Compression studies on aqueous polystyrene latices

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     

K+-montmorillonite: its electric double layer extension and point of zero charge by diffusion potential

The dependence of the counterion transference number on the distance from the charged surface, that is, on the water (solution) thickness, is used for an approximation of the extension of the electric double layer (edl) in K⁺-montmorillonite.The extension of edl in K⁺-montmorillonite in 10^–2–10^–3 M KCl solutions is approximately 3.7k ^–1, wherek ^–1 is the Debye length.The dependence of the counterion transference number on the pH of water (solution) is used for estimating the point of zero charge (pzc) of K⁺-montmorillonite; the estimated pzc=1.     

Incongruent dissolution of hydroxyapatite in the presence of phosphoserine

Concentrations of phosphate and calcium ions, liberated from the surface of hydroxyapatite (HAP) during the adsorption of phosphoserine (PSer), were determined at 30°C. HAP showed a marked incongruent dissolution behavior in the presence of PSer. That is, the concentration of phosphate ion in solution increases with the addition of PSer due to the ion-exchange between PSer and phosphate ion on HAP (molar ratio of the former to the latter=32), whereas the concentration of calcium ion decreases with this release of phosphate ion, because the solubility product of HAP restricts the concentrations of both ions in solution (calculated values of — log (Ca²⁺)¹⁰ (PO ₄ ^3– )⁶ (OH^–)² were 115.8±1.0). The affinity of PSer to HAP was highest at pH 5.8 where the PSer and the HAP surface had the opposite charges. This electrostatic attraction force between PSer and HAP was shielded to some extent by the addition of KCl.     

Interactions of proteins with uniform colloidal hematite and chromium hydroxide particles. I. Adsorption

The adsorption of ovalbumin, -globulin, and lysozyme on uniform spherical hematite and chromium hydroxide particles in aqueous media has been studied as a function of the pH at a constant ionic strength. The uptake of ovalbumin and -globulin was greatest at their isoelectric points and differed little at 10^–2 and 10^–3 mol dm^–3 NaNO₃. The adsorption of lysozyme was strongly influenced by the ionic strength.The deposition of ovalbumin on hematite in the presence of Mg (NO₃)₂ was significantly greater than that with NaNO₃ under otherwise comparable conditions. Dialysis experiments with ovalbumin against magnesium nitrate solutions showed Mg²⁺ to be specifically bound to the protein.The shapes of isotherms indicated monolayer coverage for ovalbumin and multilayer coating for lysozyme for both adsorbents. The shapes of isotherms of -globulin on hematite point to a rearrangement of the protein on the particle surface, while a monolayer was found on chromium hydroxide particles.Supported by the NSF Grant CHE-9108420Part of a Ph.D. thesis     

Preparation of composite fine particles by heterocoagulation

To prepare regular composite particles comprised of organic and inorganic compounds, based on heterocoagulation theory, the properties of the mixture of small amphoteric latices (2a=250 nm) and large spherical silica (2a=240–1590 nm) were investigated as a function of pH, particle number ratio, particle size ratio and electrolyte concentration in the medium. It is apparent that under suitable conditions, we may prepare a stable mixed suspension comprising uniform composite particles, which are made up of many latices regularly adsorbed on silica surfaces, and each composite particle is undergoing Brownian motion as an isolated unit. This new composite particle is very stable for electrolyte, base and acid medium, and its surface charges (sign and magnitude) can be controlled by changing the pH of the medium.     

Effect of pH on colloidal properties of native ovalbumin aqueous systems

The effect of pH on the molecular shape and dispersed state of native ovalbumin molecules in 20 mM phosphate and acetic acid buffer solutions has been studied using small-angle x-ray scattering (SAXS) and a rheological method The degree of association of the OA molecule at the 0.5% colloid system increases slightly with decreasing pH, i.e., 2.10 at pH 7.0, and 2.88 at pH 4.0, and the radius of the OA molecule decreases slightly with decreasing pH, i.e., 24.5 Å at pH 7.0, and 22.0 Å at pH 4.0.The OA colloid shows apparent yield stress and rigidity which are due to a certain ordered arrangement of the molecules. The yield stress and the rigidity increase abruptly at a pH value near to an isoelectric point (ca. pH 4.4). In the dilute system this increment is attributed to the change in the ordered arrangement or in the interparticle interaction, and not to the change in the association state of the OA molecules. The values of the yield stress and the rigidity remain almost constant over a wide concentration range and this feature (an auto-controlled mechanism) is kept over a certain range of pH.     

