The interactions between two glass surfaces bearing grafted polymer brushes of poly(12-hydroxystearic acid) (PHS) have been controlled by altering the solvent quality. The graft density was obtained through XPS and the solvent used was a mixture of ethanol and heptane, which was varied from good to poor solvency conditions by either a change of the relative concentrations of the two solvents, or by altering the temperature. The system is shown to be remarkably sensitive to the solvency conditions around the theta position. It was also shown that hydrodynamic forces could be accurately and routinely accounted for in systems where the forces were monotonically repulsive.