Elliptical Pores Research Articles

Relating pore shape to the non-linear response of periodic elastomeric structures

By introducing a periodic array of pores in an elastic matrix, instabilities with wavelengths that are of the order of the size of the microstructure can be triggered. Interestingly, these instabilities can be utilized to design a novel class of responsive materials. Possible applications include materials with unusual properties such as negative Poisson's ratio, phononic and photonic switches and colorful and reconfigurable displays.Although shape plays an important role in the design and performance of periodic materials, so far only the non-linear response of structures with circular and elliptical pores has been investigated and the effect of the pore shape on the structural response has not yet been explored. Here, we numerically explore the effect of pore shape on the non-linear response of a square array of pores in an elastomeric matrix. Our results show that pore shape can be used effectively to design material with desired properties and to control attractive features of soft porous systems, such as their stiffness, critical strain and negative Poisson's ratio.

Teardrop shapes minimize bending energy of fusion pores connecting planar bilayers

A numerical gradient flow procedure was devised to characterize minimal energy shapes of fusion pores connecting two parallel planar bilayer membranes. Pore energy, composed of splay, tilt, and stretching, was obtained by modeling each bilayer as two monolayers and treating each monolayer of a bilayer membrane as a freely deformable surface described with a mean lipid orientation field. Voids between the two monolayers were prevented by a steric penalty formulation. Pore shapes were assumed to possess both axial and reflectional symmetry. For fixed pore radius and bilayer separation, the gradient flow procedure was applied to initially toroidal pore shapes. Using initially elliptical pore shapes yielded the same final shape. The resulting minimal pore shapes and energies were analyzed as a function of pore dimension and lipid composition. Previous studies either assumed or confined pore shapes, thereby tacitly supplying an unspecified amount of energy to maintain shape. The shapes derived in the present study were outputs of calculations and an externally provided energy was not supplied. Our procedure therefore yielded energy minima significantly lower than those reported in prior studies. The membrane of minimal energy pores bowed outward near the pore lumen, yielding a pore length that exceeded the distance between the two fusing membranes.

Distinct subtypes of zona pellucida morphology reflect canine oocyte viability and cumulus-oocyte complex quality

The aim of this study was to analyze surface morphology of the zona pellucida (ZP) and assess its relationship with oocyte viability, cumulus-oocyte complex (COC) quality, and oocyte donor age in dogs. Canine ovaries were sliced to release COCs for use in three experiments. In Experiment 1, oocytes from high-quality (grade I) COCs were viewed with scanning electron microscopy to visualize the zona surface. Four zonae, classified as types I, II, III, and IV, were detectable on high-quality oocytes. Most (95.5%) dog donors had oocytes with two or three ZP types. The ZP type I had a smooth compact surface with few pores. The ZP type II was less compact with many distinct circular or elliptical pores. The ZP type III had a rough surface with folds and many irregular shaped pores and hollows. The ZP type IV also had a rough surface with folds, but in addition, stringy filaments obscured the pores and hollows. The frequency of ZP type I in the oocyte population was low (2.7%), whereas ZP types II, III, and IV each occurred in approximately one-third of the oocyte population. In Experiment 2, oocytes from high-quality COCs were stained with propidium iodide (PI) before scanning electron microscopy to investigate the relationship of oocyte viability with ZP morphology. In Experiment 3, oocytes were collected from low-quality (grade 2) and high-quality (grade 1) COCs to investigate the role of COC quality on zona structure. Zonae types I and II were characteristic of PI-positive (dead) oocytes and oocytes from low-quality COCs, whereas ZP types III and IV were prevalent on PI-negative (living) oocytes and oocytes from high-quality COCs. We concluded that the heterogeneous ZP surface underwent structural rearrangements related to oocyte viability and COC quality. This warrants further investigation into ZP structure and may be useful for canine-assisted reproduction.

