Varying Pore Size Research Articles

A simulation and data informed approach to porosity partitioning

Information about pore shape and geometry form one of the significant inputs in determining the effective elastic properties of porous rocks. The size and structure of the pores determine the amount of fluid contents which in turn determine their bulk response. Conventionally, effective medium models have been used to study the macroscopic properties of these rocks. These models often use a fixed set of microscopic variables (like the shape parameter) to describe their bulk behavior. Barring the specification of the elastic properties of the starting host material, their original formulations often lack the provision to integrate any experimental data, later. In the context of carbonates, the rocks exhibit a large variation in pore shapes and sizes, hindering the development of rock physics models. Therefore, they eventually require calibration. This is an important issue as the size of the pores here range from nanoscale to meter scale due the presence of primary and secondary porosity systems. In this paper we develop a method that can integrate the pore shape information into differential effective medium models using simple statistical and machine learning algorithms. Avoiding the use of conceptual values for the interparticle and vug type pores, our technique facilitates a data-based inference of the shape parameters from both the image data and forward model simulations. Micro-tomography images were used to extract the pore shape information for relatively larger pores such as the vugs. The information about the interparticle pores was deduced using a simulation-based approach from well-logs. Both of these were used to specify the properties of the new inclusions, hence aiding in data informed porosity partitioning. Finally, we outline a simple regression-based scheme using a first order polynomial model that can be used to calibrate any general rock physics model.

Variations in pore size and contact angle distributions control rhizosphere rewetting

Rhizosphere wettability decreases upon severe drying leading to periods of prolonged low water content around roots after precipitation or irrigation. These observations were explained by the temporal hydrophobic character of mucilage, while structural alterations of the pore space caused by mucilage, such as pore clogging, remained mostly unexplored. In this study, time-series neutron radiography and a pore network model were used to assess the impact of pore geometry and wettability on water flow following the addition of mucilage in a sand substrate. To do so, we monitored the capillary rise of ethanol and water separately for mucilage contents, ranging from 0.0 to 2.0 mg g−1. A pore network model was developed to analyze the impact of alterations in pore geometry and wettability. Results are compared with analytical solutions of the Lucas-Washburn equation. Rewetting dynamics were explained by a combination of a decrease in effective pore throat size and a global decrease in wettability. The local distribution of wettability, however, appeared of minor importance as dynamics of water imbibition could be matched by a uniform effective contact angle. For 0.1 mg g−1 mucilage content increased wettability was predicted for both approaches: the analytical solution and the pore network model fit. At larger contents, a decrease in wettability occurred which was accompanied by a decrease in derived effective pore and pore throat size. On a minute scale, rewetting appeared to steadily progress at all mucilage contents with accelerated rewetting observed at 0.6 mg g−1 likely related to an increased wetting front length. This study highlights the importance of mucilage on pore geometry in combination with wettability modifications in the rhizosphere. Aside from rhizosphere rewetting, the presented approach provides an opportunity to investigate further wettability-related processes in other soil environments on various spatial scales.

Performance Evaluation of Ceramic Membrane Based Process for Microalgal Biomass Harvesting: Analyzing the Effect of Membrane Pore Sizes, Process Optimization and Fouling Behavior

Microalgal biofuel emerges as a potential resource of renewable energy in view of global energy demand and increasing greenhouse gases. However, substantial challenges of efficient up-concentrating of biomass act as a bottleneck in large scale production of biofuel. The study is aimed towards unravelling the obstacles encountered during dewatering of biomass from mixed-microalgae consortia using ceramic membrane based process with varying pore sizes in the microfiltration (MF) and ultrafiltration (UF) range. For clay and alumina based MF membrane, 1.2 µm pore size (average) and for alumina supported nano-alumina coated UF membrane, ∼0.01 µm pore size (average) was used. The effect of various recirculation parameters was studied for process optimization. Resistance-in-series model was employed for analyzing fouling behavior of the membranes. MF membrane was observed to have better harvesting efficiency than the UF counterpart in terms of productivity (124.41). Optimum permeate flux of microalgal suspension was found to be 315.29 L.m−2.h−1 for MF membrane. Regeneration of membranes by air assisted backpulsing process showed up to 97.71% of flux recovery for MF membrane. Volume reduction factor/ membrane area (371) was found to be considerably high compared to various reported studies. The study highlighted efficient harvesting of microalgae using indigenously developed ceramic MF membrane integrated filtration towards cost-effective production of biofuel.

