  Under many conditions, biomolecules and nanoparticles associate by means of
attractive bonds, due to hydrophobic attraction. Extracting the microscopic
association or dissociation rates from experimental data is complicated by the
dissociation events and by the sensitivity of the binding force to temperature
(T). Here we introduce a theoretical model that combined with light-scattering
experiments allows us to quantify these rates and the reversible binding energy
as a function of T. We apply this method to the reversible aggregation of
thermoresponsive polystyrene/poly(N-isopropylacrylamide) core-shell
nanoparticles, as a model system for biomolecules. We find that the binding
energy changes sharply with T, and relate this remarkable switchable behavior
to the hydrophobic-hydrophilic transition of the thermosensitive nanoparticles.
