Smooth Pore Research Articles

Effect of cassava starch gel, fish gel and mixed gels and thermal treatment on structure development and various quality parameters in microwave vacuum-dried gel slices

Three types of gels including tapioca starch gel, fish gel and mixed gels of both (cassava starch: fish = 1:1) were prepared under different thermal conditions. Slices (4 mm thick) derived from these the gels were dehydrated to a final moisture content of 7% in a microwave vacuum dryer. The micro/macro structure and selected quality parameters of the dried gel chips were measured e.g. shape, relative volume, bulk density, texture, color, sensory and microstructure. The measured gel characteristics were analyzed and related to structure development and selected quality attributes. Both fish and mixed gel chips expanded in both diameter and thickness while the starch gel chips shrank in diameter, but expanded in thickness; the former two represented a continuous cross-section composed of a cellular structure and expanded uniformly in thickness while the latter developed an open cross-section and the center expanded more than the edge region, indicative of a disc and pillow shape, respectively. The higher severity of thermal treatment favored greater expansion and reduced hardness and bulk density, and increased crispness in the mixed gel chips; they developed a smooth and fine surface and pore wall but decreased lightness and whiteness due to starch gelatinization in the starch and mixed gel chips. Only the partial dried mixed gel chips are acceptable to the panelists. A homogenous co-gel in the mixed gel contributed to the higher uniform expansion and cellular structure. These findings will help developing the restructured microwave vacuum-dried product by blending the starch with the fish.

Porosity and surface area evolution during weathering of two igneous rocks

During weathering, rocks release nutrients and store water vital for growth of microbial and plant life. Thus, the growth of porosity as weathering advances into bedrock is a life-sustaining process for terrestrial ecosystems. Here, we use small-angle and ultra small-angle neutron scattering to show how porosity develops during initial weathering under tropical conditions of two igneous rock compositions, basaltic andesite and quartz diorite. The quartz diorite weathers spheroidally while the basaltic andesite does not. The weathering advance rates of the two systems also differ, perhaps due to this difference in mechanism, from 0.24 to 100mmkyr−1, respectively. The scattering data document how surfaces inside the feldspar-dominated rocks change as weathering advances into the protolith. In the unaltered rocks, neutrons scatter from two types of features whose dimensions vary from 6nm to 40μm: pores and bumps on pore–grain surfaces. These features result in scattering data for both unaltered rocks that document multi-fractal behavior: scattering is best described by a mass fractal dimension (Dm) and a surface fractal dimension (Ds) for features of length scales greater than and less than ∼1μm, respectively. In the basaltic andesite, Dm is approximately 2.9 and Ds is approximately 2.7. The mechanism of solute transport during weathering of this rock is diffusion. Porosity and surface area increase from ∼1.5% to 8.5% and 3 to 23m2g−1 respectively in a relatively consistent trend across the mm-thick plagioclase reaction front. Across this front, both fractal dimensions decrease, consistent with development of a more monodisperse pore network with smoother pore surfaces. Both changes are consistent largely with increasing connectivity of pores without significant surface roughening, as expected for transport-limited weathering. In contrast, porosity and surface area increase from 1.3% to 9.5% and 1.5 to 13m2g−1 respectively across a many cm-thick reaction front in the spheroidally weathering quartz diorite. In that rock, Dm is approximately 2.8 and Ds is approximately 2.5 prior to weathering. These two fractals transform during weathering to multiple surface fractals as micro-cracking reduces the size of diffusion-limited subzones of the matrix. Across the reaction front of plagioclase in the quartz diorite, the specific surface area and porosity change very little until the point where the rock disaggregates into saprolite.The different patterns in porosity development of the two rocks are attributed to advective infiltration plus diffusion in the rock that spheroidally fractures versus diffusion-only in the rock that does not. Fracturing apparently diminishes the size of the diffusion-limited parts of the spheroidally weathering rock system to promote infiltration of meteoric fluids, therefore explaining the faster weathering advance rate into that rock.

Biomimetic Membrane Channels based on Carbon Nanotubes

Biological membrane channels and pore-forming proteins display a level of sophistication in managing molecular scale transport that is typically unmatched by inorganic analogs, and efforts to develop nanopores that approach the transport efficiency of biological molecules often run into fabrication or synthetic difficulties. A different approach is exploiting nanomaterial scaffolds that provide near-atomic level of control over the structure and surface properties of these structures. Carbon nanotubes provide an especially interesting system for such studies due to their inherently smooth hydrophobic pore walls that support extremely high transport rates, which are comparable to biological channels. We describe the preparation of nanotube-based membrane nanopores, their assembly into biological membranes, and single-channel measurements of molecular transport in these assemblies.

