, of 4. The W0 value of 80 is the highest for a HC-FC hybrid surfactant, matching the highest value reported for a FC surfactant which contained more FC groups. High-pressure small-angle neutron scattering measurements from FCm-HCn/D2O/CO2 microemulsions were consistent with growth of the microemulsion droplets with increasing W0. In addition, not only spherical reversed micelles but also nonspherical assemblies (rodlike or ellipsoidal) were found for the systems with FC6-HCn (n = 4-6). At fixed surfactant concentration and W0 (17 mM and W0 = 20), the longest reversed micelles were obtained for FC6-HC6 where a mean aspect ratio of 6.3 was calculated for the aqueous cores.
最近研究表明，同时含有氟碳链（FC）和碳氢链（HC）的混合表面活性剂能够在超临界二氧化碳中溶解水并形成细长的反相胶束。为了明确最有效的氟碳链和碳氢链长度，研究了混合表面活性剂FCm-HCn（氟碳链长度m/碳氢链长度n = 4/2、4/4、6/2、6/4、6/5、6/6和6/8）在W/CO₂混合物中的聚集行为和界面性质，考察了压力、温度和水与表面活性剂的摩尔比（W₀）对其的影响。混合表面活性剂对W/CO₂微乳液的增溶能力不仅受到氟碳链长度的强烈影响，也受到碳氢链长度的强烈影响。尽管具有短氟碳链和/或短碳氢链的表面活性剂（即m/n = 4/2、4/4和6/2）在超临界二氧化碳中不溶解（即使在~17 mM、≤400 bar、温度≤75°C且W₀ = 0 - 40时），但其他混合表面活性剂能够形成被鉴定为微乳液的透明单相W/CO₂混合物。FC6-HCm表面活性剂的增溶能力在碳氢链长度m为4时达到最大值（45°C和350 bar下W₀ ~ 80）。80的W₀值是碳氢-氟碳混合表面活性剂中的最高值，与含更多氟碳基团的氟碳表面活性剂报道的最高值相当。对FCm-HCn/D₂O/CO₂微乳液进行的高压小角中子散射测量结果与微乳液滴随W₀增加而生长的情况一致。此外，对于FC6-HCn（n = 4 - 6）体系，不仅发现了球形反相胶束，还发现了非球形聚集体（棒状或椭球状）。在固定的表面活性剂浓度和W₀（17 mM且W₀ = 20）下，FC6-HC6获得了最长的反相胶束，计算得出其水核的平均纵横比为6.3。
