A theoretical methodology based on quantum chemistry to calculate mechanical properties of polymer crystals has been developed and applied to representative polymers. By density functional theory calculations including a dispersion force correction under three-dimensional periodic boundary conditions, crystal structures of poly(methylene oxide) (PMO), polyethylene (PE), poly(ethylene terephthalate) (PET), poly(trimethylene terephthalate) (PTT), and poly(butylene terephthalate) (PBT) were optimized and their mechanical properties, such as crystalline moduli and linear and volume compressibilities, were calculated. The optimized crystal structures were proved to be fully consistent with those determined by X-ray and neutron diffraction. The crystalline moduli ( ) parallel to the chain axis were calculated to be 114 GPa (PMO), 333 GPa (PE), 182 GPa (PET), 7.1 GPa (PTT), and 20.8 GPa (PBT) and compared with those determined from X-ray diffraction, Raman spectroscopy, and neutron inelastic scattering experiments. Herein, the values thus determined are interpreted in terms of conformational characteristics of the polymeric chains and the validity of the homogeneous stress hypothesis adopted in the X-ray diffraction method is also discussed.
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http://dx.doi.org/10.1021/acsomega.8b00506 | DOI Listing |
J Phys Chem C Nanomater Interfaces
December 2024
Department of Chemistry, College of Staten Island, Staten Island, New York 10314, United States.
Density functional theory calculations and a finite deformation method are used to calculate second- and, most notably, third-order elastic constants of amorphous silicon and amorphous silicon dioxide, as represented by model structures generated via melt-quench force-field molecular dynamics simulations. Linear and nonlinear elastic constants are used to deduce macroscopic elastic moduli, such as the bulk and shear moduli, their pressure derivatives, and the elastic Grüneisen parameter. Our calculations show that the elastic properties of amorphous silicon reach the isotropic elastic limit within the nanometer length scale, attaining characteristics, both linear and nonlinear, comparable to those of crystalline silicon.
View Article and Find Full Text PDFJ Am Chem Soc
December 2024
Department of Bioengineering, Grainger College of Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, United States.
Adipose-derived lipid droplets (LDs) are rich in triacylglycerols (TAGs), which regulate essential cellular processes, such as energy storage. Although TAG accumulation and LD expansion in adipocytes occur during obesity, how LDs dynamically package TAGs in response to excessive nutrients remains elusive. Here, we found that LD lipidomes display a remarkable increase in TAG acyl chain saturation under calorie-dense diets, turning them conducive to close-packing.
View Article and Find Full Text PDFMaterials (Basel)
November 2024
International Institute for Nanocomposites Manufacturing (IINM), WMG, University of Warwick, Coventry CV4 7AL, West Midlands, UK.
Phys Chem Chem Phys
December 2024
Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, 108840 Moscow, Russia.
We carried out an experimental ultrasonic study of polyhydric alcohols with the general chemical formula CH(OH) with an increasing number of OH groups: glycerol ( = 3), erythritol ( = 4), xylitol ( = 5), sorbitol ( = 6). The baric and temperature dependences of the elastic characteristics of these substances in the crystalline and glassy states were studied both under isothermal compression up to 1 GPa and during the isobaric heating of 77-295 K. For glycerol, glasses were obtained at different cooling rates, glass-liquid transitions were studied at different pressures.
View Article and Find Full Text PDFMolecules
October 2024
School of Mechanical Engineering, Nanjing Vocational University of Industry Technology, Nanjing 210023, China.
Fused deposition molding (FDM) is a commonly used 3D printing method, and polylactic acid (PLA) has become one of the most important raw materials for this technology due to its excellent warping resistance. However, its mechanical properties are insufficient. Polybutylene adipate terephthalate (PBAT) is characterized by high toughness and low rigidity, which can complement the performance of PLA.
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