A Critique of Asphaltene Fluorescence Decay and Depolarization-Based Claims about Molecular Weight and Molecular Architecture

2008 ◽  
Vol 22 (2) ◽  
pp. 1156-1166 ◽  
Author(s):  
Otto P. Strausz ◽  
I. Safarik ◽  
E. M. Lown ◽  
A. Morales-Izquierdo
Keyword(s):  
Molecular Weight ◽  
Fluorescence Decay ◽  
Molecular Architecture

Role of molecular architecture in interfacial self-adhesion of polyethylene films

2017 ◽  
Vol 33 (3) ◽  
pp. 235-261 ◽  
Author(s):  
Zahra Najarzadeh ◽  
Abdellah Ajji
Keyword(s):  
Molecular Weight ◽  
Adhesion Strength ◽  
Film Surface ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Molecular Architecture ◽  
Melt Temperature ◽  
Long Chain ◽  
Long Chain Branch ◽  
Chain Branch

The influence of molecular architecture on interfacial self-adhesion above polyethylene film melt temperature was examined in this study. The investigated molecular structures include molecular weight (Mw), molecular weight distribution, long chain branch amount and distribution and short chain branch among and along polyethylene chains. The long chain branches concentration was quantified using gel permeation chromatography and short branches concentration using nuclear magnetic resonance techniques. The adhesion strength was measured immediately after melt bonding using a T-Peel test. The results showed that increasing Mw resulted in higher adhesion strength in linear metallocene ethylene α-olefins. Low long chain branch concentrations hinder reptation motion and diffusion, and result in lower adhesion strength. Low density polyethylene with highly branched chains yielded very low self-adhesion. A drastic difference in adhesion strength between metallocene and conventional linear low density polyethylene is attributed to homogeneity versus heterogeneity of composition distribution. The low interfacial self-adhesion in conventional polyethylene was concluded to be due to enrichment of highly branched low molecular weight chains at the film surface. These segregated chains at the interface diffuse before the high molecular weight chains located in the bulk.

Laser-Based Mass Spectrometric Assessment of Asphaltene Molecular Weight, Molecular Architecture, and Nanoaggregate Number

2015 ◽  
Vol 29 (5) ◽  
pp. 2833-2842 ◽  
Author(s):  
Andrew E. Pomerantz ◽  
Qinghao Wu ◽  
Oliver C. Mullins ◽  
Richard N. Zare
Keyword(s):  
Molecular Weight ◽  
Mass Spectrometric ◽  
Molecular Architecture

scholarly journals Improved Cell Morphology and Surface Roughness in High-Temperature Foam Injection Molding Using a Long-Chain Branched Polypropylene

Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2404
Author(s):  
Steven Mendoza-Cedeno ◽  
Mu Sung Kweon ◽  
Sarah Newby ◽  
Maksim Shivokhin ◽  
George Pehlert ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Surface Roughness ◽  
High Temperature ◽  
Injection Molding ◽  
Cell Morphology ◽  
Molecular Architecture ◽  
Foam Injection Molding ◽  
Branched Polypropylene ◽  
Long Chain ◽  
Long Chain Branched Polypropylene

Long-chain branched polypropylene (LCB PP) has been used extensively to improve cell morphologies in foaming applications. However, most research focuses on low melt flow rate (MFR) resins, whereas foam production methods such as mold-opening foam injection molding (MO-FIM) require high-MFR resins to improve processability. A systematic study was conducted comparing a conventional linear PP, a broad molecular weight distribution (BMWD) linear PP, and a newly developed BMWD LCB PP for use in MO-FIM. The effects of foaming temperature and molecular architecture on cell morphology, surface roughness, and mechanical properties were studied by utilizing two chemical blowing agents (CBAs) with different activation temperatures and varying packing times. At the highest foaming temperatures, BMWD LCB PP foams exhibited 887% higher cell density, 46% smaller cell sizes, and more uniform cell structures than BWMD linear PP. Linear PP was found to have a surface roughness 23% higher on average than other resins. The BMWD LCB PP was found to have increased flexural modulus (44%) at the cost of decreased toughness (−88%) compared to linear PP. The branched architecture and high molecular weight of the BMWD LCB PP contributed to improved foam morphologies and surface quality in high-temperature MO-FIM conditions.

