Ultra-thin films of cationic amphiphilic poly(2-(dimethylamino)ethyl methacrylate) based block copolymers as surface wettability modifiers

Ultra-thin films of cationic amphiphilic block and statistical copolymers were applied on silica surfaces from aqueous solutions through electrostatic interactions, and the resulting modification in the wettability of the surfaces was studied. A copolymer series from 2-(dimethylamino)ethyl methacrylate with methyl methacrylate and butyl methacrylate was polymerized by ATRP. Subsequently, the conformation of the polymers in aqueous solutions was studied by surface tension measurements, dynamic light scattering, ¹H NMR and cryogenic transmission electron microscopy. Unimeric conformation, equilibrium micelles or frozen micellar structures were observed, depending on polymer composition and the ionic strength of the solution. The polymers were applied on silica from aqueous solutions by either spin coating or adsorption. The formed ultra-thin film surfaces were studied by AFM and water contact angle measurements. The spin-coated surfaces were highly hydrophilic with rapidly dropping contact angles, whereas the surfaces prepared by adsorption had stable water contact angles between 30-60°, depending on polymer. The difference between the spin-coated and adsorbed surfaces is explained by the formation of a monolayer in the adsorbed surfaces.     

Photoinduced molecular reorientation in photoreactive liquid crystalline copolymers in a phase retarder application

Polymethacrylate copolymers, which have hexamethylene spacer groups terminated with 4-methoxyphenyl-4′-oxycinnamate (MPC) and 4-oxybenzoic acid (BA) in the side chain, were synthesized. Thin films underwent thermally enhanced photoinduced cooperative molecular reorientation using linearly polarized ultraviolet (LPUV) light and subsequent annealing. Moreover, low exposure energy (4-80 mJ cm⁻²) and annealing temperature (<140 °C) provided sufficient cooperative molecular reorientation of both side groups with a large reorientational order (S > 0.5). Tuning the copolymer composition adjusted the birefringence (?n) of homogeneously reoriented films between 0.10 and 0.22 at 517 nm. Finally, a phase retarder (?nd = 130 nm) using an oriented copolymer on a triacetylcellulose (TAC) film substrate, which exhibited a thermal stability up to 140 °C, was fabricated.     

Fabrication of polymer antireflective coatings by self-assembly of supramolecular block copolymer

We demonstrated a method of fabricating antireflective coatings based on the self-assembly of supramolecular block copolymer formed by polystyrene terminated with carboxyl (PS-COOH) and poly(methyl methacrylate) terminated with amine (PMMA-NH₂) via hydrogen bonding. Different porous films were generated by selectively removing PS-COOH from the spin-coated films with a selective solvent, cyclohexane, under different conditions. The refractive index of such porous film can be tuned from 1.49 down to 1.26 by controlling the thickness of the porous film. For the porous layer with n ˜ 1.26, the light transmittance of the glass about 97.93% was achieved in the visible range (λ ˜ 574 nm). By varying the solution concentration and exposing time in cyclohexane, inhomogeneous three-layered porous films were generated: top and bottom layers with high porosities and the middle layers with lower porosities, respectively. The light transmittance of the glass coated with this inhomogeneous film was about 98.00% in the near-infrared region corresponding to wavelength between 800 and 1400 nm. The wavelength region of the broadband antireflective films with high transmittance more than 99.00% can be fine tuned to 1200-2000 nm with increasing the film thickness.     

EIS analysis of hydrophobic and hydrophilicTiO2 film

Titanium oxide films were formed on metallic titanium substrates by employing a thermal treatment at 800 °C under air atmosphere. Component and microstructure of the oxide films were characterized by XRD and SEM method. Water contact angles on titanium oxide film surface were measured in both dark and sunlight illumination condition. Corrosion tests were carried in seawater solution under different illuminate conditions. Electrochemical impedance spectroscopy (EIS) techniques were used to study the changes on TiO₂ film. Results indicated that: hydrophilic TiO₂ film suffered a severe photo-corrosion effect in seawater due to their semiconductor properties under sunlight condition, but the hydrophobic TiO₂ film under dark condition exhibited a good corrosion resistance.     

