Preparation And Magnetic Functionalization Of PH Responsive Nano-hydrogels

Intelligent nano-hydrogel is a type of hydrogel particles in nano-meter or submicro scale,whose structuture and properties can change reversibly under the action of external stimuli.Intelligent nano-hydrogels have been used in various fields including drug delivery,diagnosis,biosensor and etc.Various functional nanoparticles such as fluorescent quantum dots and magnetic nanoparticles are introduced into the net-work structure of the nano-hydrogels to construct intelligent hybrid hydrogels.This endows them with multiple functions and more applicational advantages.At present,magnetic nano-hydrogels were reported to be prepared in organic solvent by using inverse emulsion polymerization,reverse microemulsion polymerization and distillation precipitation polymerization.However,the use of large quantities of organic solvent causes toxicity and enviromental issues.In this paper,firstly,pH-responsive poly（methacrylic acid）（PMAA）-based and poly（acrylic acid）PAA-based nano-hydrogels were prepared by modified emulsion polymerization methods in water.Then,the magnetic Fe₃O₄nanoparticles were incorporated into the network of the above nano-hydrogels by in-situ oxidation precipitation method and physical loading method,and hydrophilic magnetic nano-hydrogels were obtained.The absorption behavior of the magnetic nano-hydrogels on copper ion was studied prelimary.The size and size distribution,morphology,composition and structure of the prepared pH-responsive nano-hydrogels and magnetic nano-hydrogels were characterized by dynamic light scattering,Fourier transform infrared spectroscopy（FTIR）and transmission electron microscopy（TEM）.The effects of reaction parameters on the synthesis of PMAA-based and PAA-based nano-hydrogels,the effect of the type of the nano-hydrogel precursor on the size and size distribution,and magnetic content of the magnetic nano-hydrogels,as well as the effects of the adsorption time and the type of the nano-hydrogels on the adsorption capacity of copper ions were investigated.The formation mechanism of PAA-based nano-hydrogels was discussed.The main conclusions are as follows:1.Poly（methyl methacryalte）（PMMA）/PMAA nano-hydrogels were prepared by the seed emulsion polymerization without adding Tween 20.However,the MAA conversion was low and the obtained PMMA/PMAA nano-hydrogel dispsion was not stable during the storage.The introduction of Tween 20 can significantly improve the above defects.This method occurred in two steps,which extended the reaction cycle.2.To shorten the reaction clycle,PMMA/PMAA nano-hydrogels was synthesized by the in-situ seed emulsion polymerization method.As the amount of MAA or Tween 20 increased,the hydrodynamic diameter of the obtained nano-hydrogels increased.While as the amount of cross-linker methylene bisacrylamide（MBA）increased,both the diameter and the swelling ratio of the nano-hydrogels decreased.This method required the in-situ formation of PMMA latex particles,which made the process complex.3.To further simplify the synthesis process,stable dispersion of PMAA nano-hydrogels with uniform sizes was prepared using the emulsion polymerization method without adding MMA.4.Among the two PMMA/PMAA nano-hydrogels and one PMAA nano-hydrogels,the pH responsiveness of the PMAA nano-hydrogels was the best.When the pH value of the medium increased from 1 to 6,their size increased 3.6 folds,their volume expansion approached 50 times.5.Using AA monomer,nonionic surfactant K30 and crosslinker divinylbenze（DVB）,PMMA/PAA nano-hydrogels were prepared by the in-situ emulsion polymerization method.As the dosage of K30 or AA,the reaction temperature increased or the amount of supplementary SDS decreased,the hydrodynamic diameter of PMMA/PAA nano-hydrogel increased.As the dosage of DVB or MMA increased,both the size and the swelling ratio of the PMMA/PAA nano-hydrogels decreased.The PMMA/PAA nano-hydrogels exhibit a good pH response:as the pH value increased from 2 to 6,the size increased about 6 folds,the volume expansion reached about 220times.6.Using the above four pH-responsive nano-hydrogels as the precursor,magnetic nano-hydrogels were prepared via in-situ oxidative precipitation and physical loading methods,The magnetic nano-hydrogels prepared by the physical loading method had high magnetic contents.Compared with the precursor,the pH sensitivity of the magnetic nano-hydrogels decreased.The prepared nano-hydrogels and magnetic nano-hydrogels were used for the adsorption of copper ion.The adsorptive capacity of the nano-hydrogels reached saturated after 24 hours.The magnetic nano-hydrogels prepared by the physical loading method had the largest adsorption capacity of313.3mg/g.