Efficiency of Nanoscaled Flow Regulators

In dry powders the particle flow is mainly determined by van der Waals forces. It was proved in systematic studies that in addition to the hydrophilic silica Aerosil® 200 also hydrophobic silicas, various types of carbon black, or precipitated silicas are able to act as flow regulators if these highly aggregated nanomaterials can be broken down into smaller fragments comprising only a few primary particles. To characterize the ability of a given nanomaterial to act as flow regulator, the two terms effectiveness and efficiency were introduced. Effectiveness describes the maximum achievable reduction of the tensile strength by a given concentration of the nanomaterial. The parameter efficiency expresses the mixing time required to achieve the maximum reduction of tensile strength. The efficiency, however, is strongly dependent on the energy brought up by the mixing procedure. This energy is needed to desagglomerate the highly aggregated nanomaterials. Since up to now there is no method to measure these forces directly and methods allowing their indirect determination were looked for. A method for indirect determination of the cohesion forces of nanomaterials was evaluated. To characterize the ability of a given nanomaterial to act as flow regulator, the terms effectiveness and efficiency were introduced. It was found that the efficiency of nanomaterials used as flow regulators is strongly dependent on the strength of the aggregates formed by their primary particles.