Mechanical Properties Of Bilayer Research Articles

Microstructure and mechanical properties of bilayer B4C/Si-B4C composite

Bilayer B4C based composites, B4C/Si-B4C, consisting of B4C and B4C/Si two-layer, were obtained using hot pressing method. Effect of Si content on microstructure and mechanical properties of the B4C based layered composites was investigated. The B4C/Si-B4C samples showed good interfacial bonding with different Si additions (x = 4, 8, 12 and 16 wt.%) in the B4C/Si layer. Secondary phases SiC and/or TiB2 dispersed randomly in B4C matrices for both layers of the composite by SEM observation. Vickers hardness data for both layers were in a range from 33.1 to 35.2 GPa. Flexural strength and fracture toughness both first increased and then slightly decreased as Si content increased from 4 to 16 wt.%. The fracture toughness of the B4C/Si-B4C composite was significantly improved compared with that of pure B4C material.

Impact of Glycans on Lipid Membrane Dynamics at the Nanoscale Unveiled by Planar Plasmonic Nanogap Antennas and Atomic Force Spectroscopy.

Lateral compartmentalization of the plasma membrane is a prominent feature present at multiple spatiotemporal scales that regulates key cellular functions. The extracellular glycocalyx matrix has recently emerged as an important player that modulates the organization of specific receptors and patterns the lipid bilayer itself. However, experimental limitations in investigating its impact on the membrane nanoscale dynamics have hampered detailed studies. Here, we used photonic nanoantenna arrays combined with fluorescence correlation spectroscopy to investigate the influence of hyaluronic acid (HA), a prominent glycosaminoglycan, on the nanoscale organization of mimetic lipid bilayers. Using atomic force microscopy and force spectroscopy, we further correlated our dynamic measurements with the morphology and mechanical properties of bilayers at the nanoscale. Overall, we find that HA has a profound effect on the dynamics, nanoscale organization, and mechanical properties of lipid bilayers that are enriched in sphingolipids and/or cholesterol, such as those present in living cells.

Mechanical properties of bilayers containing sperm sphingomyelins and ceramides with very long-chain polyunsaturated fatty acids.

Sphingomyelins (SM) and ceramides (Cer) with very long chain polyunsaturated fatty acids (V) are important components of spermatozoa membranes. In this study, the mechanical properties of bilayers of SM and Cer with nonhydroxy (n-V) and 2-hydroxy (h-V) fatty acid (30:5) were studied by molecular dynamics simulation at different temperatures and in the presence and the absence of salt. From our results, it was evidenced how n-V SM and h-V SM bilayers showed similar behavior. When n-V Cer was added to a h-V SM bilayer, the Gaussian curvature modulus and Ecurve of binary bilayers decreased. This variation in the mechanical properties of the bilayer can be associated with an incipient step during the fecundation process.

Mechanical properties investigation of bilayer graphene/poly(methyl methacrylate) thin films at macro, micro and nanoscale

Mechanical properties of bilayer graphene/poly(methyl methacrylate) (GR/PMMA) and reference PMMA thin films are investigated using various macro, micro and nano mechanical test methods. The GR/PMMA bilayer film consists of the CVD graphene layer (1 nm thick) spin coated with 1 μm thick PMMA layer. Small punch test, Berkovich nanoindentation, AFM nanoindentation, AFM nanoscratch, and spherical-conical stylus nanoscratch are used as mechanical characterization techniques. The freestanding films behave as 2D-membranes and high stretching is achieved at slower tests due to the dissipation of energy during elongation. The bilayer film is more brittle with lower fracture strength, strain and toughness than the PMMA film, due to interfacial delamination between the GR and the PMMA layers at large strain. The surface elastic modulus is higher than the bulk tensile modulus due to the scale effect. The graphene layer contributes to the improvements of hardness and resistance to scratch for both freestanding and supported GR/PMMA films. Critical normal force of adhesive failure of the bilayer films is identified as an important parameter characterizing intrinsic adhesion properties of the graphene/PMMA interfaces. The GR/PMMA thin films have potential in future shielding applications for protection of electronic devices.

