Wave Propagation In Liquid Crystal Elastomers And Structures

As one kind of typical soft materials with high orientation,the study of liquid crystalline elastomers(Liquid Crystalline Elastomer,LCE)has become a new branch in the field of liquid crystal polymer research in recent 30 years.As a functional material,LCEs have both properties of elastic and liquid crystalline.The properties of LCEs,such as mechanical orientation,orientation and mobility of liquid crystalline,are shown to be better than those of general liquid crystalline polymers.LCEs are of great significance both in theory and in practice.At present,the quasi static analysis of thermo-optic-electro-mechanical coupling of LCEs has been fully developed.However,it is more difficult to describe the dynamic behavior of the material due to its multi-field sensitivity and mechanical-order coupling.This paper will use the LCE stress-strain constitutive equation and a coupled equation of thermal order fluctuation to study the wave propagation in liquid crystal elastomer and the application of this material in phononic crystals.The main contents and conclusions include:The propagation characteristics of Rayleigh waves on the surface of an infinite LCEs half space are studied.The influence of soft elastisity on wave propagation is discussed.It is found that the Rayleigh waves in liquid crystal elastomers are no longer the traditional Rayleigh waves.There is an angle between the direction of propagation and the free surface.And the polarization direction of particle vibration is related to frequency.The Rayleigh wave velocity changes with the change of frequency.And there is a critical frequency.At the critical frequency,the Rayleigh wave velocity does not change with the change of temperature.The structures of two typical phononic crystals,steel/LCE and porous LCE,are discussed.It is found that the soft elastic properties of liquid crystal elastomers can reduce the central frequency of the band gap of the phononic crystals with LCE as the matrix.The rotation of the director has a great influence on the band gap of the structure.In the steel/LCE phononic crystals,the band gap of the structure will be turned on and off with the rotation of the director.As for the porous liquid crystals,the smaller the porosity is,the more obvious the effect of the director rotation on the band gap is.The lower the temperature is,the larger the central frequency and bandwidth of the structural band gap are.Since the rotation of the director can be controlled by an external electric field or a magnetic field,the LCE phononic crystal provides a way to realize the intelligent control of the band gap.We studied the band gap properties of several typical lattice chiral gammadion structure vacuum/LCE phononic crystal.It is found that the band gap of the structure is different with the different bending angles.When the bending angle is 90° and greater than 90°,there will be no complete band gap.Similarly,the rotation of the director has a great influence on the band gap of the structure.It can be concluded that the smaller the bending angle is,the more easily the complete band gap occurs.When the bending angle is 0°,the band gap has a wide range.But when the bending angle of the pores is 90° and 135°,there is no band gap.When the bending angle is small,the bandwidth of different band gap increases with the increase of arm width b,and increases with the increase of arm length h.The other band gap decreases with the increase of b.When the bending angle is 90°and 135°,only when the h is longer,the complete band gap will appear.The band structure of the porous LCE phononic crystal is studied by thermal-mechanical coupling.The thermal deformation of a single cell is determined by the method of one-way coupling.On this basis,the band structure of phononic crystal is studied.The results show that different band gaps will change with the increase of temperature.The band gap of 3rd-4th order and 5th-6th order decreases with the increase of temperature,and the band gap of 4th-5th is only opened when the temperature is high.And the 3rd-4th and 4th-5th order band gap will increase with the increase of porosity.The variation of 5th-6thband gap with porosity is complicate,and there is no obvious trend.The calculation of the band structure of the thermo-mechanical coupling LCE is realized,which provides the theoretical basis for the terperature control and design of the band structure.