Anopore Membrane Research Articles

Effect of surface treatment on the dynamics of relaxation processes in confinement: ferroelectric liquid crystal in porous Anopore membrane

ABSTRACT Dielectric properties of a ferroelectric liquid crystal 2-methylbutyl 4-decyloxybenzylidene-4’-n-aminocinnamate (DOBAMBC) confined in untreated and treated porous Anopore membrane were investigated depending on the frequency and temperature. The confinement of a ferroelectric liquid crystal in an untreated Anopore membrane leads to the disappearance of the Goldstone mode. Moreover, despite the modification of the pore surface with various surfactants, no the Goldstone mode or other additional relaxation processes were observed. The relaxation rate of the molecular δ-process is slightly shifted for untreated and treated Anopore membrane in comparison to the bulk. Generally, the relaxation rate temperature dependence shows the Arrhenius-type course, while for lecithin-treated Anopore, it is similar to the Vogel–Fulcher–Tammann-type dependence. Dielectric spectra are dominated at low frequencies by conductivity and electrode polarization effects and are modified in geometric constraints.

The molecular dynamics of nematic liquid crystal confined in porous membranes treated by different surfactants

The molecular dynamics of the well-known nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl geometrically restricted in Anopore and Synpor porous membranes with various pore structure and treated by different surfactants (namely decanoic acid and lecithin) is compared. In the Anopore membrane the chosen surfactants induce the homeotropic orientation of the molecules on the walls of the cylindrical pores and observed corresponding relaxation processes (librational modes) are practically the same. The dielectric measurements of lecithin treated Synpor membranes reveals the reorientation of the molecules from planar to homeotropic on the complex multilayer structure present in their volume. The dielectric strengths of the observed two molecular processes (δ-process and librational mode) are inversed in the ratio compared to the untreated membranes. The observed differences in molecular dynamics results from the orientation of the liquid crystal molecules in untreated and treated membranes and the structure of the membranes themselves.

Extending the uppermost pore diameter measureable via Evapoporometry

Evapoporometry (EP) is a relatively new technique for measuring the pore-size distribution (PSD) of membranes, which is a key determinant of properties such as the permeability and rejection. EP is based on determining the pore diameter from the evaporation rate of a volatile wetting liquid that initially saturates the membrane pores using the Kelvin equation. Heretofore the pore diameter range measureable via EP was approximately from 4 to 150nm. The lower limit is because the classical Kelvin equation breaks down at small pore diameters, whereas the upper limit is because the vapor pressure depression and corresponding evaporation rate associated with large pores becomes too small to be accurately determined. The goal of this study was to extend the upper pore diameter limit for EP characterization. The classical Kelvin equation indicates that the vapor pressure depression can be increased by choosing volatile wetting liquids with a larger surface tension and molar volume, thereby allowing for larger pores to be measured accurately. In this study a range of volatile wetting liquids were explored that would permit extending the range of EP. An optimal choice was 1-butanol that was shown to permit accurately characterizing the PSD of an Anopore membrane having a nominal pore diameter of 200nm, which was not possible hitherto using EP.

Influence of food matrix on outgrowth heterogeneity of heat damaged Bacillus cereus spores

Spoilage of heat treated foods can be caused by the presence of surviving spore-formers. It is virtually impossible to prevent contamination at the primary production level as spores are ubiquitous present in the environment and can contaminate raw products. As a result spore inactivation treatments are widely used by food producing industries to reduce the microbial spore loads. However consumers prefer mildly processed products that have less impact on its quality and this trend steers industry towards milder preservation treatments. Such treatments may result in damaged instead of inactivated spores, and these spores may germinate, repair, and grow out, possibly leading to quality and safety issues. The ability to repair and grow out is influenced by the properties of the food matrix. In the current communication we studied the outgrowth from heat damaged Bacillus cereus ATCC 14579 spores on Anopore membrane, which allowed following outgrowth heterogeneity of individual spores on broccoli and rice-based media as well as standard and mildly acidified (pH5.5) meat-based BHI. Rice, broccoli and BHI pH5.5 media resulted in delayed outgrowth from untreated spores, and increased heterogeneity compared to BHI pH7.4, with the most pronounced effect in rice media. Exposure to wet heat for 1min at 95°C caused 2 log inactivation and approximately 95% of the spores in the surviving fraction were damaged resulting in substantial delay in outgrowth based on the time required to reach a maximum microcolony size of 256 cells. The delay was most pronounced for heat-treated spores on broccoli medium followed by spores on rice media (both untreated and treated). Interestingly, the increase in outgrowth heterogeneity of heat treated spores on BHI pH7.4 was more pronounced than on rice, broccoli and BHI pH5.5 conceivably reflecting that conditions in BHI pH7.4 better support spore damage repair. This study compares the effects of three main factors, namely heat treatment, pH of BHI and the effect of food matrix highlighting the impact of different (model) food recovery media on outgrowth efficiency and heterogeneity of non-heat-treated and heat-damaged B. cereus spores.