Polymer Self-Diffusion in Entangled Systems

1984 ◽  
Vol 57 (3) ◽  
pp. 523-556 ◽  
Author(s):  
Matthew Tirrell
Keyword(s):  
Molecular Weight ◽  
Reaction Rates ◽  
Current Status ◽  
Critical Conditions ◽  
Molecular Architecture ◽  
Self Diffusion ◽  
Model Free ◽  
Wide Range ◽  
Reptation Model ◽  
The Matrix

Abstract This article has focused on work in the last several years, a period during which theoretical insights and experimental techniques pertaining to polymer self-diffusion in entangled systems have advanced enormously. The point has been to lay out for the reader the means by which this information has been developed and to lay out the available information itself. The objective has been to facilitate comparisons regarding use and applicability of techniques, quality, and interpretations of data and the trends present in the various data. Presentation of the information in this style leads to a few definite conclusions and a larger number of problems which come more sharply than before into focus as ripe for continued study. Specific conclusions which seem reasonable at this point are: The molecular weight dependence of Ds is, in entangled systems, an inverse square law, consistent with the prediction of the reptation model. The self-diffusion coefficient becomes quite insensitive to the matrix molecular weight Mm at sufficiently high Mm. The variation of Ds with concentration in entangled solution is very strong, considerably higher than the c−3 law suggested by scaling arguments with the reptation model. Free volume effects on the monomeric friction coefficient are at the root of this. Outstanding problems include the following areas and questions: It is necessary to ascertain why there is, in melt Ds data, a reproducible discrepancy between NMR data and those data obtained via other methods. Is NMR sensing the slowest translational mode of motion? Is the marking which is necessary for all the other techniques affecting the measurements? In solution data, the origin of the QELS “slow mode” and the marked disparity between these data and those from other methods must be determined. Critical conditions for the onset of entangled or reptation behavior (in terms of M and c) in Ds must be studied and defined more clearly both experimentally and theoretically. Is the observation that Ds∼M−2 down to unexpectedly low molecular weight an indication that diffusion proceeds via a reptation-like mechanism even for molecular weights which show no other manifestation of entanglement, OI is there another set of conditions which produce Ds∼M−2 scaling? Incisively designed experiments to study matrix and molecular architecture effects seem likely to be most fruitful. Stars, combs, rings, and polydisperse samples hold new information on diffusion mechanisms. A comprehensive experimental and theoretical picture of polymer self-diffusion will advance the state of practice of a wide range of technological applications. The current status of available diffusion information is good enough that the time scales of many practical processes can be predicted approximately. More precise predictions of, for example, diffusion-controlled reaction rates, await the availability of more extensive data and of the resolution of some of the remaining questions and discrepancies highlighted here.

Effect of molecular weight and molecular architecture of PMMA on the phase morphology of pseudo-IPN's of PCU/PMMA

1992 ◽  
Vol 25 (26) ◽  
pp. 7334-7337 ◽  
Author(s):  
P. Zhou ◽  
X. Chen ◽  
H. L. Frisch ◽  
Z. Zhu ◽  
J. Rider ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Phase Morphology ◽  
Molecular Architecture

Evaluation of the dark field method for large association of spread DNA

1978 ◽  
Vol 36 (2) ◽  
pp. 190-191
Author(s):  
Douglas C. Barker
Keyword(s):  
Electron Microscopy ◽  
Molecular Weight ◽  
Mitochondrial Dna ◽  
Extraction Method ◽  
Field Method ◽  
Dark Field ◽  
Kinetoplast Dna ◽  
Field Electron ◽  
Field Electron Microscopy ◽  
Dark Field Electron

