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DrX Whiz Niraj
Unit 3: Coarse Dispersions
Suspensions, Emulsions & Their Stability
1. Flocculated vs Deflocculated Suspensions
A Suspension is a biphasic system jahan solid insoluble particles liquid medium mein disperse hote hain. (Particle size > 0.5 ยตm).
Suspensions mainly do tarah ke hote hain: Flocculated (jahan particles loose network banate hain) aur Deflocculated (jahan particles alag-alag rehte hain).
| Property | Flocculated Suspension | Deflocculated Suspension |
|---|---|---|
| Particle Behavior | Particles form loose aggregates (flocs). | Particles remain as separate entities. |
| Rate of Settling | Fast (large flocs settle quickly). | Slow (small individual particles settle slowly). |
| Sediment Nature | Loose sediment. No hard cake formation. | Compact sediment. Forms a hard cake. |
| Redispersion | Easily redispersed upon mild shaking. | Very difficult to redisperse (irreversible). |
๐ก Exam Tip (Stokes' Law):
Settling of particles is governed by Stokes' Law:v = 2r²(d₁ - d₂)g / 9ฮทTo prevent settling, we can decrease particle size (r) or increase viscosity of the medium (ฮท).
2. Emulsions & Their Types
An Emulsion is a biphasic system made of two immiscible liquids (like oil and water), where one is dispersed as fine droplets into the other.
1. Oil-in-Water (O/W): Oil is the dispersed phase and Water is the continuous medium. They are non-greasy and easily washable. (E.g., Milk, Vanishing Cream).
2. Water-in-Oil (W/O): Water is the dispersed phase and Oil is the continuous medium. They are greasy. (E.g., Butter, Cold Cream).
๐ HLB Scale (Hydrophilic Lipophilic Balance):
Emulsifying agents are chosen based on their HLB value.- Low HLB (3 to 6): Lipophilic (Forms W/O Emulsions. e.g., Spans).
- High HLB (8 to 18): Hydrophilic (Forms O/W Emulsions. e.g., Tweens).
3. Physical Instability of Emulsions
Ek stable emulsion banana challenge hota hai kyunki oil aur water hamesha alag hona chahte hain (due to high interfacial tension). Instability mainly 4 tarah ki hoti hai:
- 1. Creaming (Reversible): Droplets (mostly oil) float upward due to density difference (Stokes' Law). It can be redistributed simply by shaking.
- 2. Coalescence: Chote droplets aapas mein mil kar bade droplets (fusion) banate hain kyunki unke beech ki protective film toot jati hai.
- 3. Cracking / Breaking (Irreversible): Oil aur Water completely alag hokar do clear layers bana lete hain. Shaking se bhi wapas emulsion nahi banta. (Causes: Extreme temp, microbial attack).
- 4. Phase Inversion: O/W emulsion suddenly W/O emulsion mein convert ho jata hai. (Causes: Change in phase volume ratio or temp).