A fluorescence study for the critical behavior of polymethylmethacrylate doped by multiwalled carbon nanotube (PMMA-MWNT) composite bulk gel systems

Polymethylmethacrylate (PMMA) doped by multiwalled carbon nanotube (MWNT) bulk gels were prepared with different amounts of MWNTs varying in the range between 1 and 20 wt%. Free-radical cross-linking copolymerization of PMMA-MWNT composite bulk gels was characterized by the steady-state fluorescence technique. Ethylene glycol dimethacrylate (EGDM) and pyrene (P (y) ) were introduced as cross linker and fluorescence probe, respectively. Changes in the viscosity of the pregel solutions due to glass formation dramatically increased the P (y) fluorescent intensities, which were used to study the glass transition of PMMA-MWNT composite gels for various MWNT contents. The fluorescence intensity of P (y) is proportional to the average size of the glassy regions below and to the strength of the infinite network above the glass transition point. Observations around the glass transition point show that there are three regimes for MWNT concentration in which the gel fraction exponent, beta, and the weight average degree of polymerization exponent, gamma, differ drastically from percolation results, given in three dimensions as beta=0.41 and gamma=1.80.