Thermally stable antireflective coatings based on nanoporous organosilicate thin films

Thermally stable nanoporous organosilicate thin films were realized by the microphase separation of pore-generating polymers mixed with an organosilicate matrix to be antireflective coatings (ARCs), for which a thin film with a refractive index (n) of 1.23 for zero reflection is required. The refractive index of such nanoporous organosilicate films can be tuned from 1.39 down to 1.23 by incorporating nanopores within the films. With a nanoporous single layer with n approximately 1.23, the light transmittance of the glass above 99.8% was achieved in the visible range (lambda approximately 550 nm). To overcome the limitation on the narrow wavelength for high transmittance imposed by a single antireflective nanoporous thin film, bilayer thin films with different refractive indices were prepared by placing a high refractive index layer with a refractive index of 1.45 below the nanoporous thin film. UV-vis transmittance of a glass coated with the bilayer films was compared with nanoporous single-layer films and it is demonstrated that the novel broadband antireflection coatings in a wide range of visible wavelength can be easily obtained by the organosilicate bilayer thin films described in this study. Also, ARCs developed in this study demonstrate excellent AR durability owing to the hydrophobic nature of the organosilicate matrix.     

Nanoporous block copolymer micelle/micelle multilayer films with dual optical properties

We introduce a novel and versatile approach for preparing self-assembled nanoporous multilayered films with tunable optical properties. Protonated polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and anionic polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films. BCM film growth is governed by electrostatic and hydrogen-bonding interactions between the opposite BCMs. Both film porosity and film thickness are dependent upon the charge density of the micelles, with the porosity of the film controlled by the solution pH and the molecular weight (M(w)) of the constituents. PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films prepared at pH 4 (for PS(7K)-b-P4VP(28K)) and pH 6 (for PS(2K)-b-PAA(8K)) are highly nanoporous and antireflective. In contrast, PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K) films assembled at pH 4/4 show a relatively dense surface morphology due to the decreased charge density of PS(2K)-b-PAA(8K). Films formed from BCMs with increased PS block and decreased hydrophilic block (P4VP or PAA) size (e.g., PS(36K)-b-P4VP(12K)/PS(16K)-b-PAA(4K) at pH 4/4) were also nanoporous. This is attributed to a decrease in interdigitation between the adjacent corona shells of the low M(w) BCMs, thus creating more void space between the micelles. Multilayer films with antireflective and photochromic properties were obtained by incorporating a water-insoluble photochromic dye (spiropyran) into the hydrophobic PS core of the BCMs assembled in the films. The optical properties of these films can be modulated by UV irradiation to selectively and reversibly control the transmission of light. Light transmission of higher than 99% was observed with accompanying photochromism in the (PS(7K)-b-P4VP(28K)/PS(2K)-b-PAA(8K)) multilayer films assembled at pH 4/6. Our approach highlights the potential to incorporate a range of materials, ranging from conventional hydrophilic materials with specific interactions to hydrophobic compounds, into the assembled BCMs to yield multifunctional nanoporous films.     

pH-Induced antireflection coatings derived from hydrogen-bonding-directed multilayer films

Hydrogen-bonding-directed layer-by-layer assembled films, based on polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymer micelles and poly(4-vinylpyridine) (P4VP), were successfully fabricated in methanol. Varying the PAA content in the PS-b-PAA micelles afforded control over the film growth properties, especially the multilayer film thickness. Interestingly, antireflection films with refractive indices that could be tuned between 1.58 and 1.28 were obtained by treatment with an aqueous HCl solution (pH 2.27), and the transmittance obtained was as high as 98.4%. In acid solution, the pyridine group was protonated, destroying the hydrogen bonding between P4VP and PAA. A concomitant pH-induced polymer reorganization in the multilayers resulted in a porous honeycomb-like texture on the substrate.     

