Université de Tours, Laboratoire PCMB (EA 4244), équipe Chimie-physique des Interfaces et des Milieux Electrolytiques (CIME), Parc de Grandmont, 37200 Tours, France.
J Colloid Interface Sci. 2009 Dec 1;340(1):104-11. doi: 10.1016/j.jcis.2009.07.061. Epub 2009 Aug 6.
A novel class of anionic surfactants was prepared through the neutralization of pyrrolidine or imidazole by alkylcarboxylic acids. The compounds, namely the pyrrolidinium alkylcarboxylates ([Pyrr][C(n)H(2n+1)COO]) and imidazolium alkylcarboxylates ([Im][C(n)H(2n+1)COO]), were obtained as ionic liquids at room temperature. Their aggregation behavior has been examined as a function of the alkyl chain length (from n=5 to 8) by surface tensiometry and conductivity. Decreases in the critical micelle concentration (cmc) were obtained, for both studied PIL families, when increasing the anionic alkyl chain length (n). Surprisingly, a large effect of the alkyl chain length was observed on the minimum surface area per surfactant molecule (A(min)) and, hence the maximum surface excess concentration (Gamma(max)) when the counterion was the pyrrolidinium cation. This unusual comportment has been interpreted in term of a balance between van der Waals and coulombic interactions. Conductimetric measurements permit determination of the degree of ionization of the micelle (a) and the molar conductivity (Lambda(M)) of these surfactants as a function of n. The molar conductivities at infinite dilution in water (Lambda(infinity)) of the [Pyrr]+ and [Im]+ cations have been then determined by using the classical Kohlraush equation. Observed change in the physicochemical, surface, and micellar properties of these new protonic ionic liquid surfactants can be linked to the nature of the cation. By comparison with classical anionic surfactants having inorganic counterions, pyrrolidinium alkylcarboxylates and imidazolium alkylcarboxylates exhibit a higher ability to aggregate in aqueous solution, demonstrating their potential applicability as surfactant.
通过将吡咯烷或咪唑中和为烷基羧酸，制备了一类新型的阴离子表面活性剂。这些化合物，即吡咯烷烷基羧酸盐([Pyrr][C(n)H(2n+1)COO])和咪唑烷基羧酸盐([Im][C(n)H(2n+1)COO])，在室温下作为离子液体获得。通过表面张力法和电导率法研究了它们的聚集行为作为烷基链长度(n=5 至 8)的函数。对于两种研究的 PIL 系列，当增加阴离子烷基链长度(n)时，临界胶束浓度(cmc)降低。令人惊讶的是，当抗衡离子为吡咯烷阳离子时，烷基链长度对每个表面活性剂分子的最小表面面积(A(min))和最大表面过剩浓度(Gamma(max))有很大的影响。这种异常的行为可以用范德华和库仑相互作用之间的平衡来解释。电导测量允许确定胶束的电离度(a)和这些表面活性剂的摩尔电导率(Lambda(M))作为 n 的函数。然后通过使用经典的 Kohlraush 方程，确定了[Pyrr]+和[Im]+阳离子在无限稀释水中的摩尔电导率(Lambda(infinity))。这些新质子离子液体表面活性剂的物理化学、表面和胶束性质的变化可以与阳离子的性质联系起来。与具有无机抗衡离子的经典阴离子表面活性剂相比，吡咯烷烷基羧酸盐和咪唑烷基羧酸盐在水溶液中具有更高的聚集能力，证明了它们作为表面活性剂的潜在适用性。
