Pore Surface Roughness Research Articles

Role of thermodynamic and kinetic interaction of poly(vinylidene fluoride) with various solvents for tuning phase inversion membranes

An extensive study of thermodynamics and kinetics of non‐solvent induced phase separation was carried out for poly(vinylidene fluoride)/solvent/water system for four different solvents. Literature available on semicrystalline polymers was mostly based on experimental cloud points, obtained to a narrow range of polymer concentration (<10 wt%), much less than the working range for membrane preparation (20–25 wt%). Aim of this work was to model the thermodynamic phase diagram using extended Flory–Huggins theory which was used as a tool, along with the kinetic data to obtain tailor‐made membranes with desired morphology and properties. Interaction parameters involving solvent, nonsolvent, and polymer played an important role to tune the porosity of the membrane. Thermodynamic calculation showed solvent N,N‐dimethyl acetamide resulted in the most porous membrane (permeability 5.4 × 10−11 m Pa−1 s−1) followed by N,N‐dimethyl formamide (permeability 4.2 × 10−11 m Pa−1 s−1), N‐methyl pyrrolidone (permeability 3.8 × 10−11 m Pa−1 s−1), and acetone (impermeable to water even at 1380 kPa), which was the densest one. Prepared membranes were characterized in terms of surface morphology, molecular weight cut‐off, tensile strength, pore volume distribution, crystallinity, and surface roughness, which were correlated to inferences based on thermodynamic and kinetic calculations. POLYM. ENG. SCI., 58:1062–1073, 2018. © 2017 Society of Plastics Engineers

Tunable separation via chemical functionalization of polyvinylidenefluoride membranes using piranha reagent

Polyvinylideneflouride (PVDF) has considerable usage in different disciplines including sensors, piezoelectric materials, biomedical application as well as membranes. In this paper, facile and effective method for the activation of inert PVDF surface and molecular grafting of this material is presented. Mild concentration of piranha reagent used to generate hydroxyl groups on the surface of the polymer through a free radical reaction. Functionalization was investigated as a function of reaction time and concentration. For characterization, various analytical methods and techniques were employed including infrared spectroscopy, scanning electron microscopy, X-ray diffraction, atomic-force microscopy, and contact goniometry. Physicochemical properties including contact angle, surface free energy, surface tension, work of adhesion as well as morphological properties (e.g. pore size distribution and roughness) were evaluated. Subsequently, membranes were tested for desalination, volatile organic compounds removal, and apple juice concentration in various modes of membrane distillation. Significant increase in pore size (53%), surface roughness (43%), and flux (from ca. 8kgm-2 h-1 to 10.5kgm-2 h-1) were found. Fouling mitigation was also noticed in comparison to unmodified membranes. Flux decline was equal to 37.5% and 5.1% for unmodified PVDF and PVDF membrane activated for 1min by 20% Piranha reagent, respectively.

Preparation and Fundamental Research of Continuous Through-Porous Pure Aluminum Flat Pipes by Depoling Continuous Casting

Continuous through-porous pure aluminum flat pipes were prepared continuously by a self-developed depoling continuous casting technology. An online measurement and control of mold temperature at free end of graphite core rods was realized, which was critical for the preparation. The quality of flat pipes was characterized. The results show that the flat pipes could be successfully prepared with the following process parameters: melt with temperature of 750 °C, cooling water with temperature of 20 °C and flow volume of 400 L·h-1, heat insulating mattress with thickness of 2 mm, mold temperature ranged from 635°C to 655°C and continuous casting speed ranged from 1 mm∙min-1 to 4 mm∙min-1. The flat pipe had cross-section dimensions of 14 mm×5 mm, which was aligned unidirectional pore diameter of 3 mm, pore number of 3 and smooth internal and external surface. The pore surfaces of flat pipes became smoother with the reduction of the graphite core rod surface roughness. When the surface roughness of graphite core rods was 0.531 μm and 0.124 μm, the corresponding surface roughness of pores was 0.581 μm and 0.184 μm, respectively. The mold temperature at the free end of graphite core rods was kept at a low thermal temperature range which was 5~25 °C lower than the solidification point of pure aluminum that is necessary for stable depoling continuous casting.