Nanoporosity-driven superhydrophilicity: a means to create multifunctional antifogging coatings

Multifunctional nanoporous thin films have been fabricated from layer-by-layer assembled silica nanoparticles and a polycation. The resultant multilayer films were found to exhibit both antifogging and antireflection properties. The antifogging properties are a direct result of the development of superhydrophilic wetting characteristics (water droplet contact angle <5 degrees within 0.5 s or less). The nearly instantaneous sheetlike wetting promoted by the superhydrophilic multilayer prevents light scattering water droplets from forming on a surface. The low refractive index of the multilayer film (as low as 1.22) resulting from the presence of nanopores was found to impart excellent antireflection properties. Glass slides coated on both sides with a nanoporous multilayer film exhibited transmission levels as high as 99.8%. Stable superhydrophilic wetting characteristics were obtained only after a critical number of bilayers were deposited onto a surface. The assembly conditions (solution pH and nanoparticle concentration), as well as the choice of nanoparticle size, were found to strongly influence film properties. It is suggested that the superhydrophilic behavior is driven by the rapid infiltration of water into a 3D nanoporous network created under specific assembly conditions.     

Intelligent reversible nanoporous antireflection film by solvent-stimuli-responsive phase transformation of amphiphilic block copolymer

An erasure-reconstruction porous structure with reversible antireflection (AR) property at near-infrared region (NIR) was prepared for the first time based on solvent-stimuli-responsive phase transformation of polystyrene-block-poly(4-vinypyridine) (PS-b-P4VP). The inhomogeneous porous structure with a dense skin and porous underneath, which was obtained by the nonsolvent-induced phase separation of PS-b-P4VP film from micelle solution with mixed solvents (tetrahydrofuran and dimethylformamide), was used as starting porous film. Then, the film was annealed by PS-selective solvent to erase the nanopores because the PS block was swollen effectively by its selective solvent. Afterward, the nonporous film was immersed in linear aliphatic acid to reconstruct the nanoporous structure (loosely packed micelles) by the combination of the hydrogen bond interaction and the positively charge-induced repulsion between each chain. Thus, an intelligent reversible AR property in the NIR region between a high-transmittance porous state (～99.0%) and a low-transmittance nonporous state (～90.0%) was realized by alternate treatments of PS-selective solvent and linear aliphatic acids. This reversible erasure-reconstruction porous structure for switching between AR (98.0%) and non-AR (90.0%) properties could be recycled by at least four times.     

Graftlike interpolymer complexes from poly(2‐vinylpyridine) and end‐sulfonic acid polystyrene and polyisoprene: Intermediates to noncovalently bonded block copolymer‐like micelles

The complexation between narrow molecular weight distribution poly(2‐vinylpyridine) (P2VP) and polystyrene (suPS) or polyisoprene (suPI) end‐functionalized with one sulfonic acid group was examined in tetrahydrofuran dilute solutions by a combination of static and dynamic laser light scattering. Both apparent weight‐average molecular weight (M_w,app) and hydrodynamic radius (R_h) of the complexes exhibited a maximum at a certain molar ratio of suPS chains to P2VP monomeric units. This indicated that the P2VP backbone may be saturated by the grafted end‐functionalized chains because of repulsion between the grafted chains. By changing the molar mass of P2VP from 100,000 to 30,000 g/mol, the values of M_w,app and R_h decreased. When suPI was used instead of suPS, similar trends were observed. In the latter case, it was possible to prepare block copolymer‐like micelles by transferring the P2VP/suPI blend solutions in decane, which is a selective solvent for PI. The non‐covalent‐bonded polymeric micelle characteristics were investigated as a function of sulfonic acid/2‐vinylpyridine units ratio as well as temperature. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2454–2461, 2003     

Hierarchical Nanoporous Structures by Self‐Assembled Hybrid Materials Based on Block Copolymers

Hierarchical nanoporous structures are fabricated by adsorption of micelles of diblock copolymer‐templated Au‐nanoparticles onto a hydrophilic solid substrate. Gold nanoparticles are prepared using micelles (19 nm) of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) as nanoreactors. Deposition of thin films of the micellar solution, modified with a non‐selective solvent (THF), on hydrophilic surfaces leads to the formation of hierarchical nanoporous morphologies. The thin films exhibit two different pore diameters and a total pore density of 15 × 10⁸ holes per cm². The structure was analyzed in terms of topography and chemical composition using AFM, TEM and XPS measurements. The PS‐b‐P4VP template was subsequently removed by oxygen plasma etching, to leave behind metallic nanopores that mimic the original thin film morphology.

