Solvatochromic studies on the hydrogen-bond donating and dipolarity/polarizability properties of the polyethylene oxide/silica interface

The polarity of the polyethylene oxide(PEO)/silica interface in 1,2-dichloroethane as solvent is classified by means of linear solvation energy (LSE) relationships . The properties of the bare silica particle surface and the silica/PEO interface is expressed by two terms: the dipolarity/polarizability (π*) of the interface and the hydrogen-bond donating ability (α) of the surface silanols. These terms can be defined by using the Kamlet–Taft solvent parameters α and π* as a reference system. The interfacial polarity parameters α and π* were calculated by means of correlation analyses of the energy of the UV/vis absorption maxima of the surface polarity indicators: di-cyano-bis(1,10-phenanthroline) iron II, bis-4,4′-(N,N-dimethylamino) benzophenone, and 2,6-diphenyl-4-(2,4,6-triphenyl-N-pyridino)phenolate when adsorbed onto the PEO/silica particle surface. The experimental values of the E _T(30) parameter of the PEO/silica interface are compared with independently calculated values employing specific LSE relations derived for well-behaved regular solvents and functionalized silicas. PEO adsorption on silica causes a decrease in the value of the α parameter of the silica surface and an evident increase in the dipolarity/polarizability of the interface. Received: 16 December 1998 Accepted in revised form: 8 January 1999     

Control of Alq3 wetting layer thickness via substrate surface functionalization

The effects of substrate surface energy and vapor deposition rate on the initial growth of porous columnar tris(8-hydroxyquinoline)aluminum (Alq3) nanostructures were investigated. Alq3 nanostructures thermally evaporated onto as-supplied Si substrates bearing an oxide were observed to form a solid wetting layer, likely caused by an interfacial energy mismatch between the substrate and Alq3. Wetting layer thickness control is important for potential optoelectronic applications. A dramatic decrease in wetting layer thickness was achieved by depositing Alq3 onto alkyltrichlorosilane-derivatized Si/oxide substrates. Similar effects were noted with increasing deposition rates. These two effects enable tailoring of the wetting layer thickness.     

Thermal and spectral properties and induction period, interfacial energy and nucleation parameters of solution grown anthracene

Anthracene crystals were grown by solution growth technique by adopting slow evaporation method from the solvents CS₂, CCl₄ and CHCl₃. The induction period was measured at various super saturations, and hence the interfacial energies were evaluated. Using the interfacial tension value, the nucleation parameters such as radius of the critical nuclei (r*), the Gibbs free energy change for the formation of a critical nucleus (?G*) and the number of molecules in the critical nucleus (i*) were also calculated for all these solvents at two different temperatures. The effect of surface tension, viscosity and density of these solvents are correlated with interfacial tension. The solution grown crystals were subjected to UV, FTIR, NMR and X-ray diffraction studies. The purity and high-thermal stability of the grown crystals were determined using thermal analysis.     

Interface tension of silica hydroxylated nanoparticle with brine: a combined experimental and molecular dynamics study

We have used molecular dynamics simulations to calculate the interfacial tension of hydroxylated SiO(2) nanoparticles under different temperatures and solutions (helium and brine with monovalent and divalent salts). In order to benchmark the atomistic model, quartz SiO(2) interfacial tension was measured based on inverse gas chromatography under He atmosphere. The experimental interfacial tension values for quartz were found between 0.512 and 0.617 N/m. Our calculated results for the interfacial tension of silica nanoparticles within helium atmosphere was 0.676 N/m, which is higher than the value found for the system containing He∕α-quartz (0.478 N/m), but it is similar to the one found for amorphous silica surface. We have also studied the interfacial tension of the nanoparticles in electrolyte aqueous solution for different types and salts concentrations (NaCl, CaCl(2), and MgCl(2)). Our calculations indicate that adsorption properties and salt solutions greatly influence the interfacial tension in an order of CaCl(2) > MgCl(2) > NaCl. This effect is due to the difference in distribution of ions in solution, which modifies the hydration and electrostatic potential of those ions near the nanoparticle.     

