Probing the mechanical properties of graphene using a corrugated elastic substrate

The exceptional mechanical properties of graphene have made it attractive for nano-mechanical devices and functional composite materials. Two key aspects of graphene's mechanical behavior are its elastic and adhesive properties. These are generally determined in separate experiments, and it is moreover typically difficult to extract parameters for adhesion. In addition, the mechanical interplay between graphene and other elastic materials has not been well studied. Here, we demonstrate a technique for studying both the elastic and adhesive properties of few-layer graphene (FLG) by placing it on deformable, micro-corrugated substrates. By measuring deformations of the composite graphene-substrate structures, and developing a related linear elasticity theory, we are able to extract information about graphene's bending rigidity, adhesion, critical stress for interlayer sliding, and sample-dependent tension. The results are relevant to graphene-based mechanical and electronic devices, and to the use of graphene in composite, flexible, and strain-engineered materials.Comment: 5 pages, 4 figure

Inkjet Metrology: High-Accuracy Mass Measurements of Microdroplets Produced by a Drop-on-Demand Dispenser

We describe gravimetric methods for measuring the mass of droplets generated by a drop-on-demand (DOD) microdispenser. Droplets are deposited, either continuously at a known frequency or as a burst of known number, into a cylinder positioned on a submicrogram balance. Mass measurements are acquired precisely by computer, and results are corrected for evaporation. Capabilities are demonstrated using isobutyl alcohol droplets. For ejection rates greater than 100 Hz, the repeatability of droplet mass measurements was 0.2%, while the combined relative standard uncertainty (uc) was 0.9%. When bursts of droplets were dispensed, the limit of quantitation was 72 μg (1490 droplets) with uc = 1.0%. Individual droplet size in a burst was evaluated by high-speed videography. Diameters were consistent from the tenth droplet onward, and the mass of an individual droplet was best estimated by the average droplet mass with a combined uncertainty of about 1%. Diameters of the first several droplets were anomalous, but their contribution was accounted for when dispensing bursts. Above the limits of quantitation, the gravimetric methods provided statistically equivalent results and permit detailed study of operational factors that influence droplet mass during dispensing, including the development of reliable microassays and standard materials using DOD technologies

Mechanics of Chemo-Mechanical Stimuli Responsive Soft Polymers

Responsive materials, often obtained by designing the molecular structure of polymers or gels, are able to respond with detectable physical changes to external stimuli of various nature, ranging from chemical (such as pH), temperature, light radiation, mechanical stress, etc. In this paper we propose a micromechanical model, rooted in the statistical approach to the network conformation of polymeric materials, to predict the mechanical response of polymers with embedded responsive molecules. The model makes use of the so-called chains distribution function, aimed at providing the current state of the network’s chains. A univocal relation between the distribution function and the mechanical state of the material is established, so the knowledge of the evolution of such a function with the applied deformation or other external stimuli allows to get the macroscopic response of the material. Finally, the case of responsive molecules inserted into the network as crosslinkers is considered. The responsiveness of the molecules is assumed to depend either on the mechanical and/or chemical stimuli coming from the external environment. The cases involving molecules sensible to chemical stimuli, always imply the presence of a solvent carrying the triggering chemical agent, and thus require to consider the swelling phenomenon induced by the fluid absorbed by the polymer network. The theoretical framework of the micromechanical model is illustrated and some examples are finally presented and discussed