Macroporous Films Research Articles

High surface area polypyrrole scaffolds for tunable drug delivery

Intrinsically conducting polymers such as polypyrrole (PPy) are viable platforms for efficient drug delivery, where release rates can be tuned by external electrical stimulus. In this study, the successful fabrication of 3-dimensionally ordered macroporous PPy inverse opal thin films is described, and the viability of such films for controlled drug release evaluated in vitro. The PPy inverse opal thin films were obtained by electropolymerization of PPy through the interstitial voids of a colloidal crystal template composed of poly(methyl methacrylate) colloids of diameter ∼430 nm. Chemical etching of the template yielded macroporous PPy inverse opal scaffolds. The model drug risperidone was loaded into the PPy inverse opal films, and then entrapped by electropolymerization of a non-porous PPy overlayer. The morphology and chemical composition of the PPy scaffolds were evaluated by SEM and FTIR spectroscopy, respectively. The high surface area PPy inverse opal scaffolds exhibited enhanced drug loading and releasing capabilities compared to conventional non-porous PPy films. Drug release profiles could be modified by applying electrical stimulus, which caused actuation of the porous polypyrrole films. The proposed delivery system may find use as an implantable device where drug release can be electrically tuned according to patient requirements.

Structure of a macroporous silica film as an interlayer of a laminated glass

A macroporous silica film (MSF) was introduced as a buffer layer of material between a silicate glass (SG) layer and a polyurethane (PU) layer to form a new aeronautic laminated glass. Structure simulations of MSF were performed using the ANSYS software. Pore models, porosity factor models, and thickness models were established. X-direction stress, Y-direction stress, and equivalent stress of the models were determined. Simulation results indicate that the pore can effectively depress shear stress on the MSF–PU interface. Moreover, maximum X-direction stress, maximum compressive stress, and maximum equivalent stress on the MSF–PU interface all decrease rapidly and then increase slowly by increasing film thickness.

Template-assisted electrodeposition of highly ordered macroporous zinc structures from an ionic liquid

The present paper shows the template-assisted electrodeposition of highly ordered macroporous zinc films in the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate ([Py1,4]TfO). Polystyrene (PS) spheres were employed as templates, and zinc films were electrodeposited within the interstitial voids of the template. The results show that well-ordered two- or three-dimensional macroporous zinc films can easily be made. The obtained macroporous films showed diffractive light when illuminated with white light. The contact angle measurements revealed that the wettability of the employed ionic liquid on PS templates is much better than the one of aqueous solutions, leading to better infiltration into the interstitial voids of the PS spheres. Macroporous zinc is potentially interesting as host material for lithium ion batteries.

A Novel Hydrogen Peroxide Biosensor Based on the Immobilization of Catalase on Three-Dimensionally Ordered Macroporous Graphene-doped Titanium Dioxide Film

A novel hydrogen peroxide biosensor based on three-dimensionally ordered macroporous graphene-doped titanium dioxide modified ITO electrode(3DOM GR-Au-TiO2/ITO) was prepared by a sol-gel procedure using polystyrene colloidal crystals as template.Catalase has been successfully immobilized on the modified electrode.The cyclic voltammetry(CV),electrochemical impedance spectra(EIS) and chronoamperometric characterizations reveal that the modified electrode exhibits an excellent electrocatalytic activity,a wide linear range for H2O2 concentration from 3.0×10-6 mol/L to 3.6×10-3 mol/L with a detection limit of 4.2×10-7 mol/L(S/N=3),fast response,high sensitivity,good reproducibility and stability.

Physical Properties of Macroporous Tungsten Oxide Thin Films and Their Impact on the Photocurrent Density

Tungsten trioxide (WO3) films were prepared using polystyrene spheres of two different diameters as a template in order to create porous layers. X-ray diffraction data and electron microscopy images show that annealed films exhibit polycrystalline structure with monoclinic phase and pore size of approximately hundred nanometers. The optical band gap energies have been determined by photoacoustic spectroscopy as 3.17 eV, and this value was not affected by sample morphology. Low temperature photoluminescence spectra exhibit broad band in the blue region. Deconvolutions of PL spectra show that there are two transitions which intensity depends on thin film pore size. We discuss the possible origin of this emissions associated with oxygen vacancies and surface states. A comparative study of the WO3films used as photoanodes is presented and correlated with PL results.

