Summary
The diffusion coefficient as well as the dimensionality of the diffusion process can be determined by straightforward and facile data analysis, when fluorescence recovery after photobleaching ...(FRAP) is measured as a function of time and space by means of confocal laser scanning microscopy. Experiments representing one‐dimensional diffusion from a plane source or two‐dimensional diffusion from a line source are readily realized. In the data analysis, the deviations of the actual initial conditions from ideal models are consistently taken into account, so that no calibration measurements are needed. The method is applied to FRAP experiments on solutions of Rhodamine B in glycerol and aqueous suspensions of polymethyl methacrylate microspheres.
A procedure for a systematic evaluation of fluorescence recovery after photo-bleaching (FRAP) data is presented that allows one to determine distributions of diffusion coefficients. The method ...provides a straightforward and calibration-free way to quantify multiple diffusion processes when FRAP is measured as a function of time and space by means of confocal laser scanning microscopy. It is verified utilizing FRAP experiments on mixtures of differently sized fluorescent micro-spheres as realizations of discrete D distributions.
The rheological properties of highly filled nano-zirconia suspensions in water and in various water–1,2-propanediol mixtures were investigated. The influence of an electrosteric (polyacrylic acid), ...an electrostatic (triammonium citrate) and a steric dispersant (2-(2-(2 methoxy ethoxy) ethoxy) acetic acid, TODA) on the viscosity and the elastic properties of the suspensions were also recorded. For any given water–propanediol mixture TODA was the most effective of the investigated dispersants. It resulted in the lowest slurry viscosities and the highest tan
δ values, indicating best dispersing properties and the lowest elastic shear modulus, respectively. The water–propanediol proportion influenced the properties of the slurries strongly. For all dispersants the relative viscosity of the slurries decreased with increasing propanediol content. This was found to be a non-linear function in the case of TODA, where at a minimum level of 50
wt.% propanediol the properties of the slurries were the best. For the other dispersants this was a linear function, which indicates that the dispersing quality there only depended on the polarity of the dispersing medium. A screen printing paste was produced using TODA as a dispersant and a 75
wt.% propanediol–25
wt.% water mixture dispersing medium and subsequently printed. The printed layer showed 40–50
nm sized particles, indicating that the dispersing properties were also retained.
The rheological properties of poly(trimethylene naphthalene-2,6-dicarboxylate) (PTN) were studied using a dynamic stress rheometer with oscillatory parallel plates. The influence of temperature and ...molecular weight on the storage modulus, loss modulus, and complex viscosity was investigated. It was possible to express the temperature dependence of the shift factors aT with the Arrhenius equation; the activation energy was found to be 85kJ/mol. A comparison of molecular weight determined: (a) by rheological measurements and (b) by Mark–Houwink–Sakurada equation showed excellent agreement.
The adsorption of an electrosteric (polyacrylic acid, PAA), an electrostatic (triammonium citrate, TAC) and a steric dispersant (2-(2-(2 methoxy ethoxy) ethoxy)acetic acid, TODA) onto nanosized ...zirconia particles in deionised water and in a 75 wt% water-25 wt% 1,2-propanediol mixture was investigated. The amount of dispersant in deionised water yielding the lowest apparent viscosity was measured by rheology. For PAA this was 6 wt%, for TAC 2 wt% (corresponding to about 0.43 mg/m2) and for TODA 2 wt% (corresponding to about 0.34 mg/m2). In the water-propanediol mixture, the minimum viscosity was measured and the adsorbed amount was determined by adsorption isotherms using the depletion method. For TAC, this was about 0.076 mg/m2, which is five times less than the value in pure water. Zeta potential measurements were performed to confirm the dispersion mechanism. Zirconia particles in water showed the same zeta potential as in water-propanediol, although in water-propanediol less TAC molecules were adsorbed on the surface. For TODA, the adsorbed amount was calculated to be about 0.4 mg/m2, which agrees well with the value determined in water. Propanediol seems not to influence the adsorption in that case. 14 refs.
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