Assessment and comparison of Anopore and cross flow filtration methods for the determination of dissolved iron size fractionation into soluble and colloidal phases in seawater

The two most frequently used methods for determining the size fractionation of dissolved iron (dFe) in seawater, 0.02 µm pore size Anopore membrane filtration and cross flow filtration using a 10 kDa regenerated cellulose filter, were evaluated and compared. Anopore filtration was found to produce consistent soluble Fe (sFe) concentrations in the filtrate even after > 1 L unfiltered seawater was filtered, indicating that clogging is not an issue for typical open ocean filtration volumes. Cross flow filtration (CFF) only achieved a 70% to 75% mass balance regardless of flow rate and seawater preconditioning; however, Fe losses arose largely from the colloidal (not soluble) size fraction, and Fe loss was constrained to Fe clogging in/on the CFF membrane. Both Anopore membrane and cross flow filtration methods reproducibly size fractionated dFe in seawater samples. Additionally, sFe arising from these two filtration methods were compared for the first time using seawater samples from the North Pacific and Atlantic Oceans. sFe from CFF was always lower than sFe from Anopore filtration, with the ratio of sFe in CFF/Anopore filtration averaging 68 ± 23% (n = 23). This sFe difference is attributed to a combination of the smaller effective pore size of the regenerated cellulose CFF system and the spatial variability in the concentration and composition of dFe in the 10 kDa ‐ 0.02 µm size fraction. Finally, the advantages and disadvantages of each method were reviewed to offer future users a suite of factors with which to choose their ideal ultrafiltration method.

The Dynamics of Chiral 5*CB Molecules Confined in a Porous Matrix

The dielectric permittivity of chiral isopentyl-cyanobiphenyl 5*CB confined to an Anopore membrane with a diameter of 100 nm for the two orientations of molecules, radial, and axial with respect to the pore axis, was studied. We report the different polymorphism of the 5*CB from that of the bulk material. The phases sequence depends on the forced orientation of molecules. The cholesteric phase does not appear during cooling of the axially oriented sample. Moreover, we observe tumbling of the molecules in metastable solid phase.

Confinement driven effects in a room temperature ferroelectric liquid crystal: X-ray, linear and non-linear dielectric investigations

We present results of X-ray, linear and non-linear dielectric constant measurements on a room temperature ferroelectric liquid crystalline phase in its bulk form and upon confinement in an Anopore membrane. The used material exhibits smectic C* (SmC*) helical pitch of p ≅ 200 nm, which is comparable to the pore dimension of the membrane. X-ray measurements show several interesting results including unusually strong harmonic reflections, substantial broadening of the peak profile, correlation length smaller than the pore diameter, etc. The data suggest that the smectic A–SmC* transition could be very close to a tricritical point in the bulk and moving away from it upon confinement. The dielectric studies show that confinement accelerates the relaxation dynamics of both the soft and the Goldstone modes, although with a reduced strength. The non-linear component of the dielectric constant exhibits qualitatively different thermal behaviour in the bulk and Anopore samples.

Comparative study of the dielectric properties of an antiferroelectric liquid crystal in planar aligned cells and in microporous membrane

The dielectric properties of the antiferroelectric liquid crystal (AFLC) have been investigated under different confined geometries. The measurements of dielectric permittivities have been carried out in the frequency region from 10 Hz to 13 MHz in two planar aligned cells of thickness 2 μm and 10 μm, as well as in an Anopore membrane having pore diameter 0.2 μm and thickness 60 μm. In SmC ⁎ phase the Goldstone mode (GM) has been observed in both the 10 μm and 2 μm planar aligned cells. Dielectric strength of GM is significantly diminished whereas the relaxation frequency is increased in the 2 μm thick cell compared to that in the 10 μm thick cell. In SmC ⁎ A phase two antiferroelectric modes have been observed in two distinct frequency regions. In the lower frequency region below the Goldstone mode process another relaxation process is observed in both cells that arise due to the non-homogenous distribution of thermally generated ionic charges. The Goldstone mode present in planar aligned cells is not observed when the sample is confined in an anopore membrane. But two other modes are observed in the Anopore membrane. One is due to molecular reorientation around the short axis is usually observed in the quasi-homeotropic orientation of tilted smectics. The other mode is related to the internal curved surface of the anopore membrane. The results have been discussed.

