Synthesis Of Polypyrrole Nanofilm And Its Study As Optical Fiber Sensor

With the research and development of novel polymer materials, the relationshipbetween polymer materials and human life is becoming closer and closer. The humanlife has been improved tremendously by the new products based polymer materials. Inrecent years，with the development of science technology and industrial production,the general structural polymer material has been unable to meet the growing needs ofpeople. Novel functional polymer materials with special optical, electrical andmagnetic properties have attracted a great interest, such as conductive polymer withconjugated structure, polymer photographic materials in integrated circuitphotolithography process, organic light emitting semiconductor for next generationmonitors and novel polymer materials for thermal conversion.Conductive polymer as an important functional polymer material can’t be ignoredin conductive polymer family, several common conductive polymers are listed,polyaniline, polypyrrole, polyacetylene, polythiophene, Poly（p-phenylenevinylene）and Polyphenyl, etc. Polypyrrole is a representative conductive polymer, whichusually is synthesized by chemical oxidation method and electrochemical oxidationmethod, and various application based on the polypyrrole has been extensivelystudied, such as gas sensor, chemical sensor, biosensor, lithium battery, metal anticorrosive, electro-catalysis, polymer light emitting diodes and selective ionexchange membrane.In recently years, optical fiber sensing technology has also obtained a greatdevelopment, as with new polymer materials. Optical fiber sensing technology is anentirely new sensing technology, which has incomparable advantages comparing withtraditional sensors, such as light weight, small size, low power consumption,electromagnetic interference, high sensitivity, environment-friendly and durable, etc.Currently, optical fiber sensors has appeared and been used in various fields, such aschemical sensor, biosensor and physical sensor, etc.The design idea of this thesis is to combine conductive polymer and fiber opticsensor technology, study and develop novel optical fiber sensors with practicaldetecting effect. We use a relatively simple method, interfacial polymerizationtechnology, to synthesize the conductive polypyrrole nanofilm. This method avoidsthe disadvantages of traditional chemical oxidation and electrochemical oxidationmethods. The synthesized polypyrrole nanofilm is used as sensitive film in opticalfiber senor. As a classical conductive polymer, the applications of polypyrrole basedon its electrical properties are very common. However, the studies using thepolypyrrole in optical application are rarely reported. We focus on the current hotissue of environmental safety, volatile organic compounds （VOC） and aerosolparticles, and design two kinds of polypyrrole optical fiber sensors, respectively.The whole thesis consists of three parts, the first one is the synthesis ofpolypyrrole nanofilm utilizing interfacial polymerization technology, the second oneis the design and development of VOC optical fiber sensor based on polypyrrolenanofilm, the third one is the design and development of aerosol particles sensorbased on polypyrrole nanofilm.The synthesis of polypyrrole nanofilm by interfacial polymerization is verysimple. Although the polypyrrole nanofilm also can be synthesized by electrochemicalmethod, this method needs complex and expensive equipment, and the synthesizedpolypyrrole nanofilm can’t be secondarily transferred from electrode. We use twonon-soluble solvents, water and chloroform, to form the interface of interfacial polymerization. The Fe³⁺and pyrrole monomers are dissolved into the water andchloroform, respectively, and then the polypyrrole can be obtained under the4℃after several hours, the thickness can be controlled by synthesis time. Usually, thethickness of polypyrrole film with1hour synthesis is only120nm. And the surface isvery smooth, with metallic luster, and is an ideal material for optical fiber sensors.Polypyrrole volatile organic compound （PPy-VOC） optical fiber sensor utilizesthe polypyrrole nanofilm as the sensitive film which is attached on the end surface ofoptical fiber. VOC molecules can diffuse into the PPy film and induce thepolaron-bipolaron state, which can increase the visible light absorptivity of PPy film.Moreover, the VOC molecules also can cause the swelling of PPy nanofilm, whichcan reduce the refractivity of PPy film. Both of the absorptivity and refractivity areimportant optical parameters, which can affect greatly the optical properties of PPynanofilm, for example, the reflectance of PPy nanofilm is increased obviously underthe VOC condition, this kind of response provides a possibility for VOC detection.Our PPy-VOC optical fiber sensor has response for many kinds of VOC, such astoluene and chloroform, etc. The lowest concentration limit of detection is closed to1ppm. This novel PPy-VOC optical fiber sensor exist a great application potential.Polypyrrole aerosol particles （PPy-AP） optical fiber sensor also uses the PPynanofilm as the sensitive film for optical fiber sensor. We focus on the character thataerosol particles exists positive charges and utilize electrostatic effect to design theaerosol particle optical fiber sensor. Because of the conductive property of PPy, theaerosol particles with positive charges can induce the electrons of PPy nanofilm tomove to surface and cause the unequal distribution of electrons. The change ofelectron density can directly affect the refractivity, and then we can complete theaerosol particles detection. For example, our PPy-AP optical fiber sensor can detectlots of aerosol particles, such as black carbon, NaCl and polystyrene, etc. Moreover, ithas response to aerosols with different concentration. This electrostatic detectionprinciple is a totally novel detection mechanism and exist an important significance.In sum, polypyrrole can be successfully applied in development of optical fibersensor, which not only increase the sensor species, but also extend the application field of PPy. So that it is no longer confined in electrical field, but also can besuccessfully applied in optical field.