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Interaction between Astramol poly(propylene imine) dendrimers of five generations, DAB-dendr-(NH2)x (where x is equal to 4, 8, 16, 32, or 64) and linear poly(sodium acrylate), poly(acrylic) acid, poly(sodium styrenesulfonate), or native DNA was studied in salt-free solutions by means of potentiometric, argentometric, and turbidimetric titrations. In addition to x outer primary amine groups the dendrimer molecule contains x − 2 inner tertiary amine groups. It is found that the pH-controlled interpolyelectrolyte coupling reaction resulting in formation of the corresponding interpolyelectrolyte complexes occurs on mixing of the dendrimer and the polyanion solutions. A peculiar finding was that all dendrimer amine groups being protonated can form ion pairs with carboxylate or sulfonate groups of the polyanions. In other words DAB-dendr-(NH2)x molecules are fully penetrable for rather flexible oppositely charged polyelectrolyte chains. However, this is not the case for rigid negatively charged DNA double helix...

Light Scattering results on polyacrylamide networks show that the scattered intensity changes as different positions of a sample are probed. The scattered intensity from gels, measured by averaging through many different positions, was found to be much larger than the intensity scattered by the equivalent polymer solution. This excess arises from the frozen-in fluctuations due to the presence of cross-links. This additional structure in gels can be enhanced or reduced with conditions of preparation. Modeling a gel by a random network of springs is presented. The resulting scattering properties mimic real gel behavior.

A comparison is made between the clustering process occurring the sodium‐di‐2‐ethylhexyl‐sulfosuccinate microemulsion in the four organic solvents: n‐decane, iso‐octane, n‐heptane, and n‐hexane. The clustering process is studied by small angle x‐ray scattering (SAXS) and dielectric relaxation spectroscopy. The structural parameters obtained from the analysis of the SAXS experiments using the sticky hard sphere droplet model are used to calculate the dielectric permittivity and are compared with results from the dielectric relaxation experiments. It is found that an increase in the attraction between microemulsion droplets when the chain‐length of the solvent molecule is increased.

Water-oil micro-emulsions consisting of AOT-H2O isooctane of different water-surfactant, W 0, and oil-surfactant, S 0, ratios, have been studied by SAXS over a wide rang eof scattering vectors. The shape of the high angle portion of the scattered intensity is found to be independent of the microemulsion composition and furthermore, does not follow the classical 1/q 4 Porod Law. Rather an additional 1/q 2 contribution to the scattering curve is observed. These results are explained in terms of the distance correlation function for a pseudo two-phase system, water and oil, with a diffuse interface formed by a monomolecular layer of surfactant molecules. The observed 1/q 2 behavior is shown to arise from a 1/r contribution to the correlation function. A quantitative analysis shows that the total interfacial area of the microemulsion is proportional to the total number of surfactant molecules in solution. Thus the average area per surfactant molecule is independent of the microemulsion composition.

The basic notions of dynamic light scattering (DLS) on non-ergodic media are presented and discussed. We present the results, obtained by DLS, for the intermediate scattering function of polystyrene latex particles that are dispersed in aqueous polyacrylamide gels. It is shown that these systems display non-ergodic features, implying that the time-averaged intensity correlation function (ICF) is not equal to the ensemble-averaged ICF.

We consider weakly dispersive and weakly nonlinear surface waves on liquid films in which long‐range interaction forces are operative. As a first approximation, disturbances on both interfaces of the film can be described as a superposition of symmetrical and antisymmetrical waves even when considering nonlinearities. For small, but finite amplitudes, the antisymmetrical waves are free of nonlinearities, whereas for the symmetrical ones a Korteweg–de Vries equation can be derived. Depending on the particular thickness dependence of the long‐range interaction forces the symmetrical disturbances lead to solitary waves with negative amplitudes (holes) or with positive amplitudes (intumescences). Taking as an example a soap film, with electrical double layer and London–van der Waals forces as interaction phenomenon, it is shown that observable solitons can be expected. It is put forward that the theory, presented here, is a contribution towards framing more sophisticated theories of liquid film (in)stability.

