Impediments to the accurate structural characterisation of a highly concentrated emulsion studied using NMR diffusion diffraction

Yadav, Nirbhay N.; Price, William S.

doi:10.1016/j.jcis.2009.06.014

Cited by 13 publications

(4 citation statements)

References 53 publications

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“…The 129 Xe PFG-echo profile obtained with 32 gradient steps for E5 rubber presented in Figure (Figure S3, Supporting Information) showed that the echo intensities gradually decreased with an additional oscillatory component. The pattern is not evident probably due to the distributions of pore size and the length of diffusion/exchange channels, i.e., the distance between the pores. − In addition, for these rubbers, it is thought that there are quasi-closed pores connected to each other through tiny diffusion channels. Xe atoms can diffuse fast through these, suggesting that the smaller amplitude of the oscillatory component in the diffraction pattern may be a result of this tiny contribution of fast diffusing Xe atoms to the PFG-echo profile.…”

Section: Resultsmentioning

confidence: 99%

Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure ¹²⁹Xe NMR Techniques

et al. 2022

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Microsized pore parameters, such as pore size and distance between pores in a series of model EPDM rubbers, were determined in situ under the pressure of 500 psi using 129 Xe nuclear magnetic resonance (NMR) techniques: spin−lattice (T 1 ) and spin−spin (T 2 ) relaxation measurements, pulsed-field gradient (PFG) NMR, and two-dimensional exchange spectroscopy (2D EXSY). The T 1 /T 2 (≫1) ratio for the xenon confined in the pores is larger than that for nonconfined free xenon. This suggests that almost the entire pore surface interacts with xenon atoms like a closed pore. While these pores still connect each other through very narrow diffusion/exchange channels, it is possible to observe the echo decay in PFG-NMR and cross-peaks in 2D EXSY. The results show that both diffusion (D pore ≈ 2.1 × 10 −10 m 2 /s) and exchange (exchange rate, τ exch = a few tens of milliseconds) of xenon between a pore within the material and outer surface are prolonged. The exchange distances (l), which correspond to the xenon gas penetration depth, were estimated to be 70−100 μm based on the measured diffusion coefficients and exchange rate (1/τ exch ). NMR diffraction analysis reveals that pore size (a) and pore distance (b) are on the order of magnitude of micrometers and tens of micrometers, while the diffusion coefficients of xenon gas in the diffusion channels (D eff ) are about 10 −8 m 2 /s. Overall, this study suggests that the pores with a few micrometers connected through very narrow flowing channels with the length of several tens of micrometers are developed 70 to 100 μm below the rubber surface. Furthermore, the overall steady-state diffusion of xenon is slower, approximately 2 orders of magnitudes, than the diffusion in the channel between the pores. The pore and exchange distances correlated with the composition of rubbers showed that the properties of EPDM rubber as a high-pressure gas barrier could be improved by reducing the size of cracks and the depth of gas penetration by the addition of both carbon black and silica fillers.

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Section: Resultsmentioning

confidence: 99%

Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure ¹²⁹Xe NMR Techniques

et al. 2022

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“…If the condition is met, the system microgeometry must be taken into account (i.e. Eqns and cannot be used to completely describe the NMR signal attenuation, although they can be used to determine if the system behaviour deviates from free diffusion). Obtaining an expression similar to Eqn but including the effects of the system microgeometry is a tedious task and the solution is only well known for simple geometries like parallel planes, cylinders and spheres .…”

Section: Restricted Diffusionmentioning

confidence: 99%

Physical characterization using diffusion NMR spectroscopy

Zubkov

Dennis

Stait‐Gardner

et al. 2016

Magnetic Reson in Chemistry

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NMR diffusion measurements (or dNMR) provide a powerful tool for analysis of solution organization and microgeometry of the environment by probing random molecular motion. Being a very versatile method, dNMR can be applied to a large variety of samples and systems. Here, a brief introduction into dNMR and a summary of recent advances in the field are presented. The research topics include restricted diffusion, anisotropic diffusion, polymer dynamics, solution structuring and dNMR method development. The dNMR studied systems include plants, cells (cell models), liquid crystals, polymer solutions, ionic liquids, supercooled solutions, untreated water, amino acid solutions and more. It is demonstrated how a variety of dNMR methods can be applied to a system to extract the data on particular structures present among, formed by or surrounding the diffusing particles. It is also demonstrated how dNMR methods can be developed to allow probing larger geometries, low sample concentrations and faster processes. Copyright © 2016 John Wiley & Sons, Ltd.

