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This study investigates the effects of modifying commercial Nafion-212 thin films with dodecyltriethylammonium cation (DTA+) on their electrical resistance, elastic modulus, light transmission/reflection and photoluminescence properties. The films were modified through a proton/cation exchange process for immersion periods ranging from 1 to 40 h. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the crystal structure and surface composition of the modified films. The electrical resistance and the different resistive contributions were determined via impedance spectroscopy. Changes in the elastic modulus were evaluated using stress–strain curves. Additionally, optical characterization tests, including light/reflection (250–2000 nm) and photoluminescence spectra, were also performed on both unmodified and DTA+-modified Nafion films. The results reveal significant changes in the electrical, mechanical and optical properties of the films, depending on the exchange process time. In particular, the inclusion of the DTA+ into the Nafion structure improved the elastic behavior of the films by significantly decreasing the Young modulus. Furthermore, the photoluminescence of the Nafion films was also enhanced. These findings can be used to optimize the exchange process time to achieve specific desired properties.

Electrochemical characterization of alumina-based membranes obtained by two different techniques, sinterization or anodization, is performed by analyzing membrane potential values. This analysis allows us the estimation of the effective concentration of fixed charge in the membrane (Xef) and the transport number of the ions into the pores (ti), as well as the determination of ionic permselectivity (P(i)) and their correlation with the different structures (supported, symmetrical or asymmetric), geometrical parameters (pore size and porosity) and surface materials (alumina-zirconia or alumina) of the studied membranes. From these results, the electropositive character of the membranes was stated, but also the significant reduction (70%) in Xef value and around 30% in permselectivity when pore size increases from 25 nm to 100 nm, in the case of sinterized alumina-zirconia membranes with similar porosity (CRF samples), while the clear influence of pore size on the electrochemical behavior of the electrochemically synthesized alumina membranes (NPAM samples) was confirmed as well as the lower influence of membrane porosity. Moreover, the effect of protein (BSA) static fouling on electrochemical parameters for both CRF and NPAMs samples was also analyzed, and our results show a reduction in the electropositive character of both membranes, being this behavior opposite to that discussed for one of the NPAMs as a result of surface modification with a theophylline derivative (Theo 1).

CdSe quantum dots nanoparticles were coated with the thiolated (DiAminoButane based dendrimer) DAB dendrimer of fifth generation (S-DAB

Changes associated to atomic layer deposition (ALD) of SiO2 from 3-aminopropyl triethoxysilane (APTES) and O3, on a nanoporous alumina structure, obtained by two-step electrochemical anodization in oxalic acid electrolyte (Ox sample) are analysed. A reduction of 16% in pore size for the Ox sample, used as support, was determined by SEM analysis after its coverage by a SiO2 layer (Ox+SiO2 sample), independently of APTES or O3 modification (Ox+SiO2/APTES and Ox+SiO2/APTES/O3 samples). Chemical surface modification was determined by X-ray photoelectron spectroscopy (XPS) technique during the different stages of the ALD process, and differences induced at the surface level on the Ox nanoporous alumina substrate seem to affect interfacial effects of both samples when they are in contact with an electrolyte solution according to electrochemical impedance spectroscopy (EIS) measurements, or their refraction index as determined by spectroscopic ellipsometry (SE) technique. However, no substantial differences in properties related to the nanoporous structure of anodic alumina (photoluminescent (PL) character or geometrical parameters) were observed between Ox+SiO2/APTES and Ox+SiO2/APTES/O3 samples.

