Prediction of Mechanical Properties of Polymers With Various Force Fields

The effect of force field type on the predicted elastic properties of a polyimide is examined using a multiscale modeling technique. Molecular Dynamics simulations are used to predict the atomic structure and elastic properties of the polymer by subjecting a representative volume element of the material to bulk and shear finite deformations. The elastic properties of the polyimide are determined using three force fields: AMBER, OPLS-AA, and MM3. The predicted values of Young s modulus and shear modulus of the polyimide are compared with experimental values. The results indicate that the mechanical properties of the polyimide predicted with the OPLS-AA force field most closely matched those from experiment. The results also indicate that while the complexity of the force field does not have a significant effect on the accuracy of predicted properties, small differences in the force constants and the functional form of individual terms in the force fields determine the accuracy of the force field in predicting the elastic properties of the polyimide

Effects of milling on the physicochemical characteristics of waxy rice in Taiwan

Three types of mills and six milling methods were employed to mill two waxy rice varieties (TCSW1, long grain; TCW70, short grain), and the physicochemical and functional properties of rice flour were examined. The results showed that dry-milling maintained a higher level of the chemical components than other milling methods. Wet-milling slightly increased solubility as test temperatures increased, and significantly increased swelling power at 75 and 85 degrees C for TCSW1 and TCW70, respectively. Hammer and semi-dry hammer milling gave higher percentages of coarse particles (100-300 mu m); cyclone and turbo milling led to a more even particle-size distribution, and the wet-milling gave the finest particles (10-30 mu m) Dry hammer-milled rice had higher gelatinization and pasting temperatures, and semi-dry grinding milling resulted in the lowest pasting temperature, setback viscosity, and enthalpy value among the mills. The final quality of the two waxy rice varieties was profoundly affected by the mill type and milling method

Physicochemical and morphological analyses on damaged rice starches

Two types of rice cultivars, indica type (Tainung Sen 19, TNuS19) and waxy (Taichung Waxy 70, TCW70) were used as samples to investigate the changes in the physicochemical properties of damaged rice starch by ball-milling treatment. Rapid Visco Analyzer (RVA) analysis indicated that onset temperature (T-O,T-eta), peak viscosity (P), setback (C-H), and cold-paste viscosity (C) decreases were more pronounced in TNuS19 than in TCW70 starch during the ball-milling treatment. Similar phenomena were also found in peak temperature (T-p) and,enthalpy changes (DeltaH) by differential scanning calorimetry (DSC), and the peak intensities measured by X-ray diffraction. However, both types of starch showed that extended treatment time resulted in higher median particle size (PS 50). Polarized light micrographs showed that damaged starch granules lost their birefringence, suggesting that the order structure of starch granule was disrupted. The morphological changes in the microstructure of rice starch during ball-milling treatment was also examined by scanning electron microscopy (SEM). The results indicated that TNuS19 starch granules may be more susceptible to mechanical action than TCW70 starch

Hydrothermal synthesis, crystal structure, solid-state NMR spectroscopy, and ionic conductivity of Na5InSi4O12, a silicate containing a single 12-membered ring

Na5InSi4O12 has been synthesized by a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction and solid-state NMR spectroscopy. It is isotypic to Na5ScSi4O12. The structure consists of 12-membered single rings of corner-sharing SiO4 tetrahedra linked together via corner sharing by single InO6 octahedra to form a 3-D framework that delimits two types of channels along the c-axis. There are six independent sodium sites. The Na atoms within the 12-ring channels are immobile and the Na atoms within 7-ring channels are highly mobile. The Si-29 MAS NMR exhibits one Q(3) and one Q(4) resonance, each of which is split into two peaks because of inequivalent chemical environments caused by partially occupied Na sites in the 7-ring channels. Na ion conductivity measurements on a pressed pellet of the title compound were performed. The Arrhenius plot of dc conductivity shows a change in slope near 220 degreesC. We attribute this to the activation of the Na site that is situated between 7-ring channels and may serve as a connecting link between the channels. Crystal data: trigonal, space group R-3c (No. 167), a = 21.7158(9) Angstrom, c = 12.4479(7) Angstrom, and Z = 18