| Abstract
| - The complex formation between sodium carboxymethylcellulose (NaCMC) and dodecyltrimethylammoniumbromide (DTAB) at various sodium bromide concentrations (CNaBr) 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 CNaBr =0.00, 0.01, 0.02, 0.10, and 0.20 M, DTAB monomers form micelle-like aggregates on NaCMC chains toform NaCMC/DTAB complexes above the critical surfactant concentration (C1). At CNaBr = 0.23 M, DTABmolecules 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 CNaBr = 0.25 M, there is no NaCMC/DTAB complex formation because of the complete saltscreening of the electrostatic attraction between DTAB micelles and NaCMC chains. It is also surprisinglyfound that the addition of NaBr can bring out a decrease in C1 at CNaBr< 0.20 M. Moreover, the addition ofNaBr 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 competitionbetween 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.
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