The influence of geometrical parameters (pore radii and porosity) on ion transport through two almost ideal nanoporous alumina membranes (NPAMs) coated with a thin TiO2 layer by the atomic layer deposition technique (Sf-NPAM/TiO2 and Ox-NPAM/TiO2 samples) was analyzed by membrane potential and electrochemical impedance spectroscopy measurements. The results showed the significant effect of pore radii (10 nm for Sf-NPAM/TiO2 and 13 nm for Ox-NPAM/TiO2) when compared with porosity (9% and 6%, respectively). Both electrochemical techniques were also used for estimation of protein (bovine serum albumin or BSA) static fouling, and the results seem to indicate deposition of a BSA layer on the Sf-NPAM/TiO2 fouled membrane surface but pore-wall deposition in the case of the fouled Ox-NPAM/TiO2 sample. Moreover, a typical and simple optical technique such as light transmission/reflection (wavelength ranging between 0 and 2000 nm) was also used for membrane analysis, showing only slight transmittance differences in the visible region when both clean membranes were compared. However, a rather significant transmittance reduction (~18%) was observed for the fouled Sf-NPAM/TiO2 sample compared to the fouled Ox-NPAM/TiO2 sample, and was associated with BSA deposition on the membrane surface, thus supporting the electrochemical analysis results.

Optical and electrical modifications of a highly hydrophilic cellulose regenerated (RC) thin film as result of the inclusion in the film structure of cadmium-tellurium covered with mercaptosuccinic acid quantum dot nanoparticles (CdTe-MSA QDs) are analysed. CdTe-MSA QDs nanoparticles inclusion was performed by dip-coating of the RC film in an aqueous nano QDs solution, and two different immersion periods (2 h and 24 h) were considered. Impedance spectroscopy measurements, which can give information of changes in both film surface and bulk phase were performed for CdTe-MSA QDs inclusion confirmation as well as the estimation of electrical changes associated to QDs modification. Optical characterization of the original support and the CdTe-MSA(2 h) and CdTe-MSA(24 h) modified films was carried out by light transmittance and ellipsometry spectroscopy (at three different take-off angles). According to these results, the inclusion of CdTe-MSA QDs practically does not reduce the high transparency of the film support, but it increases the reflexion index and extinction coefficient of both modified films. Moreover, fluorescence and XPS measurements were also performed for more complete information on the effect caused by the presence of CdTe-MSA QDs in the cellulosic film. A comparison of changes in physicochemical properties of the cellulosic/CdTe-MSA QDs films and those modified with other nanoparticle quantum dots is also performed.

The preparation of silver nanoparticles (AgNPs) and their incorporation into the structure of a regenerated cellulose membrane by dip coating is presented. Morphological characterization of the AgNPs (average diameter of 20 ± 2 nm) was carried out by SEM/TEM, while elastic, electrical and antimicrobial properties of the hybrid membrane were also analyzed. The presence of silver nanoparticles in the membrane seems to increases its rigidity and its chemical stability against oxidation, but it only induces small changes in the transport parameters. As expected, AgNPs provide antimicrobial properties to the membrane and consequently the reduction of biofouling without affecting significantly other characteristic parameters, opening the application of the modified membrane to wastewaters treatment.

Changes associated to surface functionalization of nanoporous alumina membranes by atomic layer deposition (ALD) of metal oxides (Al2O3, SiO2, TiO2, Fe2O3, ZnO) are presented. ALD modification of the alumina membranes reveals a reduction up to 25–35% in porosity, and confirms the presence of the metal oxide layer coating the pores. Its effect on the membrane permselectivity and other characteristic transport parameters was determined from membrane potential measurements, being correlated with changes in morphology and physic–chemical characteristics of the alumina membranes. According to our results, ALD provides a straight-forward and efficient method to adjust membrane performance for specific applications.

Microcrystalline cellulose (MCC) and polyamide 66 (PA66) have been separately dissolved in solutions containing trifluoroacetic acid (TFA) as a common solvent, mixed after their dissolution and cast. After solvent evaporation, self-organized membranes have been formed with three dimensional (3D) porous, interconnected morphology, the porosity of which depends on the relative ratio of cellulose and PA66, and is lost when the initial MCC content exceeds 50% by weight. Thermal and chemical analysis and X-ray diffraction results indicate that the addition of cellulose induces the amorphisation of PA66, while possible chemical interaction exists between the amorphous parts of PA66 and the cellulose. The various membranes produced with different 3D porosities have been characterized in terms of dielectric constant and salt permeability and their relation to cellulose-PA66 ratio has been determined.

