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1.
The preparation of microlatex dispersions from microemulsions of a monomer (styrene, methylmethacrylate or vinyl acetate) is described. A simple method for preparing the microemulsion has been devised. This consists of forming a water-in-oil (w/o) emulsion using a low (HLB) surfactant (nonylphenol with 5, 6 or 7 moles ethylene oxide) and then titrating with an aqueous solution of a high HLB surfactant (nonylphenol with 15 or 16 moles ethylene oxide). A small amount of anionic surfactant (sodium lauryl sulphate, sodium dodecyl benzene sulphonate or dioctyl sulphosuccinate) was also incorporated to enhance the stability of the w/o emulsion and facilitate the inversion to an o/w microemulsion. The droplet-size distribution of the resulting microemulsion was determined using photon-correlation spectroscopy.Three different methods of polymerising the microemulsion were used. These were thermally induced polymerisation using potassium persulphate, azobis-2-methyl propamidinium dichloride (AMP-water-soluble initiators) or azobisisobutyronitrile (AIBN, an oil-soluble initiator). All these initiators required heating to 60°C, i.e. above the stability temperature of the microemulsion. In this case, the microlatices produced were fairly large (37–100 nm diameter) and had a broad particle-size distribution. The second polymerisation procedure was chemically induced using a redox system of hydrogen peroxide and ascorbic acid. This produced microlatices with small sizes (18–24 nm diameter) having a narrow-size distribution. The microlatex size was roughly two to three times the size of the microemulsion droplets. This showed that collision between two or three microemulsion droplets resulted in their coalescence during the polymerisation process. The third method of polymerisation was based on UV irradiation in conjunction with K2S2O8, AMP or AIBN initiators. In this case, the microlatex size was also small (30–63 nm) with a narrow particle-size distribution.Microlatex particles were also prepared using a mixture of monomers (styrene plus methylmethacrylate) or mixture of monomers and a macromonomer, namely methoxy (polyethylene glycol)methacrylate. The latter was used to produce hairy particles, i.e. with grafted polyethylene oxide (PEO) chains.The stability of the microlatices was determined by adding electrolytes (NaCl, CaCl2, Na2SO4 or MgSO4) to determine the critical flocculation concentration (CFC). The nonionic latices were very stable giving no flocculation up to 6 mol dm–3 NaCl or CaCl2 and a CFC of 0.6 mol dm–3 for Na2SO4 or MgSO4. Charged latices were less stable than the nonionic ones. The critical flocculation temperatures (CFT) of all latices were determined as a function of electrolyte concentration. With the nonionic latices, CFC was higher than the -temperature for polyethylene oxide at the given electrolyte concentration. This indicated enhanced steric stabilisation as a result of the dense packing of the chains and hence an elastic contribution to the steric interaction. This was not the case with the charged latex, which showed CFT values lower than the -temperature. The hairy latices [i.e. those containing methoxy polyethylene glycol (PEG) methacrylate] were also less stable towards electrolyte (CFT was much lower than -temperature), indicating a low density of PEO layers. 相似文献
2.
The aggregation of four separate polystyrene latices, ranging in diameter from 210 nm to ca. 1 m, using sodium chloride and magnesium sulphate as the electrolytes, has been examined turbidimetrically. The reversibility of the aggregation was examined using a dialysis technique. It was found that for large particle size latices, diameters 781 nm and 1 m, aggregation was reversible in sodium chloride even at concentrations up to 0.5 mol dm–3. The aggregation of smaller particles was not reversible. The aggregation of large particles in magnesium sulphate solutions was not readily reversed by dialysis. The latter result does not appear to agree with theoretical predictions.Dedicated to Professor Dr. Armin Weiss on the occasion of his 60th birthday. 相似文献
3.
An apparatus, that allows simultaneous measurements to be made of excess osmotic pressure and optical diffraction of polymer colloid dispersions, has been constructed. Results are reported for monodisperse polystyrene latices at several salt concentrations. An interesting feature of the results is a clear indication of a co-existence region occurring with particles of 182 nm diameter in sodium chloride concentrations of 10–4 mol dm–3 相似文献
4.
