Preparation Of Flexible Conductive Substrates And Sensors Application

In the field of flexible wearable devices,flexible wearable sensors have received extensive research attention due to their ability to convert mechanical stimuli into analyzable electrical signals.However,it is still a great challenge to fabricate flexible wearable sensors with stretchability,high sensitivity,fast response,low hysteresis,and wide effective working range according to the needs of practical application environments.Textiles are porous three-dimensional network structures composed of interwoven fibers and yarns,which have the characteristics of flexibility,stretchability,and wearing comfort,making them ideal substrates for flexible wearable sensors.It is mostly combined with conductive materials to realize functionalization.Melt-blown nonwoven fabrics have the advantages of ultra-fine fibers,good air permeability,easy modification,simple preparation process and low cost,hence showing great development prospects in the field of flexible wearables.Electrospun nanofibers have the advantages of extremely small diameter,large specific surface area,and good air permeability,electrospun nanofibers as ideal materials for flexible wearable fields,such as flexible sensors,electronic skin,and energy storage.In this subject,based on the advantages of fabrics,melt-blown nonwoven fabrics,and nanofiber materials in properties and structures,a series of conductive substrates based on fabrics,melt-blown nonwoven,and nanofiber films for wearable sensors were designed and constructed by using composite conductive fabrics,elastic melt-blown nonwoven fabrics,and electrospun polyurethane nanofibers as flexible substrates and silver coated yarn,conductive polymer,graphene oxide,graphene and silver nanowires as conductive materials.The electrical properties of conductive substrates and the sensing performance of sensors to mechanical stimulation are studied,and the feasibility of its application as wearable sensor to detect human movement and health is explored.The specific research contents are as follows:(1)Firstly,a variety of different conductive fabric substrates were prepared by using elastic composite conductive weft yarns and ordinary yarns in different arrangements in the weft direction and the fabric structure was designed.Then,a sensor based on the composite conductive fabric substrate was constructed.The effects of the configuration ratio of composite conductive weft yarns and ordinary yarns and the structure of the fabric on the electrical properties of the conductive substrates were explored.The prepared composite conductive substrates show that the greater the proportion of composite conductive weft yarns in all weft yarns,the better the conductive properties of the conductive substrate.Among the conductive substrates with different fabric structures under the optimal configuration ratio of1:0,the 3/3 right twill conductive substrate has the best conductivity and 2/2 the warp leveled fabric conductive substrate has the worst conductivity.Using the 3/1 right twill conductive substrate as the sensor has an effective sensing range of 0-11.60 %,and the sensitivity in this range reaches 33.45.In addition,the sensor can realize the detection of human body size and amplitude motion and weak physiological signals.(2)Secondly,in order to obtain a smart wearable strain sensor with high sensitivity,wide working range and flexibility and portability,several elastic melt-blown nonwoven substrates with excellent flexibility and high conductivity were developed by loading with poly-pyrrole through a double-dipping and double-rolling finishing method.Then,a sensor based on the elastic melt-blown nonwoven conductive substrate was constructed.The prepared substrates show that the conductivity of prepared substrates is affected by the fiber orientation,the substrate direction,the pyrrole concentration and poly-pyrrole amount deposited in nonwoven.When the pyrrole concentration is 5.5 %,the substrate with 45.30 % porosity possesses the anisotropic optimal conductivity with 23.491 S/m along winding direction and 15.063 S/m along width direction of nonwoven.In addition,the sensor based on elastic melt-blown nonwoven conductive substrate has a wide working sensing range 0 %-24.2 %,high strain sensitivity(1.94),fast response(0.023 s),tiny hysteresis(0.011 s),high durability and stability over 1000 cycles.Meanwhile,the sensor has been proven to be useful for finger bending detection and accurate recognition of human voice changes.(3)Finally,further optimization studies were carried out on the sensors of the above-mentioned fabrics and melt-blown nonwoven conductive substrates,and a polyurethane nanofiber membrane sensor with a multi-dimensional nanoscale hybrid hierarchical conductive microstructure was designed and constructed by electrospinning and electrostatic spraying techniques.The results indicate that the resistance of doped film is significantly lower than that of the undoped film,when 0.4 % graphene oxide mixes,the doped film gets the smallest resistance.With the increase of spraying layer number,the resistance of sandwich film decreases first then slowly stabilizes.The microstructure of sandwich film determines that the different roles are played for fibrous layer or the interlayer in different stages during the deformation process.The film doped 0D and 1D materials become more sensitive to the relative resistance variation at small strain,while the sandwich film acts more sensitive to the interlayer number in case of large deformation.The sandwich film strain sensor with the multi-dimensional nanoscale hybrid hierarchical conductive microstructure sprayed at intervals of 15 min shows that the output resistance signal is extremely synchronized to the input strain,and the effective sensing strain range reveals 53.16%.Within this range,the sensitivity reaches as high as 774.19,and the durability and stability can exceed 1000 cycles,and the fast response lag time appears only 0.002 s.In addition,the strain sensor can detect either various large-scale movements or subtle physiological signals of human body,such as joint movement,pulse beat,sound and breathing,which is of great significance for promoting the development of flexible wearables.