Polymer inclusion membranes (PIMs) have been prepared using cellulose triacetate (CTA) as polymer and derivatives of the commercial ionic liquid (IL) Aliquat 336, trioctyl methylammonium chloride (AlqCl), as extractants. The different ILs were prepared by exchanging chloride anion from AlqCl for other more lipophilic anions, obtaining IL derivatives AlqNO 3 and AlqSCN. PIMs containing these extractants at two different concentrations (30% and 60%) were prepared and characterized using X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), contact angle and impedance spectroscopy to obtain information on the material properties of both the surface and bulk membranes. The IL counter-anion affects the membrane's electrical parameters (dielectric constant and conductivity) as well as its hydrophobic character, which also depends on the IL concentration in the PIM formulation. Passive transport across the different PIMs using HCl and NaCl aqueous solutions was also considered, and the results obtained seem to be directly related to the hydrophilic/hydrophobic character of the studied membranes The financial support of the Spanish government through research project CTM2013-48967-C2-2-P is acknowledged. R. Vera acknowledges a grant from the Spanish Ministerio de Economía y Competitividad (ref. BES-2014-068314)

A new silicon carbide ceramic membrane consisting of a unique top layer on a SiC support for application in oily wastewaters filtration was produced and characterized in terms of morphology and chemical surface composition by scanning electron microscopy and X-ray photoelectron spectroscopy measurements. The manufacturing process of this new membrane allows time and economic savings when compared with a two layers membrane previously obtained. The new membrane has a smooth top layer with controlled porosity and a higher permeability compared to already developed commercial membranes. Moreover, it is extremely efficient to remove total suspended solids as well as oil and grease and, consequently, it can be applied to effective treatment of industrial oily wastewaters.

Nanoporous alumina-based structures (NPA-bSs) obtained by anodization of aluminum in sulfuric acid medium were coated by atomic layer deposition (ALD) of a thin conformal layer of different functional oxides (Al2O3, TiO2, Fe2O3 or ZnO), leading to samples with similar geometrical parameters but different surface materials. Morphological characterization of the NPA-bSs confirms a reduction of about 35% in pore size associated to the presence of the oxides of interest, while chemical surface analysis permits the estimation of cover layer purity and thickness. Additionally, ALD functionalization also modifies optical (band-gap, refractive index and dielectric constant) according to transmittance and spectroscopic ellipsometry results for visible and near-infrared regions, as well as electrolyte diffusive transport parameters (effective fixed charge, ion transport numbers or ionic permselectivity) of the NPA-bSs, both of which are dependent on the nature of the coating layer. Therefore, the suitability of ALD technique for geometrical and functional modification of nanoporous structures is demonstrated, thus broadening the potential application of these NPA-bSs platforms to optical sensing, nanophotonics, biosensing, microfluidics or drug delivery applications.

Surface modification of alumina nanomembrane (ANP) by theophylline derivative Theo 1 by dip-coating was successfully achieved. The hybrid material was characterized by SEM, XPS and confocal microscopy. The presence of Theo 1 on the ANP surface was established from salt diffusion and membrane potentials measurements. Changes in the electrical character and transport parameters of the modified sample, associated to Theo 1 deposition, were established. Stability of the material under diffusive flow was also ascertained. Moreover, as a result of Theo 1 bioactivation, streptavidin linkage to the ANP/Theo 1 -modified membrane was obtained, which is an indication of streptavidin capture.

Three nanoporous alumina structures (NPASs) obtained by the two-step anodization method were optically and electrochemically characterized. Two of the structures were symmetric (NPAS-Sf and NPAS-Ph) and one was asymmetric (NPAS-And), pore size ranged from 10 nm to 100 nm and porosity was 12% in the case of the symmetrical NPAS and 23% and 30% for each surface of the asymmetric structure NPAS-And(A) and (B), respectively. Optical parameters of the studied samples (refraction index and extinction coefficient) were obtained from ellypsometric spectroscopy measurements carried out for wavelengths ranging between 250 nm and 1700 nm (visible and near infrared regions), with the total average refraction indices being 1.54, 1.52, 1.14, and 1.05 for NPAS-Sf, NPAS-Ph, NPAS-And(A), and NPAS-And(B), respectively, which indicates porosity control of refraction index values. Electrochemical characterizations (concentration potential and impedance spectroscopy measurements) were performed with NaCl solutions, and they allowed us to estimate samples of effective fixed charge concentration (1.22 &times, 10&minus, 2 M, 1.13 &times, 3 M, and 1.15 &times, 3 M), ion transport numbers, permselectivity (33.0%, 3.1%, and 9.6%), and the electrical resistance of each solution/sample system as well as the interfacial effects associated to solution concentration&ndash, polarization, which seems to be mainly controlled by pore size and sample symmetry.