Summary The stoichiometry and kinetics of the oxidation of hydroxylammonium ion by the 12-tungstocobaltate(III) anion has been studied in hydrochloric acid medium. The ratio of mols of oxidant consumed per mol of hydroxylammonium ion is 11 and the evolution of nitrogen is confirmed. In the 0.1–1.0 mol dm–3 [H+] region, the oxidation is acid-independent and obeys the empirical rate law: –d[oxidant]/dt=k[oxidant] [reductant] where k=(3.51±0.18)×10–4 mol–1dm3s–1 at 22.4±0.1C and I=2.0 mol dm–3 (NaCl). Possible reaction steps and mechanism are suggested. 相似文献
5.
Ljubiša M. Ignjatović Jiří Barek Jiří Zima Dragan A. Marković 《Mikrochimica acta》1996,122(1-2):101-108
The optimum conditions were established for the determination of the genotoxic substance 1-(4-bromophenyl)-3,3-dimethyltriazene by differential-pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 × 10–4 to 1 × 10–7 mol dm–3. The sensitivity of the determination can be improved through adsorptive accumulation of the investigated substance on the surface of the hanging mercury drop electrode: differential pulse adsorptive stripping voltammetry can be used in the concentration range 1 × 10–7 to 2 × 10–10 mol dm–3. The relative standard deviation (for ten determinations at 2 × 10–10 mol dm–3) was 7.5%. 相似文献
6.
The solvent extraction of tin(IV) from chloride media withtris(2-ethylhexyl)phosphate is presented. Tin(IV) is extracted quantitatively from 2.75–3.20 mol dm–3 hydrochloric acid using 6.38–6.91 mol dm–3
tris(2-ethyl-hexyl)phosphate dissolved in toluene as an extractant. After back-extraction of tin(IV) with water from thetris(2-ethylhexyl)phosphate phase, it is estimated spectrophotometrically following complexation with pyrocatechol violet. The recommended range for determination of tin(IV) is 10–100 g. The probable extracted species is SnCl4·2TEHP. The method is applicable to the analysis of alloy samples with a detection limit of 0.4 g/ml (for 10 g of tin) and a relative standard deviation between 0.21–0.32%. 相似文献
7.
G. Horányi 《Reaction Kinetics and Catalysis Letters》1996,59(2):211-217
The adsorption of Cl– ions on rhodium black layer (rhodized electrodes) was studied by radiotracer technique at low Cl– ion concentrations (c10–5 mol dm–3) in 1 mol dm–3 H2SO4 supporting electrolyte. The specific adsorption of Cl– ions was treated in terms of partition between solution phase and electrodeposited Rh black layer. The potential dependence of the partition coefficient is determined. 相似文献
8.
The anionic chelate of iron(III)-2,2-dihydroxyazobenzene (H2L), [FeL2]–, formed 1 1 ion-pair with crystal violet cation (CV+), CV+ [FeL2]–, and was adsorbed on a surface of transparent polyvinyl chloride (PVC) film plasticized with di-n-octyl phthalate. Enrichment of the blue violet species of the ion-pair onto the transparent PVC film has enabled a highly sensitive and simple method for the determination of iron(III). The detection limits are 1 × 10–8 mol dm–3 (0.6 ppb) by spectrophotometry at 592 nm, and 4 × 10–8 mol dm–3 (2 ppb) by visual colorimetry. The method has been successfully applied to the determination of iron in water samples and human serum. No preparatory procedures for the separation of serum protein and other coexisting substances are required, since ion-pair adsorption process provides a new method to prevent interference of serum matrix. 相似文献
9.
P. C. Schulz M. A. Morini R. M. Minardi J. E. Puig 《Colloid and polymer science》1995,273(10):959-966
The aggregation of dodecyltrimethylammonium hydroxide (DTAOH) aqueous solutions has been studied by several methods. It is stepwise and four critical points were found. AtC
T=(2.51±0.10)×10–4 mol · dm–3 the surface excess becomes zero, atC
T=(1.300±0.041)×10–3 mol · dm–3 small aggregates from, which grow with concentration. AtC
T=(1.108±0.010)×10–2 mol · dm–3 true micelles form (CMC) and at (3.02±0.28)×10–2 mol · dm–3 the structure of micelles probably changes affecting their properties. The DTAOH micelles are highly ionized (=0.8) at the CMC, and decreases to reach very small values when the total concentration increases. 相似文献
10.
