Permeability of Buccal Mucosa

The buccal mucosa provides an alternative route of drug delivery that can be more beneficial compared to other administration routes. Although numerous studies and reviews have been published on buccal drug delivery, an extensive review of the permeability data is not available. Understanding the buccal mucosa barrier could provide insights into the approaches to effective drug delivery and optimization of dosage forms. This paper provides a review on the permeability of the buccal mucosa. The intrinsic permeability coefficients of porcine buccal mucosa were collected. Large variability was observed among the published permeability data. The permeability coefficients were then analyzed using a model involving parallel lipoidal and polar transport pathways. For the lipoidal pathway, a correlation was observed between the permeability coefficients and permeant octanol/water partition coefficients (Kow) and molecular weight (MW) in a subset of the permeability data under specific conditions. The permeability analysis suggested that the buccal permeation barrier was less lipophilic than octanol. For the polar pathway and macromolecules, a correlation was observed between the permeability coefficients and permeant MW. The hindered transport analysis suggested an effective pore radius of 1.5 to 3 nm for the buccal membrane barrier.

Zeta Potential, Effective Membrane Charge and Donnan Potential for TiO2 NF Ceramic Membrane

Nanofiltration (NF) ceramic membrane have found increasing applications particularly in wastewater and water treatment. In order to estimate and optimize the performance of NF membranes, the membrane should be characterized correctly in terms of their basic parameters such as effective pore radius (rp) and equivalent effective thickness as well as effective surface charge ( ), the effective charge density ( ) and Donnan potential ( ). The impact of electrokinetic (zeta) potential on the membrane surface charge density, effective membrane charge density and Donnan potential at two different concentrations of the reference solutions 0.001, 0.01 M sodium chloride at various pH values from 3 to 9, and effective pore radius (rp) for nominal 0.9 nm ceramic TiO2 NF membrane were evaluated. Experiments were conducted at cross flow (1.0 m/s) using Microelectrophoresis technique for measuring membrane zeta potential, effective pore radius, and Donnan steric pore model (DSPM). The TiO2 membrane isoelectric point (net membrane charge equals zero) was found at pH of 3.7, 3.5 for 0.001 and 0.01 M NaCl respectively. The results showed that the NF membrane zeta potential changes its sign from positive to negative after the isoelectric point. The evaluated effective pore radius was found to be equal to 0.56 nm by using (DSPM) and the membrane equivalent effective thickness equals to (2×10-6 m).

Superpermeable nanoporous carbon-based catalytic membranes for electro-Fenton driven high-efficiency water treatment

Based on the Hagen–Poiseuille equation, theoretical membrane permeability is inversely and directly proportional to its thickness and pore-radius, respectively, indicating that a thin membrane with an effective pore-radius is extremely permeable.

Electron Percolation In Copper Infiltrated Carbon

The work describes the dependence of the electrical conductivity of carbon materials infiltrated with copper in a vacuum-pressure autoclave on copper concentration and on the effective pore radius of the carbon skeleton. In comparison with non-infiltrated material the electrical conductivity of copper infiltrated composite increased almost 500 times. If the composite contained less than 7.2 vol% of Cu, a linear dependence of the electrical conductivity upon cupper content was observed. If infiltrated carbon contained more than 7.2 vol% of Cu, the dependence was nonlinear – the curve could be described by a power formula (x − xc)t. This is a typical formula describing the electron percolation process in regions containing higher Cu fraction than the critical one. The maximum measured electrical conductivity was 396 × 104 Ω−1 m−1 for copper concentration 27.6 vol%. Experiments and analysis of the electrical conductivity showed that electron percolation occurred in carbon materials infiltrated by copper when the copper volume exceeded the critical concentration. The analysis also showed a sharp increase of electrical conductivity in composites with copper concentration higher than the threshold, where the effective radius of carbon skeleton pores decreased to 350 nanometres.

