Study Of Preparation,Structure And Sensing Properties Of Amyloid Fibrils And Epoxidized Natural Rubber-based Functional Materials

Natural polymer materials（such as natural rubber,protein,cellulose,etc.）have many advantages including good availability,large yield,diverse varieties,unique physical and chemical properties,biodegradability,biocompatibility,and so on.Developing new materials and related products based on natural polymers is of great significance to alleviate the issues related to petrochemical resource depletion,white pollution,and energy crisis.By taking advantage of the unique physical properties（such as the mechanical properties,nanostructures,microstructures,etc.）,chemical properties（such as the rich functional groups,chemical reactivity,etc.）and biological properties（such as biocompatibility,biodegradability,bio-enzyme sensitivity,etc.）of natural polymer materials,designing and developing natural polymer based functional,smart and high-performance materials,devices and equipment are of significant importance to promote the large-scale and high-value utilization of natural polymer materials.In this thesis,based on natural polymer materials such as amyloid fibrils and epoxidized natural rubber,we design and develop a series of conductive composite materials with different micro-/nano-structures.The template effect,interfacial interaction,and self-healing properties of the used natural polymers in the prepared composites are systematically studied through various characterization methodologies.Taking advantage of the unique properties of natural polymer materials,a series of sensors and devices with good responsive characteristics to external stimuli have been developed,such as pressure sensors,strain sensors,magnetic field sensors,and enzyme activity sensing platforms.The application prospects of the above-mentioned sensing devices in the emerging fields of human motion monitoring,smart fabrics,and biological detection have been explored.The main research contents and conclusions of this thesis are summarized as follows:1.Intrinsically conducting polymers exhibit low solubility,poor processability,and poorly controlled morphology,which limit their application range.In this thesis,by using natural amyloid fibrils as a bio-template for intrinsically conducting polymers,we develop a new kind of conductive aerogel composite material with uniform pore size,controllable morphology,high conductivity,and intelligent sensing properties.Firstly,based on in-situ polymerization of intrinsically conducting polymers on the surface of amyloid fibrils,a conductive nanocomposite with high aspect ratio is prepared.Then,via introducing polyvinyl alcohol and utilizing its freeze-thaw gelation mechanism combined with supercritical CO₂ drying technology,a conductive aerogel material with low density,good conductivity,high specific surface area and uniform pores is successfully prepared.Based on the compressibility and high conductivity of the conductive aerogel,a flexible pressure sensor is fabricated,and its response behaviors to external pressure stimuli such as fingertip touch and object loading are explored.In addition,utilizing the sensitivity of the amyloid fibrils template to protease,a protease activity sensing platform is designed and developed.This platform can quantitatively detect the activity of the protease and can also distinguish the response characteristics of different types of protease,exhibiting good application prospects in the fields of protease activity assessment and biological rapid detection.2.Based on the poor film-forming properties,poor controllability,and complex preparation processes of amyloid fibrils membranes,for the first time,we report a convenient,efficient,and controllable protein membrane fabrication methodology directly from amyloid fibrils.Using a phytic acid aerosol spraying process,a layer of amyloid membrane with uniform thickness is successfully constructed at the air-liquid interface based on the electrostatic interaction between amyloid fibrils and phytic acid and the controllable aggregation mechanism of amyloid fibrils.The thickness of the amyloid membrane can be effectively controlled via precise regulation of the preparation conditions.By introducing functional nanomaterials（such as conductive carbon nanotubes,magnetic ferroferric oxide nanoparticles,etc.）,amyloid membrane materials with different functionalities can be constructed.Via combining the above-mentioned conductive and magnetic amyloid membranes,a smart magnetic sensing device with high sensitivity is fabricated,which can be used for real-time detection and continuous monitoring of external magnetic fields.3.Conventional self-healable conductive composites suffer from complex synthesis processes,unsatisfactory self-healing performance,and poor sensitivity to external stimuli.In this thesis,a conductive elastomer composite with simple synthesis,high strain sensitivity,and good self-healing ability is developed.First,a self-healing elastomer at room temperature is prepared via modifying epoxidized natural rubber with polydopamine and then introducing Fe³⁺ions to construct a kind of reversible coordination bond interaction between the catechol functional groups of polydopamine and Fe³⁺.Secondly,based on a segregated conductive structure design and a double-layer device structure design,a new type of strain sensing material with high sensitivity to external strain stimuli and good self-healing capability is developed.The designed segregated conductive structure endows the sensing material with high sensitivity（gauge factor=15.4）,low detection limit（0.05%）,good cycling stability（more than 50,000 times）and good environmental stability.The designed double-layer device structure endows the strain sensors with good mechanical flexibility and outstanding self-healing performance.The potential application prospects of the fabricated strain sensors in human motion detection,speech recognition and other fields are explored.4.In most cases,the mechanical healing ability and electrical healing ability of self-healing conductive elastomers are mutually restricted and are difficult to realize simultaneously.In this thesis,chemical molecular design and physical microstructure design are utilized synergistically to address the above issue.Firstly,boric acid is introduced into gallic acid-modified epoxidized natural rubber matrix to synthesize a new type of self-healing elastomer based on dynamical crosslinking points consisting of boronic ester bonds.The self-healing elastomer exhibits rapid healing speed（15 s）,high healing efficiency（90.3%）,and multiple healing capability.On the other hand,inspired by the Archimedes spiral structure in nature,a spiral layered conductive structure is constructed in the self-healing elastomer matrix using a spray-curl process.This spiral structure maintains the good mechanical healing ability of the elastomer material,and meanwhile,endows the resultant conductive composite material with good electrical healing ability,with rapid healing speed（0.25 s）and high healing efficiency（nearly 100%）.The proposed alliance of the above-mentioned chemical molecular design and physical microstructure design breaks the intrinsic contradiction between the mechanical and electrical healing performance of traditional conductive composites.Based on the prepared self-healing conductive composite materials,a strain sensor with self-healing capability is developed,and its potential applications in human motion monitoring,intelligent electronic fabrics and other fields are explored.In summary,based on the unique chemical,physical,and biological characteristics of natural polymer materials,a series of novel conductive composite materials and smart sensing devices have been developed.This thesis provides a number of new principles and new technologies for the functional and high-value utilization of natural polymer materials,which have great theoretical significance and practical value.