I am investigating the stability of a colloid suspension and want to look at accelerating the sedimentation rates using centrifuges.

I have set up an experiment with a control sample left on a bench to settle under gravity and have also  calculated what the RPM to spin the centrifuge at to generate 9.81 N (gravitational force g). Assuming they are both exposed to the forces for the same length of time, they should both experience the same force and therefore, sediment at the same rate.

If I wanted to look at longer duration times by spinning the centrifuge faster, is it correct in saying that exposing a sample to 2 x g is the same as leaving a sample for 2 days, assuming the same length of time is applied or is it not as straight forward as that? 

I don't think so - What is the relationship between force and speed? If doubling the force doubled the speed then you would be right  -  but doubling the force doubles the acceleration of the particles...  therefore they will continue to get faster at swifter rate and should settle much quicker if spun at 2g over 1 day than at 1g over 2 days.