Aggregation and Polymerization of PEG-Based Macromonomers with Methacryloyl Group as the Only Hydrophobic Segment

Aggregation behavior in aqueous solution of a series of poly (ethylene glycol) (PEG)-based macromonomers with methacryloyl group as the only hydrophobic segment has been investigated using surface tension, steady-state and time-resolved fluorescence spectroscopy using pyrene as a probe, and small-angle neutron scattering techniques. The general formula of these macromonomers is CH₂=C(CH₃)–CO–O–E_m–CH₃, where E is the ethylene glycol unit and m=8 (ME₈), 18 (ME₁₈), 49 (ME₄₉), and 120 (ME₁₂₀). The results indicate that a macromonomer with 8 ethylene glycol units forms as an aggregate above a certain critical concentration, which can be defined as critical aggregation concentration. The observed high value of I₁/I₃ in pyrene emission spectra at the interface of these aggregates and the inability to scatter a neutron beam by these aggregates indicate that the hydrophobic cluster formed by this macromonomer is remarkably solvated. ME₁₈ has a tendency to aggregate but others do not form any hydrophobic cluster. The homopolymerization behaviors of these macromonomers in an aqueous medium at 70°C are consistent with these possibi- lities.     

Silylating Agents Grafted onto Silica Derived from Leached Chrysotile

Silica from leached chrysotile fibers (SILO) was silanized with trialkoxyaminosilanes to yield inorganic–organic hybrids designated SILx (x=1–3). The greatest amounts of the immobilized agents were quantified as 2.14, 1.90, and 2.18 mmol g⁻¹ on SIL1, SIL2, and SIL3 for –(CH₂)₃NH₂,–(CH₂)₃NH(CH₂)₂NH₂, and –(CH₂)₃NH(CH₂)₂NH(CH₂)₂NH₂ groups attached to the inorganic support. The infrared spectra for all modified silicas showed the absence of the Si–OH deformation mode, originally found at 950 cm⁻¹, and the appearance of asymmetric and symmetric C–H stretching bands at 2950 and 2840 cm⁻¹. Other important bands associated with the organic moieties were assigned to ν_as(NH) at 3478 and ν_sym(NH) at 3418 cm⁻¹. The NMR spectrum of the solid precursor material suggested two different kinds of silicon atoms: silanol and siloxane groups, between −90 and 110 ppm; however, additional species of silicon that contain the organic moieties bonded to silicon at −58 and −66 ppm appeared after chemical modification. These modified silicas showed a high adsorption capacity for cobalt and copper cations in aqueous solution, in contrast to the original SILO matrix, confirming the unequivocal anchoring of silylating agents on the silica surface.     

Molecular Interactions in Mixed Monolayers of Octadecanoic Acid and Three Related Amphiphiles

Binary mixed monolayers of octadecanoic acid and three related amphiphilic compounds (octadecanamide, octadecylamine, octadecylurea) have been investigated at the air/water interface by surface pressure–area (Π–Â) isotherms and their resistances to water evaporation (r). In addition, the excess free energies of mixing (ΔG^E) were calculated using the Goodrich method. Both the ln r vs x and ΔG^E vs x plots exhibit marked deviations from linearity, indicating a high degree of miscibility and nonideal behavior of the components in the mixed films. For all of these binary systems the excess free energies of mixing have been found to be minimum for a certain composition corresponding almost to a maximum in evaporation resistances. Weak interactions were detected in octadecanoic acid/octadecanamide monolayers, whereas significant condensation effects were observed in 1 : 1 mixed films containing octadecanoic acid and octadecylamine. This is attributed to an acid–base equilibrium followed by the formation of a well-ordered arrangement of COO⁻ and NH₃⁺ head groups bound to each other by electrostatic forces. The unusual polymorphism of octadecylurea monolayers could be influenced by adding small amounts of octadecanoic acid. The formation of the low-temperature phase (β-phase) is completely suppressed, if the acid content exceeds 8 mol%. The octadecanoic acid seems to induce the formation of the high-temperature phase (α-phase), which is characterized by a vertical orientation of the hydrocarbon chains.     

