Diatom selection experience

[Hobbyst46]

Thanks 75RR !

[MichaelG.]

[…] 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 would have great difficulty trying to provide a convincing technical description of the process ... But, intuitively, that seems very reasonable.
I’m sure that adhesion and cohesion [see, surface tension] are your friends.

MichaelG.

[Hobbyst46]

[…] 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 would have great difficulty trying to provide a convincing technical description of the process ... But, intuitively, that seems very reasonable.
I’m sure that adhesion and cohesion [see, surface tension] are your friends.

MichaelG.

No way I can prove this process...
On the one hand, the most remarkable mounted diatom artworks dating from so many decades indicate, that it is possible to arrange and mount them densely and in a particular order on the glass surface, then make it permanent.
On the other hand, mounting with a resin, that needs 180C to harden, along with the boiling of the solvent, seems to be complex. How can an the adhesive fulfill all demands:
adhere strongly to the glass AND to the frustules even under these high-temp conditions -

• stay transparent
  do not fill the frustules
  do not lower the refractive index too much
  do not crystallize or form lumps
  do not discolor
  have a decent shelf-life
  be easy to evenly spread

My experience stems from a limited number of experiments. Just laying the diatoms on a dry coverslip, then mounting in Pleurax, sent them far away beyond the borders of the coverslip. Exactly as previously mentioned by Charles. Methods a and b above provided a viable though not ideal solution.

The polyacrylamide adhesive might work better; however, the stuff is very expensive and the shelf life of the liquid is limited.

[MichaelG.]

Sorry, Doron ... I’m confused by your latest post

It quotes my response to a previous one, but that seems irrelevant to what you are saying.

Apologies if I am missing something

MichaelG.

[Wes]

Hi 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

Thanks 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.

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]

Hi 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

Thanks 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.

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.

Good news, thanks ! I thought that any ionic substance is bound to crystallize or form lumps. Sigma-Aldrich prices for polyacrylamide are very high.

BTW - another advantage of the "water adhesive" over gelatine is that the background is fairly clean, gelatine showed various artifacts, perhaps tiny cracks. These were formed during application, since the gelatine adhesive itself was filtered through a 0.45um filter prior to use. Admittedly the gelatine was ~2% in strength, whereas the final strength of the polyacrylamide adhesive is ~0.004% as described by M. Haak.

[MicroBob]

Hi Doron,
for your single diatom mouts I had another idea: You might set the diatom in a tiny drop of Pleurax on a cover slip and cure it. Then mount the cover slip on the slide with a different mountant that doesn't need a bubbling curing action, like an UV glue. This way you would be sure that the diatom will be in the tiny spot of Pleurax.

Bob

[hans]

...mountant that doesn't need a bubbling curing action...

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?

[Hobbyst46]

...mountant that doesn't need a bubbling curing action...

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.