Micropore Geometry Research Articles

Poly(ethylene glycol) diacrylate based hydrogel filled micropore with enhanced sensing capability

Ionic current rectification (ICR) phenomena conventionally occurs in nanopores which dimensions are comparable to the thickness of their electrical double layers. However, the microscale ICR in a micropore can also exist under some conditions. Here, the charged hydrogel filled conical micropore was constructed to realize microscale ICR. To better understand the micropore ICR, the influences of space charge density of the hydrogel, micropore geometry, the hydrogel filling length as well as the electrolyte concentration and pH were investigated. Furthermore, we developed a PEGDA-based hydrogel filled micropore sensing platform which sensing performance was enhanced due to the weakly charged PEGDA. The promyelocytic leukemia (PML)/retinoic acid receptor alpha (RARA) fusion genes and adenosine triphosphate (ATP) were respectively used as model analytes and the measured detection limits of 0.1 pM were achieved. The successful realization of microscale ICR in a homogenous and functional hydrogel filled micropore suggests that the fabrication, characterization and operation of ICR based devices can be more robust and facilitated for the wider applications.

Transmembrane transport in inorganic colloidal cell-mimics.

A key aspect of living cells is their ability to harvest energy from the environment and use it to pump specific atomic and molecular species in and out of their system-typically against an unfavourable concentration gradient1. Active transport allows cells to store metabolic energy, extract waste and supply organelles with basic building blocks at the submicrometre scale. Unlike living cells, abiotic systems do not have the delicate biochemical machinery that can be specifically activated to precisely control biological matter2-5. Here we report the creation of microcapsules that can be brought out of equilibrium by simple global variables (illumination and pH), to capture, concentrate, store and deliver generic microscopic payloads. Borrowing no materials from biology, our design uses hollow colloids serving as spherical cell-membrane mimics, with a well-defined single micropore. Precisely tunable monodisperse capsules are the result of a synthetic self-inflation mechanism and can be produced in bulk quantities. Inside the hollow unit, a photoswitchable catalyst6 produces a chemical gradient that propagates to the exterior through the membrane's micropore and pumps target objects into the cell, acting as a phoretic tractor beam7. An entropic energy barrier8,9 brought about by the micropore's geometry retains the cargo even when the catalyst is switched off. Delivery is accomplished on demand by reversing the sign of the phoretic interaction. Our findings provide a blueprint for developing the next generation of smart materials, autonomous micromachinery and artificial cell-mimics.

Coaxial electrospun membranes with thermal energy storage and shape memory functions for simultaneous thermal/moisture management in personal cooling textiles

Developing textiles with simultaneous thermal regulation capability and adaptive moisture permeability is of great significance for not only reducing energy consumption but also enhancing personal comfort. To meet the above requirements, coaxial electrospun microfibers based on polyurethane (PU) and polyethylene glycol (PEG) were fabricated, in which PU worked as a supporting shell and PEG worked as an energy-storage core. The coaxial electrospinning technique made PEG to be uniformly encapsulated inside the microfibers to form a ‘core-shell’-like structure, imparting the membranes with a high phase change enthalpy (60.4 J/g), good encapsulation effect, thermal energy storage property and robust mechanical property (sustaining 125 times mass of load). Furthermore, the PU/PEG porous membranes exhibit excellent thermal-actuated shape memory effect, which enables macroscopic shape deformation and adaptive micropore geometry upon heating. The PU/PEG membranes with both thermal regulation capability and temperature-sensitive moisture permeability can generate excellent cooling and drying performances (7.6 °C cooler and better breathability than commercial cotton textile). Therefore, our work may provide a new strategy to design smart textiles with dynamic thermal and moisture management functions for improving the comfort of wearers under hot situations.

Gaining Micropattern Fidelity in an NOA81 Microsieve Laser Ablation Process.

