Wetting Property OF A Substance PDF

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WETTING PROPERTY OF A SUBSTANCE. Theory: Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces. The wettability of a substance depends on the surface tension and contact angle. The efficiency of a pharmaceutical product is influenced by the tendency of a liquid to wet a pharmaceutical solid. Poor wettability can be a problem in preparation of suspensions, granulation of powders, dissolution of powders and consequently bioavailability issues. For proper wetting, the liquid should be able to displace the air surrounding the solid surface, which depends on the affinity between the liquid and the solid. If this affinity is weak/nonexistent, there is a difficulty in displacing the air around the solid particles; hence an angle of contact develops between the solid and the liquid surface. This contact angle ( Ø) results from an equilibrium between 3 interfacial tensions, γsl, γlv, γsv, which is due to unbalanced forces at the 3 interfaces: solid, liquid & vapour/gas/air. If γsv > γsl, spontaneous wetting occurs; while if γsv < γsl, work must be done to wet the surface. Wetting can be improved by addition of surfactants and hydrophilic colloids. Surfactants or surface-active agents can be defined as substances that orient at the surface or interface to reduce the surface tension or interfacial tension. Eg: Sodium lauryl sulphate, Dioctyl sulfosuccinate etc. Contact angle measurement (Telescopegoniometer), wet point method, flow point method, capillary rise method etc comprise of some common techniques to determine the wetting tendency of a substance.

EXPERIMENT RequirementsTest sample powders-Talc and Calamine Surfactants-Tween20, Tween 80. Apparatus: Beakers, Petriplates, Glass rod

Wet Point Method Procedure: 1) In a series of tared petri plates, take 5 g of accurately weighed talc. 2) To each plate add each surfactant in graded concentrations as given in Table 1 3) Mix the powder and surfactant thoroughly. Add water dropwise to each petriplate and mix till a coherent mass that does not separate is obtained. 4) Determine the amount of water added and calculate in terms of ml/100 g of talc. 5) The sharpness of the endpoint depends on the powder, the wetting agent and the vehicle employed. Table 1

S A) Talc Surfactant1- Surfactant 2 – No Tween 20(g) Tween 80(g) 1 5g 0 0 2 5g 0.5 0.5 3 5g 1 1 4 5g 1.5 1.5 5 5g 2 2 6 5g 2.5 2.5 Establish a comparative result for the wetting tendency of Tween 20 and Tween 80. Set II :-Repeat the above experiment using Calamine as the powder and Tween 20 and Tween 80 as surfactants. (Table 2) Table 2 S B) Surfactant 1- Surfactant 2 – No Calamine Tween 20(g) Tween 80(g) 1 5g 0 0 2 5g 0.5 0.5 3 5g 1 1 4 5g 1.5 1.5 5 5g 2 2 6 5g 2.5 2.5 Establish a comparative result for the wetting tendency of Tween 20 and Tween 80. Flow Point Method Procedure: 1) In a series of tared beakers, take 5 g of accurately weighed talc. 2) To each, add each surfactant in graded concentrations as given in Table 3 3) Mix the powder and surfactant thoroughly. Add water dropwise to each beaker and mix till a flowable uniform dispersion is obtained

4) Determine the amount of water added and calculate in terms of ml/100 g of talc. 5) The sharpness of the endpoint depends on the powder, the wetting agent and the vehicle employed. 6)Table 3 S A)Talc Surfactant 1- Surfactant 2 No Tween 20(g) -Tween 80(g) 1 5g 0 0 2 5g 0.5 0.5 3 5g 1 1 4 5g 1.5 1.5 5 5g 2 2 6 5g 2.5 2.5 Establish a comparative result for the wetting tendency of Tween 20 and Tween 80. Set Il Repeat the above experiment using Calamine as the powder and Tween20 and Tween 80 as surfactants. (Table 4) Table 4 S B) Surfactant 1- Surfactant 2 No Calamine Tween 20(g) Tween 80(g) 1 5g 0 0 2 5g 0.5 0.5 3 5g 1 1 4 5g 1.5 1.5 5 5g 2 2 6 5g 2.5 2.5 Establish a comparative result for the wetting tendency of Tween 20 and Tween 80.

OBSERVATION TABLE 1:Sr.No. TALC + TWEEN 20 Wetting point 1 2 3 4 5 6

TALC + TWEEN 80 Flow point

Wetting point

Flow point

OBSERVATION TABLE 2:Sr.No. CALAMINE + TWEEN 20 Wetting point

Flow point

CALAMINE + TWEEN 80 Wetting point

Flow point

1 2 3 4 5 6

Result: The Wetting point for Tween20 and Tween 80 was found to be ……and …… ml/100 gm of Talc respectively. The Flow point for Tween 20 and Tween 80 were found to be .…… and …… ml/100 gm of Calamine respectively. Based on the wetting point method, wetting tendency of Tween 20 and Tween 80 were found in the order :…………..>…………..

Result: The Wetting point for Tween20 and Tween 80 was found to be ……and …… ml/100 gm of calamine respectively. The Flow point for Tween 20 and Tween 80 were found to be .…… and …… ml/100 gm of Calamine respectively. Based on the Flow point method, wetting tendency of Tween 20 and Tween 80 were found in the order :………..>……………...