Microcalorimetric determination of the entropy change upon the electrochemically driven surface aggregation of dodecyl sulfate.
The aggregation of amphiphilic molecules (e.g., the formation of micelles or membranes) is usually entropy-driven. We use electrochemical microcalorimetry to directly determine the entropy change a dodecyl sulfate molecule experiences upon potential-induced adsorption from aqueous solution into a surface aggregate. From measurements of the heat, which is reversibly exchanged during the adsorption or desorption process, we determined a value of 37 ± 9 J/(mol K) for the aggregation entropy. This value is in accordance with entropies of micellization of dodecyl sulfate in solution. A comparison with estimates of the entropy of aggregation of dodecane in aqueous solutions reveals that the aggregation is driven by the entropic contribution of the hydrophobic hydrocarbon tail, in accordance with general models for the aggregation of amphiphilic molecules.
Institute of Physical Chemistry, Karlsruhe Institute of Technology , D-76131 Karlsruhe, Germany.
Katrin R
KR
Bickel
Axel Eric
AE
Timm
Detlef
D
Nattland
Rolf
R
Schuster
D002151:Calorimetry / Q000379:methods*; D004563:Electrochemistry / Q000379:methods*; D019277:Entropy; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*
D012967:Sodium Dodecyl Sulfate; C028913:dodecyl sulfate