Department of Physical Chemistry, Showa Pharmaceutical University, Machida, Tokyo, Japan.
J Colloid Interface Sci. 2012 Aug 1;379(1):72-7. doi: 10.1016/j.jcis.2012.04.043. Epub 2012 Apr 26.
Double or triple quaternary ammonium head groups were designed to improve the solubility of supralong alkyl chain surfactants. In the surfactant head group, quaternary ammonium groups are connected by an ethylene spacer. Micellar shapes of divalent surfactants [C(n)H(2n)(+1)N(+)(CH(3))(2)-(CH(2))(2)-N(+)(CH(3))(3) 2Br(-): C(n)-2Am (n=18, 20, and 22)] and trivalent surfactants [C(n)H(2n)(+1)N(+)(CH(3))(2)-(CH(2))(2)-N(+)(CH(3))(2)-(CH(2))(2)-N(+)(CH(3))(3) 3Br(-): C(n)-3Am (n=18, 20, and 22)] were studied in aqueous solutions by means of dynamic light scattering (DLS) and transmission electron microscopy (TEM). Changes in the surfactant concentration have a small influence on the apparent hydrodynamic radii (r(h)) of the molecular aggregates in both surfactant series. Average values of r(h) of aggregates are 60-90 nm for C(n)-2Am (n=18, 20, and 22) and 2-40 nm for C(n)-3Am (n=18, 20, and 22). TEM micrographs showed that aggregates of C(n)-2Am (n=18, 20, and 22) typically formed rod-like micelles. In contrast, trivalent surfactants of C(n)-3Am (n=18, 20, and 22) formed spherical (C(18)-3Am) or ellipsoidal micelles (C(20)-3Am and C(22)-3Am). Moreover, the degree of micellar counterion binding for these surfactants was determined by using a bromide ion-selective electrode, which indicated relatively high values (0.8-0.9) for C(n)-2Am (n=18, 20, and 22) and more common values (0.5-0.8) for C(n)-3Am (n=18, 20, and 22). The size of the aggregates is closely related to the degree of counterion binding.
双或三季铵头基被设计用来提高超长链表面活性剂的溶解度。在表面活性剂的头基中，季铵基团通过亚乙基间隔基连接。二价表面活性剂[C(n)H(2n)(+1)N(+)(CH(3))(2)-(CH(2))(2)-N(+)(CH(3))(3) 2Br(-): C(n)-2Am(n=18,20 和 22)]和三价表面活性剂[C(n)H(2n)(+1)N(+)(CH(3))(2)-(CH(2))(2)-N(+)(CH(3))(2)-(CH(2))(2)-N(+)(CH(3))(3) 3Br(-): C(n)-3Am(n=18,20 和 22)]在水溶液中的胶束形状通过动态光散射(DLS)和透射电子显微镜(TEM)进行了研究。在这两个系列的表面活性剂中，表面活性剂浓度的变化对分子聚集体的表观水动力半径(r(h))影响很小。C(n)-2Am(n=18,20 和 22)的聚集体的平均 r(h)值为 60-90nm，而 C(n)-3Am(n=18,20 和 22)的聚集体的平均 r(h)值为 2-40nm。TEM 显微照片显示，C(n)-2Am(n=18,20 和 22)的聚集体通常形成棒状胶束。相比之下，三价表面活性剂 C(n)-3Am(n=18,20 和 22)形成球形(C(18)-3Am)或椭圆形胶束(C(20)-3Am 和 C(22)-3Am)。此外，通过使用溴离子选择性电极测定了这些表面活性剂的胶束抗衡离子结合度，其结果表明 C(n)-2Am(n=18,20 和 22)的值相对较高(0.8-0.9)，而 C(n)-3Am(n=18,20 和 22)的值则更为常见(0.5-0.8)。聚集体的大小与抗衡离子结合度密切相关。