The aqueous polymerization of methacrylamide initiated by potassiumpersulfate-L-cystein hydrochloride redox system has been studied at 35±0.01 C under nitrogen atmosphere. The initial rate of polymerization has been found to be directly proportional to the monomer and activator concentration, in the range of 1.0 × 10–1 to 4.0 × 10–1 mol dm–3 and 1.25 × 10–3 to 5.0 × 10–3 mol dm–3 respectively. The order with respect to initiator has been found to be 0.5, indicating thereby that the termination takes place by bimolecular process. The overall energy of activation has been found to be 53±1 KJ/mol. 相似文献
11.
Refat Abdel-Hamid 《Monatshefte für Chemie / Chemical Monthly》1988,119(4):429-438
The electrochemical reduction of phenolphthalein in dimethylformamide solution containing 0.1 mol dm–3 tetraethylammonium perchlorate at the hanging dropping mercury electrode showed an irreversible two-electron voltammetric peak. It was found that the CV peak is diffusion-controlled at low concentrations (0.4 mmol dm–3). At higher concentration (0.5 mmol dm–3) a postpeak was developed besides the diffusion-controlled one which was assigned to the adsorbed depolarizer. Cyclic voltammetric studies indicate that phenolphthalein follows an ECEC mechanism. Convolution and deconvolution potential sweep voltammetry confirm that mechanism.
Mechanismus der voltametrischen Reduktion von Phenolphthalein an der Quecksilberelektrode inDMF
Zusammenfassung Die elektrochemische Reduktion von Phenolphthalein an der tropfenden Quecksilberelektrode in Dimethylformamidlösung mit einem Gehalt von 0.1 mol dm–3 an Tetraethylammoniumperchlorat zeigte ein irreversibles voltametrisches Maximum für zwei Elektronen. Es zeigte sich, daß der CV-Peak bei niederen Konzentrationen (0.4 mmol dm–3) diffusionskontrolliert ist. Bei höheren Konzentrationen (0.5 mmol dm–3) entwickelte sich ein nachkommendes Maximum neben dem diffusionskontrollierten, welches dem adsorbierten Depolarisator zugeordnet wurde. Untersuchungen mittels cyclischer Voltametrie zeigten, daß Phenolphthalein einem ECEC-Mechanismus folgt. Konvolutions-und Dekonvolutions-Potential-Sweep-Voltametrie bestätigten diesen Mechanismus.相似文献
12.
Isothermal titration calorimetry (ITC) measurements of the mixture of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB) with negatively charged, hairy copolymer latices (poly-(2,3-epoxypropylmethacrylate-co-methacrylic acid) in different ratio) at high water excess indicate a monomer adsorption mechanism of CTAB by the polymer particles. The number of adsorbed CTAB molecules at saturation corresponds approximately to the number of negative elementary charges bound at the surface of the latices. The mixing enthalpy is the sum of demicellization and sorption enthalpies. At 25 °C for CTAB the demicellization enthalpy amounts to 10 kJ/mol, whereas the adsorption enthalpy varies from –7 kJ/mol (surface charge density of the latices
=–0.37 C/m2) to +3 kJ/mol (=–0.085 C/m2). The hydrodynamic radius
RH of the latex particles upon titration of cationic detergent and salt (NaBr) decreases by about 2 nm until the onset of aggregation near the isoelectric point. Titration of nonionic or anionic detergents has much less influence on the hydrodynamic radius and produces no measurable adsorption heat. The results are consistent within a model of latex particles with extended negatively charged polymer chains interacting predominantly via Coulombic forces with detergents. 相似文献
13.
