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Various linear hydrocarbons in nature such as n-alkanes are usually found as mixtures of molecules of various chain-lengths. Molecular mechanisms of self-organization and underlying molecular motions in the mixtures are of great scientific and technological interest. By molecular dynamics simulations we here study crystallization in mixtures and diffusion in crystals in multicomponent systems of n-alkanes...
The crystal structures of poly(nonamethyleneoxamide) (nylon-9,2) were investigated by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry. Nylon-9,2 shows a polymorphism with two different structures depending on the conditions of sample preparation. Monoclinic form I is the dominant crystalline phase for the solution-crystallized sample. For melt-crystallized samples, form I...
Poly (2-methyl-1,8-octametyleneoxamide) (nylon-MOMD-2) was prepared from dibutyl oxalate and 2-methyl-1,8-octamethylenediamine. The chemical structure was investigated by 13 C nuclear magnetic resonance ( 13 C NMR). The 13 C NMR spectrum revealed that the methyl groups distribute among the four β-sites at random. The crystal structure and its temperature dependence were also...
Fiber formation from highly stretched melt and mechanical deformation of the fiber are investigated by molecular dynamics simulations. Polyethylene molecules of moderate chain length comprising 513 united atoms are simulated under constant temperature and stress (NTτ) conditions. Rapid crystallization into fiber structures of alternating crystalline amorphous layers is observed, where emergence of...
Kinetics of the solid–solid II–I phase transition of isotactic polybutene-1 was investigated. The fraction W I of phase I as a function of time t tr during the phase transition was measured by X-ray diffraction at various temperatures T tr . The Avrami indices n of the W I –t tr plots are approximately unity for T tr >288K. A bell-shaped temperature...
Crystalline polymers are very interesting and useful materials with great versatility through their potential morphology control. Recent surge in computer modeling studies has its origin both in increasing need for efficient methods of materials' design and in tremendous developments in computer power that is expected to meet the need. In this paper, we briefly survey the present state of computer...
Dynamic viscoelastic properties of a series of cyclic olefin copolymers have been investigated. The specimens differ in total molecular weight as well as molecular weight between entanglements. The angular frequency (ω) dependence curves of dynamic storage and loss moduli (G′ and G″, respectively) of the specimens have shown that G′ ∝ ω 2 and G″ ∝ ω in the terminal region, and a plateau region...
Molecular pathways to polymer crystallization and the structures of crystal-melt interfaces are investigated by molecular dynamics simulation. We adopt a simplified molecular model for polymethylene-like chains; the chain is made of CH 2 -like beads connected by harmonic springs, and the lowest energy conformation is a linear stretched sequence of the beads with slight bending stiffness being...
The interdiffusion process of n-alkane molecules in the crystal and the temperature dependence of the diffusivity are investigated in situ by optical microscopy. The optical observation of the molecular interdiffusion is possible owing to the mixing-induced solid state transition to the rotator phase; the molecularly mixed region and the low-temperature phase matrix form a sharp interphase boundary...
Molecular processes in large uniaxial stretching of amorphous polyethylene are studied by molecular dynamics simulation. An initial isotropic amorphous sample nearly free from internal strain is made at 200 K with the aid of Monte Carlo chain generation followed by relaxation of residual strain by the molecular dynamics simulation. The initial sample is cooled to 100 K, and then subjected to a uniaxial...
The interdiffusion of n-alkane molecules in the crystal state is investigated in the binary system of C 21 H 44 and C 23 H 48 . A mechanical junction between a single crystal of C 23 and polycrystalline C 21 is held at a temperature just above the transition to the rotator phase in C 21 , and optical changes...
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