This paper describes the application of the numerical solution of the Percus–Yevick approximation for a multicomponent system of sticky hard spheres to small angle x‐ray scattering experiments. The effect of polydispersity on the pair correlation function is quantitatively described, thus enabling the analysis of experimental data. In this way quantitative estimates of the size distribution width, interaction radii and the measure of attraction between particles can be obtained. The attractive interaction in a system of sticky spheres is known to give rise to a transition analogous to a gas–liquid phase transition. The effect of polydispersity on this transition is discussed. Finally it is shown how the model can be used to describe small angle x‐ray scattering from an AOT microemulsion system.

The time dependent changes of the lamellar gel structure in a nonionic O/W cream were studied. It appeared that the changes were connected with alterations in the hydrophilic layers of this lamellar gel structure. The structure of the hydrocarbon layers did not change. The alterations were induced by an increasing hydration of the surfactant molecules on cooling from the preparation temperature to room temperature. Ageing of the cream involves a decrease of the thickness of the hydrophilic layers and a change of the distribution of the surfactant molecules, resulting in, among other things, a decrease of the release rate of a hydrophilic drug. Ageing of the cream can be prevented by using the appropriate amount of starting materials or by the use of polymerizable surfactants. In the former case a cream, from which a drug is slowly released, is obtained. On the other hand, creams containing polymerized surfactants can release drugs at a relatively high rate.

As a part of a study of the colloidal structures present in nonionic ointments, the interaction between polyoxyethylene and water is investigated. A series of mixtures of polyoxyethylene 1550 and water is studied using differential scanning calorimetry. Heating as well as cooling experiments are performed. The effects of the heat of mixing, supercooling and melting point depression on the measured enthalpy changes are discussed. From the non-freezing water fraction it is concluded that 2 water molecules per oxyethylene unit are tightly bound to the polymer chain. The observed differences between the cooling and the heating curves lead to a possible explanation for the alterations in the samples occurring at low temperatures. A hydrate structure of polyoxyethylene at low temperatures is proposed. Finally, comment is made on the phase diagram of the system polyoxyethylene/water.

The structure of a nonionic O/W cream and its separate components were investigated by X-ray diffraction and microscopic methods. The results presented in this paper are combined with the results obtained with DSC in order to elucidate these structures. The very important role of water with respect to the formation of the colloidal structures is discussed. The influence of water on the polymorphic behaviour of cetylstearylalcohol is attributed to a good structural fit of itsα-modification and water. Hydration induces a tilt of the alkyl chains of poly(oxyethylene)20glycerylmonostearate (PGM20). For this surfactant an antiparallel arrangement of the molecules is proposed. The lamellar structures present in mixtures of cetylstearylalcohol, PGM20 and water are discussed extensively.

Electrical double layer and London — van der Waals forces in soap films are studied as a function of thickness by means of time-averaged light scattering and Photon Correlation Spectroscopy. The free films are drawn from a solution containing 10−2 mol/dm3 of the cationic surfactant dodecyltrimethylammonium bromide. Thermally excited surface waves on the interfaces of a film give rise to a measurable diffuse reflection, being a combination of squeezing mode and bending mode scattering. Because of the large difference in the characteristic time scales the dynamics of the squeezing and bending modes can be studied separately. The relaxation of the bending mode was measured using Photon Correlation Spectroscopy yielding the surface tension of the soap film. Up to frequencies of about 4 MHz this tension appears to be equal to the bulk value of the surface tension. From thickness and angle dependent time-averaged light scattering experiments we obtained V″, being the second derivative of the free energy of film formation with respect to film thickness. The experimental data are interpreted by the DLVO theory using the Lifshitz theory for the London — van der Waals part of V″. We found an exponential thickness dependence of the electrical double layer contribution to V″. The experimental decay length of the latter contribution agrees very good with the theoretical value of the Debye length. For the surface potential a value of 95 mV was found.