Effect of β-Cyclodextrin on the Photoinduced Charge Transfer in Sodium 1-Anilino-8-naphthalene Sulfate (ANS)/CdS Colloidal System

The S-center radical (ANS^·) of sodium 1-anilino-8-naphthalene sulfate (ANS) generated by photoinduced charge transfer in ANS/CdS and ANS/CdS/β-cyclodextrin(β-CD) systems has been studied by using spin trapping electron spin resonance techniques, UV-visible spectroscopic methods, and fluorescence spectroscopic methods. It was found that the S-centered radical (ANS^·) was produced by the charge transfer reaction between the ground state ANS and the positive hole h⁺(CdS) from the valence band of CdS colloids, by the charge transfer from the excited singlet state ¹ANS* to the conduction band of CdS colloids, or by both in the ANS/CdS and ANS/CdS/β-CD systems. The ESR signal intensity of the spin adduct (5,5′-dimethyl-1-pyrroline-N-oxide (DMPO)–ANS)^·, which is formed from ANS^· trapped by DMPO, in the latter system is 15 times stronger than that in the former system. The apparent association constants between ANS and CdS colloids in the absence and presence of β-CD determined from fluorescence quenching experiments are 1097 and 1606 M⁻¹, respectively. From ESR and fluorescence results, it is estimated that the efficiency of photoinduced charge transfer from ANS to CdS colloids in the ANS/CdS/β-CD system is 12.5 times that in the ANS/CdS system.     

Adsorption of 1,4-Benzenedithiol on Gold and Silver Surfaces: Surface-Enhanced Raman Scattering Study

The adsorption behavior of 1,4-benzenedithiol (1,4-BDT) on colloidal gold and silver surfaces has been investigated by means of surface-enhanced Raman scattering (SERS). 1,4-BDT chemisorbed dissociatively on both gold and silver surfaces but as mono- and dithiolate, respectively. Regardless of the bulk concentration of 1,4-BDT, only a monolayer was assembled on the silver surface with a flat orientation by forming two Ag–S bonds. On the gold surface, the monothiolate species,1,4-BDT⁻¹, appeared to assume a rather flat orientation at a very low surface coverage, but as the surface coverage was increased, the adsorbate took a perpendicular orientation. Furthermore, when the bulk concentration of 1,4-BDT was close to that required for a full-monolayer coverage limit, a band assignable to the S–S stretching vibration appeared at 536 cm⁻¹ in the gold sol SERS spectra. A separate ellipsometry measurement performed with vacuum-evaporated gold substrates revealed that up to tetralayers could be assembled on gold in 1 mM n-hexane solution of 1,4-BDT while at best a bilayer formed in either methanol or ethanol solution. The different adsorbate structure of 1,4-BDT on gold and silver was overall quite comparable to that of p-xylene-α,α′-dithiol.     

A Phenomenon of the Change in Particle Drift Velocity Direction in High-Field Electrophoresis

The sign–alternating electric field in rectangular impulses has been used to eliminate linear electrophoresis and to study nonlinear electrophoresis in water at strong fields. We found out that the particle drift velocity could change its direction with the growth of the strength of the field. This new phenomenon has obtained its explanation in the framework of the Debye–Hückel theory of strong electrolyte where we consider a particle as a “heavy” effective ion and take into account all relevant nonlinear effects, grounding ourselves on basic physics. With the help of our theory we have succeeded in good fitting of our experimental data on black oil and Al₂O₃ particles in distilled water using reasonable values for the basic parameters such as the Debye screening length.     

