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Amphiphilic copolymers with poly (alkyl acrylate) as hydrophobic and poly (acrylic acid) (AA) as hydrophilic block have been synthesised. The alkyl chain was varied from butyl to dodecyl, thereby varying systematically the polarity of the hydrophobic block whose length was between 35 and 70, while the PAA block had ~ 100 units. Such relatively short amphiphiles should equilibrate quickly in aqueous solution, and their corresponding self-assembly properties were characterised by means of critical micelle concentration (cmc) determination. Detailed information regarding the aggregate structures was obtained by static light scattering (SLS) and small angle neutron scattering (SANS). This could be correlated with the molecular architecture of the copolymers and the degree of ionisation of the PAA block. Generally, it is found that the aggregation numbers become smaller upon fully charging the PAA head group and only for dodecyl acrylate really well-defined micellar aggregates are formed. This means that the extent of hydrophobicity of the alkyl acrylate block and its length determine in a clear fashion the propensity for micelle formation and the mass and aggregation number of the formed micelles. [ABSTRACT FROM AUTHOR]

While spherical particles are the most studied viscosity modifiers, they are well known only to increase viscosities, in particular at low concentrations of approx. 1%. Extended studies and theories on non-spherical particles in simple fluids find a more complicated behavior, but still a steady increase with increasing concentration. Involving platelets in combination with complex fluids—in our case, a bicontinuous microemulsion—displays an even more complex scenario that we analyze experimentally and theoretically as a function of platelet diameter using small angle neutron scattering, rheology, and the theory of the lubrication effect, to find the underlying concepts. The clay particles effectively form membranes in the medium that itself may have lamellar aligned domains and surfactant films in the case of the microemulsion. The two-stage structure of clay and surfactant membranes explains the findings using the theory of the lubrication effect. This confirms that layered domain structures serve for lowest viscosities. Starting from these findings and transferring the condition for low viscosities to other complex fluids, namely crude oils, even lowered viscosities with respect to the pure crude oil were observed. This strengthens our belief that also here layered domains are formed as well. This apparent contradiction of a viscosity reduction by solid particles could lead to a wider range of applications where low viscosities are desired. The same concepts of two-stage layered structures also explain the observed conditions for extremely enhanced viscosities at particle concentrations of 1% that may be interesting for the food industry. [ABSTRACT FROM AUTHOR]

Thermoresponsive core-shell hybrid microgels with different core sizes were prepared by radical precipitation polymerization of the monomer N-isopropylacrylamide (NIPAM) in the presence of functionalized silica cores. The size of the cores was varied in a range of 70-170 nm in diameter. Characterization of the hybrid microgels was done by means of imaging techniques such as transmission electron microscopy (TEM) and atomic force microscopy (AFM). In addition, scattering techniques were used to study the swelling behavior and network structure of the responsive polymer shells. While dynamic light scattering (DLS) was employed to investigate the overall particle dimensions, SANS allowed to determine the correlation length ξ of the polymer network. Additionally, SANS also provides the average core size and the polydispersity of the cores in-situ using the method of contrast variation. [ABSTRACT FROM AUTHOR]

The coalescence of latex particles is investigated through small-angle neutron scattering and electron microscopy. The particles are made of a soft polymeric core protected by a hydrophilic membrane, and they are dispersed in water. This dispersion is spread on a substrate, and water is removed to form a dry film. As the membranes of neighboring particles come into contact, they may break up to allow fusion of the particle cores. This is found to occur when the membranes are made of short-chain surfactant molecules; then all hydrophilic material is expelled to the film surface or to large isolated lumps. Alternatively, the membranes may remain until the film is completely dry; this is found to occur when they are made of hydrophilic polymers which are grafted onto the core. Hence, the fusion of particles is controlled by the connectivity of membranes. [ABSTRACT FROM AUTHOR]

