Sulphamerazine, suspension

Bonds between particles in flocculated sulphamerazine suspension. 

The degree of flocculation of sulphamerazine suspensions has been determined as a function of surfactant (sodium dod yl polyoxyethylene sulphate) concentration and electrolyte concentration [14]. At low surfactant levels the system is flocculated, with sedimentation volume fractions of about 0.9 at higher levels the sedimentation volume falls to about 0.6. On the addition of 0.24 m NaCl a dramatic decrease in sedimentation volume is observed, indicating a dense sediment with cloudy supernatant. Further addition of NaCl results in reestablishment of a flocculated state perhaps by adsorption of ions on to the particles. 

Sulphamerazine suspensions are in a deflocculated state when prepared with polysorbate 40 [33] (2 %). On standing, the sedimentation volume is around 0.15 and the system is impossible to redisperse after two weeks. Addition of high concentrations of propylene glycol (i.e. greater than 50 %) flocculates the system and renders the suspension dispersible. Propylene glycol dehydrates the surfactant molecules (the cloud point is lowered) hence reducing its stabilizing properties. 

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