Drying dissipative structures of the deionized aqueous suspensions of colloidal silica spheres ranging from 29 nm to 1 μm in diameter

Macroscopic and microscopic dissipative structural patterns formed in the course of drying a series of the colloidal silica spheres ranging from 29 nm to 1 m in diameter have been observed in the aqueous deionized suspension on a cover glass. The broad ring patterns of the hill accumulated with the silica spheres are formed around the outside edges in the macroscopic scale for all spheres examined. The spoke-like cracks are also observed in the macroscopic scale and their number decreases sharply as sphere size increases. The pattern area and the time for the dryness have been discussed as a function of sphere size and concentration. The convection flow of water accompanied with that of the silica spheres and interactions among the silica spheres and substrate are important for the macroscopic pattern formation. The microscopic fractal structures of the wave-like patterns and branched strings are formed. Their fractal dimensions are determined. Microscopic patterns form in the narrow range of sphere sizes and concentrations and are determined mainly by the electrostatic and polar interactions between the spheres and/or between the sphere and substrate in the course of solidification.     

Distorted colloidal crystal of similar-sized aggregates (1.5 μm in diameter) of nano-sized diamond particles (4 nm in diameter)

Distorted colloidal crystal suspension of similar-sized aggregates of diamonds (1.5 μm in diameter) was obtained by the deionization of aqueous suspension of the pre-particles of diamond, 4 nm in diameter. The stability, characteristics, and the rigidity of the crystal-like suspensions were studied. The main cause for the formation of the similar-sized aggregates is deduced to be the cooperation between the van de Waals inter-particle attraction and the repulsion induced by the vigorous thermal motion of the pre-particles. The rigidity was evaluated from the microscopic observation in the sedimentation equilibrium. Fluctuation parameters of the distorted colloidal crystals estimated from the rigidities were between 0.03 and 0.06, which are quite similar to those of typical colloidal crystals and solids of hard spheres.     

Drying dissipative structure of similar sized aggregates (1.5 μm in diameter) of nano-sized diamond particles (4 nm in diameter)

Macroscopic and microscopic drying patterns were observed on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of aqueous suspensions of similar sized aggregates of diamonds (CD1), which formed from the deionization of the pre-particles of diamond 4 nm in diameter. Two kinds of macroscopic patterns, i.e., outer and inner broad rings, and spoke lines were formed. Cooperative drying processes of the convection, sedimentation, and solidification were clarified. Microscopic drying patterns showing the formation of very large dendritic aggregates from the CD1 particles were observed only when the excess amount of sodium chloride higher than 2 mM coexisted in the initial suspensions before dryness and further initial CD1 concentration is lower than 0.17 wt%.     

Drying dissipative structures of cationic gel spheres of lightly cross-linked poly(2-vinyl pyridine) (170 ∼ 180 nm in diameter) in the deionized aqueous suspension

Drying dissipative patterns of cationic gel crystals of lightly cross-linked poly(2-vinyl pyridine) spheres (AIBA-P2VP, 170?～?180 nm in diameter) were observed on a cover glass, a watch glass, and a Petri glass dish. Convectional patterns were recognized with the naked eyes. Two kinds of the broad rings were observed at the outside edge and inner region in the macroscopic drying pattern, and their size at the inner regions first decreased and then turned to increase as gel concentration decreased. Formation of the similar-sized aggregates, i.e., hierarchical aggregation and their ordered arrays were observed. This work supported strongly the formation of the microscopic drying structures of (a) ordered rings, (b) flickering ordered spoke-lines, (c) net structure, and (d) lattice-like ordered structures of the aggregated particles. The ordering of the similar-sized aggregates of the cationic gel spheres (AIBA-P2VP) in this work is similar to that of the large cationic gel spheres of poly(2-vinyl pyridine) (385?～?400 nm in diameter) and further to that of the anionic thermosensitive gel spheres of poly(N-isopropyl acrylamide). Role of the electrical double layers around the aggregates and their interaction with the substrates during dryness are important for the ordering. The microscopic drying patterns of gel spheres were different from those of linear-type polymers and also from typical colloidal hard spheres, though the macroscopic patterns such as broad ring formation were similar to each other.     

