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Surfactant solutions containing rodlike micelles have been investigated by small angle neutron scattering and by light scattering at rest and under laminar and turbulent flow conditions. At rest and at room temperature long rods of average length 249 nm are found with static light and small angle neutron scattering. To interprete the orientation of these rods in a laminar shear gradient the a ssumption of an increased average rod length is necessary. In turbulent pipe flow the rod-like micelles are initially oriented in the bulk flow direction with more pronounced orientation in the near wall regions compared to the core regions of the pipe. Eventually a destruction of the initially rod-like micelles takes place leading to a rearrangement of the surfactant molecules into smaller aggregates part of which, in turn, build up loose but lasting (over several months at room temperature) superstructures. [ABSTRACT FROM AUTHOR]

The binding and exchange of stabilizing ligands on the surface of colloidal silver particles is studied by surface enhanced Raman spectroscopy. Primary stabilizers present during colloid synthesis, e.g. the dianion of ethylene-diamine-tetraacetic acid, can be replaced by the cationic surfactant cetyl-trimethyl-ammonium bromide. To further elucidate this process, model systems are investigated. Choline ions are found to bind to colloidal silver particles through the trimethyl-ammonium head grop; the molecule exclusively exhibits the gauche conformation with respect to the Cα-Cβ-bond. Coadsorbed anions are important for the binding to the silver surface, which is covered by a layer of Ag+ ions: SERS intensities are increasing in the sequence Br− < Cl− < OH−. — Polyvinyl alcohol is an excellent stabilizer for small (≈ 3 nm radius) colloidal silver particles prepared by γ-irradiation in the group of A. Henglein. Surface enhanced Raman spectroscopy reveals that the polymer is bound to the silver surface via the hydroxyl groups. Strong signals observed for CH2 deformational vibrations are consistent with an adsorption geometry in which segments of the polymer chain are running parallel to the colloid surface in a disordered conformation. Acetate groups present on the polymer due to incomplete hydrolysis of the polyvinyl acetate precursor give rise to intensive SERS signals, indicating that the carbonyl groups participate in the bonding to the colloid surface. [ABSTRACT FROM AUTHOR]

The method of simultaneous analysis of multiple fluorescece decay curves, also referred to as global fluorescence analysis, is presented. By taking into account existing relationships among the various decay curves, the method allows better parameter recovery and model testing, compared to the usual single curve analysis. The application of the method, using simulated fluorescence decays, in micellar systems is discussed. [ABSTRACT FROM AUTHOR]

The swelling of an n-butylammonium vermiculite in solutions of n-butylammonium chloride has been studied as a function of temperature, hydrostatic pressure, uniaxial pressure, and the concentration of the soaking solution, by neutron diffraction. On heating the swollen clays a transition to the crystalline phase takes place at a well defined temperature, which depends on the external electrolyte concentration. The application of hydrostatic pressure induces macroscopic swelling of the vermiculite in the region of 1 kbar. The transition is completely reversible and also depends on temperature. — The dependence of interparticle distance on applied uniaxial pressure varies semiquantitatively with ionic strength in a similar way to the forces between mica plates in electrolyte solution. — Approximate dimensions of the Stern layer have been obtained from isotopic substitution of the counterion. The Stern layer is 5.5 ± 1 Å thick. [ABSTRACT FROM AUTHOR]

The morphology of particles in the isotropic phases of mixed aqueous colloids of lecithin and glycocholate are studied using small-angle neutron scattering. At the highest concentrations globular mixed micelles are present and have a radius of gyration of 24 Å. At lower concentrations rod-like structures are present. In each and every case the rod radii are about 27 Å. It is proposed that the rods form by aggregation of disk-like micelles about 27 Å radius and height 50 Å. The rods grow larger as the solutions are diluted and appear to associate into loose networks just before the occurrence of a concentration-induced transition to vesicles. The vesicles have walls that are a single lipid bilayer of lecithin and glycocholate. [ABSTRACT FROM AUTHOR]

