Flow visualisation techniques
Micro Particle Image Velocimetry (µPIV)  
The flow induced by capillary or electro-osmotic forces will be investigated by means of micro Particle Image Velocimetry (µPIV), which is an optical full-field planar velocity measurement method yielding information on the flow pattern. For this purpose the flow is seeded with small fluorescent tracer particles (with a dimension of the order of 0.1-1µm), that are illuminated by means of a pulsed laser. The correlation of the particles motion between two laser pulses provides the spatial velocity field. The correlation of the particles motion between two laser pulses provides the spatial velocity field.
This image-processing based method has the advantage of capturing the position and motion of the flow front meniscus simultaneously with the spatial distribution of the flow field, providing a unique opportunity to investigate the two-way coupling of meniscus and flow motion.
Three-dimensional flow effects will be studied by means of specifically developed stereoscopic µPIV method.
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
Nano Particle Image Velocimetry (NanoPIV) 
The velocity distribution in the Debye layer of electroosmotic flow and the influence of coatings and nanostructured surfaces will be investigated with a combination of evanescent wave illumination and µPIV.
The principle is called NanoPIV, due to the thickness of the evanescent wave illumination of about 40 nm to 250 nm depending on the optical conditions, namely the refractive index of the microchannel cover lid that serves as optical wave guide.
Specialized glasses with a refractive index up to n= 1.65 are expected to be tested.
 

In the figure below is shown a schematic of the illumination part in the lens-based system used for realizing the evanescent-wave illumination Nano-PIV.  

 
      

In the figure below is shown a schematic of the flow measurement setup, based on the evanescent-wave illumination Nano-PIV, particularly applied for nano-structured surfaces.