Molecular Simulations of Tilted Chain Crystal - Amorphous Interfaces in Polymers

ABSTRACTSemi-crystalline polymeric materials exhibit metastable interfaces which must simultaneously feature molecular connectivity through chain bonding and disorder across the interface. To address this, off lattice molecular simulations have been constructed to capture the structure and properties of crystal-amorphous interfaces in polyethylene with freely rotating chains. Monte-Carlo simulations were performed on systems having {001 }, {201} and {502} interfaces (polymer chains tilted to the lamella normal by 0°, 34.4° and 41° respectively.)Results of the simulations reveal changes in interfacial structure with variation in the chain-tilt angle. The degree of tight folding decreases with increasing tilt, from predominantly [110] loops in the {001} interface to [200] and [310] loops on the other interfaces. The topology shifts towards an increase in loosely folded loops along with longer bridges and tails. The results also compare well with a Gaussian chain length distribution model. The {201} interface exhibits the lowest interfacial energy, in apparent agreement with experimental data.

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Properties of starch from potatoes differing in glycemic index

Food & Function ◽

10.1039/c4fo00354c ◽

2014 ◽

Vol 5 (10) ◽

pp. 2509-2515 ◽

Cited By ~ 23

Author(s):

Kai Lin Ek ◽

Shujun Wang ◽

Jennie Brand-Miller ◽

Les Copeland

Keyword(s):

Size Distribution ◽

Hydrothermal Treatment ◽

Glycemic Index ◽

Length Distribution ◽

Potato Cultivar ◽

Granule Size ◽

The Other ◽

Chain Length Distribution ◽

Potato Starches ◽

Low Glycemic Index

Starch from a low glycemic index (GI) potato cultivar (Carisma, shown in the ESEM image) was more resistant to hydrothermal treatment than other potato starches, but was not differentiated from the other starches by granule size distribution, amylose and P contents, and amylopectin chain length distribution.

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Method of Moments Applied to Most-Likely High-Temperature Free-Radical Polymerization Reactions

Processes ◽

10.3390/pr7100656 ◽

2019 ◽

Vol 7 (10) ◽

pp. 656 ◽

Cited By ~ 5

Author(s):

Hossein Riazi ◽

Ahmad Arabi Shamsabadi ◽

Michael Grady ◽

Andrew Rappe ◽

Masoud Soroush

Keyword(s):

High Temperature ◽

Free Radical ◽

Radical Polymerization ◽

Chain Length ◽

Method Of Moments ◽

Length Distribution ◽

Free Radical Polymerization ◽

Polymer Chains ◽

Rate Equations ◽

Chain Length Distribution

Many widely-used polymers are made via free-radical polymerization. Mathematical models of polymerization reactors have many applications such as reactor design, operation, and intensification. The method of moments has been utilized extensively for many decades to derive rate equations needed to predict polymer bulk properties. In this article, for a comprehensive list consisting of more than 40 different reactions that are most likely to occur in high-temperature free-radical homopolymerization, moment rate equations are derived methodically. Three types of radicals—secondary radicals, tertiary radicals formed through backbiting reactions, and tertiary radicals produced by intermolecular chain transfer to polymer reactions—are accounted for. The former tertiary radicals generate short-chain branches, while the latter ones produce long-chain branches. In addition, two types of dead polymer chains, saturated and unsaturated, are considered. Using a step-by-step approach based on the method of moments, this article guides the reader to determine the contributions of each reaction to the production or consumption of each species as well as to the zeroth, first and second moments of chain-length distributions of live and dead polymer chains, in order to derive the overall rate equation for each species, and to derive the rate equations for the leading moments of different chain-length distributions. The closure problems that arise are addressed by assuming chain-length distribution models. As a case study, β-scission and backbiting rate coefficients of methyl acrylate are estimated using the model, and the model is then applied to batch spontaneous thermal polymerization to predict polymer average molecular weights and monomer conversion. These predictions are compared with experimental measurements.

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The selectivity of nanoparticles for polydispersed ligand chains during the grafting-to process: a computer simulation study

Physical Chemistry Chemical Physics ◽

10.1039/c7cp07818h ◽

2018 ◽

Vol 20 (3) ◽

pp. 2066-2074 ◽

Cited By ~ 2

Author(s):

Ji-Yuan Xing ◽

Zhong-Yuan Lu ◽

Hong Liu ◽

Yao-Hong Xue

Keyword(s):

Computer Simulation ◽

Chain Length ◽

Simulation Study ◽

Length Distribution ◽

Reaction Model ◽

Polymer Chains ◽

Polydispersity Index ◽

Computer Simulation Study ◽

Chain Length Distribution ◽

Grafting Density

By constructing a grafting-to reaction model of polydispersed polymer chains to bind onto nanoparticles (NPs), we elucidate the changes of grafting density, polydispersity index and chain length distribution of grafted ligand chains as a dependence of the feeding polymer chains.

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Direct Observation of Chain Lengths and Conformations in Oligofluorene Distributions from Controlled Polymerization by Double Electron-Electron Resonance

10.26434/chemrxiv.10002785 ◽

2019 ◽

Author(s):

Dennis Bücker ◽

Annika Sickinger ◽

Julian D. Ruiz Perez ◽

Manuel Oestringer ◽

Stefan Mecking ◽

...

