Maybe these will strike a cord, get you goin’, etc:
With Particle Playgound, “Text that Blows away like Sand”:
https://library.creativecow.net/articles/eriksson_emanuel/sand.php
With Particular, “Building Up Particles “, reverse this maybe:
https://library.creativecow.net/articles/lee_james/particle_build_up.php
Also, methinks, Shatter can do this.
And I think the quickest (dirtiest?) would be CC Ball Action (Decrease Grid Size and Ball Size, Up Scatter) followed with Scatter or CC Scatterize (uncheck Randomize every frame). I think I’d try Ball Action and Scatter first.
Andromeda Strain a fun oldie, but I remember squirming in my theater set when the virus mutated en-mass, every virus in that population at the same instant… hmmm… I couldn’t buy that one.