Anomalous neutron reflectivity of H2O-D2O mixtures at the silicon/liquid interface

The neutron reflectivity from Si/D2O and Si/H2O-D2O interfaces at room temperature has been investigated in considerable detail. The silicon wafer used had a hydrophobic coating. The analysis of the experimental results shows: (1) the behaviour of the reflectivities R(Q) for Q less than or similar to Q(c) (Q(c) being the wave number of the total reflection edge) follows the conventional theory; (2) the mixtures exhibit enhanced reflectivities - as compared with conventional expectations - for momentum transfers Q higher than Q(c). Result (2) reveals a new phenomenon which among other aspects shows that one of the basic hypotheses in all previous H2O-D2O contrast variation work, the assumption of homogeneity in the isotopic concentration in the liquid, is questionable. This phenomenon can be a signature of (a) protonic quantum entanglement as suggested by one of the authors (C.A.C.-D.), or (b) of a hitherto unexplored physical chemistry of isotope mixtures near surfaces. (C) 1998 Elsevier Science B.V. All rights reserved.