  Carbon black (CB)-elastomers can serve as low-cost, highly deformable sensor
materials, but hardly any work exists on their structure-property
relationships. We report on flow-induced anisotropy, considering CB-silicone
films generated via doctor blade coating. Cured films showed slight electrical
anisotropy, with conductivity parallel to the coating direction being lower
than perpendicular to it. Furthermore, piezoresistive sensitivity was much
larger for stretch perpendicular to the coating direction than for parallel
stretch. Structural analysis for length scales up to the CB agglomerate level
yielded only weak evidence of anisotropy. Based on this evidence and insight
from CB network simulations, we hypothesize that shear flow during coating
fragments the CB network and then induces a preferential aggregate alignment,
as well as increased inter-particle distances, parallel to the coating
direction. As a practical conclusion, already weak anisotropic structuration
suffices to cause significant electric anisotropy.