Micellization characteristics and counterion binding properties of cetyltrimethyl ammonium bromide (CTAB) in presence of urea and a nonionic surfactant polyoxyethylene sorbitan monolaurate (PSML), and of sodium dodecyl sulphate (SDS) in presence of urea as well as of several mixtures of CTAB with a bile salt, sodium cholate (NaC), and sodium chloride have been studied. Both urea and PSML have increased the critical micelle concentration (CMC) of the surfactants, the former being more effective than the latter. The analysis of the results supports the pseudophase micellar model to hold over the mass action model. Pure CTAB micelles bind more counterions (96 %) than pure SDS micelles (87 %), and the decreasing effect of urea on the binding is less in case of the former than the latter. A 41 mixture of CTAB and sodium cholate (NaC) can micellize and the micelles bind 87 % bromide ion, whereas 21 and 11 mixtures do not micellize. Micelles of 11 mixture of CTAB and NaCl can bind counter bromide ions to the extent of 92 %. The limiting concentrations of urea required to effect counterion binding by CTAB and SDS micelles are 0.15 mol dm–3 and 0.25 mol dm–3, respectively. Such effect is shown by PSML on CTAB at a ratio 0.281. The activation energy of conduction of SDS has increased in the presence of urea up to a concentration of 4 mol dm–3, at higher concentrations the activation energy has decreased, the effect being more for surfactant concentration above CMC than below. 相似文献
14.
Holder Alvin A. Brown Ross F. G. Marshall Sophia C. Payne Vince C. R. Cozier Maria D. Alleyne Walter A. Bovell Christopher O. 《Transition Metal Chemistry》2000,25(5):605-611
A detailed investigation of the oxidation of L-ascorbic acid (H2A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 [ascorbate]
T
0.045 mol dm–3, 3.62 pH 5.34, and 12.0 30.0 °C, 0.50 I 1.00 mol dm–3, and at ionic strength 0.60 mol dm–3 (NaClO4). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k
obs = (k
1
K
1)[ascorbate]
T
/(K
1 + [H+]). The second order rate constant, k
1 [rate constant for the reaction of the cobalt(III) complex and HA–] at 25.0 °C is 2.31 ± 0.13 mol–1 dm3 s–1. H
= 30 ± 4 kJ mol–1 and S
= –138 ± 13 J mol–1 K–1. K
1, the dissociation constant for H2A, was determined as 1.58 × 10–4 mol dm–3 at an ionic strength of 0.60 mol dm–3, while the self exchange rate constant, k
11 for the title complex, was determined as 1.28 × 10–5 dm3 mol–1 s–1. An outer-sphere electron transfer mechanism has been proposed. 相似文献
15.
Summary The kinetics of the first step of base hydrolysis oftrans-bis(Hmalonato)bis(ethylenediamine)cobalt(III) [malH–=HO2CCH2CO
2
–
] has been investigated in the 15–35° C range, I=0.3 mol dm–3 (NaClO4) and [OH–]=0.015–0.29 mol dm–3. The rate law is given by –d In[complex]T/dt=k1[OH–] and at 30° C, k1=8.5×10–3 dm3 mol–1s–1, H=117.0±7.0 kJ mol–1 and S=99.0±24.0 JK–1mol–1. The activation parameters data are consistent with the SN1 cb mechanism. 相似文献
16.
Guo Yanhe Ge Qingchun Lin Hai Lin Huakuan Zhu Shourong 《Transition Metal Chemistry》2003,28(6):668-675
The ligands 1,10-N,N-bis(2-hydroxymethylbenzoyl)-1,4,7,10-tetraazadecane (L1) and 1,11-N,N-bis(2-hydroxymethylbenzoyl)-1,4,8,11-tetraazaundecane (L2) have been synthesized. The stability constants of NiII complexes of ligands L1 and L2 have been studied at 25 °C using pH titrations. The kinetics of general acid (HCl, 0.04–2.34 mol dm–3) or buffer (DEPP or DESPEN, 0.05 mol dm–3, pH 4.83–5.72)-catalyzed dissociation of these NiII complexes have been investigated at 25 °C using a stopped-flow spectrophotometer. The ionic strength of solution was controlled at I = 2.34 mol dm–3 (KCl + HCl) and I = 0.1 mol dm–3 (KNO3, buffer), respectively. The kinetic dissociation of NiII complexes catalyzed by HCl obeys the equilibrium k
obs = k
1d + k
2H[H+], whereas in buffer solution the observed rate constant k
obs = k
d + k
1H[H+]. At pH < 1.5, both the proton-assisted and direct protonation pathways contribute to the rates, whereas solvation is the dominant pathway at pH > 6. In the 4.8–5.7 pH range, the complexes dissociate mainly through a proton-assisted pathway. 相似文献
17.
