Preparation And Dielectric Properties Of Acrylic Resin Based Composites

Dielectric elastomers（DEs）,a typical kind of electroactive polymers,can be stimulated to change their shapes under external electrical field and directly convert electrical energy into mechanical work.This process is reversible after the removal of the electric field.Therefore,they have a very broad prospect in actuators,sensors and other electromechanical transition field.The main factors affecting the driving strain of the dielectric elastomer are the Young’s modulus and dielectric constant.This research is dedicated to the development of dielectric elastomer materials with high dielectric constant and good mechanical properties.The free radical polymerization method is employed to prepare an acrylic resin elastomer（AE）with 2-hydroxyethyl acrylate,styrene and n-butyl acrylate as the reaction monomers.Based on AE,two new high dielectric constant composite systems have been developed.The methanesulfonyl chloride and 4-hydroxydiphenylamine were used as raw materials to synthesize the intermediate products by a series of substitution reactions with AE.Then,the acrylic resin grafted aniline oligomer（AE-g-OANI）was obtained by oxidative coupling polymerization.¹H-NMR and FT-IR results demonstrated the successful synthesis of AE-g-OANI.Aniline was used to synthesize hydrochloric acid-doped polyaniline（PANI）under ice bath conditions.Then,PANI was stirred with AE to prepare PANI/AE composites.The SEM and TEM results showed that the dispersion of OANI in the matrix was better than that of PANI,and the particle size of OANI was much smaller than that of PANI.DSC and TGA analysis proved that the addition of OANI improved the thermal stability of AE.The percolation thresholds of AE-g-OANI and PANI/AE were 8.75 vol.%and 5.94 vol.%,respectively,after linear fitting the conductivity values of the two composites.Compared with PANI/AE composite,AE-g-OANI exhibited better dielectric properties.At room temperature and 100 Hz,the dielectric constant and loss of the AE-g-OANI composite were 227 and0.38,respectively,near the percolation threshold,which were 1.53 and 0.24 times than that of the PANI/AE composite.At the same time,the elastic modulus of the AE-g-OANI composite film remained at a low value（5.3 MPa）.The MXene phase Ti₃C₂T_x was obtained by etching the Al layer of the corresponding MAX phase Ti₃AlC₂with HCl-LiF etchant.To obtain more single or few layers Ti₃C₂T_x,dimethyl sulfoxide was added to strengthen the ultrasonic delamination process.MXene was modified by polypyrrole（PPy）.In situ polymerization of pyrrole was achieved on the surface as well as between the layers of d-Ti₃C₂T_xwithout using oxidant and the well-aligned PPy-d-Ti₃C₂T_xwas obtained.Polymerization of pyrrole was confirmed by FTIR and Raman spectroscopy.XRD and TEM results indicated that the PPy chains were inserted and well-aligned between the Ti₃C₂T_x sheets.Then,the d-Ti₃C₂T_x and PPy-d-Ti₃C₂T_xfillers were mixed with AE,respectively,and the d-Ti₃C₂T_x/AE and PPy-d-Ti₃C₂T_x/AE composite films with different filler contents were prepared by solution casting method.TEM showed that the PPy-d-Ti₃C₂T_x flakes were uniformly dispersed in the matrix.After linear fitting the conductivity,the percolation thresholds of PPy-d-Ti₃C₂T_x/AE and d-Ti₃C₂T_x/AE were 6.39 vol.%and6.07 vol.%,respectively.Dielectric properties were tested under room temperature.At 100 Hz,the dielectric constants of PPy-d-Ti₃C₂T_x/AE and d-Ti₃C₂T_x/AE near the percolation threshold were 493and 265,respectively,which were 140 and 76 times higher than that of pure AE.The dielectric loss values of PPy-d-Ti₃C₂T_x/AE at 100 and 10³ Hz were 0.36 and 0.23,respectively,which were lower than that of the d-Ti₃C₂T_x/AE composite（0.71 and 0.44）.In addition,the elastic modulus of the 6.36vol.%PPy-d-Ti₃C₂T_x/AE composite film was 3.7 MPa,which was appropriate for actuators.