A generalized method to calculate diffusion rates in polydisperse systems. Further results on Rouse dynamics in the concentrated regime

Tomba, J. Pablo; Carella, José M.; Pardo, Enrique; López, Sonia Martín; Pastor, J. M.

doi:10.1002/1521-3927(20000901)21:14<983::aid-marc983>3.0.co;2-3

Cited by 4 publications

(7 citation statements)

References 6 publications

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“…This is demonstrated by the fact that the physical diffusion model used for calculations and simulations in this work has also been used with success for the study of liquid−liquid diffusion experiments using the same polymer pair at temperatures above the PPO-rich-layer T g . ,, The diffusion process is characterized by the transport of PS from the original PS-rich thin layer into layers that are richer in PPO, and the PPO transport is always realized toward layers with lower local T g values. The whole dynamics for the faster-diffusing species (PS) is Rouse-type, as shown in earlier works. ,, For the entire chemical composition range used, the monomeric friction factor for the PS species follows the WLF dependence on temperature, through the parameter ( T − T g ) …”

Section: Resultssupporting

confidence: 81%

“…As expected from the physical diffusion model, the highest slope, associated with a higher T g , is located next to the glassy matrix, and a gradually decreasing slope shows the influence of the rapidly changing T g profile along the diffusion path. For experiments conducted 1 K below the glassy matrix T g value in earlier work, it has been shown that when the local T g changes by about 80 K along the diffusion path, the PS monomeric friction coefficient changes by about 7 orders of magnitude, 33 thus justifying the chemical composition profile shape shown in Figure 2. Similar agreement between convoluted model calculations and experimental Raman data was obtained for all of the diffusion experiments of types A-C.…”

Section: Resultsmentioning

confidence: 99%

“…The whole dynamics for the fasterdiffusing species (PS) is Rouse-type, as shown in earlier works. 24,25,33 For the entire chemical composition range used, the monomeric friction factor for the PS species follows the WLF dependence on temperature, through the parameter (T -T g ). 33 Figure 6 shows local T g value versus diffusion coordinate profiles for the same type B experiment shown in Figure 2.…”

Section: Resultsmentioning

confidence: 99%

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Diffusion of Liquid Polystyrene into a Glassy Poly(phenylene oxide) Matrix. Diffusion Mechanisms and Experimental Verification

et al. 2001

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The diffusion of a liquid polymer into a glassy polymer matrix has been studied in a range of temperatures below the glassy matrix glass transition temperature (T g) and for different diffusion times. The liquid polymer used is low-molecular-weight polystyrene (PS) with a narrow molecular weight distribution, and the glassy matrix is poly(phenylene oxide); the two are miscible at any concentration. A simple physical diffusion model is proposed to correlate and predict diffusion rates, assuming a relatively rapid dissolution of the high-Tg polymer at the liquid-solid interface and a relatively slow diffusion process that produces a thick interphase. The local chemical compositions, local glass transition temperatures, and local PS monomeric friction coefficients change markedly along the diffusion path across the interphase; these changes are well predicted by the diffusion model and have also been experimentally verified. The large changes in local T g values cause huge changes in the PS monomeric friction factor across the interphase, and this fact explains the asymmetrical local chemical composition profiles experimentally measured for the PS-rich interphase. The results obtained by other authors for the diffusion of liquid polymers and bulky plasticizers into glassy matrixes are analyzed and discussed on the basis of the diffusion model predictions, and it is found that all of them behave following the same pattern as was observed in our experiments. It is concluded that the Case II diffusion mechanism must not be expected for the diffusion of liquid polymers into glassy matrixes, because of the negligible osmotic pressure. Furthermore, all of the analyzed data for diffusion of liquid polymers and bulky plasticizers into glassy matrixes show evidence for relatively rapid dissolution of the glassy matrix at the interface, together with a relatively slow diffusion process across the interphase.

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Section: Resultssupporting

confidence: 81%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Diffusion of Liquid Polystyrene into a Glassy Poly(phenylene oxide) Matrix. Diffusion Mechanisms and Experimental Verification

et al. 2001

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“…This observation could be accounted for in the framework of reptation considering the temperature dependence of the friction coefficient of eq that was assumed to be constant in eq . Indeed, several authors have clearly pointed out the strong ζ-dependence on temperature , that is unfortunately often ignored . This ζ temperature dependence that applies for reptation should also apply for “sideways motions” or “segmental rather to macromolecular mobility” which are likely to contribute to interface healing after melting explosion.…”