     

Investigation of Electrochemical Copolymerization of 1‐Naphthylamineaniline in the Presence of Various Organic Sulfonic Acids

The electrochemical and electro activity properties of poly(aniline‐co‐1‐naphthylamine) thin films have been investigated in the presence of various organic sulfonic acids. Homo and copolymer thin films are synthesized electrochemically, under cyclic voltammetric conditions in aqueous solution of organic sulfonic acids (1 M), viz p‐toluene‐sulfonic acid (P‐TSA), methane‐sulfonic acid (MSA), 5‐sulfosalicylic acid (5‐SSA), camphor‐sulfonic acid (CSA) and dodecylbenzene‐sulfonic acid (DBSA) (0.25 M) on glass carbon (GC) electrode at room temperature. The cyclic voltammograms (CVs) show that the current densities are strongly influenced by the size and acidity of the organic acids which are present in electrolyte. Electocopolymerization was carried out at different ratios of NPA to ANI (0.07, 0.05, 0.03, 0.02, 0.014). The formation of copolymer was proved by cyclic voltammogram study.     

One-step route to the fabrication of highly porous polyaniline nanofiber films by using PS-b-PVP diblock copolymers as templates

We report a new method to control both the nucleation and growth of highly porous polyaniline (PANI) nanofiber films using porous poly(styrene-block-2-vinylpyridine) diblock copolymer (PS-b-P2VP) films as templates. A micellar thin film composed of P2VP spheres within a PS matrix is prepared by spin coating a PS-b-P2VP micellar solution onto substrates. The P2VP domains are swollen in a selective solvent of acetic acid, which results in the formation of pores in the block copolymer film. PANI is then deposited onto the substrates modified with such a porous film using electrochemical methods. During the deposition, the nucleation and growth of PANI occur only at the pores of the block copolymer film. After the continued growth of PANI by the electrochemical deposition, a porous PANI nanofiber film is obtained.     

Selective swelling induced pore generation of amphiphilic block copolymers: The role of swelling agents

Swelling of block copolymers by selective solvents has emerged as an extremely simple and efficient process to produce nanoporous materials with well‐controlled porosities. However, the role of the swelling agents in this pore‐making process remains to be elucidated. Here we investigate the evolution of morphology, thickness, and surface chemistry of thin films of polystyrene‐block‐poly (2‐vinyl pyridine) (PS‐b‐P2VP) soaked in a series of alcohols with changing carbon atoms and hydroxyl groups in their molecules. It is found that, in addition to a strong affinity to the dispersed P2VP microdomains, the swelling agents should also have a moderate swelling effect to PS to allow appropriate plastic deformation of the PS matrix. Monohydric alcohols with longer aliphatic chains exhibit stronger ability to induce the pore formation and a remarkable increase in film thickness is associated with the pore formation. High‐carbon alcohols including n‐propanol, n‐butanol, and n‐hexanol produce cylindrical micelles upon prolonged exposure for their strong affinity toward the PS matrix. In contrast, methanol and polyhydric alcohols including glycol and glycerol show very limited effect to swell the copolymer films as their affinity to the PS matrix is low; however, they also evidently induce the surface segregation of P2VP blocks. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 926–933     

Block copolymer film with sponge-like nanoporous strucutre for antireflection coating

We prepared nanoporous films by spin-coating of polystyrene-block-poly(methyl methacrylate) copolymers (PS-b-PMMA) to a glass and irradiating by ultra-violet source followed by selective removal of PMMA blocks with acetic acid. When spin-coated PS-b-PMMA was no longer annealed at high temperatures, microphase separation between two blocks occurred only in the short-range scale. The porous films prepared from PS-b-PMMA with the volume fraction of PMMA block of 0.69 exhibited a spongelike nanoporous structure over the entire film thickness and showed excellent antireflection with a minimum reflection less than 0.1% at visible and near-infrared wavelengths. The observed reflectances were in good agreement with the predictions based on the characteristic matrix theory.     

