Chain-End Modification: A Starting Point for Controlling Polymer Crystal Nucleation

2021 ◽  
Vol 54 (4) ◽  
pp. 1599-1610
Author(s):  
Kyle Wm. Hall ◽  
Simona Percec ◽  
Wataru Shinoda ◽  
Michael L. Klein
Keyword(s):  
Crystal Nucleation ◽  
Polymer Crystal ◽  
Starting Point

scholarly journals Monodisperse Polymer Melts Crystallize via Structurally Polydisperse Nanoscale Clusters: Insights from Polyethylene

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 447 ◽  
Author(s):  
Kyle Wm. Hall ◽  
Timothy W. Sirk ◽  
Simona Percec ◽  
Michael L. Klein ◽  
Wataru Shinoda
Keyword(s):  
Large Scale ◽  
Polymer Melts ◽  
Polymeric Materials ◽  
Crystalline Polymer ◽  
Crystal Nucleation ◽  
Stem Length ◽  
Polymer Crystal ◽  
Polyethylene Melts ◽  
Nanoscale Clusters ◽  
Entangled Polymer Melts

This study demonstrates that monodisperse entangled polymer melts crystallize via the formation of nanoscale nascent polymer crystals (i.e., nuclei) that exhibit substantial variability in terms of their constituent crystalline polymer chain segments (stems). More specifically, large-scale coarse-grain molecular simulations are used to quantify the evolution of stem length distributions and their properties during the formation of polymer nuclei in supercooled prototypical polyethylene melts. Stems can adopt a range of lengths within an individual nucleus (e.g., ∼1–10 nm) while two nuclei of comparable size can have markedly different stem distributions. As such, the attainment of chemically monodisperse polymer specimens is not sufficient to achieve physical uniformity and consistency. Furthermore, stem length distributions and their evolution indicate that polymer crystal nucleation (i.e., the initial emergence of a nascent crystal) is phenomenologically distinct from crystal growth. These results highlight that the tailoring of polymeric materials requires strategies for controlling polymer crystal nucleation and growth at the nanoscale.

scholarly journals Polymer Nucleation under High-Driving Force, Long-Chain Conditions: Heat Release and the Separation of Timescales

2018 ◽  
Author(s):  
Kyle Hall ◽  
Simona Percec ◽  
Michael Klein
Keyword(s):  
Conformational Changes ◽  
Driving Forces ◽  
Early Stage ◽  
Polymer Crystallization ◽  
Crystal Nucleation ◽  
Crystal Formation ◽  
Polymer Crystal ◽  
Dynamics Simulations ◽  
New Research ◽  
Chain Level

<p>This study reveals two important features of polymer crystal formation at high-driving forces in entangled polymer melts based on molecular dynamics simulations of polyethylene, a prototypical polymer. First, in contrast to existing literature on small-molecule crystallization, it is demonstrated that the heat released during polymer crystallization does not appreciably influence molecular-level structural details of early-stage, crystalline clusters (i.e., polymer crystal nuclei). Second, it is revealed that early-stage polymer crystallization (i.e., crystal nucleation) can occur without substantial chain-level relaxation and conformational changes, which is consistent with previous experimental work and yet in contrast to many previous computational studies. Given the conditions used to process polyethylene, the separation of timescales associated with crystallization and chain-level processes is anticipated to be of substantial importance to processing strategies. This study thus provides insights that highlight new research directions for understanding polymer crystallization under industrially-relevant conditions while also providing guidance as to how this work can be undertaken.</p>

scholarly journals Property Decoupling across the Embryonic Nucleus–Melt Interface during Polymer Crystal Nucleation

2020 ◽  
Vol 124 (23) ◽  
pp. 4793-4804
Author(s):  
Kyle Wm. Hall ◽  
Simona Percec ◽  
Wataru Shinoda ◽  
Michael L. Klein
Keyword(s):  
Crystal Nucleation ◽  
Polymer Crystal

scholarly journals Application of the Nucleation Theorem to Crystallization of Liquids: Some General Theoretical Results