Preparation and Characterization of Ceramic Hollow Microspheres for Heavy Metal Ion Removal in Wastewater

Ceramic hollow microspheres (CHMSs) were prepared to use as supports for the removal of heavy metal ions from industrial waste-water. A water extraction sol–gel technique was used to prepare porous CHMS by extracting water from an emulsion of LUDOX (silica colloid; SiO₂, Aldrich Co.) and 2-ethyl-1-hexanol. Experiments were conducted to control pore size, wall thickness, and separation yield by examining the ratio of precursors (LUDOX and 2-ethyl-1-hexanol), catalyst (NH₄OH), sintering temperature, surfactant (SPAN 80), extractant (n-butanol), stirring speed, and concentration of precursor (LUDOX). The results revealed that the optimum conditions were 20 ml of a 10 wt% solution of LUDOX, 10 ml of NH₄OH, a sintering temperature of 500°C, 0.4 ml of SPAN 80, 200 ml of n-butanol, and a stirring speed of 730 rpm/100 ml of 2-ethyl-1-hexanol. CHMSs were impregnated in Cyanex 272 and examined for their ability to remove heavy metal ions from a solution. Based on an experiment involving the removal of metal ions using CHMSs that were prepared under optimum conditions, Zn ion was removed at a level of 0.354 mmol/g at pH 4, which was about twice the adsorption capacity of CHMSs prepared by Wilcox (Mater. Res. Soc. Symp. Proc.346, 201 (1994)).     

Electronic Properties of Q-CdS Clusters Stabilized by Adenine

Adenine-capped Q-CdS has been synthesized in an aqueous medium. IR spectroscopy indicates an interaction between Q-CdS and adenine through Cd²⁺. The amount of adenine controls the size of the clusters. A typical 5×10⁻³ mol dm⁻³ of adenine produces nanoclusters having the onset of absorption and an emission band at 2.8 and 2.35 eV, respectively. Adenine binds to the shallower traps and enhances the emission intensity of the 530-nm band without causing any shift in emission. Thermolysis of these colloids leads to the production of larger CdS clusters with changed electronic properties. Relaxation kinetics of charge carriers shows their average lifetime to increase with a decrease in particle size. Illumination of these particles does not lead to their photodissolution. This catalyst is, however, photoactive. The addition of indole causes the quenching of its emission. The photocatalytic oxidation of indole produces indigo with a quantum efficiency of 0.03.     

Electrooptics of β-FeOOH Particles in Aqueous Media: 1. Reversing-Pulse Electric Birefringence in the Low Field Region

Reversing-pulse electric birefringence (RPEB) of a nearly monodisperse iron(III) hydroxide oxide sample in the β-form (β-FeOOH) was measured at 25°C and at a wavelength of 633 nm in aqueous media in the presence of NaCl. The concentrations of β-FeOOH and added NaCl varied between 0.00111 and 0.0555 g/L and 0.03 and 2.0 mM, respectively. Except for the suspensions with high salt concentrations, each RPEB signal showed a dip or minimum in the reverse process upon electric field reversal, together with a smooth rise in the buildup and a fall in the decay process. The observed signals were analyzed with a new RPEB theory, which takes into account not only the permanent electric dipole moment (μ) but also the root-mean-square ionic dipole moment (m^21/2) due to the ion fluctuation in ion atmosphere, in addition to the field-induced electronic (covalent) dipole moment Δα′ E. The results showed that the slowly fluctuating moment of m^21/2 is by far the most predominant one for the field orientation of the β-FeOOH particle, though the permanent dipole moment μ may not be completely excluded. The rotational relaxation time of the whole particle was evaluated from the decay signal, while the relaxation time for fluctuating ions was estimated from RPEB signal fitting. The sign of the steady-state birefringence for β-FeOOH suspensions was positive without exception under the present conditions. The birefringence signals in the steady state (δ/d) were proportional to the second power of the applied field strength (E) in the low field region; thus, the Kerr law was verified to hold for β-FeOOH suspensions. The specific Kerr constant was evaluated for each suspension by extrapolating the values of δ/d to zero field (E→0).     