Functionalized Nanoporous Thin Films From Photocleavable Block Copolymers

A polystyrene‐block‐poly(ethylene oxide) block copolymer bearing a photocleavable junction between the blocks is used to form nanoporous thin films with carboxylic acid functions homogeneously distributed on the pore walls. The presence of the carboxylic acid groups is evidenced by fluorescence spectroscopy after their reaction with a diazomethane functionalized fluorescent dye. In addition, the initial light‐responsive thin film, acting as a photoresist, can be easily patterned to selectively generate porosity in predetermined areas. In that way, fluorescent patterns can be obtained as evidenced by fluorescent microscopy.     

Self‐organization and luminescent properties of nanostructured europium (III)–block copolymer complex thin films

We introduce a simple method to create nanosized, ordered, and highly luminescent thin film of Eu (III)–block copolymer complex. Micelles of polystyrene–block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) in P4VP‐selective solvents (ethanol/N,N‐dimethylformamide (DMF) mixture) serve as nanoreactors for the synthesis of Eu(III)–block copolymer complex with the presence of 1,10‐phenanthroline (Phen) as cooperative ligand. The resulted quaternary complexes were characterized by FT‐IR spectra, ¹⁵N NMR spectra, and elemental analysis, indicative of a composition of Eu(III)–(PS‐b‐P4VP)–Phen–5DMF. Atomic force microscopy and transmission electron microscopy investigations reveal that the Eu(III)–(PS‐b‐P4VP)–Phen–5DMF complex can self‐organize into hexagonally ordered thin films when dip‐coated from the solution onto silicon or silica glass substrates. Such ordered thin films can emit red fluorescence of Eu³⁺ with strong intensity and long lifetime. This method can be easily extended to prepare other ordered luminescent rare earth–polymer complexes thin films. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2181–2189, 2005     

Fabrication of an open Au/nanoporous film by water-in-oil emulsion-induced block copolymer micelles

Water-in-oil (W/O) emulsion-induced micelles with narrow size distributions of approximately 140 nm were prepared by sonicating the polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer in the toluene/water (50:1 vol %). The ordered nanoporous block copolymer films with the hydrophilic P2VP interior and the PS matrix were distinctly fabricated by casting the resultant solution on substrates, followed by evaporating the organic solvent and water. The porous diameter was estimated to be about 70 nm. Here, we successfully prepared the open nanoporous nanocomposites, the P2VP domain decorated by Au (5+/-0.4 nm) nanoparticles based on the methodology mentioned. We anticipate that this novelty enhances the specific function of nanoporous films.     

Block Copolymer‐Templated Approach to Nanopatterned Metal–Organic Framework Films

The fabrication of patterned metal–organic framework (MOF) films with precisely controlled nanoscale resolution has been a fundamental challenge in nanoscience and nanotechnology. In this study, nanopatterned MOF films were fabricated using a layer‐by‐layer (LBL) growth method on functional templates (such as a bicontinuous nanoporous membrane or a structure with highly long‐range‐ordered nanoscopic channels parallel to the underlying substrate) generated by the microphase separation of polystyrene‐b ‐poly(2‐vinylpyridine) (PS‐b ‐P2VP) block copolymers. HKUST‐1 can be directly deposited on the templates without any chemical modification because the pyridine groups in P2VP interact with metal ions via metal‐BCP complexes. As a result, nanopatterned HKUST‐1 films with feature sizes below 50 nm and controllable thicknesses can be fabricated by controlling the number of LBL growth cycles. The proposed fabrication method further extends the applications of MOFs in various fields.     

Immobilization of Tris-(8-hydroxyquinoline) aluminum onto P4VP polymer thin films by UV irradiation cross-linking

We report a novel method for the immobilization of Tris-(8-hydroxyquinoline) aluminum (Alq₃) onto poly(4-vinylpyridine) (P4VP) thin polymer films by UV irradiation cross-linking. The polymer films were prepared by spin-coating of P4VP onto cleaned silicon wafer surface followed by UV irradiation. The thicknesses of the polymer thin films were measured by ellipsometry with different irradiation times. The immobilization of Alq₃, orientation and the surface activity were followed using photoluminescence and UV-visible spectroscopy. The surface morphology was investigated by using field emission scanning electron microscopy and atomic force microscopy. Patterning of Alq₃ on P4VP film was obtained using photolithography technique. Our experimental results show that the cross-linked P4VP thin film is a universal surface modifier.     

