Wang Xiaoyong, Li Yajuan, Li Junxin, Wang Jinben, Wang Yilin, Guo Zhixin, Yan Haike
Key Laboratory of Colloid and Interface Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, People's Republic of China.
J Phys Chem B. 2005 Jun 2;109(21):10807-12. doi: 10.1021/jp0450585.
The complex formation between sodium carboxymethylcellulose (NaCMC) and dodecyltrimethylammonium bromide (DTAB) at various sodium bromide concentrations (C(NaBr)) has been studied by microcalorimetry, turbidimetric titration, steady-state fluorescence measurements, and the fluorescence polarization technique. The addition of salt is found to influence the formation of NaCMC/DTAB complexes markedly. At C(NaBr) = 0.00, 0.01, 0.02, 0.10, and 0.20 M, DTAB monomers form micelle-like aggregates on NaCMC chains to form NaCMC/DTAB complexes above the critical surfactant concentration (C1). At C(NaBr) = 0.23 M, DTAB molecules first form micelles above a 2.46 mM DTAB concentration prompted by the added salt, and then, above C1 = 4.40 mM, these micelles can aggregate with NaCMC chains to form NaCMC/DTAB complexes. However, at C(NaBr) = 0.25 M, there is no NaCMC/DTAB complex formation because of the complete salt screening of the electrostatic attraction between DTAB micelles and NaCMC chains. It is also surprisingly found that the addition of NaBr can bring out a decrease in C1 at C(NaBr) < 0.20 M. Moreover, the addition of NaBr to a mixture of 0.01 g/L NaCMC and 3.6 mM DTAB can directly induce the formation of NaCMC/DTAB complexes. This salt-enhancing effect on the complex formation is explained as the result of competition between the screening of interaction of polyelectrolyte with surfactant and the increasing of polyelectrolyte/surfactant interaction owing to the growth of micelles by added salt. When the increasing of polyelectrolyte/surfactant interaction exceeds the screening of interaction, the complex formation can be enhanced.
通过微量量热法、比浊滴定法、稳态荧光测量法和荧光偏振技术，研究了在不同溴化钠浓度（C(NaBr)）下羧甲基纤维素钠（NaCMC）与十二烷基三甲基溴化铵（DTAB）之间的络合物形成情况。发现添加盐会显著影响NaCMC/DTAB络合物的形成。在C(NaBr) = 0.00、0.01、0.02、0.10和0.20 M时，DTAB单体在NaCMC链上形成类似胶束的聚集体，在临界表面活性剂浓度（C1）以上形成NaCMC/DTAB络合物。在C(NaBr) = 0.23 M时，添加的盐促使DTAB分子在2.46 mM DTAB浓度以上首先形成胶束，然后在C1 = 4.40 mM以上，这些胶束可以与NaCMC链聚集形成NaCMC/DTAB络合物。然而，在C(NaBr) = 0.25 M时，由于DTAB胶束与NaCMC链之间的静电吸引力被完全盐屏蔽，没有形成NaCMC/DTAB络合物。还令人惊讶地发现，在C(NaBr) < 0.20 M时添加NaBr会导致C1降低。此外，向0.01 g/L NaCMC和3.6 mM DTAB的混合物中添加NaBr可以直接诱导形成NaCMC/DTAB络合物。这种盐对络合物形成的增强作用被解释为聚电解质与表面活性剂相互作用的屏蔽与由于添加盐使胶束生长导致的聚电解质/表面活性剂相互作用增加之间竞争的结果。当聚电解质/表面活性剂相互作用的增加超过相互作用的屏蔽时，络合物的形成可以得到增强。