Enhancing the bioactivity of Poly(lactic-co-glycolic acid) scaffold with a nano-hydroxyapatite coating for the treatment of segmental bone defect in a rabbit model

PurposePoly(lactic-co-glycolic acid) (PLGA) is excellent as a scaffolding matrix due to feasibility of processing and tunable biodegradability, yet the virgin scaffolds lack osteoconduction and osteoinduction. In this study, nano-hydroxyapatite (nHA) was coated on the interior surfaces of PLGA scaffolds in order to facilitate in vivo bone defect restoration using biomimetic ceramics while keeping the polyester skeleton of the scaffolds.MethodsPLGA porous scaffolds were prepared and surface modification was carried out by incubation in modified simulated body fluids. The nHA coated PLGA scaffolds were compared to the virgin PLGA scaffolds both in vitro and in vivo. Viability and proliferation rate of bone marrow stromal cells of rabbits were examined. The constructs of scaffolds and autogenous bone marrow stromal cells were implanted into the segmental bone defect in the rabbit model, and the bone regeneration effects were observed.ResultsIn contrast to the relative smooth pore surface of the virgin PLGA scaffold, a biomimetic hierarchical nanostructure was found on the surface of the interior pores of the nHA coated PLGA scaffolds by scanning electron microscopy. Both the viability and proliferation rate of the cells seeded in nHA coated PLGA scaffolds were higher than those in PLGA scaffolds. For bone defect repairing, the radius defects had, after 12 weeks implantation of nHA coated PLGA scaffolds, completely recuperated with significantly better bone formation than in the group of virgin PLGA scaffolds, as shown by X-ray, Micro-computerized tomography and histological examinations.ConclusionnHA coating on the interior pore surfaces can significantly improve the bioactivity of PLGA porous scaffolds.

A LUTTINGER LIQUID CORE INSIDE HELIUM-4 FILLED NANOPORES

As helium-4 is cooled below 2.17 K it undergoes a phase transition to a fundamentally quantum mechanical state of matter known as a superfluid which supports flow without viscosity. This type of dissipationless transport can be observed by forcing helium to travel through a narrow constriction that the normal liquid could not penetrate. Recent experiments have highlighted the feasibility of fabricating smooth pores with nanometer radii, that approach the truly one-dimensional limit where it is believed that a system of bosons (like helium-4) may have startlingly different behavior than in three dimensions. The one-dimensional system is predicted to have a linear hydrodynamic description known as Luttinger liquid (LL) theory, where no type of long range order can be sustained. In the limit where the pore radius is small, LL theory would predict that helium inside the channel behaves as a sort of quasi-supersolid with all correlations decaying as power-law functions of distance at zero temperature. We have performed large scale quantum Monte Carlo simulations of helium-4 inside nanopores of varying radii at low temperature with realistic helium–helium and helium-pore interactions. The results indicate that helium inside the nanopore forms concentric cylindrical shells surrounding a core that can be described via LL theory and provides insights into the exciting possibility of the experimental detection of this intriguing low-dimensional state of matter.

Improved properties and microstructure of porous silicon nitride/silicon oxide composites prepared by sol–gel route

Porous Si3N4 ceramics with high porosity prepared by gelcasting and pressureless sintering were used as frames for Si3N4–SiO2 composites. Various contents of amorphous SiO2 were introduced into porous Si3N4 frames by repeating the sol–gel infiltration and sintering process. The sol–gel process resulted in the increase of density and the formation of well-distributed micro-pores with both uniform pore size and smooth pore wall. The mechanical properties and thermal shock resistance of Si3N4–SiO2 composites were also largely improved. As the SiO2 content increased from 0 to 25.9vol%, the porosity of Si3N4–SiO2 composites decreased from 49.3% to 22%, with the density of composites increased from 1.62g/cm3 to 2.18g/cm3. The flexural strength and fracture toughness also increased from 92.6MPa and 1.05MPam1/2 to 148.1MPa and 1.70MPam1/2, respectively. The dielectric constant increased from 2.65 to 3.61, but the dielectric loss did not increase much from 3.23×10−3 to 3.84×10−3. The residual flexural strength of porous Si3N4 ceramics retained to a ΔT of 700°C, while the Si3N4–SiO2 composites with 25.9vol% of SiO2 showed much better thermal shock resistance and had a ΔT of 900°C.

