Transition of deformation modes from bending to auxetic compression in origami-based metamaterials for head protection from impact.

For the protection of the human head by energy absorption structures, a soft mechanical response upon contact with the head is required to mitigate the effect of impact, while a hard mechanical response for highly efficient energy absorption is required to stop the movement of the head. This study realized the opposite mechanical properties during head protection by transitioning the deformation mode from bending to auxetic compression. First, non-linear finite element (FE) models were constructed to numerically reproduce the bending behavior. The calculated force responses agreed well with forces in bending tests. Using the FE models, the EA structures with proper transition of deformation modes were designed and installed in the seat headrests of real vehicles. Head protection was evaluated by dynamic loading in sled testing, in which the force on the head of the crash test dummy was measured. The head injury criterion improved from 274 to 155, indicating the superior performance of the tested structures compared to that achieved by energy absorption structures based on steel plates. Moreover, the deformation of auxetic structures prevented neck bending by holding the head. These findings present new possibilities for effectively protecting the human body by mitigating impact, facilitating energy absorption, and ensuring head stability.

Wettability of Primer-Treated Al2O3 Surfaces by Bisphenol A Diglycidyl Ether: Determination of the Mechanism from Molecular Dynamics Simulations and Experiments.

This study aims to develop a molecular dynamics (MD) simulation procedure to investigate the wettability of primer-treated Al2O3 surfaces by bisphenol A diglycidyl ether (BADGE) and to understand the interaction between the surface and the liquid. The MD simulation results were compared with those obtained by contact angle measurements, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM) and were found to be in agreement with the experimental evaluations. The results obtained from both the MD simulations and the experiments suggest that the configuration of the primers on the surface affect its wettability. In other words, silanes lying flat on the surface, such as mercapto silane, make it easy for BADGE to access any polar functional groups of the silane, thereby leading to a strong interaction and good wettability. For amino silane, although the configuration is similar to that of mercapto silane, its amino groups are bound to the surface owing to their high polarity, which results in a reduced accessibility for BADGE and a relatively poor wettability in comparison with mercapto silane. On the contrary, for silanes that stand up on the surface, including trifluoroalkyl silane, BADGE is hindered from approaching the silanol groups and interacting with them, and the surface shows poor wettability.

Wettability of Al2O3 Surface by Organic Molecules: Insights from Molecular Dynamics Simulation.

We use molecular dynamics (MD) simulations to investigate the wettability of Al2O3 (0001) by organic molecules. Diffusion coefficients estimated for organic molecules are clearly correlated with the contact angles observed experimentally. The results of the MD simulations suggest that molecular flexibility influences wettability. In other words, wettability owing to flexible molecules, such as an epoxy tridecamer, improves with increasing temperature because the interaction between the droplet and the surface increases due to changes in molecular conformation. Conversely, for phenylene sulfide tetramer, wettability does not change with temperature because of the molecular rigidity. In addition, for epoxy monomers, we analyze the different molecular structures responsible for modifying the droplet-surface interaction. For hydrogens in aromatic rings and in methyl groups, the interaction with the surface clearly decreases with increasing temperature.

Enzymatic polymerization of coniferyl alcohol in the presence of cyclodextrins.

The dehydrogenative polymerization of coniferyl alcohol by horseradish peroxidase was performed in 0.10 M phosphate buffer at 27 degrees C. Dehydrogenative polymer (DHP) from coniferyl alcohol was characterized by size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. The ratio of 8-O-4':8-5':8-8' linkages was determined by the 1H NMR spectrum of DHP acetate which had good solubility. In "end-wise like" polymerization (the slow addition of hydrogen peroxide), addition of alpha-cyclodextrin to the medium led to DHP with increased 8-O-4' content and a decrease in 8-5' linkages. Under higher pH conditions, DHP with higher 8-O-4' and 8-5' content was obtained in the presence of alpha-cyclodextrin. In the end-wise polymerization (the slow additions of coniferyl alcohol and hydrogen peroxide), using alpha-cyclodextrin also gave DHP with a 8-O-4' richer structure than that prepared in no additive system. The analysis of thioacidolysis products from DHP supported the results of the alpha-cyclodextrin effects on the 8-O-4'-rich structure of DHP. The 8-O-4' structure in DHP prepared in the presence of alpha-cyclodextrin had racemic form as shown by ozonation.

Side chain-directed assembly of triangular molecular panels into a tetrahedron vs. open cone.

Despite their structural similarity, triangular tetradentate ligands 2b and 2c experience different assembly pathways on complexation with (en)Pd(NO3)2 to give M8L4 tetrahedral (3) and open cone (4) structures, respectively, due to steric restriction by side chains at the corner or on the edge of the ligands.

Molecular Paneling by Coordination: An M15 L6 Hexahedral Molecular Capsule having Clefts for Reversible Guest Inclusion.

Only one positional isomer is obtained from the assembly of 21 small components. A triangular molecular panel with five coordination sites is assembled upon complexation with [PdII (en)] (en=ethylenediamine) into a unique M15 L6 hexahedral coordination capsule (see X-ray structure). The capsule can encapsulate/exchange organic guests reversibly through the clefts at the nonbinding sites of the capsule.