Rigid Additives Research Articles

Effect of high aspect ratio flaky aluminum on mechanical properties of epoxy‐based particulate composites

AbstractEpoxy‐based polymer composites are used in the aerospace industry due to high strength, less shrinkage, and ready availability. However, they are brittle and this limitation is usually addressed by using additives. Soft additives typically increase the toughness at the cost of stiffness and are usually not preferred for high strength applications. On the contrary, rigid additives such as carbon nanotubes (CNTs) and nanoclay increase the stiffness and tensile strength, but at the expense of strain at failure, indicating embrittlement. Also, these additives are expensive and this adds up to the overall product cost, limiting its application. Thus, this study aims to introduce a new low‐cost, high aspect ratio additive that toughens epoxy without compromising on its strength. Tensile test and impact test were conducted to procure mechanical properties for the composite, along with fractography using electron microscopy. These tests revealed that this new additive increased the tensile strength, impact strength, and strain at failure by 56%, 60%, and 200% for a very low weight fraction of 0.5% of the additive.

Fluid Mechanical Matching of H +-ATP Synthase Subunit c-Ring with Lipid Membranes Revealed by 2H Solid-State NMR

The F 1F o-ATP synthase utilizes the transmembrane H + gradient for the synthesis of ATP. F o subunit c-ring plays a key role in transporting H + through F o in the membrane. We investigated the interactions of Escherichia coli subunit c with dimyristoylphosphatidylcholine (DMPC- d 54) at lipid/protein ratios of 50:1 and 20:1 by means of 2H-solid-state NMR. In the liquid-crystalline state of DMPC, the 2H-NMR moment values and the order parameter ( S CD) profile were little affected by the presence of subunit c, suggesting that the bilayer thickness in the liquid-crystalline state is matched to the transmembrane hydrophobic surface of subunit c. On the other hand, hydrophobic mismatch of subunit c with the lipid bilayer was observed in the gel state of DMPC. Moreover, the viscoelasticity represented by a square-law function of the 2H-NMR relaxation was also little influenced by subunit c in the fluid phase, in contrast with flexible nonionic detergents or rigid additives. Thus, the hydrophobic matching of the lipid bilayer to subunit c involves at least two factors, the hydrophobic length and the fluid mechanical property. These findings may be important for the torque generation in the rotary catalytic mechanism of the F 1F o-ATPse molecular motor.