We studied the micropattern fidelity of a Norland Optical Adhesive 81 (NOA81) microsieve made by soft-lithography and laser micromachining. Ablation opens replicated cavities, resulting in three-dimensional (3D) micropores. We previously demonstrated that microsieves can capture cells by passive pumping. Flow, capture yield, and cell survival depend on the control of the micropore geometry and must yield high reproducibility within the device and from device to device. We investigated the NOA81 film thickness, the laser pulse repetition rate, the number of pulses, and the beam focusing distance. For NOA81 films spin-coated between 600 and 1200 rpm, the pulse number controls the breaching of films to form the pore’s aperture and dominates the process. Pulse repetition rates between 50 and 200 Hz had no observable influence. We also explored laser focal plane to substrate distance to find the most effective ablation conditions. Scanning electron micrographs (SEM) of focused ion beam (FIB)-cut cross sections of the NOA81 micropores and inverted micropore copies in polydimethylsiloxane (PDMS) show a smooth surface topology with minimal debris. Our studies reveal that the combined process allows for a 3D micropore quality from device to device with a large enough process window for biological studies.

Using Ultrasonic Waves to Determine the Microstructure of Snow

High frequency (ultrasonic) acoustic wave propagation measurements were inverted to determine important near-surface parameters of snow including porosity, tortuosity, and pore geometry, using a newly-designed, oblique-reflection transducer apparatus. Acoustic signals interact with the physical structure of porous media, are particularly sensitive to porosity and tortuosity, and can be used to measure physical properties in a non-destructive manner. Given the fragile nature of freshly fallen snow, non-contact, non-destructive characterization methods made possible via acoustic signals, are desirable. High frequency wave propagation methods can be used to determine in situ near surface micro-pore geometry parameters in snow using methods demonstrated on cohesive porous materials including manufactured foams, porous metals, and sintered glass beads. Here, we conducted high frequency, oblique-angle and near vertical reflection measurements on snow samples to demonstrate the feasibility of acoustic response detection. We compared the acoustically derived snow physical parameters, including porosity and tortuosity, with values determined from X-ray micro-computed tomography (μCT) and gravimetric methods. Preliminary results using different snow types, and following the methods from previous work for cohesive porous media (i.e. fused glass beads) show good agreement between values of porosity determined from the acoustic measurements and the values determined from μCT image analysis.

A dusty gas model-direct simulation Monte Carlo algorithm to simulate flow in micro-porous media

A new efficient direct simulation Monte Carlo (DSMC) method is proposed for the simulation of microporous media based on the dusty gas model (DGM). Instead of simulating gas flow through a microporous medium with a complex geometry of micropores that mimics the physical pore morphology, the DGM-DSMC method replaces it with the gas flow through a system of randomly distributed motionless virtual particles with simple spherical shapes confined in the considered domain. In addition, the interactions of gas molecules with the porous particles are simulated stochastically. For the aim of our study, the DGM is implemented in Bird’s two-dimensional DSMC code. The obtained results for the average velocity of gas flow through microscale porous media with given porosity are verified for different pressure gradients with those reported in the literature where porous particles are modeled physically in the domain. Thereafter, the effective parameters in porous media such as porosity, particle diameter, and rarefaction on flow behavior including velocity profile, apparent gas permeability, and mass flow rate are investigated. A comparison with the results predicted by the Open source Field Operation and Manipulation (OpenFOAM) software suggests that the employed DGM-DSMC is more accurate in highly porous media and its computational cost is considerably low.

Bacterial Extracellular Polymeric Substances Amplify Water Content Variability at the Pore Scale

The function of microbial communities in soil is inextricably linked with the complex physical, chemical and biological structure of the soil itself. Pore-scale water content controls the hydraulic connectivity of microbial communities and microbes’ access to aqueous and gaseous substrates. In turn, soil bacteria directly influence local moisture conditions through the secretion of extracellular polymeric substances (EPS). However, the effect of a soil’s physical geometry on EPS-mediated water retention is not well understood. In this study, we systematically measured the rate and extent of water evaporation from pore structures as a function of both EPS concentration and pore size. Three different chamber types were employed: (i) glass capillary tubes (1.2 mm pore diameter) to represent a uniform macropore geometry; (ii) emulated soil micromodels (pore widths ~ 10 µm to > 300 µm) to represent an aggregated sandy loam pore geometry; and (iii) microfluidic capillary arrays (uniform channels 20 µm wide) to represent a uniform micropore geometry. All chambers were initially saturated with dilute EPS solutions collected from stationary-phase Sinorhizobium meliloti cultures and then the infiltration of air was tracked over time. In the largest chambers, EPS concentration had no effect on the extent of evaporation or on the magnitude or variability of the evaporation rate. However, in the chambers with micropore-sized physical features, EPS concentration strongly influenced rate, extent, and variability of pore water evaporation. In micropores, higher EPS concentrations enhanced water retention and led to greater variability in pore-scale water distributions. In real soil, these phenomena could act together to promote the intermediate water contents associated with productive soil systems, and more variable pore-scale water distributions could increase microbial community diversity and the resiliency of soil systems.

