Effective Pore Diameter Research Articles

Evapoporometry determination of pore-size distribution and pore fouling of hollow fiber membranes

Hollow fiber (HF) membranes are used in many applications for which characterization of the pore-size distribution (PSD) is necessary. Current techniques for determining the PSD require relatively expensive dedicated equipment. Moreover, most techniques are not applicable for characterization of fouled membranes. Evapoporometry (EP) is a novel characterization technique based on vapor-pressure depression that can detect the full spectrum of pore sizes in ultrafiltration (UF) membranes. In prior studies EP was used to determine the PSD of only flat sheet membranes using just isopropyl alcohol (IPA) as the volatile wetting test liquid. Here it is extended to HF membranes using both IPA and water as the test liquids. The average pore diameter of polyvinylidene fluoride (PVDF) HF membranes using IPA and water as the test liquids was 30.2±1.4nm and 27.4±2.0nm, respectively. The average pore diameter using IPA and water for polyacrylonitrile (PAN) HF membranes was 11.8±1.0nm and 12.1±2.8nm, respectively. Liquid displacement porometry (LDP) gave a markedly smaller average pore diameter of 20.7±3.8nm for the PVDF membranes compared to evaluating the pore diameter with EP owing to compaction under displacement pressures as high as 6MPa. LDP gave a substantially larger average pore diameter of 26.5±1.0nm for the PAN membranes compared to evaluating the pore diameter with EP owing to its inability to characterize pores smaller than 14nm. EP characterization of the PSD before and after fouling the PVDF membrane with humic acid and bentonite showed a 35% reduction in the effective average pore diameter owing to internal pore fouling.

Mixed polyamide-based composite nanofiltration hollow fiber membranes with improved low-pressure water softening capability

Mixed polyamide-based composite nanofiltraiton (NF) hollow fiber membranes with suitable characteristics for water softening under ultrafiltration (UF)-range low operating pressure were successfully developed. The thin-film selective layer of the composite membrane was formed via interfacial polymerization on the inner surface of a microporous polyethersulfone (PES) hollow fiber substrate with trymesoyl chloride (TMC) being the organic phase monomer, and a mixture of branched polyethyleneimine (PEI) and piperazine (PIP) being the monomers in the aqueous phase.In was found that there was a synergetic effect of PEI and PIP on the formation of the selective layer. The water permeability and salt rejection of the resultant membrane were both enhanced with a small amount of PIP added into the PEI aqueous phase, but dropped quickly with a higher PIP to PEI ratio. The optimized NF membrane possessed a molecular weight cut-off (MWCO) of 380Da, an effective pore diameter of 1.27nm, and pure water permeability (PWP) of 18.2l/m2hbar. Under an operating pressure of 2bar, the membrane exhibited rejection of 96.3% and 93.8% to 1000ppm MgCl2 and MgSO4 feed solutions, respectively. The capability of the newly developed membrane for low-pressure water softening was evaluated by employing simulated hard water feed solutions with different ionic compositions and total hardness. By the combining effect of electrostatic repulsion and size exclusion, the mixed PEI/PIP-based composite hollow fiber offered superior water softening performance compared with the membranes made with PEI or PIP alone as the aqueous phase IP monomer.

The Prediction Methods for Potential Suspended Solids Clogging Types during Managed Aquifer Recharge

The implementation and development of managed aquifer recharge (MAR) have been limited by the clogging attributed to physical, chemical, and biological reactions. In application field of MAR, physical clogging is usually the dominant type. Although numerous studies on the physical clogging mechanism during MAR are available, studies on the more detailed suspended clogging types and its prediction methods still remain few. In this study, a series of column experiments were inducted to show the process of suspended solids clogging process. The suspended solids clogging was divided into three types of surface clogging, inner clogging and mixed clogging based on the different clogging characteristics. Surface clogging indicates that the suspended solids are intercepted by the medium surface when suspended solids grain diameter is larger than pore diameter of infiltration medium. Inner clogging indicates that the suspended solids particles could transport through the infiltration medium. Mixed clogging refers to the comprehensive performance of surface clogging and inner clogging. Each suspended solids clogging type has the different clogging position, different changing laws of hydraulic conductivity and different deposition profile of suspended solids. Based on the experiment data, the ratio of effective medium pore diameter (Dp) and median grain size of suspended solids (d50) was proposed as the judgment index for suspended solids clogging types. Surface clogging occurred while Dp/d50 was less than 5.5, inner clogging occurred while Dp/d50 was greater than 180, and mixed clogging occurred while Dp/d50 was between 5.5 and 180. In order to improve the judgment accuracy and applicability, Bayesian method, which considered more ratios of medium pore diameter (Dp) and different level of grain diameter of suspended solids (di), were developed to predict the potential suspended solids types.

