Aggregation of a dense suspension of particles in a microwell using surface acoustic wave microcentrifugation

  • A. Sudeepthi
  • A. K. SenEmail author
  • L. Yeo
Research Paper


We investigate the aggregation of a dense suspension of particles (volume fraction, \(\varphi \sim 0.1\)) in a PDMS microwell by employing surface acoustic wave (SAW) microcentrifugation. In spite of acoustic attenuation at the LiNbO3–PDMS interface, a significant portion of the energy (> 80%) is available for driving fluid actuation, and, in particular, microcentrifugation in the microwell via acoustic streaming. Rapid particle aggregation can then be affected in the microcentrifugation flow, arising as a consequence of the interplay between the hydrodynamic pressure gradient force \(F_{\text{p}}\) responsible for the migration of particles to the center of the microwell and shear-induced diffusion force \(F_{\text{SID}}\) that opposes their aggregation. Herein, we experimentally investigated the combined effect of the particle size \(a\) and sample concentration \(c\) on these microcentrifugation flows. The experimental results show that particles of smaller size and lower sample concentration (such that \(F_{\text{p}} > F_{\text{SID}}\)) are concentrated efficiently into an equilibrium spot, whose diameter scales with the initial particle volume fraction as \(d_{\text{cs}} \sim \varphi^{0.3}\). In contrast, we found that as the local particle volume fraction at the center of the microwell approaches \(\varphi \sim 0.1\) such that \(F_{\text{SID}} \ge F_{\text{p}}\), the particle aggregation fails. Additionally, we also investigate the effects of the well diameter, and the height, lateral positioning of microwell and the liquid volume on the microcentrifugation.



This work was supported by the MHRD, India via grant no. 35-16/2016-T.S.-I and IIT/SRIC/ME/GDD/2016-17/242, SERB, DST, India via grant no. EMR/2014/001151 and IIT Madras (MEE1516843RFTPASHS). The authors acknowledge the CNNP, IIT Madras for supporting the device fabrication. The authors thank Mr. Karthick S. for the fruitful discussions and technical suggestions and Mr. Kumar N. for helping with the micromilling facility for PMMA mold fabrication.

Supplementary material

10404_2019_2243_MOESM1_ESM.docx (12.8 mb)
Supporting Information: Materials and methods used in the experiments, Effect of PDMS microwell wall thickness on acoustic attenuation, NPI plot: concentration of 10 µm particles in a 4.0 mm diameter and 0.5 mm height well, Liquid evaporation rates in microwell vs. sessile droplet, Particle concentration in well vs. droplet, Concentration of particles of different sizes and concentrations, Comparison of expected (as per the closed packing fraction) and the observed aggregation spot diameters from the experiments, Variation of aggregation spot diameter with the particle size and initial particle volume fraction, particle relaxation dynamics for various particle sizes, Size segregation of 10 µm and 30 µm microparticles in a sessile droplet at 20 MHz, Aggregation of particles for irradiation of the SAW at different lateral positions across the microwell, NPI plot for particle concentration in microwell at 108 particles/ml, Aggregation of 1 µm and 3 µm microparticles, Aggregation of particles for irradiation of the SAW at different lateral positions across the microwell. (DOCX 13140 kb)

Supplementary material 2 (AVI 2023 kb)


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Microfluidics Laboratory, Department of Mechanical EngineeringIndian Institute of Technology MadrasChennaiIndia
  2. 2.Micro/Nanophysics Research Laboratory, School of EngineeringRoyal Melbourne Institute of Technology (RMIT University)MelbourneAustralia

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