Modification of a regenerated cellulose thin film by inclusion of different non-toxic nanodots (silicon-dots (SiDs), carbon-dots (CDs)) or nitrogen-doped carbon dots (N-CDs)) by aqueous nanodots solution immersion was performed. Nanodots presence into the cellulosic structure was evidenced by confocal microscopy images at different depth and changes in film mechanical, electrical and optical parameters. Our results reveal that the inclusion of the different nanodots in the cellulosic support increases, indifferent percentages, the mechanical resistance and electrical conductivity of modified films, but they hardly affect light transmittance. Particularly, modification with N-CDs largely favored film conductivity due to the presence of the higher number of charged functional groups (CNH2 and OCNH2) groups) on N-CDs surface, allowin gus the attainment of a flexible, fluorescent and transparent high conductive eco-friendly film. In fact, the non-toxic character of both support-film and nanodots, endorses the use of these new nano-engineering films in biomedical applications.

Geometrical, chemical, optical and ionic transport changes associated with ALD of TiO2-coating on the porous structure of two nanoporous alumina membranes (NPAMs), which were obtained by the two-step aluminum anodization method but with different pore size and porosity, are presented. Chemical and morphological changes were determined by analyzing XPS spectra and SEM images, showing practically total coverage of the NPAMs surface and leading to a reduction in the geometrical parameters of both samples, while SAED and high resolution TEM measurements allowed us to determine the crystalline structure and thickness of the TiO2-coating, with the latter confirmed by depth-profile XPS analysis. Spectroscopic ellipsometry measurements were also carried out in order to detect changes in characteristic optical parameters (refractive index, n, and extinction coefficient, k), due to the TiO2-coating of NPAMs. Considering the common application of NPAMs in solute/ion diffusion processes, the effect of the TiO2-coverage on electrochemical parameters was analyzed by measuring the concentration potential with a typical model electrolyte (KCl solutions), leading to an increase of the electropositive character for both kinds of samples.

Electrical parameters for a commercial positively charged membrane and after submerged for 1 month in 0.1 M acidic solution (HCl) or 0.1 M basic solution (NaOH) were determined by measuring membrane potential and electrical resistance using NaCl solutions. Changes in the values of the cation transport number in the membranes and in the conductivity as a result of chemical treatments were determined, while membrane surface modification was obtained from contact angle measurements. Moreover, the effect of pilot plant wastewaters on both membrane transport number and conductivity have also been determined and compared with those obtained for the model solutions. According to these results, membrane immersion in the HCl solution hardly affects to transport parameters and membrane surface, while the NaOH treatment significantly modified all the studied parameters and its effect is even more important than that caused by plant wastewaters.

Diaminobutane based poly(propyleneimine) dendrimer functionalized with sixteen thiol groups, DAB-3-(SH)16, was successfully embeded in a swollen cellulosic support in order to achieve an easily handle engineered membrane. The membrane was characterised by physicochemical, electrical and transport measurements, and the effect of the dendrimer was established by comparing these results with those obtained for the original cellulosic support. Results show that dendrimer inclusion improves the membrane elastic behaviour (Young modulus increase around 20%), while a significant reduction in the permeation of toxics heavy metals (Cd2+, Hg2+ and Pb2+) was also obtained, which avails the possible application of dendrimer-modified membrane in electrochemical devices for water remediation, The authors would like to thanks to Andalucía Tech Program (Universidad de Málaga, Spain) and the CICYT (MINECO, Spain, research project CTQ/2011-27770 FEDER funds) for partial financial support. Spanish Ministerio de Ciencia e Innovación (Project CTQ2009-12332-C02-01) is also acknowledged

