The purpose of this paper is to discuss the role of multiwalled carbon nanotube in the swelling of polyacrylamide–multiwalled carbon nanotube composites. Swelling experiments were performed in water at various temperatures by real-time monitoring of the decrease in pyranine (Py) and emission light intensity ( Iem). The Stern–Volmer equation is modified for low-quenching efficiencies to interpret the behavior of pyranine intensity during the swelling of polyacrylamide–multiwalled carbon nanotube composites. The Li–Tanaka equation was used to determine the swelling time constants, τ, and cooperative diffusion coefficients, D, from fluorescence intensity, weight, and volume variations of the composite at various temperatures. It was observed that when τ decreased, naturally D increased by increasing temperatures.

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In this work, chitosan/graphene nanoplatelets (CS/GNP) and chitosan/multi-walled carbon nanotube (CS/MWCNT) biocomposite films were prepared using a simple, eco-friendly and low-cost method. The electrical, optical and mechanical properties of these composite films were investigated. The optical, mechanical and electrical properties of the biocomposites were significantly improved, which make them promising materials for food packaging, ultraviolet protection and biomedical applications. With the increase of carbon filler content (GNP or MWCNT) in CS biocomposites, the surface conductivity ( σ), the scattered light intensity ( I sc) and the tensile modulus ( E) increased significantly. This behaviour in the electrical, optical and mechanical properties of the CS/carbon filler biocomposites was explained by percolation theory. The electrical percolation thresholds were determined as R σ = 25.0 wt.% for CS/GNP and R σ = 10.0 wt.% for CS/MWCNT biocomposites, while the optical percolation thresholds were found as R op =12.0 wt.% for CS/GNP and R op = 2.0 wt.% for CS/MWCNT biocomposites. Conversely, the mechanical percolation thresholds for both CS/GNP and CS/MWCNT biocomposites were found to be negligibly small ( R m = 0.0 wt.%). The electrical ( β σ), optical ( β op) and mechanical ( β m) critical exponents were calculated for both CS/carbon filler biocomposites and found compatible with the applied percolation theory.

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Polyacrylamide (PAM) doped by multiwalled carbon nanotube (MWNT) gels were prepared with different amounts of MWNTs varying in the range between 0.1 and 15 wt%. The PAM-MWNT composite gels were characterized by the steady state fluorescence technique (SSF). The alternative electrical conductivity (AC) of PAM-MWNT composite gels was measured by the dielectric spectroscopy technique. Observations around the gel point, t(gel) for PAM-MWNTs composite gels showed that the gel fraction exponent beta obeyed the percolation result. The critical exponent r of AC electrical conductivity for the composite PAM-MWNT gel was also measured and found to be about 2.0, which agrees with a random resistor network. (C) Koninklijke Brill NV, Leiden, 201

Disk-shaped acrylamide (AAm) gels were prepared from AAm with various N,N -methylenebisacrylamide (Bis) contents as cross-linker in the presence of ammonium persulfate as an initiator by free-radical cross-linking copolymerization in water. Polyacrylamide (PAAm) gels were dried before using for swelling experiments. Steady-state fluorescence spectrometer was employed during the swelling of PAAm hydrogels in water. Pyranine was introduced as a fluorescence probe. Fluorescence intensity of pyranine from various Bis content gel samples was measured during in situ swelling process. It was observed that fluorescence intensity decreased as swelling has proceeded. Gravimetric and volumetric experiments were also performed. The Li-Tanaka equation was used to determine the swelling time constants, τ c , and cooperative diffusion coefficients, D c , from intensity, weight, and volume variations during the swelling processes. It was observed that swelling time constants, τ c , increased and diffusion coefficients, D c , decreased as the cross-linker content was increased. C

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