Au NP Honeycomb-Patterned Films with Controllable Pore Size and Their Surface-Enhanced Raman Scattering

Honeycomb-patterned films (HPFs) of Au nanoparticles (Au NPs) with pore size controlled by varying the quantity of Au NPs or using modified agents of different mercaptans (C14H29SH, C16H33SH, and C18H37SH) were prepared. The strength of the HPFs containing Au NPs can be enhanced because of the addition of polymers including polystyrene, poly(l-lactic acid), and poly(methyl methacrylate-co-ethyl acrylate). With an increase in the amount of polymer and the number of Au NPs or the chain length of the modified agents, the pore size of HPFs decreases, indicating that the pore size can be well controlled by adjusting the above factors. Interestingly, HPFs with elliptical pores that were created by the direction of the air flow were observed. The pore diameter on the outer rim is smaller than that in the center, which should be because of the subordinate evaporation of the solvent in the center. Sponge structures were observed in the cross sections of the walls of HPFs, which should be produced by microphase separation. The HPFs consisting of Au NPs with controllable pore size exhibited stronger surface-enhanced Raman scattering. We believe that the HPFs composed of metal NPs such as Au, Ag, and Cu are exploited in multispectral scanners, nanophotons, and sensors.

A flexible, bolaamphiphilic template for mesoporous silicas

A novel symmetrical bolaamphiphile, containing two N-methylimidazolium head-groups bridged by a 32-methylene linker, was synthesized and characterized. A variety of mesoporous silicas was prepared using the bolaamphiphile as a "soft template". The effects of absolute surfactant concentration and synthesis conditions upon the morphologies of these silicas were investigated. For a given surfactant concentration, particle morphology; pore size; and pore ordering were modified through control of the template to silica-precursor ratio and synthesis conditions. Observed morphologies included: lenticular core-shell nanoparticles and decorticated globules, truncated hexagonal plates, and sheets. In all cases the mesopores are aligned along the shortest axis of the nanomaterial. Decorticated materials displayed surface areas of up to 1200 m(2) g(-1) and pore diameters (D(BJH)) of 24-28 Å. Small-angle X-ray diffraction and transmission electron microscopy measurements revealed that the majority of the materials has elliptical pores arranged in rectangular lattices (c2mm). Adoption of this symmetry group is a result of the template aggregate deformation from a regular hexagonal phase of cylindrical rods to a ribbon phase under the synthetic conditions.

Effects of crossflow velocity and transmembrane pressure on microfiltration of oil-in-water emulsions

This study addresses the issue of oil removal from water using hydrophilic porous membranes. The effective separation of oil-in-water dispersions involves high flux of water through the membrane and, at the same time, high rejection rate of the oil phase. The effects of transmembrane pressure and crossflow velocity on rejection of oil droplets and thin oil films by pores of different cross-section are investigated numerically by solving the Navier–Stokes equation. We found that in the absence of crossflow, the critical transmembrane pressure, which is required for the oil droplet entry into a circular pore of a given surface hydrophilicity, agrees well with analytical predictions based on the Young–Laplace equation. With increasing crossflow velocity, the shape of the oil droplet is strongly deformed near the pore entrance and the critical pressure of permeation increases. We determined numerically the phase diagram for the droplet rejection, permeation, and breakup depending on the transmembrane pressure and shear rate. Finally, an analytical expression for the critical pressure in terms of geometric parameters of the pore cross-section is validated via numerical simulations for a continuous oil film on elliptical and rectangular pores.

Structure of Organic Spines in the Rhizarian Protist Belonocystis tubistella Rainer, 1968, and a Description of Belonocystis quadrangularis n. sp. (Cercozoa, Insertae Sedis)

Summary. Several Ontario (Canada) populations of the “heliozoan-like” protist Belonocystis Rainer, 1968 were studied to help elucidate the taxonomic position of this genus relative to other rhizarian protists with fine pseudopodia. The Ontario material presently includes two distinct species – B. tubistella Rainer and B. quadrangularis n. sp., described here as a new species based on cell morphology and microstructure of the spiny investiture encasing its cell. The organic nature of the spiny structures of both species has been confirmed by their dissolution in 6% sodium hypochlorite solution. Median cell diameters of B. tubistella and B. quadrangularis were 10.5 µm and 7 µm, respectively. As revealed by transmission electron microscopy, the spine bases in B. tubistella consisted of a complex structure of four curved ribs interconnected by a membranous sheet replete with closely-appressed, large circular to elliptical pores, while in B. quadrangularis the spine bases consisted of a simple four-cornered “pyramid” of struts that supported the main shaft of the spine. These findings strengthen the status of the genus Belonocystis and it placement outside the realm of the Centrohelida and Rotosphaerida.

