Matrix Water Content Research Articles

Mechanical Characterization of Soil–Rock Mixture Under Varying Block Parameters, Matrix Properties and Matrix Water Content Using Destructive and Non-Destructive Testing

Mechanical Characterization of Soil–Rock Mixture Under Varying Block Parameters, Matrix Properties and Matrix Water Content Using Destructive and Non-Destructive Testing

Factors Affecting the Sensitivity of Hydroxyl Group Content Analysis of Biocrude Products via Phosphitylation and 31P NMR Spectroscopy

A useful method for quantifying concentrations of various hydroxyl group containing molecular species in biocrudes involves chemically converting species into nonionizable, P-functionalized derivatives independently observed and quantified by phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy. Full validation of this method requires improved understanding of its applicability to different biocrude matrixes. The limits of detection (LODs) and limits of quantitation (LOQs) for this method are herein determined for concentrations of hydroxyl group containing analytes, grouped by molecular class, within three different biocrude matrixes: a biocrude (BC) product, a fast pyrolysis (FP) product, and an artificial matrix (AM). Matrix water content, known to affect method sensitivity, varies from <1 to 18.31 wt %. Each matrix is used to prepare a series of samples spiked to varying concentrations with three hydroxyl group containing model compounds, which represent (aliphatic) alcohol, phenolic, and carboxylic acid analyte types. Samples are then phosphitylated with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane to enable 31P NMR spectroscopic determination of native hydroxyl analyte concentrations. LODs and LOQs are determined for each analyte type and for each matrix. Analytical precision is affected by matrix concentrations of interfering analytes and water. Among the matrixes examined, AM, which contains no hydroxyl analytes and has the lowest water content, expectedly exhibits the lowest LODs and LOQs. Matrix LODs range from 0.04 to 0.14 mmol of OH/g, while their LOQs range from 0.10 to 0.41 mmol of OH/g, with both sets of values generally increasing in the order AM < BC < FP.

The processes of preferential flow in the unsaturated zone

AbstractPreferential flow, a major influence in unsaturated soil and rock almost everywhere, occurs by multiple phenomenologically distinct hydraulic processes. For the mode known as funneled flow, concentrated in particularly conductive portions of the medium, the surface‐tension/viscous‐flow processes of traditional unsaturated flow theory predominate. Fingered flow, through conductive paths of higher water content than surrounding material, requires amendments to traditional theory concerning instabilities and dynamic flow‐regime boundaries. Macropore flow, the most recognized preferential flow mode, poses unanswered questions and major difficulties in practice. Accumulated evidence shows that water flows preferentially mostly through macropores that are (a) only partially filled with water, and (b) surrounded by matrix material that is drier, sometimes much drier, than saturation. With partial filling, geometric characteristics such as aperture have much less influence than was previously thought, and the intra‐macropore configuration of the flowing water phase, about which little is conclusively known, is then a dominant controlling influence. With unsaturated surroundings, macropore/matrix exchange interactions control, for given input and medium, the initiating circumstances, conveyed flux, and duration of macropore flow. The multiple processes in play during such interactions have different sensitivities to the matrix water state and different directions of influence. The net influence of matrix water content on macropore flow is thus highly complex and a major research need. Additional high‐priority topics are: flowpath connectivity, for watersheds as well as small scales; intra‐macropore processes, to discern their importance and possible means of quantification; and the identification of measurable soil and rock properties that can be utilized predictively.

Coal Permeability Evolution Under Different Water-Bearing Conditions

The seepage problem of coal-bed methane (CBM) has attracted increasing attention from the research and industry communities. Coal permeability, which is a key parameter for CBM production, has been extensively studied through both laboratory and field tests, mathematical modeling, and numerical simulations. However, relatively little work has been done to investigate the effect of matrix water content on coal permeability evolution. Because most coal seams contain water, it may have direct impact on the CBM seepage capacity. Therefore, in this paper, CBM seepage at different matrix water contents was investigated experimentally. Results demonstrate that coal permeability decreases with the increase in water content. It was also found that both pore pressure and water content can greatly affect CBM migration characteristics and that the sorption strain and permeability were mostly controlled by pore pressure. In addition, water can have an impact on gas adsorption and sorption-induced deformation, which can further affect seepage channel width, leading to change in coal permeability. In general, coal permeability was observed to decrease exponentially with the increase in water content and pore pressure. Moreover, a coal adsorption model and an adsorption-permeability model were established, considering water content and excess adsorption under constant external stress and triaxial strain conditions. The proposed permeability model showed good agreement with the experimental results. The present study provides for better understanding of coal permeability evolution in a water-bearing condition and for developing an improved model to simulate the CBM migration process under such condition more accurately.