Hydrogen Bonds at Silica – Polyvinylpyrrolidone – Water Interfaces

The effect of the adsorption of polyvinylpyrrolidone on the surface of highly dispersed silica on the state of interfacial water was studied by ¹H NMR spectroscopy and thermally stimulated depolarization with freezing out of the bulk water.     

Preparation of mesoporous submicrometer silica capsules via an interfacial sol-gel process in inverse miniemulsion

Mesoporous silica capsules with submicrometer sizes were successfully prepared via the interfacial hydrolysis and condensation reactions of tetraethoxysilane (TEOS) in inverse miniemulsion by using hydrophilic liquid droplets as template. The inverse miniemulsions containing pH-controlled hydrophilic droplets were first prepared via sonication by using poly(ethylene-co-butylene)-b-poly(ethylene oxide) (P(E/B)-PEO) or SPAN 80 as surfactant. TEOS was directly introduced to the continuous phase of an inverse miniemulsion. The silica shell was formed by the deposition of silica on the surface of droplets. The formation of capsule morphology was confirmed by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The mesoporous structure was verified by nitrogen sorption measurements. The specific surface area could be tuned by the variation of the amount of cetyltrimethylammonium bromide (CTAB) and TEOS, and the pore size by the amount of CTAB. The influences of synthetic parameters on the particle size and morphology were investigated in terms of the amount of CTAB, pH value in the droplets, TEOS amount, surfactant amount, and type of solvent with low polarity. A formation mechanism of silica capsules was proposed.     

Micellar solutions of sulfobetaine surfactants in water-ethylene glycol mixtures: surface tension, fluorescence, spectroscopic, conductometric, and kinetic studies

Micellization in water-ethylene glycol (EG) N-dodecyl, N-tetradecyl, and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB3-12, SB3-14, and SB3-16, respectively) micellar solutions, with the weight percent of EG changing within the range 0-40, was studied by means of surface tension measurements. Information about the influence of the added EG on the aggregation number of the sulfobetaine micelles and on the polarity of the interfacial region of micelles was obtained through fluorescence and spectroscopic measurements. Surface tension measurements also provide information about the dependence of the surface excess concentration, the minimum area per surfactant molecule, the surface pressure at the cmc, and the standard Gibbs energy of adsorption on the added weight percent of the organic solvent. The Gordon parameter of the water-EG mixtures was also estimated by means of surface tension measurements. The thermodynamic and structural changes originated by the presence of EG control the micellar kinetic effects observed in the reaction methyl 4-nitrobenzenesulfonate + Br(-) occurring in the water-EG sulfobetaine micellar solutions. Information about the distribution of bromide ions between the bulk and micellar pseudophases was obtained through conductivity measurements. The kinetic micellar effects were quantitatively explained by using the pseudophase kinetic model.     

The influence of mixed cationic–anionic surfactants on the three-phase contact parameters in silica–solution systems

The formation of thin wetting films on silica surface from aqueous solution of (a) tetradecyltrimetilammonium bromide (C₁₄TAB) and (b) surfactant mixture of the cationic C₁₄TAB with the anionic sodium alkyl- (straight chain C₁₂–, C₁₄– and C₁₆–) sulfonates, was studied using the microscopic thin wetting film method developed by Platikanov. Film lifetimes, three-phase contact (TPC) expansion rates, receding contact angles and surface tension were measured. It was found that the mixed surfactants caused lower contact angles, lower rates of the thin aqueous film rupture and longer film lifetimes, as compared to the pure C₁₄TAB. This behavior was explained by the strong initial adsorption of interfacial complexes from the mixed surfactant system at the air/solution interface, followed by adsorption at the silica interface. The formation of the interfacial complexes at the air/solution interface was proved by means of the surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants controls the strength of the interfacial complex and causes synergistic lowering in the surface tension. The film rupture mechanism was explained by the heterocoagulation mechanism between the positively charged air/solution interface and the solution/silica interface, which remained negatively charged.     

