Crystallization Of Polymer Chains Research Articles

Crystallization and melting of polymer chains on graphene and graphene oxide.

This study employs all-atomistic (AA) molecular dynamics (MD) simulations to investigate the crystallization and melting behavior of polar and nonpolar polymer chains on monolayers of graphene and graphene oxide (GO). Polyvinyl alcohol (PVA) and polyethylene (PE) are used as representative polar and nonpolar polymers, respectively. A modified order parameter is introduced to quantify the degree of two-dimensional (2D) crystallization of polymer chains. Our results show that PVA and PE chains exhibit significantly different crystallization behavior. PVA chains tend to form a more rounded, denser, and folded-stemmed lamellar structure, while PE chains tend to form an elongated straight pattern. The presence of oxidation groups on the GO substrate reduces the crystallinity of both PVA and PE chains, which is derived from the analysis of modified order parameter. Meanwhile, the crystallization patterns of polymer chains are influenced by the percentage, chemical components, and distribution of the oxidation groups. In addition, our study reveals that 2D crystalized polymer chains exhibit different melting behavior depending on their polarity. PVA chains exhibit a more molecular weight-dependent melting temperature than PE chains, which have a lower melting temperature and are relatively insensitive to molecular weight. These findings highlight the critical role of substrate and chain polarity in the crystallization and melting of polymer chains. Overall, our study provides valuable insights into the design of graphene-based polymer heterostructures and composites with tailored properties.

Cold Crystallization of Glassy Polylactide during Solvent Crazing.

Uniaxial tension accompanied by the orientation and crystallization of polymer chains is one of the powerful methods for the improvement of mechanical properties. Crystallization of amorphous isotropic polylactide (PLA) at room temperature is studied for the first time during the drawing of films in the presence of liquid adsorption-active media (ethanol, water-ethanol mixtures, and n-heptane) by the solvent crazing mechanism. The crystalline structure arises only under simultaneous actions of a liquid medium and a tensile stress and does not depend on the nature of the environment. The degree of polymer crystallinity increases nearly linearly with the growth in the fraction of the fibrillar material and reaches a maximum value of 42-45%. It has been stated that polymer crystallization happens in crazes involving nanofibrils with a diameter of about 10-20 nm without affecting the bulk polymer parts. Wide-angle X-ray scattering has been used to confirm that the crazing-induced crystallization is accompanied by the formation of the α'-crystalline phase with crystallite sizes (X-ray coherent scattering region) of 3-5 nm, depending on the nature of the liquid medium. After stretching in liquid media to a high tensile strain, the strength of a PLA film has increased to 200 MPa.

Branched Crystalline Patterns Formed Around Poly(ethylene oxide) Dots in Humidity

Branched patterns reminiscent of diffusion-limited aggregation form around poly(ethylene oxide) dots on Au surfaces in humidity by crystallization of polymer chains in water-assisted diffusion, involving fractal-like structure and dense branching-like morphology (DBM). Higher humidity leads to a slower growth of crystal lamellae. Crystal growth promotes outward diffusion. Fractal-like lamellae are viewed flat-on. Due to the reduction of chain availability in the diffusion field, the fractal-like structure turns into DBM.

A differential scanning calorimetry study on poly(ethylene terephthalate) isothermally crystallized at stepwise temperatures: multiple melting behavior re-investigated

The multiple melting behavior of poly(ethylene terephthalate) (PET) was investigated with differential scanning calorimetry (DSC) by examining PET samples having been subjected to special schemes of crystallization and annealing treatment at multiple descending temperatures. Upon such step-wise annealing in decreasing temperatures, the existence of doublet melting peaks in addition to a series of multiple minor peaks in the PET has been demonstrated using carefully designed thermal schemes. Using the Hoffman theory, multiple lamellae populations, might be suggested to be simultaneously present in the PET subjected to such thermal treatments. However, direct experimental evidence has yet to be provided. The low-temperature minor crystals simply melt during normal scanning without having time enough to reorganize into higher-melt crystals. Nevertheless, the effect of scanning on non-isothermal crystallization does exist but is primarily confined to the temperature range much below the main melting region where the crystallization of polymer chains can progress at a reasonable rate. At higher temperatures near the main melting region, annealing for extended times is required in order to result in relative changes of the melting endotherms of the upper and lower peaks in the main melting doublet. In all we have shown that interpretations of the multiple melting phenomenon in semicrystalline polymers can be better refined.

Crystallization of nanoscale-confined diblock copolymer chains

Crystallization of polymer chains between hard glassy walls or between amorphous domains in a nanoscale lamellar structure has been observed using simultaneous small-angle and wide-angle X-ray scattering (SAXS/WAXS). Semicrystalline symmetric diblock copolymers containing poly(ethylene) (PE) and a room-temperature glassy or amorphous component were shear oriented in the high temperature lamellar melt, then quenched below the PE melt temperature. For the glassy sample, the orientation of chain-folded PE stems was deduced from SAXS/WAXS peak positions to be parallel to the lamellar interface. Diffuse scattering bars consistent with lateral positional correlations of the PE crystallites were observed only in the SAXS patterns for the glassy sample with the X-rays incident parallel to the lamellae. In contrast, in a sample containing amorphous lamellae, PE crystallization occurred with weak crystallite orientation and no lateral positional correlations of crystallites.

Silica-poly(dimethylsiloxane) mixtures: n.m.r. approach to the crystallization of adsorbed chains

This work deals with the crystallization of polymer chains within silica-poly(dimethylsiloxane) mixtures, irrespective of the type of crystalline structure that is actually present in the system. An analysis of the transverse magnetization relaxation function is proposed as a method for melting point determination as well as for determination of the extent of crystallization as a function of time during an isothermal crystallization. We first pay attention to pure poly(dimethylsiloxane) (PDMS), for which we have measured the enthalpy of fusion per mole of structural units and defined the isothermal crystallization kinetics. The results obtained for the mixtures are compared to those obtained for pure PDMS. It turns out that the presence of silica particles does not affect the dimensionality of the crystalline growth. However, it reduces the extent of crystallization and has two antagonistic effects on the overall rate of crystallization. The first is a nucleation effect which is dominant at low silica volume fractions, and the second effect is a topological constraint which becomes dominant and hinders the crystalline growth at high silica volume fractions. As a result of the competition between these two effects, the overall rate of crystallization goes through a maximum with increasing silica volume fraction.

Morphology and structure of polymer electrets and ferroelectric polymers

The author considers how the heterogeneous microstructure of semicrystalline polymers used in electret applications can influence the mechanisms of charge trapping and charge transport. The crystallization of polymer chains is described, and the control of the semicrystalline morphology is discussed. Ferroelectric properties essentially controlled by the structure of the crystals are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>