2024-03-29T07:03:13Z
http://digitalcommons.unl.edu/do/oai/
oai:digitalcommons.unl.edu:chemengmolecular-1000
2018-08-01T23:06:48Z
publication:chemengmolecular
publication:chemengall
publication:chemicalengineer
publication:cbmefaculty
publication:cbmetimm
publication:chemeng_researchpub
Deterministic Solutions for a Step-growth Polymerization
Choi, Sungjae
Liu, Xiangdong
Timm, Delmar C.
Chain topology, including branch node, chain link and cross-link dynamics that contribute to the number of elastically active strands and junctions, are calculated using purely deterministic derivations. Solutions are not coupled to population density distributions. An eigenzeit transformation assists in the conversion of expressions derived by chemical reaction principles from time to conversion space, yielding transport phenomena type expressions where the rate of change in the molar concentrations of branch nodes with respect to conversion is expressed as functions of the fraction of reactive sites on precursors and reactants. Analogies are hypothesized to exist in cross-linking space that effectively distribute branch nodes with i reacted moieties between cross-links having j bonds extending to the gel. To obtain solutions, reacted sites on nodes or links with finite chain extensions are examined in terms of stoichiometry associated with covalent bonding. Solutions replicate published results based on Miller and Macosko’s recursive procedure and results obtained from truncated weighted sums of population density distributions as suggested by Flory.
2003-10-17T07:00:00Z
text
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https://digitalcommons.unl.edu/chemengmolecular/1
https://digitalcommons.unl.edu/context/chemengmolecular/article/1000/viewcontent/auto_convert.pdf
Papers in Molecular Chemistry
DigitalCommons@University of Nebraska - Lincoln
cross-linking
gelation
modelling
nonlinear polymers
step-growth polymerization
Chemical Engineering
oai:digitalcommons.unl.edu:chemengmolecular-1002
2018-08-01T23:12:51Z
publication:chemengmolecular
publication:chemengall
publication:chemicalengineer
publication:cbmefaculty
publication:cbmetimm
publication:chemeng_researchpub
Kinetic Reaction Analysis of an Anhydride-Cured Thermoplastic Ep-oxy:PGE/NMA/BDMA
Chian, Wei
Timm, Delmar C
A comprehensive reaction analysis of a linear epoxy resin cured with an anhydride was performed to evaluate the reaction rate expressions. Monomers included phenyl glycidyl ether and methyl- 5-norbornene-2,3-dicarboxylic anhydride or nadic methyl anhydride; the catalyst was N,N-dimethylbenzylamine; the initiator was n-propanol. Emphasis was initially placed on the molar dynamics of monomeric and oligomeric molecules. Molecular fractionations were achieved using reversed phase, high performance liquid chromatography. Chemical reaction rate constants were examined as a function of degree of polym-erization. For the chain-initiated polymerization, the initiation rate constant was observed to be approximately 3 times greater than the propagation constant associated with oligomeric molecules. Both Poisson and Gold distributions were used to fit data. Examinations of polymeric fractions obtained by gel permeation chromatography in conjunction with a multiangle laser light scattering photometer revealed a minor side reaction that broadened the polydispersity index and resulted in the reduc-tion of the cumulative, molar concentration of molecules as a function of conversion.
2004-09-17T07:00:00Z
text
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https://digitalcommons.unl.edu/chemengmolecular/3
https://digitalcommons.unl.edu/context/chemengmolecular/article/1002/viewcontent/auto_convert.pdf
https://digitalcommons.unl.edu/context/chemengmolecular/article/1002/filename/0/type/additional/viewcontent/Document.doc
Papers in Molecular Chemistry
DigitalCommons@University of Nebraska - Lincoln
Chemical Engineering
oai:digitalcommons.unl.edu:chemengmolecular-1001
2018-08-01T23:11:48Z
publication:chemengmolecular
publication:chemengall
publication:chemicalengineer
publication:cbmefaculty
publication:cbmetimm
publication:chemeng_researchpub
Chemical/Mechanical Analyses of Anhydride-Cured Thermosetting Epoxys: DGEBA/NMA/BDMA
Chian, Wei
Timm, Delmar C
The chemical state of cure in a thermosetting resin was used to predict the resin’s equilibrium modulus. High performance liquid chromatography analyses of the sol fraction yielded molar dynamics for monomeric, oligomeric, and polymeric molecules. Their population density distributions were compared with theoretical predictions based on a chain-growth polymerization mechanism. The resulting chemical estimates of the state of cure were integrated into calculations yielding concentrations of network structures within the gel that contribute to the density of elastically active strands and junctions. The theory of rubber elasticity was then used to predict the equilibrium modulus. Measurements incorporated dynamic mechanical analysis. A comprehensive understanding of the polymerization mechanism and cure history are required for accurate simulations of contributions from branch nodes and chain links. Deterministic models based solely on chemical reaction analysis were used to estimate chain connectivity with the gel. Results were interpreted using stochastic-based reasoning.