Osteoblast and osteoclast responses to A/B type carbonate-substituted hydroxyapatite ceramics for bone regeneration

The influence of carbonate substitution (4.4 wt%, mixed A/B type) in hydroxyapatite ceramics for bone remodeling scaffolds was investigated by separately analyzing the response of pre-osteoblasts and osteoclast-like cells. Carbonated hydroxyapatite (CHA) (Ca9.5(PO4)5.5(CO3)0.5(OH)(CO3)0.25-CHA), mimicking the chemical composition of natural bone mineral, and pure hydroxyapatite (HA) (Ca10(PO4)6(OH)2-HA) porous ceramics were processed to obtain a similar microstructure and surface physico-chemical properties (grain size, porosity ratio and pore size, surface roughness and zeta potential). The biological behavior was studied using MC3T3-E1 pre-osteoblastic and RAW 264.7 monocyte/macrophage cell lines. Chemical dissolution in the culture media and resorption lacunae produced by osteoclasts occur with both HA and CHA ceramics, but CHA exhibits much higher dissolution and greater bioresorption ability. CHA ceramics promoted a significantly higher level of pre-osteoblast proliferation. Osteoblastic differentiation, assessed by qRT-PCR of RUNX2 and COLIA2, and pre-osteoclastic proliferation and differentiation were not significantly different on CHA or HA ceramics but cell viability and metabolism were significantly greater on CHA ceramics. Thus, the activity of both osteoclast-like and osteoblastic cells was influenced by the carbonate substitution in the apatite structure. Furthermore, CHA showed a particularly interesting balance between biodegradation, by osteoclasts and chemical dissolution, and osteogenesis through osteoblasts’ activity, to stimulate bone regeneration. It is hypothesized that this amount of 4.4 wt% carbonate substitution leads to an adapted concentration of calcium in the fluid surrounding the ceramic to stimulate the activity of cells. These results highlight the superior biological behavior of microporous 4.4 wt% A/B CHA ceramics that could beneficially replace the commonly used HA of biphasic calcium phosphates for future applications in bone tissue engineering.

Preparation of PVDF/SiO2 composite membrane for salty oil emulsion separation: Physicochemical properties changes and its impact on fouling propensity

In this study, polyvinylidene fluoride (PVDF)/silica (SiO2) composite membranes were prepared by diffusion induced phase separation through direct blending method. The roles of SiO2 particles concentration on membrane physicochemical properties were evaluated through oil emulsion separation under high ionic strength environment whereby hydrophobic interaction is prevalent. Membranes were characterized using field emission scanning electron microscope (FESEM), atomic force microscopy (AFM), contact angle measurement, membrane porosity and pore size distribution. It was expected that by adding the monodispersed SiO2, it will render the membrane with hydrophilic characteristic. However, it is concomitantly changing the physical properties of the membrane. Addition of SiO2 caused the changes to the physicochemical properties of the composite membrane and its effects on the fouling propensity were evaluated. It was found that the mean pore size of the membranes increased with the increase of SiO2 concentration. The addition of hydrophilic SiO2 had accelerated the precipitation of the membrane dope solution resulting in changes of membrane cross section morphology. FESEM images showed the membrane cross-section morphology of PVDF/SiO2 composite membrane had gradually changed from finger-like to macrovoid-like structure with the increased of SiO2 concentration. The hydrophilicity of the PVDF/SiO2 composite membrane was enhanced which is a desired property for water purification. However, the changes in physical properties (pore size, porosity, and surface roughness) had played more dominant role in the oil emulsion fouling behaviour rather than hydrophilicity enhancement. Due to the salting out effect under high ionic strength environment, hydrophobic interaction played an important role in the oil adsorption. The increment in membrane pore size, porosity, and surface roughness after incorporation of SiO2 particles had encountered more serious relative flux reduction and lower flux recovery ratio.

