Behaviour of poly(N-vinylcaprolactam) macromolecules in the presence of organic compounds in aqueous solution

Dynamic light scattering measurements have been performed for aqueous solutions of thermosensitive linear poly(N-vinylcaprolactam) (PVCa) macromolecules in the presence of NaCl and different water soluble amphiphilic organic compounds: pyrogallol (neutral amphiphilic compound), cetylpyridinium chloride (cationic surfactant) and sodium dodecylsulfate (anionic surfactant). A decrease in the macromolecular hydrodynamic diameter is observed upon addition of ionic surfactants (SDS, CPC) at low surfactant concentrations. This trend changes to an increase in the macromolecular hydrodynamic diameter at high surfactant concentration at temperatures below the temperature of polymer aggregation. This effect is in contrast with the behaviour of the systems of PVCa–non-ionic organic compounds (pyrogallol) and NaCl where we always observed the weak monotonic decrease of the hydrodynamic diameter with the increase in the concentration of organic compound, NaCl.

The behaviour of ternary systems PVCa macromolecules–ionic surfactant–pyrogallol and PVCa macromolecules–ionic surfactant–NaCl was studied. The addition of pyrogallol leads to the suppression of the intermacromolecular aggregation induced by temperature increase that is still observed at low surfactant concentrations and to the decrease of macromolecular hydrodynamic diameter. Also, the addition of NaCl to the PVCa/ionic surfactant systems results in the increase of the macromolecular hydrodynamic diameter. It is speculated that these results are due to the suppression of the cross-linking role of surfactant aggregates upon the addition of NaCl and pyrogallol.