The effect of the base-polymer and carrier concentration on the physical–chemical characteristics of polymer inclusion membranes (PIMs) is investigated. Two typical polymers used to manufacture PIMs have been tested, i.e. poly(vinyl chloride) (PVC) and cellulose triacetate (CTA), and different amounts of the ionic liquid (IL) Aliquat 336, used as extractant, were the PIMs constituents. The resulting PIMs have been characterized using different techniques to provide information on both the surface and bulk material properties. XPS results do not practically show differences in the surfaces of CTA and PVC based membranes with similar Aliquat 336 content, and the total surface coverage for Aliquat 336 concentration higher than 40% (w/w) was obtained, which was also corroborated with the results of contact angle measurements. However, membrane elastic response seems to be strongly dependent on both base-polymer and Aliquat 336 concentration, which affect Young modulus and elongation at break. The IL concentration also increases dielectric constant and the conductivity of the PIMs from both polymers according to impedance spectroscopy results, providing a rather conductive character to both kind of samples for Aliquat 336 content higher than 40% (w/w) (average conductivity around 10 −3 (Ω m) −1 ). CTA and PVC-based PIMs with Aliquat 336 content around 45% have been used in order to compare the influence of the polymer on the transport of As(V).

Changes in a protonated Nafion-112 membrane as a result of the incorporation of the cation n-dodecyltrimethylammonium (DTA+) by proton exchange mechanism are studied. Membrane surface modifications were analysed by AFM, XPS and contact angle measurements in order to obtain information about changes in the membrane surface roughness, chemical nature and hydrophobic character, while electrochemical impedance spectroscopy (EIS) and methanol permeation measurements were carried out to establish changes in the bulk membrane. The reduction obtained for the surface roughness and the hydrophobic character of Nafion-112/DTA+ equilibrated membrane as well as for the fluorine atomic concentration percentage and the increase in nitrogen percentage indicates modification of Nafion-112 membrane surface, while the increase of electrical resistance and the decrease of methanol permeability give information on bulk membrane changes. The higher thermal stability and lower water loss of the Nafion-112/DTA+ membrane are points of interest for applications such as PEMFC or DMFCs, respectively.

Poly(vinylidene fluoride) (PVDF) and regenerated cellulose (RC) membranes were surface-modified by the adsorption of one adenosine receptor antagonist: the theophylline-oligo(ethylene glycol)-alkene derivative, Theo1. Surface modification was carried out by immersion of the membrane in a dichloromethane solution of Theo1 (PVDF+Theo1 and RC+Theo1 samples). Membrane surfaces with partial coverage by theophylline and/or its inclusion in the membrane structures were studied by X-ray photoelectron spectroscopy (XPS), solid-state nuclear magnetic resonance (SNMR), impedance spectroscopy (IS) and contact angle (CA) measurements. The Theo1 orientation was inferred from the data. Streptavidin (SA) was immobilized onto the membrane/Theo1 hybrid material. The protein-theophylline Theo1 interaction was visualized with bright field microscopy (BFM).

Diffusive transport of neutral and charged solutes across a nanoporous alumina membrane (NPAM) with a pore size of 24 nm and interpore distance of 65 nm obtained by the two-step anodization method in sulphuric acid solution (Sf/NPAM sample) is studied. Diffusion experiments were performed with tritiated water (neutral solute) to demonstrate frictional effects, while charged solute measurements (NaCl solutions at different concentration gradients and 22Na radiotracer) allow us to estimate also the contribution of electrical interactions in the movement of ionic species in the charged membrane nanopores as well as electrolyte/membrane interface effects. Values for water, NaCl, and Na+ diffusion coefficients in the membrane were determined from these measurements as well as the electropositive character of the Sf/NPAM sample and its fixed charge concentration by analyzing the diffusion–concentration curve. According to these results, ion-pore wall frictional and electrical effects are both involved in the re...

