The Preparation And Applications Of Flexible Micro/nano Structures Based On PDMS Membrane

PDMS(poly(dimethylsiloxane))film-based micro-structures are the key components of flexible electronic,because of their unique properties including flexibility and stretchability.This kind of micro-structures always can be created via two methods.The first method is related to the good extensibility of PDMS film:that is,if a stiff film with poor extensibility is pasted or deposited on a PDMS film,in turn,constituting a bilayer film,the micro-structure always can be induced in the surface of bilayer film under mechanical manipulation or heat treatment,because of the mismatch of stress response between the stiff film and the PDMS film.The second method is depending on the castability of mixture of liquid PDMS and curing agent,that is,if spinning the mixture on the mold with micro-structure,the micro-structures of mold can be well replied by PDMS film after curing.In this work,we prepare an orthogonally coupled wrinkles and grooves on bilayer film depending on the first method,which is flexible orthogonally coupled sinusoidal and rectangular phase grating;and a similar pyramid-structure on PDMS/WMCNTs(multi-walled carbon nanotubes)composite film through the second method,which is used to construct a pressure sensor with super performance.Micro or nano-structure patterns always can be assembled in bilayer film surface,which often includes wrinkles and cracks.However,most of the reported patterns in these systems are irregular and contain large amounts of defects.For instance,the wrinkles have non-uniform profile,and the distribution of cracks is in random manner.These defects significantly hamper the application of this kind of patterns,especially the application in the light manipulation field.Therefore,the construction of a pattern with no(or at least fewer)defects is highly desired.In order to address these problems,we prepare a bilayer film with uniform thickness of SiOx layer depending on O2 plasma treatment with uniform density of O2+ions firstly.Secondly,we create parallel and equidistant cracks pattern in stiff layer side via peeling method,that is,the SiOx layer is cut into parallel and equidistant SiOx ribbons.The wrinkles with uniform profile can be created in SiOx ribbon through further stretching the bilayer film in the direction perpendicular to the cracks orientation.In the other word,we can develop a micro-pattern in bilayer film that combines parallel and equidistant grooves with highly sinusoidal wrinkles.Actually,this micro-pattern is a composite phase grating,which orthogonally couples sinusoidal phase grating and rectangular phase grating.Its structural parameters can be well tuned by mechanical stretching in the uniaxial direction.Naturally,it allows tunable manipulation of light propagation,that is,a single incident laser beam can be split into two-dimensional diffraction beams array,and the intensity and propagation angle of each diffraction beam can be precisely controlled through simple stretching or releasing the grating.We further develop a theoretical model,which can quantitatively describe and accurately predict this light manipulation.Significantly,after additional irradiation treatment of electron beam,the tunable structures can be immobilized.Based on this property,local patterns arrays are created to act as address bits for information storage.In addition,the tunable opacity effect in bilayer film has attracted considerable attention because of its potential applications in intelligent window displays.However,an accurate and in-depth interpretation of this tunable opacity effect is still absent,and at present there is no rational guidance for well realizing its applications.Here,we demonstrate that this effect is induced by the diffractive behaviors of micro-structure emerging and evolving in the brittle film under stretching.If the micro-structure is a perfect pattern,that is,the wrinkles and cracks coupled in orthogonal manner,the light manipulation behaviors of this pattern include the diffraction of wrinkles and the coupled items of wrinkle's diffraction and crack's diffraction.Whereas,for pattern in which the wrinkles have uniform profile while the cracks distribute in a random manner,the diffractive behaviors is dominated by the diffraction of the wrinkles,rather than the cracks diffraction,which plays a negligible role.Depending on castability of the mixture of liquid PDMS and elastomer curing agent,the micro-structure can be created in PDMS film surface,that is,if spinning the mixture on a mold with micro-structures,the micro-structures can be replied on the surface of PDMS film after curing.According to this method,we prepare a composite film of PDMS/MWCNTs with micro-structured surface,and then,prepare a pressure sensor via resting the micro-structure face downward on the indium tin oxide(ITO)-coated flexible poly(ethyleneterephthalate)(PET)film.This method can efficiently improve the performance of pressure sensor,because pressure independent resistance of sensor is eliminated as much as possible and the elastic modulus is improved by 2 times.As a result,the sensitivity our sensor is improved up to 474.13 kPa-1,and response time is shortened to be as small as 2 ?s.Benefiting from the high performance,the functionalities of sensors are successfully extended to the accurate detection of high frequency mechanical vibration(-300 Hz),which are not achieved before.