Quantitative aspects of the growth of (charged) silica spheres

It is shown that the growth of monodisperse, charged silica spheres in ethanolammonia upon addition of tetraethoxysilane can be adequately studied with static light scattering. The resulting growth curves (radius vs time) are analyzed in terms of a model for diffusion-controlled growth of (charged) spheres in a solution of reactive (charged) monomers, the bulk concentration of which decreases due to this growth. This decrease is sufficient to account for the essential shape of the curves. A coulombic sphere-monomer repulsion is theoretically shown to modify the growth rate only with a constant factor.     

Hemimicelle shape and size

Based on the assumption of spherical hemimicelle with a hydrophobic core of diameter of maximum hydrocarbon chain length of surfactant, the aggregation numbers of hemimicelles have been calculated for several values ofn, the carbon atoms of surfactant alkyl chain. The results are in reasonable good agreement with the hemimicelle aggregation number from experimental data for several corresponding systems. The other possibilities of the hemimicelle shape which allow to incorporate a larger number of hydrocarbon chains in a hemimicelle have also been discussed.On leave from Department of Chemistry, Peking University, Beijing, China     

On the shape of giant micelles in aqueous solutions of cetyltrimetylammoniumbromide (CTAB)

Low-temperature electron microscopy was used to image fracture faces of shock-frozen aqueous solutions containing the very large micelles of CTAB existing in the presence of N-methyl-N,N-diphenylamine (MDPA) and 9-anthracene carboxylic acid (9-AC) as solubilizates. When MDPA is present, large globular micelles are formed which have total aggregation numbers of the order of 10⁵ and are seen to be clusters of smaller disc-like structures containing some thousand CTAB-units. Thread-like features are visualized in solutions containing 9-AC which is known to induce the formation of micellar rods.     

Dielectric relaxation in polymeric solids Part 1. A new model for the interpretation of the shape of the dielectric relaxation function

A model is proposed which explains the shape of the dielectric relaxation function at the glass transition of polymers. The model is based on the idea that the molecular mobility at the glass transition is controlled by intra- and intermolecular interaction. In addition, a specific model for the local chain dynamics in amorphous polymer systems is used. According to the scaling hypothesis of molecular dynamics the model relates the high frequency dependence of the dielectric loss curve to the local chain dynamics and the low frequency dependence to the intermolecular correlation.     

The interaction of modified 7S soy protein with mono- and di-glycerides at the oil-water interface and its effect on the stability of concentrated corn oil-in-water emulsions

The influence of chemically modified 7S fraction of soybean protein (7MSPF), and its partial replacement by mono- and di-glycerides in various ratios, on the rate of drop coalescence in concentrated corn oil-in-water emulsions has been investigated. A total emulsifier concentration of 2.0 % (wt/wt) was used. The minimum drop coalescence rate was achieved when using 1.0% (wt/wt) 7MSPF in conjunction with 0.5% (wt/wt) monoglyceride and 0.5 % (wt/wt) di-glyceride at pH 5.5. At other mono-/di-glycerides and protein/glycerides ratios, and at other pHs, the rate of drop coalescence was higher than when 2.0% (wt/wt) 7MSPF was used. The reduction in drop coalescence rate under these conditions is attributed to association of 7MSPF with the glycerides at the oil-water interface. The influence of protein/glycerides ratio on the viscoelastic properties of mixed interfacial films supports this view.     

Effect of pH on the binding of alkyl sulfates to gelatin

A surfactant-selective eletrode in which the membrane is an o-nitrotoluene phase containing a dissolved complex of cetyltrimethylammonium-dodecyl sulfate has been applied to investigations of the interaction between gelatin and alkyl sulfates as well as gelatin and alkyltrimethylammoniumions in dilute aqueous solutions.The binding isotherms were obtained by comparing emf-values obtained for surfactant in water to the electrode potentials in gelatin solutions plotted in terms of surfactant concentration.The binding of alkyl sulfates was measured as a function of pH at constant free surfactant concentration. At pH values 7 the degree of binding is indpendent of the pH of the solution. The level of binding of alkyl sulfates to gelatin increases strongly with increasing chain length of the alkyl sulfate. At pH values 6 the extent of binding increases steeply with decreasing pH. Octyl sulfate shows a very low level of binding even at low pH. Cationics show much weaker interactions with gelatin than anionic surfactants of comparable alkyl chain length.     

Effect of random copolymerization on growth transition and morphology change in polypropylene

The growth rate of an ethylene-propylene random copolymer with a 2.8% w/w ethylene content was studied in a similar manner to polypropylene. A growth regime transition associated with a birefringence change was observed at 130C, while the same phenomena appeared at 138C in isotactic polypropylene. In both polymers positive birefringence corresponds to Regime III, whereas negative birefringence of spherulites is associated with Regime II. The birefringence change is attributed to a change in the organization of crystalline lamellae: quadritic arrays of intercrossing lamellae at low temperature (Regime III) and preferentially radiating lamellae at higher temperature (Regime II). We confirm that such a morphological change can be interpreted using the concept of non-adjacent re-entry introduced in Hoffman's kinetic theory. Thus, quadritic morphology seems to have a partly kinetic origin. The shift of the transition temperature in the copolymer is due to the rejection of ethylene segments at the surface of crystalline lamellae of polypropylene.     