Substituent Effects on Binding Constants of Carotenoids to n-Heptane/AOT Reverse Micelles

The absorption spectra of 6′-apo-β-caroten-6′-ol (1), 6′-apo-β-caroten-6′-oic acid (2), and ethyl 6′-apo-β-caroten-6′-oate (3) were analyzed in homogeneous media and in reversed micelles of AOT (sodium 1,4-bis(2-ethylhexyl) sulfosuccinate) in n-heptane. The possible solute–solvent interactions of these compounds were analyzed in pure solvents by Taft and Kamlet's solvatochromic comparison method. These carotenoids show sensitivity similar to that of medium polarity-polarizability as measured by π*. Moreover, the absorption spectra of carotenoid 3 and to much less extent carotenoid 2 display broadening of the visible bands induced by polar solvents characteristic of carotenoids that contain a carbonyl functional group in conjugation with the carbon–carbon π-electron system. They are also sensitive to the ability of the solvent to accept protons in a hydrogen bond interaction measured by β. This sensitivity follows the expected order: 2>1>3. In the reverse micellar system, while the spectra for 3 remain unchanged, the intensity of the absorption band characteristic of n-heptane for 1 and 2 decreases as the AOT concentration increases, and a new band develops. This new band is attributed to the solute bound to the micelle interface. These changes allowed us to determine the binding constant (K_b) between these compounds and AOT. At W₀=[H₂O]/[AOT]=0 the values of K_b of 326±5 and 6.2±0.3 were found for the acid 2 and the alcohol 1, respectively. The strength of binding is interpreted considering their hydrogen-bond donor ability and the solubility in the organic pseudophase. For 1K_bdecreases as W₀ is increased, while for 2 no variation was observed. These effects are discussed in terms of carotenoid–water competition for interfacial binding sites.     

Influence of Surface Hydrophobic Groups on the Adsorption of Proteins onto Nonporous Polymeric Particles with Immobilized Metal Ions

Iminodiacetic acid (IDA) and octyl moieties were covalently bound on nonporous particles, which were prepared from dispersion polymerization of methyl methacrylate and glycidyl methacrylate. After being charged with copper ions, the IDA-bound particles could specifically adsorb deoxyribonuclease I (DNase I) through the affinity interaction between protein and immobilized metal ion. A mixed-ligand (metal–chelate and octyl–bound) support was obtained after hydrophobic (octyl) groups were also introduced to the particle surface. The affinity adsorption of DNase I on the copper–IDA chelate was influenced by interaction between the protein and the bound octyl group. Both the affinity and the hydrophobic interactions could be well described by the Langmuir isotherms. The equilibrium adsorption constants were estimated separately to be 0.96 and 0.50 liter g⁻¹ for affinity and hydrophobic bindings, respectively. For binding on mixed-ligand support, the adsorption constant was 0.45 liter g⁻¹. It was evident that both affinity and hydrophobic interactions are involved in the adsorption of proteins onto mixed-ligand particles. Desorption of the inactive proteins from the support was possible by increasing the hydrophobicity of the solution.     

Effects of Nonionic and Mixed Cationic-Nonionic Micelles on the Rate of Alkaline Hydrolysis of 4-Nitrophthalimide

Pseudo-first-order rate constants (k_obs) for alkaline hydrolysis of 4-nitrophthalimide show a monotonic decrease with increase in [C₁₂E₂₃]_T (total concentration of Brij 35) at constant [CH₃CN] and [NaOH]. This micellar effect is explained in terms of a pseudophase micelle model. The rate of hydrolysis becomes too slow to monitor at [C₁₂E₂₃]_T≥0.03 M in the absence of cetyltrimethylammonium bromide (CTABr) and at [C₁₂E₂₃]_T≥0.04 M in the presence of 0.006–0.02 M CTABr at 0.01 M NaOH. The plots of k_obs versus [C₁₂E₂₃]_T show minima at 0.006 and 0.01 M CTABr, while such a minimum is not visible at 0.02 M CTABr.     

