deaerate or not deaerate

Bryan L. Ford bryan.ford at orst.edu
Thu Aug 20 19:37:27 EST 1998


Peter wrote:
> 
> In article <6rhb7a$7ep$1 at info.cyf-kr.edu.pl>, "Zbigniew Rudzki"
> <mprudzki at cyf-kr.edu.pl> wrote:

> > So what is your opinion on degasing, after all rather troublesome a
> > procedure ?

> If you store your stock Acrylamide in the refrigerator than degasssing
> generally is not needed because at colder temps the stock acrylamide is
> not capable of hold much gas. (see Henry's Law)

Henry's Law not withstanding, almost all solutions of gases in liquids
run contrary to the usual expectation that solubility increases with
temperature as it does for solid and liquid solutes. Solvation of a gas
is nearly always an exothermic process and is dominated by LeChatelier's
principle. This says simply that lower temperature favor greater gas
solubility-- check your General Chemistry text(s). 

> If you use premade acrylamide( which is way safer than powder) then you
> will have to degass because a gas additive is added that inhibits
> polymerization of the stock solution.  I do not know what the
> polymerization inhibitor is but it must be removed.

I don't know what brand you are describing here, Peter, but ours--
Amresco, no connection to me-- requires no such removal. Our veteran
technician never degasses and always uses the premixed solution, and
gets very good results. I always degas because I like to remove any
microbubbles and because it does seem to make for somewhat faster and
possibly more consistent polymerization, but my results are really no
better than the veteran tech's.

As for my opinion of the "troublesome" nature of degassing mentioned by
Zbigniew: I find that it takes only a couple of minutes with a water
pump aspirator to pull out a large amount of gas (much is water vapor
since the mix is initially warm) from my mix after I have dissolved the
urea by swirling a 250 ml vacuum flask with stopper under the hot water
tap for perhaps a minute. I never degas native gels, by the way.

Respectfully,
Bryan



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