Entropy ◽  
2019 ◽  
Vol 21 (12) ◽  
pp. 1147 ◽  
Author(s):  
Jürn W. P. Schmelzer
Keyword(s):  
Liquid Phase ◽  
Basic Assumption ◽  
Thermodynamic Description ◽  
Heterogeneous Systems ◽  
Nucleation Theory ◽  
Crystal Nucleation ◽  
Classical Nucleation Theory ◽  
Starting Point ◽  
Component Systems ◽  
Nucleation Theorem

Different aspects in applying the nucleation theorem to the description of crystallization of liquids are analyzed. It is shown that, by employing the classical Gibbs’ approach in the thermodynamic description of heterogeneous systems, a general form of the nucleation theorem can be formulated that is valid not only for one-component but generally for multi-component systems. In this analysis, one basic assumption of classical nucleation theory is utilized. In addition, commonly employed in application to crystallization, it is supposed that the bulk properties of the critical clusters are widely identical to the properties of the newly evolving crystal phase. It is shown that the formulation of the nucleation theorem as proposed by Kashchiev [J. Chem. Phys. 76, 5098-5102 (1982)], also relying widely on the standard classical approach in the description of crystal nucleation, holds for multi-component systems as well. The general form of the nucleation theorem derived by us is taken then as the starting point for the derivation of particular forms of this theorem for the cases that the deviation from equilibrium is caused by variations of either composition of the liquid phase, temperature, or pressure. In this procedure, expressions recently developed by us for the curvature dependence of the surface tension, respectively, its dependence on pressure and/or temperature are employed. The basic assumption of classical nucleation theory mentioned above is, however, in general, not true. The bulk and surface properties of the critical crystal clusters may differ considerably from the properties of the evolving macroscopic phases. Such effects can be incorporated into the theoretical description by the application of the generalized Gibbs approach for the specification of the dependence of the properties of critical crystal clusters on the degree of metastability of the liquid phase. Applying this method, it is demonstrated that a similar formulation of the nucleation theorem, as derived based on classical nucleation theory, holds true also in cases when a dependence of the state parameters of the critical clusters on the degree of deviation from equilibrium is appropriately accounted for.

Confinement Effects in Polymer Crystal Nucleation from the Bulk to Few-Chain Systems

2006 ◽  
Vol 97 (24) ◽  
Author(s):  
Michael V. Massa ◽  
Jessica L. Carvalho ◽  
Kari Dalnoki-Veress
Keyword(s):  
Crystal Nucleation ◽  
Confinement Effects ◽  
Polymer Crystal

Polymer crystal nucleation with confinement-enhanced orientation dominating the formation of nanohybrid shish-kebabs with multiple shish

RSC Advances ◽  
2016 ◽  
Vol 6 (56) ◽  
pp. 50451-50459 ◽  
Author(s):  
Yijing Nie ◽  
Tongfan Hao ◽  
Ya Wei ◽  
Zhiping Zhou
Keyword(s):  
Crystal Nucleation ◽  
Polymer Crystal

An unexpected NHSK structure with multiple shish is observed. The aligned fillers act as multiple shish and the polymer crystal lamellae form kebabs.

A New Defect in Polyethylene Single Crystals

1973 ◽  
Vol 31 ◽  
pp. 70-71
Author(s):  
E. L. Thomas ◽  
S. L. Sass
Keyword(s):  
Single Crystals ◽  
Screw Dislocation ◽  
Small Distance ◽  
Dipole Model ◽  
Dislocation Dipole ◽  
Chain Folding ◽  
Black And White ◽  
Polymer Crystal ◽  
Different Types

In polyethylene single crystals pairs of black and white lines spaced 700-3,000Å apart, parallel to the [100] and [010] directions, have been identified as microsector boundaries. A microsector is formed when the plane of chain folding changes over a small distance within a polymer crystal. In order for the different types of folds to accommodate at the boundary between the 2 fold domains, a staggering along the chain direction and a rotation of the chains in the plane of the boundary occurs. The black-white contrast from a microsector boundary can be explained in terms of these chain rotations. We demonstrate that microsectors can terminate within the crystal and interpret the observed terminal strain contrast in terms of a screw dislocation dipole model.

