| The wearable electronics industry has been booming in recent years,and functional flexible fiber or fabric devices have been widely noticed for their small size,light weight,high suppleness and flexibility.With the development of micro and nano high-performance conductive materials and advances in manufacturing processes,the performance of functional fiber or fabric devices has been greatly improved and they can be prepared on a large scale by large textile systems.However,the safety,stability and multifunctional integration of devices in practical applications still need to be further improved,and multifunctional materials with environmental friendliness,excellent performance and high economic value should be developed and applied.Polymerizable deep eutectic solvents(PDES)are a class of green,sustainable and highly customized materials,and their advantages(e.g.,higher reactivity,lower reaction temperature,100%atom utilization)for the fabrication of conductive elastomers,especially liquid-free ionic conductors,are gradually being emphasized,and a series of PDES-based flexible materials have been successfully synthesized and have shown application advantages in various fields.From this,this thesis is devoted to the development of PDES-based flexible functional fibers and fabrics as well as their application as optoelectronic sensing devices.In addition,in response to the defect that the mechanical properties and electrical conductivity of liquid-free ionic conductors are easily disturbed by water molecules,we have developed poly(PDES)materials that are stable in high humidity environments and underwater.The specific research work is carried out in the following parts:(1)The volatility of liquid components in extreme environments and at high frequency strains often leads to a decrease in the electrical stability of polymer-based ion-conductive fibers.Here,we develop liquid-free flexible ionic conductive fibers for this problem.A highly transparent(average transmittance>90%),stretchable(strain up to 300%)and weavable poly(PDES)fiber based on acrylic acid(AA)and choline chloride(ChCl)PDES was prepared,which can be molded in 15 s by convenient photopolymerization.In electrical signal testing,the poly(PDES)fibers showed excellent linearity,sensitivity and negligible hysteresis,and maintained signal stability during 10 000 cyclic stretches at a high frequency(1 Hz).Since the poly(PDES)fibers are macroscopically solvent-free,they exhibit notable environmental stability with negligible weight loss of components in harsh environments such as low humidity and high/low temperatures.A plain-weave method is selected to integrate poly(PDES)fibers into the garment to prepare a 2D fabric sensor,which sensitively transmits stretch,bend,and twist signals from different directions,providing breathability,comfort,and all-round stable monitoring of body movement.(2)Fiber-optic sensing devices are less susceptible to electromagnetic interference and electrical safety issues underwater,while traditional rigid optical fibers are not suitable for wearable flexible sensors.The reported stretchable fibers(e.g.hydrogel fibers)possess poor thermal stability and adhesion to hydrophobic materials at the same time.Based on the experimental basis of the previous section,the PDES monomer can be molded into transparent and stretchable amorphous polymer fibers with extreme environmental tolerance in a short time by a UV-photoinitiated polymerization process.At the same time,the commercial silicone tubes used as spinning molds have excellent hydrophobicity,strong flexibility and high transparency.Therefore,the UV-photoinitiated spinning strategy of poly(PDES)fibers as fiber core and hollow commercial silicone tubes as fiber cladding was proposed for the rapid preparation of flexible hydrophobic step-index core-cladding poly(PDES)optical fibers(CPOF).The superior supramolecular structure endows the poly(PDES(AA-CDC-OAD))core with wide temperature range tolerance(-27℃-156℃),strong self-adhesion(guaranteeing strong bonding capability at the core-cladding interface)and optical self-healing capability(autonomous repair of the fiber core when it is broken).In addition,CPOF exhibits low optical attenuation(propagation attenuation of about 0.77 dB cm-1 and bending attenuation of about 0.032 dB o-1)and stable optical sensing performance,thus being used as fiber-optic sensors for underwater motion monitoring,avoiding electrical safety issues that tend to arise with electrical sensing devices in underwater environments.This advantage facilitates the development of additional potential applications for CPOF in the fields of underwater motion monitoring,environmental detection and soft robotics.