Mean-square displacement relationship in bioprotectant systems by elastic neutron scattering

Neutron intensity elastic scans on trehalose, maltose, and sucrose/H2O mixtures as a function of concentration, temperature, and exchanged wave vector are presented. The experimental findings show a crossover in molecular fluctuations between harmonic and anharmonic dynamical regimes. A new operative definition for the degree of fragility of glass-forming systems is furnished by using explicitly the connection between viscosity and mean-square displacement. The procedure is tested for the investigated mixtures and for a set of glass-forming systems. In this frame, the stronger character of trehalose/H2O mixture indicates a better attitude in respect to maltose and sucrose/H2O mixtures to encapsulate biostructures in a more rigid matrix.