Coordination Features of a Polyaza-Bipyridine-Macrocyclic Ligand toward Co(II) and Cd(II) in Water and Dimethylsulfoxide

The coordination features of a polyaza macrocycle, containing the diverse bipyridine unit 4,4′-(2,5,6,11,14-pentaaza[15]-[15](2,2′)-bipyridylophane (L3), with Co(II) and Cd(II) have been studied in aqueous solution and in the aprotic solvent dimethylsulfoxide (DMSO). The study was carried out at 298 K by means of potentiometric, spectrophotometric and calorimetric techniques. The formation of the dinuclear species M₂ L3 is observed for Co(II) both in water and in DMSO, whereas Cd(II) is able to form this type of dinuclear complex only in DMSO. The FT-IR spectra of the mononuclear species ML3, formed in both solvents, provide evidence that the rigid structure of the polyaminic chain prevents metal ions from being coordinated by all of the nitrogens of the macrocyclic cavity, in good agreement with the behavior suggested by the thermodynamic parameters. The results are compared with those for the complexation of Co(II) and Cd(II) with similar polyazamacrocycles containing a bipyridine unit directly inside the cavity. Semi-empirical calculations were also performed to obtain structural information.     

Cationic gel crystals of lightly cross-linked poly(2-vinylpyridine) spheres (170∼180 nm in diameter) in the deionized aqueous suspension

Colloidal crystallization of deionized suspensions of the cationic gel spheres of lightly cross-linked poly(2-vinylpyridine), AIBA-P2VP (170～180 nm in diameter) has been studied from the microscopic observation, morphology, phase diagram, and elastic property. Critical concentrations of melting that coexisted with ion-exchange resins were low compared with those without resins and decreased as the degree of cross-linking decreased. The density of a gel sphere in suspension state (ρ), i.e., weight percent of the gel spheres divided by the corresponding volume percent, was between 0.5 and 0.8, and decreased as the degree of cross-linking of the spheres decreased. The ρ values also decreased with decreasing size of gel spheres, which supports the small P2VP gel spheres being softer than the large ones. The closest intersphere distances of the crystals were much longer than the hydrodynamic diameters of the gel spheres especially at low sphere concentrations. Fluctuation parameters evaluated from the rigidities of the crystals of AIBA-P2VP (0.05～0.09) were similar to those of gel crystals of cationic gel spheres of lightly cross-linked poly(2-vinylpyridine) spheres coated with poly(ethylene glycol), 400 nm in diameter, and thermo-sensitive gel spheres of pNIPAm, poly(N-isopropylacrylamide), but larger than those of typical colloidal hard spheres. The stable crystal phase formed beyond the adsorbed monolayer of cationic gel spheres on the surface of the substrate. These experimental findings support important role of the extended electrical double layers around the cationic gel spheres in addition to the excluded volume effect of the sphere themselves on the crystallization.     

Morphological,mechanical, and in vitro cytocompatibility analysis of poly(vinyl alcohol)–silica glass hybrid scaffolds reinforced with cellulose nanocrystals

Cellulose nanocrystal-reinforced poly(vinyl alcohol)/silica glass hybrid scaffolds were fabricated using the freeze-drying method. In this study, we develop molecular-level-based hybrid scaffolds with possible bioactivity behavior by adding silica sol–gel. The results showed a highly porous structure and a significant improvement in mechanical performance (stiffness) of hybrid scaffolds with an increased content of cellulose nanocrystals followed by the addition of silica-based bioactive glass. In vitro cell study with MC3T3-E1 cells on hybrid scaffolds for 1 and 3 days revealed good cell adhesion and growth. Thus, the obtained hybrid scaffold may be a competitive candidate for bone tissue engineering applications.     

