MOSSBAUER STUDY OF THE STRUCTURE OF LIQUID NANOPHASES TRAPPED IN POROUS SILICATE AND SOLID MICROEMULSION MATRIX

Mossbauer spectra of liquid solutions fixed as submicroscopic (nanosiz e) droplets in solid carriers were taken at room temperature and 77 K. A porous silicate (''thirsty glass'') and microemulsions prepared wit h a paraffin/naphthalene mixture as dispersion medium served as carrie rs. Solutions of Mowssbauer-active tin(IV) and iron(II) complexes were incorporated in these carriers as nanosize droplets. The Mossbauer ef fect was observed at temperatures above the freezing point of the solu tions. For comparison, the systems were also studied in frozen state. Depending on the nature of the system (carrier-solute-solvent) the pre sence of three types of species was shown in the droplets on the basis of the Mossbauer parameters: (a) situated in bulk position with no in teraction with the walls; (b) adsorbed on the internal surface of the holes in the carrier and (c) in bulk position, but with Mossbauer para meters reflecting the influence of the carrier. In some cases surface- bound and bulk species were present together in the sample. The appear ance of the Mossbauer effect in liquid state reveals that the Mossbaue r-active atoms are fixed in the nanosize pores by a network of hydroge n bonds which form between the solvent molecules, between solvent and solute molecules and between the solvent molecules and the walls of th e pores in the carrier. The main parameters determining the rigidity o f the network and the situation of the probe molecules are the hydroge n-bonding ability and the polarity of the components of the system. On the basis of the above observations, a new procedure was elaborated f or the Mossbauer study of solutions fixed as nanosize droplets in rigi d carriers. The analysis of the Mossbauer parameters gives a qualitati ve picture regarding the solution structure in the interior of the por es, and the adsorption and wetting properties of the system.