| Because of the excellent thermal and corrosion resistance,outstanding insulation and adhesion,as well as good film reforming properties,epoxy polymers have been widely used in engineering,electronics and energy-related technologies.Liquid crystals(LCs)are a specific family of soft materials,in which the molecules can self-organize to form an ordered microstructure and the molecular arrangement can be controlled by external fields.Therefore,the combination of epoxy polymers with excellent physical properties and liquid crystal materials with external field response properties can provide a new approach to optimize the materials'properties and expand their applications.In this thesis,the optical films based on epoxy polymer/liquid crystal composites were fabricated by the thermal curing reaction between epoxy monomer and thiol monomer,the two-step thermal curing of liquid crystalline epoxide and non-liquid crystalline epoxy monomers,and the photoinitiated cationic polymerization of liquid crystalline epoxide in mesogenic solvents.The effects of preparation conditions and material composition on the microstructure of epoxy polymers and the properties of optical films were also investigated.The study in this thesis can provide experimental and theoretical guidance for the regulation of epoxy polymer microstructure,the optimizing of the performance of smart f-ilms,as well as the development of new epoxy-based liquid crystal films.The main research contents are as follows:(1)Seven kinds of liquid crystalline epoxides were synthesized.As a result,it was found that an increase in the length of the flexible chain,introduction of a side group(methyl group)on the benzene ring,and reduction in the number of benzene rings can reduce the melting point of the compound and the stability of the liquid crystal phase.(2)The polymer dispersed liquid crystal(PDLC)films based on the epoxy-thiol polymer/liquid crystal composites were prepared by thermal curing reaction between epoxy monomers and thiol monomers.It was found that the epoxy-thiol polymers can present porous or microsphere microstructures and coordinating the curing rate and the reduction rate of the miscibility in the system at a similar level was the decisive factor to obtain microsphere epoxy-thiol polymer.When the liquid crystal content was 40.0 wt%,Capcure 3800 was used as the curing agent,the mass ratio of the rigid epoxy monomer NDGA to that of the flexible epoxy monomer PGDE was 1:3,and the curing temperature was 60 °C,electrically switchable light transmittance smart film with epoxy-thiol polymer microsphere structure can be successfully prepared,and the film can exhibit the better overall electro-optical performance.(3)By utilizing the difference in curing reactivity between the liquid crystalline epoxide and non-liquid crystalline epoxy monomers,the performance of the thermally cured PDLC films can be controlled by two-step thermal curing method.It was found that the reactivity of the liquid crystalline epoxide E6M was significantly lower than that of the non-liquid crystalline epoxy monomers.By controlling the content of E6M,the voltage of the applied electric field during later curing process,as well as the curing temperature and time of pre-curing process,the performance of the PDLC films can be regulated and the smart film with lower driving voltage or selective light scattering can be successfully fabricated.Moreover,the competition of the anchoring effect on the LC molecules from the liquid crystalline epoxy polymer(LCEP)network and the conventional epoxy resin matrix was crucial to the electro-optical performance of the films.(4)The epoxy-based polymer stabilized liquid crystal(EPSLC)films were prepared by the photo initiated cationic polymerization of liquid crystalline epoxide in mesogenic solvents.It was found that the combined effect of the low reactivity in cationic polymerization of E6M and the suppression effect from cyano group induced that the LCEP only can be formed in the liquid crystalline solvents with lower cyano group content.After the cationic polymerization of the liquid crystalline epoxide in mesogenic solvents,the as-formed LCEP network can stabilize the alignment of the LC molecules.The increase of E6M content,initiator content and UV light intensity will result in that the LCEP network had a greater stabilizing effect on the LC molecules.However,the increase of polymerization temperature will lead to a sparser LCEP network,and the LCEP network will have a weaker effect on the LC molecules. |
PDF Full Text Request