Modeling 1H NMR transverse magnetization decay in polysiloxane-silica composites

Mayer, Brian; Chinn, Sarah C.; Maxwell, Robert S.; Reimer, Jeffrey A.

doi:10.1016/j.ces.2009.01.020

Cited by 12 publications

(9 citation statements)

References 11 publications

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“…as opposed to a molecular weight dependent C n , the assumption that the end-to-end distance squared is Gaussian, and that motions about this end-to-end vector are ideal. 22,47,48 Despite these assumptions the NMR data is observed to behave roughly as expected:…”

Section: Multiple Quantum Nmrmentioning

confidence: 89%

Linking Network Microstructure to Macroscopic Properties of Siloxane Elastomers Using Combined Nuclear Magnetic Resonance and Mesoscale Computational Modeling

et al. 2011

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It is well established that many fundamental properties of polymer materials are directly governed by chain dynamics, and both experimental and computational efforts to probe this motional spectrum have been manifold. Recently, multiple quantum (MQ) nuclear magnetic resonance (NMR) has afforded the capability to extract meaningful quantities from such measurements, namely, an effective molecular weight distribution between various topological constraints (cross-links, entanglements, etc.). We describe herein the results of recent work on model end-linked poly(dimethylsiloxane) networks where mesoscale computational studies were used to calculate elastic moduli using the NMR-derived molecular weight distributions as their sole input. These results are then compared to dynamic mechanical analysis measurements to assess the degree to which this new methodology can predict the mechanical properties of these simple elastomers. The results of this initial study suggest a high confidence in prediction and portend a nondestructive methodology capable of monitoring subtle changes in network structural motifs associated with material performance and age.

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Section: Multiple Quantum Nmrmentioning

confidence: 89%

Linking Network Microstructure to Macroscopic Properties of Siloxane Elastomers Using Combined Nuclear Magnetic Resonance and Mesoscale Computational Modeling

et al. 2011

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“…The application of the MSE yields an FID that is a superposition of decaying exponentials whose amplitudes and time constants are representative of unique molecular motion distributions within the material. However, the extraction of this information is mathematically nontrivial. , Direct nonlinear regression to an unknown sum of exponentials is possible yet impractical as it requires a priori knowledge of the relaxation behavior of the material of study. Ideally, a mathematical transform is sought to deconvolute the time domain data into a spectral domainmuch akin to a fast Fourier transform.…”

Section: Experimental Sectionmentioning

confidence: 99%

“…However, the extraction of this information is mathematically nontrivial. 25,26 Direct nonlinear regression to an unknown sum of exponentials is possible yet impractical as it requires a priori knowledge of the relaxation behavior of the material of study. Ideally, a mathematical transform is sought to deconvolute the time domain data into a spectral domainmuch akin to a fast Fourier transform.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Reduced Phase Separation and Slowing of Dynamics in Polyurethanes with Three-Dimensional POSS-Based Cross-Linking Moieties

et al. 2015

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Octa-OH-functional POSS has been incorporated into a model polyurethane elastomer as a comparatively massive and notionally "robust" 3-dimensional cross-linking core. The effects of this cross-linking moiety on the morphology and molecular dynamics of the system are studied over a range of size and time scales. Microscopy, scattering, spectroscopic, thermal, and dielectric techniques, in agreement with each other, show that the covalent inclusion of the crosslinking particles restricts microphase separation, inhibits the formation of hard-block domains, and decelerates the motional dynamics of the polyurethane backbone. The effects on both the morphology and the dynamics of the polyurethane system are not continuous but occur in a steplike manner in the loading region of 4−6 wt % POSS. This critical region is thought to correspond to a sterically induced transition from one dominant morphology (microphase segregated) to an increasingly homogeneous nanophase segregated domain morphology. Contrary to expectations, cross-linking, even by the presumably rigid siliceous nanoparticles, reduces the mechanical modulus. In conjunction with the reduction of microphase separation, this observation indicates that the hard microdomains reinforce the polymer more effectively than the chemical cross-links.

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“…26,33 Though a gross simplification, however, the relative amount of long T 2 domains can be treated as proportional to the sol fraction, and relative fractional changes in the long T 2 domains are thus related to the relative changes in sol fraction.…”

Section: Nmr Methodsmentioning

confidence: 99%

MQ NMR and SPME Analysis of Nonlinearity in the Degradation of a Filled Silicone Elastomer

et al. 2010

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Radiation-induced degradation of polymeric materials occurs through numerous, simultaneous, competing chemical reactions. Although degradation is typically found to be linear in adsorbed dose, some silicone materials exhibit nonlinear dose dependence due to dose-dependent dominant degradation pathways. We have characterized the effects of radiative and thermal degradation on a model filled-PDMS system, Sylgard 184 (commonly used in electronic encapsulation and in biomedical applications), using traditional mechanical testing, NMR spectroscopy, and sample headspace analysis using solid-phase microextraction (SPME) followed by gas chromatography/mass spectrometry (GC/MS). The mechanical data and 1H spin−echo NMR spectra indicated that radiation exposure leads to predominantly cross-linking over the cumulative dose range studied (0−250 kGy) with a rate roughly linear with dose. 1H multiple-quantum NMR spectroscopy detected a bimodal distribution in the network structure, as expected from the proposed structure of Sylgard 184. The MQ NMR spectra further indicated that the radiation-induced structural changes were not linear in adsorbed dose and that competing chain scission mechanisms made a greater contribution to the overall degradation process in the range of 50−100 kGy (although cross-linking still dominated). The SPME−GC/MS data were analyzed using principal component analysis (PCA), which identified subtle changes in the distributions of degradation products (the cyclic siloxanes and other components of the material) as a function of age that provide insight into the dominant degradation pathways at low and high adsorbed dose.

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Modeling 1H NMR transverse magnetization decay in polysiloxane-silica composites

Cited by 12 publications

References 11 publications

Linking Network Microstructure to Macroscopic Properties of Siloxane Elastomers Using Combined Nuclear Magnetic Resonance and Mesoscale Computational Modeling

Linking Network Microstructure to Macroscopic Properties of Siloxane Elastomers Using Combined Nuclear Magnetic Resonance and Mesoscale Computational Modeling

Reduced Phase Separation and Slowing of Dynamics in Polyurethanes with Three-Dimensional POSS-Based Cross-Linking Moieties

MQ NMR and SPME Analysis of Nonlinearity in the Degradation of a Filled Silicone Elastomer

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