Structure Of Porous Films Research Articles

Structure and properties of porous films based on aliphatic copolyamide developed for cellular technologies.

The effect of concentration and viscosity of the copolyamide (copolymer of ε-caprolactam and hexamethylendiaminadipate) solutions in aqueous/alcoholic solvents on its phase state was studied. The films obtained by the coagulation method were characterized by monodisperse pore distribution with an average pore size of 1.3 μm. The films processed by electrospinning from copolyamide solutions were characterized by a bimodal distribution of macropores with one peak of pore radius at 2.0 μm and second peak of pore radius at 20 μm. The adhesion and proliferation of mesenchymal adhesion stem cells (ASCs) stem cells to copolyamide matrix were studied. With the help of scanning electron microscopy it was shown that both tapes porous films were characterized by good adhesion of mesenchymal ASCs stem cells. It was shown that the porous structure, transport and mechanical properties of these copolyamide films allow their use as two-dimensional matrices for cellular technology.

Graded porous inorganic materials derived from self-assembled block copolymer templates.

Graded porous inorganic materials directed by macromolecular self-assembly are expected to offer unique structural platforms relative to conventional porous inorganic materials. Their preparation to date remains a challenge, however, based on the sparsity of viable synthetic self-assembly pathways to control structural asymmetry. Here we demonstrate the fabrication of graded porous carbon, metal, and metal oxide film structures from self-assembled block copolymer templates by using various backfilling techniques in combination with thermal treatments for template removal and chemical transformations. The asymmetric inorganic structures display mesopores in the film top layers and a gradual pore size increase along the film normal in the macroporous sponge-like support structure. Substructure walls between macropores are themselves mesoporous, constituting a structural hierarchy in addition to the pore gradation. Final graded structures can be tailored by tuning casting conditions of self-assembled templates as well as the backfilling processes. We expect that these graded porous inorganic materials may find use in applications including separation, catalysis, biomedical implants, and energy conversion and storage.

Facile Fabrication and Characterization of Three-Dimensional Ordered Films of TiO2 Hollow-Spheres

High-quality three-dimensional ordered TiO2 hollow-spheres (3DOH-TiO2) materials were fabricated using polystyrene spheres colloidal crystals (ca. 290 nm in center-to-center distance) as sacrificial templates and titanium tetrachloride as titanium sources. The obtained samples were characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and N2 adsorption–desorption. The results showed that the films are composed of a closely packed, hexagonal array of the TiO2 hollow-spheres with a center–center separation of ca. 260 nm. The homogeneity in the shell thickness (ca. 40 nm), the physical contact among adjacent hollow-spheres, and the long-range order in the sample were also confirmed by FESEM and TEM analysis. HRTEM results indicated the walls of the hollow-spheres consist of anatase TiO2 nanoparticles (15–20 nm). The porous framework structure of the 3DOH-TiO2 films was further characterized using N2 physical adsorption, and the Brunauer–Emmett–Teller specific surface area and the total pore volume are around 77.72 m2/g and 0.262 cm3/g, respectively.

Determination of the Model for the Chemical Structure of Porous PECVD Low-k Films

Scaling of Cu interconnect structures requires insulating materials with a low dielectric constant that also have adequate mechanical characteristics and good chemical resistance. These macro characteristics depend on the actual mechanical and chemical nanostructure of the porous low-k films. Unfortunately, there is no direct way to determine this exact nanostructure; e.g. neither Atom Probe nor Transmission Electron Microscopy are able to produce adequate images of an amorphous, porous low-k film. In this paper, we propose a new model for the chemical structure of PECVD low-k films: a strong hydrophobic layer, consisting of methyl groups covers the top surface of the porous film; besides, the pore walls are also covered with hydrophobic methyl groups. With this model, we are able to explain the macro characteristics of the low-k films. The model is supported by the test results obtained by modifying the top surface and immersing the pristine and modified films into diluted HF solutions.

