Thermodynamic studies on thin liquid films. III: Miscibility in adsorbed films at film interfaces

Thermodynamic treatment of surfactant mixture was developed for the adsorption at interfaces of thin liquid films and applied to the study of the foam film stabilized by decyl methyl sulfoxide (DeMS) in the presence of NaCl. The total surface density of NaCl and DeMS and the mole fraction of DeMS in the adsorbed film at the film surface were numerically evaluated by applying thermodynamic equations to the film tension as a function of the total molality of NaCl and DeMS and the mole fraction of DeMS in the mixture. Miscibility of NaCl and DeMS at the film surface was clarified by a phase diagram of adsorption and compared with that at the meniscus adjacent to the foam film. Judging from a phase diagram of phase transition, the transition in the DeMS foam film between common black and Newton black films, observed in part II, is a negative azeotropic transformation caused by the attractive interaction between the head group of DeMS molecule and Na⁺ or Cl^– in the adsorbed film.     

Surfactant in the gaseous phase I. Formation of foams and thin liquid films

A new possibility of obtaining foams and single thin liquid films by supplying a surfactant through the gaseous phase is presented. Argon saturated with vapors ofn-amyl orn-decyl alcohol was passed through the water phase and formation of the foam was measured as a function of time, gas flow rate, and volume of the water phase. Formation and properties of microscopic thin liquid films were measured as a function of the time of their contact with the surfactant vapors. Two possible mechanisms of foam formation by supplying surfactant via the gaseous phase are discussed. A theoretical model of surfactant dissolution is presented and its predictions are compared with the experimental results. It is shown that foam formation resulted mainly from dissolution of the surfactant vapors in the water phase.     

Measurements of the viscosity of thin fluid films between two surfaces with and without adsorbed polymers

A new method has recently been introduced for making detailed measurements of hydrodynamic effects in very thin liquid films between two surfaces. The method is used to obtain viscosity profiles, i. e. the viscosity as a function of the separation, between surfaces with adsorbed polymer layers. Results are presented for pure cyclohexane between two mica surfaces and for polystyrene (M _w=9×10⁵) adsorbed onto mica from cyclohexane at 26°C (i. e. below the-temperature of 34.5°C). The range of distances over which the concept of an effective hydrodynamic layer is applicable is established, and a simple correspondence is found between the effective hydrodynamic thickness, the radius of gyration of the polymer and the range of the steric force between the two polymer-covered surfaces. Further experimental evidence is presented which suggests that, depending on the solvent conditions, similar correlations apply more generally to other polymer systems.     

Surfactant in the gaseous phase II. Influence on stability of foams and thin liquid films

The influence of the vapors ofn-amyl orn-decyl alcohol on the stability of single thin liquid films, single bubbles, and foam columns was determined. It was found that the presence of surfactant vapors lowered the stability of foams and single foam films. The mechanism of the destabilizing action of the surfactant vapors on wet, dynamic foams under dynamic conditions is discussed. It is shown that the destabilizing action of the surfactant vapors is a further indication that surface elasticity forces are the main factor determining stability of wet, dynamic foams.     

Coating lysozyme molecularly imprinted thin films on the surface of microspheres in aqueous solutions

The polymerization of 3‐aminophenylboronic acid in an aqueous environment was used for the first time to modify polystyrene microspheres for protein (lysozyme) molecular imprinting. Polystyrene microspheres were prepared by styrene polymerization in an aqueous emulsion with poly(vinyl alcohol) as a surfactant. Poly(3‐aminophenylboronic acid) was then grafted onto the surface of the polystyrene microspheres through oxidation by ammonium persulfate in an aqueous solution in the presence or absence of lysozyme or hemoglobin. Rebinding experiments were conducted to establish the equilibrium time and to detect the specific binding capacity and selective recognition. The results indicated that the microspheres, imprinted by the template protein lysozyme or hemoglobin, possessed specific recognition sites on the shells and had a high specific binding capacity for template proteins. The imprinted particles did not need to be ground or sieved and could easily reach the adsorption equilibrium, thus avoiding some problems of the bulk polymer. All these results demonstrate that the particles have potential applications as substitutes for bulk polymers in biological macromolecular affinity studies. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1911–1919, 2007     

Summary of development of the theory of stability of colloids and thin films

In this review, the research of the author in the field of colloidal systems is summarized. The factors influencing colloidal stability are systematized and analyzed. Examples are presented to illustrate the practical utilization of the theory of stability of colloids and thin films.This review was prepared on the basis of the works of the author, which were awarded the State Premium for 1991 in the field of science and technology, chemistry section.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1708–1717, August, 1992.     

