Proton multiple-quantum NMR for the study of chain dynamics and structural constraints in polymeric soft materials

Saalwächter, Kay

doi:10.1016/j.pnmrs.2007.01.001

Cited by 379 publications

(395 citation statements)

References 129 publications

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“…A faster and more isotropic chain dynamics reduces the residual dipolar couplings, leading to a slower transverse relaxation and a smaller D m , and thus a slower SD process within the mobile phase. We have determined the average residual dipolar coupling of the mobile phase by MP-filtered multiplequantum experiments 10,20 and found that the soft phase of SB is indeed characterized by lower residual dipolar couplings than KR. This is consistent with the T 2m results and confirms that chains grafted on both ends, as is the case in the multiblock structure of KR, have a more network-like and anisotropic behavior than the unilaterally grafted chains in diblock copolymers such as SB.…”

Section: Sd Coefficientsmentioning

confidence: 99%

Proton NMR spin-diffusion studies of PS-PB block copolymers at low field: two- vs three-phase model and recalibration of spin-diffusion coefficients

Meyer

Schneider

Saalwächter

2012

Polym J

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Low-field proton nuclear magnetic resonance (NMR) methods were used to assess the phase fractions, domain thicknesses, T 1 relaxation properties and spin diffusion (SD) coefficients D of different phases in nanophase-separated polystyrenepolybutadiene block copolymers. At low field, SD experiments are challenged by rather short longitudinal relaxation times (T 1 ), requiring careful consideration of the interplay of T 1 relaxation and SD effects. Building on earlier work, we used a numerical fitting procedure for a separate as well as combined analysis of phase-resolved rigid-and mobile-phase filtered SD, as well as saturation recovery curves taken on a well-defined lamellar sample. We demonstrate the advantages in using three-component model, distinguishing a rigid and a mobile, as well as an interphase that can be resolved by fits to the refocused free-induction decay. We further use domain sizes from small-angle X-ray scattering as a gauge and find that SD coefficients from literature calibrations are overestimated. Under static low-field conditions, D for the rigid polystyrene phase is found to be 0.38 ± 0.06 nm 2 ms À1 , and we propose a rescaling of a literature calibration correlating D for the mobile phase with its T 2 relaxation time.

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Section: Sd Coefficientsmentioning

confidence: 99%

Proton NMR spin-diffusion studies of PS-PB block copolymers at low field: two- vs three-phase model and recalibration of spin-diffusion coefficients

Meyer

Schneider

Saalwächter

2012

Polym J

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“…Forty years of research have led to a complex relaxation scenario based on a combination of local Rouse dynamics, reptation, contour length fluctuations, and constraint release [4]. The development and validation of a quantitative, microscopic theory crucially depends on the availability of experimental and simulation data for model systems.Entangled polymers are studied experimentally using rheology [1,2,7], dielectric spectroscopy [8], small-angle neutron scattering [9,10], and nuclear magnetic resonance [11,12]. Computer simulations [13][14][15][16] offer some advantages in the preparation of well-defined model systems and the simultaneous access to macroscopic behavior and microscopic structure and dynamics.…”

mentioning

confidence: 99%

Stress Relaxation in Entangled Polymer Melts

et al. 2010

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We present an extensive set of simulation results for the stress relaxation in equilibrium and stepstrained bead-spring polymer melts. The data allow us to explore the chain dynamics and the shear relaxation modulus, G(t), into the plateau regime for chains with Z = 40 entanglements and into the terminal relaxation regime for Z = 10. Using the known (Rouse) mobility of unentangled chains and the melt entanglement length determined via the primitive path analysis of the microscopic topological state of our systems, we have performed parameter-free tests of several different tube models. We find excellent agreement for the Likhtman-McLeish theory using the double reptation approximation for constraint release, if we remove the contribution of high-frequency modes to contour length fluctuations of the primitive chain. High molecular weight polymeric liquids display remarkable viscoelastic properties [1,2]. Contrary to glassy systems, their macroscopic relaxation times are not due to slow dynamics on the monomer scale, but arise from the chain connectivity and the restriction that the backbones of polymer chains cannot cross while undergoing Brownian motion. Modern theories of polymer dynamics [3,4] describe the universal aspects of the viscoelastic behavior based on the idea that molecular entanglements confine individual polymers to tube-like regions in space [5,6]. Forty years of research have led to a complex relaxation scenario based on a combination of local Rouse dynamics, reptation, contour length fluctuations, and constraint release [4]. The development and validation of a quantitative, microscopic theory crucially depends on the availability of experimental and simulation data for model systems.Entangled polymers are studied experimentally using rheology [1,2,7], dielectric spectroscopy [8], small-angle neutron scattering [9,10], and nuclear magnetic resonance [11,12]. Computer simulations [13][14][15][16] offer some advantages in the preparation of well-defined model systems and the simultaneous access to macroscopic behavior and microscopic structure and dynamics. In particular, the recently developed primitive path analysis (PPA) [17][18][19][20][21][22][23][24] reveals the experimentally inaccessible mesoscopic structures and relaxation processes described by the tube model and allows parameter-free comparisons between theoretical predictions and data. However, the long relaxation times pose a particular challenge to computational techniques. Here we present simulation results for model polymer melts in equilibrium and after a rapid, volume-conserving uni-axial elongation, where we have been able to follow the full relaxation dynamics deep into the entangled regime. The data allow us to perform the first parameter-free test of the predictions of tube models for dynamical properties, to pinpoint a problem in the current theoretical description, and to validate a suitable modification.Our numerical results are based on extensive molecular dynamics (MD) simulations of bead-spring polymer melts [13]. Each ...

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“…17,18 MQ-NMR is sensitive to motion of polymer chains under the influence of various topological constraints (cross-links, physical entanglements, filler adsorption, etc. ), and these dynamics can be related directly in principle to effective dynamic chain lengths (vide infra).…”

mentioning

confidence: 99%

“…), and these dynamics can be related directly in principle to effective dynamic chain lengths (vide infra). Further, many of the macroscopic properties of engineering materials can be directly related to the mobility of chains comprising the elastomer network, and MQ-NMR data has been therefore used to obtain quantitative insight into network changes due to swelling, 17,19,20 thermal treatment, 16 filler content, 1 and radiation exposure. 21,22 It remains poorly understood, however, the degree to which the NMR distributions reflect actual molecular weight (MW) distributions in these soft solids and how much the distributions obtained by MQ-NMR can be relied on to predict material properties such as elastic shear modulus.…”

mentioning

confidence: 99%

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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Proton multiple-quantum NMR for the study of chain dynamics and structural constraints in polymeric soft materials

Cited by 379 publications

References 129 publications

Proton NMR spin-diffusion studies of PS-PB block copolymers at low field: two- vs three-phase model and recalibration of spin-diffusion coefficients

Proton NMR spin-diffusion studies of PS-PB block copolymers at low field: two- vs three-phase model and recalibration of spin-diffusion coefficients

Stress Relaxation in Entangled Polymer Melts

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

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