Micropore Geometry Manipulation by Macroscopic Deformation Based on Shape Memory Effect in Porous PLLA Membrane and its Enhanced Separation Performance.

An effective strategy to tailor the microporous structures has been developed based on the shape memory effect in porous poly(l-lactic acid) membranes in which tiny crystals and amorphous matrix play the roles of shape-fixed phase and reversible-phase, respectively. Our results indicate that not only PLLA membranes but micropores exhibit shape memory properties. The proportional deformations on two scales have been achieved by uniaxial or biaxial tension, providing a facile way to manipulate continuously the size and the orientation degree of pores on microscale. The enhanced separation performance has been validated by taking polystyrene colloids with varying diameters as an example.

DIMENSION AND STRUCTURAL TRAITS OF SOIL MICROPORES IN CULTIVATIONS DIFFERING IN THE DURATION OF ORGANIC MANAGEMENT

The objectives of this study were to investigate: a) whether the duration of organic farming influences the dimension, shape and geometry (fractal dimension) of soil micropores (<50 m) and b) for relationships of morphometric traits with certain chemical and biochemical soil variables (microbial biomass, N- and C-mineralization rates, NH4+, NO3-, organic C and N, extractable P, Mg+2, K+, Ca+2). We compared soil micromorphometric traits (area, perimeter, compactness, solidity, eccentricity) among fields with different duration of organic farming (2 (O2), 3 (O3), 5 (O5), and 6 years (O6)): these were planted with Asparagus officinalis and one was conventional cultivation (CV). .o significant differences were observed among the morphometric traits of all fields. However, the soil of the older organic areas (O6, O5 and O3) was characterized by small-sized pores (<10 m) while the newest (O1) and the conventional field were characterized by medium-sized micropores (10-20 m). The fractal dimension D2 of the larger pores was found to be significantly higher in .2 and O3 fields, indicating larger outline irregularity for these particular pores. Higher fractal dimension could be related to more heterogeneous distribution of the microbial community in space. All micropores were correlated with the concentration of soil mineral nutrients (Mg+2, K+, Ca+2). In the small pore size category (=10 m), N-microbial and NO3-concentrations, parameters involved in the nitrogen cycle, were found to be correlated to the structure characteristics. Taking into account that the three older organic fields are characterized mainly by small sized pores (=10 m), it is suggested that improved soil quality is mainly related with the N-cycle.

Quantitative microporosity evaluation using mercury injection and digital image analysis in tight carbonate rocks: A case study from the Ordovician in the Tazhong Palaeouplift, Tarim Basin, NW China