Nanocomposite hydrogels with rapid thermal-responsibility by using surfactant detergent as template

To improve thermal-responsibility of poly N-isopropylacrylamide/inorganic hectorite hydrogels, inorganic hectorite severed as physical cross-linker, a kind of nonionic surfactant detergent polyoxyethylene 20 cetyl ether (POECE) was used as template to prepare nanostructured hydrogels (THPN hydrogels). The structure, morphology, temperature-sensitivity and swelling behavior of THPN hydrogels were characterized. Comparing to pure PNIPA hydrogel, THPN hydrogels exhibited higher swelling ratio as well as faster response rate. In the case of temperature-sensitivity, the volume phase transition temperature (VPTT) of THPN hydrogels was between 32 and 34°C, slightly different from pure PNIPA hydrogel. The results of FTIR, 1H NMR and TGA showed that a small amount of POECE adsorbed onto surface of hectorite, and it is maybe one of the reasons of higher swelling ratio and faster response rate. SEM and FESEM images showed that THPN hydrogels have more regular and smoother pore structure due to the POECE which severed as the effect of POECE template, and the hectorite dispersed homogeneously in THPN hydrogels regardless of adsorption of POECE, respectively.

Annealing effects on the microstructure of combustion synthesized Eu3+ and Tb3+ doped Y2O3 nanoparticles

Eu3+ and Tb3+ doped Y2O3 powders having different Eu3+/Tb3+ concentrations were prepared by gel-combustion process using glycine as fuel (reducing agent) and corresponding metal nitrates as oxidant, followed by annealing at 600 and 1200°C. From XRD, SEM and TEM studies, it is inferred that for these samples, the extent of aggregation and average particle size strongly depends on the annealing temperatures. Small angle X-ray scattering (SAXS) studies on these samples revealed that the scattering intensity at large values of momentum transfer vector (Q) vary as Q−4, establishing the lack of surface fractal nature as well as existence of a non-diffusive and smooth pore grain interface in both 600 and 1200°C annealed samples. Dopant ions up to 10at.% do not have any effect on particle/pore morphology of the samples. Improved luminescence from 1200°C heated sample compared to 600°C heated sample has been explained based on the difference in particle size and associated difference in the surface area.

Mechanics of the slaking of shales

Waste fills resulting from coal mining should consist of large, free-draining sedimentary rocks fragments. The successful performance of these fills is related to the strength and durability of the individual rock fragments. When fills are made of shale fragments, some fragments will be durable and some will degrade into soil particles resulting from slaking and inter-particle point loads. The degraded material fills the voids between the intact fragments, and results in settlement. A laboratory program with point load and slake durability tests as well as thin section examination of sixty-eight shale samples from the Appalachian region of the United States revealed that pore micro-geometry has a major influence on degradation. Under saturated and unsaturated conditions, the shales absorb water, and the air in their pores is compressed, breaking the shales. This breakage was more pronounced in shales with smooth pore boundaries and having a diameter equal to or smaller than 0.060 mm. If the pore walls were rough, the air-pressure breaking mechanism was not effective. However, pore roughness (measured by the fractal dimension) had a detrimental effect on point load resistance. This study indicated that the optimum shales to resist both slaking as well as point loads are those that have pores with a fractal dimension equal to 1.425 and a diameter equal to or smaller than 0.06 mm.

Silver Nanoparticle Synthesis: Novel Route for Laser Triggering of Polyelectrolyte Capsules

We have demonstrated the synthesis of light-sensitive polyelectrolyte capsules (PECs) by utilizing a novel polyol reduction method and investigated its applicability as photosensitive drug delivery vehicle. The nanostructured capsules were prepared via layer by layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on silica particles followed by in-situ synthesis of silver nanoparticles (NPs). Capsules without silver NPs were permeable to low molecular weight (M(w), 479 g/mol) rhodamine but impermeable to higher molecular weight fluorescence labeled dextran (FITC-dextran). However, capsules synthesized with silver NPs showed porous morphology and were permeable to higher molecular weight (M(w) 70 kDa) FITC-dextran also. These capsules were loaded with FITC-dextran using thermal encapsulation method by exploiting temperature induced shrinking of the capsules. During heat treatment the porous morphology of the capsules transformed into smooth pore free structure which prevents the movement of dextran into bulk during the loading process. When these loaded capsules are exposed to laser pulses, the capsule wall ruptured, resulting in the release of the loaded drug/dye. The rupture of the capsules was dependent on particle size, laser pulse energy and exposure time. The release was linear with time when pulse energy of 400 μJ was used and burst release was observed when pulse energy increased to 600 μJ.

