Enthalpy and Entropy of Scission in Wormlike Micelles.
Authors of this article are:
Jiang H, Vogtt K, Thomas JB, Beaucage G, Mulderig A.
A summary of the article is shown below:
The free scission energy is the thermodynamic parameter that governs the contour length of wormlike micelles (WLMs). It is the contour length and the propensity to coil and entangle that determines the visco-elastic properties of this commercially important substance class. The free scission energy ΔFsc, as well as the associated enthalpy ΔHsc, and entropy ΔSsc, have been determined for a mixed anionic/zwitterionic surfactant system (sodium laureth sulfate and cocoamidopropyl betaine) at various salt concentrations (3-5 wt. % NaCl). Both the enthalpy ΔHsc and entropy ΔSsc decrease linearly with increasing NaCl concentration. At NaCl concentrations above 4 wt. %, ΔSsc even adopts negative values. The term T ΔSsc decreases more rapidly than ΔHsc around room temperature and causes the observed elongation of WLMs upon addition of NaCl. It is suggested that ΔSsc is initially positive due to fewer bound counter ions per surfactant molecule at end caps compared to the intact, cylindrical parts prior to scission, leading to a net release of ions upon scission. Negative values of ΔSsc are attributed to hydrophobic hydration occurring at the end caps at high salt concentrations.
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