Tutorial: Determination of Thermal Boundary Resistance by Molecular Dynamics Simulations

Due to the High Surface-To-Volume Ratio of Nanostructured Components in Microelectronics and Other Advanced Devices, the Thermal Resistance at Material Interfaces Can Strongly Affect the overall Thermal Behavior in These Devices. Therefore, the Thermal Boundary Resistance, R, Must Be Taken into Account in the Thermal Analysis of Nanoscale Structures and Devices. This Article is a Tutorial on the Determination of R and the Analysis of Interfacial Thermal Transport Via Molecular Dynamics (MD) Simulations. in Addition to Reviewing the Commonly Used Equilibrium and Non-Equilibrium MD Models for the Determination of R, We Also Discuss Several MD Simulation Methods Which Can Be Used to Understand Interfacial Thermal Transport Behavior. to Illustrate How These MD Models Work for Various Interfaces, We Will Show Several Examples of MD Simulation Results on Thermal Transport Across Solid-Solid, Solid-Liquid, and Solid-Gas Interfaces. the Advantages and Drawbacks of a Few Other MD Models Such as Approach-To-Equilibrium MD and First-Principles MD Are Also Discussed

Surface Structure and Dynamic Adhesive Wettability of Wheat Straw

The structural features of wheat straw differ from those of wood. By means of an Optical Microscope (OM) and a Scanning Electron Microscope (SEM), three kinds of tissues (epidermis, parenchyma, and vascular tissue) were observed on the cross section of wheat straw. A smooth cuticle was found on the exterior surface. The exterior surface of wheat straw treated by NaOH solution at room temperature appeared to be chemically etched. After this treatment, the wettability of the exterior surface was improved substantially. In this study, using a wetting model describing the dynamic contact angle process, a parameter (K) was used to quantify the adhesive spreading and penetrating during the wetting process. By applying the wetting model, the adhesive wettabilities associated with resin type (UF, PF, and PMDI), drop location on the wheat straw surface (exterior and interior), and grain direction (along and across) were compared. The results of this study showed that PMDI resin had a lower contact angle (both initial and equilibrium) and a greater spreading and penetrating constant compared to UF and PF resins on natural (untreated) wheat straw surfaces. The K value of the interior surface was higher than that of the exterior surface for the same resin on the untreated wheat straw. In addition, the K values of the three resins on the treated wheat straw surfaces were higher than those on untreated wheat straw surfaces. This indicates that the alkali treatment was an effective method for improving the wettabilty of wheat straw surfaces. The wheat straw grain direction also significantly affected the adhesive wetting process. The K values of adhesive wetting along the wheat straw grain direction were always greater than those across the grain direction for the same resin

Spectroscopic Analysis of the Interface for Wheat Straw Specimen Glued with PMDI

In order to obtain information about chemical characteristics on the interaction between wheat straw and PMDI, the exterior and interior surfaces of wheat straw, and the interface of wheat straw specimen glued by polymeric diphenylmethane diisocyanate (PMDI) resin were scanned by micro-Fourier Transform Infrared Spectroscopy (micro-FTIR) and Electron Spectroscopy for Chemical Analysis (ESCA), respectively. The specimens of pure cellulose and the reacted mixture of cellulose with PMDI resin were analyzed by FTIR and cross polarization/magic angle spinning carbon-13 nuclear magnetic resonance (CP/MAS C-13 NMR). Scanning by micro-FTIR showed that the major differences in functional groups between exterior and interior surfaces for the same section of wheat straw appeared in the fingerprint region (400 cm-1 to 1500 cm-1). There were a few differentiated peaks in the region of 1174~1000 cm-1 for the interior surface, whereas there was greater absorption in the exterior surface than in the interior surface, especially at 987 cm-1. Generally, there were reaction functional groups (-OH) on exterior and interior surfaces for wheat straw. ESCA scanning and curve-fitting of the C1S peaks showed that the relative content of the functional group on the exterior surface differed from that of the interior surface. Results of ESCA scanning of the interface for wheat straw specimen glued with PMDI indicated that the glued interface chemically adsorbed PMDI resin. Furthermore, the contents of functional groups of the interface specimen glued with PMDI differed from those of the specimen without PMDI. Using FTIR and CP/MAS C-13 NMR, the results imply that N=C=O functional group for PMDI could react with cellulose

5,8-Dibromo-15-nitro-2,11-dithia­[3.3]paracyclo­phane

In the title compound [systematic name: 13,15-dibromo-6-nitro-3,10-dithia­tricyclo­[10.2.2.25,8]octa­deca-1(14),5,7,12,15,17-hexa­ene], C16H13Br2NO2S2, the dihedral angle between the two benzene rings is 0.93 (2)°. The crystal structure is stabilized by weak π–π inter­molecular inter­actions [centroid–centroid distance = 3.286 (5) Å]. One S atom and the H atoms on neighboring C atoms are disordered over two sets of sites (occupancy ratios: S = 0.91:0.09 and H = 0.93:0.07)