Showing papers in "Colloid and Polymer Science in 1995"

Self-aggregation and phase behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers in aqueous solution

Abstract: The phase behavior and aggregation properties of block copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronics, poloxamers) in aqueous solution have recently attracted much attention. Both experimental and theoretical studies are reviewed, not comprehensively, but with the focus on studies, partly cooperative, partly independent, performed by groups in Uppsala (light scattering and fluorescence), Roskilde (rheology and calorimetry), Riso (SANS), Graz (x-ray and speed of sound), and Lund (theoretical model calculations).

A fascinating new field in colloid science: small ligand-stabilized metal clusters and possible application in microelectronics

Abstract: Small metal clusters, like Au55(PPh3)12Cl6, which fall in the size regime of 1–2 nm are colloidal nanoparticles with quantum properties in the transitional range between metals and semiconductors. These chemically tailored quantum dots show regarding the Quantum Size Effect (QSE) a level splitting between 20 and 100 meV, increasing from small particle sizes to the molecular state. The organic ligand shell surrounding the cluster acts like a dielectric “spacer” generating capacitances between neighboring clusters down to 10−18 F. Therefore, charging effects superposed by level spacing effects can be observed. The ligand-stabilized colloidal quantum dots in condensed state can be described as a novel kind of artificial solid with extremely narrow mini or hopping bands depending on the chemically adjustable thickness of the ligand shell and its properties. Since its discovery, the Single Electron Tunneling (SET) effect has been recognized to be the fundamental concept for ultimate miniaturization in microelectronics. The controlled transport of charge carriers in arrangements of ligand-stabilized clusters has been observed already at room temperature through Impedance Spectroscopy (IS) and Scanning Tunneling Spectroscopy (STS). This reveals future directions with new concepts for the realization of simple devices for Single Electron Logic (SEL).

A fascinating new field in colloid science: small ligand-stabilized metal clusters and their possible application in microelectronics: Part II: Future directions

Abstract: Small metal clusters, like Au 55 (PPh 3 ) 12 Cl 6 , which fall in the size regime of 1 - 2 nm are colloidal nanoparticles with quantum properties in the transitional range between metals and semiconductors These chemically tailored quantum dots show by the Quantum Size Effect (QSE) a level splitting between 20 and 100 meV, increasing from small particle sizes to the molecular state The organic ligand shell surrounding the cluster acts like a dielectric «spacer» generating capacitances between neighboring clusters down to 10 -18 F Therefore, charging effects superposed by level spacing effects can be observed The ligand-stabilized colloidal quantum dots in condensed state can be described as a novel kind of artificial solid with extremely narrow mini or hopping bands depending on the chemically adjustable thickness of the ligand shell and its properties Since its discovery, the Single Electron Tunneling (SET) effect has been recognized to be the fundamental concept for ultimate miniaturization in microelectronics The controlled transport of charge carriers in arrangements of ligand-stabilized clusters has been observed already at room temperature through Impedance Spectroscopy (IS) and Scanning Tunneling Spectroscopy (STS) This reveals future directions with new concepts for the realization of simple devices for Single Electron Logic (SEL) Part II presents models and connections between microscopic and macroscopic level, regardless of whether there already exist suitable nanoscale metal cluster compounds, and is aimed at the ultimate properties for a possible application in microelectronics

Memory effects in isothermal crystallization II. Isotactic polypropylene

Abstract: The effects of temperature and duration of melting on the rate of isothermal crystallization of isotactic polypropylene were investigated by differential scanning calorimetry (DSC). Crystallization rates were found to decrease with increasing melt temperature and melting time. The results were discussed in the framework of the theoretical model of transient isothermal crystallization developed by the present authors [1]. The results suggest gradual destruction of predetermined nuclei with activation energyEa=89±7 kJ/mole as a main mechanism of the observed effects.

Flow birefringence experiments showing a shear-banding structure in a CTAB solution

Abstract: Experiments of flow birefringence have been performed on a concentrated solution of CTAB submitted to shear in a Couette cell. Qualitative observations of the flow in the annular gap of the Couette device let us clearly see that the flow is divided into two layers when the shear rate exceeds a critical value. This shear banding structure is shown on a set of photographs. The extinction angle χ and the retardation ϕ were measured as a function of the shear rate\(\dot \gamma \) for different temperatures. The results are in agreement with the predictions of the shear banding theory.