Evidence for a tilted smectic phase in Anopore membranes by dielectric spectroscopy

Collective relaxation processes are completely undetectable in a ferroelectric liquid crystal confined in porous Anopore membranes, as a result of perfect orientation of the smectic layers perpendicular both to the long axis of the pores and the direction of the measuring electric field. In the ferroelectric liquid crystal – Anopore composite only one relaxation process, assigned to rotation of the molecule around the molecular short axis, appears throughout all smectic phases. The temperature dependence of the relaxation frequency and of the dielectric strength of this process also shows no irregularity at the point of polarization sign reversal. The temperature dependence of the relaxation frequency follows the Arrhenius law with an activation energy slightly higher in the ferroelectric SmC* phase. Analysis of the non‐linear changes of temperature dependence of the dielectric strength at the SmA–SmC* phase transition enables one to obtain the temperature dependence of the tilt angle of the molecules in the SmC* phase in the Anopore membrane. Dielectric measurements confirm the existence of the tilted smectic phase in Anopore cylindrical channels with no tilt anomaly at the point of polarization sign reversal.

A Single-Tube Nucleic Acid Extraction, Amplification, and Detection Method Using Aluminum Oxide

A disposable 0.2-ml polymerase chain reaction (PCR) tube modified with an aluminum oxide membrane (AOM) has been developed for the extraction, amplification, and detection of nucleic acids. To assess the dynamic range of AOM tubes for real-time PCR, quantified herpes simplex virus (HSV) DNA was used to compare AOM tubes to standard PCR tubes. AOM PCR tubes used for amplification and detection of quantified HSV-1 displayed a crossing threshold (C(T)) shift 0.1 cycles greater than PCR tube controls. Experiments with HSV-1-positive cerebrospinal fluid (CSF) examined the extraction, amplification, and detection properties of the AOM tubes compared to the Qiagen DNA blood mini kit. The AOM extraction, amplification, and detection of HSV-1 in CSF displayed differences of less than one C(T) when compared to Qiagen-extracted samples. Experiments testing the AOM method using clinical CSF samples displayed 100% concordance with reported results. AOM tubes have no adverse effects on amplification or fluorescence acquisition by real-time PCR and can be effectively used for the extraction, amplification, and detection of HSV from CSF. The AOM single tube method is a fast, reliable, and reproducible technique for the extraction, amplification, and detection of HSV in CSF.

Synthesis and Characterization of Uniform Alumina−Mesoporous Silica Hybrid Membranes

The synthesis and characterization of alumina-mesoporous silica (alumina-MS) hybrid membranes are reported. The hybrids are formed using a variation of the evaporative-induced self-assembly (EISA) process reported by Hayward et al. (Langmuir 2004, 20, 5998) based on dip coating of an Anopore 200 nm membrane with a Brij-56/TEOS/HCl/H2O solution. Numerous analytical methods are used to probe both the hybrid material and the silica phase after dissolution of the Anopore substrate. Most importantly, He/N2 permeation measurements show that the effective pore size of the membrane can be tuned from 20 to 5 nm based on the number of dip-coating cycles used. The observed He/N2 permselectivity of 2.7 +/- 0.11 is nearly identical to the theoretical value obtained (2.65) assuming Knudsen diffusion dominates. The selectivity of these membranes is higher than that of most commercial "5 nm" membranes (2.29), which is ascribed to the lack of pinhole defects in the materials reported here. The hybrid membranes as well as the silica obtained after dissolution of the Anopore substrate have been characterized using scanning and transmission electron microscopy and X-ray diffraction. Those results indicate that the silica deposited in the Anopore membrane possesses uniform pores approximately 5 nm in size, consistent with the permeation studies. The current work presents an alternative approach to materials that possess many of the properties of mesoporous silica thin films (i.e., pores of controlled size and topology) without the difficulty of growing mesoporous silica thin films on porous supports.

Comparative x-ray measurements of a de Vries smectic-Amaterial in bulk and confined geometries

X-ray investigations have been carried out on a material exhibiting the de Vries smectic-A (Sm-A) phase in bulk and confined geometries. In the confined geometry realized by confining the material in an Anopore membrane, while the minimal layer shrinkage feature characteristic of the de Vries materials is retained, the overall change of the layer spacing from the Sm-A to the Sm-C phase is much less compared to the bulk geometry and also the transition gets smeared out. A "crossover" behavior, which has been recently ascribed to different molecular packing arrangements within the Sm-A phase, is seen in both geometries. With the support from data on another non-de Vries type of material we suggest that the associated feature may not be due to a phase transition, but competition between the thermally driven stretching and molecular tilt.

Cyclic CVD Modification of Straight Pore Alumina Membranes

Alumina oxide was deposited in the straight nanosize pores of Anopore alumina membrane by the alternative introduction of trimethylaluminum (TMA) and water vapor to the membrane pores. The chemical vapor deposition (CVD) modification was conducted under two different schemes: (1) cyclic CVD with residual pressure and (2) cyclic CVD with purge. The membranes were characterized by single gas helium permeance and water vapor/oxygen multiple gas permeation. Helium gas permeation results show that the modification by the residual pressure scheme caused greater reduction in the pore size than porosity, suggesting the deposition of alumina in a fractal structure in the Anopore membrane pores. Such a structure is caused by combined homogeneous and heterogeneous reactions taking place respectively on the pore wall and randomly in the pores. The membranes modified with CVD under the purge scheme exhibited greater reduction in porosity than the pore size, indicating that the alumina in the latter case was deposited on the pore wall in an atomic layer fashion. The structure in the latter case is caused by homogeneous reactions taking place on the pore wall. Membranes modified under the purge scheme exhibited improved water vapor/oxygen separation properties.