The technique of small angle neutron scattering (SANS) has been used to study the conformation of polystyrene chains in dilute solution under a constant shear gradient. The experiments reveal a distinct anisotropy of the molecular dimensions with regard to the directions parallel and perpendicular to the flow direction on the 2D-multidetector. The deformation ratio of the single polymer chain (〈 R〉/〈 R〉)−1 as a function of the reduced shear gradient β=([η] · η · MG)/ RT shows a transition from the ideal β-behaviour for dynamic infinitely flexible coils found at small gradients, to a behaviour with smaller increase at larger β. These results are qualitatively consistent with the theory of Cerf for a polymer with finite internal viscosity in a shear gradient. At low β(β<1), a better agreement with the model of a free-draining coil (Rouse behaviour) than with the Zimm model is observed. [ABSTRACT FROM AUTHOR]

Particle coalescence in latex films is investigated by measuring the 'smearing out process' of perdeuterated nPBMA latex particles in a matrix of protonated nPBMA using SANS. It is found that-at least in this system-there is massive interdiffusion of material of different latex particles. Diffusion constants for 70 °C and 90 °C tempering temperatures are determined. In addition, the effect of molecular mass, crosslinking and incompatibility of the matrix material is investigated. As expected, the interdiffusion decreases with increasing molecular mass, but, surprisingly, dense crosslinking of the matrix latex particles accelerates the smearing out process. Increasing incompatibility lowers the rate of the smearing out process. [ABSTRACT FROM AUTHOR]

Small angle neutron scattering was used to examine the organization of silica spheres which had been flocculated by various cationic copolymers. When the adsorbed polymers bound the spheres without compensating their surface charge, the resulting aggregates had a liquid-like short range order. When the polymers compensated for the surface charges, we found only tenuous aggregates with self-similar structures. [ABSTRACT FROM AUTHOR]

Casein is the main protein component of milk and is of remarkable colloidal stability. Under the influence of milk clotting enzymes casein shows the striking behaviour of coagulation. This clotting process has already been studied by other groups, neglecting the fact that casein is not a homogeneous protein. The purpose of the present study is focused, in this first stage, on the determination of the structure of the various casein components. In cooperation with other laboratories we have been able to obtain the well separated individual proteins. Studies have been performed so far with β- and χ-casein. For detailed structural information we carried out small angle neutron scattering and combined static and dynamic light scattering measurements and determined the molecular weight, M, the radius of gyration, 〈 S〉 the hydrodynamic radius, R, the ϱ-value and the particle scattering factor, P( q). The two caseins show a strikingly different behaviour. For the β-casein we found a star-like structure, i. e. an aggregation pattern that is expected for a common micelle. The micelle consists of about 38 monomer chains. The aggregates of χ-casein appear to be composed of star-like submicelles, where each submicelle contains nine χ-casein chains and the total degree of aggregation is about 140. [ABSTRACT FROM AUTHOR]

We have studied salt free semi dilute polyelectrolyte solutions by small angle neutron scattering. Specific labelling associated with an extrapolation method has allowed the separation of the form factor of a single polyelectrolyte chain S( q) and the structure factor S( q). Two lengths are deduced from these two factors: the persistence length b which characterizes the electrostatic interactions along the chain by a fitting of S( q) with calculation of the scattering function for a wormlike chain, and from S( q), q which characterizes the interactions between chains. These two lengths vary in the same way with the concentration of polyions ( b ∝ C, q ∝ C) and a constant relation exists between them: only one length is then necessary to describe the structure of polyelectrolyte soltuion on this semidilute concentration range. [ABSTRACT FROM AUTHOR]

The deformation of the overall conformation of polystyrene, M=280000 g/ mole in dilute solution in a constant shear gradient has been investigated by small angle neutron scattering (SANS). The experiments were performed with a new Couette-type apparatus, consisting of two concentric quartz cylinders in which the outer one rotates and the solution is confined in the gap between both cylinders. The observation of the elastic coherent small angle scatterring intensity at a shear gradient of G=400 s has revealed a distinct anisotropy of the scattering pattern on the two dimensional detector, as estimated from equilibrium chain dynamics. After extrapolation to zero angle and zero concentration two different values for the overall size of the single macromolecule parallel and perpendicular to the flow-direction are deduced. [ABSTRACT FROM AUTHOR]

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Small angle neutron scattering studies have been made on solutions of dodecylhexaoxyethylene glycol in DO above the critical micelle concentration and as a function of temperature. It was possible to fit the experimental data at low values of scattering vector using a cylindrical model for the micelle shape. [ABSTRACT FROM AUTHOR]