A simple method for assessing fineness and stability of pigment and dye dispersions Available to Purchase

In recent work on the preparation of small samples of dye dispersions, a simple method has been developed of quantifying particle sizes and stability in dispersion. A method sometimes used by laboratories is to spot a filter paper with a dilute dispersion and observing the lateral spread of the dye or pigment. Particles lacking adequate stabilisation will tend to be precipitated near the centre of the spot, the carrier medium spreading out to leave a translucent halo. It is considered that precipitation is caused by the electrostatic charges on the fibres of the filter paper. This method can, in many instances, offer a guide to the quality of the dispersion, but an objection is that the results embody variable causative factors, making the test subjective and unless great care is taken, the test may fail to answer the criterion of repeatability and reproducibility. The authors have found that a dispersion with particles of dye with a medium size of one micron show vigorous Brownian motion over several hours of storage time and yet the sample offers anomalous results with a spot test on filter paper.