What are asphalt emulsions and why are they important?
They are liquid asphalt cement emulsified in water. They compose of bitumen, water, and an emulsifying agent or surfactant. Asphalt emulsions are integral to the optimum mechanical properties. Modified asphalt emulsions improve resistance to permanent deformation at high temperature, increased low temperature flexibility, improved fatigue resistance, increased tensile strength, and reduced temperature susceptibility.
Why measure their size and zeta potential?
Their size and zeta potential are indicators of stability for optimum performance. These metrics affect the rheological behavior of your emulsions. If you want to increase the solid content of your sample but keep the viscosity the same, then increase the particle size distribution. If you want to increase the viscosity and keep the average particle size the same, then narrow the particle size distribution. Zeta potential is also another important metric for asphalt emulsions. Low shear viscosity increases with increasing zeta potential due to the larger effective phase volume. A high charge will help slow down any sedimentation.
How can you measure size?
The Mastersizer 3000 uses the technique of laser diffraction to determine the particle size distribution by measuring the angular intensity of light scattered as a laser beam passes through a particle dispersion – large particles scatter light at small angles and small particles scatter light at large angles. The particle size distribution is obtained by analyzing the scattering pattern using a model such as the Mie theory of light. The Mastersizer can provide accurate particle size distributions for both wet and dry dispersions in the size range of nanometers to millimeters. Laser diffraction provides a droplet size distribution, showing the size population distribution of millions of droplets. The Zetasizer can be used to measure particle size through dynamic light scattering (DLS). DLS measures the diffusion of particles moving under Brownian motion and convers this to particle size and particle size distribution using the Stokes-Einstein relationship. Non-Invasive Back-Scatter (NIBS) technology is incorporated to give the highest sensitivity within the broadest range of sizes and concentrations. Furthermore, the Zetasizer Ultra now includes a new cuvette design called the Low Volume Capillary Sizing Cell. This new cell requires only 3 microliters of sample and extends the size measurement range for dynamic light scattering to 10 microns without the need to density-match the dispersant. The cell enables repeatable analysis even at the ultra-low sample volumes, delivering high quality data whilst reducing cost.
How can you measure zeta potential?
The Zetasizer can measure zeta potential through Electrophoretic Light Scattering. With ELS or zeta potential analysis, an electric field is applied to a dispersion of particles which move with a velocity related to their surface charge. The velocity is measured using a patented laser interferometric technique called M3-PALS (Phase Analysis Light Scattering). This enables the calculation of electrophoretic mobility, and from this, the zeta potential and zeta potential distribution of a sample. The new Zetasizer Ultra can measure zeta potential of particles up to 100 microns in size which complements the size analysis of the Mastersizer.
Where can you learn more about asphalt emulsion analysis? Check out our newly released application note that highlights both Mastersizer and Zetasizer analysis of different asphalt emulsions.