(3)Rigid optical fibers are susceptible to breakage when subjected to tensile stress or large-angle bending,and detecting and fusing the breakage site would be labor-intensive and time-consuming.Besides,when a single sensing unit presents multiple stimulus responses,the signals tend to interfere with each other.Here,glycerol(Gly)is introduced as a second hydrogen bond donor into hard-type acrylamide(AAm)/choline chloride(ChCl)PDES(PDES(AAm-ChCl)),and the UV-photoinitiated spinning method is chosen to fabricate the fast optical self-healing multimodal CPOF in succession.Acting as a "lubricant",Gly evenly fill the polymer networks,increasing the free volume required for the self-healing process and reducing the friction between the polymer chains.The segmental mobility is further facilitated by the fluid motion due to the strong hydrogen bonding between Gly and the polymer chains,which reconstruct the damaged areas and enable the CPOF to achieve optical self-healing.So that it can be applied to implantable fibers demonstrating ultra-high optical signal recovery efficiency after breakage.In addition,the CPOF exhibits high stretchability(tensile strain>800%),low optical attenuation(0.31 dB cm-1),wide temperature tolerance(-77168℃),and biocompatibility.Moreover,CPOF possesses intrinsic electrical and optical sensing capabilities,and the feasibility of the CPOF as a multimodal sensor was demonstrated based on the difference in sensitivity of optical and electrical signals to pressure and temperature.(4)The vulnerability of mechanical properties and electrical conductivity to interference by water molecules has been a major pain point for liquid-free ionic conductors.In order to enhance the stability and durability of poly(PDES)fibers in high humidity environment,in this chapter we chose a polymerizable quaternary ammonium salt(acryloyloxyethyltrimethyl ammonium chloride)as the hydrogen bond acceptor,and soft monomer maleic acid as the first hydrogen bond donor is mixed with it to form deep eutectic solvent.Moreover,hard monomer acrylic acid can be used as the second hydrogen bond donor to enhance the toughness of polymer chains after participating in copolymerization.The mass of the fully polymeric DES elastomer(FPDE)only increased by 26.8%after 10 h storage in 90%RH,and the degradation of mechanical properties and electrical conductivity of it by environmental water molecules decreased by 40.2%and 64.8%,respectively,compared to typical liquid-free ionic conductors.FPDE still exhibits ultra-high strain sensitivity(GF>4.13)and high frequency sensing stability when used as a resistive sensor.Based on this,an environmentally stable,water-washable,and weavable fully polymeric DES fiber(FPDF)sensor was prepared.The stable and highly sensitive sensing characteristics were demonstrated by monitoring each joint movement of human body and temperature variations.The design strategy and successful preparation of FPDE will inspire the development and refinement of liquid-free ionic conductors.(5)The formation of PDES depends on intermolecular hydrogen bonding,however,high hydrogen bonding tendency leads to hydrophilicity on the one hand,and it is more difficult to dissolve hydrophobic monomers on the other hand,so the development of hydrophobic poly(PDES)is extremely challenging.Here,the solid quaternary ammonium salt methyltrioctylammonium bromide(MTAB)containing three long-chain alkyl groups is chosen as the hydrogen bond acceptor,and the free hydrophobic side chains underwater can effectively prevent water molecules from intruding through hydrophobic interactions.After mixing with the hydrogen bond donor AA to form PDES,the melting point is drastically reduced and possesses melt properties,which enables the introduced fluorinated polymerizable monomer 2,2,3,4,4,4-hexafluorobutyl acrylate(HA)to be well dissolved in it,further enhancing the stability of PDES in underwater environment.Under the initiation of UV light,poly(PDES)liquid-free hydrophobic elastomer(PLHE)can be prepared in a short time.After 10 days of soaking underwater,the bulk and mechanical properties of PLHE remained almost unchanged and good optical transparency was maintained,thanks to the presence of a large number of weak interactions within the material that are not easily disturbed by water molecules.In addition,the supramolecular properties of PLHE give it excellent underwater self-adhesion and self-healing capabilities.PLHE has an adhesive strength of up to 534 kPa on the substrate underwater,a mechanical self-healing efficiency of more than 60%after 12 h,and an ultra-fast electrical healing capability.When used as a resistive sensor,the sensing characteristics of PLHE underwater remain basically the same as in air,which facilitates the stable operation of the sensor devices in different environments for a long time. |
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