An experimental investigation of three-dimensional particle aggregation using digital holographic microscopy

• Use of digital holographic microscopy for determining dense particle aggregation.
• Introduces a new particle image identification technique in the 3D reconstruction method.
• The number of particle images detected is significantly improved.
• Relatively few particles were aggregates and the number did not change with time.

The tendency of particles to aggregate depends on particle-particle and particle-fluid interactions. These interactions can be characterized but it requires accurate 3D measurements of particle distributions. We introduce the application of an off-axis digital holographic microscopy for measuring distributions of dense micrometer (2 μm) particles in a liquid solution. We demonstrate that digital holographic microscopy is capable of recording the instantaneous 3D position of particles in a flow volume. A new reconstruction method that aids identification of particle images was used in this work. About 62% of the expected number of particles within the interrogated flow volume was detected. Based on the 3D position of individual particles, the tendency of particle to aggregate is investigated. Results show that relatively few particles (around 5–10 of a cohort of 1500) were aggregates. This number did not change significantly with time.