Sulfonic acid doped thermoreversible polyaniline gels. 3. Structural investigations

The surface morphology of the thermoreversible polyaniline WAND gels prepared with dinonylnaphthalenesulfonic acid (DNNSA), dinonylnaphthalenedisulfonic acid (DNNDSA), (+/-)-camphor-10-sulfonic acid (CSA), and n-dodecyloxy sulfonic acid (DOSA) are studied using atomic force microscopy (AFM) for 15% PANI concentration (w/w). The AFM study clearly reveals the formation of lamellar morphology in the gel. X-ray scattering experiments of these gels also support the lamellar structure formation, and the lamellar thickness measured from it remains invariant with composition for the PANT-DNNSA and PANI-DNNDSA systems. In PANI-CSA and in PANI-DOSA systems the lamellar thicknesses vary with PANI concentration. Both X-ray diffraction and electron diffraction experiments on the gels of different compositions of PANI-DNNSA and PANI-DNNDSA systems indicate new spacings of lower d(hkl) values which are invariant with composition. Similar observations are also found in PANI-CSA and PANI-DOSA systems. These results indicate the formation of new unit cells in the lamella due to the micro crystallization of elongated surfactant tails formed under the doped condition. The d(hkl) values characterizing the lamellar thickness, bilayer thickness, and monolayer thickness are discussed in view of molecular mechanics calculations using the MMX program. The composition dependency of the lamellar thickness is discussed from the cohesive force of the surfactant tails within the lamella.