Properties and structure of interfacial layers formed by hydrophilic silica dispersions and palmitic acid

The properties and structure of different types of interfacial layers obtained from aqueous dispersions of nanometric silica and palmitic acid (PA) have been studied and characterized by different diagnostics and measurements. The investigations concern PA monolayers spread on the silica dispersions, dispersions in contact with PA solutions in oil and silica dispersions containing PA, aiming at elucidating the role of the PA interaction with the particles and investigating the surface-activity of the originated silica-PA complexes. Drop shape tensiometry was utilized to measure the dynamic surface and interfacial tension while a Langmuir trough apparatus was used to obtain compression isotherms of the spread PA layers and to measure the dilational viscoelasticity according to the oscillating barrier method. Brewster angle microscopy and ellipsometry were utilized to investigate the lateral and vertical structure of the interfacial layers. From this multifold approach emerges a complex picture of the features of these interfacial layers that can be rationalized on the basis of the adsorption of PA on the particle surface. The results evidence a threshold in PA adsorption above which particles change from hydrophilic to partially hydrophobic, promoting their incorporation into the interfacial layer.     

溶剂极性对聚苯醚离聚体微乳液相反转影响的研究

以乙酰磺酸为磺化剂制备了磺化度为 3%～ 1 7% (摩尔比 )的磺化聚苯醚 (SPPO)。在一定的温度和搅拌速度下 ,加水将SPPO离聚体溶液乳化成水包油的稳定水基微乳液。用电导率、粘度、表面张力等表征了SPPO离聚体溶液在微乳化过程中的相反转 ,研究了溶剂的极性对SPPO微乳化过程相反转的影响。     

General synthesis of mesoporous spheres of metal oxides and phosphates

Monodisperse and high-surface-area mesoporous inorganic spheres of various compositions including metal oxides, mixed oxides, and metal phosphates are prepared by templating mesoporous carbon spheres which are replicated from spherical mesoporous silica. Due to the rigid and thermally stable framework of carbon template, the crystalline phases of the obtained metal oxide spheres can be readily tailored by controlling crystalline temperatures. Moreover, the sphere morphologies can be changed from solid structure to hollow structure in some cases by changing the polarity of the precursor, due to the hydrophobic nature of carbon template.     

Interactions of hydrophilic silica nanoparticles and classical surfactants at non-polar oil-water interface

The interfacial and bulk properties of submicron oil-in-water emulsions simultaneously stabilised with a conventional surfactant (either lecithin or oleylamine) and hydrophilic silica nanoparticles (Aerosil?380) were investigated and compared with emulsions stabilised by either stabiliser. Emulsions solely stabilised with lecithin or oleylamine showed poor physical stability, i.e., sedimentation and the release of pure oil was observed within 3 months storage. The formation and long-term stability of silica nanoparticle-coated emulsions was investigated as a function of the surfactant type, charge, and concentration; the oil phase polarity (Miglyol?812 versus liquid paraffin); and loading phase of nanoparticles, either oil or water. Highly stable emulsions with long-term resistance to coalescence and creaming were formulated even at low lecithin concentrations in the presence of optimum levels of silica nanoparticles. The attachment energy of silica nanoparticles at the non-polar oil-water interface in the presence of lecithin was significantly higher compared to oleylamine in line with good long-term stability of the former compared to the sedimentation and release of oil in the latter. The attachment energy of silica nanoparticles at the polar oil-water interface especially in the presence of oleylamine was up to five-times higher compared to the non-polar liquid paraffin. The interfacial layer structure of nanoparticles (close-packed layer of particle aggregates or scattered particle flocs) directly related to the free energy of nanoparticle adsorption at both MCT oil and liquid paraffin-water interfaces.     