Effect of pore diameter and structure of mesoporous sieve supported catalysts on hydrodesulfurization performance

A series of mesoporous sieves with different pore diameters and structures have been controllably synthesized by adding variable amounts of swelling agent 1,3,5-trimethylbenzene in the preparation process for SBA-15. NiMo catalysts supported by mesoporous sieves are prepared by using the newly proposed Mo-based organic–inorganic hybrid nanocrystals as precursors to load Mo and subsequently using wetness impregnation to load Ni. The hydrodesulfurization (HDS) activity of these obtained catalysts is evaluated in a continuously flowing tubular fixed-bed microreactor using 1wt% dibenzothiophene (DBT) in heptane as a model compound. The results show that HDS ratio has gradually increased as the pore diameter of supports is enlarged from 7 to 11nm with the mesostructure keeping an ordered two-dimensional hexagonal symmetry. When the structure is in the intermediate stage of structural transition from ordered hexagonal mesostructure to mesocecullar structure, HDS ratio is decreased dramatically due to the disordered and collapsed structure to block the pore channels. After the mesocecullar structure with three-dimensional open pore channels is formed which is more convenient for the molecular diffusion, HDS ratio has increased again as a result. It is concluded that both the pore size and window size connecting the adjacent pores play an important role in the HDS activity but the window size is of more significant importance, which is the key point for the enhanced catalytic performance.

Rules-of-Thumb for Predicting Air-Entry Value of Disturbed Sands from Particle Size

With the goal of finding empirical direct relationships between the air-entry values (AEV) and characteristic particle diameters (i.e., d10, d20, d30,… d90,) determined from the particle-size distribution, we examined the AEV values for a variety of disturbed sands. It was found that the AEVs were, in general, strongly correlated to the characteristic diameters. The correlation was more distinct for uniform sands with uniformity coefficient of 2 or smaller. For those with larger uniformity coefficient values, the AEVs were highly correlated to smaller characteristic particle sizes d10 to d50 but less with larger characteristic particle sizes, d60 to d90. For all the sands examined in this study, the AEVs showed the least scatter when plotted against d30. The large particles do not necessarily control the AEVs because the pores between the large particles are often filled with smaller particles. The following best-fit power functions with respect to the frequently used characteristic particle diameters were found to have high r2 values; AEV = 8.2 d30−0.99 and AEV = 9.5 d50−1.05 (with AEV in cm and d in mm). The exponent close to -1 in both relationships confirms a strong “inverse” proportionality. The effective pore diameter, de, estimated from the AEVs agreed closely with the mean pore diameters measured with mercury porosimetry and X-ray micro-tomography. All these findings suggest that the AEVs are strongly controlled by the particle sizes which determine the mean pore size, and that the capillary rise theory is applicable in terms of the effective pore diameter. Finally, easy-to-implement rule-of-thumb expressions, AEV [cm] = 8/d30[mm] and AEV [cm] = 10/d50[mm] were proposed with some limitations for a quick but reasonably accurate prediction of the AEV.