By use of neutron small angle scattering (SANS) the structural properties of various saturated and unsaturated phosphatidylcholine model biomembrane systems have been investigated in the temperature range from 0°C to 70°C and at pressures from ambient up to 3.5 kbar. The analysis of the diffraction data allowed to determine the effect of chemical constitution (like the length and degree of unsaturation of the hydrocarbon chains) of the lipids on the thermotropic and barotropic phase behaviour, and the detection of different phases which lead to the ealuation of the temperature-pressure phase diagrams of the different phospholipids. The structural data are compared with recent results obtained from high pressure Raman, NMR and ultrasonic experiments on these model membrane systems. High pressure is also a characteristic feature of certain natural membrane environments. The biological relevance of the high pressure experiments on model biomembranes is also discussed in detail. [ABSTRACT FROM AUTHOR]

The interfaces between water and alkanes in the presence of a monolayer of nonionic surfactant (polyethylene glycol alkyl ether) have been studied as a function of temperature for surfactants of different chain lengths. At low temperatures and moderate surfactant concentration, the aqueous phase is an oil in water microemulsion; at high temperatures, the oil phase is a water in oil microemulsion. In our study, the middle of the studied temperature range corresponds to the inversion temperature where a middle phase microemulsion coexists with both oil and water. — The interfacial tensions, which are very low, have been measured with surface light scattering and the interfacial film roughness with ellipsometry. From these data, the bending elastic constant of the surfactant monolayer is determined. The calculated persistence length of the monolayer is compared to the characteristic size in the middle phase microemulsion measured with neutron scattering. [ABSTRACT FROM AUTHOR]

The application of new technique of specular neutron reflection to the study of the solution/air and solid/solution interfaces is reviewed. Examples are given of the determination of the structures of adsorbed layers of tetramethy-lammonium dodecyl sulphate (TMDS) and decyl trimethylammonium bromide (DTAB) at the air/liquid interface. In both of these systems the layer consists of an outer alkyl chain region, which is not close-packed and which contains no water, and a head group region containing the head groups, counterions, water and a small fraction of alkyl chains. The non-ionic surfactant hexaoxyethylene glycol monododecyl ether (C12E6) is shown to form a bilayer at the quartz/aqueous solution interface at concentrations close to the c.m.c. However, this bilayer is found to be defective and might be better described as a layer of flattened micelles. The structure persists down to coverages where less than half the geometric surface is covered with bilayer. [ABSTRACT FROM AUTHOR]

The specular reflection of neutrons is now becoming an established technique for the study of surfaces and interfaces. A discussion of the experimental requirements is presented, and particular emphasis on the advantages for the study of problems in surface chemistry is included. A description of the reflectometer, CRISP, on the pulsed neutron source ISIS is given. Recent experimental results on the adsorption of mixed surfactants at the air-water interface are described. [ABSTRACT FROM AUTHOR]

In our previous work, we have shown that a general feature of saturated phosphatidylethanolamines is that they exhibit lamellar — inverse hexagonal (HII) phase transitions with increasing temperature, at all water contents. We have found that the effect of decreasing the lipid chainlength to C12(didodecyl) is to cause the appearance of three intermediate bicontinuous cubic phases in different regions of the binary phase diagram. We have identified these phases as being of cubic aspects 4, 8 and 12, corresponding to probable spacegroups Pn3m (Q224), Im3m (Q229) and Ia3d (Q230). Furthermore, we find that for the C16(dihexadecyl) lipid, cubic phases are also induced in qualitatively the same regions of the phase diagram by methylation of the polar headgroup, which increases its hydrophilicity. We have investigated whether the chirality of the lipid influences the chirality of the cubic phase formed, and have found that, at least for these phospholipids, it does not. We have also found that cubic phases are formed by hydrated phosphatidylcholine/fatty acid 1/2 (mol/mol) stoichiometric mixtures, when the chainlength is reduced, and we report preliminary results obtained by X-ray and neutron diffraction on these systems. [ABSTRACT FROM AUTHOR]

We performed molecular dynamics simulations on one and two component Yukawa systems. Cooling the system down and inspecting pair distribution functions (pdf) and bond correlation functions (bcf) we found the one component system to crystallize into a bcc-like lattice rather than an fcc lattice which is the stable phase of the simulated system at low temperatures. Upon cooling the two component system freezes into a glassy state without exhibiting crystalline structure in pdf or bcf. We define particle excess functions which show that spacial fluctuations in the number density of particles of the different components decay quite slowly. Therefore we believe that a well defined state of the two component system can only be reached in simulations long enough to allow those fluctuations to decay. [ABSTRACT FROM AUTHOR]