Formation of uniform silver particles from bis (1,2-ethanediamine)silver(I) complex

Uniform spherical silver particles were produced by decomposing the bis(1,2-ethanediamine)silver(I) complex, by aging a solution of 1.0×10^–3 mole dm^–3 in silver (I) nitrate, 1.0 mole dm^–3 in 1,2-ethanediamine, and 2.5×10^–1 mole dm^–3 in nitric acid (basic solution) at 100°C for 42 min. The average modal diameter was estimated to be 0.52 m with a relative standard deviation of 0.10. A moderately oxygenrich layer, 40 Å thick, on the surface of the particles was detected by means of photoelectron surface microanalysis (XPS). The silver particles grew through a polynuclear-layer mechanism, as judged from the concentration change in soluble silver(I) species in the supernatant solution. The particles' point of zero charge (PZC) was estimated at pH 6.5 by potentiometric titration.     

The effect of carrier solution on the particle size distribution of inorganic colloids measured by steric field-flow fractionation

The number average and the weight average particle diameters for suspended inorganic colloids found by the new technique of steric field-flow fractionation may be successfully used provided that the most suitable carrier solution is selected, in order to minimize the coagulation and adhesion phenomena.In the present work polydisperse, irregular colloidal particles of FePO₄·2H₂O (strengite) were studied. The average particle diameters were found to vary with the electrolyte concentration in the suspending medium. A strong variation of the number and weight average particle diameters was also observed with the quantity of the surfactant added to aquatic medium in order to increase colloidal stability. The influence of the electrokinetic charge of the FePO₄·2H₂O particles in relation to the surface charge of the material of the column employed, on the particle size measured was investigated. The proper carrier solution for minimizing coagulation and adhesion phenomena in the FePO₄·2H₂O colloidal particles was found to contain either 1.5% (v/v) detergent FL-70 and 0.1 MKNO₃ or 0.5% (v/v) detergent FL-70 and 0.033 MNa₂SO₄.     

Estimation of the critical micelle concentrations and the aggregation numbers of sodium alkyl sulfates by capillary-type isotachophoresis

The analytical procedure for the separation and quantification of bulk and micellar phases for sodium alkyl sulfates has been investigated by a capillary-type isotachophoresis using a potential gradient detector. Monomer solutions were distinguished from micellar solutions at pH 5.5–6.0; hydrochloric acid — L-Histidine mixture was used as the leading electrolyte and 2-(N-Morpholino) ethanesulfonic acid as the terminating electrolyte.The potential unit value (PU value) due to the monomer solutions was larger than that due to the micellar solutions. The zone length due to monomer solutions increased with increasing concentration of surfactant until a given concentration (CMC); beyond this point the values became constant. On the other hand, the zone length due to micellar solutions increased from this point. We report an applicability of capillary-type isotachophoresis to determination of the CMC's and aggregation number for various sodium alkyl sulfates.     

Spinodal decomposition of the polymer blend deutereous polystyrene (d-PS) and polyvinylmethylether (PVME) studied with high resolution neutron small angle scattering

Decomposition of a polymer blend in the miscibility gap has been studied by small angle scattering of neutrons, using a double crystal diffractometer. It covers a range of 10^–5 to 10^–3 Å^–1, which connects the region of elastic light scattering and, at the upper end, the region of conventional neutron small angle scattering instruments. The decomposed structure in the miscibility gap can be described by a characteristic lengthR which increases with time,t ^1/3 between 7 and 25 min. At longer times, the growth follows a more linear power law. This behaviour is consistent with predictions of the domain growth for liquid mixtures and is estimated by using the self diffusion constant, viscosity, and the surface energy of the polymer.on leave ESFM-IPN Mexico     

Micelle structure in isotropic aqueous colloids of a poly(oxyethylene) amphiphile C12E8

Micelle structure in aqueous colloids in the isotropic liquid phase (L₁) of a nonionic amphipile (n-dodecyl octa(oxyethylene glycol) monoether (C₁₂E₈) has been investigated as a function of concentration and temperature using light scattering (LS), viscometry, NMR, and small-angle X-ray scattering (SAXS).The spherical micelles, having a radius of 28–31 Å, remain in a wide concentration range from very dilute to ca. 42 wt %. The micelle size increases sligthly with increasing temperature in the range of 25–60 °C. In the concentrated colloids, the spherical micelles are likely to be arranged in a certain ordered structure. Even at such a high concentration as 30 wt %, the isotropic colloid shows Newtonian flow. This suggests that interaction between micelles in the ordered structure is very weak and the structure is very fragile. Moreover, coexistence of the isotropic phase and the ordered structure in L₁ phase is discussed.     

