Hi,
As the subject suggests, this question is regarding the intensity of
rhodamine dye.

I have mixed rhodamine 6g in ethanol and the concentration is
0.5gm/litre. I inject this solution to a micromixer as two streams,
the third one being pure ethanol.

Therefore for a case of streams 1 , 2, 3 where 1 and three are dye
solution and 2 is pure ethanol. I take a photograph of the three
streams side by side at the entrance of the micromixer, where the
follow is laminar and there are no structures to enchance mixing. If i
draw a instensity profile across the image the intensity values are
about 120 counts on the left most end of stream 1 and the intensity
count is about 95 counts on the right end of stream 3. This variation
in intensity value of the same solution at the same flow rate could be
because of uneven illumination from the xenon bulb source. The stream
2 has about 60 counts, which is just camera noise as there is no dye
to fluoresce in that stream.

Now to quantify this, i replace stream 2 with dye solution which was
orignally prepared. Now if i take a photograph of the the streams side
by side and draw an intensity profile along the same line as the
previous case, the intensity count on the left end of the stream 1
drops to about 90 and the intensity count on right end of the stream 3
drops to about 75. The flow rates  in both cases are the same, the
streams 1,2 and 3 are all dye solution of same concentration, the
lighting condition remains the same. the exposure time remains the
same. But why the change in intensity value?

Has any one of you faced this problem? If so, can you suggest as to
why this is happening.

The micromixer is made of PDMS

Thanks in advance
Vishwa