A Superhydrophobic Surface Fabricated by an Electrostatic Process

We describe the fabrication of a biomimically designed superhydrophobic poly(ε‐caprolactone) surface, which was obtained using a modified electrostatic process. The fabricated surface exhibits a micron‐sized pyramid structure consisting of accumulated droplets and nanofibres. By using this simple one‐step process, we can achieve a superhydrophobic surface having both a high water contact angle and low threshold sliding angle, similar to that of the superhydrophobic plant leaf.

     

Covalently Attached Liquids: Instant Omniphobic Surfaces with Unprecedented Repellency

Recent strategies to prepare “omniphobic” surfaces have demonstrated that minimizing contact angle hysteresis (CAH) is the key criterion for effectiveness. CAH is affected by chemistry and topography defects at the molecular and higher levels, thus most surfaces exhibit significant CAH. Preparative methods for stable coatings on smooth substrates with negligible CAH (<2°) for a broad range of liquids have not been reported. In this work, we describe a simple and rapid procedure to prepare omniphobic surfaces that are stable under pressure and durable at elevated temperatures. Consistent with theory, they exhibit sliding angles that decrease with liquid surface tension. Slippery omniphobic covalently attached liquid (SOCAL) surfaces are obtained through acid‐catalyzed graft polycondensation of dimethyldimethoxysilane. The smooth, stable, and temperature‐resistant coatings show extremely low CAH (≤1°) and low sliding angles for liquids that span surface tensions from 78.2 to 18.4 mN m^?1.     

Forward and backward pericyclic photochemical reactions have intermediates in common, yet cyclobutenes break the rules.

Photochemical pericyclic reactions are believed to proceed via a so-called pericyclic minimum on the lowest excited potential surface (S(1)), which is common to both the forward and backward reactions. Such a common intermediate has never been directly detected. The photointerconversion of 1,3-butadiene and cyclobutene is the prevailing prototype for such reactions, yet only diene ring closure proceeds with the stereospecificity that the Woodward-Hoffmann rules predict. This contrast seems to exclude a common intermediate. Using ultrafast spectroscopy, we show that the excited states of two cyclobutene/diene isomeric pairs are linked by not one, but by two common minima, p* and ct*. Starting from the diene side (cyclohepta-1,3-diene and cycloocta-1,3-diene), electrocyclic ring closure passes via the pericyclic minimum p*, whereas ct* is mainly responsible for cis-trans isomerization. Starting from the corresponding cyclobutenes (bicyclo[3.2.0]heptene-6 and bicyclo[4.2.0]octene-7), the forbidden isomer is formed from ct*. The path branches at the first (S(2)/S(1)) conical intersection towards p* and ct*. The fact that the energetically unfavorable ct* path can compete is ascribed to a dynamic effect: the momentum in C=C twist direction, acquired--such as in other olefins--in the Franck-Condon region of the cyclobutenes.     

Chemical insight into electron density and wave functions: software developments and applications to crystals, molecular complexes and materials science

This paper overviews the work made by our group during the past 10–15 years on crystalline systems, semiconductor surfaces, molecular complexes and on materials of interest for technological applications, such as the defective silicon or the novel generation thermoelectric materials. Our main aim of extracting chemical insight into the analysis of electron densities and computed wave functions is illustrated through a number of examples. The recently proposed Source Function analysis is reviewed and a few of its more interesting applications are summarized. Software package developments, motivated by the need of a direct comparison with experiment or by the help these packages can provide for interpreting complex experimental outcomes, are described and future directions outlined. A particular emphasis is given to the TOPOND and TOPXD programs, which enable one to analyze theoretical and experimental crystalline densities using the rigorous framework of the Quantum Theory of Atoms in Molecules, due to Bader.     

Atomic simulation of the point defects in three low‐index surfaces of BCC transition metals with the MAEAM

The favorable position of an adatom and the formation energies of a single vacancy and an adatom‐vacancy pair in three low‐index surfaces of body‐centered cubic (BCC) transition metals have been calculated by using the modified analytical embedded atom method (MAEAM). The favorable position of an adatom is at the fourfold and twofold positions above the (100) and (110) surfaces respectively, but it is deviated from the threefold position of the (111) surface. Either the heights of the adatom from the top atomic layer, or the formation energies of a single vacancy, or an adatom‐vacancy pair decrease in sequence of the (110), (100) and (111) surfaces for each metal. Furthermore, the formation energy of an adatom‐vacancy pair is always lower than that of a single vacancy for each low‐index surface of each metal, which shown the formation of adatom‐vacancy pair is more energetically favorable than the vacancy for the BCC transition metals. Copyright © 2007 John Wiley & Sons, Ltd.     