Surface-enhanced Raman scattering characteristics of 4-nitrobenzenethiol adsorbed on palladium and silver thin films

Palladium is an important catalytic metal, and it is desirable to develop a surface-enhanced Raman scattering (SERS) technique to investigate the reagent and product species adsorbed on its surface. Unfortunately, Pt-group metals, e.g., Pt and Pd, have been commonly considered as non- or weak-SERS-active substrates. In this work, Ag and Pd thin films were deposited very efficiently and evenly onto the surface of glass substrates by using only corresponding metal nitrate salts (AgNO₃ and Pd(NO₃)₂) with butylamine in ethanolic solutions. In this process, pure ethanol was used for Ag deposition, while an ethanol–water (8:2) mixture was used for Pd deposition. The as-prepared Ag and Pd films exhibited SERS activity over a large area. The surface-induced photoconversion capabilities of these Ag and Pd films were then tested on 4-nitrobenzenethiol by means of SERS. It was found that at least under visible laser irradiation, the surface-catalyzed photoreaction occurs more readily on a Ag film than on a Pd film for the conversion of 4-nitrobenzenethiol to 4-aminobenzenethiol, even though Pd is known to be an important transition metal with high catalytic activity.     

Performance of the diffusive gradients in thin films technique for measuring Ca and Mg in freshwater

Measurements of the major cations Ca and Mg by the technique of diffusive gradients in thin films (DGTs) were systematically evaluated. The concentration in solution was calculated using Fick’s first law of diffusion from the directly measured flux to the DGT device. A selective cation exchange resin (Bio-Rad Chelex^®100), which has been used extensively with DGT for trace metals, such as Cd²⁺, Cu²⁺ and Ni²⁺, was used for this work.

Elution of Ca and Mg from the resin with 1 M HNO₃ was very reproducible. Measurements of Ca and Mg concentrations in synthetic solutions agreed well with the theoretical predictions. The negative response on uptake caused by lowered pH was investigated. Uptake was found to decline below pH 5. The capacity of the DGT device for Ca and Mg was also investigated to establish maximum deployment times for given concentrations.

Experiments with filtered and modified lake water show that DGT can be used to measure Ca and Mg when trace metals are present in the solution. An in situ deployment of DGT combined with an ultrafiltration study suggest that the Mg concentration measured by DGT is similar to the concentration found in the fraction <1 kDa.     

Chain orientation and anisotropies in optical and dielectric properties in thin films of stiff polyimides

Thin films of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the precursor poly(amic acid) on substrates, have been investigated by optical waveguide, ultraviolet-visible (UV-VIS), infrared (IR), and dielectric spectroscopies. The polyimide films exhibit an extraordinarily large anisotropy in the refractive indices with the in-plane index n_∥ = 1.806 and the out-of-plane index n_⊥ = 1.589 at 1064 nm wavelength. No discernible effect of the film thickness on this optical anisotropy is found between films of ca. 2.1 and ca. 7.8 μm thickness. This large birefringence is attributed to the preferential orientation of the biphenyltetracarboximide moieties with their planes parallel to the film surface, coupled with the strong preference of BPDA-PDA chains to align along the film plane. The frequency dispersion of the in-plane refractive index n_∥ is consistent with the results calculated by the Lorentz–Lorenz equation from the UV-visible spectrum exhibiting several absorption bands in the 170–500 nm region. The contribution from the IR absorption in the range 7000–400 cm,^?1 computed by the Spitzer-Kleinmann dispersion relations from the measured spectra, adds ca. 0.046 to the in-plane refractive index n_∥. Tilt-angle–dependent polarized IR results indicate nearly the same increase for the out-of-plane index n_⊥. Application of the Maxwell relation then leads to the out-of-plane dielectric constant ε^⊥ ? 2.7 at 1.2 × 10¹³ Hz, as compared with the measured value of ca. 3.0 at 10⁶ Hz. Assuming this small difference to remain the same for the in-plane dielectric constants ε_∥, we obtain a very large anisotropy in the dielectric properties of these polyimide films with the estimated in-plane dielectric constant ε_∥ ? 3.4 at 1.2 × 10¹³ Hz, and ε_∥ ? 3.7 at 10⁶ Hz. © 1992 John Wiley & Sons, Inc.     