Biotinyl moiety-selective polymer films with highly ordered macropores

Macroporous polymer films with long-range uniformity and biotinyl-moiety selective recognition sites have been developed. A hierarchical molecular imprinting strategy afforded significant enhancements in quartz crystal microbalance (QCM) sensitivities towards biotinylated compounds.

Maleimide-containing polymer inverse opals: a new kind of reactive photonic structure with significant extendibility

In this work, maleimide-containing polymer inverse opals have been successfully prepared by utilization of an acrylate monomer bearing a masked (protected) maleimide unit. As an ideal clickable functional group, maleimide can promote the Michael addition of thiol-containing molecules and the thermoreversible Diels–Alder reaction of furan derivatives, providing tremendous opportunities to produce various functional materials from one maleimide-containing polymer. As a demonstration, four chemical systems were facilely evolved from the prepared maleimide-containing inverse opal. By exploiting the nucleophilic thiol–ene reaction of maleimide, the zwitterionic pH-responsive inverse opal and electroactive inverse opal were first fabricated by reacting with cysteine and thiol-containing ferrocene derivatives, respectively. Based on the same reaction, it was also found that the maleimide-containing inverse opal could serve as a self-reporting sensing platform to sensitively detect the reduction of oxidized glutathione by specific enzymes. On the other hand, the thermoreversible nature of the Diels–Alder reaction of the maleimide groups made it possible to construct a dynamic molecule gating system by reacting with alkyl-chain-substituted furan derivatives from the prepared interconnected macroporous film. In fact, due to the unlimited variety provided by the two kinds of reactions mentioned above, the described photonic material exhibits a significant extendibility and could be easily post-modified for special purposes with maintenance of the opaline structure. Thus, this novel clickable maleimide-containing polymer inverse opal could serve as a reactive platform for producing a variety of functional photonic materials.

Macroporous Oxide Platforms Templated by Non‐Close‐Packed Spherical Copolymer Aggregates

Exclusive organic templating of macroporous oxide films is reported by using non-close and lose packing of spherical copolymer aggregates, in combination with facile control of condensation degree/density of inorganic oxide frameworks. Unique macroporous oxide films, mainly titania showing highly porous, crystalline, and versatile properties, can be fabricated with continuous design from unusual 3-D net-shape to tunable spherical macrostructures, which expands the preparation of other inorganic oxide films (silica, alumina, and zirconia) and possibly adapts the use of other assembled organic polymers. The macroporous structures are helpful for effective accommodation of bulky biomoleculeshigh and diffusivity of organic molecules (useful for photocatalysts). Unusual structural variation, expansion of spherical voids, is also observed, being useful for fine tuning of optical property.

Assembly of graphene nanocomposites into honeycomb-structured macroporous films with enhanced hydrophobicity

Nature-inspired porous films have attracted great interest from researchers because of their fascinating structures and unique properties. In this paper, honeycomb-structured macroporous films of graphene nanocomposites were prepared by the breath figure method at both an air/solid interface and an air/water interface. Electrostatic complexes of graphene oxide (GO) and dimethyldioctadecylammonium bromide (DODA) have shown interfacial activities to stabilize the templating water droplets by adsorbing at water/solution interfaces. They can also form honeycomb structures of nanocomposites with gold nanoparticles (AuNPs) and induce the formation of highly ordered honeycomb films of polystyrene (PS), which have shown enhanced hydrophobicity. The process to fabricate such honeycomb structures is fast, easy, and low-cost, providing a universal approach for the preparation of multifunctional materials, which have potential application in the fields of catalysis, bioscience and sensors.

Electrodeposition of Macroporous Zn and ZnO Films from Ionic Liquids

Electrodeposition of Macroporous Zn and ZnO Films from Ionic Liquids

Electrophoretic deposition of macroporous carbon nanotube assemblies for electrochemical applications

Electrophoretic deposition of macroporous assemblies of single-walled carbon nanotubes (SWCNTs) is described. The macroporous structure was created thanks to the presence of polystyrene (PS) beads which were co-deposited with the carbon nanotubes in a 60V potential field. The ratio between the quantity of carbon nanotubes and polystyrene beads in the solution for deposition was found to be critical for the proper self-assembly of the composite film during electrophoretic deposition. The macroporous films have been characterized by scanning electron microscopy, atomic force microscopy and profilometry. The macroporosity was revealed after template removal (calcination of the PS beads). Access to the internal surface was assessed by electrochemical characterization using methylene green as a redox probe likely to adsorb on the SWCNT surface. Platinum nanoparticles and a sol–gel layer with encapsulated dehydrogenase and NAD+ cofactor have been deposited on the macroporous SWCNT electrodes in order to illustrate the use of the macropore texture for the detection of H2O2 and for biosensor applications, respectively.