Stabilization of an excess electron on molecular surfaces by a pair of HF molecules

This work presents the results of solvation of electrons on several hypothetical cyclooctane and cyclohexane molecular surfaces, using the hydrogen fluoride (HF) dimer. These complexes were constructed with extensive OH groups on one side of a hydrocarbon surface (i.e., cyclohexane sheets), which creates hydrogen‐bonded networks that can form, increasing the dipole moment of the system. Concurrently, the hydrogen atoms on the opposite side of the surface form a pocket of positive charge that can attract excess electrons. Two possible orientations for HF dimer solvation on eight molecular surfaces that have been demonstrated to be stable toward electron detachment are examined. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Efficient modification on PLLA by ozone treatment for biomedical applications

RGDS (Arg-Gly-Asp-Ser) is immobilized on poly(L-lactic acid) (PLLA) with ozone oxidation and the addition of an intermediate reactant, acryl succinimide (ASI) to promote the grafting efficiency. A DPPH (2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl) assay has revealed that the peroxide concentration can be controlled by adjusting the ozone treatment time. The immobilization of ASI is verified by elemental analysis. The peptide concentrations are in the effective order, as shown by means of high performance liquid chromatography (HPLC), and the grafting efficiency is proven to be relatively high compared with the previous studies. The culture of rat osteosarcoma 17/2.8 (ROS), osteoblastic-like cells, demonstrates that the grafting of RGDS can enhance the attachment and osteogenesis of ROS cells on PLLA. With the addition of ASI, the cultured ROS cells express normal function in proliferation and mineralization. From in vivo experiments, ASI immobilized on the surface is shown to be biocompatible. These results lead to the conclusion that the ozone treatment with the intermediate reactant ASI is an efficient, biocompatible, and easily controllable procedure to modify PLLA. Furthermore, the immobilization of RGDS in significant amounts following the ozone oxidation could further promote the biocompatibility and the osteoinduction of PLLA.     

Neural network and ReaxFF comparison for Au properties

We have studied how ReaxFF and Behler–Parrinello neural network (BPNN) atomistic potentials should be trained to be accurate and tractable across multiple structural regimes of Au as a representative example of a single‐component material. We trained these potentials using subsets of 9,972 Kohn‐Sham density functional theory calculations and then validated their predictions against the untrained data. Our best ReaxFF potential was trained from 848 data points and could reliably predict surface and bulk data; however, it was substantially less accurate for molecular clusters of 126 atoms or fewer. Training the ReaxFF potential to more data also resulted in overfitting and lower accuracy. In contrast, BPNN could be fit to 9,734 calculations, and this potential performed comparably or better than ReaxFF across all regimes. However, the BPNN potential in this implementation brings significantly higher computational cost. © 2016 Wiley Periodicals, Inc.     

Stability of atomic oxygen chemisorption on Pt‐alloy surfaces

A density functional theory calculation is used to investigate the atomic oxygen (O) stability over platinum (Pt) and Pt‐based alloy surfaces. Here, the stability is connected with the preferential adsorption sites for O chemisorptions and the adsorption energy. Thus, the interaction mechanism between atomic O and metal surfaces is studied by using charge transfer analysis. In this present paper, atomic structure and binding energy of oxygen adsorption on the Pt(111) are in a very good agreement with experiment and previous density functional theory calculations. Furthermore, we obtained that the addition of ruthenium (Ru) and molybdenum (Mo) on the pure Pt surface enhances the adsorption energy. Our charge transfer analysis shows that the largest charge transfer contributing to the metal‐O bonding formation is observed in the case of O/PtRuMo surface followed by O/PtRu surface. This is in consistency with metal d‐orbital characteristic, where Mo has much more empty d‐orbital than Ru in correspondence to accept electrons from atomic oxygen. Copyright © 2016 John Wiley & Sons, Ltd.