Abstract
In this study the properties of polypyrrole (PPy) nanocoating over poly(styrene- co-methacrylic acid) (PS-MAA) particles were investigated. Monodisperse PS-MAA templates were obtained by free surfactant emulsion polymerization. The addition of methacrylic acid into the monomer feed mixture reduced particle size, ionic charge and hydrophobicity of the template surface. Correlations between template sizes and compositions, PPy confinement (granularity, shell size, etc.) and electrical conductivity, σ, are discussed. After dissolving the PPy/PS-MAA composites in tetrahydrofurane, PPy void spheres are obtained proving the core-shell nature of the coated particles. Bare styrene templates show densely packed PPy coatings and electrical conductivities near 7 S cm −1 at high PPy loadings; on the contrary, at the same PPy mass percentage, the richer methacrylic acid particles show low packed PPy grains and conductivities that fall to 0.8 S cm −1. In core-shell particles the PPy mass per unit area, Γ, is the key parameter which determines the insulator–conductor transition for any particle size. The conductivity values of PPy/PS-MAA composites follow a percolation law: σ ∝ ( Γ − Γ c ) t , with a critical threshold Γ c=(0.262 ± 0.002)×10 −6 g cm −2. The critical exponent obtained t = 1.98 ± 0.07 agrees with the predicted value t = 2.0 for three-dimensional lattices of random resistors.
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