The role of adsorption of sodium bis(2-ethylhexyl) sulfosuccinate in wetting of glass and poly(methyl methacrylate) surface

Advancing contact angles, θ, for aqueous solutions of the anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) were measured on glass and poly(methyl methacrylate) (PMMA) surface. Using the obtained results we determined the properties of aqueous AOT solutions in wetting of these surfaces. It occurs that the wettability of glass and PMMA by these solutions depends on the concentration of AOT in solution. There is almost linear dependence between the contact angle (θ) and concentration of AOT (log C) in the range from 5 × 10⁻⁴ to 2.5 × 10⁻³ M/dm³ (value of the critical micelle concentration of AOT—CMC) both for glass and PMMA surface. For calculations of AOT adsorption at solid (glass, PMMA)-solution drop-air system interfaces the relationship between the adhesion tension (γ_LV cos θ) and surface tension (γ_LV) and the Gibbs and Young equations were taken into account. From the measurement and calculation results the slope of the γ_LV cos θ − γ_LV curve was found to be constant and equal 0.7 for glass and −0.1 for PMMA over the whole range of AOT concentration in solution. From this fact it can be concluded that if Γ_SV is equal zero then Γ_SL > 0 for the PMMA-solution and Γ_SL < 0 for glass-solution systems. It means that surfactant concentration excess at PMMA-solution interface is considerably lower than at solution-air interface, but this excess of AOT concentration at glass-solution interface is lower than in the bulk phase. By extrapolating the linear dependence between the adhesion and surface tension the value of the critical surface tension (γ_c) of wetting for glass and PMMA was also determined, that equaled 25.9 and 25.6 mN/m for glass and PMMA, respectively. Using the value of the glass and PMMA surface tension as well as the measured surface tension of aqueous AOT solutions in Young equation, the solid-liquid interface tension (γ_SL) was found. There was a linear dependence between the γ_SL and γ_LV both for glass and PMMA, but there were different slope values of the curves for glass and PMMA, i.e. −0.7 and 0.1, respectively. The dependence between the work of adhesion (W_A) and surface tension (γ_LV) was also linear of different slopes for glass and for PMMA surface.     

The wettability of polytetrafluoroethylene and polymethylmethacrylate by aqueous solutions of Triton X-100 and short chain alcohol mixtures

Measurements of advancing contact angles (θ) were carried out for aqueous solutions of Triton X-100 (TX-100) and methanol and ethanol mixtures at constant TX-100 concentration equal to 1 × 10⁻⁷, 1 × 10⁻⁶, 1 × 10⁻⁵, 1 × 10⁻⁴, 6 × 10⁻⁴ and 1 × 10⁻³ M, respectively, on polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA). Using measured contact angle values the relationships between cos θ, adhesion tension and surface tension of the solutions were determined, and on their basis the critical surface tension of PTFE and PMMA wetting was calculated. The obtained average value of the critical surface tension of PTFE wetting is lying in the range of the PTFE surface tension values which can be found in the literature, while for PMMA it is even lower than the Lifshitz-van der Waals component of its surface tension. From the relationship between the adhesion and surface tension and Lucassen-Reynders equation it results that in the case of PTFE the adsorption at the PTFE-solution and solution-air interfaces is the same, which was confirmed by a linear relationship between the cos θ and 1/γ_LV and intercept on cos θ axis equal to −1. However, for PMMA the adsorption of the surface active agents at solution-air interface is higher than at PMMA-solution. Using the values of the contact angle the values of the adhesion work of solution to the PTFE and PMMA surface were also determined, which are constant for PTFE, but for PMMA decrease with alcohol concentration increase. Next, using the contact angle values in the Young equation, the PTFE(PMMA)-solution interface tension was also calculated. The obtained values of PTFE-solution interface tension were compared with those evaluated from the Szyszkowski, Connors and Fainerman and Miller equations, and good agreement between these values was observed for all series of TX-100 and alcohol mixtures at a low alcohol concentration.     

