Collision rates between two molecules in a liquid How would I calculate the collision rate between kaolinite and amylopectin particles in a liquid with a density of ($\pu{1.01g/m^3}$) and a viscosity of ($\pu{0.000434 Pa s}$)? I know this is related to orthokinetic flocculation, however, I do not know the exact equation. If anyone knows the equation, can you please inform me of it?
If you assume that the reaction is diffusion controlled  then this is the fastest that a bimolecular solution phase reaction can be and the second order rate constant is $k=8000RT/(3\eta)$ (dm$^3$/mol/s) where $\eta$ is the solution viscosity and assuming that the molecules are approximately the same size and even if they are not its still a good estimation. In mobile solvents (hexane, water etc)  $k\approx 10^{10} \to 10^{11}$ dm$^3$/mol/s.

If the species a, b are ions (charge $Z_{a,b}$) then the rate constant is multiplied by $\delta/(e^{\delta}-1)$ where  $\displaystyle \delta = \frac{Z_aZ_bq^2}{(4\pi\epsilon_0)\epsilon k_BTd_{ab}}$ where $d_{ab}$ is the centre to centre molecules size, $q$ electronic charge, $k_B$ the Boltzmann constant, $\epsilon$ the solvent dielectric constant and $\epsilon_0$ the permittivity of free space. 

[If the species are not the same size radius $r$ then $\displaystyle k= \frac{2000RT}{\eta}\frac{(r_a+r_b)^2}{r_ar_b}$.  ]