A novel device for swift and efficient CD44 protein digestion of pipette tips in human serum

For molecular diagnostics in modern biomedical research, electrospray ionisation mass spectrometry (ESI-MS) based on proteome profiling is important. Now a days, sample preparation such as proteolysis and protein extraction remain incredibly challenging and inefficient. Recent sample-preparation methods based on micro tips show promising results toward the aim “a proteome in an hour”. Proteolysis at the tip, is still infrequently observed and does not represent the processing of complex bio-samples. In this study, we outline a unique technique for detecting and extracting human serum CD44 biomarkers by ligand–protein interactions. This method employs macropores silica particles (MPSP) or (MOSF) modified with hyaluronic acid (HA). In order to assist in the profile of the human serum proteome, we limitations of immunoassays for rapid and multimodal proteolysis. For effective in situ proteolysis, in micropipette tips, MPSP were designed as nanoreactors with variable pore size and surface chemistry. In MS-based bottom-up proteome analysis, the device as-built demonstrated favourable sensitivity (LOD of 0.304 ± 0.007 ng/mL and LOQ of 0.973 ± 0.054 ng/mL), selectivity, durability (at −20 °C for 2 months), reuse (at least 10 times), and minimal memory impact. In addition, we examined into specific surface chemistries of nanoparticles for the absorption of proteins in serum and profiled the HA-binding serum proteome, setting a new preliminary benchmark for future databases. Our study not only helped establish a new platform for extracting/detection of CD44 and identifying the HA-binding proteome, but it also offered design recommendations for ligand affinity-based techniques for the antibody-free study of serum biomarkers with a view towards diagnostic applications.

Structural, spectral, and dynamical behaviors of biodegradable choline-based ionic liquids (CBILs) confined inside neutral and charged mxene nanopores for supercapacitor applications

This study explores the potential of using biodegradable choline-based ionic liquids (CBILs) as a more sustainable and eco-friendly alternative to classical ILs in the field of electrolyte media for energy storage devices. While previous studies have focused on electrostatic and capacitance properties, it is important to also consider dynamics and structural behavior when choosing adjustable electrolytes and electrodes. In this regard, molecular dynamics simulations were used to study the structural, spectral, and dynamical behaviors of two CBILs ([Ch][Sa] and [Ch][β-Ala]) inside MXene nanopores with varying pore size and surface charge density. As the pore size decreases, the number of hydrogen bonds in the first layer decreases from 0.447 to 0.122 and 0.154–0.063 in [Ch][Sa] and [Ch][β-Ala], respectively. Also, the presence of an aromatic ring benefits packing efficiency, causing [Sa]- to have a parallel orientation relative to MXene surface. Applying a fixed charge (1.8–7.2 μC/cm2) on MXene electrodes results in the formation of an electric double layer (EDL). At higher surface charge densities, there is slower dynamics and lower structural correlations between anions and cations. Moreover, Infrared (IR) spectra show blue and red shifts for the O-H bond in choline and carbonyl C-O stretching vibrational modes in anions, respectively, due to the interaction of anions with the MXene surface in the first layer reducing their interaction with cations. The results of our research may potentially lead to the creation of novel energy storage devices that are eco-friendly, utilizing MXene electrodes and CBILs as electrolytes.

Survival of Zirconium-Based Metal-Organic Framework Crystallinity at Extreme Pressures.

Recent research on metal-organic frameworks (MOFs) has shown a shift from considering only the crystalline high-porosity phases to exploring their amorphous counterparts. Applying pressure to a crystalline MOF is a common method of amorphization, as MOFs contain large void spaces that can collapse, reducing the accessible surface area. This can be either a desired change or indeed an unwanted side effect of the application of pressure. In either case, understanding the MOF's pressure response is extremely important. Three such MOFs with varying pore sizes (UiO-66, MOF-808, and NU-1000) were investigated using in situ high-pressure X-ray diffraction and Raman spectroscopy. Partial crystallinity was observed in all three MOFs above 10 GPa, along with some recovery of crystallinity on return to ambient conditions if the frameworks were not compressed above thresholds of 13.3, 14.2, and 12.3 GPa for UiO-66, MOF-808, and NU-1000, respectively. This threshold was marked by an unexpected increase in one or more lattice parameters with pressure in all MOFs. Comparison of compressibility between MOFs suggests penetration of the pressure-transmitting oil into MOF-808 and NU-1000. The survival of some crystallinity above 10 GPa in all of these MOFs despite their differing pore sizes and extents of oil penetration demonstrates the importance of high-pressure characterization of known structures.

