Amorphous Structure and Dynamics

FIGURE 13.1 Experimental T values resulting from the antiplasticization effect of PVP90 (o), PVP12 (o), or MD simulated values for PVP ( t) in amorphous mixtures with indomethacin. r predicted is based on the Gordon-Taylor equation with the value of K estimated using the Couchman and Karasz relationship. 

In the polymer field, XRD and neutron scattering are the two most widely used techniques for validating results from MD simulations. Whereas XRD experiments can provide structural features over the relevant length scales, neutron scattering can reveal both structural and dynamic properties. Studies that combine MD simulations with one or both of these experimental tools have been relatively few in number, but interest in this approach is growing because of obvious synergies. 

FIGURE 13.2 Comparison of measured PVP X-ray diffraction pattern at 550 K( ) with that obtained from MD simulation (- -). Source Adapted from Busselez et al. [35]. Reproduced with permission of AIP Publishing LLC. 

The pair distribution function (G(r)), which is proportional to the probability of finding an atom at a position r relative to a reference atom chosen to be at the origin, can be determined from the Fourier transform of the experimental structure factor, (0exp (jygj. j, sufficiently wide range of reciprocal space QnaJ within which 

FIGURE 13.3 Comparison of results (data with error bars) for normalized dynamic structure factors near obtained from neutron spin echo experiments on deuterated samples with MD simulation data (open circles) at the same Q value [39]. Timescales for the experimental data were shifted-15 K in (see text). Source Narros et al. [39]. Reprinted with permission of AIP Publishing LLC. 

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