The role of adsorption of dodecylethyldimethylammonium bromide and benzyldimethyldodecylammonium bromide surfactants in wetting of polytetrafluoroethylene and poly(methyl methacrylate) surfaces

The role of adsorption of dodecylethyldimethylammonium bromide (C₁₂(EDMAB)) and benzyldimethyldodecylammonium bromide (BDDAB) at water-air and polytetrafluoroethylene (PTFE)-water and poly(methyl methacrylate) (PMMA)-water interface, in wetting of PTFE and PMMA surface, was established from the measured values of the contact angle (θ) of aqueous C₁₂(EDMAB) and BDDAB solutions in PTFE (PMMA)-solution drop-air system, and from the measured values of the surface tension of aqueous C₁₂(EDMAB) and BDDAB solutions. Adsorption of C₁₂(EDMAB) and BDDAB at water-air interface was determined earlier from the Gibbs equation. Adsorption at solid-water interface was deduced from the Lucassen-Reynders equation based on the relationship between adhesion tension (γ_LV cos θ) and surface tension (γ_LV). The slope of the γ_LV cos θ-γ_LV curve was found to be constant and equal to −1, and about −0.3 for PTFE and PMMA surface, respectively (in the case of both surfactant studied: C₁₂(EDMAB) and BDDAB, and in the whole range of surfactants concentration in solution). It means that the amount of the surfactant adsorbed at the PTFE-water interface, Γ_SL, was essentially equal to its amount adsorbed at water-air interface, Γ_LV. However, Γ_SL at the PMMA-water interface was about three times smaller as compared to that at water-air interface. By extrapolating the linear dependence between γ_LV cos θ-γ_LV and dependence between cos θ-γ_LV and cos θ = 1 we determined the value of the critical surface tension of PTFE and PMMA surface wetting, γ_c. The obtained values of γ_c for PTFE surface were equal 23.4 and 23.8 mN/m, 23.1 and 23.2 mN/m for C₁₂(EDMAB) and BDDAB, respectively and they were higher than the surface tension of PTFE (20.24 mN/m). On the other hand, the obtained values of γ_c for PMMA surface were equal 31.4 and 30.9 mN/m, 31.7 and 31.3 mN/m for C₁₂(EDMAB) and BDDAB, respectively and they were smaller than the surface tension of PMMA (39.21 mN/m). Using the values of PTFE and PMMA surface tension and the measured values of the surface tension of aqueous C₁₂(EDMAB) and BDDAB solutions in the Young equation, the PTFE (PMMA)-solution interfacial tension, γ_SL, was also determined. Next, the work of adhesion (W_A) was deduced, and it occurred that the dependence between the W_A and the surface tension (γ_LV) for both studied solids was linear. However, the values of the W_A for PMMA change as a function of log C (C—surfactant concentration) changed from 91.7 to 68.5 mJ/m² and from 91.8 to 65.1 mJ/m² for C₁₂(EDMAB) and BDDAB, respectively. On the other hand, the work of adhesion of both studied surfactants solutions to the PTFE surface was practically constant (an average value was equal 45.8 and 45.4 mJ/m², respectively). These values were close to the value of the work of water adhesion to PTFE surface (45.5 mJ/m²).     

Adsorption of sodium bis(2-ethylhexyl) sulfosuccinate and wettability in polytetrafluoroethylene-solution-air system

