The barrier properties of polymers are a significant factor in determining the shelf or device lifetime in polymer packaging. Nanocomposites developed from the dispersion of nanometer thick platelets into a host polymer matrix have shown much promise. The magnitude of the benefit on permeability has been different depending on the polymer investigated or the degree of dispersion of the platelet in the polymer. In this dissertation, the effect of density changes in the bulk and at the polymer-platelet interface on permeability of polymer nanocomposites is investigated. Nanocomposites of nylon, PET, and PEN were processed by extrusion. Montmorillonite layered silicate (MLS) in a range of concentrations from 1 to 5% was blended with all three resins. Dispersion of the MLS in the matrix was investigated by using one or a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Variation in bulk density via crystallization was analyzed using differential scanning calorimetry (DSC) and polarized optical microscopy. Interfacial densification was investigated using force modulation atomic force microscopy (AFM) and ellipsometry. Mechanical properties are reported. Permeability of all films was measured in an in-house built permeability measurement system. The effect of polymer orientation and induced defects on permeability was investigated using biaxially stretched, small and large cycle fatigue samples of PET and nylon nanocomposites. The effect of annealing in nylon and nanocomposites was also investigated. The measured permeability was compared to predicted permeability by considering the MLS as an ideal dispersion and the matrix as a system with concentration dependent crystallinity.

Call number: LD2668 .T4 1961 S27

Infiltration of highly concentrated solutions into unsaturated sand is suspected to be affected by the liquid-gas interfacial tension between the resident water and that of the infiltrating solution. The wetting of non-porous solid surfaces by liquids is commonly quantified by contact angle measurements. However, it is well known that wettability of porous solids cannot be accurately obtained by optical inspection because the liquid is penetrating into the pores of the solid in question. The main objective of this investigation was to find an effective method to measure contact angle in coarse porous media such as sandy soils. In this study, we compare both static and dynamic methods to estimate the contact angle formed by solutions of varying surface tension on silica sands. In addition, the contact angle of the imbibing solutions is estimated in both dry and water-wetted sand. Experiments in this study employed three clear acrylic columns of known volume to determine contact angles using two methods, one static method and one dynamic method. The three acrylic columns were packed with the same mass of each grade of Accusand�� (40/50, 30/40, 20/30, and 12/20 grades respectively) for triplicate measurements. The solutions used in this study included (1) pure water and (2) 5 molal NaNO��� and (3) n-hexane as a reference. The static method estimated contact angles in initially dry sand of 23�� for 40/50 sand, and 30�� to 33�� for 12/20, 20/30, and 30/40 sands, with the same values obtained for both solutions. Contact angles of these solutions observed in the dynamic test, were twice those found in the static test (averaging 45�� and 62�� respectively). In the case of pre-wetted sands, dynamic imbibition with water provided an estimated contact angle of 2��, while the NaNO��� solution yielded 21�� contact. Based on relative surface tensions of water and the 5 molal NaNO���, the Young's equation predicts a contact angle of 25��. These results strongly support recent claims of effective contact angles between these miscible, but contracting, fluids. The observed data suggest that the zero contact angle assumption is a poor one even for clean dry silica sand. In a dynamic system, gravitational forces cannot be ignored in course porous media. An analytical method, used to model imbibition of the solutions into the silica sands, was both accurate and useful for estimating contact angle. / Graduation date: 2002

The current state of shale gas reservoir dynamics demands understanding long-term production, and existing models that address important parameters like fracture half-length, permeability, and stimulated shale volume assume constant permeability. Petroleum geologists suggest that observed steep declining rates may involve pressure-dependent permeability (PDP). This study accounts for PDP in three potential shale media: the shale matrix, the existing natural fractures, and the created hydraulic fractures. Sensitivity studies comparing expected long-term rate and pressure production behavior with and without PDP show that these two are distinct when presented as a sequence of coupled build-up rate-normalized pressure (BU-RNP) and its logarithmic derivative, making PDP a recognizable trend. Pressure and rate field data demonstrate evidence of PDP only in Horn River and Haynesville but not in Fayetteville shale. While the presence of PDP did not seem to impact the long term recovery forecast, it is possible to determine whether the observed behavior relates to change in hydraulic fracture conductivity or to change in fracture network permeability. As well, it provides insight on whether apparent fracture networks relate to an existing natural fracture network in the shale or to a fracture network induced during hydraulic fracturing.