Interfacial properties of water + alcohol mixtures

Mixtures of water with alcohol are important in numerous engineering applications. Caused by the polarity of water and alcohol self-association of water and alcohol as well cross-association between water and alcohol appear in such complex mixtures. These features show significant impact on physical and chemical properties, especially phase equilibrium behaviour and hence interfacial properties. The Cahn–Hilliard theory was combined with original statistical associated fluid theory equation of states (SAFT EOS) in order to describe both the phase behaviour and interfacial properties with respect of association. The paper focuses on theoretical investigations of surface tension, density profiles, surface thickness in vapour–liquid or vapour–liquid–liquid equilibrium of mixtures of water with ethanol or 1-butanol. Results of vapour–liquid equilibrium surface tension calculations were compared with experimental data taken from the literature.     

Effect of silicon oxidation on long-term cell selectivity of cell-patterned Au/SiO2 platforms

Cellular patterning on silicon platforms is the basis for development of integrated cell-based biosensing devices, for which long-term cell selectivity and biostability remain a major challenge. We report the development of a silicon-based platform in a metal-insulator format capable of producing uniform and biostable cell patterns with long-term cell selectivity. Substrates patterned with arrays of gold electrodes were surface-engineered such that the electrodes were activated with fibronectin to mediate cell attachment and the silicon oxide background was passivated with PEG to resist protein adsorption and cell adhesion. Three types of oxide surfaces, i.e., native oxide, dry thermally grown oxide, and wet thermally grown oxide, were produced to illustrate the effect of oxide state of the surface on long-term cell selectivity. Results indicated that the cell selectivity over time differed dramatically among three patterned platforms and the best cell selectivity was found on the dry oxide surface for up to 10 days. Surface analysis results suggested that this enhancement in cell selectivity may be related to the presence of additional, more active oxide states on the dry oxide surface supporting the stability of PEG films and effectively suppressing the cell adhesion. This research offers a new strategy for development of stable and uniform cell-patterned surfaces, which is versatile for immobilization of silane-based chemicals for preparation of biostable interfaces.     

Understanding the effect of filler shape induced immobilized rubber on the interfacial and mechanical strength of rubber composites

Styrene butadiene rubber (SBR) composites with silica, halloysite nanotubes (HNTs) and montmorillonite (MMT) were prepared and the interfacial and mechanical properties were compared to understand the reinforcing behaviours of these fillers based on the results of SEM, DSC, DMA, etc. Due to the formation of interparticle domain, HNTs immobilized more rubber approaching their surface than silica and MMT. Interestingly, only tightly immobilized rubber chains made contribution to the enhancement of interfacial and mechanical strength of SBR composites. This was because the tightly immobilized rubber acted as a bridge in the filler-rubber interface and induced the formation of stretched rubber chains linked filler network when the composites were loaded in tension, while loosely immobilized rubber were easy to slip off from filler surface, causing the separation between filler and bulk rubber. Therefore, silica with more tightly immobilized rubber approaching its surface showed better reinforcing effect on rubber than HNTs and MMT.     

高分子共混体系界面张力的研究

<正> 在高分子多相体系中,相间界面张力(γ_(12))是微区的重要控制因素,无论是Donatelli,Sperling等提出的IPN体系微区尺寸关系式,还是Tokita提出的共混体系中分散相粒径表达式,都含有界面张力因子。 然而,由于高分子体系中界面张力测定的诸多实际困难,当前在国内外非常多的研究工作中,广泛地采用了一些替代的办法,应用较多的有以表面张力差来代替界面张力的Antonow原则延伸及一些近似的计算方法,如Wu及Girifalco和Good提出的由表     

Characterization of Interfacially Active Fractions and Their Relations to Water-in-Oil Emulsion Stability.