Electrochemically controlled detection of adrenaline on poly(2‐aminobenzylamine) thin films by surface plasmon resonance spectroscopy and quartz crystal microbalance

In this study, we present an electrochemically controlled surface plasmon resonance (EC‐SPR) biosensor to detect adrenaline on poly(2‐aminobenzylamine) (P2ABA) thin films. The P2ABA thin films are stable and display electroactivity in a neutral PBS solution. Specific detection of adrenaline was performed on P2ABA thin films because the benzylamine groups in the P2ABA structure could specifically react with adrenalines. Adrenaline was detected in real time by EC‐SPR spectroscopy, which provides an EC‐SPR reflectivity change on the P2ABA thin film upon adrenaline injection. The measured responses were quite different from those for uric acid and ascorbic acid, which are major interferences in adrenaline detection. The electrochemically applied potential facilitates the specific detection of adrenaline. In addition, the detection of adrenaline on the P2ABA thin films was investigated by a quartz crystal microbalance technique. The detection limit for adrenaline at open circuit potential was 10 pM. The present study provides a useful information on the detection of adrenaline on the P2ABA thin films. Copyright © 2013 John Wiley & Sons, Ltd.     

The morphology and structure of PS‐b‐P4VP block copolymer films by solvent annealing: effect of the solvent parameter

Lamellae (symmetric) forming polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) block copolymers (BCPs) were used to produce nanostructured thin films by solvent (toluene) casting (spin‐coating) onto silicon substrates. As expected, strong micellization of PS‐P4VP in toluene results in poorly ordered hexagonally structures films. Following deposition the films were solvent annealed in various solvents and mixtures thereof. A range of both morphologies including micelle and microphase separated structures were observed. It was found that nanostructures typical of films of regular thickness (across the substrate) and demonstrating microphase separation occurred only for relatively few solvents and mixtures. The data demonstrate that simple models of solvent annealing based on swelling of the polymer promoting higher polymer chain mobility are not appropriate and more careful rationalization is required to understand these data. Analysis suggests that regular phase separated films can only be achieved when the copolymer Hildebrand solubility parameter is very similar to the value of the solvent. It is suggested that the solvent anneal method used is best considered as a liquid phase technique rather than a vapor phase method. The results show that solvent annealing methods can be a very powerful means to control structure and in some circumstances dominate other factors such as surface chemistry and surface energies. Copyright © 2009 John Wiley & Sons, Ltd.     

New antireflection coatings on silicate glass, deposited from a silicon dioxide sol containing a nonionogenic surfactant and an oligoether based on ethylene oxide

Transparent nanoporous thin films with low refractive index (1.23–1.25) were produced on glass substrates by application of a formulation based on a silicon dioxide sol into which two organic compounds, an oligoether based on ethylene oxide and a nonionogenic surfactant, are introduced. It is shown that the antireflection capacity of the nanoporous coating can be substantially raised at comparatively low concentrations of silicon dioxide and organic additives in the sol by making higher the rate at which the formulation is applied to the substrate.     

Temperature-triggered micellization of block copolymers on an ionic liquid surface

In situ neutron reflectivity was used to study thermally induced structural changes of the lamellae-forming polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer thin films floating on the surface of an ionic liquid (IL). The IL, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, is a nonsolvent for PS and a temperature-tunable solvent for P2VP, and, as such, micellization can be induced at the air-IL interface by changing the temperature. Transmission electron microscopy and scanning force microscopy were used to investigate the resultant morphologies of the micellar films. It was found that highly ordered nanostructures consisting of spherical micelles with a PS core surrounded by a P2VP corona were produced. In addition, bilayer films of PS homopolymer on top of a PS-b-P2VP layer also underwent micellization with increasing temperature but the micellization was strongly dependent on the thickness of the PS and PS-b-P2VP layers.