Variable cross-section nanopores fabricated in silicon nitride membranes using a transmission electron microscope

Nanopores were fabricated using a transmission electron microscope (TEM). By manipulating TEM parameters, such as relative stage settings, electron beam shape and dwell time, it was possible to fabricate both single and ordered arrangements of nanopores with controlled geometries in silicon nitride membranes supported on a silicon window. Three distinct nanopore geometries with circular, elliptical and triangular cross-sections were fabricated. The smallest critical dimension reported here is on the order of 3 nm for the elliptical pore.

Slow release kinetics of mitoxantrone from ordered mesoporous carbon films

High porosity and surface areas of ordered mesoporous materials provide substantial capacity for loading of guest molecules, and the well-defined morphology of such materials can control their transport for controlled release. Here, the loading and release of mitoxantrone from unmodified ordered mesoporous carbon films is monitored using UV/Vis spectroscopy. Organic–organic self-assembly of Pluronic F127 with phenolic resin leads to interconnected elliptical pores (≈2nm) in the film after carbonization. Interestingly, the total loading (2.6±0.4μg/cm2) and release of mitoxantrone is independent of film thickness (50–400nm), suggesting diffusion limitations in pore filling. With an alternative template, the pore size increases to ≈5nm and the mitoxantrone loading increases to 3.5±0.9μg/cm2, but the loading still remains thickness independent. Using phosphate buffered saline at 37°C, less than 60% of the loaded mitoxantrone is readily released from the mesoporous carbon films over a two-week period. The release profile includes an initial burst with a modest fraction (<20%) of the loaded drug released within the first day, followed by a near linear release over the subsequent 5–9days. Interestingly, the smaller pores (ca. 2nm) release nearly 50% more mitoxantrone over 2weeks than the larger pores (ca. 5nm), despite the lower initial loading. These results illustrate potential limitations as well as opportunities for the use of highly hydrophobic porous materials for the controlled release of hydrophobic biologically active compounds as drug delivery systems.

From aperture characterization to hydraulic properties of fractures

A methodology is suggested to measure the aperture and estimate the hydraulic properties of desiccation and tectonic fractures in heterogeneous soils. The aperture of desiccation fractures is quantified by the fluctuating distance between two opposite faces and is modelled as a network of parallel plates of variable opening. The aperture of tectonic fractures is modeled as a 2-dimensional network of elliptical channels with parameters the major and minor axis lengths. Scanning electron microscope (SEM) images of the 2-dimensional cross-sections of resin-impregnated fractures are employed to estimate the statistics of the fracture aperture parameters in both cases. This information is coupled with effective medium approximation for the calculation of the mean hydraulic fracture aperture which allows us to estimate approximately the permeability of the fracture networks over the various zones of the soil. The estimated values of permeability are comparable to corresponding ones measured with gas permeation tests on the field. Invasion percolation models are used to simulate the quasi-static and pressure-controlled immiscible displacement of oil/water drainage in single fractures and estimate the relevant capillary pressure and relative permeability curves, which are similar to corresponding ones resulting from the inverse modelling of two-phase flow experiments in planar glass-etched networks of elliptical pores.

A new water bear, Minibiotus julianae, from the Caribbean Island of Dominica (Tardigrada: Eutardigrada: Parachela: Macrobiotidae)

A new species of tardigrade, Minibiotus acadianus, is described from a moss sample collected in June 2009 from a rainforest palm tree on the island of Dominica, West Indies. The new species has a buccal tube with a single anterior curvature, two macroplacoids, and a microplacoid. The cuticle is smooth with small, evenly-distributed circular or elliptical pores. Eggs have a reticulated shell surface and short inverted goblet egg process; a dentate margin on the distal dish of the processes bears 10–12 short teeth. The new species is most similar to Minibiotus acadianus Meyer & Domingue, 2011; both have wider buccal tubes than other species in the genus. The new species is easily distinguished from M. acadianus in lacking cuticular gibbosities and in some characters of the egg.