Enthalpy recovery and structural relaxation in layered glassy polymer films

Recent studies of physical aging in confined polymer glasses have revealed that aging behavior in confinement often differs from bulk behavior. This study used DSC to characterize physical aging and structural relaxation in bulk polysulfone (PSF) and co-extruded multilayered films of PSF and an olefin block copolymer (OBC) that have average PSF layer thicknesses of 640 nm, 260 nm, and 185 nm. The films were aged isothermally at 170 °C, and the recovered enthalpy upon reheating was measured over time. The films with 640 nm and 260 nm PSF layers had aging rates very similar to that of bulk PSF, while the film with 185 nm PSF layers had an aging rate slightly greater than the bulk value. The cooling rate dependence of the limiting fictive temperature (T_f′) in multilayered and bulk PSF samples was also characterized. Values of T_f′ were similar for all films at each cooling rate. The results of this work are in general agreement with our previous gas permeation aging study of multilayered PSF films aged at 35 °C, in which the effect of layer thickness on aging behavior was minimal. This stands in contrast to studies with thin, freestanding PSF films, which exhibit accelerated aging relative to bulk and have aging rates that depend strongly on film thickness.     

Contact Angles and Coating Film Thickness

The effect of film thickness and surface preparation techniques on contact angles of water, 1-bromonaphtalene, and n-hexadecane on Teflon® AF 1600 polymeric surfaces is studied. It was found that contact angles of water on different thicknesses of spin-coated films ranging from 27?nm to 420?nm are essentially constant. This is due to the homogeneity and smoothness of the coating layers as shown by the scanning force microscopy of the samples. Furthermore, the contact angle measurements with these three liquids on both dip-coated and spin-coated films suggested that the film preparation technique does not affect contact angles dramatically. Interestingly, slightly higher contact angles on dip-coated surfaces were measured. It is also argued that the anomaly of the water contact angle—in the sense that the measured contact angle is much higher than the expected ideal value—is due to specific interactions between water and Teflon®.     

Effect of oxygen plasma treatment on non-thrombogenicity of diamond-like carbon films

The non-thrombogenicity of oxygen-plasma-treated DLC films was investigated as surface coatings for medical devices. DLC films were deposited on polycarbonate substrates by a radio frequency plasma enhanced chemical vapor deposition method using acetylene gas. The deposited DLC films were then treated with plasma of oxygen gas at powers of 15 W, 50 W, and 200 W. Wettability was evaluated by water contact angle measurements and the changes in surface chemistry and roughness were examined by X-ray photoelectron spectroscopy and atomic force microscope analysis, respectively. Each oxygen-plasma-treated DLC film exhibited a hydrophilic nature with water contact angles of 11.1°, 17.7° and 36.8°. The non-thrombogenicity of the samples was evaluated through the incubation with platelet-rich plasma isolated from human whole blood. Non-thrombogenic properties dramatically improved for both 15 W- and 50 W-oxygen-plasma-treated DLC films. These results demonstrate that the oxygen plasma treatment at lower powers promotes the non-thrombogenicity of DLC films with highly hydrophilic surfaces.     

Novel N-isopropylacrylamide based polymer architecture for faster LCST transition kinetics

Temperature-responsive p(N-isopropylacrylamide-co-ethylene glycol dimethacrylate) (p(NIPAAm-co-EGDMA) films, graded in composition to provide a NIPAAm-rich surface, were synthesized successfully via initiated chemical vapor deposition (iCVD). Their dynamic response to temperature changes as monitored using quartz crystal microbalance with dissipation monitoring (QCM-D) was clearly distinguishable from the response of control iCVD-prepared films of homogeneous composition. The lower critical solution temperature (LCST) of the homogeneous copolymer (15 °C) was less than that reported for pure NIPAAM (32 °C) due to the hydrophobicity of the comonomer, EGDMA. The graded films displayed a broader transition over the range from 16 to 28 °C. The time constants associated with the response to small step changes in temperature around the LCST transition were significantly smaller in the graded (<143 s) than in the homogeneous films (1000-8000 s). The novel graded film architecture is promising for facilitating fast switching in applications requiring responsiveness to temperature swings.     