Tunable adhesion of superoleophilic/superhydrophobic poly (lactic acid) membrane for controlled-release of oil soluble drugs

Superhydrophobic membranes with tunable adhesion have attracted intense interests for various engineering applications. In this work, superhydrophobic sustainable poly (lactic acid) (PLA) porous membrane with tunable adhesive force from 101μN to 29μN was successfully fabricated via one-step phase separation method. The incorporation of Perfluoro-1-decene (PFD) into the PLLA/PDLA membrane via the in situ polymerization can facilely tune the PLLA/PDLA stereocomplex crystallization during phase inversion, which consequently caused the unique morphology blooming evolution from bud to full-blown state. The resulted membrane showed tunable pore size, porosity, surface area, surface roughness and superhydrophobicity, which enabled the membrane with controlled-release of oil soluble drugs.

SEM-image textural features and drug release behavior of Eudragit-based matrix pellets

Matrix pellets of acetaminophen were prepared by extrusion-spheronization using a high proportion of several varieties of Eudragit; namely, 40% RSPO or RLPO, and 17% RS30D or RL30D. The pellets were characterized using textural analysis of gray-level scanning electron microscopy (SEM) images and through the cumulative pore volume distribution obtained by mercury intrusion porosimetry. Surface roughness and distribution of pores at pellet surface were characterized in terms of gray-level non uniformity (GLN) and fractal dimension of pellet surface. Both parameters were strongly dependent on the procedure followed to incorporate the polymer (in powder form or as liquid dispersion) and, to a lesser extent, on the polymer variety (RL or RS). The curing of pellets at 105 °C for 30 min led to the smoothing out and to a decrease in the pore size at the surface, which notably slowed down acetaminophen release rate. Strong correlations between the drug release rate and the surface roughness of the pellets were found.

Determination of Isosteric Heat of Adsorption by Quenched Solid Density Functional Theory

The heat of adsorption is one of the most important parameters characterizing energetic heterogeneity of the adsorbent surface. Heats of adsorption are either determined directly by calorimetry or calculated from adsorption isotherms measured at different temperatures using the thermodynamic Clausius-Clapeyron equation. Here, we present a method for calculating the isosteric heat of adsorption that requires as input only a single adsorption isotherm measured at one temperature. The proposed method is implemented with either nonlocal (NLDFT) or quenched solid (QSDFT) density functional theory models of adsorption that are currently widely used for calculating pore size distributions in various micro- and mesoporous solids. The pore size distribution determined from the same experimental isotherm is used for predicting the isosteric heat. The QSDFT method has advantages of taking into account two factors contributing to the structural heterogeneity of adsorbents: the molecular level roughness of the surface and the pore size distribution. The method is illustrated with examples of low temperature nitrogen and argon adsorption on selected samples of carbons of different degree of graphitization and MCM-41 mesoporous silicas of different pore size. The isosteric heat predictions from the NLDFT and QSDFT methods are compared against relevant experiments and the results of Monte Carlo (MC) simulations, with good agreement found in the cases where the surface model adequately reflects the pore surface roughness. Analyses with the QSDFT method show that the isosteric heat of adsorption significantly depends of the molecular level roughness of the adsorbent surface, which is ignored in NLDFT and MC models. The proposed QSDFT method with further verification can be used for calculating the isosteric heat as an additional parameter characterizing the adsorbent surface in parallel with routine calculations of the pore size distribution from a single adsorption isotherm.

Evolution of the pore structure during the early stages of the alkali-activation reaction: an in situ small-angle neutron scattering investigation

The long-term durability of cement-based materials is influenced by the pore structure and associated permeability at the sub-micrometre length scale. With the emergence of new types of sustainable cements in recent decades, there is a pressing need to be able to predict the durability of these new materials, and therefore nondestructive experimental techniques capable of characterizing the evolution of the pore structure are increasingly crucial for investigating cement durability. Here, small-angle neutron scattering is used to analyze the evolution of the pore structure in alkali-activated materials over the initial 24 h of reaction in order to assess the characteristic pore sizes that emerge during these short time scales. By using a unified fitting approach for data modeling, information on the pore size and surface roughness is obtained for a variety of precursor chemistries and morphologies (metakaolin- and slag-based pastes). Furthermore, the impact of activator chemistry is elucidated via the analysis of pastes synthesized using hydroxide- and silicate-based activators. It is found that the main aspect influencing the size of pores that are accessible using small-angle neutron scattering analysis (approximately 10–500 Å in diameter) is the availability of free silica in the activating solution, which leads to a more refined pore structure with smaller average pore size. Moreover, as the reaction progresses the gel pores visible using this scattering technique are seen to increase in size.

