{"id":1797,"date":"2015-01-09T08:00:28","date_gmt":"2015-01-09T14:00:28","guid":{"rendered":"https:\/\/www.ulprospector.com\/knowledge\/?p=1797"},"modified":"2018-07-11T13:06:53","modified_gmt":"2018-07-11T19:06:53","slug":"pc-dilatancy","status":"publish","type":"post","link":"https:\/\/ulprospector.ul.com\/1797\/pc-dilatancy\/","title":{"rendered":"Dilatancy – A Rheology Phenomenon"},"content":{"rendered":"

By Christina Kremers<\/a><\/em><\/p>\n

The optimization of shear-thinning properties of paints is more important for application properties than is shear thickening. The paint follows the viscosity profile as shear is increased, according to the predefined shear rate profile of the application. It is useful to first comprehend why shear thinning occurs so that one may recognize the cause and factors that influence the opposite shear profile that is a non-linear increase in viscosity as shear rate increases. This relationship between shear rate and shear stress helps to gain the necessary knowledge to modify formulations to improve application properties.<\/p>\n

\"Illustration<\/a>
Click for a larger image.<\/figcaption><\/figure>\n

Dispersions respond by four mechanisms to shear rates (Fig. 1<\/em>[1]) that reduce the resistance to flow. This figure illustrates the structural ordering observed upon induction of flow, such as impact of a shear rate.<\/p>\n

Dilatant<\/strong> systems react \u2013 especially at high shear rates- by an increase of volume (formation of holes) with a tremendous increase in viscosity by a \u201csucking in\u201c of the fluid[2]. Simultaneously, particles move very closely to each other. Dilatants are non-Newtonian.<\/p>\n

Another mechanism is somewhat similar to the behaviour of tensides, which build overstructures at high concentrations beyond their critical micelle concentration (CMC). Hard particles form structures as well[3].<\/p>\n

 <\/p>\n

Dilatancy Measurement<\/h4>\n

In order to calculate the dispersion composition in an agitator bead mill, to optimize both economically and efficiently and prevent equipment damage, the virtual ideal flow point is determined using the Daniel Titration (Fig. 2<\/em>). This investigation of several binder\/solvent mixtures (e.g., water as solvent) permits determination of wet- and flow- points (WP and FP, respectively ) as well as the DDI: Daniel Dilatancy Index. The following classification is in use in practice: 5-15% DDI, – tacky, poorly mixable, strongly dilatant<\/strong>; 15-30% DDI, somewhat dilatant<\/strong>, somewhat tacky; >30% DDI, not dilatant<\/strong>, poor mixability, very tacky. The wet point (WP) corresponds to the overall consistency of the mass, and is similar to the oil number test. The flow point (FP) indicates the extra volume of binder mixture per mass of solid necessary to permit the mass to just drop from a rod.<\/p>\n

 <\/p>\n

\"Click<\/a>
Click for a larger image.<\/figcaption><\/figure>\n

Dilatant Examples<\/h4>\n