Diffusion characteristics of agarose hydrogel used in diffusive gradients in thin films for measurements of cations and anions

The agarose hydrogel has been increasingly used as a diffusive layer in diffusive gradients in thin films (DGT) measurements. However its diffusive characteristics have not been examined in detail. In this study, the performance of agarose gel was tested in DGT measurements of eight cations (Fe(II), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Pb(II), and Cd(II)) and eight anions (P(V), As(V), Cr(VI), Mo(VI), Sb(V), Se(VI), V(V), and W(VI)). It was found that the thickness of agarose, a key parameter in the calculation of DGT measured concentration, remained unchanged after hydration followed by storage under the following conditions: pH 2–11, ionic strength 0–1.0 M, temperature 4–40 °C, and with the storage time extending to 300 d. Enrichment of cations and repelling of anions were observed in the gel under the ionic strengths of < 2–3 mM and <1 mM (NaNO₃), respectively, which was attributed to the electrostatic interactions of these ions with the fixed negatively charged groups (mainly pyruvate) in the gel. The diffusion coefficients of cations and anions through the agarose gel (plus a PVDF filter membrane) were on average 1.10 ± 0.04 times of the reported diffusion coefficients through the agarose cross-linked polyacrylamide (APA) hydrogel, typically used in DGT technique. The working pH ranges for the agarose gel-assembled DGTs were 4–10 and 5–9 for anions and cations, respectively. The use of agarose gel, either individually or along with different filter membranes, affected the overall diffusion rates of cations and anions. The measured DGT concentrations of cations and anions in filtered natural freshwater and seawater were mostly in line with those measured directly. The results showed that the agarose gel can be used as one of the standard diffusive layers in DGT measurements for a wide range of inorganic and organic analytes.     

Mechanism and kinetics of ordering in diblock copolymer thin films on chemically nanopatterned substrates

Lamellae forming diblock copolymer domains can be directed to assemble without defects and in registration with chemically nanopatterned substrates. Initially, thin films of the lamellar poly(styrene-b-methyl methacrylate) block copolymer form hexagonally close-packed styrene domains when annealed on chemical nanopatterned striped surfaces. These styrene domains then coalesce to form linear styrene domains that are not fully registered with the underlying chemical surface pattern. Defects coarsen, until defect-free directed assembly is obtained, by breaking linear styrene domains and reforming new structures until registered lamellae have been formed. At all stages in the process, two factors play an important role in the observed degree of registration of the block copolymer domains as a function of annealing time: the interfacial energy between the blocks of the copolymer and the chemically nanopatterned substrate and the commensurability of the bulk repeat period of the block copolymer and the substrate pattern period. Insight into the time-dependent three-dimensional behavior of the block copolymer structures is gained from single chain in mean field simulations. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3444–3459, 2005     

Kinetics of photocatalytic degradation of gaseous p-xylene on UiO-66-NH2 and LaFeO3 thin films under combined illumination of ultraviolet and visible lights