The role of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) adsorption at water-air and polytetrafluoroethylene-water (PTFE) interfaces in wetting of low energy PTFE was established from measurements of the contact angle of aqueous AOT solutions in PTFE-solution drop-air systems and the aqueous AOT solution surface tension measurements. For calculations of the adsorption at these interfaces the relationship between adhesion tension (γ_LV cos θ) and surface tension (γ_LV), and the Gibbs and Young equations were taken into account. On the basis of the measurements and calculations the slope of the γ_LV cos θ-γ_LV curve was found to be constant and equal −1 over the whole range of surfactant concentration in solution. It means that the amount of surfactant adsorbed at the PTFE-water interface, Γ_SL, is essentially equal to its amount adsorbed at water-air interface, Γ_LV. By extrapolating the linear dependence between γ_LV cos θ and γ_LV to cos θ = 1 the determined value of critical surface tension of PTFE surface wetting, γ_C, was obtained (23.6 mN/m), and it was higher than the surface tension of PTFE (20.24 mN/m). Using the value of PTFE surface tension and the measured surface tension of aqueous AOT solution in Young equation, the PTFE-solution interface tension, γ_SL, was also determined. The shape of the γ_SL-log C curve occurred to be similar to the isotherm of AOT adsorption at water-air interface, and a linear dependence existed between the PTFE-solution interfacial tension and polar component of aqueous AOT solution. The dependence was found to be established by the fact that the work of adhesion of AOT solution to the PTFE surface was practically constant amounting 46.31 mJ/m² which was close to the work of water adhesion to PTFE surface.     

Adsorption behavior of weak hydrophilic substances on low-energy surface in aqueous medium

Through the methods such as measurements of contact angle and surface tension, calculations of surface energy and interfacial interaction free energy, and four weak hydrophilic substances (WHS) were taken as research objects, some interesting conclusions were obtained as follow. In aqueous medium, the WHS give priority to adsorb on low-energy surface that is low polar or particularly non-polar. There is a clear corresponding relationship between the free energy and Lewis base component γ⁻ or the hydrophile index of low-energy surface, and the specific relationship is obtained. Finally, we find hydrophobic attractive force of the Lewis acid-base interaction is mainly responsible for the absorption of WHS on low-energy surface. In short, an initial insight into adsorption behavior of WHS on low-energy surface is demonstrated in this paper.     

Calculations of the level of primary radiation defects (displacements per atom) taking into account surface sputtering

The results of analytical estimates and computer simulations of the primary radiation damage level in the number of displacements per atom (dpa) in solids are presented and compared, taking into account the material sputtering under ion bombardment. Calculations were performed for the bombardment of carbon-based materials by Ar⁺, Ne⁺, and N⁺ ions with energies of 2?C30 keV, when considerable ion-induced changes in the material??s structure are observed. A comparison shows the close fit of the analytical and computer calculations.     

The wettability of poly(tetrafluoroethylene) by aqueous solutions of ternary surfactant mixtures

Contact angle measurements on poly(tetrafluoroethylene) (PTFE) surface were carried out for the systems containing ternary mixtures of cetyltrimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycols), Triton X-100 (TX100) and Triton X-165 (TX165). The aqueous solution of ternary surfactant mixtures were prepared by adding the third surfactant to the binary mixture of the surfactants where the synergetic effect in the reduction of the surface tension of water was determined, to compare the influence of the third surfactants on the values of surface tension of this binary mixture and the values of the contact angle on PTFE. The obtained results and calculations indicate that the ternary mixtures of CTAB + TX165 (αCTAB = 0.2, γ_LV = 60 and 50 mN/m) + TX100 (C = 10⁻⁸ to 10⁻² M) have the biggest efficiency of the reduction of contact angle of water on PTFE in comparison to aqueous solutions of the single surfactants and their binary and ternary mixtures. Also in the case of all studied ternary mixtures of surfactants at concentrations of the bulk phase corresponding to unsaturated monolayer at water-air interface the adsorption of surfactants at PTFE-water interface is different than that at water-air interface, but is the same at concentrations near the critical micelle concentration (CMC). Thus the linear dependences between γ_LV cos θ − γ_LV and cos θ − 1/γ_LV, in the range of concentration studied for all systems confirm the same adsorption at two interfaces only at C near the CMC.     

