This paper outlines a simple method to fabricate a bilayer membrane consisting of a thin nanoporous gold layer infused with uncured polydimethylsiloxane. The fabrication technique offers excellent adhesion due to mechanical interlocking between porous layer and elastomer, and excellent electrical conductivity up to 25% strain, despite a very low effective elastic modulus (∼1.35 MPa) due to cracks in the embedded gold layer. Initially freestanding circular membranes displayed significant out of plane buckling, and created difficulties in extraction of membrane mechanical properties. The underlying mechanisms of compressive stress accumulation that lead to membrane buckling and remedies to prevent it are discussed.

We report a new experimental method for the characterization of the electromechanical properties of polyelectrolyte gels (PG). PGs have been studied extensively, but with limited success, as mechanical actuators. However, they are also promising as potentially biocompatible mechanical sensors. In order to integrate them into actual devices, their electromechanical transduction properties need to be characterized in a reproducible manner.

We have therefore developed a technique to measure the mechanically induced change in electrostatic potential in PGs. The polyelectrolyte gel is subjected to a well-defined pressure gradient by placing a thin, flat sample on a substrate with integrated concentric Platinum electrodes and indenting it with a spherical indenter. The potential values at the electrodes are measured using a MOSFET operational amplifier circuit with an input impedance of 1014 Ù and an effective dynamic range better than 16 bit. This method can be directly used to quantify electromechanical coupling in polyelectrolyte gels.

Single wall carbon nanotubes (SWNTs) have drawn considerable attention from the scientific community based on their potentially unique 1-D electronic and optical properties as well as mechanical properties. These characteristics result from the one dimensional quantum wire structure of CNTs, which have the spike-like van Hove singularities (vHs) in the electronic density of states. The detailed shape of the density of states function depends sensitively on CNT type semiconducting (sem-) versus metallic (met-)), diameter and chirality. Using the preferential affinity of amines towards sem -SWNTs, our group has been able to attain bulk separation by type based on a differential solubility of SWNTs according to the amine organization interaction on the nanotube surface. It has been argued that stable dispersions of sem -SWNTs with surfactant-amines originate from the organization of the aliphatic chain along the nanotube sidewalls, along with a small amount of zwitterions. The separation of sem-enriched SWNTs assisted by octadecylamine (ODA) had been depicted in the form of either small amount of zwitterionic interaction between carboxylic acid groups of acid-purified SWNTs or the physisorption on the SWNTs sidewall, leaving met -SWNTs in the precipitate.

Aluminum tris-(quinoline-8-olate) (Alq3) is the most widely used electron transport material for organic light emitting diodes. The Alq3 molecule exists as two different isomers: meridianal and facial, which differ by the symmetry of the arrangement of ligands around the aluminum ion. Various crystalline polymorphs of Alq3 have been identified to contain one of these isomers. In this paper we present experimental results that show that the facial and meridianal isomers of Alq3 can be distinguished in the solid state by 27Al nuclear magnetic resonance (NMR) spectroscopy under magic angle spinning (MAS). Our results prove that the recently discovered δ-phase of Alq3 exclusively contains the facial isomer. The same technique is also used to characterize the amorphous deposit of Alq3 showing that it is the meridianal isomer that predominantly exists in the amorphous state.

We present a detailed nanoindentation study of micron-scale thin films of polystyrene (PS), poly(phenylene oxide) (PPO), poly(methyl methacrylate) (PMMA), a metal-centered PMMA-Ruthenium block copolymer, and a PS-poly(ethylene-propylene) (PS-PEP) block copolymer with lamellar morphology. The results show that size-dependence is most readily noticeable for the lamellar PS-PEP film, indicating that the nanoidentation approach has sufficient sensitivity to capture scale dependence on scales in the range of tens of nanometers. The less pronounced scale-dependence (or lack thereof) in the other films is discussed in the context of identifying the physical length-scale of elementary processes of plastic deformation. The results indicate that the upper limit on the size of plastic shear zones in amorphous polymers is approximately 1200-9600 nm3 (i.e. a sphere with a diameter in the range of 20-40 nm).

The shear activation volumes of miscible polystyrene-poly(2,6-dimethyl-1,4-phenylene oxide) (PS-PPO) blends at different PS-PPO ratios were determined experimentally by both plane strain and uniaxial compression at constant strain rates. We find that the same correlation between the shear activation volume and the entanglement density ρe holds for the blend as well as for various pure glassy polymers: . Since the shear activation volume is closely related to the size of the plastic shear zones, this correlation suggests that the cooperativity of the elementary processes of plastic deformation in glassy polymers scales with the entanglement density.

Plastic yielding in glassy solids has been interpreted as a strain-biased relaxation process, or, equivalently, as a strain-induced glass transition. In the present work, the atomic motions caused by athermal plastic deformation of a binary Lennard-Jones glass are compared to thermal motion in the liquid in terms of the self part of the intermediate structure factor. We find that like at finite temperature, athermal plastic deformation leads to diffusive atomic motion at all length scales beyond about one interatomic distance, effectively promoting structural relaxation. The present approach allows to study the interplay of deformation-induced and thermal relaxation. Preliminary evidence is presented that these two processes occur independently of each other over a wide range of strain rates.

A highly efficient algorithm for the reconstruction of microstructures of heterogeneous media from spatial correlation functions is presented. Similar to previously proposed algorithms, the new method relies on Monte Carlo optimization, representing the microstructure on a discrete grid. An efficient way to update the correlation functions after local changes to the structure is introduced. In addition, the rate of convergence is substantially enhanced by selective Monte Carlo moves at interfaces. Speedups over prior methods of more than two orders of magnitude are thus achieved. The algorithm is ideally suited for parallel computers. The increase in efficiency brings new classes of problems within the realm of the tractable, notably those involving several different structural length scales and/or components.