Structural studies of water in confined geometry by neutron diffraction

Water in confined geometry shows significant modification in its structural characteristics from water in the bulk phase. Neutron diffraction studies may be used to investigate the modifications to the local molecular environment. It is found that the hydrogen bonding is enhanced in the confined state and the nucleation temperature is depressed. The diffraction studies show that there is a systematic variation in the structure factor, which is similar to that of the bulk phase but shifted in temperature. The behaviour at low temperatures is due to the formation of an extended hydrogen-bonded network similar to that of amorphous ice. The confined liquid eventually nucleates with the formation of a defective form of cubic ice rather than hexagonal ice formed in the bulk phase. The studies have been made primarily for mesoporous silicas but some preliminary results are also given for water in a lamellar liquid crystal. The results have relevance to the behaviour of interfacial water in membranes and biological systems. (C) 2000 Published by Elsevier Science B.V. All rights reserved.