Inclusional association as studied by the drying dissipative structure. Part 1. Drying patterns of α-, β- and γ-cyclodextrin

Macroscopic and microscopic drying patterns were observed on a cover glass, a watch glass, and a Petri glass dish during the course of dryness of aqueous solutions of α-cyclodextrin (αCD), β-cyclodextrin (βCD), and γ-cyclodextrin (γCD), i.e., cone shape oligomers of polysaccharide. For all CD molecules, two kinds of macroscopic patterns, outside and inner broad rings and spoke lines formed. Multi-broad rings were formed for βCD in the inner region of the main broad ring at the outside edge especially at the high concentrations. Cooperative drying processes of the convection, sedimentation, and solidification were clarified. Microscopic drying patterns showing the formation of rod-like and/or sward-like crystals were observed mainly in the direction along the spoke lines. The microscopic patterns of βCD were similar to those of some of polysaccharides and polynucleotides the authors studied previously. α- and γ-cyclodextrins were slightly hygroscopic, and clear-cut drying patterns were not observed.     

Redox-active silica nanoparticles. Part 4. Synthesis, size distribution, and electrochemical adsorption behavior of ferrocene- and (diamine)(diphosphine)-ruthenium(II)-modified Stöber silica colloidal particles

Stöber silica nanoparticles with a diameter of approximately 800 nm are covalently modified by redox-active ferrocene or (diamine)(diphosphine) ruthenium(II) units attached to a spacer. The particles are characterized by NMR spectroscopic and chemical techniques. Two variants of modification by condensation are compared. Besides an estimation of the size and the particle porosity, the agglomeration behavior in solvents of different polarity is investigated. The adsorption of the particles to an electrode surface is followed.     

Dielectric relaxation processes and ionic conduction behaviour in poly(ethylene oxide)–montmorillonite clay nanocomposite aqueous colloidal suspensions

The relative complex dielectric function, electric modulus, alternating current (ac) electrical conductivity and complex impedance spectra of poly(ethylene oxide) (PEO)–montmorillonite (MMT) clay aqueous colloidal suspension (hydrocolloids) were investigated over the frequency range 20 Hz to 1 MHz at 27 °C. The relaxation time corresponding to electrode polarisation and Maxwell–Wagner polarisation processes (ionic conduction) were determined from these plots. The direct current (dc) electrical conductivity is evaluated from the fitting of real part ac conductivity data to the Jonscher power law. A correlation of increase in dc conductivity and decrease of ionic conduction relaxation time with increase of clay concentration is discussed considering intercalation of PEO chains and its dynamics and exfoliation of MMT clay nanoplatelets in these complex fluids. The formation of PEO–MMT clay supramolecular lamellar nanostructures with increase in continuity of lamellae arrangements were explored for the structural conformation of these nanocomposite novel materials.     

Adsorption, desorption, and surface-promoted hydrolysis of glucose-1-phosphate in aqueous goethite (α-FeOOH) suspensions

Adsorption, desorption, and precipitation reactions at environmental interfaces govern the fate of phosphorus in terrestrial and aquatic environments. Typically, a substantial part of the total pool of phosphorus consists of organophosphate, and in this study we have focused on the interactions between glucose-1-phosphate (G1P) and goethite (α-FeOOH) particles. The adsorption and surface-promoted hydrolysis reactions have been studied at room temperature as a function of pH, time, and total concentration of G1P by means of quantitative batch experiments in combination with infrared spectroscopy. A novel simultaneous infrared and potentiometric titration (SIPT) technique has also been used to study the rates and mechanisms of desorption of the surface complexes. The results have shown that G1P adsorption occurs over a wide pH interval and at pH values above the isoelectric point of goethite (IEP(goethite) = 9.4), indicating a comparatively strong interaction with the particle surfaces. As evidenced by IR spectroscopy, G1P formed pH-dependent surface complexes on goethite, and investigations of both adsorption and desorption processes were consistent with a model including three types of surface complexes. These complexes interact monodentately with surface Fe but differ in hydrogen bonding interactions via the auxiliary oxygens of the phosphate group. The apparent desorption rates were shown to be influenced by reaction pathways that include interconversion of surface species, which highlights the difficulty in determining the intrinsic desorption rates of individual surface complexes. Desorption results have also indicated that the molecular structures of surface complexes and the surface charge are two important determinants of G1P desorption rates. Finally, this study has shown that surface-promoted hydrolysis of G1P by goethite is base-catalyzed but that the extent of hydrolysis was small.     

