Study On Organic-inorganic Hybrid Materials And Paper-based Devices Applied For Humidity Monitoring

In recent years,with the increasingly realization of the significant effect of humidity on industry processes and human life,considerable efforts were putted into the development of high-performance humidity sensors.With the continuous improvement of the sensing performance,many new requirements,such as high stability,low-cost,portable and environment-friendly,are getting more attention.This paper focused on the development of sensitive materials,novel devices and the application of humidity sensors.The organic-inorganic hybrid materials with stable structure and the low-cost paper-based humidity sensors were fabricated.Finally,the application of humidity sensors for respiration monitoring was explored.This paper mainly focuses on following research:1.Mesoporous silica based composites are widely used for humidity sensors.But a physical mixing is needed to load humidity sensitive materials in the mesoporous silica materials,so the uniform dispersion of humidity active materials could not be guaranteed.A chemically modification method has been used to ensure the uniform dispersion and stable structure of the humidity active units in the first part.The SBA-15-PSS and SBA-15-DMC hybrid materials were fabricated.The hydrophilic organic units are chemically-modified on the mesoporous silica to ensure the stability of the hybrid materials under high RH,while the stable mesoporous skeleton is beneficial for transporting water molecules.Humidity sensors based on the obtained hybrid materials show good sensing properties and rapid response to RH change.2.In the second part,novel small-sized organic-inorganic hybrid spheres with core-shell structure were designed and prepared.Silica nanoparticles(SNs)were employed as a stable hydrophobic core to guarantee the stability of the hybrid materials,while the hydrophilic polyelectrolyte,poly(vinylsulfonic acid,sodium salt)(PSS),was applied to form the shell layer and supplies the solution process and humidity sensing ability.The obtained PSS@SNs materials could be dispersed in water with a concentration of 50 mg/m L.The good dispersibility is attributed to the small SNs size and the modification of hydrophilic polyelectrolyte,which endows the ability of preparing films with the solution process method.By anchoring on SNs,the stability of PSS under high humidity environment could be guaranteed.Furthermore,the presence of the SNs skeleton could provide large quantity of channels for water molecules transport,which is beneficial for realizing fast response to humidity change.3.Drawn on paper devices have gradually caused extensive concern due to their advantages of low-cost,portable and simple preparation method.Many efforts focus on paper-based chemical sensors have been reported by drawing the sensitive layer with functionalized pencils or wax pencils via a solid-phase process.In this part,we describe a paper-based humidity sensor fabricated by drawing sensitive region by a marker with oxidized multi-walled carbon nanotubes(o-MWCNTs)ink.Through liquid-phase process,o-MWCNTs could permeate into top layer of the paper substrate,such structure could increase the contacting area between o-MWCNTs and gaseous water molecules.Meanwhile,the top layer of hydrophilic cellulose paper could participate in the water adsorption process and further enhance the response of the humidity sensors.The response of the optimized paper-based sensor exhibits about five times larger than sensors fabricated on the ceramic substrate.In addition,the dispersion of sensitive material alleviates the inner stress of sensitive layer,leading to good mechanical stability.4.A composite structure was fabricated by cross-linking poly(ionic liquid)s(PILs)in the cellulose fibers of printing paper by in situ photoinitiated “thiol-ene” click reaction,applied for humidity monitoring.In this composite structure,both paper and PILs are great potential materials for humidity sensing application,but barely untapped.Cellulose paper could provide strong hydrophilic property which is beneficial for the moisture adsorption.However,the lack of conductive species in paper causes the difficulty for transforming adsorption of moisture into the electric signal,which results in most of paper-based humidity sensors could not exhibit high sensitivity.Hence,we introduced the PILs,which is famous for high ionic conductivity,into paper substrate as the conductive species donor,via photoinitiated “thiol-ene” click cross-linking reaction.When relative humidity(RH)goes up,the cellulose fibers adsorbed abundance water molecules and,then,the ion could ionize from PILs and participate in conduction process,leading to a significant decrease of impedance modulus.This work provides a potential method for preparing paper-based humidity sensors with good stability and high sensitivity in mass.