I don't know the density off-hand but it should be easy to measure.
Different ratios will lead to differences in the Young's modulus but for
most practical purposes, small variations will not make much difference.
I've used 3:1 which is noticeably stiffer but still casts/plasma bonds OK. I
heard some people using 20:1 (I think in a paper by Stephen Quake who
exploited different ratios to enable bonding of PDMS sheets). Below a
certain ratio, the PDMS will become more like a gel due to insufficient
polymerisation.

Curing temperature also has some influence on the Young's modulus. As with
different curing temperatures, I would think the ratio would also have
some influence on shrinkage too.


On Mon, Mar 8, 2010 at 19:24, DEBASHIS MAJI  wrote:

> Dear all,
>
> I have a small question regarding mixing up of the PDMS base and the
> hardner
> in 10: 1 ratio. Generally it is specified as mixing up of the two in 10:1
> ratio by weight. But can anyone tell me whether their will be a lot of
> difference in the PDMS property if one use the ratio of 10:1 by volume (
> eg.
> 10ml : 1ml ). Normally we can correlate the weight ratio to volume ratio,
> but in that case can anyone please tell me the density of the base and
> the hardner ? The density of the PDMS is about 0.97 kg/m3 .
>
> Thanks in advance.
>
> Debashis Maji,