The thin film photocatalysts were prepared from solvothermal UiO-66-NH₂ and sol-gel perovskite LaFeO₃ by a dip-coating technique. The properties of obtained catalysts were investigated by the methods of Brunauer-Emmett-Teller adsorption, XRD, SEM, FT-IR, TGA, and UV-vis spectroscopies. The results proved that the thin film of the thickness of 4.2 and 4.7 µm was successfully prepared from micro-mesoporous UiO-66-NH₂ and LaFeO₃ nanocrystals. Possessing small crystals (9-35 nm) and the band gap energy of 2.83 and 1.92 eV, respectively, UiO-66-NH₂ and LaFeO₃ are shown to be a highly active visible-light photocatalyst for photodegradation of p-xylene-contained gas. The kinetics of photocatalytic degradation of p-xylene under combined illumination of ultraviolet and visible lights over obtained UiO-66-NH₂ and LaFeO₃ thin films were carried out in a gradientless flow circulating system at room temperature and atmospheric pressure. The results showed that the Langmuir-Hinshelwood kinetic model was successfully applied to correlate the obtained data. The kinetics of the reaction on both catalysts were found to be written by the fractional equation, describing the dependence of the reaction rate on the concentration of p-xylene, oxygen molecules, dissociative adsorbed water vapor, the photon flux, and the inhibition of CO₂ product. It implies that the reaction occurred at high surface coverages, molecular p-xylene, and oxygen participated in the reaction in the form of surface molecular; water—in the forms of ^•OH and H⁺. Although there is a general kinetic equation for reaction on various catalysts, the different affinities of the catalysts with the compounds present in the reaction create the kinetic feature of the reaction on each catalyst. Because of the high affinity of catalysts with water vapor, the given reactant increased the rate of p-xylene photocatalytic degradation at low concentration but inhibited it in the high concentration region. The adsorption affinity of LaFeO₃ to oxygen is higher compared to UiO-66-NH₂; then, there was an optimum concentration of oxygen in the photodegradation of p-xylene on the former, whereas in the latter monotonically increasing relationship was found.     

Vertical confinement and interface effects on the microstructure and charge transport of P3HT thin films

Using X-ray diffraction-based pole figures, we present quantitative analysis of the microstructure of poly(3-hexylthiophene) thin films of varying thicknesses, which allows us to determine the crystallinity and microstructure at the semiconductor-dielectric interface. We find that the interface is approximately one fourth as crystalline as the bulk of the material. Furthermore, the use of a self-assembled monolayer (SAM) enhances the density of interface-nucleated crystallites by a factor of ∼20. Charge transport measurements as a function of film thickness correlate with interface crystallinity. Hence, we establish the crucial role of SAMs as nucleating agents for increasing carrier mobility in field-effect devices. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Impact of chain architecture (branching) on the thermal and mechanical behavior of polystyrene thin films

The modulus and glass transition temperature (T_g) of ultrathin films of polystyrene (PS) with different branching architectures are examined via surface wrinkling and the discontinuity in the thermal expansion as determined from spectroscopic ellipsometry, respectively. Branching of the PS is systematically varied using multifunctional monomers to create comb, centipede, and star architectures with similar molecular masses. The bulk‐like (thick film) T_g for these polymers is 103 ± 2 °C and independent of branching and all films thinner than 40 nm exhibit reductions in T_g. There are subtle differences between the architectures with reductions in T_g for linear (25 °C), centipede (40 °C), comb (9 °C), and 4 armed star (9 °C) PS for ≈ 5 nm films. Interestingly, the room temperature modulus of the thick films is dependent upon the chain architecture with the star and comb polymers being the most compliant (≈2 GPa) whereas the centipede PS is most rigid (≈4 GPa). The comb PS exhibits no thickness dependence in moduli, whereas all other PS architectures examined show a decrease in modulus as the film thickness is decreased below ～40 nm. We hypothesize that the chain conformation leads to the apparent susceptibility of the polymer to reductions in moduli in thin films. These results provide insight into potential origins for thickness dependent properties of polymer thin films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Determination of the optical constants of solar‐control amorphous silicon thin films on float glass

An improved method employing a modified Forouhi and Bloomer disperse model with a hybridized simulated annealing algorithm is implemented in this paper, allowing the determination of refractive index, extinction coefficient, and thickness of a‐Si films at one time by fitting reflectance and transmitted spectra. The thickness of films obtained by this method has a reasonable agreement with the result by ellipsometric measurement, especially for samples with thickness in the range of 40–80 nm. The presented method exhibits low time consumption and cost, which implies a possibility of usage in real‐time on‐line measurement of solar‐control coatings on float glass. Copyright © 2009 John Wiley & Sons, Ltd.     