3D Porous Scaffold-Based High-Throughput Platform for Cancer Drug Screening.

Natural polymer-based porous scaffolds have been investigated to serve as three-dimensional (3D) tumor models for drug screening owing to their structural properties with better resemblance to human tumor microenvironments than two-dimensional (2D) cell cultures. In this study, a 3D chitosan-hyaluronic acid (CHA) composite porous scaffold with tunable pore size (60, 120 and 180 µm) was produced by freeze-drying and fabricated into a 96-array platform for high-throughput screening (HTS) of cancer therapeutics. We adopted a self-designed rapid dispensing system to handle the highly viscous CHA polymer mixture and achieved a fast and cost-effective large-batch production of the 3D HTS platform. In addition, the adjustable pore size of the scaffold can accommodate cancer cells from different sources to better mimic the in vivo malignancy. Three human glioblastoma multiforme (GBM) cell lines were tested on the scaffolds to reveal the influence of pore size on cell growth kinetics, tumor spheroid morphology, gene expression and dose-dependent drug response. Our results showed that the three GBM cell lines showed different trends of drug resistance on CHA scaffolds of varying pore size, which reflects the intertumoral heterogeneity across patients in clinical practice. Our results also demonstrated the necessity to have a tunable 3D porous scaffold for adapting the heterogeneous tumor to generate the optimal HTS outcomes. It was also found that CHA scaffolds can produce a uniform cellular response (CV < 0.15) and a wide drug screening window (Z' > 0.5) on par with commercialized tissue culture plates, and therefore, can serve as a qualified HTS platform. This CHA scaffold-based HTS platform may provide an improved alternative to traditional 2D-cell-based HTS for future cancer study and novel drug discovery.

Energy-efficient reuse of bio-treated textile wastewater by a porous-structure electrochemical PbO2 filter: Performance and mechanism

In this work, a novel porous-structure electrochemical PbO2 filter (PEF-PbO2) was developed to achieve the reuse of bio-treated textile wastewater. The characterization of PEF-PbO2 confirmed that its coating has a variable pore size that increases with depth from the substrate, and the pores with a size of 5 μm account for the largest proportion. The study on the role of this unique structure illustrated that PEF-PbO2 possesses a larger electroactive area (4.09 times) than the conventional electrochemical PbO2 filter (EF-PbO2) and enhanced mass transfer (1.39 times) in flow mode. The investigation of operating parameters with a special discussion of electric energy consumption suggested that the optimal conditions were a current density of 3 mA cm−2, Na2SO4 concentration of 10 g L−1 and pH value of 3, which resulted in 99.07% and 53.3% removal of Rhodamine B and TOC, respectively, together with an MCETOC of 24.6%. A stable removal of 65.9% COD and 99.5% Rhodamine B with a low electric energy consumption of 5.19 kWh kg−1 COD under long-term reuse of bio-treated textile wastewater indicated that PEF-PbO2 was durable and energy-efficient in practical applications. Mechanism study by simulation calculation illustrated that the part of the pore of the PEF-PbO2's coating with small size (5 μm) plays an important role in this excellent performance which provides the advantage of rich ·OH concentration, short pollutant diffusion distance and high contact possibility.

Research on surface morphology characteristics and micro-damage mechanism of asphalt mastic based on charge transfer principle

