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Paper   IPM / Nano-Sciences / 15043
School of Nano Science
  Title:   Surface Proximity Effect in Sedimentation by Digital Holographic Microscopy
1.  Mohammad Charsooghi
2.  Alireza Moradi
  Status:   Published
  Journal: App. Optics
  No.:  7
  Vol.:  57
  Year:  2018
  Pages:   179
  Supported by:  IPM
In this paper we measure the proximity effect of a flat wall on the sedimentation of colloidal particles by the use of digital holographic microscopy (DHM). DHM provides quantitative phase contrast and three dimensional (3D) imaging in arbitrary time scales that is suitable to investigate various phenomena including dynamic behavior of colloids. 3D information are obtained by post-processing of the recorded digital holograms through the angular spectrum propagation (ASP) approach for numerical reconstruction. We have measured the trajectory and velocity of spherical colloids in various distances from a flat wall while they sediment under the gravity. The results are in agreement with theoretical studies of Goldman et al. We observed an increase in the drag force due to the proximity to the flat wall, which was effective for the distances up to several particle sizes. The presented method is capable of being used for different applications in study of colloidal dynamics where 3D information in real time is required.

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