Alternate sign reversal in the ζ potential and synchronous expansion and contraction in the absorbed multi-layers of poly(4-vinyl-N-n-butylpyridinium bromide) cations and poly(styrene sulfonate) anions on colloidal silica spheres

Alternative multiple absorbed layers of up to ten macrocations [poly(4-vinyl-N-n-butylpyridinium bromide)] and macroanions [sodium poly(styrene sulfonate)] are formed on colloidal silica spheres above the critical concentration of macroions, m*. The m* value is the minimum number of macroions required to reverse the sign of the ζ potential of the spheres in the first absorption step. Alternative sign reversal in the ζ potential and expansive–contractive thickness changes are observed by the repeated and alternate addition of macrocations first and macroanions next. During multiple absorption, the pH and conductivity values decrease and increase continuously as the number of absorbed layers increases. When the macroanions are added first, sign reversal in the ζ potential and reversible expansion and contraction do not occur. Breaking of the alternate multiple-type absorption occurs when equivalency in the number of dissociative groups of macrocations and macroanions is broken. Synchronous conformational changes of macrocations and macroanions in the multiple- absorbed layers, where balancing of the conformational rigidities with the multiple electrostatic attraction and repulsion between macrocations and anions occurs, are supported strongly. Received: 12 January 1999 Accepted in revised form: 25 March 1999     

Stability and Coordination Mode of Complexes of Polyphosphates and Polymetaphosphates with Copper(II) Ions in Aqueous Solution—Potentiometric,Spectral and Theoretical Studies

Complexes of copper(II) with a number of polyphosphate and polymetaphosphate anions have been studied in aqueous solutions by potentiometric, spectroscopic and theoretical methods. Stability constants of the complexes have been determined as well as their coordination modes. Results of the equilibrium studies provided evidence for the formation of ML, MHL and ML(OH) _x type complexes with the ligands studied. The length of the polyphosphate chain was found to affect the oxygen atom charge that is reflected in the stability constants of the ML type complexes. Moreover, the stability of the complex is also influenced by the spatial arrangement of the phosphate groups in phosphates and metaphosphates. The spectral parameters observed for certain complexes have permitted us to deduce the inner coordination sphere of the studied complexes.     

Synthesis,structural characterization,and in vitro antimicrobial properties of salicylate and pyrazoline complexes of bismuth(III)

Displacement reactions of dichlorobismuth(III)pyrazolinates with oxygen donors such as sodium salicylate and acetate in 1?:?1 and 1?:?2 molar ratio in refluxing anhydrous benzene yields (C₁₂H₁₅N₂OX)Bi(C₆H₄O₃), (CH₃COO)BiCl(C₁₅H₁₂N₂OX), and (CH₃COO)₂Bi(C₁₅H₁₂N₂OX) [C₁₂H₁₅N₂OX?=?3(2′-hydroxyphenyl)-5-(4-X-substituted phenyl) pyrazoline X?=?H in 1,5,9, CH₃ in 2,6,10, OCH₃ in 3,7,11, and Cl in 4,8,12, respectively, (C₆H₄O₃)?=?salicylate and (CH₃COO)?=?acetate]. Newly synthesized derivatives are brown solids, soluble in organic solvents like benzene, chloroform, and acetone. The compounds have been characterized by elemental analyses (C, H, N, Cl, and Bi), molecular weight measurements, and spectral (IR, ¹H NMR, ¹³C NMR) studies. The (C₁₂H₁₅N₂OX) and (C₆H₄O₃) are bidentate while (CH₃COO) is monodentate to bismuth(III), leading to a distorted trigonal bipyramidal structure. The complexes were screened against different bacteria and fungi showing potential antibacterial and antifungal activities.     