Asphalt mastic damage is a major element influencing the mechanical qualities of the asphalt mixture. Based on electrochemistry theory, the idea of charge transfer of moisture between asphalt-asphalt and asphalt-mineral powder is proposed in this study to explore the damage mechanism of asphalt mastic under the operation of freeze–thaw cycles.On this basis, the damage mechanism of asphalt mastic was analyzed at multiple scales using relevant experimental means (Scanning electron microscopy-Energy dispersion spectrum(SEM-EDS) experiment, Fourier Transform Infrared(FT-IR) experiment and Atomic Force Microscope(AFM) experiment). FT-IR and AFM experiments results showed that: Water molecules in asphalt mastic might compete for asphaltene electrons in the asphalt mastic, causing the carboxyl dimer formed between asphaltenes to be disrupted. This causes asphaltene dispersion and a reduction in asphaltene concentration. Asphalt colloid structure changes from gel to sol, causing asphalt mastic degradation. Furthermore, freeze–thaw cycles accelerate the damage. On the other hand, the results of FT-IR and SEM-EDS experiments showed that: Freeze-thaw processes in asphalt mastics can also result in varying pore sizes and higher carbon concentration. Water molecules can create structural water on the subsurface of mineral powder crystals as well as physical water on the surface of mineral powder. This affects the adsorption of structural asphalt on the subsurface of the mineral powder crystals, resulting in the dissociation of the adsorbed asphalt from the mineral powder crystals' surface. The results of the study have some theoretical value to further explore the damage mechanism of asphalt mastic.

Zeolite Supported Pt for Depolymerization of Polyethylene by Induction Heating.

We demonstrate that for polyethylene depolymerization with induction heating (IH), using a bifunctional (Pt- or Pt-Sn-containing zeolite) hydrocracking catalyst, we can obtain high hydrocarbon product yields (up to 95 wt % in 2 h) at a relatively low surface temperature (375 °C) and with a tunable product distribution ranging from light gas products to gasoline- to diesel-range hydrocarbons. Four zeolite types [MFI, LTL, CHA(SSZ-13), and TON] were chosen as the supports due to their varying pore sizes and structures. These depolymerization results are obtained at atmospheric pressure and without the use of H2 and result in an alkane/alkene mixture with virtually no methane, aromatics, or coke formation. We also demonstrate how IH helps overcome diffusional resistances associated with conventional thermal heating and thereby shortens reaction times.

Manipulating multi-spectral slow photons in bilayer inverse opal TiO2@BiVO4 composites for highly enhanced visible light photocatalysis

Manipulation of light has been proved to be a promising strategy to increase light harvesting in solar-to-chemical energy conversion, especially in photocatalysis. Inverse opal (IO) photonic structures are highly promising for light manipulation as their periodic dielectric structures enable them to slow down light and localize it within the structure, thereby improving light harvesting and photocatalytic efficiency. However, slow photons are confined to narrow wavelength ranges and hence limit the amount of energy that can be captured through light manipulation. To address this challenge, we synthesized bilayer IO TiO2@BiVO4 structures that manifested two distinct stop band gap (SBG) peaks, arising from different pore sizes in each layer, with slow photons available at either edge of each SBG. In addition, we achieved precise control over the frequencies of these multi-spectral slow photons through pore size and incidence angle variations, that enabled us to tune their wavelengths to the electronic absorption of the photocatalyst for optimal light utilization in aqueous phase visible light photocatalysis. This first proof of concept involving multi-spectral slow photon utilization enabled us to achieve up to 8.5 times and 2.2 times higher photocatalytic efficiencies than the corresponding non-structured and monolayer IO photocatalysts respectively. Through this work, we have successfully and significantly improved light harvesting efficiency in slow photon-assisted photocatalysis, the principles of which can be extended to other light harvesting applications.

Influence of Pore Size and Surface Functionalization of Mesoporous Silica Nanoparticles on the Solubility and Antioxidant Activity of Confined Coenzyme Q10.

Coenzyme Q10 is a potent antioxidant that plays an important role in the maintenance of various biochemical pathways of the body and has a wide range of therapeutic applications. However, it has low aqueous solubility and oral bioavailability. Mesoporous silica nanoparticles (MCM-41 and SBA-15 types) exhibiting varying pore sizes and modified with phosphonate and amino groups were used to study the influence of pore structure and surface chemistry on the solubility, in vitro release profile, and intracellular ROS inhibition activity of coenzyme Q10. The particles were thoroughly characterized to confirm the morphology, size, pore profile, functionalization, and drug loading. Surface modification with phosphonate functional groups was found to have the strongest impact on the solubility enhancement of coenzyme Q10 when compared to that of pristine and amino-modified particles. Phosphonate-modified MCM-41 nanoparticles (i.e., MCM-41-PO3) induced significantly higher coenzyme Q10 solubility than the other particles studied. Furthermore, MCM-41-PO3 led to a twofold decrease in ROS generation in human chondrocyte cells (C28/I2), compared to the free drug in a DMSO/DMEM mixture. The results confirmed the significant contribution of small pore size and negative surface charge of MSNs that enable coenzyme Q10 confinement to allow enhanced drug solubility and antioxidant activity.

