Universality and Percolation in Biodegradable Poly(ε-caprolactone)/Multiwalled Carbon Nanotube Nanocomposites from Broad Band Alternating and Direct Current Conductivity at Various Temperatures

Abstract

Dc and ac conductivities in a broad angular frequency, 2π × 10−3 s−1 < ω < 2π × 107 s−1, and temperature range, 133 K < T < 323 K, were measured in poly(ε-caprolactone)/multiwalled carbon nanotube nanocomposites as a function of weight concentration (0 wt % ≤ p ≤ 3 wt %) . The universal dynamic response was observed at low p values, and the parameters were adjusted by working in several domains. Scaling laws predicted by the variation of dc conductivity as a function of p or characteristic frequency in percolation theory were followed and showed the formation of a 3D percolative cluster at concentration values as low as 0.3 wt %. The existence of tunneling conduction was proved, and its independence on temperature indicates that we are in the presence of a conventional tunnel effect among nanoparticles not yet in physical contact, through energy barriers made by the polymer chains. All these combined facts allowed construction of a master curve evidencing the time−temperature−composition superposition existing in the poly(ε-caprolactone)/multiwalled carbon nanotube nanocomposites studied here.