Re: Diatom selection experience
Posted: Wed Sep 09, 2020 7:48 pm
Thanks 75RR !
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I would have great difficulty trying to provide a convincing technical description of the process ... But, intuitively, that seems very reasonable.Hobbyst46 wrote: ↑Wed Sep 09, 2020 3:46 pm[…] it appears that for some reason, wet diatoms attach better (to glass) than dry diatoms. Perhaps, this holds for gently cleaned frustules, that still contain trace amounts of protein or other organic residue that may function as adhesive. But it worked for me with chemically cleaned fossil diatoms as well.
No way I can prove this process...MichaelG. wrote: ↑Wed Sep 09, 2020 9:26 pmI would have great difficulty trying to provide a convincing technical description of the process ... But, intuitively, that seems very reasonable.Hobbyst46 wrote: ↑Wed Sep 09, 2020 3:46 pm[…] it appears that for some reason, wet diatoms attach better (to glass) than dry diatoms. Perhaps, this holds for gently cleaned frustules, that still contain trace amounts of protein or other organic residue that may function as adhesive. But it worked for me with chemically cleaned fossil diatoms as well.
I’m sure that adhesion and cohesion [see, surface tension] are your friends.
MichaelG.
The polyacrylamide adhesive works, I tested it. Whats not mentioned in this link is that he uses a special anionic PAM variant. I however used regular PAM and it worked really well.Hobbyst46 wrote: ↑Wed Sep 09, 2020 7:48 pmThanks Bob, I stand corrected ! it is far apart... yet both substances are soluble in water and not in alcohol (or at least, much less in alcohol). The amide chemical groups makes them so.MicroBob wrote: ↑Wed Sep 09, 2020 7:26 pmHi Doron,
nice to hear of you progress!
According to your note 2: Michel Haak suggests polyacrylamide, not polyamide. I'm no chemist and don't know how far this is apart. http://www.diatoms.eu/de/node/77
The high curing temperature of Pleurax really narrows down the number of possible candidates for adhesives.
Bob
Good news, thanks ! I thought that any ionic substance is bound to crystallize or form lumps. Sigma-Aldrich prices for polyacrylamide are very high.Wes wrote: ↑Thu Sep 10, 2020 12:42 pmThe polyacrylamide adhesive works, I tested it. Whats not mentioned in this link is that he uses a special anionic PAM variant. I however used regular PAM and it worked really well.Hobbyst46 wrote: ↑Wed Sep 09, 2020 7:48 pmThanks Bob, I stand corrected ! it is far apart... yet both substances are soluble in water and not in alcohol (or at least, much less in alcohol). The amide chemical groups makes them so.MicroBob wrote: ↑Wed Sep 09, 2020 7:26 pmHi Doron,
nice to hear of you progress!
According to your note 2: Michel Haak suggests polyacrylamide, not polyamide. I'm no chemist and don't know how far this is apart. http://www.diatoms.eu/de/node/77
The high curing temperature of Pleurax really narrows down the number of possible candidates for adhesives.
Bob
I see bubbling mentioned a lot with these diatom mountants -- is it necessary for some physical/chemical reason, or is it just difficult to remove the solvent in a reasonable amount of time without bubbling?
It is difficult to remove the solvent within a reasonable time period without boiling. Every 10C difference in temperature implies lengthening the time by roughly X 2.5.
After many more isolated diatom preparations, my results are indeed that PAM works well, and is compatible with Pleurax, although the exact positioning of the diatoms relative to one another on the slide is unimportant for me.
Did you synthesize the PAM yourself and procured it from a commercial source?Hobbyst46 wrote: ↑Sun Jun 13, 2021 3:59 pmUpdate:
After many more isolated diatom preparations, my results are indeed that PAM works well, and is compatible with Pleurax, although the exact positioning of the diatoms relative to one another on the slide is unimportant for me.
Gelatin works too, but only when it is freshly made, and the gelatin coated slides are not as clean, so PAM is recommended.
It is a commercial product, from Sigma perhaps, got a tiny sample from a friend. Prepared a concentrated stock solution. Dilute and filter to make the adhesive. The adhesive still works OK after 3 months storage in a stoppered vial at room temperature (here, around 20-25C most of the time so far).
Just asking cause I always prepared it fresh by polymerizing acrylamide and I am not too keen on working with acrylamide. Never tested the shelf life tho. Could you link the exact product from Sigma?Hobbyst46 wrote: ↑Fri Jun 18, 2021 9:46 amIt is a commercial product, from Sigma perhaps, got a tiny sample from a friend. Prepared a concentrated stock solution. Dilute and filter to make the adhesive. The adhesive still works OK after 3 months storage in a stoppered vial at room temperature (here, around 20-25C most of the time so far).
I was told that it is Sigma 92560 non-ionic PAM. Very old package. A tiny amount suffices for many slides. The Sigma catalogue appears to specify a MW of 5*10^6 or so. It swelled in water, and I brought to solution by heating.