Small angle neutron scattering and electron microscopy are used to investigate the ordering of soft latex particles which have been dispersed in water and then brought into contact through evaporation of the solvent. We observe a succession of metastable states where the particles are kept separated by their hydrophilic surface layers: colloidal liquid (short range order only) to colloidal crystal (long range order) to foam (dense packing of polyhedral cells with latex interior and hydrophilic walls). At each stage the structure may collapse into a homogeneous latex phase through coalescence of the particles and expulsion of the hydrophilic material. [ABSTRACT FROM AUTHOR]

We have studied the irreversible aggregation of colloidal polystyrene spheres using a particle counter technique. The mode of cluster growth is found to be modelled by a reaction limited aggregation process. Elementary grains disappear by collision with larger aggregates, which, in return, are only slowly formed. This complex process has one important characteristic: at each time, the concentration of small aggregates of g elementary grains scales like g−τ, τ being a universal exponent in reaction limited processes. [ABSTRACT FROM AUTHOR]

Static and dynamic light scattering are major experimental tools to study colloidal aggregates. The theoretical methods for a proper analysis of such experiments are reviewed. It is shown how several interrelated features of the aggregation process determine the experimentally accessible quantities. These features are the structure of the clusters as characterized by their fractal dimension and their anisotropies and the shape of the cluster mass distribution. Using computer-generated clusters, obtained under the conditions of diffusion-limited and of reaction-limited cluster aggregation, and using results for the cluster mass distribution obtained from the Smoluchowski equation for irreversible growth, the static scattering intensity and the correlation function of quasi-elastic light scattering are calculated. The latter is shown to depend sensitively on rotational diffusion processes and on the cluster mass distribution. Finally, it is shown how the growth kinetics can be extracted from the angle dependence of the first cumulant. [ABSTRACT FROM AUTHOR]

Cytochemical markers prepared by labelling colloidal gold with a variety of bioactive molecules have gained wide acceptance both in transmission and scanning electron microscopy. However, details on the process and on the extent of adsorption of macromolecules to gold particles are scarce. The quantitative aspects of labelling colloidal gold with macromolecules were examined using proteins differing widely in size and shape such as protein A (single polypeptide chain), β-lactoglobulin (dimeric protein) and monoclonal IgE (four polypeptide chains). Adsorption isotherms were constructed at different pH's and the association constants evaluated by Scatchard plot analysis. At low protein concentration, practically all molecules were adsorbed and the isotherm was largely pH independent. Adsorption was maximal at the isoelectric point of the molecules (most compact form). At high coverage only β-lactoglobulin was irreversibly adsorbed. The proportion of labelled particles binding to immobilized ligands decreased sharply at low coverage. Particles labelled with IgE were unreactive towards the immobilized antigen, probably due to a restriction in the bending capacity of IgE. The results indicated that the empirical conditions generally used for preparing gold markers are valid in most cases. [ABSTRACT FROM AUTHOR]

Our interest in human platelets is based on the pathological activity of platelets during formation of thrombi in connection with atherogenesis. The shape change is the first step of platelet activation and aggregation. Thus starting with the appearance of blebs and pseudopods a change in surface charge density and hydrodynamic radius of the cells in physiological solution occurs. These parameters and their changes can be measured by quasi-elastic light scattering. We also found that platelets slightly activated by mechanical stress recover when incubated at 37°C for about half an hour. Significant differences in the electrophoretic mobility as well as in the diffusion constant could be found when the sample was cooled down from 37°C to 20°C indicating shape change. These findings with laser light scattering correspond very well with electronmicroscopic results. Moreover, the temperature dependent activation of platelets is not occuring continuously but there seems to be a critical temperatue range for activation of human blood platelets of healthy donors. To see activation caused by addition of an agent, we observed dose-dependent change of electrophoretic mobility with thrombin. [ABSTRACT FROM AUTHOR]

Long chain Nα-Acyl-L-arginine methyl esters are cationic lipoaminoacid surfactants obtained in our laboratories by condensation of a fatty acid with the α-amino group of L-Arginine. As part of systematically studying the properties of these surfactants, their phase behavior in binary and multicomponent systems has been investigated as a function of chain length of the fatty acid residue. It has been found that Krafft temperature and critical micelle concentration (CMC) increase and decrease respectively with the increase in the alkyl chain length, as expected in a homologous series of surfactants. The Nα-Myristoyl-L-arginine methyl ester (MAM)/water phase diagram showed three liquid crystalline regions with hexagonal, cubic, and lamellar structures. Phase behavior of ternary Nα-Acyl arginine methyl ester/water/n-alkanol systems was found to conform to that of ionic surfactant systems. Microemulsion formation was investigated in quaternary Nα-Lauroyl-L-arginine methyl ester (LAM)/water/n-alkanol/hydrocarbon systems. [ABSTRACT FROM AUTHOR]

