In product development, formulators seek to optimize coating characteristics such as flow behavior film thickness, uniformity, opacity and storage stability. The Acorn Area and the Acorn Drop measurements provide the pigments and coatings industry with a valuable tool to enhance product performance in development, and later, during manufacturing, to monitor product quality.
Formulation Development
The smallest particles have the biggest influence on flow behavior. Light based particle size measurements have difficulty detecting small particles mixed with large ones, especially at high concentrations. Particle wetted surface area measurements like those from the Acorn Area are very sensitive to the smallest particles and don’t assume that the particles are spherical. They provide a much more relevant tool to optimize particle size for a given flow behavior.
Reducing the particle size (e.g. by milling) will significantly increase the particle surface area. When particles are small, they want to stick together. Formulators add substances such as surfactants, dispersants, and polymers to coat the particles to keep them separated. Understanding how these substances adsorb onto the particle surface and interact is essential to optimize performance properties such as storage stability, flow, and adhesion. Competitive adsorption and/or displacement of polyelectrolytes, macromolecules and surfactants at the particle surface can be monitored using the Acorn Area. It is easy, especially using the flow-through option of the Acorn Area, to determine “optimum coverage” of a surfactant or polymer to achieve the best storage stability.
Despite the importance of the particle surface-liquid interface on product performance, until the Acorn Area, no particle analyzing technology was available to determine the wetted surface area of suspensions and slurries. The particle analyzers using gas adsorption (BET/N2) require that the particles first be separated from the suspending liquid and dried and degassed, a tedious process which often produces misleading results. Surface area measurement on a dry powder can yield values that are not relevant to the material in the (wetted) dispersed state.
Stability
Changes in the particle-liquid interface can be detected with the Acorn Area. Coating formulations can be measured non-invasively, without further preparation. The same aliquot of sample can be monitored over days, weeks or months. The effects of temperature can also be studied using one of the Acorn Area temperature control options.
The Acorn Drop measures droplet size and distribution for emulsions without dilution. Drop size measurements using light based techniques involve significant dilution, influencing the delicate balance of the emulsion formulation. The Acorn Drop measurements are also non-invasive, enabling similar advantages to the Acorn Area, but for emulsions.