This paper here:
http://web.njit.edu/~dave/Dry-Coating-Flow.pdf
describes the theory of van der Waals forces causing particles to clump as well as being the adhesion source of the silica nanoparticles to the surface of the corn strach particles.
This is identical to the effects of coating anthrax spores with silica as the CDC/Dugway paper studies.
The paper at the above link used many different grades of silica - some with small primamry particles - some larger. Some of the SEM pictures look remarkably similar to the Dugway picture.
I suggest you get the person you are corresponding with to state in plain, clear English that there is no connection whatsover with this work on powder flowability and aerosol behavior of nanoparticle silica coated powders to their work on aerosol studies of nanoparticle silica coated spores.
As I said, he told me there was no agreement between the authors of the article as to what causes the silica to bind to the spores.
I mentioned my web page about this subject to him and asked if he knew anyone willing to discuss it. Maybe he'll get back to me.
Hmmm. It's five p.m. The whistle just blew. Time to shut down for the night. I'll be back tomorrow.
TTFN