Structural Design and Properties of the Self-healing Silicone Polymer

Author:Zhao Li Wei

Supervisor:jiang bo


Degree Year:2019





Polymers and polymer-based composites possess many excellent properties,therefore,they are widely used in many fields.However,traditional polymer materials are affected by internal fatigue or external influences during use,which in turn affects the durability and service life of the material or product.Scientists developed self-healing synthetic materials by mimicking the nature of organisms that can repair themselves.The self-healing polysiloxane material can solve the problem that the substrate material for flexible electronic device cannot be self-healing.This can not only expand its applications,endow products with new functionality,but also contribute to saving energy,reducing polymer product pollution.Therefore,the design and development of flexible polysiloxane with self-healing properties is of great significance.This work mainly studied the construction and performance of new types of self-healing flexible polysiloxanes,and explored their applications in the field of matrix materials for flexible sensors.The relationship between its dynamic viscoelastic characteristics and self-healing process was analyzed and studied to establish"structure-performance-application"relationship.An intrinsic self-healing polysiloxane elastomer was constructed by thermoreversible Diels-Alder(DA)addition reaction.The structures of the polysiloxane precursors,reaction process of the self-healing system,thermal reversibility and self-healing properties of the polysiloxane elastomers were characterized and studied.The results showed that the self-healing polysiloxane elastomer based on DA bond exhibited excellent thermal reversibility.Tensile strength and elongation at break were affected by reaction time and linear maleimide functionalized polydimethylsiloxane(PDMS-M)content in the system.The self-healing efficiency of polysiloxane elastomer was over 90%.After three consecutive"destruction-healing"cycles,the self-healing efficiency of20%-PDMS-M system can still maintain as high as 93%.The introduction of conductive graphene nanosheets into the self-healing system improved the mechanical properties of the composite,and endowed the polysiloxane with excellent electromechanical properties.The pressure sensitivity of the nanocomposites containing 35 wt%graphene could reach 0.765 kPa-1.They also exhibited good sensing characteristics in bending,twisting and vibration modes.Besides,they also have high reliability,stability and excellent solvent resistance.Thermally reversible covalent bonds can be formed between furan functionalized graphene and polysiloxane matrix,which hardly affect the enthalpy of endothermic reaction of the composites,thus maintaining a high self-healing efficiency of the self-healing nanocomposites.Room temperature self-healing polysiloxane elastomers were constructed by using dynamic disulfide bonds.The effects of siloxane molecular weight and disulfide bond compound(AFD)content on the properties of elastomers were studied.Self-healing conductors and strain sensors were prepared and the performances were studied.When the molecular weight of the siloxane is 362,and its molar ratio to AFD is1:0.95,the polysiloxane elastomer exhibited good mechanical strength,outstanding tensile properties,excellent restoring properties and fast and efficient self-healing properties at room temperature.Its tensile strength and elongation at break were over 0.5 MPa and 1000%,respectively.This self-healing elastomer demonstrated high self-healing speed and it could recover an elongation at break of 357±15%after healing for one minute at room temperature.The self-healing efficiency of the polysiloxane elastomer could reach 95±3%after healing at room temperature for 8hours.The self-healing efficiency of the surface aging and overlap joints was greater than 90%.After three consecutive“destruction-repair”cycles,a healing efficiency of 94±3%can be obtained.When the siloxane has a molecular weight of 800 and its molar ratio to AFD is 1:1,the elastomer(P800-11)can reach a healing efficiency of 74±4%after healing for 24 h at-20?C.The self-healing stretchable conductor and strain sensor were prepared by using self-healing elastomer as the matrix material and indium gallium eutectic(EGaIn)as the conductive material.The EGaIn/P800-11 strain sensor exhibited self-adhesive properties.It showed excellent sensing performance for different motion angles,motion frequencies and motion modes when monitoring finger movement.The self-healing strain sensor maintained excellent sensing performance.The dynamic viscoelasticity of the polysiloxane materials constructed by DA reaction and disulfide bond in the self-healing process was studied.The self-healing polysiloxane elastomers based on DA reaction undergo elastic state-viscous state-elastic state transition during rheological test,which corresponded to a complete self-healing process.The transition from elastic state to viscous state provided a prerequisite for molecular diffusion in self-healing process.The transition from viscous state to elastic state was a necessary step for material to restore its mechanical properties.For polysiloxane based on disulfide bond,stress relaxation and creep were more likely to occur at room temperature for self-healing polysiloxane elastomers with high AFD content.For highly crosslinked disulfide-based polysiloxanes,the storage modulus above Tg did not change with the increase of temperature.The apparent activation energies were 71.8 kJ/mol and 60.9kJ/mol,respectively.The topology freezing transition temperature(Tv)were-12.5?C and-41.4?C,respectively.The calculated Tv were 17.5?C and 22.4?C lower than those of the respective Tg of polysiloxane elastomers.This proved that there was a fast dynamic disulfide bond exchange in the crosslinked polysiloxane.The two types of self-healing polysiloxane elastomers synthesized and prepared herein exhibited excellent self-healing properties and showed good application prospects in the field of flexible sensors.The design ideas and strategies of self-healing polysiloxane materials can provide a reference for the preparation of high performance and multi-functional self-healing polysiloxane materials.