Preparation And Properties Of Silk Fibroin/Graphene Composite Flexible Conductive Materials

With the rapid development of flexible and wearable electronic devices,flexible conductive materials have received widespread attention.Due to its potential applications related to human health,flexible conductive materials have strict requirements for biocompatibility.Silk fibroin has the advantages of good biocompatibility,mechanical properties and can be processed into a variety of material forms.It is an ideal substrate for flexible bioconductive materials.Graphene has excellent electrical properties and can be used as a conductive medium to compound with silk fibroin materials.However,due to the chemical inertness and hydrophobicity of graphene,it is difficult to uniformly integrate silk fibroin and graphene into the composite material.Generally,graphene oxide(GO)with better chemical activity can be combined with silk fibroin,and then GO can be reduced to obtain silk fibroin/graphene composite material.However,the obtained composite materials often have problems such as low graphene loading,large resistance,and poor stretchability.In this paper,silk fibroin material is used as a flexible biological carrier,and graphene is used as a conductive medium to prepare two types of silk fibroin/graphene composite flexible conductive materials.Through the structural design of silk fibroin materials,the conductivity and tensile properties of the composite materials are further improved.Also,the resistance of the resulting composite material is sensitive to its strain changes and can be used in wearable strain sensors to identify human activities.The main research contents and results of this article are as follows:(1)The modified Hummers method is used to prepare graphene oxide(GO).The obtained GO contains a large number of oxygen-containing functional groups.Most of it can be reduced by chemical reduction,and the conjugated structure is partially restored to improve its performance.The prepared GO has good water dispersibility and stability.The GO solution with a concentration of 0.1 g/L has no obvious loss of absorbance and no precipitation after 15 days of storage.It can be used as a functional finishing agent to conduct conductive finishing of silk fabrics.(2)Use GO solutions of different concentrations to impregnate-reduce the silk fabrics.The silk fabrics after finishing have a certain conductivity,but the surface resistance is large.The CaCl2-EtOH-H2O ternary dissolution system was used to microdissolve the silk fabric,and the fabric after the microdissolution treatment was further impregnated-reduced and the conductivity was greatly improved.Using the surface resistance of the silk fabric as an index,the optimal number of impregnation-reduction times is 6,the optimal GO solution concentration is 2 g/L,and the optimal dissolution time is 3 minutes.At this time,the fabric surface resistance reaches 237 Ω/cm.The conductive silk fabric still retains good tensile properties,and its electrical resistance is sensitive to strain changes,and can be used for flexible sensors to record the movement of human joints.In addition,the conductive silk fabric also has good heat resistance and hydrophobicity.(3)Use two systems of lithium bromide and calcium chloride/formic acid to dissolve silk,mix with graphene slurry to obtain a stable silk fibroin/graphene solution system,and obtain a silk fibroin/graphene composite film by casting into a film.The morphology and structure of the composite film were analyzed by scanning electron microscope,infrared spectroscopy and Raman spectroscopy.The results showed that the two components of silk fibroin and graphene were successfully integrated on the composite film.We found that the composite film containing Ca2+exhibited better tensile properties.When the graphene content was 40%,the elongation at break of the composite film reached 55.3%,and the resistance was 23 kΩ/cm.The composite film has good bending resistance,and its resistance will change regularly with its strain.