Stability of 2-D Colloidal Particle Aggregates Held against Flow Stress in an Ultrasound Trap
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- 作者：Larisa A. Kuznetsova ; Despina Bazou ; W. Terence Coakley
- 刊名：Langmuir
- 出版年：2007
- 出版时间：March 13, 2007
- 年：2007
- 卷：23
- 期：6
- 页码：3009 - 3016
- 全文大小：214K
- 年卷期：v.23,no.6(March 13, 2007)
- ISSN：1520-5827
文摘
The formation of a two-dimensional aggregate of 25 
m latex particles in a 1.5 MHz ultrasound standing wave(USW) field and its disintegration in a flow were studied. The aggregate was held in the pressure node plane, whichallowed continuous microscope observation and video recording of the processes. The trajectories and velocities ofthe particles approaching the formation site were analyzed by particle image velocimetry (PIV). Since the directradiation force on the particles dominated the drag due to acoustic streaming, the acoustic pressure profile in the vicinityof the aggregate was quantifiable. The drag coefficients Dcoef for 2- to 485-particle aggregates were estimated fromthe balance of the drag force FD and the buoyancy-corrected gravitational force during sedimentation on terminationof the ultrasound when the long axis of the aggregate was in the vertical plane. Dcoef were calculated from FD asproportional to the aggregate velocity. Experiments on particle detachment by flow (in-plane velocity measured byPIV) from horizontal aggregates suspended in deionized water and CaCl2 solution of different concentrations showedthat the mechanical strength of the aggregates depended on the acoustic pressure amplitude P0 and ionic strength ofthe solution. In deionized water the flow velocity required to detach the first single particle from an aggregate increasedfrom 1 mm s-1 at P0 = 0.6 MPa to 4.2 mm s-1 at P0 = 1.4 MPa. The balance of forces acting on particles in a USWtrap is discussed. The magnitude of the shear stress employed (~0.05 Pa) and separation forces suggests that thistechnique can be applied to studying the mechanical responses of cell aggregates to hydrodynamic flow, wherecell-cell interaction can be separated from the effects of solid substrata.
m latex particles in a 1.5 MHz ultrasound standing wave(USW) field and its disintegration in a flow were studied. The aggregate was held in the pressure node plane, whichallowed continuous microscope observation and video recording of the processes. The trajectories and velocities ofthe particles approaching the formation site were analyzed by particle image velocimetry (PIV). Since the directradiation force on the particles dominated the drag due to acoustic streaming, the acoustic pressure profile in the vicinityof the aggregate was quantifiable. The drag coefficients Dcoef for 2- to 485-particle aggregates were estimated fromthe balance of the drag force FD and the buoyancy-corrected gravitational force during sedimentation on terminationof the ultrasound when the long axis of the aggregate was in the vertical plane. Dcoef were calculated from FD asproportional to the aggregate velocity. Experiments on particle detachment by flow (in-plane velocity measured byPIV) from horizontal aggregates suspended in deionized water and CaCl2 solution of different concentrations showedthat the mechanical strength of the aggregates depended on the acoustic pressure amplitude P0 and ionic strength ofthe solution. In deionized water the flow velocity required to detach the first single particle from an aggregate increasedfrom 1 mm s-1 at P0 = 0.6 MPa to 4.2 mm s-1 at P0 = 1.4 MPa. The balance of forces acting on particles in a USWtrap is discussed. The magnitude of the shear stress employed (~0.05 Pa) and separation forces suggests that thistechnique can be applied to studying the mechanical responses of cell aggregates to hydrodynamic flow, wherecell-cell interaction can be separated from the effects of solid substrata.