The enthalpy is negative (favourable) for both surfactants at all deposit-DCA distances. For the zwitterionic surfactant, there are two clear enthalpy minima (-15 kcal mol -1 ) before and after the first solvent density peak (∼ 4 Å). For PIBSI, there is just one broad enthalpy minima (-6 kcal mol -1 ) above the first density peak of the solvent.