Bench Life (Work Time) of Moulding and Core Sands with Chemical Binders – a New, Ultrasound Investigation Method

Abstract The obtained results of the investigations of influences of the selected technological factors on the bench life (work time) of moulding and core sands with chemical binders are presented in the hereby paper. The bench life assessment is performed by the new, author’s method with the application of the ultrasound technique. This method was patented by the author. The influence of such factors as: matrix (surroundings) temperature, matrix water content, ratio of binding components hardener/binder (h/b) and the reclamation - on the bench life of furan moulding sands was determined. The empirical dependencies (regressions) were determined, which allowed forecasting the bench life (BL) of moulding sands as functions: BL = f(W%), BL = f(T) for the fresh and after the reclamation sands, BL = f(h/b). These dependencies should be treated as examples of the new method application for investigating the bench life of moulding sands with chemical binders.

Combined evaporation and salt precipitation in homogeneous and heterogeneous porous media

While soil evaporation studies have typically focused on pure or low salinity water evaporation, higher salinity soil conditions are becoming more prevalent. This work explores the combined effect of matrix heterogeneity and salt precipitation on evaporation from soils. Long‐term evaporation processes were studied using sand columns, in which heterogeneity consisted of two layers with different grain sizes, and X‐ray computed tomography (CT) scanning to quantify salt deposition within pores. For saline solutions, three new stages of evaporation were defined: SS1, SS2, and SS3. SS1 exhibits a low and gradual decrease in evaporation rate because of increasing osmotic potential. During SS2, evaporation rate falls progressively because of salt‐crust formation. SS3 is characterized by a constant low evaporation rate. Even though phenomenologically similar to the well‐defined classical evaporation stages for pure water, these saline stages correspond to different mechanisms. It is shown that SS2 and SS3 take place while matrix water content can still support first‐stage evaporation. Salinity suppressed evaporation more strongly in homogeneous rather than in heterogeneous media. CT scans indicated preferential salt precipitation in the fine‐textured regions. Heterogeneous spatial distribution of salt precipitates within the media enabled vapor transport via large pores, while small pores were clogged with precipitated salts. A mathematical model was formulated that simulates evaporation for saline solutions from homogeneous and heterogeneous soils. The model was used to differentiate and quantify the mechanisms controlling each stage of the evaporation process.

Study on Substrate Humidity, EC and Salinity &lt;i&gt;In Situ&lt;/i&gt; Detection Technology

Considering the greater character differences between matrix and soil, and the great disparity in physicochemical properties of various substrate, now there is no special equipment to test matrix moisture, electrical conductivity (EC) and salinity of medium .On the basis of analyzing physicochemical properties of various substrate, the relationship between output voltage and water content is studied through piezoelectric type soil moisture probe trial. With "voltage-current" four-terminal method, multi-parameter integrated sensor testing medium moisture and electrical conductivities developed, and through the solution calibration EC measuring model is established. Then relationships among matrix water content, electrical conductivity and salinity are analyzed, and salinity testing model is established. A portable low-cost in-situ multi-parameter detection apparatus, testing substrate humidity, EC and salinities, developed by adopting MCU SPCE06A. Experimental results indicate that detection accuracy of the equipment can meet the need of soilless culture production, and it has greater application and dissemination value.

Glass-transition behaviour of plasticized starch biopolymer system – A modified Gordon–Taylor approach

Two plasticizers namely, glycerol and xylitol, based on their similar molecular size (˜6.3 Å) but different molecular weights (Glycerol-92; Xylitol-152) were selected for studying the glass-transition behaviour (rubber like behaviour) in multi-plasticized starch biopolymer with about 70% amylopectin structure. In the calorimetry measurements, glass-transition temperatures (onset temperature for bulk viscous flow) of plasticized samples were higher than non-plasticized samples at low water activities, thus showing typical antiplasticization behaviour. However, when plasticizer concentration was increased up to 15% and 20% wt, all plasticized samples showed significant reduction in glass-transition temperature. We used a modified Gordon–Taylor model to understand the competitive plasticization of glycerol and xylitol in presence of water, and suggest that competitive plasticization exists and occurs at a threshold amount of matrix free water content, due to strong three-way interactions: starch–plasticizer, plasticizer–plasticizer/water and starch–water. This competitive interaction is significant in determining the onset temperature for viscous flow behaviour; at higher matrix water content, the Gordon–Taylor constant was relatively unaffected by the plasticizer amount, and water was the dominant plasticizer. A new interaction parameter that separates the starch–plasticizer interaction in a starch–plasticizer–water system is also discussed.