The heterogeneity of tight carbonate rocks is directly related to the morphology of micropores and the connectivity of the pore network, which have a great influence on the intrinsic microporosity and fluid flow properties of porous media. However, neither can be quantitatively evaluated by conventional techniques. Based on core observation and thin section analysis, combined with high-resolution field emission-scanning electron microscopy (FE-SEM) and mercury injection capillary pressure (MICP) measurements, we can identify carbonate rock types, determine the microporosity and microstructure and calculate the pore structure parameters. Digital image analysis (DIA) and the fractal dimension (FD) method are used to study the relationship between the quantified pore structure parameters, heterogeneity and fluid flow properties. The results indicate that rock types in 12 carbonate samples are dominated by grainstone and packstone, followed by wackestone and dolomitic packstone. The microporosity of rock types has various microstructure characteristics. Crystalline types of microporosity (the small and large intercrystalline pores) increase pore network connectivity whereas micromoldic pores show variations in connectivity of different lithofacies. However, the small intercrystalline pores contribute little to the permeability because of narrow and complex pore networks for fluid flow. MICP data of samples reveal that these samples are relatively tight with low porosity (avg. 3.7%) and permeability (avg. 0.452mD). The pore-throat radius mainly ranges from 0.1 μm to 1.0 μm, which contributes the highest proportion of permeability to the samples. Fractal dimensions calculated from the “J-curve” models vary between 2.0746 and 2.8551 (avg. 2.331), indicating high heterogeneity. Moreover, the fractal dimension is strongly negatively related to the permeability, average pore throat radius and separation coefficient. Additionally, quantified pore geometric parameters from DIA, including dominant pore size (DOMsize), perimeter over area (PoA), pore body-to-throat ratio (BTR) and average roundness (γa), greatly influence the pore structure and fluid flow behavior. The samples with large DOMsize, high γa, low PoA and low BTR show a low fractal dimension and simple pore network but high permeability. Diagenesis can also affect the fractal pore space and self-similarity pore geometries of carbonates across all length scales. This information about the micropore geometry and microstructure of the carbonate rock will further improve the assessment of its reservoir properties.

Highly compressed nanosolution restricted in cylindrical carbon nanospaces

We shed light on the specific hydration structure around a zinc ion of nanosolution restricted in a cylindrical micropore of single-wall carbon nanotube (SWNT) by comparison with the structure restricted in a cylindrical mesopore of multi-wall carbon nanotube (MWNT) and that of bulk aqueous solution. The average micropore width of open-pore SWNT was 0.87 nm which is equivalent to the size of a hydrated zinc ion having 6-hydrated water molecules. We could impregnate the zinc ions into the micropore of SWNT with negligible amounts of ion-exchanged species on surface functional groups by the appropriate oxidation followed by heat treatment under an inert condition. The results of X-ray absorption fine structure (XAFS) spectra confirmed that the proportion of dissolved species in nanospaces against the total adsorbed amounts of zinc ions on the open-pore SWNT and MWNT were 44 and 61%, respectively, indicating the formation of a dehydrated structure in narrower nanospaces. The structure parameters obtained by the analysis of XAFS spectra also indicate that the dehydrated and highly compressed hydration structure can be stably formed inside the cylindrical micropore of SWNT where the structure is different from that inside the slit-shaped micropore whose pore width is less than 1 nm. Such a unique structure needs not only a narrow micropore geometry which is equivalent to the size of a hydrated ion but also the cylindrical nature of the pore.

Numerical Analysis on Sealing Properties of Mechanical Seals with a Laser-Textured Face

An analytical model is developed to study the sealing performance of the mechanical seals with a laser-textured micro-pore face. The pressure distribution between the seal faces at various operation conditions and micro-pore geometry parameters can be obtained from a solution of the Reynolds equation by finite difference method, and then opening force and liquid film stiffness can be calculated. Seal face geometry parameters can be optimized by analyzing regulation of their effect on opening force and liquid film stiffness. Results of parametric study demonstrate that substantial hydrodynamic effect can be produced on the seal face with micro-pores.

Displacement of Methane by Coadsorbed Carbon Dioxide Is Facilitated In Narrow Carbon Nanopores

By using simulation methods, we studied the adsorption of binary CO2–CH4 mixtures on various CH4 preadsorbed carbonaceous materials (e.g., triply periodic carbon minimal surfaces, slit-shaped carbon micropores, and Harris’s virtual porous carbons) at 293 K. Regardless of the different micropore geometry, two-stage mechanism of CH4 displacement from carbon nanospaces by coadsorbed CO2 has been proposed. In the first stage, the coadsorbed CO2 molecules induced the enhancement of CH4 adsorbed amount. In the second stage, the stronger affinity of CO2 to flat/curved graphitic surfaces as well as CO2–CO2 interactions cause the displacement of CH4 molecules from carbonaceous materials. The operating conditions of CO2-induced cleaning of the adsorbed phase from CH4 mixture component strongly depend on the size of the carbon micropores, but, in general, the enhanced adsorption field in narrow carbon ultramicropores facilitates the nonreactive displacement of CH4 by coadsorbed CO2. This is because in narrow carbon ultramicropores the equilibrium CO2/CH4 selectivity (i.e., preferential adsorption toward CO2) increased significantly. The adsorption field in wider micropores (i.e., the overall surface energy) for both CO2 and CH4 is very similar, which decreases the preferential CO2 adsorption. This suppresses the displacement of CH4 by coadsorbed CO2 and assists further adsorption of CH4 from the bulk mixture (i.e., CO2/CH4 mixing in adsorbed phase).

