Construction And Performance Control Of Dynamic Crosslinking Networks For Silicone Elastomers

Polysiloxane materials are widely used in chemical industry,protective coatings,energy materials,electronic devices,medical devices,aerospace and artificial intelligence materials in various forms such as fluid,elastomer and resin.However,such materials would inevitably be damaged by physical and chemical factors in the process of use,resulting in micro cracks and local damage,which will reduce the performance of materials,shorten the service life,and even cause safety problems.Inspired by the biological world,if an organism was damaged,it could restore its original performance through self-repair.Therefore,endowing silicone materials with self-healing performance is of great significance to improve their application safety,applicability and reliability.In this paper,the silicone elastomer crosslinking networks with self-healing ability were constructed by using a variety of dynamic bonds through the structural design of silicone macromolecules.The modified conductive nano materials and conductive metal nanoparticles were introduced to prepare composite conductive materials.The mechanical properties,thermal stability,self-healing,dynamic mechanical properties,antibacterial properties and conductive sensing properties of silicone elastomer dynamic crosslinking networks and composite conductive materials were systematically discussed.The contents of this paper are as follows:1.Starting from the inspiration of nature and using the synergistic effect of various interactions in the structure of mussel foot silk to enhance the toughness of foot silk,the backbone of amino functionalized polysiloxane(PDMS-NH₂)was modified by introducing soft domain and hard domain,the disulfide bond of 3,3'-dithiodipropionic acid(DTPA)was used as the soft domain to dissipate energy,and the complex of 3,4-dihydroxybenzoic acid(DHBA)and zinc ion was used as the hard domain to maintain the stiffness of the network.Thus,silicone elastomer dynamic crosslinking network(SS-PDMS-DH)was prepared.Dynamic disulfide bonds and metal coordination bonds ensure the stretchability and self-healing of SS-PDMS-DH.In addition,silver nanoparticles(Ag NPs)with conductive properties were introduced into SS-PDMS-DH network through the interaction between S-Ag to give the conductive properties of silicone elastomer.The elastomer containing 10 wt%Ag NPs had excellent tensile strength(2.4 MPa stress)and significant tensile properties(1762%strain).Due to the existence of various dynamic bonds,conductive elastomer(SS-PDMS-DH-Ag)had excellent self-healing ability at room temperature,and the healing efficiency was 91.2%.The bactericidal effects of Ag NPs and zinc ions and the bacteriostatic effects of silicone hydrophobic surface give the conductive elastomer high antibacterial performance.In addition,SS-PDMS-DH-Ag had excellent strain sensing performance as well as can accurately monitor the bending motion of human joints.Therefore,it can be used as a reliable strain sensor and has potential application value in the fields of medical equipment,motion monitoring and so on.2.Using double crosslinking mechanism synergistic self-healing,the backbone of amino functionalized polysiloxane(PDMS-NH₂)was modified by introducing multiple hydrogen bonds and disulfide bonds.The disulfide bonds of 3,3'-dithiodipropionic acid(DTPA)were used as reversible covalent bonds,and the quadruple hydrogen bonds formed between UPy were used as dynamic physical crosslinking points to prepare silicone elastomer dynamic crosslinking networks(PDMS-X).In addition,the two-dimensional conductive filler MXenes were modified with small molecules rich in amide bonds,and then introduced into PDMS-X.The modified MXene was evenly distributed in the network by forming hydrogen bond interaction with PDMS-X,so as to prepare organic silicon conductive elastomers(C-MXenes/PDMS)with good conductivity.The mechanical strain and stress of C-MXenes/PDMS reached 413%and 4.78 MPa respectively.The GF of conductive elastomer was 3.3821,and the change of stress state can be monitored sensitively.In addition,due to the synergistic effect of dynamic disulfide bonds and multiple hydrogen bonds,C-MXenes/PDMS can spontaneously realized self-healing of multiple cycles.Even if the sample was repaired,it can still accurately perceive human motion.This stable and sensitive silicone conductive material paves the way for the development of electronic skin and wearable devices.3.Amino functionalized polysiloxane(PDMS-NH₂)backbone and two-dimensional conductive nano material MXene were modified by introducing lipoic acid(TA),and the ring opening reaction of TA was cleverly used to endow PDMS-NH₂ and MXene with hyperbranched structure of carboxyl end group.Iron ion as the dynamic crosslinking point was introduced into the organosilicon supramolecule with terminal carboxyl group,then the dynamic crosslinking network of silicone elastomer(PDMS@Fe)was prepared.In addition,MXenes with terminal carboxyl group were added to the silicone supramolecule with terminal carboxyl groups,which was crosslinked by iron ions and hydrogen bonds,so that MXene was cleverly embedded in the silicone supramolecule,so as to prepare silicone conductive elastomer with good organization(PDMS@MXene).The elongation at break of PDMS@MXene-9 was 482%,and the tensile strength was 1.49 MPa.Its excellent toughness and high ductility enable it to meet more demanding working conditions.After spontaneous repair,the mechanical properties of PDMS@MXene conductive elastomer can be recovered by 91.7%.The material was further developed as strain sensor,which can accurately monitor the bending state of human joints.This kind of well-organized composite has high tensile properties,excellent tensile strength and strain sensing ability,which enhances its application prospect in the fields of soft robot,motion monitoring and so on.