The two-step percolation behavior in aggregating systems was studied both
experimentally and by means of Monte Carlo (MC) simulations. In experimental
studies, the electrical conductivity, σ, of colloidal suspension of
multiwalled carbon nanotubes (CNTs) in decane was measured. The suspension was
submitted to mechanical de-liquoring in a planar filtration-compression
conductometric cell. During de-liquoring, the distance between the measuring
electrodes continuously decreased and the CNT volume fraction φ
continuously increased (from 10−3 up to ≈0.3% v/v). The two
percolation thresholds at φ1≲10−3 and φ2≈10−2 can reflect the interpenetration of loose CNT aggregates and
percolation across the compact conducting aggregates, respectively. The MC
computational model accounted for the core-shell structure of conducting
particles or their aggregates, the tendency of a particle for aggregation, the
formation of solvation shells, and the elongated geometry of the conductometric
cell. The MC studies revealed two smoothed percolation transitions in
σ(φ) dependencies that correspond to the percolation through the
shells and cores, respectively. The data demonstrated a noticeable impact of
particle aggregation on anisotropy in electrical conductivity σ(φ)
measured along different directions in the conductometric cell.Comment: 10 pages, 6 figure