Numerical Analysis on Tribological Properties of Mechanical Seals with a Laser-Textured Face

An analytical model is developed to study the effects of operation conditions and micro-pore geometry parameters on the friction performance of the mechanical seals with a laser-textured micro-pore face. Seal opening forces at various operation conditions and micro-pore geometry parameters are obtained from the solution of the Reynolds equation by the finite difference method. A derivative expression of the friction torque of the mechanical seals with a laser-textured micro-pore face is calculated and contributing factors of the friction torque are analyzed. It is shown that fiction torque increases with increase of the rotating speed. An optimum pore size that corresponds to minimum friction torque is found and is consistent with experimental results.

Development, fabrication, and characterization of hydrogel based piezoresistive pressure sensors with perforated diaphragms

Hydrogels have been demonstrated to swell in response to a number of external stimuli including pH, CO 2, glucose, and ionic strength making them useful for detection of metabolic analytes. To measure hydrogel swelling pressure, we have fabricated and tested novel perforated diaphragm piezoresistive pressure sensor arrays that couple the pressure sensing diaphragm with a perforated semi-permeable membrane. The 2 × 2 arrays measure approximately 3 × 5 mm 2 and consist of four square sensing diaphragms with widths of 1.0, 1.25, and 1.5 mm used to measure full scale pressures of 50, 25, and 5 kPa, respectively. An optimized geometry of micro pores was etched in silicon diaphragm to allow analyte diffusion into the sensor cavity where the hydrogel material is located. The 14-step front side wafer process was carried out by a commercial foundry service (MSF, Frankfurt (Oder), Germany) and diaphragm pores were created using combination of potassium hydroxide (KOH) etching and deep reactive ion etching (DRIE). Sensor characterization was performed (without the use of hydrogels) using a custom bulge testing apparatus that simultaneously measured deflection, pressure, and electrical output. Test results are used to quantify the sensor sensitivity and demonstrate proof-of-concept. Simulations showed that the sensitivity was slightly improved for the perforated diaphragm designs while empirical electrical characterization showed that the perforated diaphragm sensors were slightly less sensitive than solid diaphragm sensors. This discrepancy is believed to be due to the influence of compressive stress found within passivation layers and poor etching uniformity. The new perforated diaphragm sensors were fully functional with sensitivities ranging from 23 to 252 μV/V-kPa (FSO = 5–80 mV), and show a higher nonlinearity at elevated pressures than identical sensors with solid diaphragms. Sensors (1.5 × 1.5 mm 2) with perforated diaphragms (pores = 40 μm) have a nonlinearity of approximately 10% while for the identical solid diaphragm sensor it was roughly 3% over the entire 200 kPa range. This is the first time piezoresistive pressure sensors with integrated diffusion pores for detection of hydrogel swelling pressure have been fabricated and tested.

Analysis of the Hydrodynamic Effect in Laser-Textured Mechanical Seal Faces

A calculation model is developed for mechanical seals with a laser-textured micro-pore face. The dimensionless hydrodynamic pressure distribution on the seal face at various operating conditions and micro-pore geometry parameters is obtained from a solution of the Reynolds equation by the finite difference method. An optimum micro-pore geometry parameter is found and consistent with experimental results. Results of parametric study demonstrate that the substantial hydrodynamic effect can be produced on the seal face with micro-pores.