Formation and stabilization of a biodegradable polymeric colloidal suspension of nanoparticles

Abstract: The formation of a colloidal suspension of nanoparticles was obtained, in a very simple manner, by transferring a solution of poly-ɛ-caprolactone in a good solvent (L1) into a non-solvent (L2). Photon Correlation Spectroscopy (PCS) measurements confirmed by microscopic observations were used to determine the morphological aspects of the preparations. The influence of several factors on nanoprecipitation was examined: polymer concentration, L1/L2 ratio, dielectric constant of the final mixture. An experimental model of the phenomenon, which takes into account the flocculation concentration and the L1/L2 ratio, is proposed. It allows the optimal conditions for nanoparticles formation to be determined.

Surface charge density on spherical silica particles in aqueous alkali chloride solutions

Abstract: Experimental data concerning the dependence of the surface charge density of AEROSIL 300 in aqueous alkali chloride solutions on pH are analyzed under application of two different models for a spherical electrical double layer. Data for the alkali ions Li+, Na+, K+, Rb+ and Cs+ are included at five electrolyte concentrations. In the first model a counterion binding in combination with a pure diffuse spherical double layer is considered; here, a good agreement between the recalculated plots and the experimental data is found for low electrolyte concentrations (c<0.05 mol/l) only. The second model with a charge free Stern layer and without counterion binding seems to be applicable for higher electrolyte concentrations also. Furthermore the surface charge density constants from the second model agree better with those published and determined with other models or experimental methods.

The use of rotation matrices in the mathematical description of molecular orientations in polymers

Abstract: The orientational distribution of chain segments or crystals in polymeric materials is most conveniently described as a series expansion of rotation matrix elements. Rotation matrices are representations of rotation operators, and their elements form a complete set of orthogonal functions. Their use in the mathematical description of molecular orientations therefore yields the advantage that the moments in the series expansion of the orientational distribution, also called order parameters, are the averages of the rotation matrix elements themselves. Furthermore, rotations between molecular and macroscopic frames can easily be carried out to link molecular orientation to a macroscopic observable. In the third place, various symmetries reduce the number of non-vanishing order parameters in a straightforward way. In the case of fiber symmetry and axially symmetric molecular elements, the rotation matrix elements reduce to Legendre polynomials.

Formation and coexistence of the micelles and vesicles in mixed solution of cationic and anionic surfactant

Abstract: In the aqueous mixtures of sodium alkylcarboxylate and alkyltrimethylammonium bromide, large unilamelar vesicles can be formed spontaneously or by sonication as the total carbon number in the HC chains is 19 (or larger). Vesicle formation can be influenced by changes of pH, molar ratio of the two surfactant components, and the polar head group of cationic surfactant. Micelles may coexist with the vesicles in these mixed systems. The larger hydrodynamic radius (∼200 nm) and aggregation number (∼800) illustrate that the shape of the micelle in 1:1 C9H19COONa−C10H21N(CH3)3Br is rod-like. In some mixed systems, the micelles can be transformed into stable vesicles by sonication — a phenomenon revealed for the first time. The surface-chemical properties of these catanionic surfactant solutions and the stabilities of vesicle have been studied systematically.

Enthalpy-entropy compensation in ionic micelle formation

Abstract: The enthalpy-entropy compensation in ionic surfactant micellization process over a large temperature range is examined. The surfactants SDS and C16TAB are investigated experimentally, and the enthalpy and entropy changes are evaluated based on phase separation or mass action models together with the other three surfactant systems. The relationship between compensation temperature and the reference temperatures is discussed.

Synthesis of nanosize metallic and alloyed particles in ordered phases

Abstract: Functionalized reverse micelles have been used to synthesize Copper and Cobalt nanoparticles differing by their size and shape. They can be also used to synthesize Fe−Cu alloy (at 30% Fe) and composite (at 70% Fe) particles. In the case of Fe−Cu system, the magnetic properties are presented.

Dynamic surface elasticity of polymer solutions

Abstract: The surfaces of surfactant solutions exhibit viscoelastic dilational behavior which may be investigated by modern optical and mechanical methods. The present study focuses on the dynamic dilational properties of the polymer solution — gas interface. Linear flexible polymer chains at the surface are considered as consisting of “trains,” lying on the surface, and “loops” and “tails” that protrude into the liquid. The Rouse model is used to describe the inner dynamics of the trains, whereas their motion relative to their neighbors on the surface can be described with the help of the reptation conception. An expression for the complex dynamic dilational surface elasticity has been derived. Although, in general, the relaxation of the surface tension is characterized by an infinite series of relaxation times, it is shown that for many systems the dynamics of the surface layer can be described approximately by only two main relaxation times. The dispersion equation, which was obtained earlier for solutions of conventional surfactants, is shown to be fulfilled for polymer solutions also.