The interfacial tension data were determined for 5,8-diethyl-7-hydroxydodecan-6-oxime at toluene/water interface and used to discuss the mechanism of copper extraction is very probable. The adsorbed hydroxyoxime molecule reacts in the first quick step with copper hydrated ion forming hydrophilic partly hydrated and charged intermediate 1:1 complex, which in the slow step reacts with hydroxyoxime molecule present in aqueous layers near the interface. [ABSTRACT FROM AUTHOR]

Modification of water-soluble polymer such as Xanthan gum is made by means of a synthetic reactive fluoralkylating agent: FLUOTAN B830. The resultant fluorinated macromolecule greatly increases the polar liquid repellency of the multipurpose foam compound while decreasing the polymer quantity and as a result the concentrate viscosity. Comparative tests are made with commercial and FLUOTAN B830-containing foams. Results concerning foam resitance on isopropylic alcohol and fire tests on acetone and heptane are given and discussed. [ABSTRACT FROM AUTHOR]

Nucleophilic displacement reactions and ester hydrolysis have been performed in microemulsions stabilized by a nonionic amphiphile. The effect of the reactants added on the phase behaviour was studied as well as the effect of the progress of the reaction. The latter causes changes of the phase boundaries of the microemulsions with time. These changes were followed for tracing the progress of the reaction. The knowledge of the phase behaviour of mixtures of water, oil and nonionic amphiphile permits separating reactants and products. [ABSTRACT FROM AUTHOR]

The size and shape of petroleum asphaltenes in solvents have been determined by small angle neutron scattering. Their most likely morphology is a membrane like particle. Their size decreases with temperatur, this change being quite reversible. It is very solvent dependent: the more polar the solvent the smaller the aggregates. Similarly, the more polar the asphaltene the larger the particles. [ABSTRACT FROM AUTHOR]

The formation of chains of polystyrene spheres in an aqueous suspension submitted to an electric field is studied by light scattering. We analyse the change in the diffraction pattern from an isotropic to a very anisotropic structure. The dynamics of the breakdown of the chains by Brownian motion, when the field is switched off, is studied by recording the decrease of the scattered intensity. The coefficient of diffusion perpendicular to the chain is obtained and compared to some theoretical predictions. [ABSTRACT FROM AUTHOR]

Steady-shear viscosity measurements on colloidal hard-sphere dispersions were paralleled by light and neutron scattering experiments on sheared dispersions. In the viscosity experiments, we found concentrated dispersions to be shear-thinning but no shear-thickening was observed. The viscosity is determined by two dimensionless groups only: the volume fraction and the Peclet number. This underlines the hard-sphere nature of these dispersions. We designed a parallel — plate flow cell which we used in neutron scattering experiments with the D11-diffractometer (ILL, Grenoble). In these experiments we were able to probe a scattering plane containing the flow velocity and vorticity axis (planes of constant velocity) as well as the velocity — gradient plane (or shear plane) which contains the flow velocity and the gradient axis. These experimental results show an increasing deformation of the liquid-like equilibrium micro-structure with increasing shear rate. However, no evidence for strong ordering phenomena is found. In this paper we relate the observations made in the steady-shear viscosity measurements to those made in the scattering experiments. [ABSTRACT FROM AUTHOR]

The results of time dependent small angle neutron scattering (SANS) experiments on the alignment of four samples are described. The relaxation times encountered vary in magnitude from 150 ms to 60 min. For the shorter relaxation times a sampling method was used. The four different processes of which results are reported are:-the transient alignment of p-TES fibrilles in an electric field-the rotation of a prealigned nematic phase in a magnetic field-the build up and decay of a shear induced micellar structure in a shear field-the overshoot during the alignment of rodlike micelles in a shear field. [ABSTRACT FROM AUTHOR]

We give a brief review of the concept of hydrodynamic interactions in fluid suspensions. We discuss their relevance for the calculation of effective viscosity, collective mobility and self-mobility. [ABSTRACT FROM AUTHOR]