Rheology of Concentrated Dispersions of Copper Phthalocyanine Pigments in Organic Solvents

• Published in: Langmuir 1999-12, Vol.15 (26), p.8795-8799
• Main Authors: Hughes, D. F. Kevin, Robb, Ian D
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la990055i

This paper deals with the rheology of concentrated (12−14% w/v) dispersions of copper phthalocyanine pigments in organic solvents. Dilute dispersions (0.3% w/v) of one of these pigments (Z-CuPc) had previously been shown to be stabilized by charge but flocculated by added polymer. The rheology of the concentrated dispersions is determined principally by the state of flocculation of the particles. For concentrated systems of Z-CuPc (14% w/v) containing polymer and organic solvent, G‘ and G‘ ‘ increased with polymer concentration, probably due to the increased attraction between the particles arising from depletion flocculation. The apparent yield stress of a dispersion of an alternative pigment (B-CuPc), which did not flocculate even in the presence of 20−50% polymer, was much lower than that of Z-CuPc. Slip at the walls of the parallel plate geometry occurred after preshearing dispersions containing higher polymer concentrations. The preshearing appeared to allow the structure of the floc to shrink, leaving a solvent-rich layer adjacent to the plate surface. Addition of organic acids or electrolytes had little effect on the rheological properties of the concentrated dispersions.