Natural surfactants from four crude oils have been extracted by adsorption on silica after precipitation of the asphaltenes by means of centrifugation or decantation. The extracted fractions have been characterized, analytically by FT-IR spectroscopy (chemical functions) and chromatography (molecular weight and polarity) and by their interfacial properties with emulsification and interfacial tension measurements on the model system water/decane with interfacially active fractions in different concentrations. The importance of these fractions (precipitated and adsorbed) on the stability of w/o emulsions is investigated. The influence of some extraction parameters (centrifugation or decantation, different adsorbents) on the nature and the emulsion behaviour of the fractions is studied and shows that the classification of the surfactants (asphaltenes, resins) is diffuse. It also shows that all the interfacially active constituents of the crude are interacting and are involved in the interfacial processes.     

Study of the surface and interfacial tensions in systems containing a low molar mass liquid crystal

The surface tension of a low molar mass liquid crystal (LMMLC), 4-cyano-4'-n-heptyloxybiphenyl (70CB), was measured as a function of temperature using the pendant drop method, forming drops of different volumes ranging from 5 to 11 mm³. Contact angles formed by drops of 70CB in the nematic and isotropic phases on plates of polystyrene (PS) and of a liquid crystal polymer (LCP), VECTRA A910, were also measured. Only large drops could be used for surface tension analysis. It was shown that in the nematic phase the surface tension of 70CB decreases with increasing temperature, and that in the isotropic phase the surface tension increases with increasing temperature. Using the values of contact angle and of surface tension of 7OCB it was possible to evaluate the interfacial energy between 7OCB and PS and between 7OCB and VECTRA. The interfacial energy between 7OCB and PS, and between 7OCB and VECTRA, decreased with increasing temperature for ranges of temperatures corresponding to both phases of 70CB.     

Estimation of trioctylphosphine oxide (TOPO) diffusion coefficients by dynamic adsorption measurements in model extraction systems

Equilibrium interfacial tension and surface excess isotherms for trioctylphosphine oxide (TOPO) were determined and interpreted. Despite its high hydrophobicity, TOPO adsorbs at the hydrocarbon/water interfaces and decreases effectively the interfacial tension. The interfacial activity of TOPO is affected by the type of organic diluent and the composition of the aqueous phase, i.e., the kind (HNO(3), KNO(3)) and the concentration of nonorganic electrolyte present in the system. Significant lowering of TOPO interfacial activity is observed with an increase of the aqueous phase acidity. The dynamic interfacial tension for TOPO was measured by using the drop volume technique. With the aid of the Ward and Tordai equation the values of the diffusion coefficients of TOPO were estimated. The values determined were in the right order of magnitude compared with the literature data.     

Effect of ac electrodeposition conditions on the growth of high aspect ratio copper nanowires in porous aluminum oxide templates

The effect of several deposition parameters on the uniformity of copper electrodeposition through the alumina barrier layer into porous aluminum oxide templates grown in sulfuric or oxalic acid was systematically investigated. A fractional factorial design of experiment was conducted to find suitable deposition conditions among the variables: frequency, voltage, pulsed or continuous deposition, electrolyte concentration, and barrier layer thinning voltage. Continuous ac sine wave deposition conditions yielded excellent uniformity of pore-filling but damaged the porous aluminum oxide templates when deposition was continued to grow bulk copper on the surface. Pulsed electrodeposition yielded comparable uniformity of pore-filling and no damage to the porous aluminum oxide templates, even when bulk copper was deposited on them. Further optimization of pulsed deposition conditions was accomplished by comparing square and sine waveforms and pulse polarity. Pulsed square waveforms produced better pore-filling than pulsed sine waveforms. For sine wave depositions, the oxidative/reductive pulse polarity was more efficient than the commonly used reductive/oxidative pulse polarity. For square wave depositions into sulfuric acid grown pores, the reductive/oxidative pulse polarity produces more uniform pore-filling, likely as a result of enhanced resonant tunneling through the barrier layer and reoxidation of copper in faster filling pores.