The thermal conversion of coal impregnated with ZnCl2

ABSTRACTCoal is a porous combustible solid fuel. The pores can easily absorb the liquid solution of salts. ZnCl2 have the capability to absorb within the pores of coal and causes to increase the roughness of internal pore surface. The chemisorbed ZnCl2 posses the ability to effect the thermal conversion of coal. In this study, catalytic behavior of ZnCl2 for thermal decomposition of coal for low-temperature gasification was studied by varying concentration, time, and temperature.

Enhancement of the upconversion photoluminescence of hexagonal phase NaYF4:Yb3+,Er3+ nanoparticles by mesoporous gold films.

Efficient enhancement of photoluminescence in rare-earth activated upconversion materials is of great significance for their practical applications in various fields. In this work, three-dimensional mesoporous gold films were fabricated by a low-cost and facile dealloying approach to improve the upconversion photoluminescence efficiency. The mesoporous Au films exhibit good chemical stability, large-area uniformity and abundant distribution of porous nanospaces. Varying the time of the dealloying process leads to modification of the pore size distribution, surface roughness and residual Ag content, resulting in effective tuning of the wavelength of the broadband localized surface plasmon resonance (LSPR). Enhancement factors were identified to be a function of the dealloying time. With the optimized upconversion photoluminescence enhancement, a 41-fold increase was achieved with the mesoporous gold substrate which had been dealloyed for 8 days. These results pave the way to overcome the limitation of poor upconversion efficiency for widespread practical applications in life science and energy fields.

The pore structure and fractal characteristics of shales with low thermal maturity from the Yuqia Coalfield, northern Qaidam Basin, northwestern China

The continental shales from the Middle Jurassic Shimengou Formation of the northern Qaidam Basin, northwestern China, have been investigated in recent years because of their shale gas potential. In this study, a total of twenty-two shale samples were collected from the YQ-1 borehole in the Yuqia Coalfield, northern Qaidam Basin. The total organic carbon (TOC) contents, pore structure parameters, and fractal characteristics of the samples were investigated using TOC analysis, low-temperature nitrogen adsorption experiments, and fractal analysis. The results show that the average pore size of the Shimengou shales varied from 8.149 nm to 20.635 nm with a mean value of 10.74 nm, which is considered mesopore-sized. The pores of the shales are mainly inkbottle- and slit-shaped. The sedimentary environment plays an essential role in controlling the TOC contents of the low maturity shales, with the TOC values of shales from deep to semi-deep lake facies (mean: 5.23%) being notably higher than those of the shore-shallow lake facies (mean: 0.65%). The fractal dimensions range from 2.4639 to 2.6857 with a mean of 2.6122, higher than those of marine shales, which indicates that the pore surface was rougher and the pore structure more complex in these continental shales. The fractal dimensions increase with increasing total pore volume and total specific surface area, and with decreasing average pore size. With increasing TOC contents in shales, the fractal dimensions increase first and then decrease, with the highest value occurring at 2% of TOC content, which is in accordance with the trends between the TOC and both total specific surface area and total pore volume. The pore structure complexity and pore surface roughness of these low-maturity shales would be controlled by the combined effects of both sedimentary environments and the TOC contents.

“Butterfly Effect” from finite dope chemical composition variations on the water/oil separation capabilities of super rough polyvinylidene difluoride (PVDF) porous membranes

Polyvinylidene fluoride (PVDF) porous membranes with superwetting amphophilic surfaces were prepared by in situ cross-linking polymerization of varied triethoxyvinylsilane (VTES) and N-vinyl-2-pyrrolidone (VP) composition ratios during none-solvent induced phase separation (NIPS) processes, utilizing template stripping method. The extreme powers of surface roughness, in amplifying the finite differences in chemical composition of initial dope solution to the properties of the resulted membranes, were revealed by comparing the structures and surface properties of these membranes with super rough surfaces, to their analogues with medium-rough surfaces and films with smooth surfaces. “Butterfly Effect” was observed on the water/oil separation capability of the formed PVDF membranes from the finite variation on the initial chemical composition caused by the change of VTES/VP molar ratio in the dope solution from 0 to 0.33, 0.38, 0.43, 0.48 and 0.53. Huge variations in the oil and water fluxes and removal efficiencies in separating water-in-oil and oil-in-water emulsions of the formed membranes from the “Butterfly Effect” were studied relating to their differences in water-in-air contact angles, oil-in-air contact angles, oil-in-water contact angles and water-in-oil contact angles as well as pore sizes and surface roughness.

