Light Scattering Analysis Technique

CCDs were originally developed and used for high-sensitivity and high-resolution requirements of imaging for astronomy. The Saturn DigiSizer II captures the scattering pattern using a patented optical design that employs a CCD as the light detector. A high-definition digital representation of the scattering pattern, which contains all of the information required to determine the particle size distribution, is captured.

Micromeritics’ application of the CCD array eliminates the need for mechanical fine-tuning of optical alignment. The instrument is automatically aligned by re-mapping the CCD array so that the scattering angle assigned to each element is exact to less than 0.005 degree relative to the central, unscattered light beam. The Saturn DigiSizer II’s CCD array has more than three million detector elements. The resulting extremely high resolution makes it possible to detect subtle differences in the scattering patterns and, therefore, subtle differences in particle size distributions. These minute differences in sample particle size may indicate a manufacturing variance, corroborate or refute theoretical studies, or help explain natural processes. Higher resolution means greater knowledge about differences between samples.

Advanced design features enable the Saturn DigiSizer to measure a light scattering pattern over a broad range of scattering angles with a dynamic intensity range from 1 to 1x1010. Combined with the high angular resolution of the CCD, the detector system provides an effective resolution of several million pixels at different positions in the scattering pattern, each detecting minute variations in light intensity. The Saturn DigiSizer’s high resolution enables the instrument to detect extremely small variations in the scattering pattern that are not detected by lower resolution instruments. It is this high level of accuracy that allows the Saturn DigiSizer to provide more detailed and precise particle size information than laser diffraction particle sizing systems of conventional design

The Saturn DigiSizers high resolution enables the instrument to detect extremely small variations in the scattering pattern that are not detected by lower resolution instruments.

This is primarily because of measurement of too few data points in the scattering pattern and the inadequate attempts to compensate for low resolution and other shortcomings using software-based algorithms.

Micromeritics has taken a new and more effective design approach to measuring the scattering pattern. Rather than use a photodiode array to capture average light intensity readings over extended regions of the scattering pattern, the Saturn DigiSizer II uses a high-resolution CCD array in a stepwise manner to capture a true digital representation of the scattering pattern – not simply the 50- or 100-light measurements within the pattern as taken with non-digital techniques.

With this high-resolution, closely spaced array of data, the intensity versus angle plot of data is practically continuous. Thus, Mie theory can be applied directly, without compensation algorithms and without concern over whether the distribution is monomodal or multimodal. The quality of the Saturn DigiSizer II analysis is apparent upon overlaying the angle verses intensity plot of experimental data from an analysis of a reference material (or a mixture of different size reference materials) with the angle versus intensity plot of data calculated from Mie theory for the reference size(s). Such a comparison is a standard report provided by the Saturn DigiSizer II.