Yes, I do realize that temperature is very important to the RI of liquids. The working temp will be very close to 20C, but I could consider a heating stage, I suppose. If a polymer of ri ca. 1.34-1.48 could be identified, however, I could get the same precision by mixing liquids of diff RIs.
The full context is that I work for the Smithsonian, and we have embarked on a very large project to image our most valuable biological specimens. Many of these are stored in 75% EtOH and are small (~500um). It is difficult to take decent pictures of small things submerged in liquids. For the photos to be useful scientifically, the specimens must be posed in individually idiosyncratic ways. The informal solution has been to pose them in plain sand (i.e. partially submerged or nestled), but sand as a background is aesthetically inferior.
Thus the quest for clear, "sand-like" particles immersed in a liquid of matching refractive index. Spheres are the optimal shape.
The lowest glass RI's are ~1.45-1.474, but liquids that match are not particularly compatible with 75% EtOH, are oils, or toxic, etc. It's do-able, but not ideal.
So rather than high-tech liquids, how about high-tech spheres? Hence the question about fluoropolymer beads w RI ~1.36?
The component in the adhesive mentioned above in the abstract sounds good, but it's from an abstract at a meeting given by a corporate chemist reporting R&D--likely proprietary and probably unavailable.
Nafion reportedly would work, but it is extremely expensive. Other optical fluoropolymers seem to come in bars or films, and there are thousands of them.
I thought someone reading this forum might happen to know of some promising leads.
