- Published on Tuesday, 25 June 2013 08:50
Thin films of liquids and polymers are interesting systems for those seeking to test glass transition theories and their prediction of a characteristic transition length scale of a few nanometers. The anomalous phenomena observed in some of these nano-confined films has greatly advanced our understanding of theoretical and experimental soft matter physics.
These films are treated as equilibrium systems where surfaces and interfaces introduce monotonous long-range mobility gradients. Considering finite size and interfacial effects provides an intuitive but oversimplifies picture that falls short of explaining many phenomena, such as enhancement of segmental mobility near an absorbing surface or long-lasting metastable states in the liquid.
The authors propose a new picture of the dynamics of these confined soft matter systems, which focuses on non-equilibrium states and on the impact of irreversible chain adsorption on the structural relaxation.
This EPJ E Colloquium reviews the experimental approaches that have been used to study the structural relaxation of films with one, two or no free surfaces by means of dielectric spectroscopy. Then proposes methods to determine gradients of mobility in thin films and discussed the as-yet untapped potential of analyses based on the time, temperature and thickness dependence of the orientational polarization.
Glassy dynamics of soft matter under 1D confinement: How irreversible adsorption affects molecular packing, mobility gradients and orientational polarization in thin films. Simone Napolitano, Simona Capponi, and Bram Vanroy (2013), European Physical Journal E 36: 61, DOI 10.1140/epje/i2013-13061-8