Combined study of confined water in controlled pore glasses by differential scanning calorimetry and positron annihilation lifetime spectroscopy

The solidification/melting of water confined in controlled pore glass CPG126 has been studied by differential scanning calorimetry (DSC) and positron annihilation lifetime spectroscopy. Samples with variable coefficient of filling of water were prepared and analysed. DSC measurements revealed, besides effects related to the melting or freezing point depression of the confined liquid, a shift of freezing peaks towards lower temperatures with decreasing water content and due to the heat treatment. An attempt of interpretation of this effect based on microstructural properties has been made, which is supported also by detected freezing of confined water by homogenous nucleation. Positron annihilation lifetime spectroscopy shows the difference between the bulk and confined water in the global trends of temperature dependence of the ortho-positronium lifetime and also confirms some results of calorimetric measurements connected with the phase transitions.