What are the factors affecting critical micelle concentration (CMC)?

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Accepted Answer

Amphiphile Structure: Hydrophobicity and ionic nature can affect critical micelle concentration.

Increased hydrophobicity of surfactants lowers the CMC.
The CMC of ionic surfactants in aqueous solutions is higher than that of non-ionic surfactants.

Bulky Hydrophilic or Hydrophobic Groups: The presence of bulky hydrophilic or hydrophobic groups in surfactants makes it harder for them to incorporate into the micelle’s core, which raises the CMC.
Experimental Conditions: Temperature and pH can also affect CMC.

High temperatures can decrease the hydration of hydrophilic groups, which promotes micellization and lowers the CMC. However, at extremely high temperatures structured water around head groups gets destabilized, which increases the CMC.
The CMC varies with pH. High pH increases the CMC for –NH2 head groups while low pH increases the CMC for – COOH head group.

Presence of Additives: Critical micelle concentration can also be affected by presence of ions and organic impurities.

Solutions with high ionic strength reduce repulsion between head groups because of the presence of counter ions. This leads to a lower CMC.
Organic chemicals or impurities may cross into micellar areas or disrupt the solvent-micelle interactions. Some substances such as formaldehyde and urea can disrupt hydrogen bonding, increasing the CMC.

What are the factors affecting critical micelle concentration (CMC)?

Posted August 22, 2024