Heterogeneous systems motional fluctuations

We have emphasized here that the dynamic aspects of NMR studies are crucially important for structurally or dynamically heterogeneous systems such as synthetic or natural hydrogels, protein fibrils and membrane proteins. This is in order to characterize their unique chemical, physical and biological properties in terms of a variety of fluctuation frequencies, including high (> 108 Hz) or intermediate (104-105 Hz) frequency fluctuations. It turns out that the presence of the high-frequency motions, which are readily evaluated by comparative CPMAS and DDMAS studies, is... 

In nanofilled systems, the X-ray scattering contrast comes from the electron density difference between the polymer matrix and the nanoparticle, such as silica. The dynamics of the polymer matrix will cause the position of the nanoparticles to fluctuate. A good analogy is the movement of small particles in a suspension due to Brownian motion. The relaxation of polymer matrix is found to be very complicated and heterogeneous. Indeed, stretched exponential functions that are commonly used in bulk polymers, = exp[-(t/r/] with / < , were not able to desaibe the correlation function and the polymer matrix behavior. ... 

The present phase transition mechanism interpretations are based on the fluctuation theory [1,2]. The process of phase destmction in a system usually occurs when its stability is lost. Chaotic heat motion of molecules in single-phase solutions or coexisting components of liquid blends leads to a spontaneous change of concentration A on cpA = cp -local domain cp/, where cpav is the average volume concentration. These fluctuations of concentration (heterogeneities) can have relatively broad scale distribution (A/) and root-mean-square amplitude (Acp ) depending on system state parameters. A system is stable if spontaneous concentration fluctuations with any scale and amplitude disappear (they may appear in another area of the system) in the eourse of time. This effect occurs when system is not in binodal. If fluctuations remain when the state parameters change, further evolution of the system to an equilibrium state can lead to phase destruction. 

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