Polymer-Polymer Interdiffusion

1984 ◽  
Vol 40 ◽  
Author(s):  
Edward J. Kramer
Keyword(s):  
Molecular Weight ◽  
Diffusion Mechanism ◽  
Linear Chain ◽  
Tracer Diffusion ◽  
Polymer Chains ◽  
Polymer Interfaces ◽  
Topological Constraints ◽  
Constraint Release ◽  
Polymer Interdiffusion ◽  
Kinetics Of

AbstractInterdiffusion of polymer chains plays an important role in establishing good adhesion at polymer interfaces as well as in the kinetics of phase separation and mixing in polymer blends. Reptation, a process in which a given linear chain crawls along a primitive path defined by the topological constraints due to the surrounding chains, is thought to be the most important diffusion mechanism. A reptating chain of Volecular weight M should have a tracer diffusion coefficient given by D =DR =Do M−2, where D depends on the Rouse mobility of the chain and an entang ement molecular weight, Me. Because the topological constraints are assumed to be fixed, DR is independent of the molecular weight P of the polymer into which the M-chains are diffusing. In principle however if M is large enough and P is small enough the M-chain can diffuse by rearrangement of the P-chains surrounding it, a process called constraint release. The D for this process, DCR= αCRDoMe2/(MP3), where αCR is a constant approximately equal to 13, increases strongly with decreasing P. Recent experimental results, which give evidence for both reptation and constraint release, will be reviewed. These results have important implications for the diffusion of nonlinear polymer chains, e.g. stars and rings.

scholarly journals Prediction of Viscoelastic Properties of Enzymatically Crosslinkable Tyramine–Modified Hyaluronic Acid Solutions Using a Dynamic Monte Carlo Kinetic Approach

2021 ◽  
Vol 22 (14) ◽  
pp. 7317
Author(s):  
Filippos F. Karageorgos ◽  
Costas Kiparissides
Keyword(s):  
Molecular Weight ◽  
Monte Carlo ◽  
Hyaluronic Acid ◽  
Kinetic Model ◽  
Average Molecular Weight ◽  
Polymer Concentration ◽  
Polymer Chains ◽  
Finite Sample ◽  
Dynamic Monte Carlo ◽  
Kinetics Of

The present study deals with the mathematical modeling of crosslinking kinetics of polymer–phenol conjugates mediated by the Horseradish Peroxidase (HRP)-hydrogen peroxide (H2O2) initiation system. More specifically, a dynamic Monte Carlo (MC) kinetic model is developed to quantify the effects of crosslinking conditions (i.e., polymer concentration, degree of phenol substitution and HRP and H2O2 concentrations) on the gelation onset time; evolution of molecular weight distribution and number and weight average molecular weights of the crosslinkable polymer chains and gel fraction. It is shown that the MC kinetic model can faithfully describe the crosslinking kinetics of a finite sample of crosslinkable polymer chains with time, providing detailed molecular information for the crosslinkable system before and after the gelation point. The MC model is validated using experimental measurements on the crosslinking of a tyramine modified Hyaluronic Acid (HA-Tyr) polymer solution reported in the literature. Based on the rubber elasticity theory and the MC results, the dynamic evolution of hydrogel viscoelastic and molecular properties (i.e., number average molecular weight between crosslinks, Mc, and hydrogel mesh size, ξ) are calculated.

Ion Beam Analysis of Diffusion in Polymer Melts

1984 ◽  
Vol 40 ◽  
Author(s):  
P. F. Green ◽  
P. J. Mills ◽  
C. J. Palmstrom ◽  
J. W. Mayer ◽  
E. J. Kramer
Keyword(s):  
Molecular Weight ◽  
Rutherford Backscattering Spectrometry ◽  
Ion Beam ◽  
Depth Profiling ◽  
Kirkendall Effect ◽  
Tracer Diffusion ◽  
Polymer Chains ◽  
Self Diffusion ◽  
Beam Depth ◽  
Good Agreement