Signalling cascades in mechanotransduction: cell–matrix interactions and mechanical loading

Mechanical loading of articular cartilage stimulates the metabolism of resident chondrocytes and induces the synthesis of molecules to maintain the integrity of the cartilage. Mechanical signals modulate biochemical activity and changes in cell behavior through mechanotransduction. Compression of cartilage results in complex changes within the tissue including matrix and cell deformation, hydrostatic and osmotic pressure, fluid flow, altered matrix water content, ion concentration and fixed charge density. These changes are detected by mechanoreceptors on the cell surface, which include mechanosensitive ion channels and integrins that on activation initiate intracellular signalling cascades leading to tissue remodelling. Excessive mechanical loading also influences chondrocyte metabolism but unlike physiological stimulation leads to a quantitative imbalance between anabolic and catabolic activity resulting in depletion of matrix components. In this article we focus on the role of mechanical signalling in the maintenance of articular cartilage, and discuss how alterations in normal signalling can lead to pathology.

Matrix Modifications Modulate Ophthalmic Drug Delivery From Photo-Cross-Linked Poly(propylene Fumarate)-Based Networks

In this work, different modifications of photo-cross-linked poly(propylene fumarate)/poly(N-vinyl pyrrolidone) (PPF/PNVP) matrices were studied for their effect on the release kinetics of two ophthalmic drugs. The hydrophilicity of solid PPF/PNVP matrices loaded with acetazolamide (AZ) or timolol maleate (TM) was increased by adding various amounts of poly(ethylene glycol) (PEG) or by increasing the amount of N-vinyl pyrrolidone (NVP) in the polymer mixture prior to cross-linking. The in vitro release studies that utilized high-performance liquid chromatography for quantification revealed highly accelerated drug release from the matrices with increasing contents of the hydrophilic modifier. AZ was released from matrices containing 5% PEG in 56 days, which equals approximately 25% of the release period found for the unmodified matrices. A comparable acceleration in drug release was found for TM-loaded samples modified with 5% PEG. These studies further revealed that 1% PEG is sufficient to shorten the TM release duration by one-third. A significant acceleration in drug release was also found for the samples that were fabricated from a PPF–NVP mixture with increased NVP content. Matrix water content and erosion were assessed gravimetrically. Micro-computed tomography was used to image structural changes of the release systems and shed light on the drug-release mechanism. This study showed that hydrophilic matrix modifications of PPF/PNVP matrices accelerate the drug release of two ophthalmic drugs and represent a suitable tool to adjust drug-release rates from PPF-based matrices for different therapeutic needs.

Biodegradable fumarate‐based drug‐delivery systems for ophthalmic applications

The function of a photocrosslinked poly(propylene fumarate) (PPF)/poly(N-vinyl pyrrolidone) (PVP) matrix for the sustained release of three ophthalmic model drugs, acetazolamide (AZ), dichlorphenamide (DP), and timolol maleate (TM), was investigated. The drugs differ in molecular weight and degree of dissociation in aqueous environments; both are parameters that significantly influence drug diffusivity. AZ, DP, and TM-loaded cylindrical rods (10 mm length, 0.6 mm diameter) were fabricated by photoinduced cross-copolymerization of PPF and N-vinyl pyrrolidone (NVP) in molds. The released amounts of AZ, DP, TM, and NVP were determined by high-performance liquid chromatography (HPLC). The effects of drug properties and loading on the release kinetics were investigated. The in vitro release of AZ, DP, and TM was well sustained from the polymer matrices over a period of approximately 210, 270, and 250 days, respectively. The release kinetics correlated with the HPLC retention profiles of the different drugs. Following a small initial burst release (<10%), a dual modality release controlled by diffusion and bulk erosion was found for all drugs. Drug release rates of up to 4 microg/day were reached. Matrix drug loading generally affected the extent of the burst release, release kinetics, as well as the matrix water content and matrix degradation that were determined gravimetrically. Microcomputed tomography was used to image structural and dimensional changes of the devices. A preliminary rabbit implantation study revealed promising ocular biocompatibility of drug-free PPF/PVP matrices. All results indicate the potential of photocrosslinked PPF-based matrices as polymeric carriers for long-term ophthalmic drug delivery.

