Self-Assembly Behavior Of AB Amphiphilic Diblock Copolymers In Microfluidic Chips And Its Kinetic Control

Amphiphilic block copolymers?BCPs?can self-assemble in selective solvents into well-defined structures with abundant morphologies?such as spherical micelles,cylinders and vesicles?.Comparing with small molecules,BCPs have special relaxation behavior,and many metastable states exist in the self-assembly system.Therefore,the kinetic factors can significantly affect the self-assembled structures and it is crucial to obtain the complex hierarchical structures through kinetic control.In this dissertation,we mainly investigated theself-assemblyofABamphiphilicdiblockcopolymer polystyrene-block-poly?4-vinylpyridine??PS-b-P4VP?in the microfluidic chips.On one hand,we studied how to control the formation of complex hierarchical assemblies in microfluidic channels by manipulating kinetic factors.On the other hand,we investigated the structural transformation by varying kinetic parameters in the microfluidic chips.Details of the research contents and the results are summarized below:1.Kinetically controlled self-assembly of block copolymer into segmented worm-like micelles?SWMs?:SWMs was successfully prepared by controlling the kinetic and thermodynamic factors,and the structures can be well adjusted.It was found that the SWMs were metastable,and it forms by three different processes:?1?Spherical micelles are generated firstly with high energy immediately after two flows meet at the orifice of the chip;?2?Afterward,consecutive flow moves micelles in and out of the high-shear corners as the flows travel through the channel,and water content kept increasing thus promoted the preformed spherical micelles aggregated orderly into segmented worm-like micelles;?3?Internal chain rearrangements within SWMs driven by localized free energy would take place,giving rise to the formation of more stable SWMs.2.Flow field induced micellar structural ordered transformation under nonequilibrium state:from disordered aggregates to spherical micelles.By controlling the kinetical factors?flow velocity ratio?and thermodynamical factors?initial polymer concentration,addition of homopolymer and temperature of selective solvent?,the self-assembly behavior of PS-b-P4VP were systematically investigated.Our research showed that with the increase of flow velocity ratio,micellar structures were transformed from disordered aggregates to ordered spherical micelles.The mixing time(t_mix)between two solutions was remarkably different.The t_mix in higher flow velocity ratio is larger than that in lower flow velocity ratio,thus,the polymer chain can be well stretched which results in more ordered structures.Moreover,combined with the computation flow dynamics?CFD?,we found that the local concentration had significant difference when two different solvents mixed in the microfluidic chips.The local concentration is higher at high flow velocity ratio than that at low flow velocity ratio.Thus,stable spherical micelles tended to be form at high flow velocity ratio.This research provides a new pathway to micellar structural disorder-order transformation.