AbstractTwo ion beam depth profiling methods have been used to measure the diffusion of polymer chains of molecular weight M into a matrix of polymer of molecular weight P. In the first the displacement xm of Au markers at the original interface of a diffusion couple between polystyrene with P=2×107 and a thin film of PS with M<P is measured using Rutherford backscattering spectrometry. From this modern version of the Kirkendall effect we find x=0.4t8(D*t) 0 5, where D* the tracer diffusion coefficient of the M chains at 174°C, is found to be D*=O.007M−2cm2/sec, in good agreement with the D*=DR expected for the reptation mechanism. Forward recoil spectrometry, a technique in which the energies of recoiling deuterons are detected, is used to obtain concentration profiles, and hence D*, of deuterated PS M-chains diffusing into a hydrogenated PS P-chain matrix. When P>>M, D*=0.008M−2, in good agreement with the marker data. When P<P*(M) however D*; increases greatly as P decreases; P* increases slowly with increasing M. The results are predicted quantitatively by D*=DR+DCR, where DCR=0.10Me2/(Mp 3 ) describes the diffusion of the M-chain by release of its topological constraints (by diffusion of the surrounding P-chains) and Me is an entanglement molecular weight. D* for self-diffusion (M=P) is dominated by reptation except for M's close to Me.

Synthesis of silsesquioxane nanocomposites

2008 ◽  
Vol 62 (5) ◽  
Author(s):  
Ondřej Smrtka ◽  
Josef Jančář
Keyword(s):  
Molecular Weight ◽  
Functional Group ◽  
Polymerization Rate ◽  
Polymer Chains ◽  
Low Molecular Weight ◽  
Polyhedral Oligomeric Silsesquioxanes ◽  
Kinetics Of Polymerization ◽  
Inorganic Particles ◽  
Hydrosilylation Reaction ◽  
Kinetics Of

AbstractIn order to investigate the effect of presence of well defined nano-sized inorganic particles on the molecular mobility a conformation statistics of polymer chains, well defined polystyrene (PS) and poly(methyl methacrylate) (PMMA) macromolecules containing polyhedral oligomeric silsesquioxanes nanoparticles (POSS) were synthesized by copper-mediated atom transfer radical polymerization (ATRP). Two approaches were used for the synthesis — the first involves POSS as the initiator of ATRP; the second way considers an addition of POSS to the polymer (prepared by ATRP) with an appropriate functional group. Kinetics of polymerization was determined using common analytical methods and it was compared to the polymerizations initiated by low-molecular weight initiators, regarding the polymerization rate, initiation efficiency and polydispersity of the polymer. Efficiency of the initiation with POSS-containing initiators was low, causing remnants of inseparable free POSS in polymer. The second approach bypassed these disadvantages —POSS is connected to the polymer through a pending allyl group using the very efficient hydrosilylation reaction.

Direct observations of radiation-enhanced transformations in glass

1983 ◽  
Vol 41 ◽  
pp. 354-355
Author(s):  
J. F. DeNatale ◽  
D. G. Howitt
Keyword(s):  
Glass Matrix ◽  
Diffusion Mechanism ◽  
Bubble Formation ◽  
Silicate Glasses ◽  
Phase Decomposition ◽  
Direct Observations ◽  
Thin Foils ◽  
Oxygen Bubble ◽  
Electron Energy Loss ◽  
Kinetics Of

The electron irradiation of silicate glasses containing metal cations produces various types of phase separation and decomposition which includes oxygen bubble formation at intermediate temperatures figure I. The kinetics of bubble formation are too rapid to be accounted for by oxygen diffusion but the behavior is consistent with a cation diffusion mechanism if the amount of oxygen in the bubble is not significantly different from that in the same volume of silicate glass. The formation of oxygen bubbles is often accompanied by precipitation of crystalline phases and/or amorphous phase decomposition in the regions between the bubbles and the detection of differences in oxygen concentration between the bubble and matrix by electron energy loss spectroscopy cannot be discerned (figure 2) even when the bubble occupies the majority of the foil depth.The oxygen bubbles are stable, even in the thin foils, months after irradiation and if van der Waals behavior of the interior gas is assumed an oxygen pressure of about 4000 atmospheres must be sustained for a 100 bubble if the surface tension with the glass matrix is to balance against it at intermediate temperatures.