Aqueous solution behavior of new thermoassociative polymers

Abstract: A new kind of water-soluble polymer was obtained by grafting side chains, characterized by a phase separation on heating (Lower Critical Solution Temperature LCST), on a hydrosoluble backbone. For semidilute solutions, the side chains associate as the temperature exceeds a critical temperature (Tass), which is close to their LCST. Microdomains are formed which act like physical crosslinking units between the main chains, and an increase in the aqueous solution viscosity is observed. Systems based on 2-Acrylamido-2-methyl propane sulfonic acid (AMPS) backbone and polyethylene oxide (PEO) side chains were developed. Their rheological behavior in both dilute and semi-dilute states was studied by varying differents parameters such as polymer and salt concentrations, grafting ratio, etc. Fluorescence measurements indicate the formation of hydrophobic microdomains on heating, in agreement with the thickening properties of the solutions.

Preparation of monodispersed polystyrene microspheres uniformly coated by magnetite via heterogeneous polymerization

Abstract: Composite microspheres of core-shell type were prepared by a seeded polymerization using monodispersed polystyrene seed latex (Ps) combined with an in situ dispersion of magnetite (Fe3O4) fine particles. The heterogeneous polymerization was carried out in aqueous dispersions of the Fe3O4 particles modified with sodium oleate. All the synthetic processes were carried out in a wet state to avoid serious agglomeration. The morphology of the composite particle and the size distribution were examined to discuss the effects on the polymerization parameters, such as monomer concentration, type and concentration of an initiator, magnetite particle concentration and the method of surface modification of Fe3O4.

Disjoining pressure and stratification in asymmetric thin-liquid films

Abstract: We directly measure, for the first time, disjoining pressure isotherms for asymmetric oil/aqueous surfactant/gas (i.e., pseudoemulsion) films using a modified version of the porous-plate technique first developed by Mysels in conjunction with thin-film interferometry. Dynamic film-thinning experiments are also performed on individual foam and pseudoemulsion films. At SDS surfactant concentrations above the critical micelle concentration (CMC) (0.1 M SDS), the pesudoemulsion films exhibit the same step-wise layer thinning observed in foam films under similar conditions. Further, we conduct dynamic thinning experiments on solid/liquid/gas systems and show that aqueous 0.2 M CTAB films sandwiched between glass and air also display discrete thinning transitions. All of these stratification transitions arise from oscillations in the disjoining pressure isotherm, generated by amphiphilic structuring within the film. For 0.1 M SDS dedecane/air pesudoemuslion films, the slope and peak height of the disjoining-pressure oscillations increase with each subsequent amphiphilic layer as film thickness decreases. Magnitudes of the structural forces are low (<100 Pa) but the length scale of the oscillations is large (∼10 nm) and rathe far reaching (∼50 nm). Moreover, for 0.1 M SDS solutions, the capillary pressures associated with film rupture are significantly lower for pseudoemulsion films (∼0.1 kPa) when compared to foam films (∼15 kPa) at equivalent conditions. Taken together, our dynamic thinning and equilibrium disjoining pressure measurements indicate that stratification in 0.1 M SDS films has little effect on both kinetic and thermodynamic films stability.

Phase behavior in mixtures of cationic and anionic surfactants in aqueous solutions

Abstract: Phase behavior of cationic/anionic surfactant mixtures of the same chain length (n=10, 12 or 14) strongly depends on the molar ratio and actual concentration of the surfactants. Precipitation of catanionic surfactant and mixed micelles formation are observed over the concentration range investigated. Coacervate and liquid crystals are found to coexist in the transition region from crystalline catanionic surfactant to mixed micelles. The addition of oppositely charged surfactant diminishes the surface charge density at the mixed micelle/solution interface and enhances the apparent degree of counterion dissociation from mixed micelles. Cationic surfactants have a greater tendency to be incorporated in mixed micelles than anionic ones.