Preparation of super‐hydrophobic film with fluorinated‐copolymer

Organic superhydrophobic films were prepared by utilizing TA‐N fluoroalkylate (TAN) and methyl methacrylate (MMA) copolymer as water‐repellent materials and inorganic silica powder as surface roughness material has been developed. Coating solutions prepared by adding silica powders into copolymer solution directly (one‐step method) and by adding silica powders into monomers and allowing them to react (two‐step method). The results showed that contact angles of the films prepared by one‐step method (37.6 wt % of silica powders in the coating solution) were greater than 150°, but the transmittance of the film at visible light was only 30%. On the other hand, the contact angle of films prepared by two‐step method (20 wt % of silica powders in the coating solution) was greater than 160° and the transmittance of the film was greater than 90%. The contact angle of the film prepared by poly(octyl acrylate), POA, was 32.1°, but while introducing silica powder into the system, the contact angle of the film was reduced to be smaller than 5°. Thus, superhydrophobic and superhydrophilic films can be obtained by introducing a roughening material on the hydrophobic surface and the hydrophilic surface, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1646–1653, 2007     

Properties of organic–inorganic composite materials prepared from acrylic resin emulsions and colloidal silicas

To design an organic–inorganic composite material with colloidal silica as the inorganic component, an acrylic resin emulsion and an organic silane hybridized acrylic resin emulsion were prepared by emulsion polymerization. The organic–inorganic composite films were prepared by blending the emulsion and the colloidal silica. The contact angles for water, gloss at 60°, and the transparencies of those films were measured. The dispersion state of colloidal silica in films was observed with a scanning electron microscope (SEM) and a transmission electron microscope (TEM). From these results, the contact angle for water of the organic–inorganic composite film obtained from the silane hybridized acrylic resin emulsion was lower than that of the organic–inorganic composite film obtained from an acrylic resin emulsion. The contact angles for water in organic–inorganic composite films with colloidal silicas were lower than those of the films without the colloidal silicas. The films prepared from silane hybridized acrylic resin emulsion composites with colloidal silicas of less than 100 nm were more hydrophilic. SEM and TEM observations demonstrated that some aggregations of the small colloidal particle silica were densely dispersed on the film surface. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2051–2056, 2006     

Physical aging of layered glassy polymer films via gas permeability tracking

The physical aging of polymers in confined environments has been an area of intensive study in recent times. The rate of physical aging in thin films of many polymers used in gas separation membranes is dependent on film thickness and accelerated relative to bulk. In this study, the physical aging of polymer films with alternating glassy polysulfone and rubbery polyolefin layers was monitored by measuring the gas permeability of O₂ and N₂ as a function of aging time at 35 °C. The alternating layer structures were formed by a melt co-extrusion process. The polysulfone layers have thicknesses ranging from 185 to 400 nm, and the overall thicknesses of the films are on the order of 80-120 μm. The aging of freestanding thin films of polysulfone is rapid and exhibits clear thickness dependence, whereas the aging of multilayered films was observed to be similar to bulk and showed no dependence on layer thickness. At 1000 h of aging time, a 400 nm freestanding PSF film decreased in O₂ permeability by 35%, whereas on average the bulk and multilayered films only experienced a decline of 10-15%. A slight increase in O₂/N₂ selectivity for the multilayered films was observed over the course of aging.     

Preparation and Characterization of Covalently Binding of Rat Anti-human IgG Monolayer on Thiol-Modified Gold Surface

The 16-mercaptohexadecanoic acid (MHA) film and rat anti-human IgG protein monolayer were fabricated on gold substrates using self-assembled monolayer (SAM) method. The surface properties of the bare gold substrate, the MHA film and the protein monolayer were characterized by contact angle measurements, atomic force microscopy (AFM), grazing incidence X-ray diffraction (GIXRD) method and X-ray photoelectron spectroscopy, respectively. The contact angles of the MHA film and the protein monolayer were 18° and 12°, respectively, all being hydrophilic. AFM images show dissimilar topographic nanostructures between different surfaces, and the thickness of the MHA film and the protein monolayer was estimated to be 1.51 and 5.53 nm, respectively. The GIXRD 2θ degrees of the MHA film and the protein monolayer ranged from 0° to 15°, significantly smaller than that of the bare gold surface, but the MHA film and the protein monolayer displayed very different profiles and distributions of their diffraction peaks. Moreover, the spectra of binding energy measured from these different surfaces could be well fitted with either Au4f, S2p or N1s, respectively. Taken together, these results indicate that MHA film and protein monolayer were successfully formed with homogeneous surfaces, and thus demonstrate that the SAM method is a reliable technique for fabricating protein monolayer.     

