Studies of the Depletion-Induced Self-Assembly of Key and Lock Particles

In colloidal suspensions containing large and small articles a peculiar attraction force appears, which can lead to the aggregation of large particles. Especially, if a nonadsorbing polymer (depletant) is introduced into a colloidal system flocculation has often been observed. The interaction range of the attractive force is approximately equal to the diameter of the polymer coils. Recently, it is possible to experimentally synthesize a lock-like particle by producing a cavity on a spherical particle. The selectivity of binding between lock nanoparticles and the corresponding key nanoparticles induced by depletion force triggers broad discussion and investigation. Inthis thesis, we adopt dissipative particle dynamic (DPD) method to explore the depletion-induced self-assembled behavior between key and lock particles. It is found that the bindings between key and lock nanoparticles increase as the concentration and size of the depletants increase. Moreover, for a temperature responsive polymeric depletant, the size of the depletant varies with temperature and thus the binding capability of lock and key particles can be manipulated by adjusting temperature. Furthermore, it is observed that the geometric matchness between key and lock particles is of crucial importance for lock-key binding. The degree of key-lock binding increases as the matchness grows due to the significant increase in the overlapping of the excluded volume. Finally, we calculate and analyze the effective,repulsion and depletion forces between one pair of key and lock particles at different distances. The results demonstrate that depletion force is proportional to the excluded volume released from binding. As a consequence, the effective attractive force between key and lock rises as matchability or depletant concentration increases which is consistent with the experimental observation.