I am using Materials Studio 5. I want to construct a polyamide nano-composite amorphous cell with a specific weigth percentage of silica nanoparticles. Also, I want to do some surface modifications (add a surfactant) to the interface between  the nanoparticles and the nylon6 particles to increase the adhesion. I can't seem to figure out how to do this. If I use the amorphous cell construction module to construct the cell, I am not able to specify the weight percentage. Moreover, I get errors when I run the job because the cell optimization process that follows construction fails.

I am new to Materials Studio and any help in this matter will be much appreciated. Thank you.