Nanoporous anodic alumina membranes (NPAMs) were produced by the two-step anodization method in sulphuric, oxalic and phosphoric acidic electrolytes displaying a hexagonally ordered spatial arrangement of pores with well controlled nanopore size distribution and low porosity. Some selected NPAMs were further modified by conformal coating their surface and inner pore walls with a thin layer of SiO2 by means of atomic layer deposition (ALD), which reduces both the pore radii and porosity but it also seems to affect to the electric fixed charge on the membranes surface. A comparative study about the influence of silica modification of NPAMs surfaces on the ionic transport through the nanoporous membranes has been performed by measuring membrane potentials and electrochemical impedance spectroscopy with NaCl solutions. According to these results, a direct correlation between the membrane effective fixed charge and the NaCl diffusion coefficient can be established. The coating with a SiO2 thin layer causes a r...

The behavior of a fluorescent nanocomposite, obtained by means of a thiol polypropylenimine dendrimer of third generation coated with CdSe quantum dots, and embedded in a hydrophilic cellulosic membrane as support is electrochemically studied in order to evaluate its applicability as a sensor in liquid media. The characterization of the nanocomposite by TEM and EDAX shows uniform nano morphology (size comprised in the range 60–90 nm) and composition, respectively. The analysis of the engineered hybrid cellulose-dendrimer quantum dots material by confocal fluorescence microscopy indicates almost mono-dispersion distribution of the nanocomposite when irradiated under UV light, while its presence on the film surface was determined by X-ray photoelectron spectroscopy. Impedance spectroscopy measurements performed with dry membrane samples show a decrease in the conductivity and dielectric constant of the modified membrane in comparison with the raw support. Electrical changes in the modified film associated to the presence of Cd(II) uptakes from a Cl 2 Cd solution were also obtained. These results support the possible application of this nanocomposite material as heavy metal sensor in liquid media.

Surface and bulk chemical changes in a Nafion membrane as a result of room temperature ionic liquids (RTILs) incorporation were determined by X-ray photoelectron spectroscopy (XPS) and elemental analysis, respectively. RTILs with different physicochemical properties were selected. Two imidazolium based RTIL-cations (1-octyl-3-methylimidazolium and 1-butyl-3-methylimidazolium) were used to detect the effect of cation size on membrane modification, while the effect of the RTIL hydrophilic/hydrophobic character was also considered by choosing different anions. Angle resolved XPS measurements (ARXPS) were carried out varying the angle of analysis between 15° and 75° to get elemental information on the Nafion/RTIL-modified membranes interactions for a deepness of around 10 nm. Moreover, changes in the RTIL-modified membranes associated to thermal effect were also considered by analyzing the samples after their heating at 120 °C for 24 h. Agreement between both chemical techniques, bulk and destructive elemental analysis and surface and non-destructive XPS, were obtained.

Highly ordered Nanoporous Alumina Membranes (NPAMs) with a precise control of the pore size and different porosity but thickness around 63 μm were fabricated by the two-step anodization process using different acidic aqueous solutions, oxalic (Al-Ox), sulfuric (Al-Sf), and phosphoric (Al-Ph) acids, respectively. The pore size was controlled by properly changing the anodization voltage and the electrochemical bath conditions, obtaining the following average pores diameter values, d(p), as determined by scanning electron micrographic analysis: Al-Ox (d(p)=46±2 nm), Al-Sf (d(p)=27±2 nm), and Al-Ph (d(p)=240±20 nm). A pore increasing of around 5% for samples Al-Ox and Al-Sf was obtained after membranes immersion in 5 wt.% phosphoric acid for a certain etching time. Electrochemical characterization of NPAMs was performed with the samples in contact with NaCl solutions at different electrolyte concentrations. Ionic transport numbers and effective membrane fixed charge were determined from membrane potential measurements, which clearly show the significant influence of the pore diameter on ions transport. Moreover, frictional and electrical effects on mass transfer parameters (salt and ions diffusion coefficients) into the pores of alumina membranes were also evaluated from these results.

