𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞 : 𝐖𝐡𝐲 𝐄𝐦𝐮𝐥𝐬𝐢𝐨𝐧𝐬 𝐚𝐫𝐞 𝐭𝐡𝐞𝐫𝐦𝐨𝐝𝐲𝐧𝐚𝐦𝐢𝐜𝐚𝐥𝐥𝐲 𝐮𝐧𝐬𝐭𝐚𝐛𝐥𝐞 𝐬𝐲𝐬𝐭𝐞𝐦𝐬?

 𝐓𝐨𝐝𝐚𝐲'𝐬 𝐊𝐍𝐎𝐖𝐋𝐄𝐃𝐆𝐄 𝐒𝐡𝐚𝐫𝐞

𝐖𝐡𝐲 𝐄𝐦𝐮𝐥𝐬𝐢𝐨𝐧𝐬 𝐚𝐫𝐞 𝐭𝐡𝐞𝐫𝐦𝐨𝐝𝐲𝐧𝐚𝐦𝐢𝐜𝐚𝐥𝐥𝐲 𝐮𝐧𝐬𝐭𝐚𝐛𝐥𝐞 𝐬𝐲𝐬𝐭𝐞𝐦𝐬❓

➡️ Let us consider for an oil in water(O/W) emulsion where oil droplets are dispersed in water.

This temporary mixture of two immiscible liquids will naturally separate over time to reach a state of minimum free energy.

👉 The key factors behind this instability are the increase in surface area during emulsification and inherent interfacial tension between the immiscible phases.

◾The basis of thermodynamic instability:

🔹The thermodynamic stability of an emulsion is determined by the change in Gibbs free energy (∆G).

🔹For a system to be thermodynamically stable, the overall change in Gibbs free energy must be negative (∆G<0) and spontaneous.

🔹The equation for Gibbs free energy is expressed as: ∆G = ∆H - T∆S

where:

∆H is the change in enthalpy.

T is the temperature.

∆S is the change in entropy.

🔸For an emulsion, the change in Gibbs free energy can be viewed as the sum of the interfacial energy and the entropy of mixing.

∆G = Y∆A - T∆S

where:

Y is the interfacial tension.

∆A is the change in interfacial surface area.

T∆S is the entropy of mixing term.

🔺In a conventional emulsion:

▪️ Positive interfacial energy: When one immiscible liquid is dispersed into another, it dramatically increases the total interfacial surface area (∆A), as breaking into countless droplets. Since the interfacial tension (Y) is positive, the (Y∆A) term is large and positive, making the emulsion thermodynamically unfavorable.

▪️Negligible entropy of mixing: While dispersing the droplets increases the system's disorder and entropy(∆S), this effect is typically too small to overcome the large positive interfacial energy term.

🔹Overall result: The overall change in Gibbs free energy (∆G) is positive, which means emulsions are thermodynamically unstable and will eventually phase separate. 

source : Dr. Akshoy Jamadar