Design of hierarchically meso–macroporous tetragonal ZrO2 thin films with tunable thickness by spin-coating via sol–gel template route

Hierarchically meso–macroporous tetragonal ZrO2 (t-ZrO2) thin films with tunable thickness were prepared by spin-coating method via Pluronic P123 templated sol–gel route. This hierarchically porous ZrO2 was characterized by field-emission scanning electron microscope, atomic force microscope, nitrogen adsorption–desorption isotherm, X-ray diffraction, and ultraviolet–visible spectrometer. Effects of rotation speed and by coating another layer of sol on the first layer during spin-coating on the thickness and mesoporous structure of ZrO2 thin films formed were investigated. The meso–macroporous ZrO2 film coated on a glass substrate possessed an average transmittance higher than 80% in the visible range. It was suggested that the structure of Pluronic P123 was changed as concentration of deposited sol varied over time, which led to the formation of worm-like mesospores coexisted with macropores and rod-like ZrO2 framework. Formation of cracks on ZrO2 thin films was initiated by the structure of meso–macropores and shrinkage of respective films.

Two modes in macroporous Cu2O growth through template-assisted electrodeposition method

Macroporous materials with three dimensional pores and channels are anticipated to exhibit improved performance in numerous applications such as photonic band gap crystals, battery electrodes and gas sensors due to their special structure. In this work, macroporous Cu2O thin films were prepared by template-assisted electrodeposition method. The mechanism of electrodeposition infiltrating procedures indicated that the target architectures can basically maintain its original shape, and the fabrication of spherical-porous shaped Cu2O controlled by crystalline structures is firstly studied systematically. The morphology of macroporous material along the (1 1 1) direction demonstrated that the target architecture can copy both the crystalline structures and the colloidal crystal template. Moreover, models are set up to discuss the evolution of the morphology (the shapes of the pore mouths and pore walls), which indicated that the pore mouths and pore walls were deeply influenced by the deposition depth.

Controllable low dielectric porous polyimide films templated by silica microspheres: Microstructure, formation mechanism, and properties

In the paper, controllable low dielectric macroporous polyimide (PI) films were prepared using silica microspheres as template, based on the solvent-evaporation-assisted in situ self-assembly of polyamic acid (PAA, precursor of PI) and silica microspheres in N,N-Dimethylformamide (DMF) solution. The interior microstructure of the macroporous PI films and its relationship with mechanical and dielectric properties were investigated. It was found that the macroporous PI films had triple-layer porous structures: ordered porous surface, dense layer in the middle, and interconnected porous structure at the bottom. The thickness of the dense layer in the middle changed with increasing weight content of silica. When SiO2 wt% was above 40%, the dense layer nearly disappeared. The interconnected porous structure at the bottom was quite homogenous, and the pore size could be controlled by the diameter of silica microspheres. Based on the experimental results, possible formation mechanism of the macroporous PI films was addressed. The mechanical properties of the macroporous PI films were degraded due to the introduction of air void. It was found that the degradation of mechanical properties of macroporous PI films with porosity of 37% is more obvious than that of PI films with porosity below 31%, which could be attributed to the triple-layer microstructure of the films. The air void introduction could effectively reduce the dielectric constant from 4.11 of PI dense films to 2.57 of porous PI films with porosity of 37%. The dielectric constant was only closely related to porosity and had no obvious connection with pore size.

Spontaneous photoinduced formation of hybrid polymer films with functionalized macroporous patterns

Sol–gel phase separation of 3-(glycidyloxypropyl)trimethoxysilane (GPTMS) in presence of a long-chain hydrophobic precursor ((H3C(CH2)n−1Si(OCH3)3), n=12–16) served to synthesize macroporous hybrid films, without the requirement of any template or additives. The method used was both simple and fast; proceeding through a sol–gel process triggered by UV light, and based on efficient Brönsted supercid photocatalysts. The film surface was characterized by a three-dimensional network of relatively well-defined and homogeneously dispersed micro- or nanopatterns as assessed by a variety of microscopy techniques. The concentration and structure of the n-alkylsilane as well as the film thickness were critical parameters in controlling the macrostructuration and the size of the perforations. Time-resolved Fourier transformed infrared spectroscopy allowed to probe in situ the compositional changes during the sol–gel process. By using spatially-resolved confocal Raman spectroscopy, we showed a preferential localization of the condensed n-alkylsiloxane species at the surface of the pores to form conformationally ordered monolayers. This self-assembly process was presumably driven by the surfactant properties of the hydrolyzed alkylsilane species formed in situ and stabilizing the macropores.

