Diffusion and interaction in gels and solutions. 3. Theoretical results on the obstruction effect

Johansson, Lennart; Elvingson, Christer; Loefroth, Jan Erik

doi:10.1021/ma00022a019

Cited by 144 publications

(169 citation statements)

References 7 publications

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“…9, the model (Eq. [43]) provided an excellent fit to the data. The value of P(A/V ␣ ) ϭ 4.73 (error ϭ 0.24%) will later be used in the analysis of the effective relaxivities.…”

Section: Figmentioning

confidence: 83%

“…Other approaches, including hindered transport theory (40,41), have also been used to describe the effects of solute size on diffusion. Experimental data typically has been interpreted on the basis of a stretched exponential equation (36,(42)(43)(44) which can be justified theoretically through comparison with Monte Carlo simulations or derived using a specific arrangement of a unit cell. Despite these studies, a full range of experimental measurements on probe diffusion in polyacrylamide gels as functions of gel composition, including crosslinker density, has not been reported; in addition, the effects of media geometry and solute-gel interactions have not been incorporated within one comprehensive approach.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Proton Diffusion andT1Relaxation in Polyacrylamide Gels: A Unified Approach Using Volume Averaging

Penke

Kinsey

Gibbs

et al. 1998

Journal of Magnetic Resonance

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The structure of polyacrylamide gels was studied using proton spin-lattice relaxation and PFG diffusion methods. Polyacrylamide gels, with total polymer concentrations ranging from 0.25 to 0.35 g/ml and crosslinker concentrations from 0 to 10% by weight, were studied. The data showed no effect of the crosslinker concentration on the diffusion of water molecules. The Ogston-Morris and Mackie-Meares models fit the general trends observed for water diffusion in gels. The diffusion coefficients from the volume averaging method also fit the data, and this theory was able to account for the effects of water-gel interactions that are not accounted for in the other two theories. The averaging theory also did not require the physically unrealistic assumption, required in the other two theories, that the acrylamide fibers are of similar size to water molecules. Contrary to the diffusion data, T 1 relaxation measurements showed a significant effect of crosslinker concentration on the relaxation of water in gels. The model developed using the Bloch equations and the volume averaging method described the effects of water adsorption on the gel medium on both the diffusion coefficients and the relaxation measurements. In the proposed model the gel medium was assumed to consist of three phases (i.e., bulk water, uncrosslinked acrylamide fibers, and a bisacrylamide crosslinker phase). The effects of the crosslinker concentration were accounted for by introducing the proton partition coefficient, K eq , between the bulk water and crosslinker phase. The derived relaxation equations were successful in fitting the experimental data. The partition coefficient, K eq , decreased significantly as the crosslinker concentration increased from 5 to 10% by weight. This trend is consistent with the idea that bisacrylamide tends to form hydrophobic regions with increasing crosslinker concentration.

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“…9, the model (Eq. [43]) provided an excellent fit to the data. The value of P(A/V ␣ ) ϭ 4.73 (error ϭ 0.24%) will later be used in the analysis of the effective relaxivities.…”

Section: Figmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Proton Diffusion andT1Relaxation in Polyacrylamide Gels: A Unified Approach Using Volume Averaging

Penke

Kinsey

Gibbs

et al. 1998

Journal of Magnetic Resonance

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“…Solute behavior in hydrogels has been explained in terms of reduction in hydrogel free volume [20,21,22], enhanced hydrodynamic drag on the solute [23,24], increased path length due to obstruction [25,26], and a combination of hydrodynamic drag and obstruction effects [27].…”

Section: Amsden's Obstruction Scaling Theorymentioning

confidence: 99%

Effect of Cross-Linking on the Diffusion of Water, Ions, and Small Molecules in Hydrogels

2009

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Understanding the diffusion of small molecules in hydrogel system is of major importance in a variety of applications including drug delivery systems, tissue engineering and contact lens. Cross-linking density of hydrogels has been commonly used to tune key parameters like mesh size and molecular weight between cross-linkers, in order to change macroscopic properties of hydrogels. In this thesis, molecular dynamics investigations of chemically-cross-linked poly(ethylene glycol) (PEG) hydrogels are reported with the aim of exploring the diffusion properties of water, ions, and rhodamine within the polymer at the molecular level.The water structure and diffusion properties were studied at various cross-linking densities with molecular weights of the chains ranging from 572 to 3400. As the cross-linking density is increased, the water diffusion decreases and the slowdown in diffusion is more severe at the polymer-water interface. The water diffusion at various cross-linking densities is correlated with the water hydrogen bonding dynamics. The diffusion of ions and rhodamine also decreased as the cross-linking density is increased. The variation of diffusion coefficient with cross-linking density is related to the variation of water content at different cross-linking densities.Comparison of simulation results and obstruction scaling theory for hydrogels showed similar trends.ii To Father and Mother.iii

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“…The same scaling relation applies for diffusion of solutes through or out of a hydrogel, although here the relevant diffusivity corresponds to restricted Brownian motion of solute inside the hydrated polymer network. [53][54][55][56][57] Thus, while millimeter-sized hydrogels respond on time scales of hours or days to changes in external environment, micron-or submicron-sized hydrogels respond nearly instantaneously, or within seconds. Unfortunately, size-reduction also reduces loading capacity of individual hydrogels for releasable solutes, which may be a disadvantage when multiple cycles of solute release and retention are desired.…”

Section: Introductionmentioning

confidence: 99%

Integration of Hydrogels with Hard and Soft Microstructures

Lei¹,

Ziaie²,

Nuxoll³

et al. 2007

j nanosci nanotechnol

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Hydrogels, i.e., water-swollen polymer networks, have been studied and utilized for decades. These materials can either passively support mass transport, or can actively respond in their swelling properties, enabling modulation of mass and fluid transport, and chemomechanical actuation. Response rates increase with decreasing hydrogel dimension. In this paper, we present three examples where incorporation of hydrogels into solid microstructures permits acceleration of their response, and also provides novel functional capabilities. In the first example, a hydrogel is immobilized inside microfabricated pores within a thin silicon membrane. This hydrogel does not have a swelling response under the conditions investigated, but under proper conditions it can be utilized as a part of an electrolytic diode. In the second example, hydrogels are polymerized under microcantilever beams, and their swelling response to pH or glucose concentration causes variable deflection of the beam, observable under a microscope. In the third example, swelling and shrinking of a hydrogel embedded in a microfabricated valve structure leads to chemical gating of fluid motion through that valve. In all cases, the small size of the system enhances its response rate.

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Diffusion and interaction in gels and solutions. 3. Theoretical results on the obstruction effect

Cited by 144 publications

References 7 publications

Proton Diffusion andT1Relaxation in Polyacrylamide Gels: A Unified Approach Using Volume Averaging

Proton Diffusion andT1Relaxation in Polyacrylamide Gels: A Unified Approach Using Volume Averaging

Effect of Cross-Linking on the Diffusion of Water, Ions, and Small Molecules in Hydrogels

Integration of Hydrogels with Hard and Soft Microstructures

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