Rheology and stability of oil-in-water nanoemulsions stabilised by anionic surfactant and gelatin 1) addition of nonionic, cationic and ethoxylated-cationic co-surfactants

Oil-in-water emulsions stabilised by anionic surfactant and gelatin provide the bulk of photographic coating fluids. Their rheology is of crucial importance to the fluids' performance in coating and their concentration in drying. Gelatin complexes with non-adsorbed micelles and adsorbs to the oil-surfactant-water interface, which effects an increase in the viscosity of the continuous phase and the volume of the nano-sized oil droplets, respectively. The consequences of these interactions are high viscosity and strong shear thinning. Here, the effects on the emulsion rheology of a series of bulk, commercially available surfactants were studied. These co-surfactants were chosen so as to weaken the interactions between gelatin and the anionic surfactant and hence reduce viscosity and thinning thus enabling the emulsions to be concentrated. The co-surfactants had polar head groups of three types: simple nonionic based on polyethylenenoxide, simple cationic based on a quaternary alkyltrimethyl ammonium, and combined nonionic-cationic based on a quaternised bis-ethoxylated primary amine. This last type proved the most effective at reducing the low-shear viscosity of the emulsion and reducing the shear thinning, although, at high concentrations the polyethoxylated cationic surfactants induced flocculation and coalescence of the oil droplets.     

Controlling porosity within colloidal heteroaggregates

Heteroaggregates of cationic poly(2-vinylpyridine) microgels and anionic polystyrene latex particles have been made by mixing dilute, aqueous suspensions. The growth of the heteroaggregates was arrested by the addition of anionic silica particles that adsorbed to the free surface of the cationic microgel particles. The resulting heteroaggregates were then concentrated by vacuum filtration, freeze-dried, and characterized by mercury porosimetry and electron microscopy. The inclusion of soft, deformable microgels resulted in heteroaggregates with higher porosity than obtained with heteroaggregates of anionic and cationic latex particles. Control of the pore volumes within the freeze-dried filter cakes was demonstrated by two approaches. In the first approach, heteroaggregation at a constant KCl concentration of 0.01 mM was arrested at different times after mixing the latex and microgel particles, thereby limiting the size of the aggregates. The porosity of the resulting filter cake increased from 61 to 65 vol % as the aggregation time increased from 15 to 120 s. In the second technique, the aggregation time prior to arrest was maintained at 120 s while the KCl concentration was varied between 0.01 and 10 mM. The pore volume of the aggregates decreased from 65 to 57 vol % as the electrolyte concentration increased, a trend explained in terms of the effect of the Debye length on the aggregation process.     

Proton conductivity and phase relationship in solid KOH between 248 and 406°C

Existing evidence indicates that between 248°C and the melting point at 406°C, KOH is a rotator phase. We have shown that, as might be expected, this results in enhanced proton conductivity, and a value of 2×10⁻³ ohms⁻¹ cm⁻¹ was found at 350°C, which is the highest reported for proton conducting solid electrolytes in this temperature range. Excess protons are provided by water molecules residing on the normal OH^- sites, and charge compensation is provided by CO²⁻₃ ions in the solid solution of KOH(≈ 1 m/o K₂CO₃, 1.3m/o H₂O). The activation energy for proton hopping between adjacent H₂O and OH⁻ species probably accounts for most of the observed activation energy of 53±3 kJ mol⁻¹. From TGA studies the isobars at 0.05 and 10 Torr were established for KOH-rich compositions in the KOH---H₂O system, and it was shown that the rotator phase of KOH is stable between these vapour pressures.     

The unitary representation theory of GL(n) of an infinite discrete field

IfK is an infinite field and ifG=GL(n, K) with the discrete topology, then all principal-series representations ofG are irreducible, and any two such with the same central character ψ are weakly equivalent to one another and to the ψ-regular representation. In addition, every irreducible unitary representation ofG which is not one-dimensional weakly contains a representation of the principal series. We deduce that every maximal ideal ofC*(G) is either of codimension 1 or else a kernel of a principal-series representation. In particular, except in the exceptional case whereK is an infinite algebraic extension of a finite field, the reducedC*-algebra of PGL(n, K) is simple, as was also shown by de la Harpe in many cases. Partially supported by NSF Grant DMS-85-06130. It is a pleasure also to acknowledge the hospitality of the Institute for Advanced Studies, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel, from January to August, 1988. Partially supported by NSF Grants DMS-84-00900 and DMS-87-00551. Much of this work was done while visiting at, and partially supported by, the Department of Mathematics and Computer Science, Bar-Ilan University, 52100 Ramat Gan, Israel.     

The Stability of Graded Multiplicity in the Setting of the Kostant-Rallis Theorem

From a combinatorial point of view, we approach the problem of finding a graded generalization of the Kostant-Rallis theorem concerning the K-harmonic polynomials on p. Specifically, for each classical symmetric pair we obtain a stable range where the multiplicity of an irreducible K-representation in the degree d harmonic polynomials can be expressed in terms of Littlewood-Richardson coefficients.     

Unconventional titania photocatalysis: direct deployment of carboxylic acids in alkylations and annulations

Under dry, anaerobic conditions, TiO(2) photocatalysis of carboxylic acid precursors resulted in carbon-carbon bond-forming processes. High yields of dimers were obtained from TiO(2) treatment of carboxylic acids alone. On inclusion of electron-deficient alkenes, efficient alkylations were achieved with methoxymethyl and phenoxymethyl radicals. In reactions with maleic anhydride or maleimides, phenoxyacetic acid produced chromenedione derivatives in addition to adducts. These photocatalytic reactions are simple and cheap to perform, and the TiO(2) is easily removed by filtration. The anaerobic photocatalysis strategy offers a range of synthetic possibilities.