Research On Polymers Modified QCM Sensor Based On Interfacial Adsorption

Real time monitoring of harmful gases,such as formaldehyde and BTEX,has attracted wide attention.Some researchers have employed polymer materials to modify quartz crystal microbalance(QCM)based on interfacial adsorption to detect harmful gases.This paper focuses on the two hot points of polymer materials and QCM gas sensors,carries out a series of studies on gas sensing.In addition,the adsorption mode between polymer materials and harmful gases is explored by experiments and simulation calculations.The results obtained in this paper are listed as follows:1.Polypropylene microfiltration membrane(PPMM)modified by polydopamine(PDA)particles was facilely synthesized and loaded on QCM for the first time for formaldehyde(HCHO)sensing.By scanning electron microscopy(SEM)characterizing of PDA with different polymerization time,it is found that when the polymerization time is 4 h,the PDA particles can be evenly dispersed into the pore channel of PPMM.When the polymerization time is 6 h,the PDA particles will becomes over-aggregation and block the pore channel of PPMM,which was not conducive to the free import and export of the HCHO gas.The sensing test also verified that the PDA modified PPMM with 4 h polymerization time had the maximum response to HCHO.The response of PDA modified PPMM to HCHO gas is obviously larger than that of other common gases at the same concentration.Using the method of variable temperature adsorption experiment,we extracted the adsorption enthalpy between the material and HCHO,and concluded that the adsorption mode between the material and HCHO belongs to chemical adsorption,indicating that the material has excellent stability for selective HCHO detection.Through the simulation calculation by Gaussian 09 software,it is found that the weak hydrogen bond adsorption between the imino group of PDA and HCHO play a key role in the sensing process.2.In order to overcome the aggregation weakness of PDA and provide more imino group sites for HCHO gas adsorption,we added polyethyleneimine(PEI)molecules in the process of dopamine self-polymerization to change the polymerization process of PDA and obtaining another copolymer(PDA-PEI).The copolymer is made up of polydopamine and polyethyleneimine.SEM images show that PDA-PEI don't exist obvious aggregation.The pore channel of PPMM is completely coated by PDA-PEI.Moreover,when the polymerization time is more than 6 h,the PPMM modified by PDA-PEI can still maintains its pore structure.The results of gas sensing test show that the response of PDA-PEI modified PPMM to different concentrations of HCHO is larger significantly than that of PPMM modified by PDA.At the same time,the copolymer modified PPMM has excellent steady detection ability and selectivity for HCHO.The adsorption enthalpy between PDA-PEI modified PPMM and HCHO was extracted by the method of temperature variation adsorption experiment.It is indicating that the adsorption mode between the material and HCHO is chemisorption.There are many imino groups in the PDA-PEI copolymer.We use Gaussian 09 to simulate the adsorption enthalpy between imino groups and HCHO,respectively.It is found that the imino group in PDA structure plays the most important role in HCHO sensing.3.PDA is a common hydrophilic polymer.When the humidity of the environment increases,PDA can adsorb a large number of water molecules,leading to the false alarm and unnecessary panic.It is obvious that this defect greatly limits the practicability of PDA as gas sensing material.In order to solve this problem,we used superhydrophobic polymerized n-octadecylsiloxane(PODS)film to cover the PDA film to avoid false response.The gas sensing test shows that the response of the composite film to 97.9% relative humidity is further less than that of 10 ppm HCHO.In addition,the continuous response ability and selectivity of the composite film to HCHO are also satisfactory.4.One superhydrophobic polymerized noctadecylsilane with micronano hierarchical pore structure was self polymerized by different solvents on the surface of QCM.When the solvent is acetone,the polymer shows most notable hydrophobicity.Based on the hydrophobic adsorption,the superhydrophobic polymer can detect toluene gas steadily in different relative humidity environment.Moreover,the adsorption mode of toluene on the surface of polymerized noctadecylsilane belongs to weak chemical adsorption.5.One porous superhydrophobic polymer polymerized from divinylbenzene was prepared by one-pot procedure.The pore structure was characterized by transmission electron microscopy and Brunauer-Emmett-Teller(BET)treatment of the isotherms.This polymer is rich in aromatic ring structure and rich in pore structure.It can be used as sensing material to detect 1 ppm concentration toluene.Besides,the response of the porous polymer to toluene can remain stable under different relative humidity environments.The adsorption mode between toluene and porous polymer is proved to be weak chemisorption via using variable temperature adsorption experiment.