Sodium-aluminium-silicates in the washing process part IX: Mode of action of zeolite A additive systems

The mode of action of additives in laundry detergents containing zeolite A has been investigated. Proper additives improve soil removal and reduce deposits on fabrics. They show threshold and carrier effects, which retard aggregation and crystal growth of precipitates and/or accelerate their dissolution in the presence of zeolite A. The results are significant with respect to the formulation of non-phosphate zeolite built laundry detergents.Lecture given at the 7th International Zeolite Conference, New Developments in Zeolite Science and Technology, Tokyo, August 17–22, 1986.     

Interactions of mixed surfactant solution with liposome membrane

Interactions of the mixed surfactant solution of dodecylamido propyl dimethyl aminoacetate and sodium dodecyl sulfate with the liposomal membrane were studied. Lytic activities of the surfactants were measured as a function of the concentrations of surfactant and phospholipid and the composition of mixed surfactants. The solubilization limits of phospholipid by surfactants were determined from the change of their aggregation behavior in suspensions at equilibrium by means of quasi-elastic light scattering. The mixed surfactant solutions showed lower lytic activity than single component surfactant solution in spite of the strong adsorption onto the liposome surface. This was attributed to low solubilization power of binary mixture for phospholipid.     

Crystallization kinetics of isotactic polypropylene blended with atactic polystyrene

Crystallization kinetic parameters, such as spherulitic growth rates, nucleation densities, and Avrami-exponents, have been determined by optical microscopy for isotactic polypropylene blended with atactic polystyrene. It is found that the crystallization of iPP is strongly influenced by the presence of polystyrene. With increasing PS concentration in the blend, the nucleation densities decrease, while the spherulitic growth rates as well as the positions of thermal peaks, measured by DSC, remain independent of sample composition. Due to the formation of interfaces as a consequence of increasing dispersion of polystyrene the nucleation changes from preferentially thermal to athermal.     

Cubic phases in surfactant and surfactant-like lipid systems

Cubic liquid crystalline phases are common in surfactant and surfactant-like lipid systems at temperatures above the Krafft point. They are optically isotropic and very stiff. Therefore, they are often not recognized as independent phases and separated in pure state. The liquid crystalline nature is evidenced by a low-angle diffraction pattern with sharp reflections having Bragg-values above 20 Å coupled with a diffuse wide-angle reflection at 4.5 Å, proving that the hydrocarbon moiety is in a liquid state. The cubic phases occur in a variety of lipid/water systems (also with liquid organic solvents), such as simple soaps, amphiphilic lipids of biological origin, and extracts from membrane lipids. The location of the cubic phases in a phase diagram varies.The original concept of a cubic structure composed of closed globular aggregates, either of oil-in-water or water-in-oil type in face-centered array seems to be obsolete. The present structure concepts include closed anisotropic aggregates, short rod-like aggregates forming continuous networks or lamellar aggregates with zero curvature forming networks of Infinite Periodic Minimal Surfaces (IPMS). The structure is mostly primitive or body-centered cubic.     

Polarity and hydrophile-lipophile balance of polydisperse polyoxyethylene 4-alkylphenyl amines as determined by gas chromatography

Gas chromatography was used to determine the polarities of polydisperse polyoxyethylene 4-alkylphenyl amines. The relationships between polarity parameters and the amine structures are discussed and used to estimate the hydrophile-lipophile balance of polyoxyethylene 4-alkylphenyl amines. Increments for some characteristic fragments present in the considered compounds were determined; they can be used to estimate the polarities of polyoxyethylene 4-alkylphenyl amines for their formulae. The polarity index and the retention index of methanol can be predicted with the average relative errors of 1.6% and 2.3%, respectively.     

Spherical shape instability induced changes in the structure of microemulsions

The dispersed phase of a microemulsion in equilibrium with the excess dispersed phase is in the form of spherical globules. A change in the structure of the microemulsion near the transition from two to three phases is predicted on the basis of thermodynamic considerations. This change occurs because the spherical interface of the globules becomes unstable to perturbations. Because this instability is a result of the condition of equilibrium itself, there is a similarity (but not identity) to the behavior near a critical point. The spherical interface can also become unstable to perturbations in some single-phase microemulsions, although it is stable in microemulsions that coexist with the excess dispersed phase. Thermodynamic considerations also indicate that at the transition from two to three phases, the curvature of the spherical globules must be zero. This result is extended to the entire middle-phase microemulsion as the condition of zero mean-time or space-average curvature. Such a condition can be satisfied in the neighborhood of the transition points from two to three phases and again from three to two phases via the oscillations of the globular interface; in the central region of the middle phase, where the volume fraction of oil0.5, this condition is likely to be satisfied via the oscillations of the interface of a bicontinuous sponge.     

