Measuring the solidification time of silicone rubber using optical inspection technology

A room temperature vulcanization silicone rubber was widely used as the mold making material due to its high elasticity, good heat-resistance and low surface energy. To enhance the efficiency of making the silicone rubber mold, accurately measuring the solidification time is an important issue. This study demonstrated a non-invasive measurement system to measure the solidification time of silicone rubber. The solidification time can be determined rapidly from the thickness of silicone rubber according to the predicted equation. The maximum relative error of the predicted equation is about 8.26%. The temperature rise of the silicone during the solidification process is an important phenomenon to determine the solidification behavior of silicone rubber. The solidification mechanism of silicone rubber mold is demonstrated.     

Effect of Surface‐Hydroxylated CdS Nanoparticles on the Morphological Transformation of Polystyrene‐block‐Poly(ethylene oxide) Thin Films

Summary: Polystyrene‐block‐poly(ethylene oxide) (SEO) block copolymer thin films, in which CdS clusters have been sequestered into the PEO domains of the SEO block copolymers, are found to induce the morphological transformation of PEO from cylinders to spheres, as shown by using atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). This transformation is caused by the presence of hydrogen‐bonding interactions between surface‐hydroxylated CdS and PEO, as confirmed by nuclear magnetic resonance (NMR) studies.

Morphological transformation of PEO cylinders into CdS/PEO spheres by hydrogen‐bonding interactions between surface‐hydroxylated CdS and PEO.     

Wound Healing Attributes of Polyelectrolyte Multilayers Prepared with Multi‐l‐arginyl‐poly‐l‐aspartate Pairing with Hyaluronic Acid and γ‐Polyglutamic Acid

Biodegradable multi‐l ‐arginyl‐poly‐l ‐aspartate (MAPA), more commonly cyanophycin, prepared with recombinant Escherichia coli contains a polyaspartate backbone with lysine and arginine as side chains. Two assemblies of polyelectrolyte multilayers (PEMs) are fabricated at three different concentration ratios of insoluble MAPA (iMAPA) with hyaluronic acid (iMAPA/HA) and with γ‐polyglutamic acid (iMAPA/γ‐PGA), respectively, utilizing a layer‐by‐layer approach. Both films with iMAPA and its counterpart, HA or γ‐PGA, as the terminal layer are prepared to assess the effect on film roughness, cell growth, and cell migration. iMAPA incorporation is higher for a higher concentration of the anionic polymer due to better charge interaction. The iMAPA/HA films when compared to iMAPA/γ‐PGA multilayers show least roughness. The growth rates of L929 fibroblast cells on the PEMs are similar to those on glass substrate, with no supplementary effect of the terminal layer. However, the migration rates of L929 cells increase for all PEMs. γ‐PGA incorporated films impart 50% enhancement to the cell migration after 12 h of culture as compared to the untreated glass, and the smooth films containing HA display a maximum 82% improvement. The results present the use of iMAPA to construct a new layer‐by‐layer system of polyelectrolyte biopolymers with a potential application in wound dressing.     

Controllable Assembly of Highly Oxidized Cobalt on Graphdiyne Surface for Efficient Conversion of Nitrogen into Nitric Acid

The manufacture of nitric acid (HNO₃) consumes large amounts of energy and causes serious environmental pollution. Electrochemical synthesis is regarded as a key way to eliminate carbon emissions from the chemicals industry. The selective electrosynthesis of HNO₃ from nitrogen was achieved by controllable assembly of cobalt metal on graphdiyne surface using a powerful tool of electrochemistry at ambient conditions. As an advanced material, graphdiyne (GDY) has a large conjugated structure on its surface and is rich in sp-C triple bond skeleton, which can achieve strong interaction with metal atoms, resulting in incomplete charge transfer between graphdiyne and cobalt atoms. The experimental and theoretical calculation results show that the highly oxidized cobalt on graphdiyne (HOCo/GDY) can selectively and efficiently activate and convert the nitrogen into the key intermediate *NO, which promotes the efficient overall conversion performance of nitrogen to nitric acid. Thus, the highest nitric acid yield (192.0 μg h⁻¹ mg⁻¹) and Faradaic efficiency (21.5 %) were achieved at low potentials.     

Effect of incorporated CdS nanoparticles on the crystallinity and morphology of poly(styrene‐b‐ethylene oxide) diblock copolymers

Surface‐modified CdS nanoparticles selectively dispersed in hexagonally packed poly(ethylene oxide) (PEO) cylinders of poly(styrene‐b‐ethylene oxide) (PSEO) block copolymers were prepared. The photoluminescence and ultraviolet–visible characteristics of the presynthesized CdS nanoparticles in N,N‐dimethylformamide and in PEO domains of the PSEO block copolymers were determined. Because of strong interactions between the CdS nanoparticles and PEO chains, as shown by Fourier transform infrared spectroscopy, the incorporation of the CdS nanoparticles prevented the PEO cylinders from properly crystallizing; this was confirmed by differential scanning calorimetry and wide‐angle X‐ray diffraction measurements. The intercylinder distance between the swollen and reduced‐crystallinity CdS/PEO cylinders in turn increased, as confirmed by small‐angle X‐ray scattering and transmission electron microscopy. At a high CdS concentration (43 wt % or 8.3 vol % with respect to PEO), however, the hexagonally packed cylindrical nanostructure of the PSEO diblock copolymers was destroyed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1220–1229, 2005     