Role of graded microstructure and electrolyte distribution in electrochemical capacitance of compressible three-dimensional carbon nanotubes-polymer foam based supercapacitor

Three-dimensional microstructure of carbon materials has a prime importance in supercapacitor for energy storage. Carbon nanotubes (CNT) provide microstructurally porous structure via entangled nodes that dynamically changes with the uniaxial compression. A unique graded CNT-polymer based three-dimensional compressible cellular foam is used as an electrode material for the solid-state supercapacitor. A direct correlation was established between the applied strain and resulting electrochemical capacitance when the foam electrode was soaked and unsoaked in the electrolyte. In a novel finding, unsoaked electrodes revealed in an extraordinary enhancement of ∼1216% in gravimetric capacitance measured at a uniaxial strain of 80% and to no surprise, the electrochemical capacitance of electrolyte-soaked electrodes remained nearly invariant from its uncompressed state. The response of electrochemical capacitance under compression is also observed varying with the mode of compression i.e. quasi-static versus pre-compressed state to a targeted strain. The role of graded microstructure during uniaxial compression was verified by using as-grown CNT mat for the electrodes of a supercapacitor. The results demonstrated a dominating contribution of dynamic variation in the density of nodes in the compressed CNT mat. The impact of macroscopic variation on the response of electrochemical capacitance of a compressed cellular CNT-polymer foam was further understood using the separators of varying pore sizes. Our results pave the way to engineer the three-dimensional compressible cellular structures for extraordinarily large energy storage capacity.

Performance comparative evaluation of three thin vapor chambers with different wick structures

Enhancing the performance of cooling modules is crucial for mitigating the heat dissipation problem of high-power-density electronic devices and simultaneously improving the energy efficiency of cooling systems. In this study, three 2-mm-thick vapor–liquid channel separation vapor chambers with different wick structures were fabricated. A novel radial-gradient sintered copper powder wick was firstly developed to improve the vapor–liquid conversion efficiency of working fluid, while the other two had homogeneous porosity wick structures with varying pore sizes. Experiments were systematically conducted with forced air cooling to comprehensively examine the effects of internal wick structures on heat transfer performance. The results indicated that the thermal performance of the vapor chamber can be improved by implementing the radial-gradient porosity wick. Specifically, the vapor chamber with a radial-gradient wick exhibited an improved thermal resistance of merely 0.052 °C/W, representing a 55.8% reduction in thermal resistance compared to a copper plate. Furthermore, when the improved vapor chamber was coupled with a heat sink to serve as the cooling module for a 100 W LED in practical applications, the operating temperature was kept below 49.4 °C. The proposed vapor chambers provide a highly efficient and reliable solution for thermal management in a wide range of applications.

Impact of support pore properties on the performance of layer-by-layer self-assembly nanofiltration membrane

This paper investigates the impact of the porous structure of the support on the permselectivity and backwash resistance of Layer-by-Layer (LBL) nanofiltration (NF) membranes. Four different polyethersulfone (PES) hollow fiber membranes with varying pore sizes were coated with poly(allylamine hydrochloride)/poly(sodium-4-styrenesulfonate) (PAH/PSS) polyelectrolyte pairs. The study found that adjusting the number of bilayers in the coating process enabled the production of LBL membranes with similar molecular weight cut-off (MWCO) around 250 Da and high Mg2+ rejection of 95 %. However, Na2SO4 rejection decreased as the number of bilayers increased, as the positively charged PAH overcompensated. The study also found that the pore size of the support did not significantly impact the backwash resistance of the LBL membranes, indicating that the polyelectrolyte chains can penetrate through the pores of the supports regardless of pore size. This finding can guide the design of suitable supports for LBL NF membranes with tailored performances.