Fabrication of conjugated polymeric nanochannels from star-shaped supramolecular liquid crystals containing two different photoreactive groups

New conjugated polymeric nanochannels were prepared via photopolymerisation and core extraction of star-shaped supramolecular liquid crystals formed by simple hydrogen bonding between a phloroglucinol core and pyridine derivatives containing two different photoreactive groups. The polymerisable supramolecular liquid crystal exhibited a discotic columnar mesophase. Photopolymerisation of supramolecular liquid crystalline monomer provided cross-linked conjugated polymeric columns in which the diacetylene and acrylate moieties were selectively polymerised along the vertical and horizontal axes, respectively. Chemical treatment of the cross-linked conjugated columns with sodium hydroxide resulted in the removal of the phloroglucinol core to produce the cross-linked conjugated polymeric nanochannels with an estimated effective pore diameter of about 1 nm. The controlled methodology in the present study can be used to design and fabricate conjugated nanoporous organic materials with intriguing ordered structures.

Effect of a macromolecular- or bio-fouling layer on membrane distillation

Membrane distillation (MD) is a continuous process whereby a hot aqueous feed provides the latent heat to vaporize water that diffuses through a hydrophobic microporous membrane and condenses. MD is attractive for saline and wastewater treatment as well as concentrating heat-sensitive solutions such as fruit juices and biological fluids since it operates at moderate temperatures and atmospheric pressure, rejects particulates and nonvolatile solutes, uses non-selective membranes, and has low capital costs. However, MD and MD bioreactor (MDBR) performance is compromised by fouling. The effect of fouling layers with reasonably large pores (>50nm) is reasonably well-understood and has been incorporated into MD models. However, the effect of fouling layers with very small pores or free volume (<50nm) owing to macromolecular- and bio-fouling (MMBF) is not well-understood. While MMBF introduces an additional resistance to heat transfer, it can also reduce the vapor-pressure driving force. This latter effect is unique to MD fouled by MMBF. In this analysis the vapor pressure reduction has been incorporated into a model that indicates the large flux declines observed in prior studies can be explained by the vapor-pressure reduction associated with pore diameters ranging from 3.9 to 8.5nm, which agree well with evapoporometry characterization of MMBF sludges. The predicted flux decline and temperature polarization coefficient indicate that the vapor-pressure reduction increases markedly for effective pore diameters less than 10nm, but can be mitigated by increasing the thermal resistance of the membrane and by fabricating a dual-layer membrane for which the feed side is hydrophilic with relatively large pores.

A PREDICTIVE BUBBLE POINT PRESSURE MODEL FOR POROUS LIQUID ACQUISITION DEVICE SCREENS

This article presents a simplified model for porous screen channel liquid acquisition devices based on a maximum bubble point pressure method from Adamson and Gast (1997). To validate the model, three 304 stainless steel (325 × 2300, 450 × 2750, and 510 × 3600) mesh samples were tested in methanol, acetone, isopropyl alcohol, and water. Screen pores are estimated based on analysis from scanning electron microscopy, historical data, and current test data. Results show that the bubble point pressure is proportional to the surface tension of the fluid only when accounting for nonzero contact angles. The previous assumption that bubble point pressure scales inversely with effective pore diameter is shown to be invalid, as the second finest 450 × 2750 produced the highest bubble point of the three screens. The simplified bubble point model can be used to make predictions for any pure fluid when pore diameters are based on bubble point tests and not SEM analysis.

Depth and performance evaluation of a laboratory scale sand filtration system for wastewater treatment

Intermittent sand filtration (ISF) was adopted in the treatment of synthetic wastewater having septic tank effluent's properties in the laboratory. Over a period of 84 days synthetic wastewater was intermittently dosed onto two sand filters of 50 cm and 100 cm depths at an interval of 4 h. The filter material has an effective size d$_{10}$ of 0.42 mm, d$_{60}$ of 0.92 mm, coefficient of uniformity, Cu, of 2.2, and hydraulic conductivity of 4.632 $\times $ 10$^{-3\, }$ms$^{-1}$ with an effective pore diameter of 0.094 mm. The hydraulic loading was 0.144 m/day and the BOD$_{5}$ of the wastewater was 172.3 mg/L. The removal of suspended solids, ammonium-nitrogen (NH$_{4}$-N), and BOD$_{5}$ in 100- and 50-cm columns was 91.4% and 88.6%, 98.7% and 99.8%, and 92% and 90%, respectively, while PO$_{4}$-P removal was about 45% in both columns. Unlike other parameters, NO$_{3}$-N was increasing, which signifies that denitrification did not take place in the filter columns. Based on the results, the filter column of 50 cm is economically preferable due to the insignificant difference when compared with the 100-cm filter column. The bacteria removal was slightly higher in 100 cm depth (99.88%) than in 50 cm depth (99.68%).