2004-09-17T07:00:00Z
text
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https://digitalcommons.unl.edu/chemengmolecular/2
https://digitalcommons.unl.edu/context/chemengmolecular/article/1001/viewcontent/auto_convert.pdf
https://digitalcommons.unl.edu/context/chemengmolecular/article/1001/filename/0/type/additional/viewcontent/Figures.doc
Papers in Molecular Chemistry
DigitalCommons@University of Nebraska - Lincoln
Chemical Engineering
oai:digitalcommons.unl.edu:chemengmolecular-1003
2018-08-01T23:16:23Z
publication:chemengmolecular
publication:chemengall
publication:chemicalengineer
publication:cbmefaculty
publication:cbmetimm
publication:cbmenoureddini
publication:chemeng_researchpub
Reaction Kinetics Analysis of Urethane Polymerization to Gelation
Liu, B
Noureddini, Hossein
Dorsey, J S
Timm, Delmar C
A chemical reaction analysis of a thermosetting, urethane resin formulated from a triol and a diisocyanate is reported. Population density distributions of oligomeric molecules, monomer concentration, the cumulative molar concentration of intramolecular bonds, the resin's average molecular weights, and extent of reaction were determined as a function of time. Rate expressions for intermolecular reactions were first order with respect to the concentration of each reactant and were proportional to the functionality of their respective chemical moieties. Rate expressions for intramolecular reactions were first order with respect to the concentration of the reactant and were proportional to the functionality of the limiting chemical moiety on the reactant. The initial ratio of the chemical equivalents and effects of dilution were incorporated into numerical simulations. Stanford and Stepto's experimental data were analyzed. Gel points and the concentration of intramolecular bonds were correlated as a function of conversion. Intramolecular reaction rate expressions derived with the aid of Gaussian chain statistics require the molar concentrations of all chemical isomers of a specified chemical composition. The present reaction rate expression allows chemical isomers to be lumped into a single population density distribution variable, substantially reducing the dimensions of the simulation. Numerical results demonstrate that the simplified rate expression is an excellent.
1993-05-01T07:00:00Z
text
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https://digitalcommons.unl.edu/chemengmolecular/4
https://digitalcommons.unl.edu/context/chemengmolecular/article/1003/viewcontent/auto_convert.pdf
Papers in Molecular Chemistry
DigitalCommons@University of Nebraska - Lincoln
Chemical Engineering
oai:digitalcommons.unl.edu:chemengmolecular-1004
2018-08-01T23:18:40Z
publication:chemengmolecular
publication:chemengall
publication:chemicalengineer
publication:cbmefaculty
publication:cbmetimm
publication:cbmenoureddini
publication:chemeng_researchpub
Kinetic Analysis of Competing Intramolecular and Intermolecular Polymerization Reactions
Noureddini, Hossein
Timm, Delmar C
ABSTRACT: Kinetic reaction theory was used to model a step-growth, thermoset polymerization of a monomer of even functionality/. Intermolecular additions were represented by second-order and intramolecular reactions were expressed by first-order rate expressions. All functional groups were assumed to react with equal reactivity. Independent variables are degree of polymerization i, extent of cross-linking j, and conversion p. The normalized rate constant for intramolecular reactions is c. The solution for the normalized population density distribution............ subj Formulae for the number-, mass-, and cross-link-average molecular weights were derived.
