Porphyrin-Containing Polyimide Nanofibers:Design,Preparation And Sensing Properties

The first ten years of the 21st century is also known as the "Sensing Decade," and varieties of sensors have been used in many smart devices.The current requirements for the new generation of sensors are flexible,flexible and portable.With the development of flexible materials,flexible sensors that meet the above conditions have emerged.Polyimide(PI)material is one of the common flexible materials.PI is a kind of high performance polymer material with a rigid imide heterocyclic structure,which has excellent properties such as,high mechanical property and excellent temperature resistance.The introduction of functional molecular porphyrin into PI material can impart unique photoelectric properties to PI and can be used as a sensing device.At present,the research mainly uses porphyrin as the recognition molecule and soluble PI as the polymer carrier to prepare porphyrin-containing PI nanofibers by electrospinning,which is applied to the detection of ammonia,aniline,hydrochloric acid,methanol and trinitrotoluene(TNT)and heavy metal ions in wastewater.Although porphyrin PI materials have shown more research results in sensing,more in-depth research and detailed analysis are still needed.In addition,with the development of computer technology,computational simulation plays a crucial role in the design and development of materials.Therefore,this thesis combines molecular simulation to study the relationship between structure,properties and function of porphyrin-containing PI materials.The main research contents are as follows:1.The molecular simulation techniques are adopted to investigate the fundamental structures and properties of polyimide(PI)composed by pyromellitic dianhydride(PMDA),3,3',4,4'-biphenyldianhydride(BPDA),4,4'-hexafluoroisopropylidene diphthalic anhydride(6FDA),p-phenylene diamine(PDA),2-(4-aminophenyl)-1H-benzimidazole-5-amine(BIA),and 4,4'-oxidianiline(ODA)in hierarchical multiscale level.The results indicates that the thermal and mechanical properties follow the order of PMDA/BIA>PMDA/PDA>PMDA/ODA and BPDA/BIA>BPDA/PDA>BPDA/ODA.Although the chain rigidity of the polyimides containing BIA are lower than PDA in terms of the chemical structures,the strong hydrogen bonding strengthens the PI chain interactions,endowing the polyimides with superior thermal and mechanical property.The movement ability of polyimide chains is discussed based on the ratio of<Ree2>to<s2>and MSD at the scale of the entire polymeric chain,for which the order is ODA>PDA>BIA.For the system with high chain mobility,the movement of polyimide chains are more favorable,correspondingly resulting in lower glass transition temperature and the tensile modulus.The torsional angle distribution and X-ray diffraction of polyimides before and after stretching are studied during the tensile modulus calculation.The torsion angle distribution changes apparently,which increases the d-spacing and elongates the entire molecular chain simultaneously,serving as the main cause of polyimide deformation.Besides,it is noted particularly that the introduction of ODA unit would increase the amount of vertical segments conformation,therefore leading to large deformation under small external force.These simulation results provide the basis for the subsequent optimization experiments.2.Two kinds of novel porphyrinated polyimides,BPDA/ODA/iron 5,10-bis(4-aminophenyl)-15,20-dipheny lporphyrin(FeDATPP)and 6FDA/ODA/FeDATPP,abbreviated as BOFe and 60Fe,were synthesized and electrospun into nanofibers for dissolved oxygen(DO)sensing.The effects of electro-activity(i.e.,electron-withdrawing ability of BPDA,6FDA and FeDATPP when these units were binding with DO)and the roles of the nanofiber orientation in DO sensing were investigated.Electrochemical characterization indicates that the current values in Cyclic Voltammograms(CV)exhibits linear correlation with the DO concentration,with the correlation coefficient R2 varying from 0.9461 to 0.9958,suggesting the excellent DO sensing performance of the synthesized porphyrinated polyimides.Meanwhile,it is found that the oxygen reduction behaviors in DO sensing were vastly altered due to the different electro-activity and orientation structures of the porphyrinated polyimides nanofibers.An unusual side-on porphyrin-O2 configuration and charge transfer mechanism during DO sensing were clarified upon molecular simulation.3.The PMDA/ODA type PI nanofiber membrane was used as a carrier,and chloromethylation was used to activate the PI surface and graft iron porphyrin(FeDATPP).The sensing properties of grafted porphyrin PI nanofiber membranes on H2O2 were investigated.Electrochemical characterization results show that the modified electrode has good catalytic oxidation and reduction properties for H2O2.The linear detection range is 50?1100 ?mol/L,and the correlation coefficient is R2=0.9832.