Geometrical Membrane Curvature as an Allosteric Regulator of Membrane Protein Structure and Function

Transmembrane proteins are embedded in cellular membranes of varied lipid composition and geometrical curvature. Here, we studied for the first time the allosteric effect of geometrical membrane curvature on transmembrane protein structure and function. We used single-channel optical analysis of the prototypic transmembrane β-barrel α-hemolysin (α-HL) reconstituted on immobilized single small unilamellar liposomes of different diameter and therefore curvature. Our data demonstrate that physiologically abundant geometrical membrane curvatures can enforce a dramatic allosteric regulation (1000-fold inhibition) of α-HL permeability. High membrane curvatures (1/diameter ∼1/40 nm−1) compressed the effective pore diameter of α-HL from 14.2 ± 0.8 Å to 11.4 ± 0.6 Å. This reduction in effective pore area (∼40%) when combined with the area compressibility of α-HL revealed an effective membrane tension of ∼50 mN/m and a curvature-imposed protein deformation energy of ∼7 kBT. Such substantial energies have been shown to conformationally activate, or unfold, β-barrel and α-helical transmembrane proteins, suggesting that membrane curvature could likely regulate allosterically the structure and function of transmembrane proteins in general.

Morphological Analyses of Polymer Electrolyte Fuel Cell Electrodes with Nano‐Scale Computed Tomography Imaging

AbstractWe report a three‐dimensional (3D), pore‐scale analysis of morphological and transport properties for a polymer electrolyte fuel cell (PEFC) catalyst layer. The 3D structure of the platinum/carbon/Nafion electrode was obtained using nano‐scale resolution X‐ray computed tomography (nano‐CT). The 3D nano‐CT data was analyzed according to several morphological characteristics, with particular focus on various effective pore diameters used in modeling gas diffusion in the Knudsen transition regime, which is prevalent in PEFC catalyst layers. The pore diameter metrics include those based on chord length distributions, inscribed spheres, and surface area. Those pore diameter statistics are evaluated against computational pore‐scale diffusion simulations with local gas diffusion coefficients determined from the local pore size according to the Bosanquet formulation. According to our comparison, simulations that use local pore diameters defined by inscribed spheres provide effective diffusion coefficients that are consistent with chord‐length based estimations for an effective Knudsen length scale. By evaluating transport rates in regions of varying porosity within the nano‐CT data, we identified a Bruggeman correction scaling factor for the effective diffusivity.

Grand canonical Monte Carlo simulation for hydrogen uptakes based on nanoporous NaBH4

A new hydrogen storage route of 3D nanoporous sodium borohydride (NPSB) generated by removing special atoms is proposed in this work. Three different size pores of NPSB-1 (7 A), NPSB-2 (10 A) and NPSB-3 (14 A) are presented, and the hydrogen storage capacities of these NPSBs are simulated by employing a grand canonical Monte Carlo (GCMC) procedure for a temperature range of 77–298 K and a pressure range of 0.1–100 bar. The effects of pore diameter, temperature and pressure on the hydrogen adsorption have been examined. The results show that the adsorption of hydrogen decreases and increases with increasing temperature and hydrogen pressure, respectively. It also reflects that the hydrogen adsorption capacities at higher pressures are dependent on pore diameter, while independent of pore diameter at lower pressures.

