Monitoring of dynamical processes in PAAm-MWNTs composites by fluorescence method

Abstract

Polyacrylamide (PAAm)-multi walled carbon nanotube (MWNT) composites were prepared by free radical cross-linking copolymerization in water. Ammonium persulfate and N,N'-methylenebis (acrylamide) (BIS) were used as a free radical initiator and a crosslinker, respectively. The drying and swelling processes of disc shaped PAAm-MWNT composites were monitored by the steady-state fluorescence technique at various temperatures. Disc shaped composite gels were prepared with pyranine (P) doped as a fluorescence probe. Scattered, I-sc, and emission light, I-em, intensities were monitored during drying and swelling of these gels. Since the decrease and increase in I-sc corresponds to the decrease and increase in turbidity of the drying and swelling hydrogel, respectively, the corrected fluorescence intensity, I was introduced to analyse the drying and swelling processes. The Stern-Volmer equation combined with moving boundary and Li-Tanaka models were used to explain the behavior of I during drying and swelling processes, respectively. Results indicated that the desorption coefficient, D-d decreased by increasing MWNT content, until 1 weight percentage of MWNT is reached and then increased above 1 wt% MWNT for a given temperature during drying. However, cooperative diffusion coefficient, D-s behaved opposite to D-d during swelling at a given temperature. Supporting gravimetric and volumetric experiments were also carried out during drying and swelling of PAAm-MWNT composite gels.