A number of satisfactory methods are available for the electron microscopy of nicleic acids. These methods concentrated on fragments of nuclear, viral and mitochondrial DNA less than 50 megadaltons, on denaturation and heteroduplex mapping (Davies et al 1971) or on the interaction between proteins and DNA (Brack and Delain 1975). Less attention has been paid to the experimental criteria necessary for spreading and visualisation by dark field electron microscopy of large intact issociations of DNA. This communication will report on those criteria in relation to the ultrastructure of the (approx. 1 x 10-14g) DNA component of the kinetoplast from Trypanosomes. An extraction method has been developed to eliminate native endonucleases and nuclear contamination and to isolate the kinetoplast DNA (KDNA) as a compact network of high molecular weight. In collaboration with Dr. Ch. Brack (Basel [nstitute of Immunology), we studied the conditions necessary to prepare this KDNA Tor dark field electron microscopy using the microdrop spreading technique.

Introduction

1978 ◽  
Vol 36 (3) ◽  
pp. 543-544
Author(s):  
W. Bernard
Keyword(s):  
Molecular Weight ◽  
Electron Microscope ◽  
Nucleic Acid ◽  
Gene Mapping ◽  
Molecular Genetics ◽  
Cell Biology ◽  
Gene Activity ◽  
Close Connection ◽  
Basic Information ◽  
Simple Systems

In comparison to many other fields of ultrastructural research in Cell Biology, the successful exploration of genes and gene activity with the electron microscope in higher organisms is a late conquest. Nucleic acid molecules of Prokaryotes could be successfully visualized already since the early sixties, thanks to the Kleinschmidt spreading technique - and much basic information was obtained concerning the shape, length, molecular weight of viral, mitochondrial and chloroplast nucleic acid. Later, additonal methods revealed denaturation profiles, distinction between single and double strandedness and the use of heteroduplexes-led to gene mapping of relatively simple systems carried out in close connection with other methods of molecular genetics.

Study of the Molecular Architecture of Keratin Filaments by Electron Microscopy

1982 ◽  
Vol 40 ◽  
pp. 118-119
Author(s):  
U. Aebi ◽  
P. Rew ◽  
T.-T. Sun
Keyword(s):  
Electron Microscopy ◽  
Structural Organization ◽  
Cell Types ◽  
Structural Features ◽  
Molecular Architecture ◽  
The Past ◽  
Keratin Filaments ◽  
Different Types ◽  
10 Nm Filaments ◽  
Different Cell Types

Various types of intermediate-sized (10-nm) filaments have been found and described in many different cell types during the past few years. Despite the differences in the chemical composition among the different types of filaments, they all yield common structural features: they are usually up to several microns long and have a diameter of 7 to 10 nm; there is evidence that they are made of several 2 to 3.5 nm wide protofilaments which are helically wound around each other; the secondary structure of the polypeptides constituting the filaments is rich in ∞-helix. However a detailed description of their structural organization is lacking to date.

The External Shape of Human γ GI Immunoglobulin from Crystal Sections

1971 ◽  
Vol 29 ◽  
pp. 428-429
Author(s):  
L. W. Labaw
Keyword(s):  
Molecular Weight ◽  
Sodium Phosphate ◽  
Osmium Tetroxide ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
X Ray ◽  
Large Molecular Weight ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Crystallographic Axes

Crystals of a human γGl immunoglobulin have the external morphology of diamond shaped prisms. X-ray studies have shown them to be monoclinic, space group C2, with 2 molecules per unit cell. The unit cell dimensions are a = 194.1, b = 91.7, c = 51.6Å, 8 = 102°. The relatively large molecular weight of 151,000 and these unit cell dimensions made this a promising crystal to study in the EM.Crystals similar to those used in the x-ray studies were fixed at 5°C for three weeks in a solution of mother liquor containing 5 x 10-5M sodium phosphate, pH 7.0, and 0.03% glutaraldehyde. They were postfixed with 1% osmium tetroxide for 15 min. and embedded in Maraglas the usual way. Sections were cut perpendicular to the three crystallographic axes. Such a section cut with its plane perpendicular to the z direction is shown in Fig. 1.This projection of the crystal in the z direction shows periodicities in at least four different directions but these are only seen clearly by sighting obliquely along the micrograph.

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