The Effective Pore Diameter of a Three-Dimensional Numerical Model for Estimating Heat and Fluid Flow Characteristics in Metal Foams

A three-dimensional numerical model is proposed to determine heat and fluid flow characteristics in metal foams. A series of full three-dimensional numerical calculations was performed to reveal complex three-dimensional ve- locity, pressure and temperature fields within three-dimensional porous structures of the metal foams. These numerical re- sults are processed to obtain the macroscopic characteristics such as the permeability, inertia, dispersion and interstitial heat transfer coefficients. An effective pore diameter concept has been proposed to correlate the resulting heat and fluid flow characteristics with available empirical correlations. In this study, we shall conduct a numerical study on heat and fluid flow in metal foam using a three-dimensional nu- merical model of periodical structure. In order to capture irregularities in real foams, quantities calculated at specific flow angles are ensemble-averaged over the flow angle. A rational way to evaluate the effective pore diameter, which is used as the characteristic length of present three-dimensional numerical model, is proposed. Permeability, Forchheimer coefficient, thermal dispersion and volumetric heat transfer coefficient are determined by spatially averaging micro- scopic numerical results. The validity of the present numeri- cal model and the effective pore diameter are examined by comparing the numerical results with available empirical correlations. Furthermore, an interesting relationship be- tween the thermal dispersion conductivity and the volumet- ric heat transfer coefficient is elucidated.

Gas transport and subsoil pore characteristics: Anisotropy and long-term effects of compaction

Anisotropy of soil pore functions significantly affects the transport of gas and water in soil. This paper quantifies anisotropy of subsoil pores and investigates the long-term impact of soil compaction by agricultural machinery. Two long-term field experiments on soil compaction formed the basis for the investigation, one established in 1981 on a clay soil in Finland (60°49′N, 23°23′E) and another in 1995 on a sandy clay loam in Sweden (55°49′N, 13°11′E). In 2009/2010, soil cores were sampled in vertical and horizontal directions from 0.3, 0.5, 0.7 and 0.9m depth (the two lower depths only in Sweden). In the laboratory, water content, air-filled porosity (εa), air permeability (ka) and gas diffusivity (Ds/D0) were determined at selected matric potentials. For the sandy clay loam, morphological characteristics of pores (effective pore diameter, dB; tortuosity, τ; the number of effective pores per unit area, nB) were calculated using a tortuous tube model at −100hPa matric potential. Blocked air-filled porosity (εb) and a pore continuity index (N) were estimated from the relationship between ka and εa for a range of matric potentials. A factor of anisotropy (FA) was determined as the ratio of a given property measured in the horizontal direction to that in the vertical direction. ka showed anisotropic behaviour (FA<1) for the clay soil and for the 0.3m depth of the non-compacted sandy clay loam soil, while Ds/D0 displayed anisotropy for the clay soil (FA<1). In the sandy clay loam soil, dB and nB displayed significant anisotropy (FA<1) except at 0.9m. We interpreted this as effects of biological activities and physical processes in the B-horizon not being active in the C-horizon (0.9m depth). Compaction generally reduced ka, Ds/D0, dB, nB and increased τ for both sampling directions. Compaction had an effect on anisotropy for soil drained to −100hPa, but only for ka and dB in the sandy clay loam at 0.3m depth. Compaction reduced anisotropy for the N parameter, i.e. effects on soil pore continuity at the macropore scale, while it increased the anisotropy for εb. Our data thus indicate that compaction had persistent effect on soil physical properties and also affects anisotropy, especially that of macropores.

Mechanics and molecular filtration performance of graphyne nanoweb membranes for selective water purification

