Nanomaterial-functionalized Silk And Its Application In Wearable Electronics

Silk is a kind of natural protein fiber secreted by mature silkworms. Due to its elegant luster, gorgeous appearance, softness, affinity to skin, high hygroscopicity and permeability, silk has been regarded as “the second human skin” and widely applied in textile industry. However, inherent defects of silk including photo-induced aging, microbe adherence and variable wrinkle greatly limit the extensive utilization of silk fabric for fashionable apparels。With the development of miniaturization technique and intelligent wearable electronics, traditional silk products cannot meet the requirements on fashion and intelligence. Therefore, in order to extend the application of silk tremendous efforts have been dedicated to surface modification and functionalization of silk. As advances of nanotechnology, numerous nanomaterials with unique functions and structures have been synthesized and combined to silk to conquer its inherent shortcomings. Surface modification of AgNPs, AuNPs, ZnO Nanorods, TiO2 NPs renders silk with antibacterial activity. Combination of conductive polymers, metal nanoparticles and graphene endow silk with excellent conductivity for possible applications in wearable electronics and sensing. The in situ growth of ZnO nanorods arrays opens a new horizon of silk in smart wearable devices. However, during the surface functionalization process, the use of chemicals and the modified nanomaterials may severely damage the structure of silk, further hampering the practical application of the functionalized silk.Therefore, it is highly demanded to modify silk with appropriate nanomaterials via green methods for antibacterial, UV protective, flame retardant and highly conductive properties. The synthesis of ZnO nanorods array on silk surface without damaging silk is also of great significance for the applications of silk in wearable electronics.The thesis consists of the following parts:In chapter one, the background information of silk was briefly introduced firstly. Then, recent advances on silk surface functionalization, smart wearable fiber and ZnO nanorods-based piezoelectric sensors were reviewed. The motivation and the research contents were also included in this part.Chapter two describes the experimental details.Chapter three describes the fabrication of CeO2 nanoparticle-modified silk for UV protection and antibacterial applications. CeO2 nanoparticles were immobilized on silk surface via a dip-coating approach and endowed silk with UV-shielding ability antibacterial activity, flame retardant and so on. The excellent UV-shielding ability and strong antibacterial activity of the modified silk to both Gramnegative(E. coli and P. aeruginosa) and Gram-positive(S. aureu and B. subtilis) have been demonstrated clearly.Chapter four describes the fabrication of highly conductive graphene-coated silk via a repeated coating-reduction approach. In this project the coating-reduction times and other parameters were optimized to find out the best conductivity. The sheet resistance of graphene-coated silk fabrics can be 1.5 kΩ sq-1 and the electrical conductivity of a single graphene-coated silk fiber reaches to 3595 S m-1, which is the best electrical conductivity reported so far.Chapter five describes the fabrication of ZnO nanorods arrays-modified silk and its application in physiological monitoring. ZnO nanorod arrays were grown on highly conductive graphene-coated silk fabrics via electro-deposition. The ZnO nanorods can effectively convert mechanical energy into electricity due to its excellent piezoelectric property. The as-prepared sensor was successfully employed to monitor the behaviours like pressing, twisting and folding. Moreover, human physiological parameters including breathing, heart beating, coughing and singing could also be accurately collected using the ZnO nanorods arrays-modified silk fabrics.In chapter six, the research progresses were summarized and the future prospect was discussed.