| Multi-functional electronic skin（e-skin）has excellent flexibility and stretchability,can sense light,heat,force and other physical stimuli,and is easy to integrate.Therefore,it is widely used in robotics,intelligent prosthesis,health detection and other fields.At present,the flexibility of e-skin is excessively dependent on the flexible substrate,while the flexibility of sensors is poor,and even rigid sensors（Au,Ag,Pt,indium tin oxide（ITO）,etc.）are used,which makes the flexibility of the e-skin insufficient and the stretchability difficult to achieve.In addition,multi-functional sensing and high sensitivity are difficult to achieve together,the additional power supply is poor in compatibility and bulky in mass and volume.These bottleneck problems seriously restrict the practical application of e-skin.To tackle these challenges,the design and preparation of materials,mechanism establishment and multi-functional response performance were studied in this paper.The main research work and achievements are as follows:（1）A high elastic polymer with the characteristic of shape-stabilized reversible phase transition was developed（HEPCP）.Polytetrahydrofuran（PTHF）and polyethylene glycol（PEG）were used as elastic and crystalline block,which were cross-linked with isocyanates of multi-functional groups to synthesize an ultrahigh elastic（tensile strainε=800%）and high transparency functional polymer HEPCP.The crystal block could be programmed by adjusting molecular weight and the ratio of molecular segments.The reversible phase transition of microcrystals in HEPCP provided a driving force for the sensation and touch of multifunctional e-skin.（2）A passive e-skin material sensitive to near infrared light（NIR）,temperature and tension was developed.MWCNT/HEPCP,a passive e-skin nanocomposites sensitive to NIR,temperature and tension was prepared by using HEPCP as an elastic matrix driven by phase transition and multi-walled carbon nanotubes（MWCNTs）as a conductive network for photothermal conversion and conduction,showing excellent flexibility and stretchability（ε=600%）.The response performance of MWCNT/HEPCP sensors to NIR,temperature and tension were studied,and their optimal sensitivity showed that the conductivity changed by 103.7,18.0 and 1200 times,respectively.The response mechanism of MWCNT/HEPCP to three stimuli was as follows:The phase transition of microcrystals in the material induced by NIR and temperature drove MWCNTs to form dense conductive network,which made the conductivity increase rapidly.The orientation arrangement of MWCNTs and the crystallization of microcrystals caused by tension made the conductive network worse,resulting in a rapid decrease in conductivity.（3）An active e-skin material with self-powered sensing of NIR and pressure was developed.Stretchable（ε=260%）active e-skin materials polyvinylidene fluoride（PVDF）/MWCNT/HEPCP（PMH for short）with self-powered sensing of NIR and pressure were successfully prepared by electrospinning and spin coating;The correlation model among solution ratio,process parameters and micro-nano structure of electrospinning fiber was established,and PMH nanocomposite film with the optimal ratio（PVDF content of 33wt%）was obtained;The performance of self-powered PMH sensor for sensing NIR and pressure was studied.The optimal sensitivity to NIR and pressure was 977.6 m V/m W·mm-2 and 1.7 V/k Pa,respectively.The mechanism that piezoelectric nanofibers（NFs）could generate electric charge driven by the phase transition of microcrystals in polymer induced by NIR was explored.NIR self-powered e-skin could precisely locate the sensing area was realized.（4）An e-skin material which could deform and move in response to NIR irradiation was developed.Stretchable（ε=200%）e-skin materials MWCNT/LCP with deformation and motion response driven by NIR were prepared by introducing MWCNTs into liquid crystal polymer（LCP）elastic matrix as a nano-network for photoabsorption,photothermal conversion and conduction;The deformation and movement priciple of NIR regulating the movement of molecular chains in LCP to produce macroscopic mechanical deformation was studied;The mechanism that the deformation and movement of the material was precisely controlled by the position and time of NIR irradiation was established;The deformation and movement performance of MWCNT/LCP e-skin driven by NIR was studied,and a series of drastic deformation and movement tasks,such as“opening the knot”,open and recovery of“V”shape e-skin,rotate to expand“spring”,“flowering”,simulation of“reptile”walking in a straight line,simulation of bionic“insect”crawling and rolling,were automatically completed.In this paper,the design and preparation of materials,and the performance and mechanism of multifunctional response for stretchable multifunctional e-skin were studied.A scheme to realize multifunctional sensing in stretchable polymer nanocomposite films was proposed,which broke through the conventional design of e-skin with rigid sensors integrated on flexible substrate,and provided a feasible and reliable experimental basis for the realization of fully flexible and stretchable multifunctional e-skin;The mechanism that resistance change and charge movement of the material driven by the phase transition of the microcrystals in the polymer was studied.The e-skin materials proposed here solved the problem that multifunctional sensing and high sensitivity were difficult to realize simultaneously and self power supply,and provided a scientific and reasonable design concept for high sensitivity and self-powered multifunctional e-skin. |
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