Crystal structure images of large gold clusters and growing crystals by HRTEM

1984 ◽  
Vol 42 ◽  
pp. 428-429
Author(s):  
L.R. Wallenberg ◽  
J.-O. Bovin ◽  
G. Schmid
Keyword(s):  
Crystal Structure ◽  
Nucleation And Growth ◽  
Close Packing ◽  
Gold Clusters ◽  
Molecular Weight Determination ◽  
Growth Mechanisms ◽  
Starting Point ◽  
Different Types ◽  
Nucleation And Growth Mechanisms ◽  
Points Of View

Metallic clusters are interesting from various points of view, e.g. as a mean of spreading expensive catalysts on a support, or following heterogeneous and homogeneous catalytic events. It is also possible to study nucleation and growth mechanisms for crystals with the cluster as known starting point.Gold-clusters containing 55 atoms were manufactured by reducing (C6H5)3PAuCl with B2H6 in benzene. The chemical composition was found to be Au9.2[P(C6H5)3]2Cl. Molecular-weight determination by means of an ultracentrifuge gave the formula Au55[P(C6H5)3]Cl6 A model was proposed from Mössbauer spectra by Schmid et al. with cubic close-packing of the 55 gold atoms in a cubeoctahedron as shown in Fig 1. The cluster is almost completely isolated from the surroundings by the twelve triphenylphosphane groups situated in each corner, and the chlorine atoms on the centre of the 3x3 square surfaces. This gives four groups of gold atoms, depending on the different types of surrounding.

Two isoprenylated flavonoids from Dorstenia psilurus activate AMPK, stimulate glucose uptake, inhibit glucose production and lower glycemia

2019 ◽  
Vol 476 (24) ◽  
pp. 3687-3704 ◽  
Author(s):  
Aphrodite T. Choumessi ◽  
Manuel Johanns ◽  
Claire Beaufay ◽  
Marie-France Herent ◽  
Vincent Stroobant ◽  
...  
Keyword(s):  
Glucose Uptake ◽  
Human Cancer ◽  
Glucose Production ◽  
Liver Mitochondria ◽  
New Drugs ◽  
Structural Isomer ◽  
Rat Liver Mitochondria ◽  
Ionization Mass ◽  
Ampk Activation ◽  
Starting Point

Root extracts of a Cameroon medicinal plant, Dorstenia psilurus, were purified by screening for AMP-activated protein kinase (AMPK) activation in incubated mouse embryo fibroblasts (MEFs). Two isoprenylated flavones that activated AMPK were isolated. Compound 1 was identified as artelasticin by high-resolution electrospray ionization mass spectrometry and 2D-NMR while its structural isomer, compound 2, was isolated for the first time and differed only by the position of one double bond on one isoprenyl substituent. Treatment of MEFs with purified compound 1 or compound 2 led to rapid and robust AMPK activation at low micromolar concentrations and increased the intracellular AMP:ATP ratio. In oxygen consumption experiments on isolated rat liver mitochondria, compound 1 and compound 2 inhibited complex II of the electron transport chain and in freeze–thawed mitochondria succinate dehydrogenase was inhibited. In incubated rat skeletal muscles, both compounds activated AMPK and stimulated glucose uptake. Moreover, these effects were lost in muscles pre-incubated with AMPK inhibitor SBI-0206965, suggesting AMPK dependency. Incubation of mouse hepatocytes with compound 1 or compound 2 led to AMPK activation, but glucose production was decreased in hepatocytes from both wild-type and AMPKβ1−/− mice, suggesting that this effect was not AMPK-dependent. However, when administered intraperitoneally to high-fat diet-induced insulin-resistant mice, compound 1 and compound 2 had blood glucose-lowering effects. In addition, compound 1 and compound 2 reduced the viability of several human cancer cells in culture. The flavonoids we have identified could be a starting point for the development of new drugs to treat type 2 diabetes.

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