Luminescent properties of the potassium zinc phosphates of composition K1−xTlxZn(PO3)3

Crystalline and glassy K_1−xTl_xZn(PO₃)₃ polyphosphates have been synthesized and characterized. UV–visible spectroscopy was systematically used in order to analyze the optical properties of Tl⁺ ions both in crystalline and glassy forms with the similar compositions. The investigated polyphosphates can be considered as a model system since the spectroscopic properties of Tl⁺ ions in the glasses could be deduced by comparison with those in crystals. From structural point of view, in the crystalline forms the thallium ions are six-fold coordinated in a dissymmetrical oxygenated sites. Three luminescences (α, A_X, A_T) have been then observed and were attributed to the isolated Tl⁺ ions. In the glassy forms, an additional luminescence (D) has been detected in the low-energy range and was assigned to the Tl⁺ pairs formation. The relationship between the Tl⁺ site symmetry and its optical properties is discussed in the context of the Fukuda's model.     

Effect of Insoluble Surfactants on Drainage and Rupture of a Film between Drops Interacting under a Constant Force

The deformation, drainage, and rupture of an axisymmetrical film between colliding drops in the presence of insoluble surfactants under the influence of van der Waals forces is studied numerically at small capillary and Reynolds numbers and small surfactant concentrations. Constant-force collisions of Newtonian drops in another Newtonian fluid are considered. The mathematical model is based on the lubrication equations in the gap between drops and the creeping flow approximation of Navier–Stokes equations in the drops, coupled with velocity and stress boundary conditions at the interfaces. A nonuniform surfactant concentration on the interfaces, governed by a convection–diffusion equation, leads to a gradient of the interfacial tension which in turn leads to additional tangential stress on the interfaces (Marangoni effects). The mathematical problem is solved by a finite-difference method on a nonuniform mesh at the interfaces and a boundary-integral method in the drops. The whole range of the dispersed to continuous-phase viscosity ratios is investigated for a range of values of the dimensionless surfactant concentration, Peclét number, and dimensionless Hamaker constant (covering both “nose” and “rim” rupture). In the limit of the large Peclét number and the small dimensionless Hamaker constant (characteristic of drops in the millimeter size range) a fair approximation to the results is provided by a simple expression for the critical surfactant concentration, drainage being virtually uninfluenced by the surfactant for concentrations below the critical surfactant concentration and corresponding to that for immobile interfaces for concentrations above it.     

205Tl NMR studies: Ion pairing of Tl+ and (CH3)2Tl+ with NO 3 − and ClO 4 − in various solvents

The concentration dependence of the²⁰⁵Tl chemical shifts of Tl⁺ and of (CH₃)₂Tl⁺ ions was determined in several solvents with NO ₃ ^– and ClO ₄ ^– counterions. In general, increased ion pairing caused a low-frequency shift of the²⁰⁵Tl resonance, with the exceptions of (CH₃)₂TlNO₃ inn-butylamine and TlNO₃ in N,N-dimethylformamide (DMF) and in hexamethylphosphorotriamide (HMPA). In HMPA,²⁰⁵Tl linewidths of both Tl⁺ and (CH₃)₂Tl⁺ increased dramatically with dilution below 0.1M. Analysis of the data allowed ion-pair formation constants and²⁰⁵Tl chemical shifts for the ion-paired cation and for the free (solvated) cation to be estimated for some of the solvents.     