Phenol Removal by Supported Liquid Membranes

Abstract This paper examines the application of the supported liquid membrane (SLM) to phenol removal. n-Decanol was proven to be a suitable membrane liquid. The phenol transfer kinetics through the SLMs is quantitatively estimated according to models based on the resistance-in-series concept. The models can be modified to describe the performance of decayed SLMs and thereby provide insight into the effect of membrane liquid loss and penetration of aqueous solutions on the phenol flux. An experimental method is described for the measurement of mass transfer coefficients in the bulk phases using the well-characterized Anopore membrane.

Electrochemical fabrication of cadmium chalcogenide microdiode arrays

Abstract : Arrays containing greater than 10(exp 9) 2000A-diameter CdSe or graded CdSe/CdTe cylinders have been electrochemically synthesized within the pores of Anopore(tm) membranes. The alumina template suppresses the 'cauliflower' morphology that is typically observed in electrodeposited CdSe and CdTe films, although X-ray diffraction reveals the materials to be of poor crystallinity. The Anopore membrane template can be removed by treatment with aqueous 1M NaOH, resulting in an array of free-standing CdSe or CdSe/CdTe wires. Current-voltage data show that the Ni/CdSe array is rectifying, with a rectification ratio of 1000 at + or - 2 V.... Nanoparticles, Nanosemiconductors.

Ceramesh — a company and a membrane

Claimed as a major advance in microfiltration technology, Ceramesh is an inorganic composite ceramic membrane that can be produced in a flat sheet suitable for use in process-scale crossflow filtration systems. The membrane combines a metal mesh and a ceramic to give strength, formability and both chemical and heat resistance The Ceramesh membrane technology has its origins in work carried out at Alcan Separations in Banbury and has been under development since 1988. Some of the original team had also worked on the development of the Anopore membrane, since commercialised by Anotec, and these close personal links have been maintained. Ceramesh Ltd was formed in 1990 by Alcan and a venture capital company with the aim of speeding the development of the membrane and ensuring its early introduction to the commercial filtration market. These objectives have now been achieved and by the middle of 1992 the Ceramesh membrane has been evaluated for a number of specific applications, been incorporated into a range of commercial filtration equipment, and formally launched into the chemical-process industries at the Eurochem exhibition held in Birmingham in June.

Microfiltration of biomass and biofluids: Effects of membrane morphology and operating conditions

Fundamental studies carried out at the Centre for Membrane and Separation Technology (Australia) considered the effect of membrane surface properties and ionic strength using biomass microfiltration on controlled suspensions of Escherichia Coli. Anopore, Nuclepore and Millipore (hydrophilic and hydrophobic) membranes of similar pore size (0.2 μm) were characterised and subjected to flux tests with E.Coli suspension at different ionic strengths and transmembrane pressures. Membrane recovery after shear was also monitored and analysis using Scanning Electron Microscopy was performed on the cake formation. It was found that both ionic strength and membrane surface properties affected flux significantly and influenced recovery. The more porous and smooth hydrophilic Anopore membrane returned higher fluxes than the less porous Nuclepore and the rough Millipore membranes. High ionic strength solutions resulted in lower fluxes which can be explained using the colloid double-layer theory. Membrane recovery was easier for low pressure operation and low ionic strength suspensions.

An improved method for collecting and staining microorganisms for enumeration by fluorescence light microscopy

A rapid, robust method for the enumeration of total and viable microorganisms is described. A method using specific stains for viable and total cells and fluorescence light microscopy on membrane filters had been previously developed, but was suboptimal in that some non-specific staining of the filters occurred and the filters were not flat enough for automatic image analysis methods to be employed, because not all cells in a field of view were in focus simultaneously. A new membrane filter has recently become available: the Anopore membrane was described by the manufacturers as having a number of properties which would overcome these limitations. These include inorganic construction (giving resistance to solvents), high porosity (giving high flow rates), low surface adsorption (giving low background staining) and inherent hydrophilicity (simplifying wetting with aqueous solutions). Anopore membrane filters were found to produce very high contrast images of bacteria stained with ethidium bromide. Even with a relatively low power (magnification = 40) dry objective, these images could be easily thresholded for image analysis using only grey-level information. The methods developed here are considered to be a suitable basis for a fully automated procedure for the enumeration of total microbial populations.