Synthesis,characterization, and in vitro antibacterial and antifungal studies of tin(IV) thiohydrazide complexes

Reaction of tin dichloride and tin tetrachloride with cyclohexylamine-N-thiohydrazide (ChaThz) [L¹] and 1,3-propanediamine-N-thiohydrazide (PdaThz) [L²] results in [Sn(ChaThz)₂] (1), Sn(ChaThz)₂Cl₂] (2), [Sn(PdaThz)₂] (3), and [Sn(PdaThz)₂Cl₂] (4), in which the thiohydrazide coordinates to tin through imine nitrogen and thioamide sulfur. The ratio metal?:?ligand was 1?:?2 for all complexes. The tin(IV) thiohydrazide complexes were characterized by elemental analysis, IR, UV-Vis, ¹H-NMR, ¹¹⁹Sn NMR, and mass spectral studies. Using the disc diffusion method, the ligands and metal complexes were screened for in vitro antibacterial activities against four pathogenic bacteria, Escherichia coli, Staphylococcus aureus, P. aeruginosa, and Bacillus cereus and for antifungal activities against Aspergillus flavus, A. carbonarius, A. niger, and A. fumigatus. While the tin(IV) complexes exhibited moderate antifungal activities, their parent ligands showed much higher and long-lasting broad spectrum of bioactivity against fungal growth. This was particularly the case for L¹ whose fungal inhibitory activity by the end of the experimental period was comparable and, for the most part, more pronounced than that of AmB. This higher activity of L¹ was maintained specifically against S. Aureus but in general, bacteria were more susceptible to complexes than ligands.     

Influence of ethanol and ultrasound on drying,bioactive compounds,and antioxidant activity of strawberries (Fragaria × ananassa)

This study aimed to evaluate the use of ethanol (ET) and ultrasound (US) in convective drying of strawberry slices, as well as the effect on physicochemical, bioactive, and antioxidant parameters. For this, strawberry slices with a thickness of 0.005 m were pretreated with ET (in different volume fractions), US, and a combination of both. Drying kinetics were performed for control strawberry slices (without ET and US) and pretreated with 50% ethanol (ET50), 50% ethanol and ultrasonic (ET50US), 100% ethanol (ET100), and 100% ethanol and ultrasonic (ET100US) at a temperature of 60 °C. Empirical and diffusive models were fitted to the experimental data to describe the drying kinetics, and the fresh and dried slices were analyzed according to the parameters of water activity (aw), water content, total phenolic compounds (TPC), total anthocyanins (ATS), vitamin C and antioxidant activity (AA) (ABTS?+, DPPH?, and FRAP). The use of the ET100US combination provided an increase in the moisture transport process, higher drying rate, shorter process time (570 min), and reduction of a_w to a safe value (a_w <0.5), however, it sharply degraded the TPC, ATS, and AA. The ET50US pre-treatment even with a drying time of 690 min was the most efficient, since the values of TPC, ATS, and vitamin C suffered smaller reductions, where the AA varied in only 10.32%, 13.78% and 6.54% for the methods ABTS?+, DPPH?, and FRAP, respectively when compared to fresh strawberry. In this sense, it can be stated that the pre-treatment with 50% ethanol and ultrasound (ET50US) showed less reduction in the degradation of bioactive and antioxidant properties, and in the minimization of drying time for strawberry slices.     

