Robert Finsy

Particle sizing by quasi-elastic light scattering

The application of quasi-elastic light scattering for the determination of particle size distributions is reviewed. The basic principles and assumptions on which the method relies are presented on an introductory level. The practical performances are illustrated by different results including results obtained by round-robin comparative studies. Finally, new developments for on-line or in situ characterization of concentratedand opaque dispersions are briefly presented.

Inversion of static light scattering measurements for particle size distributions

Abstract The inversion of static light scattering measurements (SLS) for the evaluation of particle size distributions is reported. The performances of two inversiion methods, i.e., the maximum entropy method and a constrained regularization method (Contin), are illustrated with simulated data and experiments on samples with unimodal, bimodal, and trimodal distributions of spherical particles and on a sample with a broad size distribution. Some experimental results are compared to assessments by photon correlation spectroscopy (PCS) and electron microscopy (EM). It appears that a significantly better resolution in particle size is obtained by SLS than by PCS. However, for a sample with a broad distribution in particle sizes, not all details of the distribution observed by EM were resolved.

Singular value analysis and reconstruction of photon correlation data equidistant in time

The application of the algorithm of Zeiger and McEwen to the analysis of noisy photon correlation data is investigated. For the particular case where the data are sampled at equidistant time intervals a complete solution is given allowing reliable reconstruction of the spectrum of exponential decay rates without any a priori knowledge. A particular attractive feature of the method is that the singular value analysis of the Hankel matrix of autocorrelation functions offers a practical criterion for the decomposition of the data into a signal and a noise part. Some tests of the method are illustrated with experiments on monodisperse latices, gold sols, and binary mixtures of monodisperse latices. In the latter case comparable and even better results are obtained in significantly shorter computing time when compared to an analysis with Contin and the maximum entropy method. Since the present method does not require any a priori parameter setting, it is also complementary to these methods.

MAXIMUM ENTROPY INVERSION OF STATIC LIGHT SCATTERING DATA FOR THE PARTICLE SIZE DISTRIBUTION BY NUMBER AND VOLUME

The application of Maximum Entropy analysis of static light scattering data for the evaluation of particle size distributions by number and by volume in the submicron size ranges is reported. The practical performances for homogeneous spheres are illustrated with simulated data and experiments on unimodal, bimodal and trimodal distributions of monodisperse latices. Accurate reconstructions by number are observed. The reconstructions by volume lead to somewhat broadened distributions. The method also allows the resolution of closely spaced distributions of particle sizes.

Shape and Size Determination by Laser Diffraction: Feasibility of Data Analysis by Neural Networks

The feasibility of the inversion of laser diffraction data for size and shape distribution by neural networks has been investigated by computer simulation. Neural networks trained with diffraction patterns of elliptical particles with different sizes and aspect ratios (axis ratios) were able to recover simultaneously both the size and aspect ratio distributions in a few milliseconds on a common PC.

ALLOXAN TOXICITY IN HUMAN AND CANINE SPERMATOZOA POSSIBLE BIOCHEMICAL BASIS FOR A SPECIES DIFFERENCE IN SENSITIVITY

In view of the well known species differences in the sensitivity of pancreatic B-cells to the toxic glucose analogue alloxan, it was tested whether spermatozoa from two species with a different diabetogenic effect of alloxan displayed a similar difference in their sensitivity to this drug. In canine spermatozoa, less than 2 mM alloxan profoundly reduced the rate of glucose oxidation and cellular motility whereas more than 5 mM was required to significantly alter these parameters in human spermatozoa. Such species difference was not observed in spermatozoal sensitivity towards the inhibitory effects of tert-butyl hydroperoxide. The phenomenon is not attributable to a different rate of alloxan uptake since the drug is not incorporated by dog or human spermatozoa. The alloxan toxicity was counteracted by D-glucose and its 3-O-methyl analogue in both species, and was potentiated by ascorbic acid; however, only in man. The protective effect of D-glucose was much less marked in tert-butyl hydroperoxide-cytotoxicity. It is concluded that the observed species difference in spermatozoal alloxan sensitivity is not related to differences in alloxan uptake or in sensitivity to organic peroxides; differences in cellular scavenging of superoxide anion radicals and/or ascorbic acid metabolism may explain the lower sensitivity of human spermatozoa for alloxan.

Shape and Size Determination by Laser Diffraction:Feasibility of Data Analysis by Physical Modeling

The feasibility of the inversion of laser diffraction data for size and shape distributions by a constrained regularization method (Contin) has been investigated by computer simulation. Diffraction data are simulated for particles with elliptical projections. An iterative procedure is proposed to calculate the size and shape distribution. This method was able to recover both the size and shape distribution from simulated diffraction patterns of elliptical particles with different sizes and aspect ratios.

Ostwald ripening and solubilization in alkane in water emulsions stabilized by different surfactantsPresented at the 17th Conference of the European Colloid & Interface Science Society, Firenze, Italy, September 21?26, 2003.

The Ostwald ripening (OR) and the solubilization of alkanes in water emulsions stabilized by the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and the non-ionic surfactants hexaoxyethylene glycol n-dodecyl ether (C12E6) and polyoxyethylene (20) sorbitan monolaurate (Tween20) were investigated. For the emulsions stabilized by the anionic SDBS the mass transport in both OR and solubilization is molecular diffusion of the oil through the continuous phase and no contribution of a micellar mediated transport is observed. For the emulsions stabilized by the non-ionic surfactants three different situations occur. For emulsions prepared in one single step under the high shear conditions of a microfluidizer, the mass transport is also mainly molecular diffusion. For already prepared emulsions to which extra surfactant is added, there is, besides molecular diffusion, a small contribution by a micellar mediated mechanism. Finally, in the solubilization studies the mass transport is a fusion–fission mechanism rather than molecular diffusion.

PARTICLE SIZE DISTRIBUTION OF BIMODALS : A COMPARATIVE STUDY OF SUBMICRON SIZING INSTRUMENTATION

During the preparation of polymer colloids the formation of bi- and multimodal populations can be observed. In order to control processes and applications one should be able to monitor the phenomena underlying the formation of multimodals. Therefore the capability of different particle sizing instruments to resolve bimodals in the submicron range, has been investigated. The selected techniques were: Photon Correlation Spectroscopy (PCS), Static Light Scattering (SLS), Sedimentation Field Flow Fractionation (SF3), Disk Photosedimentometer (DCP) and Electron Microscopy (EM). For PCS the comparative study has been broadenend towards different commercial instruments and software packages located in a university as well in an industrial environment.