Preparation And Performance Of Ionic Nanocomposite Hydrogels With Temperature/pH Double Responsive Behaviors

Smart hydrogels can be applied in many fields due to their response to environmental stimuli. However, traditional chemically cross-linked hydrogels are mechanically weak, and thus restricted in actual application. Nanocomposite(NC) hydrogels cross-linked by Laponite show a distinguished mechanical stress which is 10 times higher than traditional hydrogels. However, in functional ionic monomers, Laponite dispersion is inclined to form aggregation. This makes it difficult to prepare homogeneous NC hydrogels.In this thesis, stimuli-responsive NC hydrogels with excellent mechanical properties were synthesized by in-situ copolymerization of functional monomers in suspension of Laponite XLG, which was used as the cross-linker. The main contents and results of the work are as follows:(1) Positively charged NC hydrogels with preeminent mechanical properties were successfully fabricated via in-situ free radical polymerization of N,N-diethylacrylamide(DEA) and(2-dimethylamino) ethyl methacrylate(DMAEMA) in dispersion of Laponite. The hydrogels displayed controlled transformation in optical transmittance and volume in response to small diversification of temperature and pH. The influence of molar ratio of DEA to DMAEMA and Laponite content on temperature/pH-responsive and mechanical properties of hydrogels were investigated. The lower molar ratio of DEA to DMAEMA and Laponite led to lower LCST(26oC-29oC). Swelling capacities of NC hydrogel decreased with pH increasing. Swelling behaviors in ethanol aqueous solution and acetone aqueous solution were conducted at different temperatures, respectively. Swelling capacities in pure water, ethanol and acetone were 60 g/g, 49 g/g and 34 g/g, respectively. The compressive strength decreased with increasing of DMAEMA and decreasing of Laponite, accordingly. The maximum compressive stress was as high as 2219 kPa while compressive strain was 95%. Cyclic compression measurement exhibited good elastic properties of NC hydrogels.(2) Anion NC hydrogels were synthesized by in-situ copolymerization of anionic acrylic acid(AA) in aqueous dispersion of Laponite XLG using sodium dodecyl sulfate(SDS) as a dispersant. The effect of SDS content on mechanical strength was measured. With the increase of SDS, elongation at break increased. When elongation at break was about 2000%, the maximum tensile strength was 162 kPa. The hydrogel showed reversible temperature-responsive behaviors. An increase of SDS dose led to a fast response. The temperature-responsive behavior can be completed within 150 s.(3) Properties of hydrogel and polymerization dispersion were investigated through UV, fluorescence, TEM and viscometer. The mechanism of temperature-responsive behavior was investigated. The results revealed that temperature-responsive behavior was influenced not only by the interactions between SDS, Laponite and monomers, but also the structures of monomers: The interaction between PAA and Laponite was weakened, and Laponite interacted with SDS by electrostatic or polar interaction, resulting in lower transparency at 50 oC. Laponite combined with PAA through non-covalent interaction. SDS gathered around PAA chains as “one-dimensional beads”, resulting in high transparency at 25 oC.