Spinning drop experiments on interfacial phenomena: Theoretical background and experimental evidence

Interfacial phenomena contribute strongly to structure formation in multiphase polymer blends. Spinning drop experiments allow not only to analyze the magnitude of the interfacial energy, but also to determine dynamic features such as coarsening or the break-up of elongated threads. This contribution reports the theoretical background of static and dynamic spinning drop experiments; it describes experimental evidence on the break-up dynamics of such elongated threads and it finally sketches a spinning drop apparatus designed for investigations of viscous polymer blends, even at elevated temperatures.Dedicated to Prof. H. H. Kausch on the occasion of his 60th birthday.     

Gas permeability of block copolymers of styrene and butadiene

The permeability of styrene-butadiene block copolymer foils with different composition prepared by casting and pressing has been investigated for the gases Ar, CO₂, and CH₄ at pressure difference of 400 mbar and at the temperature range 298 T [K] 333.The permeation process can be described by the solution diffusion mechanism. The diffusion coefficients decrease in the sequence of the gases Ar, CO₂, and CH₄ and the solubility coefficients increase in the sequence Ar, CH₄, CO₂.The dependence of the permeability on the composition of the block copolymer can be interpreted by the help of percolation theory and the effective medium theory. It follows the critical volume fraction of the percolation of the transport phase _PB ^c (= 0,23) and the coordination numberz (= 4) giving an information concerning the multiphase structure of the block copolymer.Presented in part at the 33^rd Annual Meeting of the Colloid-Gesellschaft, Graz, Austria, September 14–16, 1987.     

Modification of phosphatidylcholine-opiates interaction by different buffers

The influence of subphase composition and ionic strength on the interaction between opiate molecules and phosphatidylcholine has been studied. Results show that a neutral pH favours the penetration of opiate molecules in phosphatidylcholine monolayers, but the ionic strength and the chemical nature of buffer components affect also greatly these interactions. The results could explain, in part the differences in opioid binding values observed for different buffers.     

The modification of the triple helical structure of gelatin in aqueous solution I. The influence of anionic surfactants,pH-value,and temperature

The modification of the triple helical structure in aqueous gelatin solutions by changing pH and adding alkyl sulphates at 298 K and after rechilling the solution to 283 K was investigated by CD-measurement. At 298 K the triple helical content at the IEP of the gelatin has its maximum value. It is only weakly affected by adding sodium dodecyl sulphate (SDDS) at concentrations <10^–4 M/dm³. The unfolding of the triple helix affected by pH and SDDS is reversible by rechilling the solution. The triple helical content of gelatin solutions decreases at SDDS concentrations higher than 10^–4 M/dm³. In all cases the decrease of the amount of triple helical structure is connected with an increase of the cis-configuration in single chains and leads to chain reversals. At sufficiently high SDDS concentrations-sheets are formed. These changes are thermally irreversible. Sodium decyl sulphate (SDS) has a more minor influence than SDDS except in the range of the c.m.c. of SDS. At sufficiently high SDS concentrations,-turns appear.     

Lamellar phases in mixtures of low molecular weight alkanols and cetyltrimethylammonium bromide (CTAB)

Partial phase diagrams showing the domains of existence of a transparent, viscous, lamellar-structured (D)-phase that transforms reversibly into fluid single phase solutions at high temperature are presented for the system: cetyltrimethylammonium bromide (CTAB), two low molecular weight alcohols, and water with and without additives. At constant temperature and with a fixed amount of surfactant, the size and location of this phase in the phase diagram depends upon three composition variables: i) the ratio of concentrations of medium chain alcohol to long chain alcohol (R), ii) the ratio of concentrations of medium chain alcohol to surfactant (R), and iii) the concentrations of small amounts (up to 10 % by weight) of additives such as ethylene glycol, propylene glycol, and dimethylformamide, as well as NaBr. Small-angle x-ray scattering measurements of these mixtures reveal a lamellar structure. The observed lamellar repeat distances range from 60 A to 290 Å and depend upon the ratiosR andR and the concentration of the additives. The mechanical and structural properties of theseD-phases can be tuned by adjustingR andR. TheD-phase-to-isotropic transition temperature can be varied from near room temperature to above 80 °C by adjustingR andR.     

The problem of intrinsic birefringence and chain conformation in polycarbonate from bisphenol-A

The PC-monomer is found to be a good example for elucidating the problems engendered by more complex monomers when the orientation behavior is investigated. The discrepancies found in the literature regarding the intrinsic birefringence can be fully resolved with the following assumptions:The carbonyl-unit is neither in the trans nor in the cis configuration, and the absorption band at 1364 cm^–1 is a mixture of in-phase and out-of-phase symmetric bending vibrations of the isopropyl methyl-groups. Planar and helical chain conformations are found which are thought to build up the amorphous phase. It is demonstrated that the crystal structure as known from literature can be realized by the planar conformations.Dedicated to Prof. E. W. Fischer on the occasion of his 60^th birthday     

Melittin and ionic surfactant interactions in monomolecular films

The interaction between the anionic and cationic surfactants with Melittin spread monolayers at the air-water interface was investigated. The addition of anionic Cl^–, under the films of Melittin gives rise to a change in both surface pressure and surface potential. These interactions are different when surfactants are present, due to specific interactions between Melittin and the ionic-surfactants.