pH-sensitive and magnetically responsive superabsorbent nanocomposite hydroge

Abstract

Hydrogels are highly crosslinked polymer materials that are able to swell when immersed in aqueous solutions. Some hydrogels can be designed in such a way that they undergo some conformational changes in response to external stimuli such as temperature, pH, ionic strength, light, electrical signal and magnetic field etc. The hydrogels have been exploited in a wide variety of applications including drug delivery and tissue engineering, biosensors and microfluidic devices. Herein, we develop a novel strategy for combining pH - and magneto-responsiveness into one hydrogel system. Specifically, as pH -sensitive part of the hydrogel we used polyacrylamide, which was crosslinked with acrylic-functionalised silica coated magnetic nanoparticles to possess the magnetic responsiveness. Fe3O4 nanoparticles were synthesized and coated with silica, which provides the nanoparticles with a reactive surface for functionalization with −NH2 group through the silanation with 3-aminopropyl triethoxysilane. The −NH2 groups were then further functionalized by reacting with acrylic acid to generate magnetic nanoparticles containing acrylic group, which were finally crosslinked with PAA to give the desired nanocomposite hydrogel. The synthesized nanocomposite was characterized by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), energy dispersive x-ray (EDX), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) analysis. The synthesized nanocomposite hydrogel absorbed water as high as 400 greater than the mass of itself and they showed super absorbance character. Moreover hydrogel showed pH -responsive swelling when dipped in water with variable pH. On the other hand, the as-synthesized hydrogel showed magnetic behavior owing to the presence magnetite nanoparticles in the form of 3D crosslinker. The prepared nanocomposite hydrogel also exhibited nice self-healing properties due to the presence of acrylic acid groups in the system.

Contents Introduction 1 1.2.1 One Dimensional Crosslinker 3 1.2.3 Three Dimensional Crosslinker 4 1.3 Responsiveness of hydrogel 5 1.3.1 pH responsive hydrogel 5 1.3.2 Thermo-responsive hydrogel 5 1.3.3 Magneto- responsive hydrogel 6 1.3.4 light responsive hydrogel 8 1.3.5 Electric field responsive hydrogel 9 1.4 Multi responsive hydrogel 10 1.4.1 Magneto- and thermo-responsive hydrogel 10 1.4.2 pH- and Thermo-responsive hydrogel 10 1.5 Magnetic Nanoparticle synthesis method 11 1.5.1 Thermal decomposition method 11 1.5.2 Micro emulsion method 11 1.5.3 Co-precipitation method 11 1.6 Surface modification of Iron oxide nanocomponents 11 1.7 Magnetically responsive polymer nanocomponents 12 1.8 pH-responsive polymer nanocomponents 13 1.9. Swelling properties of hydrogel 13 1.11 Literature Review 15 1.12 Research Goal 16 Experimental 23 2.1 Materials and Instrument 24 2.1.1 Chemicals and Reagents 24 2.1.2 Materials 24 2.1.3 Instruments 25 2.2 Synthesis of magnetic crosslinker 25 2.2.1 Synthesis of Fe3O4 25 2.2.2 Silica coated Fe3O4 25 2.2.3 Silica coated Fe3O4 functionalized by –NH2 group 26 2.2.4 Further functionalized by –CH=CH2 group 26 2.3 Synthesis of nanocomposite 27 2.4.1 Kinetics study of swelling 27 2.4.2 pH dependent swelling study 28 2.6 Field emission scanning electron microscopy (SEM) 28 2.7 Energy dispersive x-ray (EDX) spectroscopy 29 2.8 X-ray diffraction (XRD) 29 2.9 X-ray photoelectron spectroscopy……………………………………………….29

2.10 Mechanical strength of hydrogel……………………………………………….30

Results and Discussion 32 3.1 Synthesis of magnetic nanocomposite 33 3.1.1 Synthesis of magnetic crosslinker 33 3.1.2 Polymer nanocomposite Synthesis 34 3.2 Functional group analysis using FTIR 34 3.4 X-ray photoelectron spectroscopy (XPS) 3.4.1 High Resolution C1s Spectra 40 3.4.2 High resolution N1s spectra 42 3.5 X-ray diffraction analysis (XRD) 43 3.6 Surface morphology study using scanning electron microscope (SEM) 44 3.7 Energy dispersive x-ray spectral analysis 47 3.8 Mechanical strength analysis…………………………………………………….51 3.9 Swelling measurement 36 3.9.1 Kinetics study of swelling 36 3.9.2 pH dependent swelling study 37 Conclusion…………………………………………………………………………....52