Twinning and Twisting of Tri- and Bilayer Graphene

The electronic, optical, and mechanical properties of bilayer and trilayer graphene vary with their structure, including the stacking order and relative twist, providing novel ways to realize useful characteristics not available to single layer graphene. However, developing controlled growth of bilayer and trilayer graphene requires efficient large-scale characterization of multilayer graphene structures. Here, we use dark-field transmission electron microscopy for rapid and accurate determination of key structural parameters (twist angle, stacking order, and interlayer spacing) of few-layer CVD graphene. We image the long-range atomic registry for oriented bilayer and trilayer graphene, find that it conforms exclusively to either Bernal or rhombohedral stacking, and determine their relative abundances. In contrast, our data on twisted multilayers suggest the absence of such long-range atomic registry. The atomic registry and its absence are consistent with the two different strain-induced deformations we observe; by tilting the samples to break mirror symmetry, we find a high density of twinned domains in oriented multilayer graphene, where multiple domains of two different stacking configurations coexist, connected by discrete twin boundaries. In contrast, individual layers in twisted regions continuously stretch and shear independently, forming elaborate Moiré patterns. These results, and the twist angle distribution in our CVD graphene, can be understood in terms of an angle-dependent interlayer potential model.

Thermodynamic and mechanical properties of model mitochondrial membranes

Cardiolipin is a unique four-tailed, doubly negatively charged lipid found predominantly within the inner mitochondrial membrane, and is thought to be influential in determining membrane potential and permeability. To determine the role of cardiolipin in modulating the properties of membranes, this study investigates the thermodynamics of mixed cardiolipin and phosphatidylcholine monolayers and bilayers. Gibbs free energy analysis of mixed monolayers indicates that at low cardiolipin concentrations (5–10 mol%), there is a positive deviation from ideality on a pure water subphase, while at physiological salt concentrations a negative deviation from ideality is observed. The mechanical properties of bilayers containing cardiolipin were measured using micropipette aspiration. Both apparent area compressibility modulus, as well as lysis tension, decrease with increasing cardiolipin content. This destabilization indicates a decrease in the cohesive energy of the membrane. This interplay between interactions of lipids in monolayers and bilayers, suggests cardiolipin plays a dual role in modulating membrane properties. Cardiolipin enhances lateral interactions between lipids within monolayer leaflets, while simultaneously decreasing the cohesive energy of membranes at physiologically relevant concentrations. Taken together, these findings correlate with the decreased permeability and creation of folds in the inner mitochondrial membrane.

Thermodynamic and mechanical properties of model mitochondrial membranes

Cardiolipin is a unique four-tailed, doubly negatively charged lipid found predominantly within the inner mitochondrial membrane, and is thought to be influential in determining membrane potential and permeability. To determine the role of cardiolipin in modulating the properties of membranes, this study investigates the thermodynamics of mixed cardiolipin and phosphatidylcholine monolayers and bilayers. Gibbs free energy analysis of mixed monolayers indicates that at low cardiolipin concentrations (5–10 mol%), there is a positive deviation from ideality on a pure water subphase, while at physiological salt concentrations a negative deviation from ideality is observed. The mechanical properties of bilayers containing cardiolipin were measured using micropipette aspiration. Both apparent area compressibility modulus, as well as lysis tension, decrease with increasing cardiolipin content. This destabilization indicates a decrease in the cohesive energy of the membrane. This interplay between interactions of lipids in monolayers and bilayers, suggests cardiolipin plays a dual role in modulating membrane properties. Cardiolipin enhances lateral interactions between lipids within monolayer leaflets, while simultaneously decreasing the cohesive energy of membranes at physiologically relevant concentrations. Taken together, these findings correlate with the decreased permeability and creation of folds in the inner mitochondrial membrane.