NMR Imaging of the Diffusion of Water at 310 K into Semi-IPNs of PEM and Poly(HEMA- c o -THFMA) with and without Chlorhexidine Diacetate (original) (raw)
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A proton NMR imaging study has been conducted on the diffusion of methanol into poly-(methyl methacrylate) (PMMA) after the cyclic absorption and desorption of water and methanol into PMMA. It was found that the diffusion of methanol into PMMA increases with the number of cycles and the diffusion process changes from Case I1 to Fickian. This may be attributed to the formation of voids caused by the removal of unreacted monomers and oligomers during the desorption of water and methanol between cycles. These voids increase the porosity within the PMMA and allow for increased diffusion. It was also found that, as the water content in PMMA increased, the rate of diffusion of methanol into the PMMA also increased. At the higher water contents, the diffusion of methanol also changed from Case I1 to Fickian. This may be due to the plasticizing effect of water on the PMMA which increases the polymer chain mobility to allow increased solvent penetration. Finally, the diffusion coefficients were determined for the PMMA samples in which Fickian diffusion occurred, and diffusion front velocities were calculated for the samples in which Case I1 diffusion was identified.
Polymer International, 2010
Poly(vinyl alcohol)-poly(N-vinyl-2-pyrrolidone) (PVA-PVP) polymer network hydrogels were prepared by subjecting an aqueous solution of PVA-PVP to gamma irradiation. The hydrogels had initial water contents of approximately 87%, and upon further immersion in water the hydrogels absorbed significantly more, reaching a final water content of about 95%. The use of magnetization-prepared NMR imaging enabled acquisition of T 2 -weighted NMR images from which T 2 maps were constructed and subsequently instantaneous concentration profiles of water molecules were determined. The concentration profiles could be described using Fick's second law of diffusion and the resultant diffusion coefficients were in excellent agreement with those determined from mass-uptake measurements reported previously. In addition an apparent change in water content over longer times was observed from the NMR images. This phenomenon could be attributed to changes in the distribution of T 2 relaxation times due to rearrangement of the water molecules, or alternatively diffusion of non-crosslinked polymer chains out of the hydrogel network.
OAlib, 2016
The diffusivity and distribution of water in the butyl methacrylate and methacrylic acid copolymer films swollen in water have been investigated using the NMR relaxation and pulse field gradient (PFG) NMR techniques. The contributions of polymer matrix protons, surface water and bound water have been determined from 1 H NMR spectra and relaxation functions. PFG NMR experiments showed that the echo attenuation function depends on the diffusion time indicating that water inside the swollen film is trapped in restricted confinement. The data obtained have been discussed using published physical models for diffusion of water in polymeric materials. The sizes of pores inside the film were estimated using the published model approaches giving the range of 0.8 -1.0 µm. Magnetization decays as well as the spinspin relaxation times of water saturated polymer films were also determined in this study. NMR relaxation provided additional information on the water distribution in the porous microstructure. The volume-averaged water mobility decreased with increasing hydrophobic content of the polymers.
Magnetic Resonance Imaging (MRI) of Water Diffusion in 2-Hydroxyethyl Methacrylate (HEMA) Gels
MRS Proceedings, 2006
ABSTRACTA fundamental study focusing on correlating the local water self-diffusion coefficient to the local free water content in 2-hydroxyethyl methacrylate (HEMA) gels was conducted. HEMA gels were synthesized with different nominal water content (50% to 90%). MRI measurements of local diffusion coefficient distribution and local water content profiles are conducted on a 600 MHz scanner. The local water content is measured via two spin-echo images with sufficiently long repetition time (TR) to eliminate T1-weighting and two values for the echo time (TE) in order to account for T2-weighting. The local diffusion coefficient is determined using a standard pulsed-field gradient spin-echo sequence. The measured local water content and diffusion coefficient data are compared with several single-parameter diffusion models for interstitial diffusion in the hydrogel (Makie-Meares, Stokes-Einstein, Brownian motion around overlapping spheres).
