Characterization of polymer systems by light scattering methods

WALTER SCHROEDER; VALERIA PETTARIN; GUILLERMO ELICABE

Los Cocos, Córdoba, Argentina

Simposio; III Simposio Argentino-Chileno de Polímeros ARCHIPOL III; 2005

Particle sizing in the range from about 50 nm to several micrometers has been successfully addressed using Static Light Scattering (SLS) techniques. This technique involves essentially two steps: first, intensity measurements of scattered light at several angles are recorded; then, data reduction under the assumption that scattering occurs in the so-called Mie regime is performed. The model derived under the Mie regime for one particle can be straightforwardly extended to a system of many particles only if the assumption of independent single scattering is valid, which means that the system is diluted. SLS measurements are usually performed using a laser goniometer which covers a wide range of angles, varying typically from 10 to 150 degrees. The sample holder must be cylindrical, geometry that restricts the thickness of the sample to at least several millimeters. When the concentration of particles is higher and/or the system morphology evolves during time, this configuration becomes unsuitable due to the effect of multiple scattering. Time resolving SLS can be achieved by measuring light intensities for all angles at the same time. The Fraunhofer setup, in which the geometry of the sample holder and detector are flat, is a practical arrangement around which different alternatives had been developed. Different configurations known as Small Angle Laser Scattering (SALS) apparatus (q < 40°) have been used to study systems of particles with sizes larger than 1mm. In this work, a Fraunhofer setup designed to investigate liquid systems of different nature is presented. Other authors have also presented similar configurations (Lehner et al, 1998). Polystyrene latex standards of different sizes are employed to test this instrument in a range of concentrations and sample thickness, so that to test the validity of the single scattering assumption and thus the use of the Mie equations to correlate the data. Experimental results are analyzed using inverse analysis.