Physical stability
EminTech
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| Physical stability is of major concern, especially in emulsions. Emulsion instability results in concentration gradients of active substance in the container, loss of diffusion hindrance and loss of formulation elegance. Although experience of a formulation increases the significance in a formulator forecast of long time stability, stability testing avoids potentially hazardous market situations. To save time during product development it is desired that the time for evaluation of stability is minimised. Contrary to routines used in some companies, emulsion physical stability cannot be accelerated by the use of increased temperature. A formulation that is stable at 40°C is not nessecarily more stable 20°C than other emulsions. Experience has shown that iinitial signs of physical instability in emulsions are seen in emulsion droplet size distribution or/and changes in rheological properties long before they have led to such a significant sign as phase separation. |