Titration of Surface Modified Pigment Particles

摘要

Surface modified pigments are playing an increasingly important role in high performance inkjet inks. Titration has been developed as a quantitative tool to evaluate pigment particles bearing weak acid or base functional groups. The value of total titratable groups in mmol/g pigment indicates the level of surface modification. The dissociation constants (pK_a or pK_b), which can be derived from the mathematical treatment of the titration curve, provide an insight into the colloidal stability as a function of pH. Titration studies of pigment particles have been reported before; however, due to poorly determined functional groups, data interpretation has been difficult. Cabot's surface modification technology, which introduces specific functional groups to the pigment surface, provides a unique opportunity for a systematic investigation. In this paper, a range of surface modified pigment particles has been investigated. The impact of ionic strength (I_m), inkjet ink components, and the nature of the surface functional groups have been studied and related to the pigment stability. The discrepancy between apparent pK (as measured experimentally) and the functional group pK is explained using a diffuse double layer (DDL) correction term. Using this method, the stability of the pigment dispersions can be better understood and the ability to destabilize these systems in a controlled manner through pH, ionic strength, or other environmental changes can be anticipated.