Surfactants clump together to form organized structures called micelles that can be spheres, rods, and so forth. The formation of the clump can be modeled as a “chemical” reaction, though there are no chemical bonds formed or broken. When surfactants are in solution below the critical micelle concentration, CMC, the surfactant molecules are almost all “free” in solution. At the CMC, micelles start to form. Above the CMC, the amount of free surfactant is almost constant in solution and as more surfactant is added to the solution, more micelles form. It is conventional to provide the property changes of surfactants per mol of surfactant molecules, not per mole of micelle.

(a) Given the data below for nonylglucoside (NG) demicellization in water, calculate the micellization value, ΔCP_mic, as a function of temperature. Is the heat capacity of a micelle greater than or less than the heat capacity of the molecules that make up the micelle?

(b) Calculate ΔS_mic and for the surfactant as a function of temperature. Is the overall solution (including water) more ordered or less ordered after micellization?

NG data:

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T (K) 285 293 303 313 AH demic (kJ/mol) AG demic (kJ/mol)| ACPmic (kJ/mol-K) -13.53 20.03 -9.00 20.78 -3.50 21.60 0.07 22.37