Glass transition, freezing and melting of liquids confined in the mesoporous silicate MCM-41

MCM-41 is a recently discovered mesoporous silicate that consists of a hexa gonal arrangement of cylindrical pores. Because the pores are very well def ined in size and shape, MCM-41 can be considered as a model material in com parison with previous types of porous glass and has therefore been used in the present study. Ln particular, we have focused on the properties of conf ined liquids and related phase transitions using an MCM-41 with a pore diam eter of 4 nm. We discuss here the first stage of a study where the thermody namics of a series of molecular liquids (water, cyclohexane, benzene, tolue ne, o-terphenyl and m-toluidine) are analysed by differential scanning calo rimetry. Only a moderate decrease in the melting point of organic liquids h as been observed. Moreover, analysing the freezing process, we have establi shed thermal treatments that provide temperature ranges where confined liqu ids can be studied below the melting temperatures of both the bulk and the confined phases. Surprisingly, no significant change in the glass transitio n temperature has been observed compared with the bulk.