Start with 0.01% Tween-20 by volume (e.g., 100 uL Tween-20 in 1 L of water).
According to a paper I've seen, concentrations greater than this do not
lower the surface tension, while concentrations lower than this result in
higher surface tension. From experience 0.01% is nice enough to work with,
while 0.1% produces more foaming.
    --Kirt Williams

----- Original Message -----
From: "Vishwa" 
To: "General MEMS discussion" 
Sent: Thursday, February 21, 2008 9:24 AM
Subject: [mems-talk] How much Tween 20 to add


> Hi,
> I am running some microPIV expts in a channel, the dimensions of which are
> 50mm * 2.5mm* 45um. There ends up being a lot of bubble formation in the
> channel and I was advised to use some surfactant like Tween 20. I bought a
> bottle of that. But it doesn't come with any guidelines and to how much
> should be added. I would appreciate if you could tell me some number as a
> safe starting point.
>
> The flow tracers that I use are carboxylated polystyrene beads in nanopure
> water.