The term "impervious" is commonly used in urban settings to describe the permeability of buildings, roads, and parking lots. When estimating recharge to an aquifer underlying an urbanized area, impervious cover becomes a prime consideration. It is commonly assumed that an increase in impervious cover leads to a decrease in precipitation recharge. However, even a cursory glance at most roads, sidewalks, or parking lots reveals that, far from being impervious, there are abundant fractures that may provide avenues of infiltration. For this study, method was developed to determine the secondary permeability of pavements using a double ring infiltrometer to measure the infiltration rate of water into fractured pavements. Linear extrapolation is employed to determine the infiltration rate as the water depth approaches zero, which is used as a proxy for hydraulic conductivity by assuming that the gradient is unity. Data were collected on concrete and asphalt pavements located in Austin, Texas, at each point a fracture or expansion joint intersected along 30-meter scanlines. By dividing the sum of the discharges for each fracture by the area represented by the scanline we are able to determine the equivalent-porous-media hydraulic conductivity. The equivalent hydraulic conductivities for discrete fractures were found to range at least three orders of magnitude, from >10⁻² to 10⁻⁵ cm/sec; scanline hydraulic conductivities range two orders of magnitude from >10⁻⁴ to 10⁻⁶ cm/sec; permeability along the scanlines tends to be dominated by one or two highly conductive fractures; and the hydraulic conductivity of the entire paved surface is 5.9·10⁻⁵ cm/s. Both apertures and point hydraulic conductivities were found to have logarithmic distributions but cross plots demonstrated no correlation, which indicated that a combination of the fill material and sub grade, not the fractures and expansion joints themselves, limit infiltration. By multiplying the paved surface hydraulic conductivity by the time the surface can be expected to be saturated, we find that 170 mm or 21 percent of mean annual rainfall is available as potential recharge. When coupled with an enhanced subsurface permeability structure resulting from the installation of utilities and the reduction of evapotranspiration from the reduction of vegetation, the net effect of roads and parking lots could be an increase in precipitation recharge. / text

This dissertation develops analytical expressions for the effective hydraulic conductivity Kₑ of a three-dimensional porous medium bounded by two parallel planes of infinite extent separated by a distance 2a. Head varies randomly along each boundary about a uniform mean value. The log hydraulic conductivity Y forms a homogeneous, statistically anisotropic random field having a variance σᵧ² and principal integral scales λ₁, λ₂, λ₃. Flow is uniform in the mean parallel to the principal coordinate χ₁. A solution is first derived for mildly nonuniform media with σᵧ² ≪ 1 via an approximate form of the 1993 residual flux theory by Neuman and Orr. It is then extended to strongly nonuniform media with arbitrarily large σᵧ² by invoking the Landau-Lifshitz conjecture as Kₑ = KG exp {σᵧ² [1/2 — (D + S)]} . Here, K(G) is the geometric mean of hydraulic conductivities and D and S are domain and surface integrals, respectively. Based on a rigorous limiting analysis we show that when the length scale ratio p = a / λ₁ → 0, Kₑ is equal to the arithmetic mean hydraulic conductivity K(A). This supports the theoretical finding of Neuman and Orr and the numerical result by Desbarats. When ρ → ∞ we obtain expressions for Kₑ that have been previously derived in the stochastic literature for infinite flow domains. For strongly anisotropic media with integral scale ratios ε₂ = λ₂ / λ₁ and ε₃ = λ₃ / λ₁ equal to each other and tending to zero or infinity ( ) i 0) we obtain the closed form solution Kₑ = K(G) exp {σᵧ²[exp(—p) — 0 .5]} . The latter reduces to K(A) when ρ → 0 and tends to the harmonic mean K(H) as ρ → ∞. One can think of the case ε₂ = ε₃ = 0 as mean flow along parallel channels having mutually uncorrelated hydraulic conductivities, and of the case ε₂ = ε₃ → ∞ as mean flow normal to layers having uniform hydraulic conductivities. For statistically isotropic media we show numerically that Kₑ equals K(A) when ρ = 0.01; when ρ ≥ 4, Kₑ = K(G) exp(σᵧ²/6) the three-dimensional infinite domain solution. Our results support the analytical finding of Rubin and Dagan, and predict and explain all related bounded domain numerical results. Finally, contrary to Dagan's assertion, we show that for small ρ boundary effects are extremely important; the absolute value of the surface integral S equals the value of the domain integral D.

An estimation method for predicting the saturated hydraulic conductivity (Ksat) of the soil was developed for common Nova Scotia soil types by examination of historical Ksat records. Detailed statistical analysis was performed to develop useful predictive models for Ksat based on soil physical properties and to determine the confidence limits for specific horizon-soil type combinations. Sensitivity analysis of the Hooghoudt equation was then performed to establish Ksat classes to which the confidence limits could be assigned to complete the development of the estimation method. / Model development processes proved unsuccessful due to the influence of factors not considered by the model due to their qualitative nature. Independent field testing of the estimation method with respect to core and Guelph permeameter measurement techniques produced measured values within the same class as the estimated value 34% of the time for both techniques and values within one estimated class or less 70 and 76% of the time for core and permeameter techniques respectively.

No description available.

Digitized by Kansas Correctional Industries

Call number: LD2668 .T4 1965 H789 / Master of Science