Long-term release of fluocinolone acetonide using biodegradable fumarate-based polymers

Intraocular drug delivery systems made from biodegradable polymers hold great potential to effectively treat chronic diseases of the posterior segment of the eye. This study is based on the hypothesis that crosslinked poly(propylene fumarate) (PPF)-based matrices are suitable long-term delivery devices for the sustained release of the anti-inflammatory drug fluocinolone acetonide (FA) due to their hydrophobicity and network density. FA-loaded rods of 10 mm length and 0.6 mm diameter were fabricated by photo-crosslinking PPF with N-vinyl pyrrolidone (NVP). The released amounts of FA and NVP were determined by HPLC analysis. The effects of drug loading and the ratio of PPF to NVP on the release kinetics were investigated using a 2 3-1 factorial design. Overall, FA release was sustained in vitro over almost 400 days by all tested formulations. Low burst release was followed by a dual modality release controlled by diffusion and bulk erosion with release rates up to 1.7 μg/day. The extent of the burst effect and the release kinetics were controlled by the drug loading and the matrix composition. Matrix water content and degradation were determined gravimetrically. Micro-computed tomography was used to image structural and dimensional changes of the devices. The results show that photo-crosslinked PPF-based matrices are promising long-term delivery devices for intraocular drug delivery.

Cartilage mechanobiology: the response of chondrocytes to mechanical force

Purpose of review: A comprehensive understanding of chondrocyte mechanobiology is critically important for a clear understanding of the etiopathology and treatment of osteoarthritis as well as for the long-term survival of tissue-engineered implants for cartilage repair. Recent findings: A large body of evidence has emerged documenting the effects of various mechanical loading modalities on chondrocyte biosynthesis and gene expression. Many physical forces and flows occur in cartilage during loading in vivo. For example, dynamic compression of cartilage results in deformation of cells and the extracellular matrix; hydrostatic pressurization of the tissue fluid, pressure gradients, and the accompanying flow of fluid within the tissue; and streaming potentials and currents induced by fluid convection of counter-ions through the negatively charged extracellular matrix. In addition, local changes in tissue volume caused by compression also lead to alterations in matrix water content, extracellular matrix fixed charge density, mobile ion concentrations and osmotic pressure. Any of these mechanical and physicochemical phenomena in the microenvironment of chondrocytes may affect cellular metabolism. Whereas specific components of certain mechanotransduction pathways have been identified, the exact mechanisms by which mechanical forces influence the biologic activity of chondrocytes are not yet fully understood. New genomic and proteomic techniques and methods, including systems biologic analyses, are being applied to gain a better understanding of cellular mechanotransduction. Summary: Investigators have focused on mechanoregulation of upstream signaling and responses at the level of gene transcription, protein translation, and posttranslational modifications. Intracellular pathways including those involving integrin signaling, mitogen-activated protein kinases and release of intracellular calcium have been confirmed in several laboratories.

Water content measured by proton-deuteron exchange NMR predicts bone mineral density and mechanical properties.

NMR was used to measure matrix water content in normal and hypomineralized cortical bone. Water content showed an inverse relationship with mineral content, suggesting it could serve as a surrogate measure for the bone's degree of mineralization. So far, true bone mineral density (DMB; degree of mineralization of bone) can not be measured nondestructively. Here, a new technique combining 1H nuclear magnetic resonance (NMR) spectroscopy and deuterium isotope exchange was used to measure water content in cortical bone from two groups of rabbits: a control group and a group fed a low-phosphorus (P) diet to induce hypomineralization of the bone matrix. NMR-derived water content was higher in the P-depleted group and showed an inverse relationship with mineral content (measured gravimetrically and by 31p NMR). Hypomineralized bone was found to be weaker than normal bone as demonstrated by mechanical testing. More importantly, the data showed a strong inverse correlation between water content and bone mechanical properties, which indicates that water content could be predictive of the bone's mechanical competence. Water content could potentially serve as a surrogate measure for the bone's degree of mineralization, and this technique could be used to study other disorders of mineral homeostasis known to alter the mineralization state of the matrix. Although the method presented here is not suitable for in vivo measurements of bone water content, the authors have previously shown that 1H NMR images of bone can be acquired; thus, noninvasive quantification of bone water may be feasible.

