H NMR Imaging and Spectroscopy Studies of the Polymerization of Acrylamide Gels

Ahuja, Sanjay; Dieckman, S.L.; Gopalsami, N.; Raptis, A.C.

doi:10.1021/ma960216e

Cited by 12 publications

(6 citation statements)

References 16 publications

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“…This gel must still be in fast exchange with the rest of the water, the mobility in the gel phase being significantly lower than in the pore itself. Relaxation time reductions were found in synthetic gels with strong inter-and intramolecular interactions like cross-linking (Ahuja et al, 1996;Yasunaga and Ando 1993) and probably also by loose interactions due to hydrogen bonds (Matsukawa and Ando 1997). These effects were observed in gels with water contents >200% related to the dry mass.…”

Section: Swelling Poresmentioning

confidence: 94%

H-NMR Relaxometry to Monitor Wetting and Swelling Kinetics in High-organic Matter Soils

et al. 2005

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Variations of soil moisture conditions affect sorption properties of soil organic matter and the pore size distribution of the soils and thus are expected to have an impact on the availability of pollutants and nutrients in soils. At least two principal processes that occur when a soil-water contact is established, are involved. Wetting, which is the very first step, is governed by the interactions of water with the surface of soil organic matter (SOM). The wettability of the pore walls determines the pore accessibility for water. Only in wettable soils, water will occupy the smallest pores first. In the course of wetting, the wettability of the pore walls increases, leading to water redistribution. Swelling of SOM is accompanied by an increase of volume due to the water uptake of the solid SOM phase and will change the SOM polarity. Swelling will thus affect sorption processes in the bulk SOM phase and is expected to change the pore sizes. In this contribution, we investigated swelling and wetting kinetics of soil samples by H-NMR-Relaxometry. We found different effects of wetting and swelling on the development of relaxation time distribution and thus of the pore size distribution. Both swelling and wetting can be slow processes, lasting for up to some weeks. During this time, we found changes in the pore size distribution. For swelling phenomena, we observed a continuous change of the effective pore size, and for wetting phenomena, we found a change in water distribution in a probably rigid pore system. Thus, during swelling and wetting, neither pore size distribution nor sorbent properties of SOM nor hydraulic properties remain constant. Due to the slow kinetics, both processes play an important role in sorption, transport and accessibility for water in hydrophobic areas within a time scale of weeks after e.g. a rainfall event. This will affect the environmental availability and the transport of pollutants and nutrients in the field.Abbreviations: SOM -Soil Organic Matter; DOM -Dissolved Organic Matter; T (T 2 ) -Relaxation Time (Transversal Relaxation Time); S -Surface of the pore walls occupied with water; V -Volume of the water filled pores; T S -Relaxation time of the water protons at the surface; k -Thickness of the layer within which surface relaxation can take place; q -Surface relaxivity, a parameter combined of T S and k: q ¼ k T S ; T B -Bulk relaxation time: relaxation time of the water protons at infinite distance from the pore walls; DPore diameter; r -Grain size (radius); t -Hydration time; Q -Time constant of the first order hydration process; Y, Y 0 , Y ¥ -Y acts as replacement character and is used for the parameters A PT)X , A P)X and TP X (see below), which are the Parameters for the evaluation of the hydration kinetics (Relaxation time or proportion of water). Y 0 values the parameter at the beginning of hydration (t = 0), and Y ¥ values the parameter at infinite hydration time (t fi ¥).; A P)X -Proportion of water assigned to the peak 'X' in the relaxation time distribution; T P)X -Relaxa...

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Section: Swelling Poresmentioning

confidence: 94%

H-NMR Relaxometry to Monitor Wetting and Swelling Kinetics in High-organic Matter Soils

et al. 2005

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“…Copolymerisation of methacrylamide with N,N H -methylenebisacrylamide in water has also been studied. 7 The process began upon the addition of ammonium persulfate (initiator) and tetramethylethylenediamine (accelerator). Polymerisation reduces the T 1 time of the signals observed.…”

Section: Thermal Polymerisationmentioning

confidence: 99%

“…Two-dimensional NMR images obtained using the NMR signal of water revealed homogeneous gel formation throughout the sample (no polymerisation front was observed). 7 When preparing epoxy resin based composites, it is of great importance to have a means for monitoring variations of the state of the composite during the cross-linking of polymer chains at elevated temperature. 8,9 Raising the temperature causes an increase in the T 2 time of the resin; therefore, at temperatures above 55 8C one can obtain NMR images during the cross-linking of resin reinforced with carbon fibres using the signal from the resin protons.…”

Section: Thermal Polymerisationmentioning

confidence: 99%

“…45 At 43 8C, 100% necrosis occurs in several tens of minutes. 45,46 On further increases in temperature the time taken to necrotise tissues nearly halves as the temperature increases by 1 8C 6), 100 (7) and 64 (8). Brighter regions correspond to a higher content of liquid.…”

Section: Magnetic Resonance Thermometrymentioning

confidence: 99%

“…The supply of liquid AMS increased from 0 to 0.71 mg s 71 . The temperature of the granule /8C: 109 (1, 2), 141 (3), 167 (4), 148 (5), 113(6), 100(7) and 64(8). Brighter regions correspond to a higher content of liquid.…”

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confidence: 99%

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