The interaction between two immiscible materials is related to the number of contacts per unit area formed by the two materials. For practical reasons, this information is often parametrized by the interfacial free energy, which is commonly derived via rather cumbersome approaches, where properties of the interface are described by combining surface parameters of the single materials. These combining rules, however, neglect any effect that geometry might have on the strength of the interfacial interaction. In this Article, we demonstrate that the number of contacts at the interface between a thin polymer coating and its supporting substrate is altered upon confinement at the nanoscale level. We show that explicitly considering the effect of nanoconfinement on the interfacial potential allows a quantitative prediction of how sample geometry affects the number of contacts formed at the interface between two materials.

Controlling polymer/substrate interfaces without modifying chemistry is nowadays possible by finely tuning the formation of adsorbed layers. The complex processes leading to irreversible attachment of chains onto solid substrates are governed by two mechanisms: molecular rearrangement and potential-driven adsorption. Here we introduce an analytical method to differentiate these two mechanisms. By analyzing experiments and simulations, we investigate how changes in thermal energy and interaction potential affect equilibrium and nonequilibrium components of the adsorption kinetics. We find that the adsorption process is thermally activated, with activation energy comparable to that of local noncooperative processes. On the other hand, the final adsorbed amount depends on the interface interaction only (i.e., it is temperature independent in experiments). We identify a universal linear relation between the growth rates at short and long adsorption times, suggesting that the monomer pinning mechanism is independent of surface coverage, while the progressive limitation of free sites significantly limits the adsorption rate.

Anyone who has enjoyed a glass of wine has undoubtedly noticed the regular pattern of liquid beads that fall along the inside of the glass, or ‘tears of wine.’ The phenomenon is the result of a flow against gravity along the liquid film on the glass, which is induced by an interfacial tension gradient. It is generally accepted that the interfacial tension gradient is due to a composition gradient resulting from the evaporation of ethanol. We re-examine the tears of wine phenomenon and investigate the importance of thermal effects, which previously have been ignored. Using a novel experiment and simple model we find that evaporative cooling contributes significantly to the flow responsible for wine tears, and that this phenomenon occurs primarily because of the thermodynamic behavior of ethanol-water mixtures. Also, the regular pattern of tear formation is identified as a well-known hydrodynamic instability.

Anisotropic thermal transport in a crosslinked polyisoprene (natural rubber) subjected to uniaxial elongation is investigated experimentally. Using a novel optical technique based on forced Rayleigh scattering, two components of the thermal diffusivity tensor are measured as a function of stretch ratio. The thermal diffusivity is found to increase in the direction parallel, and decrease in the direction perpendicular, to the stretch direction. The level of anisotropy for the natural rubber is substantially lower than that reported by Tautz 50 years ago but comparable to that found in our previous studies on molten polymers, quenched thermoplastics, and other crosslinked elastomers. Thermal diffusivity data along with measurements of the tensile stress were used to evaluate the stress-thermal rule, which was found to be valid over the entire range of stretch ratios. In contrast, failure of the stress-optic rule was observed at stretch ratios well below the largest value at which the stress-thermal rule was valid. This suggests that the degree of anisotropy in thermal conductivity depends on both orientation and stretch of polymer chain segments.

A new experimental method based on infrared thermography (IRT) is developed to study deformation-induced anisotropic thermal conductivity in polymers. An analytic solution for the temperature field of samples heated by a point source is utilized with a robust fit ting procedure allowing fo r quantitative measurement of two components of the normal ized thermal conductivity tensor of uniaxially stretched samples. In order to validate the method, we compare measurements on a cross-linked polybutadiene network with those obtained from a previously developed technique based on forced Rayleigh scattering (FRS). We find excellent agreement between the two techniques. Uncertainty in the measurements using IRT method is estimated to be about 2-5%. The accuracy of the method and its potential application to nontransparent materials make it a good alterna tive to extend current research on anisotropic thermal transport in polymeric materials