Search results for " solution"
showing 10 items of 3084 documents
Aggregation of Free-Base Octacarboxyphthalocyanine in Aqueous Solutions
1999
Results of spectral (UV-VIS) investigations on the aggregation phenomena of the freebase 2,3,9,10,16,17,23,24-octacarboxypthalocyanine are reported. Phthalocyanine exists mainly in associated (aggregated) froms in water. The aggregates are present even in very diluted (10-7 -10-6 mol/dm-3) solutions. The hydrogen bonding between the carboxyl groups of the adjacent molecules in considered. The increase in pH and temperature, as well as the presence of the cationic surfactant and alcohols (in an appropriate quantity) cause a prtial or full disaggregation. The spectrum of the monomeric phthalocyanine from has been observed. The increase in H2Pc(COOH)8 concentration, the decrease in pH, as well…
Influence of Anion and Cation Structure of Ionic Liquids on Carboxylic Acids Extraction
2019
A recently proposed new mechanism and a model of reactive extraction of carboxylic acids by hydrophobic ionic liquids (ILs) was tested on five systems from published as well as from new equilibrium data on liquid-liquid extraction of butyric and lactic acids (BA and LA) from aqueous solutions. Two phosphonium and one ammonium ILs were used. The model describes experimental data for all systems with a good fit. The mechanism of acid extraction by ILs is very similar for all tested systems. This indicates a more general validity of the developed model. The model allows deeper understanding of regularities in carboxylic acid extraction by hydrophobic ILs. Stability constants of the first acid-…
Dual-Diameter Laterals in Center-Pivot Irrigation System
2022
Design strategies to enhance modern irrigation practices, reduce energy consumption, and improve water use efficiency and crop yields are fundamental for sustainability. Concerning Center-Pivot Irrigation Systems, different design procedures aimed at optimizing water use efficiency have been proposed. Recently, following a gradually decreasing sprinkler spacing along the pivot lateral with constant diameter and sprinkler flow rate, a new design method providing a uniform water application rate has been introduced. However, no suggestions were given to design multiple-diameter laterals characterized by different values of the inside pipe diameter. In this paper, first the previous design pro…
Solubilization by polysoaps
1994
The aqueous solubilization power of several series of micellar homopolymers and copolymers (''polysoaps'') is investigated. Using five insoluble or poorly water-soluble dyes, comparisons of the capacities are made with respect to the influence of structural variables such as the polymer backbone, the polymer geometry, the comonomer content, and the charge of the hydrophilic group. Some guidelines for polysoap structures suited for efficient solubilization are established. Noteworthy is that the solubilization capacities of the polysoaps are neither linked to the ability to reduce the surface tension of water, nor to the polarity of the solubilization sites deduced from spectroscopic probes.
Cyclodextrins in Polymer Synthesis: Influence of Acrylate Side Groups on the Initial Rate of Radical Polymerization of Various Acrylate/Methylated β…
2001
Methylated β-cyclodextrin was used to complex the hydrophobic monomers n-propyl acrylate (1), n-butyl acrylate (2), n-pentyl acrylate (3), n-hexyl acrylate (4), and cyclohexyl acrylate (5) respectively yielding the corresponding water-soluble host/guest-complexes 1a−5a. The complexes were polymerized in water by free radical mechanism and the initial polymerization rates (v0) determined. We found that v0 increases as follows: 1a (12.5), 2a (27.5), 3a (44.2), 5a (49.4), 4a (75.8 × 10-6 mol·L-1·s-1). To investigate the influence of the hydrophobic character of the guest monomers on the reaction rate, the water solubilities of the uncomplexed monomers 1−5 were determined by HPLC measurements.…
Synthesis of CO2-responsive polymers by post-polymerization modification
2014
Abstract We describe a general method to synthesize a double responsive polymer, exhibiting a temperature and CO 2 responsive behavior. The polymer derived from a controlled radical polymerization technique of pentafluorophenyl acrylate (PFPA), followed by a sequential post-polymerization modification of a CO 2 responsive- and thermo-responsive amines. Utilizing this approach three double responsive copolymers were synthesized, poly(3- N′,N′ -dimethylaminopropyl acrylamide- co - N -isopropyl acrylamide) (poly(DMPA- co -NIPAM)), poly( L -Arginine methyl ester acrylamide- co - N -isopropyl acrylamide) (poly(AME- co -NIPAM)) and poly( L -Arginine methyl ester acrylamide- co - N -cyclopropyl ac…
Thermodynamic studies of octyltrimethylammonium chloride in water
1992
Densities, heat capacities, enthalpies of dilution at 298 K and osmotic coefficients at 310 K of octyltrimethylammonium chloride were measured as functions of concentration. From the experimental data, the partial molar volumes, heat capacities, relative enthalpies, nonideal free energies and entropies at 298 K were derived as functions of concentration. A comparison between the above data and those of dodecyltrimethylammonium chloride reported in the literature shows that the increase of the alkyl chain length shifts the apparent molar volumevs. concentration curves towards greater values and the heat capacity, relative enthalpy and free energyvs. concentration curves towards smaller value…
Small angle scattering study of poly(methylmethacrylate)-blockpoly(ethylene oxide) block co-polymer in aqueous solution
2005
A combined Small Angle X ray (SAXS) and Neutron (SANS) Scattering study of aqueous solutions of a symmetric block copolymer consisting of poly(methyl methacrylate) (PMMA) and poly(ethylene oxide) (PEO) moieties is presented. The polymer forms slightly polydisperse spherical micelles in a wide range of concentration (0.03 – 6.7 w/V) and temperature (20°C ≤ T ≤ 65°C). A good description of the SANS data is obtained using a polydisperse core-shell model with a structure factor for a modified hard sphere potential. By increasing the concentration at constant T we observed a decrease of the aggregation number and an increase of solvation of PEO groups in the shell, opposite to what happens by in…
Continuum-uniform approach calculations of the solubility of hydrocarbons in water
1993
Abstract The ransfer free energies from gas phase to water for some hydrocarbons are calculated by means of a continuum-uniform model of the solvent. For the calculation of the cavitation energy a model based on the surface tension is proposed. The calculated values are compared with the experimental free energies obtained with and without a corrective factor that accounts for the difference in the solute—solvent sizes. Good agreement between the theoretical free energies and the corrected experimental data is obtained. Our calculations seem to show that the hydrophobic effect is directly related to the molecular surface area.
Insights into catanionic vesicles thermal transition by NMR spectroscopy
2012
Oppositely charged ionic surfactants can self-assemble into hollow structures, called catanionic vesicles, where the anionic-cationic surfactant pair assumes a double-tailed zwitterionic attitude. In the present work, multilamellar- to-unilamellar thermal transition of a mixed aqueous system of sodium dodecyl sulphate (SDS) and cetyl trimethyl ammonium bromide (CTAB), with a slight excess of the anionic one, has been investigated by 1H, 2H, 14N NMR spectra and 23Na transverse relaxation measurements. It has been inferred that an increase of the temperature enhances the SDS counterion dissociation, which can be considered as one of the driving forces of the mentioned transition. Moreover, in…