The structure of a simple O/W cream and its separate components were investigated by differential scanning calorimetry. The results obtained for cetylstearylalcohol agree with those cited in literature. The thermal behaviour of the component poly(oxyethylene)20 glycerolmonostearate (= PGM20) was also investigated. It is pointed out that the thermal history of the PGM20 batch may play an important role in a study concerning the structure of this surfactant. To both components water was added to study the effects of hydration. Hydration affected the transition temperatures of either component. The melting enthalpy per unit mass of cetylstearylalcohol was not influenced, in contrast with the melting enthalpy of the hydrocarbon fraction in PGM20/water mixtures. It is supposed that hydration induces a tilt of the hydrocarbon chains with respect to the lattice plane in lamellar PGM20/water mixtures. Cooling experiments indicated that, in samples containing sufficient water, 2 water molecules were tightly bound to the polyoxyethylene chains of the surfactant. The properties of simple creams containing cetylstearylalcohol, PGM20 and water can be explained regarding their structure and considering the behaviour of the separate components.

The structure of systems containing equal weights of cetylalcohol, stearylalcohol and the nonionic surfactant poly(oxyethylene)20-glycerolmonostearate is studied as a function of the water concentration. In this paper mainly results are presented obtained by small angle X-ray-diffraction. Up to ± 22% (w/w) water several coexisting phases were observed. From ± 22% to ± 55% water a lamellar structure is found. This structure consists of lipophilic bilayers formed by the hydrocarbon tails of cetylalcohol, stearylalcohol and the surfactant, alternated by hydrophilic layers formed by the polyoxyethylene glycerol chains, the hydroxyl groups of cetylalcohol and stearylalcohol and water. From the swelling behaviour the density of the gel structure (0.9 g/cm3) and the cross sectional area of the molecules in the bilayers (0.19 nm2) have been calculated. It is concluded that the hydrocarbon chains are in a crystalline, state and are placed perpendicular to the lattice plane. Upwards of ± 55% water the lamellar phase disperses in the excess of water.

Determination de la constante dielectrique de la microemulsion eau/huile en fonction de la concentration et de la temperature (10-45 °C)

This paper deals with dynamic light scattering from liquid films. We have obtained the thermal fluctuation power spectrum of surface waves on films by solving the electrohydrodynamic equations of motion where the interaction forces (electrical double layers repulsion and London–van der Waals attraction) are included in the momentum equation. The resulting power spectrum for the mixed transversal‐longitudinal surface waves can be split up into two contributions: a squeezing mode part and a bending mode part. In this paper the general expressions for both modes are discussed for arbitrary film thicknesses and arbitary frequencies in the hydrodynamic regime. When the film is thick the spectrum exhibits the well known two peak structure of a single fluid interface. When the film becomes thin the spectrum consists of three peaks for each mode, i.e., the time evolution of both modes comprises a purely diffusive and a propagating component. It is found that the squeezing mode shows an intense diffusive peak, whe...

Stable water films covered by arachidic-acid monolayers are deposited on vertically arranged Si/SiO2 substrates which are partially pulled out of a film balance. The applicability of such asymmetric soap films to study the process of monolayer deposition on solid substrates and the fluid-solid interface interaction as a function of lateral pressure, π, is demonstrated. Equilibrium thicknesses of h01 = 17 nm and h02 = 4 nm and a decrease of h01 by 1.5 nm at decreasing π from 25 to 15 mN m-1 is observed. Light scattering experiments provide first evidence for large thickness fluctuations during thinning.

An experimental investigation of light scattered by freely suspended liquid-crystal films in the SA and the N phase is reported. Spectral analysis of the scattered light shows the existence of a propagating hydrodynamic mode. An interpretation in terms of surface fluctuations is presented.

Lamellar (L α ) and hexagonal (H 1) mesophases, formed in mixtures of water and polyethylene oxide (PEO) oleylethers (average EO-numbers 5 (a), 8.5 (b) and 14 (c)) and pure hexaoxyethylene dodecylether (d), were investigated with small-angle X-ray diffraction. Analysis of repeat spacings shows a deviation from linear one- and two-dimensional swelling ofL α andH 1, respectively, when a transition to a mesophase with a larger curvature of the interface is approached. With regard toL α , in this respect similar behaviour is observed for a pure surfactant (d) and a surfactant with an EO-length distribution (b). It is proposed that, through the formation of aggregates of limited extent, water filled pores in the mesophases arise. This is confirmed by analysis of the intensity ratio of diffraction maxima of first and second order inL α . Models for finite aggregates are introduced. These consist of (1) lamellae, infinite in one direction and with variable lengthL in a direction perpendicular to the first, with cylindrical edges and (2) cylinders with variable lengthL bounded by spherical caps. According to these models, under certain conditions, finite aggregates may be formed without an increase of the interfacial area per surfactant molecule. Applying the models to the regions where non-linear swelling is observed, reasonable values forL are found, which decrease progressively when the phase transition is approached.