Interfacial tension of alkylglucosides in different APG/oil/water systems

Abstract: The interfacial performance of pure alkylglucosides (C8G1, C10G1 and C12G1) and of technical grade alkylpolyglucoside (APG) surfactants was investigated in three different water/oil systems (decane, isopropylmyristate and 2-octyldodecanol). From the dependence of the interfacial tension on the surfactant concentration below the CMC the cross-sectional area of the molecules at the decane/water interface was estimated. The plateau values of the interfacial tension at the CMCσc are independent of temperature and almost independent of added electrolyte in the decane/water system. The ability of the surfactants to lower the oil/water interfacial tension is most pronounced for the nonpolar oil. The partition coefficient of the surfactant between oil and water phase (kc) was estimated from the CMC and the observed break point of the interfacial tension after equilibration of the two phases. In decane/water,kc is nearly zero for all surfactants studied. For the polar oils,kc increases with the chain length of the surfactant up tokc≈10 for C12G1 in octyldodecanol/water. The values ofσc in the different oil/water systems appear to be correlated withkc and exhibit a minimum nearkc=1.

Formation of “monodispersed” SnO2 powders of various morphologies

Abstract: Several procedures for the preparation of colloidal SnO2 powders, consisting of particles of narrow size distribution and of various morphologies, are described. The hydrolysis of SnCl4 aerosols in the presence of gaseous ammonia produces poorly crystalline SnO2 spheres of modal diameters <2 μm. Depending on the preparation conditions, the forced hydrolysis of acidic (HCl) SnCl4 solutions yields either prismatic particles or spherulites composed of tiny, strongly aggregated, elongated subunits. In both cases the particles are in the nanometer size range (<100 nm) having crystalline rutile structure. Rod-like SnO2 particles (∼0.3 μm) of good crystallinity can be obtained by hydrolysis of SnCl4 solutions in the presence of formamide. It is concluded that the hydrolysis of dissolved SnCl4 tends to produce elongated SnO2 particles which, depending on the experimental conditions, may be at different aggregation states.

The molecular-dynamics of thermoreversible networks as studied by broad-band dielectric-spectroscopy

Abstract: Polybutadienes modified by a small number of 4-phenyl-1,2,4-triazoline-3,5-dione form thermoreversible networks via hydrogen bonding between the polar stickers. The molecular dynamics of systems with different contents of polar stickers are investigated by broadband dielectric spectroscopy in the frequency regime of 10−1–109 Hz. Unmodified polybutadiene shows two relaxation processes, the α-relaxation which is correlated to the dynamic glass transition of the polybutadiene, and a β-relaxation corresponding to a local relaxation of polybutadiene segments. In the polar functionalized systems, besides these two relaxations, an additional relaxation process (called α*) is observed, which occurs at lower frequencies than the α-process. While the β-relaxation remains unaffected by the functionalization the cooperativity of the α-relaxation increases by the formation of reversible junctions and slows down considerably. This indicates a decreased mobility of the polymer matrix. At the same time the dipole moment of relaxing units contributing to the α-relaxation is increased by free phenyl urazole units. The α* is assigned to the local complex dynamics resulting from the dissociation and formation of dimeric contacts. Hence, for this dynamic process, the absolute value of the dipole moment fluctuates with time and causes a dielectric absorption. This interpretation is in agreement with the hindered reptation model of Leibler, Rubinstein and Colby and simultaneous measurements of infrared dichroism and birefringence.

Interactions of hydrophobically modified poly(sodium acrylate) with globular proteins

Abstract: The association of a series of hydrophobically modified poly(sodium acrylate) (HMPA) with lysozyme, a cationic globular protein, or with bovine serum albumin (BSA), an anionic globular protein, was investigated at pH=9 by rheology and to a lesser extent by steady-state fluorescence spectroscopy. Under suitable concentration conditions, this association leads to a drastic viscosity enhancement which is improved when the polymer hydrophobicity is increased. A mechanism is proposed: the hydrophobic regions of the globular proteins interact strongly with the alkyl groups of one or more polymer chains. In the later case, the macromolecules are crosslinked via the proteins, which leads to viscosity enhancement and even gelation. Analogies and differences between these systems and surfactant/HMPA systems previously studied in our laboratory are emphasized and discussed.