John E. Nicholas Andrew I. Spiers Nicholas A. Martin 《Plasma Chemistry and Plasma Processing》1986,6(1):39-51
Studies of time-resolved absorption spectra of transient species in the decomposition of NH3 by an r.f. pulse discharge together with product analysis showed that the major radical formed was NH at concentrations of the order of 10–6 mol dm–3 (105 molec. cm–3). Possible mechanisms for the formation of the radical during the discharge and its decay following pulse cut-off were tested by computer simulation of the kinetic data. Following zero-order formation with rate coefficient 0.19±0.03 mol dm–3 s–1, the decay was second order in NH with rate coefficient 2.1±0.5×109 mol–1 dm3 s–1 both for pure NH3 and where NH3/rare gas mixtures were investigated. The kinetic data are consistent with NH removal in a nonassociative radical-radical reaction proceeding via a short-lived collision complex, probably 2NH N2H2 N2 + H2. 相似文献
18.
Summary Base hydrolysis of methyl ethylenediaminemonoacetate has been studied at I=0.1 mol dm–3 (NaClO4) over the pH range 7.4–8.8 at 25 °C. The proton equilibria of the ligand can be represented by the equations, where E is the free unprotonated ester species. Values of pK1 and pK2 are 4.69 andca. 7.5 at 25° (I=0.1 mol dm–3). For base hydrolysis of EH+, kOH=1.1×103 dm3 mol–1 s–1 at 25 °C. The species E is shown to undergo lactamisation to give 2-oxopiperazine (klact
ca. 1×10–3 s–1) at 25 °C. Formation of the lactam is indicated both by u.v. measurements and by isolation and characterisation of the compound.Base hydrolysis of the ester ligand in the complex [CuE]2+ has been studied over a range of pH and temperature, k
OH
25
=9.3×104 dm3 mol–1 s–1 with H=107 kJ mol–1 and S
298
=209 JK–1 mol–1. Base hydrolysis of [CuE]2+ is estimated to be some 1055 fold faster than that of the free ester ligand. The results suggest that base hydrolysis occursvia a chelate ester species in which the methoxycarbonyl group of the ligand is bonded to copper(II). 相似文献
19.
L. Wojnárovits 《Journal of Radioanalytical and Nuclear Chemistry》1992,166(2):143-152
The -propionic acid methyl ester radical was produced in dissociative electron capture reaction of 2-chloropropionic acid methyl ester. The absorption maxima of the radical are at 310 and 300 nm in cyclohexane and water with extinction coefficients of 440±50 and 400±50 mol–1 dm3 cm–1. The second order decay rate parameter in water is (2.3±0.5)×109 mol–1 dm3 s–1. The peroxy radicals have the characteristics: max=265–270 nm, max=700–900 mol–1 dm3 and 2k=(7±2)·108 mol–1 dm3 s–1. 相似文献
20.
Nataša Pejić Slobodan Anić Vesna Kuntić Vladana Vukojević Ljiljana Kolar-Anić 《Mikrochimica acta》2003,143(4):261-267
A kinetic method is described for the microquantitative (microconcentration/microvolume) determination of rutin based on potentiometric monitoring of the concentration perturbations of the Bray-Liebhafsky (BL) oscillatory reaction being in a non-equilibrium stationary state close to a bifurcation point. The experiments are carried out in an open reactor. The response of the matrix system to perturbations by different concentrations of rutin ethanolic solutions is followed by a Pt-electrode. In the concentration range between 7.8×10–8moldm–3 and 9.1×10–6mol dm–3, we found a linear dependence of the maximal potential shift, Em, on the logarithm of the rutin concentrations. The unknown concentrations can be determined from the calibration curve up to an accuracy of ±5%. The detection limit is 3.6×10–8mol dm–3. The amount of required sample can be as small as 10µL. 相似文献