Chondrocyte Survival and Material Properties of Hypothermically Stored Cartilage

Background There is little information available on the material properties of hypothermically stored allograft specimens used to repair osteochondral defects. Purpose To analyze the effect of hypothermic storage on the material properties of fresh knee specimens over a 60-day interval. Study Design Controlled laboratory study. Methods Twelve sheep knee condyles were isolated. The femoral and tibial condyles and the patella were stored in a nutritive medium containing Dulbecco's Modified Eagle's Medium for 1, 8, 15, 29, 45, or 60 days. Total chondrocyte density, chondrocyte viability, matrix proteoglycan content, matrix water content, and matrix dynamic modulus of elasticity were determined. Results Mean chondrocyte viability decreased significantly over the storage interval: 100% (day 1), 98.2% (day 8), ∗80.2% (day 15), ∗80.6% (day 29), ∗64.6% (day 45), and ∗51.6% (day 60) (∗ P< 0.05). Qualitative analysis demonstrated a preponderance of nonviable chondrocytes in the superficial cartilage layer. Significant decreases in matrix proteoglycan were observed in day 15 through day 60 specimens (P< 0.05). The matrix dynamic modulus significantly decreased from day 1 through day 60 (P< 0.05). Conclusion The material properties of hypothermically stored knee condyles progressively decline over 60 days. Clinical Relevance This observed decline may have significant ramifications on long-term graft survival following storedallograft implantation.

Preferential flow in macroporous swelling soil with internal catchment: model development and applications

A new model of infiltration in swelling and shrinking clay soil was developed. The model consisted of two flow domains: soil matrix, with flow modelled by means of Darcy equation, and macropores; the latter was divided in turn into two sub-domains: shrinkage cracks, with aperture dynamically depending on matrix water content, and permanent macropores, independent of matrix saturation. In the shrinkage cracks sub-domain, a kinematic wave equation was derived by considering laminar motion of thin water films, along two parallel nearly vertical walls; in the permanent macropores sub-domain, a kinematic wave equation was assumed, with parameters physically related with macropores shape and dimension. Exchange of water between macropore domains and matrix was introduced in form of sink terms in the macropores mass balance equations, and as source terms in the matrix continuity equation. Infiltration through macropore walls was modelled using a diffusivity function derived from aggregates sorptivity measurements. The internal catchment was included by considering at each layer a fraction of dead end permanent macropores. Water ponding at the bottom of dead end macropores, infiltrated into the corresponding matrix layer. The model was tested against the results of infiltration transients through a large undisturbed swelling and shrinking clay soil column. Outflow rate from column bottom surface was constantly measured, while water content profile was registered at regular time intervals by means of five TDR horizontal probes. In order to quantify model parameters, characterisation of soil matrix was carried out, providing hydraulic conductivity curve, water retention curve, shrinkage characteristic and aggregates diffusivity. All of the other model parameters, thanks to their clear physical meaning, were estimated from direct observation of soil structure, except macropores morphologic parameters, some of which, although measurable, were obtained by calibration due to lack of relevant experimental data. The proposed model proved to be able to adequately simulate measured breakthrough curves as well as temporal evolution of water content profiles along the sample, especially with internal catchment process included.

Effect of impact load on articular cartilage: cell metabolism and viability, and matrix water content.

Significant evidence exists that trauma to a joint produced by a single impact load below that which causes subchondral bone fracture can result in permanent damage to the cartilage matrix, including surface fissures, loss of proteoglycan, and cell death. Limited information exists, however, on the effect of a varying impact stress on chondrocyte biophysiology and matrix integrity. Based on our previous work, we hypothesized that a stress-dependent response exists for both the chondrocyte's metabolic activity and viability and the matrix's hydration. This hypothesis was tested by impacting bovine cartilage explants with nominal stresses ranging from 0.5 to 65 MPa and measuring proteoglycan biosynthesis, cell viability, and water content immediately after impaction and 24 hours later. We found that proteoglycan biosynthesis decreased and water content increased with increasing impact stress. However, there appeared to be a critical threshold stress (15-20 MPa) that caused cell death and apparent rupture of the collagen fiber matrix at the time of impaction. We concluded that the cell death and collagen rupture are responsible for the observed alterations in the tissue's metabolism and water content, respectively, although the exact mechanism causing this damage could not be determined.