Aggregation numbers of sds micelles formed on ehec - a steady-state fluorescence quenching study

Abstract: The present investigation proves that in the interaction between an uncharged polymer and a negatively charged amphiphilic ion (surfactant) clusters are actually formed and it provides data for the cluster concentration and the cluster size and their variation with composition. The polymer bound cluster size increases after a certain critical surfactant concentration and passes through a maximum. This maximum cluster size decreases with decreasing polymer concentration and attains a limiting value at infinite dilution. For the highest polymer concentration the cluster size is close to the size of normal surfactant micelles. The cluster concentration was determined by a fluorescence quenching technique and the amount surfactant adsorbed to the polymer by dialysis equilibrium measurements. Combining these independent sets of data permits the cluster aggregation number to be unambiguously determined. Solubilization experiments indicate the possibility to regulate the amount solubilized by varying the polymer concentration. The molecular properties of the system are sensitively monitored by the variation in two vibronic peaks in the pyrene fluorescence emission spectrum which defines a “hydrophobic index”. Very good agreement is found between all three experimental methods. Finally, the model suggested is analyzed in terms of coil size and cluster-cluster distance. Depending upon the degree of adsorption saturation and the density of polymer segments in solution the interaction may switch from being intramolecular to becoming intermolecular.

A photophysical study of the urea effect on micellar properties of sodium dodecylsulfate aqueous solutions

Abstract: With the aim of studying the effect of urea on micellar properties of aqueous solutions of sodium dodecylsulfate (SDS), steadystate fluorescence experiments were carried out with different luminescence probes incorporated into the micellar phase. The increase of critical micelle concentration (CMC) of the surfactant with urea addition was followed by changes in the relative intensities of the vibrational fine structure of the pyrene fluorescence spectra. Micellar aggregation numbers were obtained from the analysis of fluorescence quenching data using ruthenium tris(bipyridyl) chloride and 9-mehylanthracene as a donorquencher pair. It was found that the decrease in the aggregation number is mainly controlled by rise in the surface area per headgroup of the surfactant. From fluorescence measurements, using several ionic probes (8-anilino-1-naphthalen-sulfonic acid, rhodamine B, and auramine O), it was found that urea decreases the polarity and increases the microviscosity of the micellar interface. These effects, which are dependent on the concentration of urea, can be explained according to a direct interaction of urea at the micellar surface.

Surface charge density on spherical silica particles in aqueous alkali chloride solutions: Part 2. Evaluation of the surface charge density constants

Abstract: Experimental data concerning the dependence of the surface charge density of AEROSIL 300 in aqueous alkali chloride solutions on pH are analyzed under application of two different models for a spherical electrical double layer. Data for the alkali ions Li + , Na + , K + , Rb + and Cs + are included at five electrolyte concentrations. In the first model a counterion binding in combination with a pure diffuse spherical double layer is considered ; here, a good agreement between the recalculated plots and the experimental data is found for low electrolyte concentrations (c < 0.05 mol/l) only. The second model with a charge free Stern layer and without counterion binding seems to be applicable for higher electrolyte concentrations also. Furthermore the surface charge density constants from the second model agree better with those published and determined with other models or experimental methods.

Preparation of monodisperse, reactive hydrogel microspheres and their amphoterization

Abstract: Monodisperse, reactive hydrogel microspheres were prepared by precipitation polymerization ofp-nitrophenyl acrylate (NPA) with acrylamide, methacrylic acid, and methylenebisacrylamide in ethanol. The size of microspheres was controlled by the monomer ratio. Some fraction of reactive ester decomposed during the polymerization. The reactive hydrogel microspheres were converted to amphoteric ones by the reaction of NPA units with diamine. The isoelectric point of the amphoteric microspheres was around 4.0, but it was different from the pH at which the microspheres have the minimum size or the most shrunken state. This was attributed to the uneven distribution of induced amine groups.

Polypyrrole core/polyacrolein shell latex for protein immobilization

Abstract: The redox polymerization of pyrrole, with ferric chloride as oxidant, carried out in the presence of polyvinylpyrrolidone (PVP), yielded polypyrrole latex particles. The polypyrrole latex was used, as seed, for the radical polymerization of acrolein. The resulting polypyrrole core/polyacrolein shell latex (poly(P/A)) was suitable for immobilization of up to 11 mg of human serum albumin (HSA) and/or 33 mg of human gamma globulin (γG) per 1 g of latex particles.