Mass Transport through Carbon Nanotube Membranes in Three Different Regimes: Ionic Diffusion and Gas and Liquid Flow

Transport phenomena through the hollow conduits of carbon nanotubes (CNTs) are subjects of intense theoretical and experimental research. We have studied molecular transport over the large spectrum of ionic diffusion to pressure-driven gaseous and liquid flow. Plasma oxidation during the fabrication of the membrane introduces carboxylic acid groups at the CNT entrance, which provides electrostatic "gatekeeper" effects on ionic transport. Diffusive transport of ions of different charge and size through the core of the CNT is close to bulk diffusion expectations and allows estimation of the number of open pores or porosity of the membrane. Flux of gases such as N(2), CO(2), Ar, H(2), and CH(4) scaled inversely with their molecular weight by an exponent of 0.4, close to expected kinetic theory velocity expectations. However, the magnitude of the fluxes was ∼15- to 30-fold higher than predicted from Knudsen diffusion kinetics and consistent with specular momentum reflection inside smooth pores. Polar liquids such as water, ethanol, and isopropyl alcohol and nonpolar liquids such as hexane and decane were dramatically enhanced, with water flow over 4 orders of magnitude larger than "no-slip" hydrodynamic flow predictions. As direct experimental proof for the mechanism of near perfect slip conditions within CNT cores, a stepwise hydrophilic functionalization of CNT membranes from as-produced, tip-functionalized, and core-functionalized was performed. Pressure-driven water flow through the membrane was reduced from 5 × 10(4) to 2 × 10(2) to less than a factor of 5 enhancement over conventional Newtonian flow, while retaining nearly the same pore area.

Frictionless Sliding of Single-Stranded DNA in a Carbon Nanotube Pore Observed by Single Molecule Force Spectroscopy

Smooth inner pores of carbon nanotubes (CNT) provide a fascinating model for studying biological transport. We used an atomic force microscope to pull a single-stranded DNA oligomer from a carbon nanotube pore. DNA extraction from CNT pores occurs at a nearly constant force, which is drastically different from the elastic profile commonly observed during polymer stretching with atomic force microscopy. We show that a combination of the frictionless nanotube pore walls and an unfavorable DNA solvation energy produces this constant force profiles.

Abnormal Anodic Aluminum Oxide Formation in Confined Structures for Lateral Pore Arrays

We report on abnormal behavior in anodic oxidation of Al in mechanically confined structures for formation of horizontal nanoporous anodic alumina oxide (H-AAO). Instead of smooth pore walls, periodic dendrite inner pore structures form, the growth rate is suppressed to 5% of its value during bulk anodization under the same conditions, and a steady-state is never reached. These anomalies associated with H-AAO originate from suppressed volume expansion and a plastic flow of confined by the hard mask. By determining new anodization conditions leading to zero volume expansion, dendritic H-AAO can be avoided and kinetic retardation minimized.

Mechanically stable flat anodic titania membranes for gas transport applications

Anodic titanium oxide (ATO) membranes were produced by two-step anodic oxidation of titanium foil in ethylene glycol electrolyte containing NH4F at the anodization voltage of 60 V. To provide the mechanical strength necessary for applying tubular anodic films as gas membranes, we utilized the formation of protective continuous TiO2 layer at the top film surface prior to second anodization. As compared to conventional two-step anodic oxidation this technique decreases dissolution rates of titanium oxide phases with oxidation states lower than +4 (Ti2O3, Ti3O5), which are forming between titania nanotubes during anodization. The structural parameters of anodic titania films were determined by small-angle X-ray scattering and scanning electron microscopy techniques. According to SEM the proposed method resulted in growth of ATO films with a flat surface without nanotube endings, which enabled to use the films as gas separation membranes. The permeance of individual gases through ATO membranes were found to depend on gas molecular weight (M−0.5), with absolute values twice exceeding theoretical permeabilities as it was predicted by Knudsen diffusion (up to 63 m3/(m2 × bar × h) for nitrogen at 298 K). Here we ascribe this phenomenon to diffusion according to Knudsen-Smoluchoski mechanism (diffusion with slip, involving specular reflections of molecules), which is appropriate for membranes with straight pores and smooth internal pore surfaces.

