Netzwerkcharakterisierung durch dampfdruckosmotische Messungen

Arndt, Karl‐Friedrich; Schreck, James O.

doi:10.1002/actp.1985.010360111

Cited by 9 publications

(8 citation statements)

References 11 publications

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“…Taking into account the equilibrium requirements (eq 2) and the mixing part defined in eq 4 and deriving eq 5 with respect to the number of moles of solvent, the classical Flory-Rehner equation is obtained (6) However, in the past years some works proposed that the phantom network model 33,34 should be more adequate to represent the behavior of the swollen networks. In that case, the expression is written as…”

Section: Rtmentioning

confidence: 99%

Uncertainties in the Determination of Cross-Link Density by Equilibrium Swelling Experiments in Natural Rubber

et al. 2008

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Equilibrium swelling is a feasible and simple experiment to determine the cross-link density of networks. It is the most popular and useful approach; however, in most of the cases, the given values are highly uncertain if not erroneous. The description of the complex thermodynamics of swollen polymer networks is usually based on the Flory-Rehner model. However, experimental evidence has shown that both the mixing term described by the Flory-Huggins expression and the elastic component derived from the affine model are only approximations that fail in the description and prediction of the rubber network behavior. This means that the Flory-Rehner treatment can only give a qualitative evaluation of cross-link density because of its strong dependence on the thermodynamic model. In this work, the uncertainties in the determination of the cross-link density in rubber materials by swelling experiments based on this model are reviewed. The implications and the validity of some of the used approximations as well as their influence in the relationship of the cross-link densities derived from swelling experiments are discussed. Importantly, swelling results are compared with results of a completely independent determination of the cross-link density by proton multiple-quantum NMR, and the correlation observed between the two methods can help to validate the thermodynamic model.

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Section: Rtmentioning

confidence: 99%

Uncertainties in the Determination of Cross-Link Density by Equilibrium Swelling Experiments in Natural Rubber

et al. 2008

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“…For the determination of reliable structure–property relationships for elastomers, knowledge of the network structure is essential. A variety of different methodological approaches, e.g., dynamical mechanical analysis, osmometry, inverse gas chromatography, dielectric measurements, and neutron and X-ray scattering, has been applied for this purpose. The most often used experiments for the estimation of the cross-link density are equilibrium swelling, mechanical measurements, such as sulfur and NMR spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Cross-Link Density Estimation of PDMS Networks with Precise Consideration of Networks Defects

et al. 2011

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Two series of randomly cross-linked poly(dimethylsiloxane) (PDMS) networks with systematically varying and well-defined dangling chain and defect content were investigated by 1 H doublequantum low-field NMR (DQ NMR), equilibrium swelling, and highresolution magic-angle spinning NMR (MAS NMR) experiments in order to obtain information about the absolute molecular weight of the polymer chains between two cross-links, M c , and its distribution. A comparison of the experimental results from swelling and DQ NMR experiments with the results of Miller−Macosko calculations, based upon the reaction turnover determined by MAS NMR, clarifies the importance of a precise estimation of the defect fraction of the polymer network for a reliable determination of M c . In order to properly account for network defects in the evaluation of equilibrium swelling as well as DQ NMR experiments, we use the elastically effective polymer volume fraction ϕ p,el (that can be obtained from DQ NMR or simple Hahn echo experiments on samples swollen in deuterated solvent) and the variable weight-averaged functionality f wa of the cross-links taken from Miller−Macosko calculations. On the basis of the dependence of the so-obtained M c on f wa , we are able to confirm the validity of the phantom model of rubber elasticity, and find good agreement between the results from the different methods. Small deviations only pertain to a proportionality factor different from unity, which for the case of equilibrium swelling is attributed to the shortcomings of the Flory−Rehner theory. We further address the quantitative interpretation of the residual dipolar coupling constant as the central result of DQ NMR on dry samples, which is confirmed to be proportional to the inverse M c , but is also subject to systematic errors.

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“…Information on the rubber network structure can be obtained by different experimental approaches, such as inverse gas chromatography, 35 osmometry, 36 mechanical analysis, 37 equilibrium swelling experiments, 38 dielectric measurements, 39 high-resolution solid-state NMR, 40,41 or scattering techniques. 42,43 Often, however, such approaches are indirect.…”

Section: Introductionmentioning

confidence: 99%

Inhomogeneities and Chain Dynamics in Diene Rubbers Vulcanized with Different Cure Systems

et al. 2010

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In this study, we focus on qualitative differences in the network structure and dynamics of natural as well as poly(butadiene) rubber in dependence of the cure system (sulfur/accelerator or organic peroxide) used in the vulcanization process. The spatial homogeneity of the distribution of chemical and physical cross-links in the network is assessed via the quantitative measurement of proton-proton residual dipolar couplings as measured by static multiple-quantum (MQ) NMR spectroscopy at low field. The experiment also provides information on the apparent correlation time of fast segmental fluctuations that dominate chain relaxation processes at lower temperature, for which we also find characteristic differences. Vulcanization via a radical mechanism (using organic peroxides) leads to networks with a high content of nonelastic defects (loops or dangling chains), a rather inhomogeneous distribution of cross-links, and modified (slower) local dynamics, as compared to networks obtained by sulfur vulcanization. These microstructural factors can be related with the well-known differences in the macroscopic properties of diene rubbers vulcanized with different cure systems.

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Netzwerkcharakterisierung durch dampfdruckosmotische Messungen

Cited by 9 publications

References 11 publications

Uncertainties in the Determination of Cross-Link Density by Equilibrium Swelling Experiments in Natural Rubber

Uncertainties in the Determination of Cross-Link Density by Equilibrium Swelling Experiments in Natural Rubber

Cross-Link Density Estimation of PDMS Networks with Precise Consideration of Networks Defects

Inhomogeneities and Chain Dynamics in Diene Rubbers Vulcanized with Different Cure Systems

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