Auto-tuning of a two-degree-of-freedom rotational pendulum absorber

A dynamic vibration absorber is effective in suppressing harmonic excitation by tuning its natural frequency to match the excitation frequency. The rotational pendulum absorber (RPA) has a wide-range of natural frequencies that are continuously tunable by setting a suitable rotational speed. In this paper it is shown how to automatically tune the rotational speed of a two-degree-of-freedom RPA by detecting the phase between the vibration of the primary structure and that of the RPA. For this purpose the speed response of the RPA is introduced in addition to the frequency response. It is seen that if the excitation frequency is above a critical value dependent on the parameters of the RPA, the second vibration mode of the RPA is effective, allowing a relatively low rotational speed for the pendulums. The speed tuning algorithm is tested on a flexible plate that is subject to excitations of around 80 Hz, which do not generate visible oscillations but emit audible noise instead. Experimental results confirm the noise-level reduction effect of the RPA.     

Electrochemical study of PEDOT-PSS-MDB-modified electrode and its electrocatalytic sensing of hydrogen peroxide

A method to fabricate poly(3,4-ethylene dioxythiophene)-poly(4-styrene sulfonate)-Meldola Blue (PEDOT-PSS-MDB)-modified electrodes had been disclosed. Firstly, the PEDOT-PSS-film-modified electrode was electrochemically prepared. Then, the PEDOT-PSS was treated as a matrix to immobilize electroactive mediator, Meldola Blue (MDB), by means of an electrostatic interaction to form the proposed film, PEDOT-PSS-MDB. Electrochemical properties of the proposed film exhibited surface confinement and pH dependence. The PEDOT-PSS-MDB electrode could electrocatalytically reduce hydrogen peroxide (H₂O₂) with a low overpotential and showed a linear response to H₂O₂ in the concentration range of 5 to 120 μM, detection limit of 0.1 μM, and sensitivity of 353.9 μA mM⁻¹ cm⁻² (S/N = 3). By comparison, the electrocatalytic activity of PEDOT-PSS-MDB electrode was found superior to that of PEDOT-PSS and MDB-PSS electrodes. It also has competitive potential as compared with other mediators, through the use of HRP to determine H₂O₂. Moreover, the potential interferents such as ascorbic acid, dopamine, uric acid, and glucose were also studied for H₂O₂ determination by the proposed film.     

Highly Selective Electrocatalytic Olefin Hydrogenation in Aqueous Solution

Selective hydrogenation of olefins with water as the hydrogen source at ambient conditions is still a big challenge in the field of catalysis. Herein, the electrocatalytic hydrogenation of purely aliphatic and functionalized olefins was achieved by using graphdiyne based copper oxide quantum dots (Cu_xO/GDY) as cathodic electrodes and water as the hydrogen source, with high activity and selectivity in aqueous solution at high current density under ambient temperature and pressure. In particular, the sp-/sp²-hybridized graphdiyne catalyst allows the selective hydrogenation of cis-trans isomeric olefins. The chemical and electronic structure of the GDY results in the incomplete charge transfer between GDY and Cu atoms to optimize the adsorption/desorption of the reaction intermediates and results in high reaction selectivity and activity for hydrogenation reactions.     

Density functional theory study of the oxidation of ammonia on the IrO2(110) surface

In this study, we employed density functional theory (DFT) to investigate the oxidation of ammonia (NH(3)) on the IrO(2)(110) surface. We characterized the possible reaction pathways for the dehydrogenation of NH(x) species (x = 1-3) and for the formation of the oxidation products N(2), N(2)O, NO, NO(2), and H(2)O. The presence of oxygen atoms on coordinatively unsaturated sites (O(cus)) of the oxygen-rich IrO(2)(110) surface promotes the oxidation of NH(3) on the surface. In contrast, NH(3) molecules prefer undergoing desorption over oxidation on the stoichiometric IrO(2)(110) surface. Moreover, the O(cus) atoms are also the major oxidants leading to the formation of oxidation products; none of the oxidations mediated by the bridge oxygen atoms were favorable reactions. The energy barrier for formation of H(2)O as a gaseous oxidation product on the IrO(2)(110) surface is high (from 1.83 to 2.29 eV), potentially leading to the formation of nitrogen-atom-containing products at high temperature. In addition, the selectivity toward the nitrogen-atom-containing products is dominated by the coverage of O(cus) atoms on the surface; for example, a higher coverage of O(cus) atoms results in greater production of nitrogen oxides (NO, NO(2)).