Fluids with short-range attractions and longer-range repulsions

Many complex fluids comprise particles with effective interactions that include short-range attractions and longer-range repulsions. In this talk, I explore---using a simple theoretical model---what behaviors one should expect to find in such systems, including the possibility of equilibrium ``cluster'' formation and its associated implications for dynamics near structural arrest. I also discuss how one might predict the onset of cluster formation from the static structure factor. Finally, some implications for concentrated liquid formulations of therapeutic proteins are addressed.