We report direct measurement of surface deformation in soft solids due to their surface tension. Gel replicas of poly(dimethysiloxane) masters with rippled surfaces are found to have amplitudes that decrease with decr...
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We report direct measurement of surface deformation in soft solids due to their surface tension. Gel replicas of poly(dimethysiloxane) masters with rippled surfaces are found to have amplitudes that decrease with decreasing gel modulus. Surface undulations of a thin elastomeric film are attenuated when it is oxidized by brief exposure to oxygen plasma. Surface deformation in both cases is modeled successfully as driven by surface tension and resisted by elasticity. Our results show that surface tension of soft solids drives significant deformation, and that the latter can be used to determine the former.
Swarms of self-propelled particles exhibit complex behavior that can arise from simple models, with large changes in swarm behavior resulting from small changes in model parameters. We investigate the steady-state swa...
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Swarms of self-propelled particles exhibit complex behavior that can arise from simple models, with large changes in swarm behavior resulting from small changes in model parameters. We investigate the steady-state swarms formed by self-propelled Morse particles in three dimensions using molecular dynamics simulations optimized for graphics processing units. We find a variety of swarms of different overall shape assemble spontaneously and that for certain Morse potential parameters at most two competing structures are observed. We report a rich “phase diagram” of athermal swarm structures observed across a broad range of interaction parameters. Unlike the structures formed in equilibrium self-assembly, we find that the probability of forming a self-propelled swarm can be biased by the choice of initial conditions. We investigate how thermal noise influences swarm formation and demonstrate ways it can be exploited to reconfigure one swarm into another. Our findings validate and extend previous observations of self-propelled Morse swarms and highlight open questions for predictive theories of nonequilibrium self-assembly.
Mathematical modeling methods were used to estimate the stress response of oxide coatings to wet cleaning at elevated temperature. Results indicate that substrate thickness strongly affects the thermal stress response...
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Using in situ atomic-resolution electron microscopy observations, we report observations of the oxide growth during the oxidation of stepped Cu surfaces. Oxidation occurs via direct growth of Cu2O on flat terraces wit...
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Using in situ atomic-resolution electron microscopy observations, we report observations of the oxide growth during the oxidation of stepped Cu surfaces. Oxidation occurs via direct growth of Cu2O on flat terraces with Cu adatoms detaching from steps and diffusing across the terraces. This process involves neither reconstructive oxygen adsorption nor oxygen subsurface incorporation and is rather different from the mechanism of solid-solid transformation of bulk oxidation that is most commonly postulated. These results demonstrate that the presence of surface steps can promote the development of a flat metal-oxide interface by kinetically suppressing subsurface oxide formation at the metal-oxide interface.
Bioceramic nanopowders, currently one of the most demanding challenges for producing new biomaterials, have been tackled only when starting from chemical reagents. There are few studies aiming at producing hydroxyapat...
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Bioceramic nanopowders, currently one of the most demanding challenges for producing new biomaterials, have been tackled only when starting from chemical reagents. There are few studies aiming at producing hydroxyapatite nanopowders from naturally derived raw materials, such as nacre shells. Natural species of sea origin, such as corals and nacres, always attract special interest in biomaterialsscience and technology. Nacre shells are made up of pure aragonite crystallized in an organic matrix. The most common way to transform aragonite structures to hydroxyapatite is via hydrothermal transformation under very high pressure. However, such ways can be very dangerous if the equipment is worn. Ultrasonic and hotplate methods are apparently very safe. This work proposes a new approach for developing highly bioactive fine powders of Ca-phosphates (which can be used afterwards to build up hydroxyapatite-based bioceramic bone-scaffolds) from sea urchins via the above mentioned methods. The suspended raw powders were put on a hotplate (i.e. ultrasound). The temperature was set to 80°C for 15 min and then, equivalent (to the amount of CaCO3 in the sea urchins) amount of H3PO4 was added drop by drop into the solution. The reaction continued for 2 h. Then, to evaporate the liquid part, the mixture was put into an incubator at 100°C for 24 h and the resultant dried sediment was collected. X-ray diffraction analysis identified various calcium phosphate phases, predominantly monetite, and tricalcium phosphate as a secondary phase. The worldwide availability and the low cost of all kinds of nacre and sea urchin shells, along with their biological-natural origin are attractive features conferring to them a high potential for preparing calcium phosphate materials for uses in biomedicine. Heart urchin, used in this study, can be an ideal candidate for producing bioceramic particles.
Central to most applications involving graphenes flakes is its mechanical response under various stress/ strain states. In this work, we present an experimental study on single, bi- and tri-layer graphene flakes under...
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ISBN:
(纸本)9788888785332
Central to most applications involving graphenes flakes is its mechanical response under various stress/ strain states. In this work, we present an experimental study on single, bi- and tri-layer graphene flakes under uniaxial tensile strain, for low levels of strain. Graphene layers were subjected to tensile loading by employing a polymeric cantilever beam assembly, where the graphene flakes are embedded into the polymer beam. The mechanical response of graphenes is monitored by simultaneous Raman measurements through the shift of the G and 2D optical phonons, and their strain sensitivities are determined. The results can be used to quantify the amount of uniaxial strain, providing a fundamental tool for graphene based nanocomposites.
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