Type I FA (Rb, Cs) and II FA (Li, Na) tunable laser activities and donor-acceptor properties of O and O at KCl (001) surface: first principle calculations

Type I F_A (Rb⁺, Cs⁺) and II F_A (Li⁺, Na⁺) tunable laser activities, adsorptivity and donor-acceptor properties of O and O⁻ adsorbates at the flat surface of KCl crystal were investigated using an embedded cluster model and ab initio methods of molecular electronic structure calculations. Ion clusters were embedded in a simulated Coulomb field that closely approximates the Madelung field of the host surface, and the nearest neighbor ions to the defect site were allowed to relax to equilibrium. Based on the calculated Stokes shifted optical transition bands, F_A tunable laser activities were found to be inversely proportional to the size of the dopant cation (Li⁺, Na⁺, Rb⁺, Cs⁺) relative to the host cation (K⁺). This relation was explained in terms of the axial perturbation of the impurity cation. The probability of orientational bleaching attributed to the RES saddle point ion configuration along the 〈110〉 axis was found to be inversely proportional to the size of the dopant cation, with activation energy barriers of ca. 0.44-3.34 eV. Surface relaxation energies of type II F_A centers were more important than those of type I F_A centers. In terms of defect formation energies, the products of type II F_A center imperfection were more stable than those of type I F_A. The difference between F or F_A band energies and exciton bands depended almost exclusively on the size of the positive ion species. As far as the adsorptivity of O and O⁻ is concerned, the results confirm that surface imperfection enhances the adsorption energies by ca. 4.38-16.37 eV. O and O⁻ penetrate through the defect-containing surface. The energy gap between the adsorbate and the defect containing surface and the donor-acceptor property of adsorbate play the dominant role in the course of adsorbate substrate interactions and the results were explained in terms of electrostatic potential curves and Mulliken population analysis.     

Kinetic electron emission due to perpendicular impact of carbon ions on tungsten surfaces

Total electron yields for perpendicular impact of C⁺ ions on W have been measured for projectile energies from 0.2 keV to 7 keV. The data are compared with the data of C⁺ bombardment of gold and graphite in order to demonstrate general trends in kinetic electron yields at low projectile velocities. The total electron yields in the studied combinations of projectiles and substrates show a similar exponential dependence Γ ∝ (v/A) exp(−A/v), where A is a constant and v is the projectile velocity.     

Elastic constants of solids and fluids with initial pressure via a unified approach based on equations-of-state

The second and third-order Brugger elastic constants are obtained for liquids and ideal gases having an initial hydrostatic pressure p₁. For liquids the second-order elastic constants are C₁₁ = A + p₁, C₁₂ = A − p₁, and the third-order constants are C₁₁₁ = −(B + 5A + 3p₁), C₁₁₂ = −(B + A − p₁), and C₁₂₃ = A − B − p₁, where A and B are the Beyer expansion coefficients in the liquid equation of state. For ideal gases the second-order constants are C₁₁ = p₁γ + p₁, C₁₂ = p₁γ − p₁, and the third-order constants are C₁₁₁ = −p₁(γ² + 4γ + 3), C₁₁₂ = −p₁(γ² − 1), and C₁₂₃ = −p₁ (γ² − 2γ + 1), where γ is the ratio of specific heats. The inequality of C₁₁ and C₁₂ results in a nonzero shear constant C₄₄ = (1/2)(C₁₁ − C₁₂) = p₁ for both liquids and gases. For water at standard temperature and pressure the ratio of terms p₁/A contributing to the second-order constants is approximately 4.3 × 10⁻⁵. For atmospheric gases the ratio of corresponding terms is approximately 0.7. Analytical expressions that include initial stresses are derived for the material ‘nonlinearity parameters’ associated with harmonic generation and acoustoelasticity for fluids and solids of arbitrary crystal symmetry. The expressions are used to validate the relationships for the elastic constants of fluids.     

