Preparation And Properties Of Agarose-based Composite Hydrogel

Agarose gel is a kind of hydrogel with charge neutrality,porosity,and good chemical stability,and is a good candidate as template and support for preparation of nanomaterials.The sol-gel reversibility of agarose gel also makes it a potential material for the self-healing process.The main work of this thesis is based on these properties of agarose gel.The morphology and size of the nanomaterials is of great importance for their performance and application.Silver nanoparticles have excellent physical and chemical properties,and can be widely used in the fields of catalysts,biomedical,optoelectronic materials and so on.Besides,the dendritic sliver nanomaterials has unique structural character and physicochemical properties.Dendritic structure can provide a large number of active atoms and a wide range of applications.For example,its typical micro/nano scale architechture is a good prerequisite for surface-enhanced Raman scattering(SERS)detection.To control the morphology of the dendritic structure is of great significance to the application of silver dendrite material.In this thesis,agarose gel was used as template,reducing agent and stabilizer to prepare agarose/nanosilver composite gel by a sol-gel method.The silver nanoparticles were obtained from the hydrogel by a freeze-drying process.The composite gel and silver nanoparticles were characterized and the effect of the heating time of mixture solution on the composite gel was studied.The results show that the extension of heating time can increase the reduction conversion of silver ions in the agarose solution.In the condition of1.5 wt% agarose and 60 mM silver nitrate,the prepared silver nanoparticles are spherical and have an average size of 20 nm with a relatively narrow size distribution.The as-prepared agarose/nanosilver composite was then reacted with aluminum foil to achieve agarose/silver dendrite composite gel.The dendritic silver structure was observed using an optical microscope and a scanning electron microscope.The growth of silver dendrite is influenced by the concentration of silver nitrate and agarose,the physical state of agarose,the reaction temperature,and the contact manner of composite gel withaluminum foil.The results show that the proper concentration of silver nitrate for the growth of silver dendrite ranges from 5 mM to 210 mM.At low concentration of agarose,the assembly of silver nanoparticles is slow,and loose dendritic structure is formed.Instead,the formation of sharp structure of sliver dendrite is achieved when the concentration of agarose is high.If agarose gel is hard to form,it is also difficult to form the dendritic structure.The higher reaction temperature,the faster the silver particles are assembled.By changing the contact manner of the composite gel with the aluminum foil,the size of the resulting silver dendrite can be adjusted.The growth of the silver dendrite is consistent with the mechanism of restricted diffusion cohesion model.In addition,we tried to develop self-healing materials based on agarose gels.The effects of pH and ionic strength on the properties of agarose gel were studied.The results show that the compression strength of gel is not much affected at pH value between 5 and10.Under the experimental condition,the ionic strength has little effect on the gelation of agarose.The hyperbranched polyamidoamine was synthesized and characterized by IR and HNMR.The degree of branching of the obtained hyperbranched polymer is 0.71.The practice of self-healing process based on agarose gel,poly(acrylic acid)and hyperbranched polyamidoamine was firstly attempted.Unfortunately,the self-healing of the composite gel isn't achieved under the experimental conditions.The experimental strategy and condition need to be carefully improved.