Montmorillonite clay nanocomposites of sulfonic acid doped thermoreversible polyaniline gel: physical and mechanical properties

Abstract

Polyaniline (PANI)-dinonylnaphthalene disulfonic acid (DNNDSA) form a thermoreversible gel when prepared from formic acid medium. Mixing of organically modified montmorillonite (om-MMT) clay during PANI-DNNDSA gel preparation produces the PANI-DNNDSA gel nanocomposites (GNCs). WAXS and TEM pictures indicate GNC-1 (number indicates percentage (w/w) of om-clay in the nanocomposite) has an exfoliated structure, whereas GNC-3 and GNC-5 have an intercalated structure. FTIR spectra indicate an interaction between om-clay and PANI-DNNDSA shifting the Q=N⁺H-B or B-N⁺H-B (Q = quinonoid and B = benzonoid unit of PANI) vibration of quinonoid structure to lower energy. The exfoliated GNC-1 has higher thermal stability than that of the intercalated GNC-3 and GNC-5 samples. The storage modulus (G') has increased dramatically on addition of clay to the gel and its relative increase is larger with increase in temperature until the gel melts. The highest increase (445%) of G' is observed for GNC-1 at 60 °C. The π band-polaron band position remains unaffected by the addition of clay in the gel and so also the dc conductivity. PANI-DNNDSA gel shows emission at 353 nm when excited with a radiation of 262 nm. But in the GNCs, fluorescence quenching occurs and it is maximum for the exfoliated GNC-1 sample. These GNCs of PANI are easily processable due to its thermoreversible nature.