The effect of pH on emulsion polymerization of styrene in the presence of an amphoteric emulsifier

An emulsion polymerization of styrene in the presence of an amphoteric emulsifier of the betaine type; N,N-dimethyl-n-laurylbetaine (LNB), has been studied at various pH values. The relationships between the physicochemical properties of LNB aqueous solutions, the emulsion polymerization process and the characteristics of the synthesized latex particles were studied under various pH conditions. The polymerization rate and the particle number concentration decreased with increasing pH of LNB aqueous solution and changed in shape at both ca. pH 4 and pH 8–10. The properties of LNB aqueous solution also changed with the pH and changed in shape at the same pH as that of the emulsion polymerization. These pH values were in good agreement with the pH at which the LNB molecule changed its ionic form. The number of synthesized latex particles was proportional to the number of LNB micelles in the solution, below pH 10. The particle size of the synthesized latex particles and the molecular weight of the latex polymers also changed with the properties of LNB aqueous solutions, accompanying the change of the ionic form of LNB molecules.     

Influence of the exchangeable cations on stability and rheological properties of montmorillonite suspensions

The effects of NaCl and CaCl₂ on the colloid stability and rheological properties of Na- and Ca-montmorillonite dispersions were studied. The distribution of cations between the surface and the bulk phase was determined. For both of monocationic montmorillonite, the critical coagulation concentration were 250 mmol NaCl/dm³ and 2 mmol CaCl₂/dm³. The changes in the Bingham yield stresses of Na- and Ca-montmorillonite dispersions as functions of the NaCl and CaCl₂ concentration could be explained in terms of the surface excess amount and equilibrium concentration of the cations, the second electroviscous effect and the formation of a gel structure.     

The association of urethane-polyethyleneoxide (HEUR) thickeners,as studied by NMR self-diffusion measurements

The concentration and molecular weight dependence of the self-diffusion coefficient (D _self) of associative polymers of HEUR-type in aqueous solution have been investigated using FT-PGSE-NMR technique. The idea of three-dimensional network formation as a result of aggregation of the hydrophobic end-groups of the polymer in junctions is supported through the observed dramatic lowering ofD _self with increased concentration. The network-formation efficiency depends on the polymer molecular weight as well as the hydrophobicity of the end-groups.A double logarithmic dependence of the self-diffusion coefficient versus concentration (c) has been observed:D _selfc ^–a1,a2 . The first exponent,a ₁, is valid at low concentration, <1% polymer per weight solution, and ranges from 0.5 to 1, whereas the second exponent,a ₂, describing systems of higher concentration, ranges from 2 to 2.7.     

Role of ionic species and valency on the steady shear behavior of partially hydrolyzed polyacrylamide solutions

Polyacrylamides are anionic polymers with a large number of charges along the polymer chains. The rheological properties of aqueous polyacrylamide solutions can be significantly modified by varying the solvent environment with the addition of salt. The presence of cations substantially reduces the inter- and intra-molecular interactions of the macroions. It was found that the valency of the cation has a strong effect on the rheological behavior of polyacrylamide solutions, but the size and type of salt have a negligible effect.The reduction in the solution viscosity with di-valent salts (e.g., CaCl₂, MgCl₂, BaCl₂, and MgSO₄) can be as high as an order of magnitude compared with mono-valent salt (KI, KC1, NaCl, and NaBr), depending on the salt concentration and shear rate. An identical viscosity function can be obtained for different types of polyacrylamide solutions by varying the salt content in solution. This interesting feature provides a useful means in the development and preparation of certain ideal fluids for simulation studies of complex flow problems.     

Mechanism of the grafting of organosilanes on mineral surfaces. IV. Phenylderivatives of sepiolite and poly (organosiloxanes)

Grafting reactions of phenyl groups on silica substrates using as reagents various phenylsilanes with variable distances between the silicon atoms and the aromatic ring by 0, 1, and 2 methylene groups [Si–(CH₂) _n –C₆H₅] were studied. Two different silicates have been selected as source of silica: sepiolite and tetraethyl-orthosilicate (TEOS). Sulfonic- and nitro-derivatives prepared from these phenyl compounds by electrophilic substitution reactions, have been obtained. The mechanism of these processes has been studied in relation to the number of methylene separating groups belonging to the starting reagents. The characterization of such systems has been achieved by XRD,²⁹Si and¹³C NMR/MAS, IR, and laser microprobe mass spectrometry.Parts I, II and III published in this Journal (1978) 256:135–139, (1979) 257:178–181 and (1985) 263:1025–1030     