Synthesis,spectroscopic characterization,and antibacterial assays in vitro of a new platinum(II) complex with methionine sulfoxide

A new platinum(II) complex with methionine sulfoxide was synthesized and characterized by chemical and spectroscopic techniques. Elemental analyses, mass spectrometric measurements (electrospray ionization quadrupole time-of-flight mass spectrometry), and thermal analyses of the solid compound fit the composition [(C₅H₁₀NO₃S)Pt(µ-Cl)₂Pt(C₅H₁₀NO₃S)]?·?2.5H₂O. Infrared spectroscopic data indicate coordination of the ligand to Pt(II) through the nitrogen of NH₂ and the sulfur of the S=O group. ¹H-¹⁵N nuclear magnetic resonance spectroscopic data confirm nitrogen coordination. Antibacterial activities were evaluated by antibiogram assays using the disc diffusion method. The platinum(II) complex showed antibacterial activity against Gram-negative Pseudomonas aeruginosa bacterial cells.     

Densities and Viscosities of Tris(acetylacetonato)cobalt(III) Complex Solutions in Various Solvents

The densities and the viscosities of tris(acetylacetonato)cobalt(III) solutions in acetonitrile, dichloromethane, chloroform, tetrachloromethane, benzene, toluene, ethylbenzene, and p-xylene were measured in the dilute concentration regions at several temperatures ranging from 278 to 313 K under ambient pressure. The partial molar volumes of the solvents and solute were calculated. They are independent of concentration and increase slightly as the temperature increases. The viscosity A- and B-coefficients of the Jones-Dole equation were obtained. The A-coefficients were found to be zero within experimental error. The B-coefficients are positive and decrease as the temperature increases. Thermodynamic quantities of activation for viscous flow were calculated on the basis of Eyring’s viscosity equation. From the quantities obtained in this study, along with some information from the literature, it is suggested that structure-making interactions occur between the segments of the complex and the solvent molecules. These interactions include electrostatic interactions between the local charge on the complex and the dipole moment of the solvent in solutions of acetonitrile and dichloromethane, interlocking packing interactions along C ₃-axis of the complex with solvent in solutions of chloroform and tetrachloromethane, and π-electron interactions between the chelate ring of the complex and the solvent in solutions of benzene, toluene, ethylbenzene, and p-xylene.     

Size,zeta potential,and semiconductor properties of hybrid CdS–ZnS nanoparticles in a stable aqueous colloidal solution

Russian Journal of Physical Chemistry A - A stable aqueous colloidal solution of core–shell CdS–ZnS nanoparticles is obtained via the chemical condensation of carboxyl-containing...     

Thermodynamic Features of the Complexation of Neodymium(III) and Americium(III) by Lactate in Trifluoromethanesulfonate Media

The protonation of lactate has been studied in a variety of electrolyte solutions using microcalorimetry to reveal a distinct medium influence imposed on the thermochemistry of the equilibrium. The thermochemistry of lactate protonation, when studied directly in 1.0 mol⋅L⁻¹ sodium lactate, agreed well with the studies performed in trifluoromethanesulfonate (triflate). This thermodynamic agreement suggests that the physical chemistry of lactate in the solutions applicable to the TALSPEAK process—a solvent extraction method for separating trivalent actinides from trivalent lanthanides within the scope of used nuclear fuel processing efforts—may be simulated in triflate solutions. Potentiometry, spectrophotometry and microcalorimetry have been subsequently used to study the thermodynamic features of neodymium and americium complexation by lactate using triflate as a strong background electrolyte. Three successive mononuclear lactate complexes were identified for Nd(III) and Am(III). The stability constants for neodymium, β ₁₀₁=2.60±0.01, β ₁₀₂=4.66±0.02 and β ₁₀₃=5.6±0.1, and for americium, β ₁₀₁=2.60±0.06, β ₁₀₂=4.7±0.1 and β ₁₀₃=6.2±0.2, were found to closely agree with the thermodynamic studies reported in sodium perchlorate solutions. Consequently, the thermodynamic medium effect, imposed on the TALSPEAK-related solution equilibria by the presence of strong background electrolytes such as NaClO₄ and NaNO₃, does not significantly impact the speciation in solution.