Section: Results and Data Analysismentioning

confidence: 99%

Diffusion versus Cocrystallization of Very Long Polymer Chains at Interfaces: Experimental Study of Sintering of UHMWPE Nascent Powder

et al. 2013

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International audienceUltrahigh-molecular-weight polyethylene (UHMWPE) has been processed by means of sintering of a nascent powder. Particular attention was paid to the precompaction of the powder just below the melting point (Tm) under vacuum. The particle welding was subsequently carried out under pressure at various temperatures above Tm for various durations. Tensile drawing experiments performed on sintered samples either at room temperature or above Tm were specifically aimed at discriminating the role of chain interdiffusion through the particle interfaces from that of cocrystallization in the mechanism of particle welding. It turned out that efficient welding occurred within a very short time. One of the novel results of the work is the much weaker influence of sintering time as compared with temperature, giving evidence that chain interdiffusion is not governed by a reptation process. The entropy-driven melting explosion over distances much larger than the chain length between entanglements is suggested to be the main mechanism of the fast chain re-entanglement and particle welding in the present case of a nascent powder consisting of nonequilibrium chain-disentangled crystals. Another major aspect of this study is the demonstration of the huge cocrystallization efficiency in the interface consolidation in the solid state that significantly hides the kinetics of chain intertwining occurring in the melt

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“…The error bars hold for the extend of the data dispersion between the highest and the lowest experimental values are not always visible at the graph scale. All of these data have been analyzed by means of statistical tests , in order to determine the regression line and the corresponding slopes reported on Figure c. A classical Student’s t test was used to check whether the slope of the regression line differs significantly from zero, whereas Snedecor’s tests enabled to confirm whether the two regression lines differ significantly from one another.…”

Section: Resultsmentioning

confidence: 99%

Mechanisms of Chain Reentanglement during the Sintering of UHMWPE Nascent Powder: Effect of Molecular Weight

et al. 2015

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Nascent powders of ultrahigh molecular weight polyethylene (UHMWPE) with different molecular weights in the range 0.6 < M v < 10.5 million g/mol have been processed by means of sintering. The interface consolidation or particle welding was carried out under pressure at various temperatures above the melting point and for various durations. Tensile drawing experiments performed above the melting point enabled to study the role of chain interdiffusion through the particle interface. The melting explosion phenomenon was demonstrated to occur for each molecular weight. The higher is M v , the greater is the efficiency of the phenomenon. But this does not allow a homogenization of the entanglement network of the sintered sample. Indeed, heterogeneity of deformation between the grain and the interface clearly appears during tensile tests above the melting temperature. The differences in mechanical behavior in the molten state between the molecular weights seem exacerbated by crystallization under tension. After melting explosion, end-chain diffusion as well as sideways motions are probably involved in the healing of very long chains polymer interfaces to reach a sufficiently high entanglement density. This latter phenomenon seems thermally activated. ■ INTRODUCTIONOne of the main issues of processing ultrahigh molecular weight polyethylene (UHMWPE) is to overcome its very high viscosity that precludes conventional melt processing such as injection or extrusion. As a consequence, a method inspired from powder metallurgy, sintering, has been developed. The polymer sintering is generally separated in three steps: 2 densification corresponding to wetting between grain, then chain diffusion across interfaces, and finally crystallization for semicrystalline polymer. This three-step separation was therefore adopted in the protocol of sintering. However, sintering mechanisms of polymer materials remain incompletely understood.In the case of sintering of semicrystalline polymers, two phenomena have been identified: (i) Chain diffusion across the interfaces of adjacent grains allowing the reentanglement of polymer chains was studied in particular in the case of amorphous polymer. 1,2 (ii) Cocrystallization, corresponding to the strengthening of the interfaces by crystallization involving chains from the adjacent grains. 3−7The diffusion of long chain polymers in the rubbery state is generally described by the reptation theory. 8,9 Moreover, it has been shown that the degree of chain disentanglement of UHMWPE nascent powders may significantly differ depending on the synthesis method so that reentanglement may be a slow and heterogeneous process. The heterogeneity of the entanglement network has consequences on the mechanical properties of both molten and semicrystalline states of the materials. 10−12 Finally, it has been shown that another phenomenon enables chain diffusion and reentanglement in much shorter time than reptation. 13−16 This phenomenon has been given evidence by molding or welding of disentangled solution-crystal...

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A generalized method to calculate diffusion rates in polydisperse systems. Further results on Rouse dynamics in the concentrated regime

Cited by 4 publications

References 6 publications

Diffusion of Liquid Polystyrene into a Glassy Poly(phenylene oxide) Matrix. Diffusion Mechanisms and Experimental Verification

Diffusion of Liquid Polystyrene into a Glassy Poly(phenylene oxide) Matrix. Diffusion Mechanisms and Experimental Verification

Diffusion versus Cocrystallization of Very Long Polymer Chains at Interfaces: Experimental Study of Sintering of UHMWPE Nascent Powder

Mechanisms of Chain Reentanglement during the Sintering of UHMWPE Nascent Powder: Effect of Molecular Weight

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