The elastic moduli of ultrathin poly(styrene) (PS) and poly(methylmethacrylate) (PMMA) films of thickness ranging from 200 nm to 5 nm were investigated using a buckling-based metrology. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically, with an order of magnitude decrease compared to bulk values for the thinnest films measured. We can account for the observed decrease in apparent modulus by applying a composite model based on the film having a surface layer with a reduced modulus and of finite thickness. The observed decrease in the apparent modulus highlights issues in mechanical stability and robustness of sub-40 nm polymer films and features.

The frequency and energy dissipation change of a quartz crystal microbalance during moisture absorption was measured for films with thickness ranging from 3 to 205 nm. Evidence of the viscoelastic nature of the films was observed for films thicker than 90 nm through the frequency and energy dissipation changes. For sufficiently thin films (t < 40 nm), the frequency change could be effectively modeled as a simple increase in mass, as predicted by the Sauerbrey equation. The viscosity of the swollen films was independent of initial polymer film thickness (93-205 nm). The equilibrium swelling ratio was independent of film thickness for all films examined (3-205 nm). The transition between the observation of a rigid film and a film showing viscoelastic character was found to be at β 1 D ) 0.26 ( 0.10, where β 1 ) 2π/λ s , λ s is the shear wavelength, and D is the film thickness. This transition agrees with the predictions of White and Schrag (J. Chem. Phys. 1999, 111, 11192).

Understanding the mechanical properties of polymers at the nanoscale is critical in numerous emerging applications. While it has been widely shown that the glass transition temperature (T(g)) in thin polymer films generally decreases due to confinement effects in the absence of strong favorable interactions between the polymer and substrate, there is little known about the modulus of sub-100 nm polymer films and features. Thus, one might use this depressed T(g) as a surrogate to estimate how the modulus of nanoconfined polymeric materials deviates from the bulk, based on constructs such as Williams-Landel-Ferry (WLF) time-temperature superposition principles. However, such relationships have not been thoroughly examined at the nanoscale where surface and interface effects can dramatically impact the physical properties of a material. Here, we measure the elastic modulus of a series of poly(methacrylate) films with widely varying bulk T(g)'s as a function of thickness at ambient temperature, exploiting a wrinkling instability of a thin, stiff film on an thick, elastic substrate. A decrease in the modulus is found for all polymers in ultrathin films (<30 nm) with the onset of confinement effects shifting to larger film thicknesses as the quench depth (T(g,bulk) - T) decreases. We show that the decrease in modulus of ultrathin films is not correlated with the observed T(g) decrease in films of the same thickness.

Specular X-ray reflectivity (XR) and quartz crystal microbalance (QCM) measurements were used to determine the absorption of water into thin poly(4-ammonium styrenesulfonic acid) films from saturated vapor at 25 degrees C. The effect of film thickness on the absorption kinetics and overall absorption was investigated in the range of thickness from (3 to 200) nm. The equilibrium swelling of all the films irrespective of film thickness was (0.57+/-0.03) volume fraction. Although the equilibrium absorption is independent ofthickness, the absorption rate substantially decreases for film thickness < 100 nm. For the thinnest film (3 nm), there is a 5 orders of magnitude decrease in the diffusion coefficient for water.

Efficiency, cost, and lifetime are the primary challenges for stationary energy storage with vanadium-redox flow and sodium-sulfur batteries as promising options. In particular, room temperature sodium-sulfur battery systems offer the potential for safe, simple, low-cost and high energy density storage, but the high reactivity or solubility of sodium polysulfides in common liquid electrolytes for carbonates or glycols, respectively, leads to rapid performance loss on cycling. Herein, we demonstrate a robust route to mostly inhibit reactivity of the sulfides with carbonate electrolytes (and also inhibit the diffusion of polysulfides