Highly Dispersed X/SiO(2) and C/X/SiO(2) (X=Alumina, Titania, Alumina/Titania) in the Gas and Liquid Media

Fumed oxides, such as silica, alumina, titania, and mixed X/silicas (X=Al₂O₃ (AS), TiO₂ (TS), CVD-TiO₂, Al₂O₃/TiO₂ (AST)), pristine or covered by carbon deposits formed due to pyrolysis of cyclohexene, were studied using nitrogen adsorption–desorption, photon correlation spectroscopy particle sizing, and electrophoresis. A significant influence of the nature of surface-active sites and structural features of oxides (individual silica, mixed fumed, or prepared using chemical vapor deposition (CVD)) on the pyrolysis of cyclohexene is observed with respect to the pore size distributions due to differences between primary particles in aggregates and on their outer surfaces in the filling of channels by pyrocarbon, resulting also in a decrease in fractal dimension. Structural characteristics and dependences of the particle size distribution and electrokinetic potential of X/SiO₂ and C/X/SiO₂ on the pH of aqueous suspensions suggest that the carbon deposit covers mainly acidic sites at the X/SiO₂ interfaces and X phase patches possessing catalytic activity in pyrolysis, as the negative charge of particles is reduced by pyrocarbon grafting.     

Contribution to the Determination of Kinetic Parameters of the Sol-Gel Transformation by Rheological Measurements

The system tetraethoxysilane(TEOS)–water–ethanol has been studied by rheological measurements. Different molar ratios of TEOS : water (1 : 4, 1 : 10, and 1 : 20) are studied at different temperatures (30, 40, and 50°C). The dynamic viscosity (rotating mode) at a constant shear rate (100 s⁻¹) and the elastic and viscous moduli (oscillating mode) at a constant frequency (1 Hz) are determined. The viscosity–time curves are evaluated by application of a nucleation and particle growth model. Good agreement between experiments and theory is observed. The model allows the determination of the complex rate constant of silica precipitation. The temperature-dependent measurements gave the possibility to determine the apparent energy of activation by common methods. The results are in agreement with data from the literature. The gel time defined as intersection point of elastic and plastic moduli and its dependence on temperature are evaluated by the Smoluchowski model. The energy of activation for the coagulation was determined and found to be in the correct order of magnitude.     

The effect of sample environment on the room-temperature phosphorescence of several polynuclear aromatic hydrocarbons

Room-temperature phosphorescence (r.t.p.) of numerous molecules has been studied with emphasis on several polynuclear aromatic hydrocarbons (PAH). The heavy atom effect has led to a significant enhancement of r.t.p. signals for the PAH studied with the trend being Tl⁺ > Ag⁺ > Pb²⁺ > Hg²⁺. The Tl⁺ also resulted in enhanced spectral features of emission bands. R.t.p. could be induced from PAH on a sodium acetate sample support as well as on filter paper. A study of the effect of different gaseous environments provided anomalous results.     

Wetting Study of Hydrophobic Membranes via Liquid Entry Pressure Measurements with Aqueous Alcohol Solutions

A new concept of liquid entry pressure measurements is applied to study the hydrophobicity of microporous membranes for aqueous alcohol solutions. The effects of alcohol concentration, type of alcohol, and temperature on liquid entry pressure of the membrane have been studied. Two theoretical equations for the determination of membrane pore size have been proposed. The former equation was developed taking into account the deviation from the Laplace–Young equation due to the membrane structure by means of the structure angle. The latter equation was established considering only the range of alcohol concentration in which the dispersion component of liquid surface tension remains practically constant. Hydrophobicity has been expressed in terms of wetting surface tension, γ_L^w. Based on these measurements, the maximum concentration before the spontaneous wetting occurs would be predicted.     

Adsorption of Amphiphilic Dimers at Surfaces

Adsorption of amphiphilic dimers is analyzed in the framework of density functional Ono–Kondo theory. There are three configurations for dimers absorbed at a surface: one parallel to the surface and two perpendicular to the surface (AB and BA, with A or B touching the surface, respectively). Densities of molecules in each configuration are calculated from density functional theory and compared to Monte Carlo simulation data. There is good agreement between theory and simulations. It is shown that the parallel configuration is preferred over the perpendicular configuration, except when there are very strong asymmetries in intermolecular forces. In most cases, the parallel configuration is even preferred over the combination of the two perpendicular configurations.