1992-01-01T08:00:00Z
text
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https://digitalcommons.unl.edu/chemengmolecular/5
https://digitalcommons.unl.edu/context/chemengmolecular/article/1004/viewcontent/auto_convert.pdf
Papers in Molecular Chemistry
DigitalCommons@University of Nebraska - Lincoln
Chemical Engineering
oai:digitalcommons.unl.edu:chemengmolecular-1005
2018-08-01T23:19:37Z
publication:chemengmolecular
publication:chemengall
publication:chemicalengineer
publication:cbmefaculty
publication:cbmetimm
publication:cbmenoureddini
publication:chemeng_researchpub
First Shell Substitution Effects: Diglyeidyl Ether of Bisphenol A cured with 4,4'-Diaminodiphenylmethane
Noureddini, Hossein
Timm, Delmar C
First shell substitution effects were incorporated into a kinetic reaction model descriptive of the polymerization of an epoxy resin formulated from diglycidyl ether of bisphenol A and 4,4'-diaminodiphenylmethane. Analysis of populaiion density distribution dynamics for the hardener and several oligomers in the sol fraction showed that the reactivity of secondary amino hydrogens is less than the reactivity of primary amino hydrogens.
1994-04-01T08:00:00Z
text
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https://digitalcommons.unl.edu/chemengmolecular/6
https://digitalcommons.unl.edu/context/chemengmolecular/article/1005/viewcontent/auto_convert.pdf
Papers in Molecular Chemistry
DigitalCommons@University of Nebraska - Lincoln
Chemical Engineering
oai:digitalcommons.unl.edu:chemengmolecular-1006
2006-10-31T18:10:05Z
publication:chemengmolecular
publication:chemengall
publication:chemicalengineer
publication:chemeng_researchpub
Direct Measurement of Ion Accumulation at the Electrode Electrolyte Interface under an Oscillatory Electric Field
Saraf, Dr.Ravi
The ionic charge accumulation at the metal-electrolyte interface is directly measured by using differential interferometry as a function of magnitude and frequency (2-50 kHz) of extemal electric field. The technique developed probes the ion dynamics confined to the electrical double layer. The amplitude of modulation of the ions is linearly proportional to the amplitude of applied potential. The linearity is observed up to high electrode potentials and salt concentrations. The frequency response of the ion dynamics at the interface is interpreted in terms of the classical RC model.
2006-04-12T07:00:00Z
text
https://digitalcommons.unl.edu/chemengmolecular/7
Papers in Molecular Chemistry
DigitalCommons@University of Nebraska - Lincoln
Chemical Engineering
oai:digitalcommons.unl.edu:chemengmolecular-1007
2007-01-10T19:30:14Z
publication:cbmesaraf
publication:chemengmolecular
publication:chemengall
publication:chemicalengineer
publication:cbmefaculty
publication:chemeng_researchpub
Stability of Order in Solvent-Annealed Block Copolymer Thin Films
Saraf, Dr.Ravi F.
Niu, Sanjun
One way to produce high order in a block copolymer thin film is by solution casting a thin film and slowly evaporating the solvent in a sealed vessel. Such a solvent-annealing process is a versatile method to produce a highly ordered thin film of a block copolymer. However, the ordered structure of the film degrades over time when stored under ambient conditions. Remarkably, this aging process occurs in mesoscale thin films of polystyrene-polyisoprene triblock copolymer where the monolayer of vitrified 15 nm diameter polystyrene cylinders sink in a 20 nm thick film at 22 °C. The transformation is studied by atomic force microscopy (AFM). We describe the phenomena, characterize the aging process, and propose a semiquantitative model to explain the observations. The residual solvent effects are important but not the primary driving force for the aging process. The study may lead to effective avenue to improve order and make the morphology robust and possibly the solvent-annealing process more effective.
2002-08-07T07:00:00Z
text
https://digitalcommons.unl.edu/chemengmolecular/8
Papers in Molecular Chemistry
DigitalCommons@University of Nebraska - Lincoln
solvent-annealing process
atomic force microscopy (AFM)
copolymer
Chemical Engineering