Interactions between cationic starch and anionic surfactants: 1. Phase equilibria and surface tensions

Abstract: The surface tensions and the phase equilibria of dilute aqueous cationic starch (CS)/surfactant systems were investigated. The degree of substitution of the CS varied from 0.014 to 0.772. The surfactants investigated were sodium dodecyl sulphate (SDS), potassium octanoate (KOct), potassium dodecanoate (KDod) and sodium oleate (NaOl). The concentrations of CS were 0.001, 0.01 and 0.1 w%. Critical association concentrations (cac) occur at surfactant concentrations well below the critical micelle concentrations of the surfactants, except for KOct, KDod and NaOl at the lowest CS concentrations investigated (0.001 w%). The surface tensions of CS/surfactant solutions decrease strongly already below the cac. This is attributed to the formation of surface active associates by ion condensation. Associative phase separation of gels formed by CS and surfactant takes place at extremely low concentrations when the surfactant/polymer charge ratio is somewhat larger than 1. The gel is higly viscous and contains 40–60% water, depending on the concentration of electrolyte, the surfactant hydrocarbon chain length and the nature of the polar head of the surfactant. The concentration at which the phase separation occurs decreases with increasing surfactant chain length and the concentration of simple electrolyte, factors that promote micelle formation. This indicates that the gels are formed by association of CS to surfactant micelles. When surfactant well in excess of charge equivalence is added, the gels dissolve because the CS/surfactant complexes acquire a high charge.

Pattern forming precipitation in gels due to coupling of chemical reactions with diffusion

Abstract: Precipitate-forming chemical reactions have been studied in chemically cross-linked poly(vinyl alcohol) gel medium. One of the reactive components was incorporated into the gel, the other was allowed to diffuse into it. Depending on the experimental conditions the reaction-diffusion process often results in patterns of different type. Experiments performed in tubes and in thin layers were carried out in order to investigate the effects of various factors (cross-linking density, swelling degree as well as the concentrations of the outer and inner electrolytes) on the morphologies of the precipitate patterns. It was found that precipitation occurs not only in the Liesegang bands, but also between bands. Beside Liesegang-type structures, tree-like patterns have been observed, showing a characteristic periodicity in the density profile obtained by digitalized image analyses.

Coupling between polymer adsorption and colloidal particle aggregation

Abstract: Studies of the adsorption of high molecular weight polymers on colloidal latex and silica particles and their subsequent flocculation were carried out. Neutral polyethylene oxide samples with both a narrow and a broad molecular weight distribution were used together with low charged cationic copolymers. The influence of the particle concentration and polymer dose on the flocculation were systematically investigated under quiescent conditions. Equilibrium bridging only occurred with polyelectrolyte, even in very dilute suspensions, at high particle coverage. In contrast to this, non-equilibrium bridging occurred with both neutral polymer and polyelectrolytes but only for more concentrated suspensions and small amounts of adsorbed polymer. Polymer adsorption in dilute suspensions, which did not show particle aggregation was measured an electrophoretic technique. In more concentrated suspensions, where flocculation takes place, we found that aggregation prevents further polymer adsorption and induces both an excluded volume and a surface effect. The consequences on the shape of the isotherms differ according to the aggregation mechanism. A significant decrease of the amount, Γ, of adsorbed polymer is observed with non-equilibrium bridging. When both mechanisms simultaneously contribute to the aggregation, the value of Γ depends on their relative importance. In the intermediate range of copolymer dose their respective contributions are critically sensitive to the details of the mixing step and stirring, leading to non reproducible experimental results.

Polysoaps with fluorocarbon hydrophobic chains

Abstract: A series of amphiphilic copolymers is prepared by copolymerization of choline methacrylate with 1,1,2,2-tetrahydroperfluorooctyl methacrylate in varying amounts. The copolymers bearing fluorocarbon chains are studied concerning their effects on viscosity, solubilization and surface activity in aqueous solution, exhibiting a general behavior characteristic for polysoaps. The results are compared with the ones obtained for an analogous series of amphiphilic copolymers bearing hydrocarbon chains.

Depolymerization of soluble silicate in dilute aqueous solutions

Abstract: Experiments with diluted solutions of a customary water glas show that the rate of depolymerization depends not only upon pH and the SiO2 concentration, but also varies systematically as a function of the type and concentration of an additional electrolyte Increasing cation activities of metal chlorides are causing a decrease of the rate constant in the order 1) Na+, K+, 2) Mn2+, Mg2+, Ca2+, Sr2+, 3) Zn2+, Ni2+, Ce3+, Cu2+ With respect to anions of sodium salts the rate constants are increasing with increasing activities in the order NO 3 − , HCO 3 − , Cl−, SO 4 2− , whereas HPO 4 2− causes a decrease The results permit to identify those components of water which are most responsible for a change of the depolymerization rate and may be used to evalute the properties of a water glass as a possible anticorrosive agent for water supply systems