Magnesium stearate and lactose are excipients commonly used in tablet formulation. The measured contact angles of water or of a saturated aqueous solution on the surfaces of compacts of these two powders are θ = 121 deg and θ = 30 deg, respectively. Their surface tensions (against air) are 72.3 and 71.6 dynes/cm, respectively. The surface tension of water (against air) at 20◦C is 72.8 dynes/cm.

(a) Compute the interfacial tension between water and each of these compacted powders.

 (b) Compute the spreading of water on the solid surfaces. 

 (c) How do you explain the quite different spreading results on these two powder compacts?

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To compute the interfacial tension between water and each of the compacted powders and determine the spreading of water on the solid surfaces we can u... View the full answer