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We study the structural properties of microgels made of poly(N-isopropylacrylamide) and acrylic acid as a function of hydrostatic pressure and temperature using small angle neutron scattering. Hydrostatic pressure induces particle deswelling by changing the mixing of the microgel with the solvent, similar to temperature. We extend this analogy to the structural properties of the particles and show that the form factor at a certain temperature is equal to the form factor at a certain hydrostatic pressure. We fit the results with an existent model for the microgel structure and carefully analyze the fitting procedure in order to obtain physically meaningful values of the free parameters in the model. [ABSTRACT FROM AUTHOR]

We have applied small angle neutron scattering (SANS), diffusing wave spectroscopy (DWS), and dynamic light scattering (DLS) to investigate the phase diagram of a sterically stabilized colloidal system consisting of octadecyl grafted silica particles dispersed in toluene. This system is known to exhibit gas-liquid phase separation and percolation, depending on temperature T, pressure P, and concentration φ. We have determined by DLS the pressure dependence of the coexistence temperature and the spinodal temperature to be dP/dT=77 bar/K. The gel line or percolation limit was measured by DWS under high pressure using the condition that the system became nonergodic when crossing it and we determined the coexistence line at higher volume fractions from the DWS limit of turbid samples. From SANS measurements we determined the stickiness parameter τB(P,T,φ) of the Baxter model, characterizing a polydisperse adhesive hard sphere, using a global fit routine on all curves in the homogenous regime at various temperatures, pressures, and concentrations. The phase coexistence and percolation line as predicted from τB(P,T,φ) correspond with the determinations by DWS and were used to construct an experimental phase diagram for a polydisperse sticky hard sphere model system. A comparison with theory shows good agreement especially concerning the predictions for the percolation threshold. From the analysis of the forward scattering we find a critical scaling law for the susceptibility corresponding to mean field behavior. This finding is also supported by the critical scaling properties of the collective diffusion. [ABSTRACT FROM AUTHOR]

We present a new 3D cross-correlation instrument that not only allows for static and dynamic scattering experiments with turbid samples but measures at four angles simultaneously. It thus extends the application of cross-correlation light scattering to time-resolved studies where we can, for example, efficiently investigate the temporal evolution of aggregating or phase separating turbid dispersions. The combination of multiangle 3D and on-line transmission measurements is an essential prerequisite for such studies. This not only provides time-resolved information about the overall size and shape of the particles through measurements of the mean apparent radius of gyration and hydrodynamic radius, but also on the weight-average apparent molar mass via the absolute forward scattering intensity. We present an efficient alignment strategy based on the novel design of the instrument and then the application range of the instrument using well-defined model latex suspensions. The effectiveness of the cross-correlation multiangle technique to monitor aggregation processes in turbid suspensions is finally shown for the acidification of skim milk during the yoghurt-making process. Due to the self-assembled nature of the casein micelles an understanding of the sol-gel process induced by the acidification is only feasible if time-resolved light-scattering experiments on an absolute scale are possible under industrially relevant conditions, where the casein solutions are highly turbid.

We have studied the dynamical and structural properties of dense charge stabilized colloidal suspensions by a combination of small-angle neutron scattering (SANS), 3D dynamic light scattering (3DDLS) and diffusing wave spectroscopy (DWS). SANS and 3DDLS extend static and dynamic light scattering techniques to the regime of opaque samples while DWS additionally provides information on short length scales, typically from 1-50 nm. This offers an increased range of accessible length and time scales perfectly suited for the (non-invasive) investigation of highly concentrated suspensions. Different systems have been examined ranging from hard sphere like suspensions over strongly repulsive charged spheres to colloidal gels. We furthermore present an extended theoretical frame for DWS to characterize the internal dynamics of turbid gels made from nanosized colloidal particles.

It has been shown that low-density plasma lipoproteins in patients with ischemic heart disease and hypertriglyceridemia are heavier in density, smaller in size, more negatively charged and more inclined to peroxide modification and aggregation than in healthy persons. The protein in the composition of such lipoproteins deviates towards the water phase, which may result in the masking of the domen, recognized by the BE-receptor and may lead to hyperlipidemia of a retaining character.

Both subfraction "2" of high density lipoproteins (HDL2) from patients with hypo-alpha-lipoproteinemia and subfraction HDL3 from persons with normal content of cholesterol were shown to accept the erythrocyte membranes cholesterol in vitro. Under these conditions HDL3 subfraction was transformed into HDL2-like particles, where content of unesterified cholesterol and its esters was increased simultaneously with enlargement of the particles size. The HDL subfraction, isolated from persons with high content of cholesterol, did not accept cholesterol under the experimental conditions. Apoprotein E, containing in the HDL subfractions, was not responsible for the particles cholesterol-accepting properties. Apoprotein E itself was capable of cholesterol elimination from erythrocytes as well as of cholesterol esters from HDL3 and HDL2-like particles with formation of a specific complex.