Two-dimensional carbon materials such as the 2D nanoweb-like graphyne membrane are promising as molecular sieves for energy and environmental applications. Based on the application of water purification - the removal of contaminants from wastewater and seawater - here we use molecular dynamics (MD) simulations to investigate the interplay between mechanical forces, filtration mechanisms, and overall performance for graphyne membranes with different pore sizes. We carry out biaxial tensile tests and verify the superior mechanical robustness and tolerance of graphyne membranes against possible deformations from the membrane installation process. A possible ultimate stress in excess of 15 GPa and an ultimate strain of 1.2-2.7% are determined. We also demonstrate their excellent filtration performance with barrier-free water permeation and perfect rejection of the representative contaminants considered here, including divalent heavy metal salts (copper sulfate), hydrophobic organic chemicals (benzene and carbon tetrachloride), and inorganic monovalent salts (sodium chloride). We find that graphtriyne, with an effective pore diameter of 3.8 Å, exhibits an optimal purification performance, because the contaminant rejection rate is more sensitive to pore size than water permeability. In addition, we find that the hydrophobic graphyne membranes exhibit higher rejection rates for hydrophilic contaminants compared to the hydrophobic ones. This size exclusion effect is a result of the larger hydrated radii of hydrophilic species due to stronger interactions between them and water molecules. Finally, we find that the maximum deformation of graphtriyne at the ultimate strain before material failure has only a minor impact on its filtration performance. One of the advantages of using graphyne for water purification is that no chemical functionalization or defects need to be introduced, which maintains the structural integrity of the membrane, and possibly, the long-term device performance.

CALHM1 is an Extracellular Ca2+- and Voltage-Gated ATP Permeable Ion Channel

We identified CALHM1 as a pore-forming subunit of a plasma membrane ion channel with weak ion selectivity and unique coupled allosteric gating regulation by voltage and extracellular Ca2+ (Ca2+o) (PNAS 109: E1963 (2012)). CALHM1 is expressed in mouse cortical neurons where it accounts for low [Ca2+]o-enhanced conductance and action potential firing. We recently determined that a CALHM1 channel is a hexamer with an estimated effective pore diameter ∼14A.Extracellular adenosine 5'-triphosphate (ATP) plays critical roles in physiological and signal transduction processes. We examined whether ATP can permeate CALHM1 channels. Reducing [Ca2+]o to activate CALHM1 induced ATP release from hCALHM1-expressing HeLa and COS-1 cells, and Xenopus oocytes. Neither CALHM1 expression nor lowering [Ca2+]o caused cell damage. Involvement of other possible mechanisms was ruled out because ATP release was unaffected by Brefeldin A (vesicular release), DCPIB (volume-sensitive Cl− channels), A438079 (P2X7 receptors), heptanol and carbenoxolone (connexins and pannexins). In contrast, ruthenium red (RuR), which inhibits CALHM1 currents, abolished low [Ca2+]o-evoked ATP release. Thus, CALHM1 expression induces a novel ATP permeability. Ca2+o inhibited ATP release with IC50 = 495 μM and Hill coefficient of 1.9, kinetic properties similar to those of its gating regulation. Membrane depolarization activates CALHM1 channels in normal [Ca2+]o. hCALHM1-expressing but not mock-transfected cells released ATP in response to high [K+]o-induced depolarization in normal [Ca2+]o, which was inhibited by RuR but not by connexin and pannexin-1 blockers. Thus, regulation of ATP release is correlated with the gating properties of CALHM1 channels, indicating that the CALHM1 channel is the conduit for ATP release. These results demonstrate that CALHM1 is a voltage-gated ATP release channel that may contribute to ATP release in physiological and pathological conditions.

Interfacially polymerized composite nanofiltration hollow fiber membranes for low-pressure water softening

Composite nanofiltration (NF) hollow fiber membranes desirable for water softening under low operating pressure (<2bar) were successfully developed in the current study. The thin-film selective layer of the composite hollow fiber was formed through interfacial polymerization on the inner surface of a polyethersulfone (PES) ultrafiltration (UF) membrane substrate with branched polyethyleneimine (PEI) and trymesoyl chloride (TMC) employed as the monomers in aqueous and organic phases, respectively.It is found that a proper molecular weight of PEI and the presence of sodium dodecyl sulfate (SDS) in the aqueous phase are important for a successful interfacial polymerization reaction. The resulting membrane prepared with optimized preparation parameters possesses a positively charged thin-film selective layer with pure water permeability (PWP) of about 17l/m2hbar and a molecular weight cut-off (MWCO) of around 500Da, which translates into the effective pore diameter of about 1.29nm. With combined separation mechanisms of Donnan exclusion and steric hindrance, it was possible to achieve MgCl2 and MgSO4 rejection of 96.7% and 80.6%, respectively, when tested for 1000ppm feed solutions at 2bar operating pressure. In addition, for a 3000ppm TDS feed stream containing salt mixtures, the membrane rejections for Mg2+ and Ca2+ ions were found to be around 90% while the water flux was about 20l/m2h at 2bar pressure, suggesting the potential of the newly developed composite hollow fibers for effective water softening application.

