Study On Rheological Properties Of Hydrogels And Organogels Based On NIPAM

N-isopropylacrylamide-based gels possess a lower critical solution temperature close to human body temperature.The feature grants these thermoresponsive polymeric gels potential application in drug delivery and biomedical engineering.Of a wide range of instrument used for characterizing gels,a rheometer is a powerful tool to investigate the properties of soft matters like gels,suspension and colloids.The gelation temperature,LCST,versatile mechanical properties and responsive to strain applied can be rheologically characterized.In this thesis,a series of NIPAM-based hydrogels or organogels were prepared and mainly understood from the perspective of rheology.The main contents are followings:Chapter 1 introduces basic concept of NIPAM-based gels,rheology and rheometer.Chapter 2 mainly involves the random copolymer gels of NIPAM and Nethylacrylamide(NEAM)synthesized in different methanol-water mixtures.Temperature ramp and uniaxial compression test were conducted to investigate the LCST and mechanical properties.It's found that the LCST of these gels is independence on solvent condition,Specifically,the shear modulus measured by temperature ramp,the compression modulus by compression test and Young's modulus by atomic force microscope were comparable since the change in these moduli with methanol fraction of solvent during synthesis is similar.Chapter 3 focuses on the research of random copolymer of NIPAM and NEAM by the abovementioned methods.The temperature-dependent rheological properties of P(NIPAM-co-NEAM)hydrogels with different monomer composition prepared in same condition were studied.The LCST and moduli decrease with more NIPAM monomers due to the change in hydrophilic–hydrophobic balance and porosity.Chapter 4 refers to the basic rheological research on PNIPAM organogels solvated in benzyl alcohol.The results of temperature ramp illustrate a fact that these PNIPAM samples with a very low tacticity or concentration are incapable of forming gels during temperature ramp.Hence they do not have sol-gel temperatures.For other samples,their gel strength and sol-gel temperature are dependent upon molar mass,tacticity and concentration.Large strain sweep tests indicate the linear viscoelastic limit tend to be smaller strain with increasing molar mass,tacticity and concentration.Chapter 5 involves the large amplitude oscillatory shear test for supramolecular gels(NIBA)formed by blends of polymer solutions of poly(N-isopropylacrylamideco-dopamine methacrylate)and poly(N-isopropylacrylamide-co-4-vinylphenylboronic acid).Both the linear and nonlinear behavior of these materials vary for different mixing ratios of two polymer solutions.A 1:1 mixtures of two polymer solutions form the strongest gels,and a 4:1 mixtures have a distinctly lower modulus and significantly different rheological behavior.The nonlinearity intensities can be evaluated by the ratio of higher odd harmonic intensity to primary harmonic intensity from Fourier transformation rheology or the degree of distortion of Lissajous curves.The nonlinearity intensities of the materials become stronger with increasing strain,followed by weaker nonlinearity intensities.These supramolecular gels,unlike typical polymer melts and solutions,show lower nonlinearity intensities at too large strain.