Synthesis And Responsive Behavior Of Tough Hydrogels Crosslinked By Core-crosslinked Micelles

Hydrogels are hydrophilic polymer materials with three dimensional networks containing a large amount of water.Responsive hydrogels are promising for many applications such as biological medicine,drug release,sensors,etc.For example,electric field responsive hydrogel can be used to fabricate sensors and artificial muscles because of the available conversion from electrical energy into mechanical energy.However,most of traditional responsive hydrogels exhibit poor mechanical strength and slow response speed,which limits their practical application.Moreover,usually used reinforcing methods are often at the expense of the responsiveness.In order to balance the mechanical properties and responsiveness,hydrogels are crosslinked by nanomicelles.This strategy is demonstrated to combine the excellent mechanical strength and fast response characteristics at the same time due to the unique network structure,further expanding the applications of the responsive hydrogels.Inspired by the above idea,this thesis focuses on(1)the preparation of hydrogels crosslinked by nanomicelles and the strengthening and toughening mechanism;(2)the preparation of electroactive hydrogels with the second charged comonomer crosslinked by nanomicelles;(3)investigating the influence of electrolyte concentration and electric field strength on the electricfield actuation of obtained electroactive hydrogels.The detailed investigations are as follows:(1)A series of PxIyR20 micelles with different core-crosslinking degrees are used as macromolecular crosslinker to prepare PxIyR20H5 hydrogels the by using in situ polymerization of hydroxyl ethyl methacrylate(HEMA).Micelles as a kind of physical junction are highly free to deform,which produces excellent fatigue resistance when loading,and offers fast self-recovery properties during the cyclic tensile test.Moreover,by comparing mechanical properties of PxIyR20H5 hydrogels with the size of PxIyR20 micelles measured by DLS,we found that the energy dissipation capacity of the PxIyR20H5 hydrogels were decided by the internal structures of the micelles and the poly(hydroxyl ethyl methacrylate)(PHEMA)molecular chain linked to the micelles.(2)Vinyl functionalized nanomicelles are used to crosslink acrylamide(AAm)and ionic monomers 2-acrylamide-2-ethyl propane sulfonic acid(AMPS)or(DMAEA-Q)for the synthesis of tough electroactive hydrogels SxMy and QxMy.These electroactive hydrogels can be actuated by an applied electric field,and electrolyte concentration.It was demonstrated that the strength of the applied electric field and young’s modulus of hydrogels can affect the actuation behavior.In detail,both bending angle and actuation rate of hydrogels are increased with increasing the strength of electric field,however,increasing young’s modulus of hydrogels leads to decreasing of bending angle and actuation rate.For the factor of electrolyte concentration,there is a “mountain-shape” evolution,namely,the bending angle and actuation rate of hydrogels have a maximum value as function of electrolyte concentration.In addition,it was found that anionic hydrogels display relatively greater influence on the bending degree and actuation rate,mainly due to the differences in ion migration rate and the mechanical properties of the hydrogels.