The effects of cis-trans configuration of cyclohexane multi-carboxylic acids on colloidal forces in dispersions: steric, hydrophobic and bridging

The effects of cis- and trans-1,2, trans-1,4-cyclohexanedicarboxylic acid, 95% cis-1,3,5-cyclohexane tricarboxylic acid and cis-l,2,3,4,5,6-cyclohexanehexacarboxylic acid on the yield stress-pH behaviour of concentrated ZrO2 dispersions are reported. Adsorbed cis-1,2,3,4,5,6-cyclohexanehexacarboxylic acid imparts predominantly steric interactions. It forms a steric barrier keeping the interacting particles apart. Adsorbed cis- and trans-1,2 increase the maximum yield stress and this was attributed to a hydrophobic force resulting from the part of the cyclohexane ring sticking out into the solution which is devoid of charged or hydrophilic group. Adsorbed trans-1,4 increases the maximum yield stress by at least threefold and its configuration favours strong bridging interaction with an adjacent particle. Predominantly, cis-1,3,5 also increases the maximum yield stress but only by 60% at the same additive concentration. This was attributed to a smaller degree of bridging. (C) 1999 Elsevier Science B.V. All rights reserved.