Keyword(s):

Chain Length ◽

Length Distribution ◽

Catalyst System ◽

Chain Conformation ◽

Controlled Polymerization ◽

Chain Length Distribution ◽

Electron Resonance ◽

Double Electron ◽

The Individual ◽

Double Electron Electron Resonance

Synthetic polymers are mixtures of different length chains, and their chain length and chain conformation is often experimentally characterized by ensemble averages. We demonstrate that Double-Electron-Electron-Resonance (DEER) spectroscopy can reveal the chain length distribution, and chain conformation and flexibility of the individual n-mers in oligo-(9,9-dioctylfluorene) from controlled Suzuki-Miyaura Coupling Polymerization (cSMCP). The required spin-labeled chain ends were introduced efficiently via a TEMPO-substituted initiator and chain terminating agent, respectively, with an in situ catalyst system. Individual precise chain length oligomers as reference materials were obtained by a stepwise approach. Chain length distribution, chain conformation and flexibility can also be accessed within poly(fluorene) nanoparticles.

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Investigation of Ring and Star Polymers in Confined Geometries: Theory and Simulations

Entropy ◽

10.3390/e23020242 ◽

2021 ◽

Vol 23 (2) ◽

pp. 242

Author(s):

Joanna Halun ◽

Pawel Karbowniczek ◽

Piotr Kuterba ◽

Zoriana Danel

Keyword(s):

Star Polymers ◽

Polymer Chains ◽

The Other ◽

Nano Particles ◽

Dilute Solution ◽

Confined Geometries ◽

Density Profiles ◽

Ideal Ring ◽

Ring Polymer ◽

Monomer Density

The calculations of the dimensionless layer monomer density profiles for a dilute solution of phantom ideal ring polymer chains and star polymers with f=4 arms in a Θ-solvent confined in a slit geometry of two parallel walls with repulsive surfaces and for the mixed case of one repulsive and the other inert surface were performed. Furthermore, taking into account the Derjaguin approximation, the dimensionless layer monomer density profiles for phantom ideal ring polymer chains and star polymers immersed in a solution of big colloidal particles with different adsorbing or repelling properties with respect to polymers were calculated. The density-force relation for the above-mentioned cases was analyzed, and the universal amplitude ratio B was obtained. Taking into account the small sphere expansion allowed obtaining the monomer density profiles for a dilute solution of phantom ideal ring polymers immersed in a solution of small spherical particles, or nano-particles of finite size, which are much smaller than the polymer size and the other characteristic mesoscopic length of the system. We performed molecular dynamics simulations of a dilute solution of linear, ring, and star-shaped polymers with N=300, 300 (360), and 1201 (4 × 300 + 1-star polymer with four arms) beads accordingly. The obtained analytical and numerical results for phantom ring and star polymers are compared with the results for linear polymer chains in confined geometries.

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Comparative Study of Ag Nanostructures: Molecular Simulations, Electrochemical Behavior, and Antibacterial Effect

Journal of Nanomaterials ◽

10.1155/2016/9372056 ◽

2016 ◽

Vol 2016 ◽

pp. 1-9 ◽

Cited By ~ 4

Author(s):

Álvaro de Jesús Ruíz-Baltazar ◽

Simón Yobanny Reyes-López ◽

D. Larrañaga ◽

R. Pérez

Keyword(s):

Cyclic Voltammetry ◽

Ethylene Glycol ◽

Comparative Study ◽

Sodium Borohydride ◽

Electrochemical Behavior ◽

Antibacterial Effect ◽

Chemical Reduction ◽

Molecular Simulations ◽

The Other ◽

E Coli

Nanoparticles of Ag with different sizes and structures were obtained and studied. Two methods for reductions of Ag ions were employed, chemical reduction by sodium borohydride and ethylene glycol. Cuboctahedral and icosahedral structures were obtained. Molecular simulations were carried out in order to evaluate the reactivity of both structures. On the other hand, the electrochemical activity and antibacterial effect (E. coli) of the cuboctahedral and icosahedral structures were measured experimentally. The results obtained by molecular simulation, cyclic voltammetry, and antibacterial effect were compared and discussed in this work.

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Natural variation in rice starch synthase IIa affects enzyme and starch properties

Functional Plant Biology ◽

10.1071/fp04009 ◽

2004 ◽

Vol 31 (7) ◽

pp. 671 ◽

Cited By ~ 108

Author(s):

Takayuki Umemoto ◽

Noriaki Aoki ◽

Hongxuan Lin ◽

Yasunori Nakamura ◽

Naoyoshi Inouchi ◽

...

Keyword(s):

Amino Acid ◽

Natural Variation ◽

Oryza Sativa L ◽

Length Distribution ◽

Starch Synthase ◽

Rice Starch ◽

Nucleotide Polymorphisms ◽

Cultivated Rice ◽

Chain Length Distribution ◽

Starch Properties

The natural variation in starch synthase IIa (SSIIa) of rice (Oryza sativa L.) was characterised using near-isogenic lines (NILs). SSIIa is a candidate for the alk gene regulating the alkali disintegration of rice grains, since both genes are genetically mapped at the same position on chromosome 6 and related to starch properties. In this study, we report that the alkali-susceptible cultivar Nipponbare lacked SSIIa activity in endosperm. However, the activity was detected with NILs having the alk allele of alkali-tolerant Kasalath. SSIIa protein was present even in Nipponbare endosperm, but it was not associated with starch granules at the milky stage of endosperm. Three single-nucleotide polymorphisms (SNPs) predicting amino acid substitutions existed between the cDNA sequences of SSIIa of Nipponbare and Kasalath were genotyped with 65 rice cultivars and four wild relatives of cultivated rice. The results obtained explain the potential importance of two of the amino acid residues for starch association of rice SSIIa. An analysis of the chain-length distribution of β-limit dextrin of amylopectin showed that without SSIIa activity, the relative number of A-chains (the short chains without branches) increased and that of B1-chains (the short chains with branches) decreased. This suggests that, given the SSIIa defect, short A-chains could not reach a sufficient length for branching enzymes to act on them to produce B1-chains.

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