The effect of polydispersity on the self-assembly of amphiphilic diblock copolymer in a selective solvent was studied by means of Monte Carlo simulation.The polydisperse diblock copolymer system was constructed via the mixing of three amphiphilic diblock copolymer chains different in length

i.e.

A2B2

A2B6 and A2B10.The simulation results show that the micelle morphologies formed by AB diblock copolymers in a selective solvent changed from vesicle to lamellae

then to spheres with an increase in polydispersity index (PDI) from 1.0 to 1.4- Through the analysis of the variations of the number and fractions of free single chains with the increase of PDI in each system

it is found that the number of short chains (i.e.A2B2) which aggregate into micelles increased with an increasing PDI.Meanwhile

the self-assembly processes of diblock copolymers with different PDI in a selective solvent reveal that the increasing number of short chains can increase the surface area of the micelles

leading to a disadvantage for the fusion between small micelles during the self-assembly.The increase of the surface area of micelles is the main reason of the morphological transition from largesized vesicles to small-sized spheres when the PDI is increased.These simulation results indicate that the micelle morphologies and their mutual transitions in a selective solvent can be tuned by the control of the polydispersity of AB diblock copolymers.