Is there any electrostatic charge on PNIPAm in aqueous solution? It is usually described as a neutral polymer but is there anybody who thinks it is slightly charged? Is it possible to use it for electrostatic LbL?
I do think that it is most often slightly charged! When the polymerization is initiated with APS (which is quite common), the polymer thus produced unavoidably contains a small fraction of sulfate groups. If I remember correctly one of the discussions I have followed, this is enough to be detected via zeta potantial measurement (cf. http://www.mpikg.mpg.de/th/people/dimova/publications/Tauer%20CollPolSci%2009.pdf) but I doubt this will be enough for LbL.
PNIPAM, by its structure, is quite neutral; but from the preparation method, there are always the iniators present that impart PNIPAM with a slight (negative) charge. This "residual" charge is sometimes not enough for LbL deposition to achieve charge reversal; having said that, it could also just be deposited through hydrophobic interaction or by just physical entanglement - all depends on what surface you are depositing. We have reported for example LbL deposition of polyelectrolytes onto PNIPAM microgels (as well as P(NIPAM-co-AA) where "intrinsic" negative charges are present due to the presence of functional groups (and in this case, of course, is pH-dependent). If you want to use microgels for LbL deposition, I would suggest copolymerizing with another monomer with some functional groups that would bring "intrinsic" charges to your microgels.
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