P. Warszynski et K. Lunkenheimer, Influence of conformational free energy of hydrocarbon chains on adsorption of nonionic surfactants at the air/solution interface, J PHYS CH B, 103(21), 1999, pp. 4404-4411
The most frequently used theories of surfactant adsorption phenomena treat
adsorbing molecules as structureless entities. However, surface active mole
cules consist of hydrophillic headgroups and hydrophobic chains. Therefore,
surfactants have additional degrees of freedom associated with conformatio
ns of the chains. An unrestricted hydrophobic chain can assume practically
any conformation at the interface. Adsorption of other surfactant molecules
provides restriction to the number of possible conformations changing the
conformational free energy. This change has to be reflected in the adsorpti
on isotherm. We present a simple model of adsorption of soluble surfactants
at the air/solution interface, taking explicitly into account the conforma
tional statistics of hydrophobic surfactant chains. The model is applied to
describe adsorption isotherms of homologous series of dimethyl-n-alkyl pho
sphine oxides with the alkyl chain length of 7-13 carbon atoms.