Electric charge clustering and migration in latex films: A study by scanning electric potential microscopy

Scanning electric potential microscopy images were acquired from coalesced poly (styrene - butyl acrylate - acrylic acid) latex films having a Tg equal to 15.9 degreesC. The micrographs show the boundaries between particles even in transparent films (transmittance > 99%), and the boundaries appear as positive domains, relative to the particle cores. Large local electric potential gradients are observed, ca. 1 V/10 nm, but these are smeared when the latex is dialyzed prior to film formation. Electric domain patterns are modified by aging, annealing and exposure to toluene or chloroform vapors. Completely independent patterns are obtained, in each case. The significance of charge distribution to latex cohesion, adhesion and swelling behavior is discussed.