Fabrication of macroporous titanium dioxide film using PMMA microspheres as template

A novel synthetic procedure is described for the fabrication of macroporous titanium dioxide (TiO2) films with an ordered, uniform pore framework comprised of nanocrystalline anatase mainly. The synthetic approach involved several processes. First, polymethyl methacrylate (PMMA) microspheres (87nm) were synthesized by using a dispersion polymerization technique in the presence of Fenton reagent (FeSO4/H2O2) as a novel initiator, which has advantages such as simple and fast polymerization process without deoxygenation. Next, the templates of PMMA microspheres were assembled on clean substrates by dip-drawing technique. Finally, the macroporous TiO2 films with the average size of pores about 87nm were obtained by sol-dipping template method and calcination to remove the templates at 550°C. The test results of X-ray diffraction indicate that the nanocrystalline of anatase formed after calcination. The mechanisms of PMMA polymerization and template formation were proposed. Furthermore, both structures and morphologies of the composite films were investigated with field emission scanning electron microscope, and the processes of the thermal decomposition of PMMA and TiO2 gel were also discussed with thermo gravimetric analysis. This ordered and uniform pore framework could be used as the promising ultrafilter membranes showing active photocatalysis without intensive fouling.

Bulk synthesis of ordered macroporous silica particles for superhydrophobic coatings

We report the bulk synthesis of ordered macroporous ceramic particles by the emulsion templating process. Large polystyrene (PS) beads and small silica nanoparticles were assembled simultaneously inside an emulsion, which formed composite structured particles during the evaporation of droplets. Then, by burning out PS beads, macroporous ceramic particle films were produced on substrate. The size of ordered macroporous particles could be controlled by adjusting the emulsification condition for confining emulsions. As well, the pore size could be controlled by changing the diameter of PS beads. The surface of the ordered macroporous particle films was coated with fluorinated molecules, which have shown superhydrophobic property due to multi-scale roughness.

Current-voltage characteristics in macroporous silicon/SiOx/SnO2:F heterojunctions

We study the electrical characteristics of macroporous silicon/transparent conductor oxide junctions obtained by the deposition of fluorine doped-SnO2 onto macroporous silicon thin films using the spray pyrolysis technique. Macroporous silicon was prepared by the electrochemical anodization of a silicon wafer to produce pore sizes ranging between 0.9 to 1.2 μm in diameter. Scanning electronic microscopy was performed to confirm the pore filling and surface coverage. The transport of charge carriers through the interface was studied by measuring the current-voltage curves in the dark and under illumination. In the best configuration, we obtain a modest open-circuit voltage of about 70 mV and a short-circuit current of 3.5 mA/cm2 at an illumination of 110 mW/cm2. In order to analyze the effects of the illumination on the electrical properties of the junction, we proposed a model of two opposing diodes, each one associated with an independent current source. We obtain a good accordance between the experimental data and the model. The current-voltage curves in illuminated conditions are well fitted with the same parameters obtained in the dark where only the photocurrent intensities in the diodes are free parameters.

Photocatalytically initiated electroless deposition of macroporous metal films onto insulating substrates

By using photocatalytically initiated electroless deposition (PIED) we have deposited macroporous metal films with highly ordered arrays of sub-μm (hemi)spherical pores directly onto the surface of insulating substrates for the first time. This has been achieved by sensitisation of the target substrate with a TiO2 photocatalyst followed by PIED of the target metal into the interstitial spaces of a template composed of hexagonally close packed polystyrene microspheres.

Freestanding Macroporous Silicon and Pyrolyzed Polyacrylonitrile As a Composite Anode for Lithium Ion Batteries

Silicon continues to draw great interest as an anode material for lithium ion batteries due to its large specific capacity for lithium. Macroporous silicon produced by electrochemical etching is one of several anode materials of interest, but its energy density is oftentimes limited due to its attachment to an unreactive silicon substrate. Here, we present a novel “lift-off” method by which a freestanding macroporous silicon film (MPSF) is electrochemically detached from the underlying bulk silicon and combined with pyrolyzed polyacrylonitrile (PAN), a conductive polymer that forms a conjugated-chain chemical structure. We report the performance of these silicon thin films with and without pyrolyzed PAN.