The relationship between the adhesion work, the wettability and composition of the surface layer in the systems polymer/aqueous solution of anionic surfactants and alcohol mixtures

Measurements of advancing contact angle (θ) were carried out on polytetrafluoroethylene (PTFE) and polymethylmethacrylate (PMMA) for aqueous solution of sodium dodecyl sulfate (SDDS) mixtures with methanol, ethanol and propanol in the range of SDDS concentration from 10⁻⁵ to 10⁻² M, and for sodium hexadecyl sulfonate (SHS) with the same alcohols at the SHS concentration ranging from 10⁻⁵ to 8 × 10⁻⁴ M at 293 K. The concentration of methanol, ethanol and propanol used for measurements varied from 0 to 21.1, 11.97 and 6.67 M, respectively. On the basis of the contact angles the critical surface tension of PTFE and PMMA wetting was determined by using for this purpose the relationship between the adhesion and the surface tension and cos θ and surface tension both at constant alcohol and surfactant concentration, respectively. The obtained contact angles were also used in the Young Dupre’ equation for calculations of the adhesion work of aqueous solution of mixtures of anionic surfactants and short chain alcohols to PTFE and PMMA surface. The adhesion work calculated in this way was compared to that of the particular components of aqueous solution to these surfaces determined on the basis of the surface tension components and parameters of the surface tension of the surface active agents, water, PTFE and PMMA from van Oss et al. equation. The calculated adhesion work was discussed in the light of the concentration of surface active agents at polymer-water and water-air interface determined from Lucassen-Reynders, Gibbs and Guggenheim-Adam equations.     

Mechanism of negative ion formation in low velocity collisions at surfaces

Theoretical calculations using the coupled angular modes (CAM) method have been used to interpret experimental findings related to the scattered oxygen negative ion fraction (O⁻) in collisions of low energy O⁺ with an Al(1 1 0) surface. The increasing O⁻ ion fraction observed experimentally at low O⁺ velocities can be explained in terms of the distance of closest approach Z_c to the Al surface and the specific charge state of the projectile at this distance. Both Z_c and the charge state influence the charge transfer process between the projectile and the surface at low collision energies.     

A spark chamber measurement of the reactions π + p → ϱ + p at 15 GeV/c

A new method, using spark chambers, for the study of the reactions π^± + p → ?^± + p is described. The charged pion and both γ rays from the π^± decay are detected. Differential and integrated cross sections σ_π⁺=50 ± 9 μb, σ_π⁻=47 ± 9 μb) for 0.0 ?|t|?1. (GeV/c)² and a laboratory momentum (p_Lab) of 15 GeV/c are presented. The momentum dependence of σ_γ^± is well fitted from 2.7 to 16 GeV/c by σ = Kp_Lab⁻ with n_γ⁺ = 1.80 ± 0.80 and n_γ⁻ = 1.87 ± 0.15.     

Fabrication of superhydrophobic surfaces based on ZnO-PDMS nanocomposite coatings and study of its wetting behaviour

Superhydrophobic surfaces based on ZnO-PDMS nanocomposite coatings are demonstrated by a simple, facile, time-saving, wet chemical route. ZnO nanopowders with average particle size of 14 nm were synthesized by a low temperature solution combustion method. Powder X-ray diffraction results confirm that the nanopowders exhibit hexagonal wurtzite structure and belong to space group P63mc. Field emission scanning electron micrographs reveal that the nanoparticles are connected to each other to make large network systems consisting of hierarchical structure. The as formed ZnO coating exhibits wetting behaviour with Water Contact Angle (WCA) of ∼108°, however on modification with polydimethylsiloxane (PDMS), it transforms to superhydrophobic surface with measured contact and sliding angles for water at 155° and less than 5° respectively. The surface properties such as surface free energy (γ_p), interfacial free energy (γ_pw), and the adhesive work (W_pw) were evaluated. Electron paramagnetic resonance (EPR) studies on superhydrophobic coatings revealed that the surface defects play a major role on the wetting behaviour. Advantages of the present method include the cheap and fluorine-free raw materials, environmentally benign solvents, and feasibility for applying on large area of different substrates.     