Films from copolyimides containing side carboxylic acid groups were prepared in –COOH and COO − Na + forms to study the effect of the side groups content on some physical properties such as water absorption, thermal stability and electrical parameters. The thermal stability was evaluated by TGA and the results showed that degradation temperatures depended not only on the side groups content but also on the membrane ionic form. This dependence was also observed in the water sorption isotherms; the polyimides with the highest –COOH content showing the highest water sorption in the equilibrium. Dielectric impedance measurements revealed how the side groups and their ionic form affect the material electrical characteristics, in such a way that resistivity decreased and permittivity increased on introducing more –COOH groups in the polymer, which is also related to a higher water uptake of the films.

Hydrogels are highly water-absorbent hydrophilic polymer networks, which show potential in many biocompatible applications. In previous work, we demonstrated the feasibility of using poly(ethylene glycol) dimethacrylate (PEG-DMA) gels polymerized with a photoinitiator for encapsulation and stabilization of painted biomimetic membrane arrays for novel separation technologies or biosensor applications. These gels were formed from PEG-DMA monomers suspended in phosphate buffered saline (PBS) solution and gelated by radical polymerization in the presence of the photoinitiator Darocur 1173. In this work, we show that the properties of a PEG-DMA hydrogel formed by photoinitiated polymerizetion can be tailored by varying the photocrosslinking time. Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy (RS) showed that the optimal crosslinking time for the gel was 6 - 10 minutes and that the water content of the gels could be tuned in the range of 50 - 90 wt%. The resistivity was between 0.8 - 3.5 Ωm, which is comparable to that of PBS. The low resistivity of the gel makes it compatible for encapsulating membranes for (ion channel based) biosensor applications. With FTIR and RS we identified spectral features of the hydrogel, which may serve as a diagnostic tool to monitor changes in the gels due to variation in parameters such as time, pH, temperature, aging or exposure to chemicals or biological material.

The effect of annealing temperature (25 °C < T < 97 °C) on transport and structural parameters for two different regenerated cellulose membranes (dense and nanoporous) is studied. Results show different temperature dependence for water permeability and NaCl diffusion coefficient depending on the membrane structure, with an increase from 25 °C to 60 °C and a more significant reduction between 70°°C and 97 °C for the dense sample, but practically constant for the nanoporous. These results seem to be directly related to the membrane’s elastic behaviour according to the temperature effect on degree of swelling. Moreover, diffusional permeability-concentration curves also allow the determination of other membrane parameters (fixed charge concentration and partition coefficient) which are independent of temperature.

Hydrogels are increasingly being recognized as having potential in bio-compatible applications. In previous work, we investigated the feasibility of poly(ethylene glycol)-dimethacrylate (PEG-1000-DMA) and poly(ethylene glycol)-diacrylate (PEG-400-DA) polymerized using either a chemical initiator (C) or a photoinitiator (P) to encapsulate and stabilize biomimetic membranes for novel separation technologies or biosensor applications. In this paper, we have investigated the electrochemical properties of the hydrogels used for membrane encapsulation. Specifically, we studied the crosslinked hydrogels by using electrochemical impedance spectroscopy (EIS), and we demonstrated that chemically crosslinked hydrogels had lower values for the effective electrical resistance and higher values for the electrical capacitance compared with hydrogels with photoinitiated crosslinking. Transport numbers were obtained using electromotive force measurements and demonstrated that at low salt concentrations, both PEG-400-DA-C and PEG-400-DA-P hydrogels presented an electropositive character whereas PEG-1000-DMA-P was approximately neutral and PEG-1000-DMA-C showed electronegative character. Sodium transport numbers approached the bulk NaCl electrolyte value at high salt concentrations for all hydrogels, indicating screening of fixed charges in the hydrogels. The average salt diffusional permeability 〈Ps〉 and water permeability 〈Pw〉 were found to correlate with EIS results. Both PEG-1000-DMA-C and PEG-400-DA-C had higher 〈Ps〉 and 〈Pw〉 values than PEG-1000-DMA-P and PEG-400-DA-P hydrogels. In conclusion, our results show that hydrogel electrochemical properties can be controlled by the choice of polymer and type of crosslinking used and that their water and salt permeability properties are congruent with the use of hydrogels for biomimetic membrane encapsulation. Copyright © 2011 John Wiley & Sons, Ltd.

