Preparation And Properties Of Stimuli-responsive Composite Films

Smart film is a kind of film material that can convert energy contained in chemical or physical stimuli into macroscopic deformation.It has the characteristics of easy modification,easy processing and easy assembly.The film can be driven by the external stimuli such as pH,temperature,ionic strength,light,electric field and magnetic field.Such smart film materials can be widely used in biological,medical,environmental,engineering,etc.as smart sensors,drivers,software robots,energy harvesters,etc.,so the research and development of multi-responsive,highly selective and sensitive stimuli-responsive films are imminent.In this thesis,a heat-sensitive composite film was prepared by using the difference of thermal expansion between two layers of composite film,and the acetone-light dual-response composite film was prepared by simple stretching orientation,which was briefly described as follows:（1）Four different glass transition temperature copolymers of PAA-co-PMMA（I₁）and PAA-co-PMMA-co-PBA(I_2-4)formed from acrylic acid and acrylates were prepared by reversible addition-fragmentation chain transfer polymerization（RAFT）through molecular designing.The azo-coumarin molecule of rigid structure was synthesized and grafted into the polymer backbone of PAA-co-PMMA（I₁）to prepare a copolymer with certain crystallinity PAA-co-PMMA-co-PACA（II）.The structure was characterized by means of ¹H NMR and FT-IR.Five heat-sensitive composite films were prepared by casting method.All films provided a fast,reversible deformation response to a certain degree of thermal stimulation.The effects of thickness,temperature and polymer crystallinity on film deformation were investigated.We found that when the thickness ratio of the polymer layer to the aluminum foil layer was 1:1,the deformation of the film was the largest;when the temperature of the hot stage was close to the Tg of the polymer layer,the deformation of the film had a large increase;when the crystalline monomer azo-coumarin was introduced into the polymer layer,the deformation of the film became faster and larger.In the meantime,the cycle properties,deformation controllability and complex deformation of the film were studied experimentally,and several application devices were designed.We could see that the heat-sensitive composite film had excellent recyclability.When the film was given a slight pre-stress,after alternating hot and cold,the film undergone a fixed reversible deformation along the direction of the pre-stress.Through the pattern design,the films could be prepared into a variety of devices with bionic significance such as caterpillars,lotus,etc.Using the excellent electrical conductivity of aluminum foil,a high temperature alarm device could be prepared by introducing the composite film into the circuit.The composite film could be used to prepare motion crawling and grasping devices through ingenious design combination to simulate the movement of some organisms in nature,which had important application value in the field of intelligent film.（2）The photo-responsive molecule 4-trifluoromethyl-4’-（N-ethyl-N-hydroxyethyl）aminoazobenzene（CF₃-AZO）was prepared by molecular design and characterized by¹H NMR,¹³C NMR,¹⁹F NMR,MS,IR and UV-vis.The film was prepared by combining CF₃-AZO with commercial polyvinylidene fluoride（PVDF）.The film was stretched and oriented to obtain an acetone-light dual responsive smart film with the fast responsive of acetone and the UV light of 365 nm.The necessity of PVDF,CF₃-AZO and stretch orientation were verified by comparative experiments.The optimal conditions for film photo-response（azo content of 7%and source distance of3 cm）and response speed（110°/s）were studied.The mechanism of photo-response of thin films was investigated by polarized light microscopy,X-ray diffractometry,polarization-attenuated total reflection infrared spectroscopyand polarized ultraviolet-visible spectroscopy,demonstrating that CF₃-AZO and PVDF were oriented.At the same time,the response of the film to acetone vapor was also studied.Under the stimulation of acetone vapor,the film would bend and deform along the vertical direction of the stretching orientation.Finally,a circuit device using photo-response was prepared.