Molecular simulation of confined ethaline‐based deep eutectic solvents for separations of carbon dioxide from methane

AbstractClassical molecular dynamics (MD) simulations were used to study the separation of carbon dioxide from methane by three formulations of the deep eutectic solvent (DES) ethaline (choline chloride: ethylene glycol at 1:2, 1:4, and 1:8 molar ratios), confined inside graphite and titania (rutile) slit pores of two different pore widths, 2 and 5 nm. In addition, equivalent DES systems in the bulk were studied, which can also be viewed as a model supported DES membrane with μm‐sized pores. Our results indicate that variations in the ratio of ethylene glycol, which in turn affect the interactions of all DES species with the gas molecules and the different pore walls, plus confinement effects resulting from varying the pore sizes, can affect the gas separation performance of these systems in complex ways. The highest permselectivities (~20), computed as the product of the diffusivity and solubility selectivities, are observed for 1:2 ethaline in a 5 nm graphite pore, followed by the 1:4 DES in a 5 nm graphite pore, 1:2 ethaline in a 2 nm graphite pore, and the 1:8 bulk DES. In bulk systems, all three selectivities reach their highest values for 1:8 ethaline. When the DESs are confined in the nanopores, the solubility selectivity for most systems improves compared to the equivalent bulk systems, with the graphite pores having the largest solubility selectivities for any given ethylene glycol ratio. In contrast, the diffusivity selectivities in confined systems tend to be similar to the values observed in the bulk DESs. Interaction energies and local density profiles were used to rationalize absorption and diffusivity of gases in our systems. Confining ethaline in graphite and rutile nanopores tends to weaken the CO2‐ethylene glycol and CO2‐cation interactions compared to the values observed in equivalent bulk ethaline systems, which also affect the local density profiles. Our results confirm that variations in ethylene glycol ratio, pore size, and pore wall material can lead to significant changes in gas separation performance. Other porous matrices, for example, nanoporous polymer formulations and graphene oxides, should be considered in follow‐up studies as they may lead to significant improvements in gas separation performance as compared to the bulk DES.

Pore size variation of nano-porous material fixer on the engine bowl and its combined effects on hybrid nano-fuelled CI engine characteristics

Environmental research is currently one of the most significant and pertinent fields of studies. Due to CI engines'unique nature, theyare widely used in densely populated cities for a variety of purposes. However, due to their impropercombustion for various acceptable reasonsat the engine cylinder, they considerably pollute the environment. This study prepared hybrid nano fuel from waste cooking oil by adding Al2O3 (aluminum oxide) and MWCNT (multi-wall carbon nanotubes) particles and adding ZnO (zinc oxide) nanoporous material fixture in the combustion chamber as an attachment for enhancing combustion efficiency to meet the aim of mitigating the CI engine emissions significantly. The research was evaluated in a 5.2 kW CI engine, and the ZnO nano-porous material is fixed to the combustor. Four distinct pores per inch (PPI) nanoporous materials of pore counts such as 60, 45, 30, and 15 PPI were considered to test the fuels such as diesel and hybrid nanofuel. The hybrid nano-fuel was created from the WCO biodiesel by mixing nanoparticles of MWCNT and Al2O3 nanoparticles in the ultrasonicator. The experiments were carried out at different engine loads from no load to full load with a 25% step-up. The performance of the results was compared with conventional diesel fuel with and without ZnO nano-porous material fixtures and ZnO nano-porous material fixtures with different PPI. The result exhibited that the nanoparticles-added biodiesel fuel in 15 PPI has produced less NOx emission, CO emission, and heat release rate by 55.2%, 7%, 26.5%, and 22.67%, respectively, and this combination also exhibited an improvement of 2.62% in the brake thermal efficiency. Finally, the present work proves that better engine characteristics are generally obtained as the pore size of nanoporous materials in the engine bowl gets smaller, and the hybrid nanoparticles usage in the biodiesel fuel ensures more efficient engine combustion, performance, and emission characteristics.

Modes of multi-mechanistic gas diffusion in shale matrix at varied effective stresses: Observations and analysis

