MicrobeHunter.com Microscopy Forum

It seems that high refractive index mountants are difficult, or at least very inconvenient, to source. I’m curious if anyone has experimented with optical adhesives available in a variety of refractive indices. Norland seems to be the most prolific, but a few other manufactures have them, as well.

Norland lists a UV curable adhesive with an index of 1.7 (and several others with indexes >1.6) these are available at Edmund, also:
https://www.norlandprod.com/adhesives/NOA170.html

Mitsubishi chemical offers a line called LumipluS. (small quantity availability unknown)
https://www.mgc.co.jp/eng/products/kc/lumiplus.html

Can search "norland" or "NOA61" on the forum. Example:
viewtopic.php?f=4&t=9004&p=77506&hilit=NOA61#p77506
I compared Norland61 to Pleurax some time ago. NOA61 was a lot easier to apply than Pleurax, yet failed to penetrate some frustules. Tried with strew slides, not arranged, so I do not know any appropriate adhesive for arranged diatoms for NOA61. Although Norland products are adhesives (very good ones!) by themselves.
Higher RI Norlands are stated to become rubber-like, not semi-solids or solids. Prices of all Norlands are not inviting (to me).

Yes, I suppose not doing a quick search on the forum was a pretty obvious oversight!

I’m curious about the high RI products not being solid, though. The NOA 170 I linked states, “when fully cured is very rigid and brittle.”

Zuul wrote: ↑

Sun Aug 09, 2020 5:02 pm

Yes, I suppose not doing a quick search on the forum was a pretty obvious oversight!

I’m curious about the high RI products not being solid, though. The NOA 170 I linked states, “when fully cured is very rigid and brittle.”

Yes, that one was indeed brittle, some others were described as rubber-like. IMO, brittle is also not good... anyway, hopefully someone will test those products.

Digging deeper (or paying attention, more correctly) it looks like the 170 is also very high viscosity. That can’t be good. The 165H is low viscosity and hardens to 55 shore D, so that’s looking like a better candidate.

I wouldn’t be opposed to giving it a try if it weren’t for 2 things. First, I have zero experience cleaning diatoms. Second, I have zero experience mounting diatoms.

There was a nice little article in the Quekett Bulletin recently by Gordon Brown. He experimented with two types of LOCA, type TP-2500 and TP-1000. Maybe if you search the net you could find the article. As a PostScript he added that "cedarwood oil works very well as a wetting agent for LOCA".
Kirby

Edit, I just realized my post wasn't really relevant. The RI of the LOCA's mentioned is 1.51.

Zuul, I remember a few weeks ago while reading about high power LEDs, there was some mention of efforts to develop high-index encapsulating materials to minimize losses due to reflection of light leaving the die. (Refractive index of gallium nitride is 2.4.) No idea what is used currently or if there is any hope of obtaining it in small quantities, but might be something to look into if you are still interested.

Hello. Ok, you won't believe it but it is true.
Elmers glue is a good mounting medium. RI 1.46
Polyeurethane glycol (miralax) is a good mounting medium . Mix 2 daily doses with 1/4 cup warm water. Stir til completely dissolved. RI 1.46.
Both will set in short order and be completely dry in 24 to 36 hours
It works ok. Been doing it for years.
Greg

Greg Howald wrote: ↑

Sat Oct 24, 2020 9:32 pm

Hello. Ok, you won't believe it but it is true.
Elmers glue is a good mounting medium. RI 1.46
Polyeurethane glycol (miralax) is a good mounting medium . Mix 2 daily doses with 1/4 cup warm water. Stir til completely dissolved. RI 1.46.
Both will set in short order and be completely dry in 24 to 36 hours
It works ok. Been doing it for years.
Greg

Yes, Polyvinyl alcohol is known to work pretty well. The late Walter Dioni wrote several articles about it. But Microbob asked in the other thread about whether you have used it with diatoms specifically. I don't think that it would work well will cleaned diatom material since the RI is too close, which makes diatoms effectively transparent. Good diatom slide makers like Klaus Kemp and Stefano Barone tend to use a mountant with a RI ~1.7.