(179m) Effect of Colloidal Surface Roughness On Colloid Force Measurements

Interactions between colloidal particles greatly affect dispersions. While several measurement techniques such as rheology and light scattering offer indirect methods for probing the dispersion interaction, AFM colloidal force measurements provide the data about surfactant-colloid, and colloid-colloid interactions. In this study, heat treatment process is optimized to achieve minimum surface roughness, which is less than 1nm. This enables us to focus on physiochemical property and illustrated how geometry affects colloids dispersion. Interactions between PS colloids are measured in absence of dispersant and in presence of three different dispersants, i.e. pentaethylene glycol monododecyl ether (C12E5), poly(ethylene oxide)₁₂₉–poly(propylene oxide)₅₆–poly(ethylene oxide)₁₂₉ (Pluronic^® F108), and one acrylic anionic surfactant Joncryl^® 60.  It is found that in absence of surfactant, adhesion increases significantly with increase of surface roughness. The presence of surfactants greatly reduces colloidal adhesion, however, colloidal surface roughness impacts colloidal interactions and therefore the surfactant performance as pigment dispersants. For example, at low concentration (0.2%), only Pluronic F108 could completely eliminate adhesion between rough PS colloids while all three dispersant show little difference for smooth PS colloids. One of the main reasons is that adsorption layer thickness of F108 is larger than others. The significance of this study directly illustrates the relationship between surfactant property – adsorption physics – colloids interaction. This also will be helpful in discovering new materials for commercial dispersant.