Surfactants are molecules with a hydrophilic head group and a hydrophobic tail. They can make micellar structures in aqueous and non-aqueous solution. But there are some new materials which are called self-assembly and have a molecular structure like surfactants and can make micelles. I would like to know if there is any difference between surfactant and self-assembly molecules?
Dear Sumit,
cannot agree on this. Pluronic type polymers are also common surfactants. I guess there is an intercept between the two and maybe partly considered from a different angle.
If you speak about two phases than we have something like particles dispersed with an interface. Otherwise we have a one phase system, i.e. a solution. As in case of a micellar solution or microemulsions then there are hydrophobic and hydrophilic domains but only one phase.
I think self-assembly molecule is actually not correct term. If you are talking about self-assembled nanostructures (or other structures) then you are using surfactants to achieve the state of self-assembly for two particles. This surfactant is called a "linker molecule". This molecule (polymeric in nature with both positive and negative heads-so they are in principle surfactants) links two different types of particles/molecules to each other, producing a self-assembled structure which is otherwise very difficult to receive by, for example, simply mixing these two particles without linker molecule.
I agree with this issue that surfactant molecule could either make a micellar structure on itself and make a layer around dispersed phase in a liquid such as magnetic nanoparticles in a liquid.
But, my question about self-assembly molecule is about a new kinds of polymeric molecules which could make self-assembled structure. A molecule with a long hydrophilic chain and many hydrophobic branch, such as a chitosan molecule which is grafted by some hydrophobic molecule such as cholesterol in different section of chitosan molecular chain.
my question is: is there any difference between this kinds of molecule and surfactant or not?
Dear Hossein,
please keep in mind that there is already a difference between each of the common surfactant molecules. The more different the molecular architecture the more pronounced will be the difference due to differences in packing, however, there will be similarities like lowering of interfacial tension, ability to solubilize organic substances with limited aqueous solubility, etc.
Dear Sobisch
Thank you for your kind wishes.
I agree with you about existence of some similarities like relationship between interfacial tension and CMC with molecular structure (such as degree of branching on polymer chain). But, during my research about packing factor and other parameter related to this factor, I found it's very complicated to calculate packing parameter for these kine of self-assembly molecule.
There might be some similarity of your amphiphilic polymers with commercial alkyl polyglucosides. Would be interesting to do some comparative studies, maybe including chitosan grafted with alkyl chains instead of cholesterol.
I believe it comes down to whom you're speaking with. In previous coursework and literature searches (including text books such as those by Israelachvili or Anderson) I've come across most often the rather loose definition of a surfactant as a component that alters the surface energy. Usually only in the case when the surface energy is the property of interest. The amphiphilic molecules are common surfactants in aqueous solutions: they alter the surface or interfacial energies of the fluid but the nature of having hydrophilic and hydrophobic components. I've had people apply the term surfactant mostly to amphiphiles in liquids, but have also heard it applied to salts in liquids (ions often increase the surface energy of water) or alloying components in (solid) metals/ceramics.
Block co-polymers (eg BPD-PEO), traditional (small molecule) surfactants (eg SDS, CTAB), lipids, etc all to some extent or another perform this action. They have also all been used for guided self-assembly but this is simply just a different label you apply that happens to have overlap. Many surfactants will have a propensity to also induce self-assembly (because of their strong size and thermodynamic tunability), but these are descriptions of two separate phenomena, similar to what Mkhitar stated.
I would argue along these lines that the idea of micelles here is an example of self-assembly behavior that naturally results (at sufficient concentration) from the physical nature of the surfactants used. Higher concentration of surfactants leads to unique self-assembled packing structures (eg as described by Helfrich). On the other hand you could make a self-assembly "molecule" or nanoparticle by coating an EM-active Janus particle with a polymer layer. Then application of a magnetic field would induce self-assembly, but these particles wouldn't act as surfactants. It's nomenclature, but for purposes of publication you likely only want to name your molecule a surfactant if it's either critical to the description of the system or you've demonstrated it has a surfactant effect.
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanoparticle Research