The Study of PTFE Wicks Application to Loop Heat Pipes with Flat Evaporator

This study investigates the application of PTFE wicks to flat-plate loop heat pipes (FLHPs). PTFE’s low heat transfer coefficient effectively prevents heat-leakage, which is a problem with using metal wicks, lowering the operating temperature and pressure. This paper uses PTFE particles to form wicks, and the effect of PTFE on flat-plate LHP performance is investigated. Experimental results shows that the highest heat load reached was 100W, with lowest thermal resistance of 0.61°C/W, and heat flux of about 10W/cm2, For the wick properties, the wick had an effective pore radius of the wick was around 9.2μm, porosity of 47%, and permeability of 1.0 x 10-12m2. Compared to the highest heat flux reported in literature thus far for PTFE flat-plate LHPs, the heat flux in this study was enhanced by around 50%.

Effect of Meniscus Recession on the Effective Pore Radius and Capillary Pumping of Copper Metal Foams

An experimental study is performed to characterize the effect of meniscus recession on the effective pore radius and capillary pumping of copper metal foams which are to be used as wicks in heat pipes for electronic cooling. Knowledge of the effective pore radius is critical in defining the capillary pumping of a wicking material but is rarely measured under operating conditions. It is known that the meniscus of a liquid recedes when evaporating from a porous media, which could impact the effective pore radius and therefore the capillary pumping capabilities of the foam. To elucidate this impact, the evaporation rate is measured from foam strips wicking ethanol from a reservoir while applying heat fluxes to the foam. Using thermocouple and IR camera measurements, the measured evaporation rates are corrected to account for different thermal losses, including natural convection, direct thermal conduction to the liquid, and evaporation from the container. An analytical model is then developed to relate the evaporated mass to the maximum capillary pressure (minimum effective pore radius) provided by the foam. It is shown for the first time, that just before the onset of dryout, the recessed meniscus will lead to 15%, 28%, and 52% decrease in effective pore radius for samples with 68%, 75%, and 82% porosities, respectively. The capillary pumping therefore increases during evaporation. This can have significant impact on the prediction of the capillary limits in two phase capillary driven devices.

Effect of Meniscus Recession on the Effective Pore Radius and Capillary Pumping of Copper Metal Foams

An experimental study is performed to characterize the effect of meniscus recession on the effective pore radius and capillary pumping of copper metal foams which are to be used as wicks in heat pipes for electronic cooling. Knowledge of the effective pore radius is critical in defining the capillary pumping of a wicking material, but is rarely measured under operating conditions. It is known that the meniscus of a liquid recedes when evaporating from a porous media, which could impact the effective pore radius and therefore the capillary pumping capabilities of the foam. To elucidate this impact, the evaporation rate is measured from foam strips wicking ethanol from a reservoir while applying heat fluxes to the foam. Using thermocouple and IR camera measurements, the measured evaporation rates are corrected to account for different thermal losses, including natural convection, direct thermal conduction to the liquid, and evaporation from the container. An analytical model is then developed to relate the evaporated mass to the maximum capillary pressure (minimum effective pore radius) provided by the foam. It is shown for the first time, that just before the onset of dryout, the recessed meniscus will lead to 15%, 28% and 52% decrease in effective pore radius for samples with 68%, 75% and 82% porosities respectively. The capillary pumping therefore increases during evaporation. This can have significant impact on the prediction of the capillary limits in two phase capillary driven devices.

Grain-size to effective pore-size transformation derived from electrokinetic theory

Most permeability models use effective grain size or effective pore size as an input parameter. Until now, an efficacious way of converting between the two has not been available. We propose a simple conversion method for effective grain diameter and effective pore radius using a relationship derived by comparing two independent equations for permeability, based on the electrokinetic properties of porous media. The relationship, which we call the theta function, is not dependent upon a particular geometry and implicitly allows for the widely varying style of microstructures exhibited by porous media by using porosity, cementation exponent, formation factor, and a packing constant. The method is validated using 22 glass bead packs, for which the effective grain diameter is known accurately, and a set of 188 samples from a sand-shale sequence in the North Sea. This validation uses measurements of effective grain size from image analysis, pore size from mercury injection capillary pressure (MICP) measurements, and effective pore radius calculated from permeability experiments, all of which are independent. Validation tests agree that the technique accurately converts an effective grain diameter into an effective pore radius. Furthermore, for the clastic data set, there exists a power law relationship in porosity between effective grain size and effective pore size. The theta function also can be used to predict the fluid permeability of a sample, based on effective pore radius. The result is extremely good predictions over seven orders of magnitude.