Effect of Co-surfactants on Bending Stiffness and Scission Energy of Wormlike Micelles: a Rheometry and Diffusing Wave Spectroscopy (DWS) Study

最近，我们建立了一个机械高频流变学和光学微观流变学的组合，以获得新的洞察蠕虫状胶束溶液的结构和动力学。我们已经使用这种方法来表明，胶束弯曲刚度（在这里表示的持久长度lp）强烈降低与结合效率的增加，而断裂能Esciss，因此轮廓长度几乎不受影响。对于渗透性胶束水杨酸钠（NaSal），增加盐/表面活性剂比导致Esciss的非单调变化和lp的强烈降低，这归因于水杨酸盐掺入胶束内部。在这个后续的项目中，我们想更深入地了解如何控制蠕虫状表面活性剂胶束的长度和灵活性，使用以下实验方法：1。烷基链中具有n = 16个碳原子的阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）与具有较短疏水尾部的其他三甲基溴化铵表面活性剂的混合物（n = 8，10，12，14）以及具有n = 14的单个表面活性剂。16和14将被用来研究疏水尾基对Esciss和lp的影响，并与文献中的模拟结果进行比较。2.将确定CTAB/NaSal系统的Esciss和lp。与混合胶束的结果以及以前的数据氯化十六烷基吡啶（CPyCl）/NaSal的比较将提供进一步的见解如何控制蠕虫状胶束的长度和灵活性。这个系统也将被用来基准我们的方法与文献数据lp从中子自旋回波实验。3.高频设置将用于准确测定具有非渗透盐NaClO 3的系统CPyCl的平台模量，因为通过经典旋转流变仪获得的文献数据不准确，并且导致对随着盐含量增加而发生的粘度降低的错误解释。

Recently, we have established a combination of mechanical high frequency rheology and optical microrheology to gain new insight into the structure and dynamics of wormlike micellar solutions. We have used this approach to show, that the micellar bending stiffness (here expressed in terms of the persistence length lp) strongly decreases with increasing binding efficiency, whereas scission energy Esciss and hence contour length are hardly affected. For the penetrating counterion sodium salicylate (NaSal) an increasing salt/surfactant ratio results in a non-monotonic variation of Esciss and a strong decrease in lp, which is attributed to the incorporation of the salicylate into the interior of the micelles. In this follow-up project we want to get deeper insight how to control length and flexibility of wormlike surfactant micelles using the following experimental approach; 1. Mixtures of the cationic surfactant hexadecyltrimethyl ammonium bromide (CTAB) with n = 16 carbon atoms in the alkyl chain with other trimethyl ammonium bromide surfactants with shorter hydrophobic tails (n = 8, 10, 12, 14) as well as the individual surfactants with n = 16 and 14 will be used to study the effect of the hydrophobic tail group on Esciss and lp systematically in comparison with simulation results from the literature. 2. Esciss and lp will be determined for the system CTAB/NaSal. Comparison of results with those for the mixed micelles as well as previous data for cetylpyridinium chloride (CPyCl)/NaSal will provide further insight how to control length and flexibility of wormlike micelles. This system will also be used to benchmark our method with literature data for lp from neutron spin echo experiments. 3. The high frequency setup will be used for an accurate determination of the plateau modulus for the system CPyCl with the non-penetrating salt NaClO3, since literature data obtained by classical rotational rheometry are not accurate and have lead to a wrong interpretation of the viscosity decrease occurring with increasing salt content.