Why do non- ionic surfactants make bigger micelles

[tammie123]

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What's the reason for why non-ionic surfactants make bigger micelles than ionic surfactants? Can someone explain this simply to me, I read it's something to do with too much repulsion with ionic surfactants, but if there's that much repulsion then how do the form micelles in the first place? I'm so confused

 

[Thestrugglez]

I will try my best to explain my interpretation of this, but I am making no guarantees.

Micelles form as a result of the hydrophobic tails and their repulsion to the hydrophilic factors of water. As a result, they form a spherical shape where the hydrophilic heads form the outer membrane.

If the heads were ionic, they would naturally repel each other. Therefore, the micelles would be smaller since they do not want to be as close to each other (since larger micelles would require that they are in closer proximity in order to prevent water from entering, I think?...). As for why they form, resonance would distribute the charges throughout the molecule, so the repulsion is still much smaller than the repulsion between the hydrophobic tails and water.

My explanation is based on my interpretation and I could be completely off. But usually, when in doubt, resonance is the answer 🙂.

 

[tammie123]

I will try my best to explain my interpretation of this, but I am making no guarantees.

Micelles form as a result of the hydrophobic tails and their repulsion to the hydrophilic factors of water. As a result, they form a spherical shape where the hydrophilic heads form the outer membrane.

If the heads were ionic, they would naturally repel each other. Therefore, the micelles would be smaller since they do not want to be as close to each other (since larger micelles would require that they are in closer proximity in order to prevent water from entering, I think?...). As for why they form, resonance would distribute the charges throughout the molecule, so the repulsion is still much smaller than the repulsion between the hydrophobic tails and water.

My explanation is based on my interpretation and I could be completely off. But usually, when in doubt, resonance is the answer 🙂.

So larger micelles are closer together and if there's repulsion involved then this isn't favourable?

 

[Thestrugglez]

Did some more research and this is what I concluded...

Larger micelles result in more "empty space" in the center of the micelle. This is unfavorable. Since ionic heads have higher repulsion than non-ionic heads, the formation of ionic micelles are much less favorable then the formation of a non-ionic micelle of the same size, hence non-ionic micelles are able to become much larger than ionic micelles. If it is too unfavorable, the micelle would not form and a more complex structure would arise.

Once again, I'm not too sure about this, but I think my earlier statement was wrong. Sorry about that.

I think it would probably be best if someone else could answer this.

 

[tammie123]

Did some more research and this is what I concluded...

Larger micelles result in more "empty space" in the center of the micelle. This is unfavorable. Since ionic heads have higher repulsion than non-ionic heads, the formation of ionic micelles are much less favorable then the formation of a non-ionic micelle of the same size, hence non-ionic micelles are able to become much larger than ionic micelles. If it is too unfavorable, the micelle would not form and a more complex structure would arise.

Once again, I'm not too sure about this, but I think my earlier statement was wrong. Sorry about that.

I think it would probably be best if someone else could answer this.

Why is 'empty space' not favourable? What's the reason for this?

 

[Thestrugglez]

Why is 'empty space' not favourable? What's the reason for this?

That goes beyond the scope of anything I've learned. There are scientific journals online that mention this, but doesn't explain.

 

[tammie123]

That goes beyond the scope of anything I've learned. There are scientific journals online that mention this, but doesn't explain.

No worries, I'm sure they won't even ask this in the exam anyway, I'm just being a bit excess. 😛

Thank you anyway 🙂