The porous structure of the fully-aromatic polyamide film in reverse osmosis membranes

In this study, the porous structures of two commercial fully-aromatic polyamide (FAPA) reverse osmosis (RO) membranes as well as homemade RO membranes were thoroughly characterized and revealed by using SEM and TEM. With a designed “inverse” interfacial polymerization experiment, it was confirmed that pores always form on the surface of the FAPA film facing the aqueous phase. Based on the SEM observation on the cross-section of FAPA film and the TEM results, a new structure model of FAPA film in RO membrane was proposed. The dense layer of the flat area and the dense layer near the top surface of the protuberances and ridges connect together to form a complete dense discriminating layer as the key barrier layer of the RO membrane. Protuberances and ridges have irregular interconnecting cavities and tunnels, through which the dense layer and the pores on the back surface of the FAPA film are connected. All these findings proved the correctness of Cadotte׳s assumption about the pores׳ forming mechanism during interfacial polymerization process.

Anti-reflection porous SiO2 thin film deposited using reactive high-power impulse magnetron sputtering at high working pressure for use in a-Si:H solar cells

Porous SiO2 thin films with low reflectance and high transmittance were obtained using reactive high power impulse magnetron sputtering (HIPIMS) at a high working pressure of 6.67Pa (50mTorr). The average transmittance (450–600nm) of the SiO2 thin films was 94.45%. In comparison, SiO2 thin films deposited at a low working pressure of 0.27Pa (2mTorr) showed an average transmittance of 91.26%. The improvement in the transmittance was attributed to the lower refractive index resulting from the porous structure of the SiO2 thin films. To examine the effect of the anti-reflection SiO2 coating, an a-Si:H solar cell was produced on fluorine-doped tin oxide (FTO) glass. The initial energy conversion efficiency for cells using the anti-reflection, SiO2-coated FTO glass was 11.75%, higher than the 10.75% for the sample using the bare FTO glass. The increase in the short-circuit current density (Jsc) due to the decreased light reflectance was the largest contributor to the increase in the a-Si:H solar cell efficiency.

Flexible supercapacitors based on carbon nanotube/MnO2nanotube hybrid porous films for wearable electronic devices

To meet the requirement of clean and efficient energy storage system for practical applications, supercapacitors (SCs) to be promising candidates for the next-generation energy storage devices have received tremendous attentions. In fact, the SCs can have broader potential if they are designed as flexible power supplies for wearable electronic devices. Herein, we develop the first flexible, low-cost and high-performance hybrid electrode based on MnO2 nanotubes (NTs) and carbon nanotubes (CNTs) by employing a facile vacuum-filtering method. The superior mechanical and electrochemical performance of these flexible electrodes is attributed to: (1) the ultra-long one-dimensional nanotube morphology, (2) the synergistic effects between pseudocapacitive MnO2 NTs and conductive CNTs, (3) hierarchical porous structure of the freestanding film, and (4) high mass loading of MnO2 (4 mg cm−2). Subsequently, the as-synthesized freestanding CNT/MnO2 NT hybrid electrodes are assembled in the form of solid-state SC devices using polyvinyl alcohol (PVA)/LiCl as gel electrolyte. The device exhibits an excellent volumetric capacitance of 5.1 F cm−3 and a high energy density of 0.45 mW h cm−3 for the entire SC volume. Finally, these SCs are integrated in a flexible power band that can drive watches and LEDs. The solid-state SC devices with outstanding flexibility and stability clearly demonstrate their broad applications as flexible, low-cost, high-performance power supplies in wearable electronic devices.

Structure and electrical properties of Nb-Ge-C nanocomposite coatings

Nb-Ge-C nanocomposite thin films were deposited by dc magnetron sputtering using three elemental targets. The films consist of substoichiometric NbCx in a nanometer-thick matrix of amorphous C and Ge. Films with no Ge contain grains that are elongated in the growth direction with a (111) preferred crystallographic orientation. With the addition of ∼12 at. % Ge, the grains are more equiaxed and exhibit a more random orientation. At even higher Ge contents, the structure also becomes denser. The porous structure of the low Ge content films result in O uptake from the ambient. With higher C content in the films both the amount of amorphous C and C/Nb-ratio increases. The contact resistance was measured by four-point technique as a function of contact force between 0 and 10 N. The lowest contact resistance (1.7 mΩ) is obtained at 10 N. The resistivity varies between 470 and 1700 μΩ·cm depending on porosity and O content.