Impact of Homopolymer Pore Expander on the Morphology of Mesoporous Carbon Films Using Organic–Organic Self-Assembly

Soft templated mesoporous carbon films (ca. 60 nm thick) are fabricated by the cooperative assembly of poly(styrene-block-ethylene oxide) (PS-b-PEO) with phenolic resin, where the pore sizes are tuned by the addition of polystyrene oligomers (hPS) to this self-assembling system. Significant differences in the morphology and pore expansion are found for the thin films in comparison to previously reported bulk powders using a similar system. The film porosity is nearly independent of swelling agent content for addition of up to 10 wt % hPS; this limited effect is attributed to surface segregation of the hPS on the basis of wetting considerations, which decreases the effective concentration of hPS in the hydrophobic domains. The templated synthesis yields a relatively narrow pore size distribution for 10 wt % hPS. Elliptical pores are formed due to the uniaxial contraction that occurs during carbonization...

Percolation Effects on Electrical Resistivity and Electron Mobility

Percolation, defined as the study of transport across a porous material, can be used to determine transport quantities of a material such as electrical and thermal conductivity. Observing the way electrons flow across a porous conductive sheet is a common way that percolation studies are performed, and has many practical applications in electronics. This study determines how elliptical pores cut into a conductive sheet affect the percolation threshold; the remaining area of the conductive sheet when the current across it first becomes zero. Past research has been performed on this topic which yielded theoretical results of the percolation thresholds, and this study aims to verify those results experimentally. This study shows that as the aspect ratio of an ellipse approaches zero, the percolation threshold approaches one. This report also establishes a novel experimental method of studying percolating networks.

Local Tissue Geometry Determines Contractile Force Generation of Engineered Muscle Networks

The field of skeletal muscle tissue engineering is currently hampered by the lack of methods to form large muscle constructs composed of dense, aligned, and mature myofibers and limited understanding of structure-function relationships in developing muscle tissues. In our previous studies, engineered muscle sheets with elliptical pores ("muscle networks") were fabricated by casting cells and fibrin gel inside elastomeric tissue molds with staggered hexagonal posts. In these networks, alignment of cells around the elliptical pores followed the local distribution of tissue strains that were generated by cell-mediated compaction of fibrin gel against the hexagonal posts. The goal of this study was to assess how systematic variations in pore elongation affect the morphology and contractile function of muscle networks. We found that in muscle networks with more elongated pores the force production of individual myofibers was not altered, but the myofiber alignment and efficiency of myofiber formation were significantly increased yielding an increase in the total contractile force despite a decrease in the total tissue volume. Beyond a certain pore length, increase in generated contractile force was mainly contributed by more efficient myofiber formation rather than enhanced myofiber alignment. Collectively, these studies show that changes in local tissue geometry can exert both direct structural and indirect myogenic effects on the functional output of engineered muscle. Different hydrogel formulations and pore geometries will be explored in the future to further augment contractile function of engineered muscle networks and promote their use for basic structure-function studies in vitro and, eventually, for efficient muscle repair in vivo.

Predicting shape and stability of air–water interface on superhydrophobic surfaces comprised of pores with arbitrary shapes and depths

An integro-differential equation for the three dimensional shape of air–water interface on superhydrophobic surfaces comprised of pores with arbitrary shapes and depths is developed and used to predict the static critical pressure under which such surfaces depart from the non-wetting state. Our equation balances the capillary forces with the pressure of the air entrapped in the pores and that of the water over the interface. Stability of shallow and deep circular, elliptical, and polygonal pores is compared with one another and a general conclusion is drawn for designing pore shapes for superhydrophobic surfaces with maximum stability.