Induced polarization and pore radius — A discussion

Permeability estimation from induced polarization (IP) measurements is based on a fundamental premise that the characteristic relaxation time [Formula: see text] is related to the effective hydraulic radius [Formula: see text] controlling fluid flow. The approach requires a reliable estimate of the diffusion coefficient of the ions in the electrical double layer. Others have assumed a value for the diffusion coefficient, or postulated different values for clay versus clay-free rocks. We have examined the link between a widely used single estimate of [Formula: see text] and [Formula: see text] for an extensive database of sandstone samples, in which mercury porosimetry data confirm that [Formula: see text] is reliably determined from a modification of the Hagen-Poiseuille equation assuming that the electrical tortuosity is equal to the hydraulic tortuosity. Our database does not support the existence of one or two distinct representative diffusion coefficients but instead demonstrates strong evidence for six orders of magnitude of variation in an apparent diffusion coefficient that is well-correlated with [Formula: see text] and the specific surface area per unit pore volume [Formula: see text]. Two scenarios can explain our findings: (1) the length scale defined by [Formula: see text] is not equal to [Formula: see text] and is likely much longer due to the control of pore-surface roughness or (2) the range of diffusion coefficients is large and likely determined by the relative proportions of the different minerals (e.g., silica and clays) making up the rock. In either case, the estimation of [Formula: see text] (and hence permeability) is inherently uncertain from a single characteristic IP relaxation time as considered in this study.

Effects of polydispersity, additives, impurities and surfaces on the crystallization of poly(ethylene oxide)(PEO) confined to nanoporous alumina

Abstract The effects of polydispersity, additives, impurities, free top layer and of surface roughness on the nucleation are studied for poly(ethylene oxide) located inside self-ordered nanoporous aluminum oxide (AAO). AAO pore diameters ranged from 400 nm to 25 nm. With the exception of a surface layer, none of the above factors is able to induce heterogeneous nucleation under confinement. Homogeneous nucleation remains the sole mechanism in pores having diameters below 65 nm. The internal pore surface roughness is small, which explains the minor effects of AAO surfaces on inducing heterogeneous nucleation especially within the smaller pores. The presence of oligomers shifts the homogeneous nucleation temperature to lower temperatures, reflecting the plasticizing effect of the oligomers on the liquid-to-glass temperature.

Effect of kaolin particle size and loading on the characteristics of kaolin ceramic support prepared via phase inversion technique

In this study, low cost ceramic supports were prepared from kaolin via phase inversion technique with two kaolin particle sizes, which are 0.04–0.6 μm (denoted as type A) and 10–15 μm (denoted as type B), at different kaolin contents ranging from 14 to 39 wt.%, sintered at 1200 °C. The effect of kaolin particle sizes as well as kaolin contents on membrane structure, pore size distribution, porosity, mechanical strength, surface roughness and gas permeation of the support were investigated. The support was prepared using kaolin type A induced asymmetric structure by combining macroporous voids and sponge-like structure in the support with pore size of 0.38 μm and 1.05 μm, respectively, and exhibited ideal porosity (27.7%), great mechanical strength (98.9 MPa) and excellent gas permeation. Preliminary study shows that the kaolin ceramic support in this work is potential to gas separation application at lower cost.

Fluid flow in porous media with rough pore‐solid interface

AbstractQuantifying fluid flow through porous media hinges on the description of permeability, a property of considerable importance in many fields ranging from oil and gas exploration to hydrology. A common building block for modeling porous media permeability is consideration of fluid flow through tubes with circular cross section described by Poiseuille's law in which flow discharge is proportional to the fourth power of the tube's radius. In most natural porous media, pores are neither cylindrical nor smooth; they often have an irregular cross section and rough surfaces. This study presents a theoretical scaling of Poiseuille's approximation for flow in pores with irregular rough cross section quantified by a surface fractal dimension Ds2. The flow rate is a function of the average pore radius to the power 2(3‐Ds2) instead of 4 in the original Poiseuille's law. Values of Ds2 range from 1 to 2, hence, the power in the modified Poiseuille's approximation varies between 4 and 2, indicating that flow rate decreases as pore surface roughness (and surface fractal dimension Ds2) increases. We also proposed pore length‐radius relations for isotropic and anisotropic fractal porous media. The new theoretical derivations are compared with standard approximations and with experimental values of relative permeability. The new approach results in substantially improved prediction of relative permeability of natural porous media relative to the original Poiseuille equation.