Study of the water uptake of polyamide 46 based copolymers by magnetic resonance imaging relaxometry
Polymer, 2004
Magnetic resonance imaging (MRI), NMR relaxometry, thermal analysis and gravimetrical experiments are performed to study the water absorption by neat PA46 and copolymers of PA46 and PA4n ðPA46-co-PA4nÞ with 4 mol% n ¼ 8; 12 and 16. The observed reduction in water uptake, ingress rate and water molecular mobility with increasing value of n is explained by a combination of several physico-chemical molecular properties. The increased [CH 2 ]/[amide] ratio and the reduced amount of crystallinity do not completely clarify the observed trends in water uptake and water molecular mobility in the copolymer series. It is shown that the increased chain mobility of the PA46 segments in the copolymers allows an improved coupling of the amide groups in the amorphous phase, explaining the observed decrease in water uptake. The important role of the morphology of the amorphous phase for water uptake is further demonstrated by annealing results and NMR relaxation experiments as a function of temperature. q
Journal of Membrane Science, 2000
The self-diffusion of water, ethanol and fluorine ions was studied by means of pulsed-field gradient nuclear magnetic resonance (PFG-NMR) spectroscopy in anion-exchange materials such as membranes and a resin containing quaternary amines as functional groups. Measurements were carried out with a NMR spectrometer at a frequency of 100 MHz for 1 H and 94.3 MHz for 19 F. The temperature dependence of the diffusion decay components in F − form membranes equilibrated with water or an aqueous solution of NH 4 F×HF was studied. The morphology of the transport channels in these materials and relationship between the structure of the membrane transport channels and self-diffusion of water and F − ions have been discussed. It was shown that the values of self-diffusion of fluorine ions in the membranes as determined by PFG-NMR are in good agreement with those obtained by means of electroconductivity measurements.
Self-Diffusion of Water in Block Copoly(ether−ester) Polymers: An NMR Study
Macromolecules, 2003
Water diffusion in four hard-soft block copolymer systems, based on poly(butylene terephthalate) as the hard segment and a copolymer with poly(ethylene oxide) (PEO) as the soft block, has been investigated by pulsed field gradient echo NMR. The water absorption and the water diffusion coefficient depend on the composition of the copolymer and the amount of water absorbed in the system. The higher the fraction PEO in the polymer, the higher the amount of absorbed water and the faster the water diffusion. The diffusion experimental results further indicate an interaction between water molecules and the PEO units in the soft segments. For all investigated systems it is found that water molecules reside near PEO units within a distance of less than 0.5 nm for a time of the order of or longer than 1 ns. The higher the amount of PEO in the soft blocks, the shorter the residence time of the water molecules near the PEO units.
Quantitative magnetic resonance imaging study of water uptake by polyamide 4,6
Polymer, 2001
Magnetic resonance imaging (MRI) and NMR relaxation experiments are used to study the water absorption by polyamide 4,6 (PA46) plates. Despite the higher crystallinity, PA46 absorbs more water as compared to the polyamides 6 and 6,6 (PA6 and PA66). Relaxation measurements demonstrate that the volume averaged molecular mobility T H 2 of the absorbed water molecules in PA46 is higher than in PA6 and PA66. Quantitative relaxation results of water saturated PA46 further suggest fast exchange between free water and water molecules bound via hydrogen bonds to amide groups. MRI reveals a gradual decrease in the amount and the T H 2 relaxation behaviour of water from the surface towards the core part of PA46 plates. This can be explained by the very high crystallisation rate of PA46, which prevents the close coupling of amide groups in the amorphous phase and results in a larger mean distance between the amide groups, especially in the outer part of the PA46 plates. Density measurements (WAXS and gradient column) show an increase of the density of the amorphous phase during annealing, resulting in a lower water uptake and a lower mobility of the absorbed water molecules. q