scholarly journals Thermal Degradation Kinetics and Modeling Study of Ultra High Molecular Weight Polyethylene (UHMWP)/Graphene Nanocomposite

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1597
Author(s):  
Iman Jafari ◽  
Mohamadreza Shakiba ◽  
Fatemeh Khosravi ◽  
Seeram Ramakrishna ◽  
Ehsan Abasi ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Molecular Weight ◽  
Thermal Degradation ◽  
High Molecular Weight ◽  
Degradation Kinetics ◽  
Graphene Nanosheets ◽  
Thermal Degradation Kinetics ◽  
Graphene Nanocomposites ◽  
Kinetics Of ◽  
Ultra High Molecular Weight

The incorporation of nanofillers such as graphene into polymers has shown significant improvements in mechanical characteristics, thermal stability, and conductivity of resulting polymeric nanocomposites. To this aim, the influence of incorporation of graphene nanosheets into ultra-high molecular weight polyethylene (UHMWPE) on the thermal behavior and degradation kinetics of UHMWPE/graphene nanocomposites was investigated. Scanning electron microscopy (SEM) analysis revealed that graphene nanosheets were uniformly spread throughout the UHMWPE’s molecular chains. X-Ray Diffraction (XRD) data posited that the morphology of dispersed graphene sheets in UHMWPE was exfoliated. Non-isothermal differential scanning calorimetry (DSC) studies identified a more pronounced increase in melting temperatures and latent heat of fusions in nanocomposites compared to UHMWPE at lower concentrations of graphene. Thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) revealed that UHMWPE’s thermal stability has been improved via incorporating graphene nanosheets. Further, degradation kinetics of neat polymer and nanocomposites have been modeled using equations such as Friedman, Ozawa–Flynn–Wall (OFW), Kissinger, and Augis and Bennett’s. The "Model-Fitting Method” showed that the auto-catalytic nth-order mechanism provided a highly consistent and appropriate fit to describe the degradation mechanism of UHMWPE and its graphene nanocomposites. In addition, the calculated activation energy (Ea) of thermal degradation was enhanced by an increase in graphene concentration up to 2.1 wt.%, followed by a decrease in higher graphene content.

scholarly journals Isothermal Crystallization Kinetics of Poly(ethylene oxide)/Poly(ethylene glycol)-g-silica Nanocomposites

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 648
Author(s):  
Xiangning Wen ◽  
Yunlan Su ◽  
Shaofan Li ◽  
Weilong Ju ◽  
Dujin Wang
Keyword(s):  
Molecular Weight ◽  
Ethylene Oxide ◽  
Crystallization Kinetics ◽  
Isothermal Crystallization ◽  
Crystallization Rate ◽  
Poly Ethylene Glycol ◽  
Isothermal Crystallization Kinetics ◽  
Poly Ethylene Oxide ◽  
Poly Ethylene ◽  
Kinetics Of

In this work, the crystallization kinetics of poly(ethylene oxide) (PEO) matrix included with poly(ethylene glycol) (PEG) grafted silica (PEG-g-SiO2) nanoparticles and bare SiO2 were systematically investigated by differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM) method. PEG-g-SiO2 can significantly increase the crystallinity and crystallization temperature of PEO matrix under the non-isothermal crystallization process. Pronounced effects of PEG-g-SiO2 on the crystalline morphology and crystallization rate of PEO were further characterized by employing spherulitic morphological observation and isothermal crystallization kinetics analysis. In contrast to the bare SiO2, PEG-g-SiO2 can be well dispersed in PEO matrix at low P/N (P: Molecular weight of matrix chains, N: Molecular weight of grafted chains), which is a key factor to enhance the primary nucleation rate. In particular, we found that the addition of PEG-g-SiO2 slows the spherulitic growth fronts compared to the neat PEO. It is speculated that the interfacial structure of the grafted PEG plays a key role in the formation of nuclei sites, thus ultimately determines the crystallization behavior of PEO PNCs and enhances the overall crystallization rate of the PEO nanocomposites.

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