title: Calorimetric study of the reactions of n-alkylphosphonic acids with metal oxide surfaces.
abstract: The reaction enthalpies for the solution-phase self-assembly of n-alkylphosphonic acids on the surfaces of TiO2 and ZrO2 have been determined using isothermal titration calorimetry at 298 K. The reaction enthalpies were negative (exothermic) for methyl- and n-octylphosphonic acids and positive (endothermic) for n-octadecylphosphonic acid with both metal oxides. The enthalpy/energy analysis showed that the net enthalpy of the formation of self-assembled monolayers (SAMs) at solid-liquid interface can be presented as follows: DeltaHr=-D-(DeltaHsol+DeltaHdil)-(ES-ESAM), where D is the binding energy of the SAM molecules with the solid; DeltaHsol and DeltaHdil are the enthalpies of dissolution and dilution; ES and ESAM are the surface energies of bare solid and SAM, respectively. This equation predicted an increase (and the sign change) of the reaction enthalpy as the alkyl group in n-alkylphosphonic acid increased, which explained the experimental data. Using this equation, the binding energy (D) in the SAMs of n-octyl- and n-octadecylphosphonic acids were estimated: 55+/-5 kJ/mol (for ZrO2) and 58+/-7 kJ/mol (for TiO2).
authors.affiliation: Department of Chemistry and Biochemistry, Seton Hall University, South Orange, NJ 07079, USA.
authors.forename: Jaime M
authors.initials: JM
authors.lastname: Ferreira
authors.forename: Stephen
authors.initials: S
authors.lastname: Marcinko
authors.forename: Richard
authors.initials: R
authors.lastname: Sheardy
authors.forename: Alexander Y
authors.initials: AY
authors.lastname: Fadeev