Neutron scattering and molecular correlations in a supercooled liquid

Area of Science:

• Condensed matter physics
• Materials science
• Physical chemistry

Background:

• Neutron scattering (ns) is a powerful technique for probing molecular dynamics.
• Understanding translational and orientational correlations in liquids is crucial for characterizing their behavior.

Purpose of the Study:

• To develop a novel expansion of the intermediate scattering function S(n)(q,t) using molecular correlation functions.
• To investigate the q-dependence of this expansion and its application to static structure factor S(n)(q).
• To analyze supercooled liquids and identify the origins of features like prepeaks in neutron scattering data.

Main Methods:

• Expansion of the intermediate scattering function S(n)(q,t) in terms of molecular correlation functions.
• Analysis of the static structure factor S(n)(q) for a model system using molecular dynamics simulation data.
• Comparison of exact S(n)(q) results with truncated series approximations.

Main Results:

• The expansion of S(n)(q,t) shows good convergence for a model supercooled liquid.
• Coupling between translational and orientational degrees of freedom is significant in the supercooled regime.
• A prepeak is observed in the neutron scattering static structure factor of a fragile glass former, indicating intermediate-range orientational order.

Conclusions:

• The developed expansion provides a complete description of two-point correlations in liquids.
• Neutron scattering can be used to determine molecular correlation functions.
• Intermediate-range orientational order is identified as the origin of prepeaks in simple molecular liquids.