Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
A substance is considered anionic if it has a net negative charge. For example, the chloride ion Cl- is anionic. Many polyelectrolytes are also anionic. Sodium polyacrylate is a one example. When this polymer is dissolved in water, the sodium ions are partly dissociated from the polymer chain. Many types of particles of interest to papermakers tend to have an anionic surface charge when suspended in water solution. Though there are an equal number of positive and negative ions in the sample as a whole, the net negative surface of an anionic particle is balanced by counter-ions in solution. The words "double-layer" are used to describe the distribution of counter-ions adjacent to a charged surface.
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