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“…In essence, the gradient pulse is treated as a delta function. This is only valid experimentally when δ ∆ and the distance diffused during the gradient pulse is much shorter than the characteristic dimension of the system [60].…”

Section: Free Diffusionmentioning

confidence: 98%

“…In neutron scattering, |S (q)| 2 is the structure factor -the mathematical description of how a material scatters radiation. Structural information is obtained directly from a plot of the signal attenuation as a function of q, where minima in the plot correspond to characteristic distances in the confining geometry [60].…”

Section: 28mentioning

confidence: 99%

Structure and Rheology of Monodisperse and Bimodal Emulsions

Monahan¹

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<p>Emulsions are the basis for many commercial products such as foodstuffs and paint due in part to their highly tunable flow properties. It is qualitatively understood that factors such as the dispersed phase droplet size and size distribution should affect how an emulsion flows because they influence how droplets can deform or pack. Since standard emulsification techniques such as blending and homogenization cannot produce emulsions with well-defined size distributions, little work has been done to, in particular, quantitatively determine the influence of droplet size distribution on emulsion flow properties. Consequently, in this investigation we have probed how the droplet size distribution affects emulsion flow properties by using model monodisperse emulsion systems with narrow, controllable droplet size distributions. Using a microfluidic flow focusing device, dodecane-in-water emulsions with diameters between 50 to 100 m with polydispersities less than 5% were produced, as characterized by pulsed field gradient nuclear magnetic resonance and optical microscopy. Due to the relatively large size of the droplets, it was only possible to examine the creamed phase of the emulsion. Samples of known polydispersity were made by mixing known quantities of two monodisperse emulsions. The monodisperse and bimodal emulsions were then subjected to rotational and oscillatory shear flow using a controlled stress rheometer to determine the effects of droplet size and size distribution on emulsion flow properties. Rotational and oscillatory rheological experiments showed that the monodisperse emulsions had two distinct behaviours: foam-like with appreciable thixotropy and yield stresses as well as emulsion-like with no evident thixotropy. The transition between these two behaviours appears to happen at a critical droplet radius between 33 and 37 micrometres. The rheological properties of the bimodal emulsions was split into three distinct behaviours. In samples that could be considered a matrix of large droplets perturbed by smaller droplets, the flow properties were similar to those of the constituent emulsion with the larger droplets. Increasing the number fraction of smaller droplets to a 1:1 ratio creates an entirely new phase with significantly reduced elastic properties. Surprisingly, when the emulsion primarily consists of small droplets, the flow properties are most similar to that of the large droplets. Additionally, despite the microstructural differences, all emulsions showed flow characteristics typical of soft glassy materials above the glass transition temperature. These results demonstrate the significant influence of microstructure on emulsion rheology, where altering the droplet size or polydispersity essentially creates a new phase with its own unique flow properties that is not simply a combination of the properties of the individual monodisperse components that make up the sample</p>

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Impediments to the accurate structural characterisation of a highly concentrated emulsion studied using NMR diffusion diffraction

Cited by 13 publications

References 53 publications

Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure ¹²⁹Xe NMR Techniques

Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure ¹²⁹Xe NMR Techniques

Physical characterization using diffusion NMR spectroscopy

Structure and Rheology of Monodisperse and Bimodal Emulsions

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Impediments to the accurate structural characterisation of a highly concentrated emulsion studied using NMR diffusion diffraction

Cited by 13 publications

References 53 publications

Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure 129Xe NMR Techniques

Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure 129Xe NMR Techniques

Physical characterization using diffusion NMR spectroscopy

Structure and Rheology of Monodisperse and Bimodal Emulsions

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Product

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Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure ¹²⁹Xe NMR Techniques

Microsized Pore Structure Determination in EPDM Rubbers Using High-Pressure ¹²⁹Xe NMR Techniques