Preparation And Tuning The Sensing Properties Of Solvatochromic Fluorescent Nanofibers

With the rapid development of smart devices,sophisticated gas sensors that can detect the surrounding environment have attracted much attention from researchers.Environmental gas detection methods include semiconductor electrical measurement,gas chromatography,and quartz crystal microbalance method.However,these methods have disadvantages of single detection,low sensitivity,weak stability,and poor portability,which limit their practical application in smart wearable sensor devices.The key to solving these problems is preparation of a simple and portable gas sensor with a wide range of detection and high identification efficiency.In view of this,this thesis reports the use of solvatochromism fluorescent molecules as a wide range of sensing molecules,to prepare two kinds of thin-film-based fluorescent gas sensors,with excellent portability and detection via electrospinning technology.It also studies in detail the best process parameters of electrospinning and the gas sensing performance of the sensor.The specific content is as follows:(1)Preparation of linear fluorescent nanofiber membranes and tuning the sensing properties of various organic gases.Polyvinyl acetate solution doped with soluble discoloration fluorescent molecules was used to construct a thin-film-based fluorescence sensor by electrostatic spinning molding process.The organic gas causes dissolution of nanofiber films and changes the microenvironment around the fluorescent molecule,so that the donor and receptor moieties in the molecule are reversed.This results into charge transfer and the mechanism of fluorescence characteristic eventually changes.We performed sensing response tests on several common organic solvents.For instance,when the sensor was placed in toluene atmosphere,fluorescence intensity decreased significantly for 10 s,and emission wavelength displayed a blue shift at 30 s.When placed in dichloromethane atmosphere for 3s,the fluorescence intensity dropped sharply,while the wavelength exhibited a blue shift.When placed in acetone atmosphere for 3s,the fluorescence intensity significantly reduced,and fluorescence emission wavelength portrayed a redshift.Placing in N,N-dimethylmethamide atmosphere for 60 s,the fluorescence intensity obtained was lower than the initial intensity,and fluorescence emission wavelength displayed a large redshift.Through numerous experiments,the effects of solution properties and the parameters of the electrostatic spinning process on fiber morphology were explored in detail.The optimum spinning conditions obtained were solution concentration of 20%,voltage of 18 k V,flow speed of 0.5 m L/h,spinneret inner diameter of 0.52 mm,and reception distance of 15 cm.In summary,a simple,portable and efficient thin-film-based fluorescent gas sensor can be prepared by electrostatic spinning,to achieve extensive detection of organic gases.(2)Preparation of cross-linked fluorescent nanofiber membranes and tuning/adjustment of the sensing properties of various organic gases.The pre-crosslinked bisphenol A type epoxy resin/polyamide curing agent solution doped with lyotropic fluorescent molecules was used to construct a thin-film-based fluorescent sensor,via an electrospinning process.Using the above-mentioned principles,sensor response detection was studied on several common organic solvents.In toluene atmosphere,both fluorescence intensity and fluorescence emission wavelength responded at 3s.Placing in dichloromethane atmosphere for 3s,only the fluorescence intensity decreased,and the fluorescence emission wavelength shifted after 30 s.In acetone atmosphere,the fluorescence intensity increased for the first 10 s,and the fluorescence emission wavelength shifted after 30 s.However,after placing the sensor in N,N-dimethylformamide atmosphere for a long period,the fluorescence intensity weakened.Through several experiments,it was found that when the ratio of bisphenol A type epoxy resin to polyamide curing agent was 2:1,pre-crosslink temperature of 40? for 2 hours,60% concentration of solution,voltage of 16 k V,advancing speed of 0.5 m L/h,0.52 mm inner diameter of the spinneret and the distance of 15 cm were used,the best fiber morphology was obtained.Therefore,cross-linked thin-film-based fluorescent gas sensors,not only have improved mechanical performance and stability,but can also achieve a wide range of organic gas detection.This expands the application field of the sensors,reduces their manufacturing costs,and develops smart wearable transmission,which can provide new ideas for the development of smart wearable sensing devices.