Morphology of sulfonated polyarylenethioethersulfone random copolymer series as proton exchange fuel cells membranes by small angle neutron scattering

Sulfonated polyarylenethioethersulfone (SPTES) copolymers with high proton conductivity (100-215 mS/cm at 65 °C, 85% relative humidity) are promising potential proton exchange membrane (PEM) for fuel cells. Small angle neutron scattering (SANS) of the hydrated SPTES copolymer membranes at 25 °C exhibit a nanostructure which can be approximated by correlated polydisperse spherical aggregates containing water molecules with liquid-like ordering (Percus Yevick approximation) and large scale water pockets. The ionic domain radius and the volume packing density of the aggregates present in the hydrated SPTES copolymer membranes at 25 °C increased with increasing degree of sulfonation. SPTES-80 with highest degree of sulfonation (71.6%) showed a Guinier plateau at the very low q range (q < 1 × 10⁻⁴ 1/Å) indicating presence of isolated large scale morphology (R_g = 1.3 ± 0.18 micron). The radius of spherical ionic aggregates present in the hydrated SPTES-50 and SPTES-60 copolymer membranes increased with increasing temperature to 55 °C, but the large scale morphology changed to a fractal network. Further increase of the sulfonation degree to 63.3% and 71.6% (SPTES-70 and SPTES-80) resulted in a substantial morphology change of the spherical aggregates to an irregular bicontinuous hydrophobic/hydrophilic morphology for the hydrated SPTES-70 and SPTES-80 copolymer membranes at 55 °C. Presence of ionic maxima followed by a power law decay of −4 for SPTES-70 and SPTES-80 copolymer membranes was attributed to the bicontinuous phase morphology at high degree of sulfonation and elevated temperature (55 °C). The disruption of the larger scale fractal morphology was characterized by significant decrease in the intermediate scattering intensity. Hydrophobic and hydrophilic domains were separated distinctly by sulfonic groups at the interface showing as power law decay of −4 for all hydrated SPTES copolymers.     

Fabrication of glassy membrane filters and characterization of its hydrophilic nature by thin layer wicking approach

Contact angle measurement of porous ceramics is difficult by goniometry application and it is impossible to determine where the water drops are immediately absorbed by the filter pores if the porous sample is of capillary type. The dynamic wicking approach is a potential technique for the contact angle measurement of capillary materials. In this study, different microstructures of glassy membrane filters were prepared and the water contact angle was determined by using thin layer wicking approach. The success of wicking results was examined. The glassy filters were shaped by two techniques (slip casting and pressing) and they were sintered at different temperatures (900, 950, 1000 and 1050 °C). Results indicated that both the shaping techniques and sintering temperature produced different microstructures and the contact angles obtained by the wicking approach were consistent with the hydrophilic nature of the filter materials. Low temperature sintering did not produce a sufficiently good glassy dispersion and high temperature led to crystallization. The best glassy filter was obtained at moderate temperatures: the sintering temperature being at 900 °C and 1000 °C for the material shaped by pressing and slip casting, respectively. At these temperatures, the glassy pore wall microstructure without crystallization could be obtained. The wicking results have been correlated with the hydrophilic nature of the filters so that the measured water contact angle was equal to or lower than 11°. Normally, the crystallization of the glassy material decreases the hydrophilic nature of the filters and the obtained wicking results are consistent with the phenomena and indicated higher contact angles.     

Syntheses and self-assembly of novel polyurethane–itaconic acid copolymer hydrogels

Novel physically crosslinked polyurethane–itaconic acid (PU–I) copolymer hydrogels were synthesized by the macroiniferter-controlled radical polymerization method. The structures of the PU–I copolymer hydrogels were characterized by ¹H NMR, FTIR, GPC, and DSC. The water contact angles and self-assembly of the PU–I copolymer hydrogels have been investigated. The results revealed that PU–I copolymer hydrogels have good hydrophilicity, so the water contact angles of polyurethane could be easily adjusted by controlling the content of the hydrophilic vinyl monomers. The PU–I copolymer hydrogels were subjected to solvent-induced self-assembly in THF + water to construct a variety of morphologies. The morphology of the PU–I copolymer hydrogels’ self-assembly was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the mechanism of self-assembly was investigated.     