Micropatterned culture of HepG2 spheroids using microwell chip with honeycomb-patterned polymer film

Microwell chip culture is a promising technique for the generation of homogenous spheroids. We investigated the relationship between the structure of the bottom surface of microwell chip and the properties of HepG2 spheroid. We developed a microwell chip, the bottom surface of which consisted of a honeycomb-patterned polymer film (honeycomb film) that had a regular porous structure (HF chip). The chip comprised 270 circular microwells; each microwell was 600μm in diameter and 600μm in depth. At the center of the honeycomb film, an area, 200μm in diameter, was modified with collagen to facilitate cell adhesion. With the exception of the collagen-coated area, the entire microwell was modified with polyethylene glycol to eliminate cell adhesion. HepG2 cells formed uniform spheroids when cultured in the microwells of HF chip. Furthermore, the cells passed through the porous structure of honeycomb film and formed spheroids at its opposite side. The spheroid growth of HepG2 cells cultured in HF chip was greater than that when the cells were culture in a microwell chip, the bottom surface of which was made of poly-methylmethacrylate (PMMA chip). The albumin secretion activity of HepG2 spheroids in HF chip was equal to that in PMMA chip. These results indicate that the microwell bottom with a porous structure enhances the cell growth and maintains well the spheroid function. Thus, HF chip is a promising platform for spheroid cell culture.

Electrochemically reduced graphene oxide with porous structure as a binder-free electrode for high-rate supercapacitors

A binder-free electrode is prepared by directly depositing electrochemically reduced graphene oxide (ERGO) on the metal current collector. Fourier transform infrared spectroscopy and Raman spectrum have been used to demonstrate the effective reduction of graphene oxide on the electrode, and the porous structure of the ERGO film was further characterized by scanning electron microscopy. The electrochemical properties of ERGO were investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). Electrochemical measurements showed that the binder-free ERGO electrode had high specific capacity, good cycle stability, as well as excellent high-rate capability. The specific capacitance of the constructed electrode was 131.6 F g−1 at a scan rate of 10 mV s−1 and maintained 66.9% of the initial value when the scan rate was increased up to 1000 mV s−1. Owing to its favorable electrochemical performance, this binder-free ERGO electrode with porous structure has great potential in future commercial electrochemical supercapacitors.

Preparation of the Working Electrode of Dye-sensitized Solar Cells Using Screen Printing with Alkyd Resins

Dye-sensitized solar cell (DSSC) showing relatively high conversion efficiency can be prepared using a simple screen printing method. While most manufactures prepared the DSSC working electrode using ethyl cellulose (EC) based coating pastes, alkyd resin (AR) based coating pastes are used in this work. Since AR is a polyester modified by the addition of fatty acids and other components, AR based paste is expected to show better contact with the poly(ethylene terephthalate) (PET) flexible substrates. The DSSC working electrode film was screen printed on a FTO glass using a stencil screen or a stainless steel cloth screen with an EC based commercial P200 paste or an AR based paste. An EC based paste shows a porous film structure and an AR based paste shows a uniform dense film and a good printing characteristic, which is ideal for multi-layer printing. According to the results of photovoltaic performances of the corresponding DSSC, DSSC with AR based pastes were found to be compatible with the performance of the reference DSSC with commercially EC based P200 pastes.