The percolation transition in AOT/water/isooctane microemulsions has been studied by means of dielectric spectroscopy. At the percolation threshold the conductivity of the system increases sharply and the static dielectric permittivity attains a large maximum. It is shown that the frequency dependence of the permittivity can be well described by simple scaling relations of percolation theory. The critical exponent u of the frequency dependence has been found to be equal to u=0.62±0.02 and independent of temperature and microemulsion composition. The temperature dependence of the critical volume fraction for percolation has been related to the temperature dependence of the permittivity of the system far away from the percolation threshold.

Mesures de la limite basse frequence de la permittivite d'une microemulsion d'Aerosol OT-eau-isooctane, entre 10 o et 45 o C. Etablissement d'equations pour cette permittivite dans le cadre d'un modele d'agregation des gouttelettes

This paper describes what information can be obtained when the spectral distribution of light scattered by thin liquid films, like free soap films, is analyzed. To this end we have worked out the so‐called long wavelength limit (i.e., when the wavelengths of the surface waves are much greater than the film thickness) of the thermal fluctuation power spectrum describing the dynamics of the interfacial displacements occurring on a film. The analysis reveals that the squeezing mode spectrum as well as the bending mode spectrum exhibit a three peak structure: two peaks shifted symmetrically around zero frequency (Brillouin doublet) and one peak centered around zero frequency (pure diffusive component). For the squeezing mode the diffusive component, which is typical for a film, is strong, whereas for the bending mode the energy contained in the Brillouin doublet is large when compared with the central peak. These observations and also the large difference in characteristic time scales, in which the two modes ...

The influence of the addition of liquid paraffin (LP) on the structure of the lamellar (Lα) and hexagonal (H1) mesophases formed in mixtures of water (W) and BRIJ 96 (B) was studied. Mesophases were identified using polarization microscopy and small angle x-ray diffraction (SAXD). Repeat spacings were also determined with SAXD. Depending on theW/B ratio, addtion ofLP toLα gives a large, almost linear one-dimensional swelling or an initial swelling followed by a gradual transition to H1.Lα with a highLP-content gives a diffraction pattern showing only the first order diffraction maximum, possibly a result of undulations of the layers. The lamellar structure, however, was confirmed using freeze fracture electron microscopy (FFEM). Addition ofLP to H1 gives an initial swelling followed by a transition to a transparent, highly viscous, isotropic phase, called the gel-phase (G). The diffraction pattern obtained fromG yields little information on its structure. A large swelling ofG withLP was observed. From the degree of swelling as a function of hydrocarbon content it was inferred that this phase consists of spherical aggregates forming a close-packed structure. Using FFEM, textures were visualized resembling those obtained from the isotropic mesophase (I1) in water-surfactant mixtures. Finally, geometrical factors are discussed that may play a role in the formation of the gel-phase.

Endotoxins of Escherichia coli, Salmonella abortus equi and Serratia marcescens were examined using freeze-etch electronmicroscopy and light scattering techniques, with emphasis on their aggregation state. These endotoxins show distinct features of particle size and mass and they may be affected by the presence or absence of Ca2+ ions. No important differences were observed in the particle characteristics of the respective endotoxins in various infusion fluids.

Light scattering techniques have proven to be a powerful tool in studying physicochemical properties of thin, free, liquid films. Both, time averaged (1,2) and dynamic (3,4,5,6) light scattering experiments have been carried out on such systems.

The experimental setup to prepare free liquid films (from solutions of hexadecyltrimethylammoniumbromide) and to perform light scattering experiments on these films is described. Dynamic light scattering experiments concerning the relaxation of the squeezing mode (i.e., periodic thickness fluctuations) are reported for films of thickness between 35 and 100 nm and for mode wavelengths between 2.3 and 17.9 μm. In part of the wavelength regime good agreement is found between the experiments and existing hydrodynamic and classical colloidal interaction theories.