Effect of sputtering parameters on the self-cleaning properties of amorphous titanium dioxide thin films

The aim of this work was to assess the effect of the direct current magnetron sputtering parameters on the photocatalytic activity and photoinduced wettability of amorphous TiO₂ films. TiO₂ films were deposited on glass using the direct current magnetron sputtering technique, without heating, at different total working pressures. Qualitative analysis using in situ X-ray photoelectron spectroscopy confirmed the TiO₂ stoichiometry of the deposited films. Surface structure was studied as a function of working pressure using scanning electron microscopy. The hydrophilicity of the TiO₂ surfaces was investigated macroscopically using measurements of the water contact angle. A threshold working pressure was observed, with a strong dependence on the film thickness. A super hydrophilic surface was observed after less than 1 h of UV irradiation. The photocatalytic activity of the films was evaluated under UV light through the degradation of methylene blue (\(\lambda_{\hbox{max} } \approx 660\;{\text{nm}}\)). The effect of UV irradiation on the photocatalytic activity was rapid, strong, and dependent on film thickness and total working pressure. Fifty percent of organic compounds were photodegraded by films with a thickness of 60 nm deposited at 10 mTorr.     

Electrochemical synthesis and characterization of poly(aniline-co-1-amino-9,10-anthraquinone), a nanosized conducting copolymer

The electrochemical copolymerization of aniline (ANI) with 1-amino-9,10-anthraquinone (1-AAQ) was carried out in 4 M sulfuric acid by potential cycling in the potential range of −0.1 V to 1.3 V vs. SCE. Copolymer films were grown from different feed ratios of ANI and 1-AAQ (0.2:0.8, 0.4:0.6, 0.5:0.5, 0.6:0.4, 0.8:0.2) on a glassy carbon electrode (GCE). Studies on the effect of scan rate on the conductivity of the copolymer film confirmed the formation of a stable conducting copolymer film. The FTIR spectrum recorded for the copolymer film provides concrete evidence of copolymer formation, since it indicates the presence of quinone units in the copolymer backbone. XRD data (particle size: 47 nm) and SEM (grain size: 100 nm) micrographs provide a clear picture of the nano-sized polymeric particles formed. It is envisaged that the newly reported copolymer could be a useful material for performing the catalytic reduction of oxygen in an acidic medium—a useful process for fuel cell applications.     

A facile approach to the fabrication of ultrathin polymer films and application to optical lenses

A facile approach to the fabrication of ultrathin polymer films on a flat or curved substrate is presented. Polymers with unsaturated pendant groups were spin-coated on a photoinitiator tethered surface, which was then photoirradiated and washed with a solvent. The obtained films were uniform, smooth (R_a < 0.2 nm) and exhibited robustness toward solvents. The thickness of the films was determined by the molecular weight of the coated polymer and was not dependent on the initial spin-coated thickness. A mechanism for the formation of the ultrathin film and application to optical lenses is presented.     

Phenylboronic acid as a sugar- and pH-responsive trigger to tune the multiple micellization of thermo-responsive block copolymer

Phenylboronic acid-containing thermo-responsive block copolymer, poly(ethylene oxide)-b-poly(methoxydi(ethylene glycol) methacrylate-co- aminophenylboronic acid ethyl methacrylate) (PEO-b-P(DEGMMA-co-PBAMA)), was employed to investigate the multiple micellization and dissociation transitions. The unique sugar- and pH-responsive properties of phenylboronic acid were interesting to provide two parallel approaches to tune the critical micellization temperature (CMT) and multiple micellization of thermo-responsive block copolymer. The block copolymers were molecularly soluble below 21 °C and underwent micellization above 21 °C at pH 8.7. After glucose was added at 24 °C, hydrophobic phenylboronic acid was changed to hydrophilic boronate-glucose complex and the CMT of the thermo-sensitive block was increased which caused the dissociation of micelles. In parallel, if the solution pH was increased from 8.7 to 11 at 25 °C, micelles were disrupted because of the formation of hydrophilic phenylboronate anion, which elevated the CMT of the thermo-sensitive block polymer. The introduction of phenylboronic acid groups into the thermo-responsive block copolymers provides a novel approach to tune the multiple micellization and dissociation transitions that might have great potentials in biomedical applications.     

Capillarity and water repellency of fabrics

A method of determining the contact angle of wetting of fibres in the capillaries of fabrics is proposed. A theoretical calculation of the angles of wetting of cotton and blended fabric fibres with water was performed in the condition of formation of a uniform hydrocarbon film on the surface of the fibres. The real contact angles of wetting of water-repellent fabrics were determined; they differ from the angles of wetting of uniform hydrocarbon films by 10-12% due to the presence of hydrophilic molecules of the emulsifiers in the modifying film.