Annealing effect on the structural and magnetic properties of nickel ferrite thin films

Nickel ferrite is a soft magnetic material with inverse spinel structure. Soft ferrite films are used in microwave devices, integrated planar circuits, etc., because of their high resistivity. In this work, thin films of nickel ferrite were deposited on Si (100) substrate by using pulsed laser deposition (PLD) technique. The thickness of the film was measured by surface profilometer and also by X‐ray reflectivity (XRR). The films were annealed at three different temperatures to observe the effect on the structural and magnetic properties of the film. The films were characterised by X‐ray diffraction (XRD), Raman spectroscopy and vibrating sample magnetometer (VSM) to study the structural and magnetic properties. Copyright © 2010 John Wiley & Sons, Ltd.     

Growth and SIMS study of d.c.‐sputtered indium oxide films on silicon

Indium oxide thin films were grown onto Si and quartz substrates by d.c. reactive sputtering of elemental indium. X‐ray diffraction and transmission electron microscopy studies confirmed the single‐phase and polycrystalline nature of the films. Secondary ion mass spectrometry investigations of In₂O₃/Si structures showed the formation of an inhomogeneous interface region ～20 nm thick between In₂O₃ and Si. The overall feature of the interface remained the same under annealing in an oxygen atmosphere, but annealing in an argon atmosphere drastically altered the nature of the interface. The observations indicate that interface formation and stability depend critically on the availability of oxygen. Copyright © 2005 John Wiley & Sons, Ltd.     

The effect of different substrate temperatures on the structure and luminescence properties of Y2O3:Bi3+ thin films

Y₂O₃:Bi³⁺ phosphor thin films were prepared by pulsed laser deposition in the presence of oxygen (O₂) gas. The microstructure and photoluminescence (PL) of these films were found to be highly dependent on the substrate temperature. X-ray diffraction analysis showed that the Y₂O₃:Bi³⁺ films transformed from amorphous to cubic and monoclinic phases when the substrate temperature was increased up to 600 °C. At the higher substrate temperature of 600 °C, the cubic phase became dominant. The crystallinity of the thin films, therefore, increased with increasing substrate temperatures. Surface morphology results obtained by atomic force microscopy showed a decrease in the surface roughness with an increase in substrate temperature. The increase in the PL intensities was attributed to the crystallinity improvement and surface roughness decrease. The main PL emission peak position of the thin films prepared at substrate temperatures of 450 °C and 600 °C showed a shift to shorter wavelengths of 460 and 480 nm respectively, if compared to the main PL peak position of the powder at 495 nm. The shift was attributed to a different Bi³⁺ ion environment in the monoclinic and cubic phases.     

Preparation and characterization of nanostructured thin films of Au and Ag nanoparticles synthesized by ascorbic acid on modified glass surface

Immobilization of Ag and Au nanoparticles (NPs) synthesized by ascorbic acid on chemically modified glass surface has been studied. 3‐[2‐(2‐Aminoethylamino)ethylamino]propyl‐trimethoxysilane (AMPTS), N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilan, and 3‐trimethoxysilyl‐1‐propanethiol (MSPT) were used as surface modifying agents. To improve immobilization efficiency, the ammonia solution has been used along with the silane reagents, which assisted to adsorb the metal NPs on glass surface. It was found that AMPTS and MSPT have considerable effect on deposition of Ag and AuNPs on glass substrate. The fabricated thin films were characterized by using UV‐Vis spectroscopy, atomic force microscopy, energy‐dispersive X‐ray spectroscopy and subjected to antimicrobial resistance test. The UV–Vis spectra show a distinctive plasmon resonance absorbance peak for thin films of Au and AgNPs prepared with MSPT and AMPTS, respectively. Atomic force microscopy images indicate that formation of Au and AgNPs with spherical morphology after immobilization on the glass substrate and also the dimensions of NPs on the surface appear larger than those observed in the parent colloidal solution. Energy‐dispersive X‐ray spectroscopy measurements confirmed the presence of silver and gold on the modified glass surface, and elemental composition was measured. The Au and AgNPs thin films show antibacterial activity against gram negative (Escherichia coli) and gram positive (Staphylococcus aureus) bacteria in comparison with a blank sample. Copyright © 2015 John Wiley & Sons, Ltd.