Solid-state complexes of poly(N-vinylpyrrolidone) and dodecyl benzene sulfonic acid: Self-assembled structure and thermal properties

Solid-state complexes of flexible polymers with long-tail surfactants (surf) exhibit mesomorphic phase and microphase-separated lamellar morphology consisting of alternating polymer and surf layers. The alkyl tails in the surf layers are highly stretched and closely packed due to the excluded volume effect. In this study, the self-assembled structure of a new polymer(surf) complex system based on complexation between poly(N-vinyl pyrrolidone) (PVP) and dodecyl benzene sulfonic acid (DBSA) was investigated by optical microscopy and small-angle X-ray scattering (SAXS). Both mesomorphic phases and microphase-separated lamellar morphology were observed in PVP(DBSA) complexes. The thicknesses of polymer and surf layers were determined from the one-dimensional correlation function. Both types of thickness are dependent on complex composition. The interplay between chain conformational entropy and interaction energies (repulsive and attractive) is suggested to control the self-organized structure in the complexes. Complexation with DBSA reduced the thermal stability of PVP, which was in contrast with poly(ethyleneimine)-DBSA complexes reported previously.