Laser Sintering of a Porous TiO2 Film in Dye-Sensitized Solar Cells

We investigate the possibility of modifying the porous structure of TiO2 films in dye-sensitized solar cells (DSSC) in its sintering by a pulsed Nd:YAG laser (wavelength 1064 nm) to improve their parameters and characteristics. Sintering at various pulse energies enabled a porosity within the range of 0.45 to 0.20. The efficiency of the energy conversion in experimental DSSC specimens with TiO2 films sintered by an optimum laser-radiation pulse energy of 150 mJ was 20–25% higher than that of commercial solar cells.

Glow discharge optical emission spectroscopy: a complementary technique to analyze thin electrodeposited polyaniline films

Glow Discharge Optical Emission Spectroscopy (GDOES) has been developed to perform depth profiles of thick metallic films, in tens of microns range. GDOES spectroscopy can also be used to analyze thin organic polymer films since this technique has a great potential thanks to its high depth resolution, multi-element capability, sensitivity, and adaptability to solids or films and to conducting or non-conducting samples. In particular thin electrodeposited conducting polymer films remain an unexplored field of investigation for GDOES technique. However GDOES was used in this work to analyze electrodeposited polyaniline films, in addition to other techniques such as profilometry, electron microscopy and X-ray diffraction (XRD). More precisely polyaniline thin films were electrodeposited from HCl solutions and the presence of an anilinium chloride excess at the top surface of the polymer film was demonstrated using GDOES and XRD. Rinsing of these films with water led to the removal of this excess and to the partial dedoping of the polymer film due to the porous structure of polymer films. Polyaniline thin films were also electrodeposited from H2SO4 solutions and an anilinium hydrogen sulfate was similarly observed at the top surface of the polymer. This excess was removed by rinsing, contrary to hydrogen sulfate anions incorporated into the polymer film during the electrochemical polymerization that were not completely expulsed from the polyaniline films as proved using GDOES.

Structure and mechanical properties of porous films based on polyethylenes of different molecular masses

The structure and mechanical properties of porous films of linear polyethylenes with different molecular masses obtained via a process including four successive stages—melt extrusion, isometric annealing, uniaxial extension, and thermal fixation—are studied. The molecular-mass range in which microporous structures containing through-flow channels can form is determined. The effects of molecular-mass characteristics of polyethylene on the morphological features of the structures, porosities, sizes of through-flow channels, specific surfaces, and permeabilities of the porous films are analyzed.

Large-Scale Fabrication of In<SUB>2</SUB>S<SUB>3</SUB> Porous Films via One-Step Hydrothermal Process

Large-scale indium sulfide (In2S3) porous films were fabricated via a facile one-step and non-template hydrothermal process using L-cysteine as a capping agent. The impact of reaction conditions such as reaction time, temperatures, and capping agents on the synthesis of the In2S3 porous films were studied. The morphology, structure, and phase composition of In2S3 porous films were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The formation process and the optical property of the In2S3 porous films were also evaluated.

Effect of Pore Structure of Nanometer Scale Porous Films on the Measured Elastic Modulus

The impact of pore structure of nanoporous films on the measured elastic modulus is demonstrated for silica-based nanoporous low-k films that are fabricated using an alternative manufacturing sequence which allows a separate control of porosity and matrix properties. For this purpose, different experimental techniques for measuring the elastic properties were compared, including nanoindentation, laser-induced surface acoustic wave spectroscopy (LAwave), and ellipsometric porosimetry (EP). The link between the elastic response of these nanoporous materials and their internal pore structure was investigated using positronium annihilation lifetime spectroscopy (PALS), EP, and diffusion experiments. It is shown that the absolute value of the Berkovich indentation modulus is very sensitive to the local pore structure and stiffness of the substrate and can be influenced by densification and/or anisotropic elasticity upon indentation, while on the other hand spherical indentation results are less sensitive to the local pore structure. The comparison of Berkovich and spherical indentation results combined with finite element simulations can potentially reveal changes in the internal structure of the film. For nanoporous films with porosity above the percolation threshold, the elastic modulus results obtained with LAwave and EP agree very well with spherical indentation results. On the other hand, below the percolation threshold, the elastic modulus values determined by these techniques deviate from the spherical indentation results. This was explained in terms of specific technique related effects that appear to be sensitive to the specific arrangement and morphology of the pores.