Impact of Electrospun Conduit Fiber Diameter and Enclosing Pouch Pore Size on Vascular Constructs Grown Within Rat Peritoneal Cavities

The generation of vascular grafts by recruiting autologous cells within the peritoneal cavity has shown promise. However, the microenvironment affects cell differentiation and elastic matrix production. Therefore, this study determined the impact of systematic changes in the average fiber diameter of electrospun poly(ɛ-caprolactone) conduits, and the pore size of pouches used to enclose the conduits, on recruited cells. After 2 weeks in the peritoneal cavity, fibrous capsules formed containing macrophages, α-smooth muscle actin (α-SMA)(+) and SM22α(+) myofibroblastic or smooth muscle like-cells, and what appeared to be mesothelial cells on the outer surfaces. These cells infiltrated and deposited matrix (e.g., collagen, hyaluoronan, and limited elastin) within conduit walls. Constructs enclosed within the largest pore pouches exhibited significantly better tissue generation responses (e.g., better cell infiltration, elongation, and matrix deposition). Additionally, the healing response was impacted by the conduit average fiber diameter, and consequently, the effective pore diameter, with the largest diameter fibers promoting the most positive healing response (e.g., greater total cellularity, extracellular matrix deposition, and α-SMA(+) cells). Six weeks post-intra-aortal grafting, constructs were occluded, but significant remodeling also occurred in the arterial microenvironment. Overall, these results demonstrate the importance of microenvironmental cues on recruited peritoneal cells and the necessity of developing strategies to further improve elastic matrix synthesis.

Influence of contact medium and surfactants on carbon dioxide clathrate hydrate kinetics

Carbon dioxide (CO2) hydrate formation kinetic was investigated in a fixed bed crystallizer at constant pressure (3.55MPa) and temperature (274K). Porous media of three different silica gels were used, with a mesh size of 60–120, 100–200 and 230–400 having different surface area. The observed trends indicate that silica gel with larger surface area leads to higher gas consumption as well as reduces the induction time. The effect of pore diameter and particle size distribution has already been reported in a previous study [1]. In this study the effect of additives on hydrate formation kinetics were also investigated. The additives studied were nonionic surfactant Tween-80 (T-80), cationic dodecyltrimethylammonium chloride (DTACl) and anionic Sodium Dodecyl Sulphate (SDS). Out of the three surfactants used in this study, SDS was found to be most effective in enhancing the rate of hydrate formation as well as reducing the induction time. The current result shows significant improvement in water to hydrate conversion in silica gel media compared to quiescent water or surfactant–water system under similar conditions.

Drug permeation behavior through thermo- and pH-responsive polycarbonate-g-poly(N-isopropylacrylamide-co-acrylic acid) composites

Poly(N-isopropylacrylamide-co-acrylic acid) hydrogel was grafted onto track-etched polycarbonate (PC) films using the free-radical polymerization method to prepare thermo-sensitive micro-porous films. Differential scanning calorimeter analysis was used to determine the lower critical solution temperature for the hydrogels. Thermo-gravimetric analysis was used to determine the thermal stability of the PC–hydrogel composite films. The composite films were characterized using Fourier transform-infrared spectra, scanning electron microscope, and effective pore diameters derived from water permeability data. 4-Acetamidophenol, citric acid, KCl, and methyl orange were used as the model drugs. For neutral drugs, the larger molecules exhibited lower permeability but higher on–off ratio than smaller ones. The strong electrolyte model molecules (KCl) exhibited depressed permeability due to enlarged hydrated ion sizes. The acidic (citric acid) model solution promoted gel shrinkage, resulting in increased drug permeability and on–off ratio.