Cloud points and phase separation of aqueous poly(N-vinylacetamide) solutions in the presence of salts

Aqueous poly(N-vinylacetamide) (PNVA) solution was found to exhibit the cloud point in the presence of salt. This cloud point was shown to correspond to a liquid-liquid phase separation, as confirmed when the PNVA-salt solutions were maintained at a temperature above the cloud point. The upper layer had a higher polymer concentration and a lower salt concentration than those in the lower layer. Thus interaction between PNVA and salts are repulsive. The lower critical solution temperatures were estimated to be 18±1°C for 1.25 molal (NH₄)₂SO₄ and 25±1°C for 0.76 molal Na₂SO₄. Divalent anions such as SO _2– ⁴ , SO _2– ³ , HPO _2– ⁴ and CO _2– ³ were effective in causing turbidity when examined at 25°C. Dependence of the effect on the cationic species was similar to but significantly different from that for acetyltetraglycine ethylester. The cloud points of PNVA decreased linearly with the increase of the polymer concentration at a fixed salt concentration or with the increase of the salt concentration at a fixed polymer concentration. A parameter analogous to the salting-out constant was empirically derived from the dependencies of the cloud points on the concentrations of polymer and salt.     

Conductivity of alkaline earth metal soaps in methanol

The conductance of the solution of calcium, strontium and barium butyrates in methanol has been measured at 35–50 °C (± 0.05 °C) in order to determine the CMC, dissociation constant, molecular conductance at infinite dilution, and thermodynamic parameters viz. enthalpy, free energy, entropy changes for both dissociation and association processes. The results show that these soaps behave as a weak electrolyte in methanol and Debye-Huckel-Onsager's equation is not applicable to the solutions of these soaps.     

Permeability of Newtonian black foam films to gas

The gas permeability of Newtonian black foam films, formed on the top of a small bubble at the solution surface, was studied experimentally. The aqueous solutions contained sodium dodecylsulphate with concentrations in the range 1.5×10^–4 to 3×10^–3 mol/dm³ and sodium chloride (constant concentration of 0.5 mol/dm³). A dependence of the gas permeability coefficient on the surfactant concentration was obtained. The experimental results are discussed on the basis of a theory assuming the presence of clusters of molecule vacancies (holes) in the bilayer foam film, their number and size depending on the surfactant concentration. The experimental results are in agreement with this film structure and confirm the existence of flow through both the hole-free bilayer film and the holes. It was found that the holes of three molecule vacancies make the main contribution to gas permeability at low surfactant concentration. The diffusion coefficients through the hole-free film and through the three-vacancy holes are calculated.Dedicated to Professor Dr. Armin Weiss on the occassion of his 60th birthday.     

Nanoparticles of varying hydrophobicity at the emulsion droplet-water interface: adsorption and coalescence stability

The coalescence stability of poly(dimethylsiloxane) emulsion droplets in the presence of silica nanoparticles ( approximately 50 nm) of varying contact angles has been investigated. Nanoparticle adsorption isotherms were determined by depletion from solution. The coalescence kinetics (determined under coagulation conditions at high salt concentration) and the physical structure of coalesced droplets were determined from optical microscopy. Fully hydrated silica nanoparticles adsorb with low affinity, reaching a maximum surface coverage that corresponds to a close packed monolayer, based on the effective particle radius and controlled by the salt concentration. Adsorbed layers of hydrophilic nanoparticles introduce a barrier to coalescence of approximately 1 kT, only slightly reduce the coalescence kinetics, and form kinetically unstable networks at high salt concentrations. Chemically hydrophobized silica nanoparticles, over a wide range of contact angles (25 to >90 degrees ), adsorb at the droplet interface with high affinity and to coverages equivalent to close-packed multilayers. Adsorption isotherms are independent of the contact angle, suggesting that hydrophobic attraction overcomes electrostatic repulsion in all cases. The highly structured and rigid adsorbed layers significantly reduce coalescence kinetics: at or above monolayer surface coverage, stable flocculated networks of droplets form and, regardless of their wettability, particles are not detached from the interface during coalescence. At sub-monolayer nanoparticle coverages, limited coalescence is observed and interfacial saturation restricts the droplet size increase. When the nanoparticle interfacial coverage is >0.7 and <1.0, mesophase-like microstructures have been noted, the physical form and stability of which depends on the contact angle. Adsorbed nanoparticle layers at monolayer coverage and composed of a mixture of nanoparticles with different hydrophobisation levels form stable networks of droplets, whereas mixtures of hydrophobized and hydrophilic nanoparticles do not effectively stabilize emulsion droplets.