Dynamic Liquid Image Analysis is a particle sizing technique that utilizes the revolutions made in digital imaging and computing power. It is simple in concept but powerful because for the first time there is a particle sizing technique that actually measures a particle size that is derived from the actual particle and not a spherical equivalent diameter as is produced by other particle sizing techniques.
Dynamic Liquid Image Analysis utilities a digital CCD detector of the same variety used in today’s digital cameras. It is paired up with some sort of magnifying optics like a microscope lens. A strobe light is usually used as the light source since the particles flow past the camera at rapid intervals. The dispersed particles are conveyed to the camera via a special flow cell that consists of a narrow flow path so that all of the particles flow through the focal plane of the magnifying optics. The liquid flow should be ceased at regular intervals in conjugation with the light source to capture images of particles that are momentarily static. In this way, the most accurate images are measured. Using a variety of algorithms, particle perimeters that are defined from the images are characterized by size and shape. These calculations can be performed in real time allowing thousands of particles to be analyzed in a short period of time. That is enough particles to build size and shape distributions something that microscopy cannot normally do. Dynamic Liquid Image Analysis can generally size particles as small as 1 micron and as large as 1000 microns. This technique can be particularly powerful when it is important to characterize fibers with very elongated shapes. Parameters such fiber length and width can be measured for each particle and with enough particles characterized, length and width distributions.
The graph contains two distributions from a paper fiber dispersion that was analyzed with the Flow Cell system. The vertical axis contains the distribution of widths of the fibers and the horizontal axis contains the elongation distribution. Elongation is a measure of the deviation of a shape from a perfect sphere. The elongation was used to select only those particles with a high aspect ratio. This was done so that the width distribution would only reflect the widths of particles which was known to be fibers and to exclude contaminate particles.
This type of analysis demonstrates the power of Dynamic Liquid Image Analysis to provide unique size and shape information for individual particles, information that cannot be obtained by any other particle size method.