Effect of dimethylsulfoxide on articular cartilage proteoglycan synthesis and degradation, chondrocyte viability, and matrix water content.

To determine the effects of dimethylsulfoxide (DMSO) exposure on cartilage proteoglycan (PG) synthesis, PG degradation, chondrocyte viability, and matrix water content. Using a cartilage explant culture system, PG synthesis, PG degradation, matrix water content, and chondrocyte viability were determined for cartilage exposed to DMSO daily for selected periods of time. Juvenile bovine (calf) carpometacarpal joint cartilage explants. PG synthesis: Explants (n = 30/group) were separated into 10 groups based on the time of daily exposure to 10% DMSO. Exposure time was repeated daily for 3 days. The control group was incubated in basal medium alone for 3 days, with daily medium changes. Once all DMSO exposure times were complete for the third day, PG synthesis was determined by analysis of incorporation of radiolabelled sulfate. Cell viability: Explants (n = 3/group) were subjected to an identical DMSO exposure protocol, and examined histologically. The percentage of viable cells/high power field (hpf) was calculated for each group. PG degradation: Explants (n = 21/group) were preincubated with radiolabelled sulfate, then subjected to a similar DMSO exposure protocol. The medium was collected from all explants daily and assayed for PG content. After 3 days, the explants were digested and total labelled PG content determined. Percent of total explant labelled PG content released into the medium daily was determined for each group. Water content: Explants (n = 21/group) were separated into three treatment groups, one of which had no treatments performed, whereas the other two groups were incubated in basal medium for 72 hours, one with, and one without, 10% DMSO. Wet and dry weights were determined, and percent water calculated, for all three groups. Separate 1-way ANOVA were performed, with appropriate post hoc tests (P < .05). PG synthesis was significantly lower than control for all time periods of DMSO exposure except for 1 and 3 hours, and decreased in a time-dependent manner after the 1-hour exposure time. The mean percentage of viable cells/hpf was significantly lower than control for the 1-, 3-, 9-, 12-, and 24-hour treatment groups. There was no significant difference in PG degradation for any group compared with control for the first 2 days of incubation. All groups except the 24-hour group had a significantly higher degradation compared with control for the third day of incubation. Cartilage exposed to DMSO for 72 hours had a significantly lower water content, and cartilage incubated in basal medium alone for 72 hours had a significantly higher water content than cartilage that received no DMSO and no incubation. DMSO, in relatively low concentration, is detrimental to articular cartilage PG synthesis in a time-dependent manner. Dehydration of the cartilage and chondrocyte death also occur with increasing time of DMSO exposure. Significant PG degradation occurs on the third day of culture with daily DMSO exposure. As a joint lavage solution, DMSO has potentially deleterious effects on the metabolism of chondrocytes.

Simulation of dense vapor migration in discretely fractured geologic media

Density‐induced advection of organic vapors has been demonstrated to be a significant transport process in granular porous media if the permeability is sufficiently high such that density‐induced advection dominates over vapor diffusion. In the context of partially saturated fractured media, the presence of a network of open fractures may lead to rapid rates of density‐induced advection of the vapors in the fractures, even though the matrix may have low permeability. To investigate the various factors which affect vapor migration in discretely fractured porous media, a two‐dimensional finite element model has been developed whereby the porous matrix is represented by rectangular elements and the fractures are represented as one‐dimensional line elements which are superimposed onto the rectangular grid. The cross‐sectional model includes the processes of advection due to density and pressure gradients, and vapor and aqueous diffusion in both the fractures and the porous matrix. Phase partitioning between the vapor and aqueous phases and the aqueous and solid phases is assumed to be at equilibrium. Results from simulations involving a single vertical fracture indicate that density‐induced advection decreases in importance as the fracture aperture decreases. In this case, there appears to be a critical fracture aperture, above which density‐induced advection is the dominant process, and below which vapor diffusion dominates. Simulations that include a network of horizontal and vertical fractures show the importance of matrix properties such as air porosity and water content. An increase in the matrix air porosity results in a higher storage capacity for vapor‐phase contaminants and allows more diffusion to occur from the fractures to the matrix, whereas a higher matrix water content results in an increase in the degree of phase partitioning between the vapor and the water phases. Although these two processes act to retard the migration of the vapor plume, they can be problematic in the context of vapor extraction in fractured porous media. The reason for this is that these processes tend to increase the amount of contaminant mass that exists in the low‐permeability matrix. As a result, vapor extraction in fractured porous media can be very difficult.