FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
Science for Extreme Environment: Advanced Materials and Interfacial Processes for Energy
05843
Theoretical Studies of Decoupling Phenomena in Dynamics
of Soft Materials
Alexei Sokolov and Vladimir Novikov
Project Description
Understanding the dynamics of soft materials is the key to understanding and controlling their unique
properties. However, current knowledge of the dynamics in these materials is very limited and many
phenomena are not yet understood even on a qualitative level. Among them is a decoupling of various
processes from a structural relaxation. It includes (1) decoupling of chain relaxation from segmental
relaxation in polymers; (2) decoupling of ionic conductivity from the structural relaxation; and
(3) decoupling of protein’s biochemical activity from the solvent’s viscosity. The major goal of the
research is to develop a solid theoretical foundation that can address and explain these decoupling
phenomena. The work will be done mostly on an analytical level using theoretical models of polymer
dynamics and the concept of dynamic heterogeneity in disordered materials. It will help in guiding the
experiments and in explaining results accumulated using various techniques, including neutron scattering
studies performed at SNS. This fundamental understanding is crucial for the development of new
materials for energy applications (such as batteries, fuel cells, organic photovoltaic cells, carbon capture),
for bio-related technologies (enzymatic activity, bio-inspired catalysis), and processing of lightweight
materials (polymers).
Mission Relevance
Soft materials (e.g., polymers, colloids, biomaterials) attract the significant attention of researchers due to
their potential application in many fields, from energy and lightweight materials to biotechnologies and
biomedical applications. Molecular motions play the key role in most of the unique properties of soft
materials. However, understanding and controlling the microscopic mechanisms of molecular motions
still remain a great challenge. The project is focused on development of a fundamental understanding of
decoupling phenomena in the dynamics of soft materials. It has direct connections to DOE missions
because it addresses problems important for electrical energy storage (batteries), carbon capture, and fuel
cells. Also, explanation of decoupling of segmental and chain relaxations in polymers and its dependence
on polymer structure is necessary for a broad variety of applications, from polymer processing to
biotechnologies.
Results and Accomplishments
We investigated the connection of decoupling phenomenon to the dynamical heterogeneity of polymeric,
molecular, and inorganic glass formers. To this end we used the inelastic light scattering to analyze the
universal feature of the dynamics in various glass-forming materials—the boson peak. This peak in the
THz frequency range is associated with a characteristic length scale of the frozen-in dynamical
heterogeneities. We estimated the (heterogeneity) length scale obtained from the boson peak spectra. It
has been shown in our previous publications that the decoupling correlates with the steepness of the
temperature dependence of structural relaxation (the so-called fragility). So, it has been expected that the
decoupling might depend on the length scale of the dynamic heterogeneities. However, our analysis
revealed that fragility does not correlate directly to the length scale of the dynamic heterogeneities. Only
its density (pressure) dependence shows some correlations with this length scale. The presented results
call for a revision of traditional view on the role of heterogeneity in structural relaxation of glass-forming
systems and, respectively, in the decoupling phenomenon. In addition, our analysis of coherent neutron
scattering data (literature data) suggests that the decoupling phenomena appears in the wave-vector
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