Transitions in chemically bonded organic phases on silica: specific heat measurements by adiabatic calorimetry

Abstract Heat capacity data of silicas chemically bonded to n -octyl, n -octadecyl, amino-butyl and 2,4-dinitroanilinobutyl groups, and of the bare silicas Merckosorb and Nucleosil, have been measured as a function of temperature by adiabatic calorimetry. By subtracting the heat capacity data of the corresponding bare silica, values for the bonded phases are obtained. The alkyl phases show second-order transitions within the examined temperature range, the enthalpy and entropy of which have been evaluated. The results are related to chromatographic solute retention behaviour on bonded silicas and compared with data for the corresponding organic compounds.