ABSTRACT
This review addresses the delicate balance between material performance and the molecular mobility in nanoscopic polymer systems. Molecular mobility will be addressed as a spectrum of relaxation modes that stems from the underlying degrees of freedom available for conformational transitions. The energetics associated with relaxation mode dynamics can be either solely enthalpic, as in small side-chain rotations, or contain a substantial entropic component, as in the cooperative crankshaft-type motions about the molecular backbone [7, 8]. The location of the modes, e.g., surface vs bulk modes [7], and the effect of interfacial interactions, such as interfacial tension [9-14], are important contributors to the resulting apparent relaxation barriers. Thus in this review, particular emphasis is given to the role of constraints, which may restrict or enable specific relaxation processes. Constraints are classified as either internal or external; where internal constraints are associated with molecular structure and interactions within the material system, and external constraints are attributed to the interactions that arise in the vicinity of system boundaries, i.e., at interfaces between the material system and its external environment.