Dopant-stimulated CuO nanofibers for electro-oxidation and determination of glucose

We described the preparation of copper oxide composite nanofibers doped with carbon nanotubes (CuO/C-NFs) or nickel oxide(CuO/NiO-NFs) by electrospinning for direct glucose determination. The interest in exploring practical CuO/C-NFs and CuO/NiO-NFs electrode materials for sensor application was fascinated by the possibility of promoting electron transfer for kinetically unfavorable glucose oxidation reactions at a lower overpotential and thus improving the selectivity of the electrode for glucose in electroanalysis. The morphologies of CuO/C-NFs and CuO/NiO-NFs were characterized by scanning electron microscopy(SEM) and X-ray powder diffraction(XRD). The electrocatalytic performances of glucose were evaluated in detail by cyclic voltammetry(CV) and chronoamperometry. Facile charge transport, enhanced current response(at a lower overpotential of +0.35 V), improved stability and selectivity, as well as excellent resistance towards electrode fouling were observed at CuO/C-NFs electrode in direct glucose electroanalysis. These merits are attributed to the highly porous three-dimensional network film structure of CuO/C-NFs electrode materials and the potential synergic catalytic effect of CuO and carbon nanotubes in composite nanofibers. This study may provide a new insight into metal oxide-based composite nanofibers obtained via electrospinning for fabricating novel and high performance sensors and devices.

Comparative Study of Structure and Permeability of Porous Oxide Films on Aluminum Obtained by Single- and Two-Step Anodization

A comparative study of the structure and transport properties of porous aluminum oxide films obtained by single- and two-step anodization was carried out. It is shown that the oxidation regime significantly affect the number of dead-ended channels, which results in more than twice the variation in membrane permeability. The effect is explained by multiple branching of channels on the initial stages of organization of the porous structure. Branching also occurs on later stages governing mass transport properties of porous anodic alumina films. A model describing transport properties of anodic aluminum oxide membranes based on pore branching on domain boundaries was suggested to fit experimental results of permeance of membranes obtained by both single- and two-step anodization.

Polyelectrolyte/silver nanocomposite multilayer films as multifunctional thin film platforms for remote activated protein and drug delivery

We demonstrate a nanoparticle loading protocol to develop a transparent, multifunctional polyelectrolyte multilayer film for externally activated drug and protein delivery. The composite film was designed by alternate adsorption of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on a glass substrate followed by nanoparticle synthesis through a polyol reduction method. The films showed a uniform distribution of spherical silver nanoparticles with an average diameter of 50±20nm, which increased to 80±20nm when the AgNO3 concentration was increased from 25 to 50mM. The porous and supramolecular structure of the polyelectrolyte multilayer film was used to immobilize ciprofloxacin hydrochloride (CH) and bovine serum albumin (BSA) within the polymeric network of the film. When exposed to external triggers such as ultrasonication and laser light the loaded films were ruptured and released the loaded BSA and CH. The release of CH is faster than that of BSA due to a higher diffusion rate. Circular dichroism measurements confirmed that there was no significant change in the conformation of released BSA in comparison with native BSA. The fabricated films showed significant antibacterial activity against the bacterial pathogen Staphylococcus aureus. Applications envisioned for such drug-loaded films include drug and vaccine delivery through the transdermal route, antimicrobial or anti-inflammatory coatings on implants and drug-releasing coatings for stents.

Effect of sulfur dopants on the porous structure and electrical properties of mesoporous TiO2 thin films

In this work, sulfur-doped mesoporous TiO2 films were formed by a chemical solution deposition technique to investigate their structure and electrical conductivity. Phase formation and crystallization of TiO2 was retarded and the optical band gap was reduced due to the presence of the sulfur dopants. As a result, enhancements in the microstructural stability and electrical conductivity of mesoporous TiO2 could be obtained by sulfur doping.