The Mechanical Property, Microstructure, and Pore Geometry of a Methyltrimethoxysilane Modified Silica Zeolite (MSZ) Film

A methyltrimethoxysilane (MTMS) modified silica zeolite (MSZ) film has been prepared using a high ratio of MTMS/tetraethyl orthosilicate (TEOS). This study investigated the effect of MTMS addition on the low-k matrix structure, elastic modulus, and pore geometry. High MTMS loading reduced the k-value of MSZ film down to 2.0, but yielded a lower elastic modulus, 2.7 GPa. Based on grazing-incidence small-angle X-ray scattering (GISAXS) 2D pattern analysis, the pore geometry of the MSZ film was found to be small but elliptical (Rin-plane ∼3.75 nm; Rout-of-plane ∼3.04 nm). The elliptical pore shape was formed by a collapse of film structure at 150–160°C as a result of ∼32% thickness shrinkage due to the decomposition of tetra-n-propylammonium hydroxide (TPAOH), a structure directing catalyst, and due to a large degree of crosslinking reaction in the silica matrix. Combining GISAXS, 29Si-NMR, and FT-IR results, we propose that the lower elastic modulus was caused by the incorporation of a large amount of methyl groups from the MTMS precursor and the elliptic pores.

Effect of Orientation Stretching on the Geometric Shape of Track-Etched Polyethylene Terephthalate Membranes

This article looks at the effect of orientation stretching of irradiated polyethylene terephthalate films on the shape of the pores formed during chemical pore etching. Shows that orientation stretching enables latent tracks in the polymer to be stretched, which gives rise to track membranes with elliptical pores. Examines the effect of deformation of irradiated polymer on the structure and physical/mechanical characteristics of the track membranes formed. It is assumed that the change in the polymer structure resulting from heavy-ion irradiation may be linked to local heating at the locations where the charged particles pass.

Polarized Raman Characterization of (2,2) Carbon Nanotubes Formed inside the Channels of AEL Crystals

A pure AlPO4-11 (AEL) zeolite crystal is optically transparent in visible region and a good insulator with thermal stability up to 1173 K. These excellent physical properties, plus their unique elliptical pore structures, make them an excellent template to fabricate ultra-thin single-walled carbon nanotubes (SWNTs).We studied the polarization dependence Raman spectra for (2,2) SWNTs formed inside the channels of AEL crystals. These (2,2) SWNTs acts as a dipolar antenna, polarized along the crystal channels axis. The polarization angle dependence of the Raman intensity indicates that the enclosed (2,2) SWNTs are highly oriented in the channels with their dipole transition moment mostly along the channels.

Boundary element method for 2D solids with fluid-filled pores

In this paper, a boundary element method is developed for solving the problems of 2D solids with fluid-filled pores. The solid is assumed as linear elastic, which contains many fluid-filled pores of various shapes, and the fluid filling the pores is assumed to be linear compressible. Two different approaches, named superposition method and multi-subdomain method have been presented. The first one is based on the principle of superposition, in which all the pressures in the fluid-filled pores will be determined first, and then all the other boundary unknowns can be computed. In the other approach, the subdomains of the fluid in pores are solved to obtain the relation of the interface displacements with the interface pressure first, and then all the boundary unknowns, including the fluid pressure in each pore, can be solved simultaneously. Two simple examples of the 2D solids containing one circular fluid-filled pore are applied to verify the accuracy and to show the efficiency of the presented methods. And then, the effective elastic modulus and effective Poisson’s ratio are simulated based on several models of the 2D solids containing 100 randomly distributed circular or elliptical fluid-filled pores. The numerical results computed by the two schemes have nearly the same accuracy, whereas the multi-subdomain method has higher computational efficiency than the superposition method. Some differences between the results obtained by the BEM and those given by Kachanov’s method in the literature have been observed, which will be further investigated in the future work.

The influence of the orientation of polyethyleneterephtalate films irradiated by heavy ions on polymer structure and track-etched membrane pores

It is shown that the orientation of polymer macromolecules after irradiation by heavy ions allows one to produce a polyethyleneterephtalate film with increased mechanical strength and chemical resistance. Chemical etching of such a film results in the formation of elliptical shape pores oriented in the direction of film elongation.