Structural Evaluation of Slow Desorbing Sites in Model and Natural Solids Using Temperature Stepped Desorption Profiles. 2. Column Results

Results from temperature stepped desorption (TSD) experiments are presented and compared with simulations from the TSD model presented in the first of this two-paper series. TSD columns were filled with a sand, a sediment, a soil, or a silica gel, all at 100% relative humidity. Next, TSD columns were equilibrated with trichloroethene (TCE), initially purged at 30 °C, and then heated to 60 °C after 100, 1000, or 10 000 min of slow desorption. One γ distribution of diffusion rate constants at 30 °C and one γ distribution of diffusion rate constants at 60 °C were used to simulate column results at all three heating times for a single solid. At each heating time, diffusion rate constants of the γ distributions at 30 °C and 60 °C were used to calculated an effective activation energy, Eact,eff. Values of Eact,eff for all solids were between 47 and 94 kJ/mol, on the order of activation energy values found for diffusion in microporous solids. Between 100 and 10 000 min heating times, the value of Eact,eff increased by a factor of 1.7 for the sand and by a factor of ∼1.1 for the sediment and the soil. This suggests that diffusion occurs from micropores with a wider distribution of widths in the sand than in the other solids and that with decreasing mass remaining diffusion occurs from successively smaller width micropores. For the sediment, values of Eact,eff and 〈D/lm2〉 were lower than those in the other solids. For a given sorbate, larger width micropores are associated with smaller values of Eact,eff and larger values of D. Hence, it is likely that micropores in the sediment are both wider and longer (i.e. larger value of lm2) than those in the other solids. These results suggest that micropore geometry varies between natural solids, and it is an important parameter that must be quantified to predict rates of slow desorption.

Structural Evaluation of Slow Desorbing Sites in Model and Natural Solids Using Temperature Stepped Desorption Profiles. 1. Model Development

In the first of this two-paper series, a new model is presented that simulates the effects of a temperature perturbation on the rate of slow desorption as a function of mass remaining. The model assumes slow desorption is controlled by one-dimensional diffusion from a single or many hydrophobic micropores and that the micropores of a geosorbent are defined by a γ distribution of diffusion rate constants. Simulation results indicate that during slow desorption the relative increase in flux upon heating increases with decreasing micropore width. Simulation results also indicate that the relative increase in flux upon heating increases with desorption time when diffusion occurs from successively smaller width micropores with decreasing mass remaining. In paper 2, the model is tested and used to examine micropore geometry in natural and model solids by simulating results from temperature stepped desorption (TSD) experiments.

Numerical analysis of sorption and diffusion in soil micropores, macropores, and organic matter

Sorption and diffusion of volatile organic compounds (VOCs) in soil are important processes in subsurface contamination, but are complicated by the heterogeneous nature of soil. The soil pore-size distribution is herein approximated as a biporous geometry of micropores and macropores. The microspheres embedded in macrospheres contain micropores. Voids between microspheres constitute the macropores. Soil organic matter is assumed present on the surface of microspheres. We develop numerical solutions for the transient diffusion processes with linear partitioning in soil organic matter and nonlinear adsorption in the biporous soil particles. The three coupled nonlinear partial differential equations describe the diffusion in micropores and organic matter in series with diffusion in macropores. The computation uses an implicit Crank-Nicolson method with a predictor-corrector scheme for fast and efficient calculations. The solutions are applied to toluene and water sorption-desorption experimental data obtained by gravimetric uptake measurements. The procedure allows the estimation of key parameters, including micropore diffusivities.

Tritium studies of catalysis over microporous aluminophosphate surfaces

AbstractMicroporous AlPO4‐5 catalysts exhibit catalytic activity for tritium isotope exchange and other reactions but the activity of the catalyst may vary widely from one batch of catalyst to another although all catalyst samples appear to show pure AlPO4‐5 phase. This catalytic activity appears to correlate with the presence of octahedral aluminium in the catalyst samples as revealed by solid sate 27Al NMR spectroscopy and this is attributed to defect sites in the lattice. The exchange patterns may show high regional specificity. These patterns have some of the features of acid catalysis but are assumed to be modified by the constraints imposed by the micropore geometry.