Experimental search for radiative decays of the pentaquark baryon Θ+(1540)

The data on the reactions K ⁺Xe → K ⁰ γX and K ⁺Xe → K ⁺ γX, obtained with the bubble chamber DIANA, have been analyzed for possible radiative decays of the Θ⁺(1540) baryon: Θ⁺ → K ⁰ pγ and Θ⁺ → K ⁺ nγ. No signals have been observed, and we derive the upper limits Γ(Θ⁺ → K ⁰ pγ)/Γ(Θ⁺ → K ⁰ p) < 0.032 and Γ(Θ⁺ → K ⁺ nγ)/Γ(Θ⁺ → K ⁺ nγ) < 0.041 which, using our previous measurement of Γ(Θ⁺ → KN) = 0.39 ± 0.10 MeV, translate to Γ(Θ⁺ → K ⁰ pγ) < 8 keV and Γ(Θ⁺ → K ⁺ nγ) < 11 keV at 90% confidence level. We have also measured the cross sections of K ⁺-induced reactions involving emission of a neutral pion: σ(K ⁺ n → K ⁰ pπ ⁰) = 68 ± 18 µb and σ(K ⁺ N → K ⁺ Nπ ⁰) = 30 ± 8 µb for incident K ⁺ momentum of 640 MeV.     

Rate constant for the infrared emission of the NO(CΠ → AΣ) transition

The reaction of O- and N-atoms produces NO(C²Π) molecules by inverse predissociation. At low total pressure NO(A²Σ⁺) molecules are exclusively formed from NO(C²Π) by

NO(C²Π) → NO(A²Σ⁺)+hv

ππ production by ee annihilation in the ϱ energy range with the Orsay storage ring

A large solid angle detector has been used to observe two body events produced by electron-positron collisions in the Orsay storage ring. From the π⁺π⁻ excitation curve in the ? region we have deduced the amplitude and the phase of the ω-? interference, and the ? resonance paramaters: M_? = (775.4±7.3) MeV, Γ_? = (149.6 ± 23.2) MeV, √B(ω→π⁺π⁻) = 0.19 ± 0.05, φ = (85.7 ± 15.3)⁰, σ(e⁺e⁻→?) = (1.00 ± 0.13) μb at S = M_?², B(?→e⁺e⁻ = (4.1 ± 0.5) × 10⁻⁵, Γ(?→e⁺e⁻) = (6.1 ± 0.7) keV, (g_?²/4π) = 2.26 ± 0.25, (g_?ππ²/4π) = 2.84 ± 0.50.     

Yrast and side bands in the odd-odd160, 162Tm nuclei

High-spin states in²⁰⁵Bi, populated in the²⁰⁵Tl(α, 4n) reaction with bombarding energies around 50 MeV have been studied usingγ-ray spectroscopic techniques. Spins and parities have been assigned on the basis of angular distribution andγ-ray linear polarization measurements. States with spins up to 39/2⁺ and excitation energies around 6 MeV have been identified. Calculations using the empirical shell model have been performed in order to assign configurations.     

Characterization of deep level defects in sublimation grown p-type 6H-SiC epilayers by deep level transient spectroscopy

In this study deep level transient spectroscopy has been performed on boron–nitrogen co-doped 6H-SiC epilayers exhibiting p-type conductivity with free carrier concentration (N_A–N_D)∼3×10¹⁷ cm⁻³. We observed a hole H₁ majority carrier and an electron E₁ minority carrier traps in the device having activation energies E_v+0.24 eV, E_c −0.41 eV, respectively. The capture cross-section and trap concentration of H₁ and E₁ levels were found to be (5×10⁻¹⁹ cm², 2×10¹⁵ cm⁻³) and (1.6×10⁻¹⁶ cm², 3×10¹⁵ cm⁻³), respectively. Owing to the background involvement of aluminum in growth reactor and comparison of the obtained data with the literature, the H₁ defect was identified as aluminum acceptor. A reasonable justification has been given to correlate the E₁ defect to a nitrogen donor.