Optimizing of porous silicon morphology for synthesis of silver nanoparticles

A group of porous silicon (PSi) samples with different surface morphologies prepared at different etching current densities were investigated as a substrate for formation of silver nanoparticles (AgNPs). Simple dipping process of PSi in silver nitrite (AgNO3) with concentrations of 10−3, 10−2, and 5 × 10−2 M was employed to synthesize AgNPs.The p-type PSi was prepared by electrochemical etching process at different values of current densities. Three different forms of PSi morphology; meso, macro, and pillar with different roughness values 1.21, 177, 89.5, and 38.7 nm were prepared with varying the current densities 30, 60, 90, and 120 mA/cm2 respectively. The structural and surface morphology properties of samples before and after dipping in AgNO3 were studied through analyzing of scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). The results show that the AgNPs sizes depend on the surface morphology and roughness of PSi. The AgNPs prepared by dipping process does not depend on the porosity of the porous layer. For meso pore-like structures the sizes of AgNPs were in the range from 0.52 to 4.09 μm for a low surface roughness, and from 0.52 to 6.83 nm for high surface roughness. For the case of macro pore-like structure which possesses the highest pore sizes and surface roughness, the AgNPs sizes vary from 0.61 to 3.42 μm. The minimum AgNPs size of about 190 nm was obtained from porous surface of pillar form.

The effect of reduction degree of GO nanosheets on microstructure and performance of PVDF/GO hybrid membranes

In this study, the effect of the reduction degree of GO nanosheets on the microstructure and performance of PVDF/GO membranes were systematically investigated via comparing four PVDF/GO membranes synthesized by the casting solutions prepared at 50, 70, 85 and 100°C, which were denoted PVDF/GO-50, PVDF/GO-70, PVDF/GO-85 and PVDF/GO-100, respectively. X-Ray Photoelectron Spectrometer (XPS) and Raman Spectroscopy results showed that the preparation temperature of the casting solution affected the reduction degree of GO nanosheets. Higher preparation temperature resulted in a higher degree of reduction. Compared with the pure PVDF membrane, PVDF/GO membranes achieved better performance in term of membrane flux and rejection. However, the optimal loading of GO nanosheets was dependent on the reduction degree. For the PVDF/GO-50 membrane, the maximal membrane flux (46L/m2h) was reached at a GO loading of 0.5%, while the membrane flux of the PVDF/GO-100 membrane increased with GO loading in the range of 0–2%. SEM and AFM characterization results also showed that both GO loading and reduction degree of GO influenced the pore structure and surface roughness of PVDF/GO membranes. It is worth noting that the mechanical strength of the PVDF/GO membranes was weaker than that of the pure PVDF membrane at all GO reduction degrees regardless GO loading. This indicates that the integrity of PVDF membranes might be impaired by GO nanosheets.

Surface structural and energetic heterogeneity of carbon materials prepared from corn grains using steam and H3PO4‐steam activations

The porous activated carbons (ACs) were prepared from corn grains through physical (steam) and chemical–physical (H3PO4‐steam) activations. The effects of steam activation temperature (700–900 °C) on pore development, surface roughness, and energetic heterogeneity were investigated in both activations. Also, the effect of prior carbonization on H3PO4‐steam activation was studied. The physical properties, surface fractal dimensions, and adsorption energy distributions of ACs were determined from nitrogen adsorption–desorption isotherm data. Both physical and chemical–physical activations show that the AC with higher surface area, relatively smoother surface, and energetically heterogeneous surface could be produced at a maximum steam activation temperature (900 °C). Copyright © 2015 John Wiley & Sons, Ltd.