Physicochemical and NaCl characteristic transport parameters determined for a lipid coated regenerated cellulose membrane are reported. The lipid studied consists of glyceryl triestearate, while l -α-phosphatidylcholine and sodium taurocholate were used as surfactants. The RC-support and the lipid-modified membrane were characterized by X-ray photoelectron spectroscopy (XPS) at three different take off angles and X-ray diffraction. Transport parameters (salt diffusion and electrical resistance) were determined from salt permeation and impedance spectroscopy measurements performed with the membranes in contact with a NaCl constant concentration ( C c = 0.01 M). These results show a reduction in the transport parameters across the lipid coated membrane due to the lipid presence as well as its stability under mass and ion fluxes, which supports its application in liquid systems.

Modifications caused in commercial dense regenerated cellulose (RC) flat membranes by low-dose γ-irradiation (average photons energy of 1.23 MeV) are studied. Slight structural, chemical and morphological surface changes due to irradiation in three films with different RC content were determined by ATR-FTIR, XRD, XPS and AFM. Also, the alteration of their mechanical elasticity has been studied. Modification of membrane performance was determined from solute diffusion coefficient and effective membrane fixed charge concentration obtained from NaCl diffusion measurements. Induced structural changes defining new and effective fracture propagation directions are considered to be responsible for the increase of fragility of irradiated RC membranes. The same structural changes are proposed to explain the reduction of the membrane ion permeability through a mechanism involving either ion pathways elongation and/or blocking.

Electrochemical characteristic parameters such as diffusional permeability, ion transport number, fixed charge concentration and electrical resistance for a regenerated cellulose/polypropylene- supported membrane (RC/PP sample) in contact with NaCl solutions at different concentrations were determined. The effect of the polypropylene support on mass and charge transport was estimated by comparing results obtained for both opposite fluxes and differences seem to be related to the stagnant solution layer embedded in the polypropylene support, which could mask membrane properties. Moreover, effective membrane thickness (RC-layer thickness) must be estimated to determine intensive membrane parameters (salt and ions diffusion coefficients or conductivity). Good agreement for ion diffusion coefficient values was obtained by comparing results obtained from different types of measurements (combination of membrane potential-salt diffusion and impedance spectroscopy, respectively).

Two highly hydrophilic regenerated cellulose planar sheets (RC-6 and RC-MD) with different morphological, structural and transport parameters were used as supports of lipid (lecithin-triestearine) nanoparticles (RC-6/LNPs and RC-MD/LNPs samples), which were embedded by immersion in a water dispersion of LNPs. Salt and ions transport (salt diffusion, ion transport numbers and effective fixed charge) were determined from measurements carried out with the samples in contact with NaCl solutions at different concentration and, consequently, osmotic pressures. Results do not show differences in the small fixed charge of the membranes as a result of nanoparticles inclusion (−0.012 M and −0.008 M for RC-6 and RC-MD, respectively) and stability of the LPNs-modified membranes for osmotic pressure up to 5 bars was established. TEM images shows the presence of LNPs in the RC-supports and Raman spectroscopy analysis was used for physic-chemical characterization of the RC-supports and RC/LNPs-modified membranes but also to determine the stability of modified samples under flow conditions. Different transport behaviour depending on the RC-support was obtained, and results seem to indicate the maintenance of nanoparticles into the dense RC-support structure till a concentration gradient of 0.1 M.

Optical changes associated with the surface coating of different metal oxides and nanolayers by the ALD technique of a nanoporous alumina structure (NPAS) obtained by the two-step anodization method were analyzed. The NPASs were coated with: (i) a single layer (SiO2 or TiO2), and (ii) a double layer of SiO2 plus Al2O3 or aluminum doped ZnO (AZO) to estimate the effect of surface layer coverage material, geometrical parameters (pore-size/porosity), and number of layers on light transmission/reflection. Chemical surface characterization of the different NPASs was carried out by analyzing XPS spectra, which allowed us to obtain an estimation of the coating layer homogeneity. Transmittance and spectroscopic ellipsometry measurements were analyzed in order to detect changes in characteristic optical parameters such as band gap, refractive index, and extinction coefficients associated with the material and the characteristics of the single or double coating layers.