Gas diffusion in the shale matrix has a dominant effect on late-stage production from shale gas reservoirs. However, adequate research on the mechanisms and contributions of gas diffusion for varied pore size populations in shale matrix under recreated in situ stress is lacking. We report gas-diffusion measurements under constant in situ stress but variable gas pressures for contrasting non-adsorbent (helium (He)) and adsorbed (methane (CH4)) gases to investigate the impact of effective stress on the evolution of dominant mechanisms of diffusion. An intact sample replicates true pore-network topology and diffusion paths. An integrated diffusion model is proposed that combines the effects of slip flow, Knudsen flow, and surface diffusion to constrain the evolution of these flow regimes and their respective contributions to the observational data. Finally, a probability density function (PDF) is employed to separate the gas content distributions of macropores and micropores from the total gas content and to investigate gas contributions in various pores. The results reveal that the diffusion coefficients of both He and CH4 in macropores and micropores increase with gas pressure but decrease with increasing effective stress. The diffusion coefficients of He and CH4 are different in macropores but remain nearly the same in micropores. The diffusion coefficients of slip flow and surface diffusion increase with decreasing effective stress except for CH4 diffusion in the micropores, while the evolution of Knudsen diffusion shows the opposite trend. Slip flow plays a dominant role in He and CH4 diffusion within macropores (pore size 45 nm). Knudsen diffusion gradually becomes significant for He diffusion in the micropores (pore size 4 nm), conversely, for CH4 diffusion in the micropores, surface diffusion becomes significant. Related to gas production from reservoirs, the contributions of the micropores will increase gradually with the duration of gas recovery, indicating the significant role of gas diffusion in micropores to steady supply during late-stage production.

Visualization of porosity and pore size gradients in electrospun scaffolds using laser metrology.

We applied a recently developed method, laser metrology, to characterize the influence of collector rotation on porosity gradients of electrospun polycaprolactone (PCL) widely investigated for use in tissue engineering. The prior- and post-sintering dimensions of PCL scaffolds were compared to derive quantitative, spatially-resolved porosity 'maps' from net shrinkage. Deposited on a rotating mandrel (200 RPM), the central region of deposition reaches the highest porosity, ~92%, surrounded by approximately symmetrical decreases to ~89% at the edges. At 1100 RPM, a uniform porosity of ~88-89% is observed. At 2000 RPM, the lowest porosity, ~87%, is found in the middle of the deposition, rebounding to ~89% at the edges. Using a statistical model of random fiber network, we demonstrated that these relatively small changes in porosity values produce disproportionately large variations in pore size. The model predicts an exponential dependence of pore size on porosity when the scaffold is highly porous (e.g., >80%) and, accordingly, the observed porosity variation is associated with dramatic changes in pore size and ability to accommodate cell infiltration. Within the thickest regions most likely to 'bottleneck' cell infiltration, pore size decreases from ~37 to 23 μm (38%) when rotational speeds increased from 200 to 2000 RPM. This trend is corroborated by electron microscopy. While faster rotational speeds ultimately overcome axial alignment induced by cylindrical electric fields associated with the collector geometry, it does so at the cost of eliminating larger pores favoring cell infiltration. This puts the bio-mechanical advantages associated with collector rotation-induced alignment at odds with biological goals. A more significant decrease in pore size from ~54 to ~19 μm (65%), well below the minimum associated with cellular infiltration, is observed from enhanced collector biases. Finally, similar predictions show that sacrificial fiber approaches are inefficient in achieving cell-permissive pore sizes.

On the Use of Temperature Measurements as a Process Analytical Technology (PAT) for the Monitoring of a Pharmaceutical Freeze-Drying Process.

The measurement of product temperature is one of the methods that can be adopted, especially in the pharmaceutical industry, to monitor the freeze-drying process and to obtain the values of the process parameters required by mathematical models useful for in-line (or off-line) optimization. Either a contact or a contactless device and a simple algorithm based on a mathematical model of the process can be employed to obtain a PAT tool. This work deeply investigated the use of direct temperature measurement for process monitoring to determine not only the product temperature, but also the end of primary drying and the process parameters (heat and mass transfer coefficients), as well as evaluating the degree of uncertainty of the obtained results. Experiments were carried out with thin thermocouples in a lab-scale freeze-dryer using two different model products, sucrose and PVP solutions; they are representative of two types of commonly freeze-dried products, namely those whose structures are strongly nonuniform in the axial direction, showing a variable pore size with the cake depth and a crust (leading to a strongly nonlinear cake resistance), as well as those whose structures are uniform, with an open structure and, consequently, a cake resistance varying linearly with thickness. The results confirm that the model parameters in both cases can be estimated with an uncertainty that is in agreement with that obtained with other more invasive and expensive sensors. Finally, the strengths and weaknesses of the proposed approach coupled with the use of thermocouples was discussed, comparing with a case using a contactless device (infrared camera).