Structure and dynamics of liquid methanol confined within functionalized silica nanopores

Molecular dynamics simulations have been carried out to investigate the structure and dynamics of liquid methanol confined in 3.3 nm diameter cylindrical silica pores. Three cavities differing in the characteristics of the functional groups at their walls have been examined: (i) smooth hydrophobic pores in which dispersive forces prevail, (ii) hydrophilic cavities with surfaces covered by polar silanol groups, and (iii) a much more rugged pore in which 60% of the previous interfacial hydroxyl groups were replaced by the bulkier trimethylsilyl ones. Confinement promotes a considerable structure at the vicinity of the pore walls which is enhanced in the case of hydroxylated surfaces. Moreover, in the presence of the trimethylsilyl groups, the propagation of this interface-induced spatial ordering extends down to the central region of the pore. Concerning the dynamical modes, we observed an overall slowdown in both the translational and rotational motions. An analysis of these mobilities from a local perspective shows that the largest retardations operate at the vicinity of the interfaces. The gross features of the rotational dynamics were analyzed in terms of contributions arising from bulk and surface states. Compared to the bulk dynamical behavior, the characteristic timescales associated with the rotational motions show the most dramatic increments. A dynamical analysis of hydrogen bond formation and breaking processes is also included.

Elucidation of consistent enantioselectivity for a homologous series of chiral compounds in homochiral metal–organic frameworks

The members of a homologous series of chiral compounds often show inconsistent enantioselectivities when separated on the same chiral stationary phase. The reasons behind this are subject to debate due to the lack of an efficient way to probe the molecular level separation mechanisms on conventional chiral stationary phases. Homochiral metal-organic frameworks (HMOFs) are a family of new porous, crystalline materials that can be used as chiral stationary phases. The regular structures of HMOFs make possible the detailed interrogation of chiral separation mechanisms through molecular modeling. In this report, molecular modeling techniques were used to study the enantioselectivities of a homologous series of chiral compounds in two different HMOFs. We demonstrate that a shift in the adsorption site is one reason for the lack of a correlation between the enantioselectivities of a homologous series of chiral compounds. In addition, we demonstrate that a smooth HMOF pore can help preserve the adsorption site and the separation mechanism, and hence achieve consistent enantioselectivity for a homologous series of chiral compounds.

Integrated structural control of cage-type mesoporous platinum possessing both tunable large mesopores and variable surface structures by block copolymer-assisted Pt deposition in a hard-template

Cage-type mesoporous Pt with tunable large mesopores possessing smooth and rough pore surfaces were prepared selectively by the deposition of Pt in the absence and presence of a block copolymer in a hard-template, respectively.

Fabrication of high density, high-aspect-ratio polyimide nanofilters

A novel fabrication process produces high porosity polymer nanofilters with smooth, uniform, and straight pores with high aspect ratios. The process utilizes electron beam lithography and energetic neutral atom beam lithography and epitaxy techniques. The method has the potential to produce a new generation of high-precision, very-high-porosity, biocompatible filters with pore sizes down to 100nm.

Separation of sericin from fatty acids towards its recovery from silk degumming wastewaters

Sericin is a valuable protein, which is currently discarded as a waste in silk industry. Silk degumming wastewaters (SDW) are abundant sources of sericin, however, they contain impurities such as salts of fatty acids (soap) in conventional degumming processes. In this study, a process consisting of centrifugation (CFG), low temperature crystallization (LTC) and ultrafiltration (UF) was developed to separate sericin from fatty acids towards its recovery from conventional SDW. Complete removal of fatty acids was achieved by CFG + LTC, where CFG possibly accelerated crystal formation and separation processes. In CFG + UF (20 kDa), sericin rejection increased as pH was reduced from alkaline to acidic levels, possibly due to decreased solubility of sericin and increased amounts of undissociated fatty acids. Fatty acids were partly retained, leading to inadequate separation. Despite very high flux declines, cakes formed by the combined foulants were removable at both pH conditions. In CFG + LTC + UF (5 kDa), sericin was rejected by 92%. Although solution pH did not affect rejection performance, flux decline decreased from 85% to 61% at alkaline pH. Different fouling mechanisms were observed for different foulant types. Only cake formation occured with combined foulant (sericin + fatty acids). The cake surfaces were irregular, with denser and more heterogeneous structure at acidic pH. However, smooth cake formation plus pore narrowing occured with sericin alone at alkaline pH. Additional pore clogging occured at acidic pH, possibly due to decreased solubility of sericin. Chemical cleaning was less effective at acidic pH due to adsorption and pore clogging. Sericin recovery from conventional SDW was achieved in a three-stage process; CFG + LTC for complete separation of sericin from fatty acids and UF for recovering sericin.

Laser drilling of nano-pores in sandwiched thin glass membranes

We report on a novel method of using an excimer laser to drill ultra-small pores in borosilicate glass membranes. By introducing a thin layer of liquid between sandwiches of two glass slides, we can shrink the pore size and smoothen the surface on the exit side. We are able to push the minimal exit pore diameter down to 90 nm, well below the laser wavelength of 193 nm. This is achieved with substrates over 150 microm thick. Compared to other methods, this technique is fast, inexpensive, and produces high quality smooth pores.