Study On The Preparation Of Nanocellulose Dielectric Thin Film By Inkjet Printing

Nanocellulose(CNF)films,with the advantages of high transparency,excellent dielectric performance,environmental-friendly and degradability,are expected to be used as dielectrics for the next generation of"green"electronic devices.At present,nanocellulose films are mainly prepared by filtration method and casting method,which suffer from some problems,such as difficulty in size control and incapability of fine patterning.This paper focused on the preparation of nanocellulose films by inkjet printing method.First,the printability of nanocellulose inks was optimized by adding different additives,and then the corresponding high-uniform film preparation method was developed based on the characteristics of nanocellulose inks,so as to achieve directly-patterned high-performance nanocellulose dielectric films.Firstly,the basic characteristics of nanocellulose and its aqueous solution were explored,and then the influence of additives such as polyvinyl alcohol(PVA),ethylene glycol(EG)and fluorocarbon surfactant(FSO)on the ink was also explored through the control variates.As a result,CNF ink suitable for the inkjet printing system was successfully obtained.It was found that PVA and EG can synergistically change the viscosity and surface tension of the ink,and EG can also slow the volatilization of the ink.When the PVA content was 0.2 wt%and the EG content was 10 wt%,the viscosity and surface tension of CNF ink were 9.6 m Pas and 45.8m N/m,respectively,which met the technical requirements of printing equipment.Furthermore,based on the inhibitory effect on outward capillary flow,which can be associated with the thixotropy of CNF ink,and the enhancement on inward Marangoni flow owing to the surfactant,we successfully obtained the highly uniform printed CNF film.When the concentration of FSO surfactant was 0.03 wt%,the coffee ring factor(CRF)of the resulting CNF film was only 1.07.It was found that the obtained CNF film had high transparency,low leakage current density and high effective capacitance,which was expected to be used as a dielectric in electronic devices.Furthermore,based on the characteristics of nanocellulose ink,this paper proposed a volatilization-gelation method to solve the common"coffee ring"effect in inkjet printing.Based on the rheological measurements,it was found that the viscosity and internal network nodes of CNF ink increased rapidly with the volatilization of solvent,which can be defined as the volatilization-gelation characteristic.Based on this characteristic,we speed up the volatilization of solvent by controlling the substrate temperature,thereby promoting the transformation of the ink from fluid to gel droplets.With the help of volatilization-gelation,the influence of"coffee ring"effect was reduced and the uniformity of the printed film was improved.In addition,it was found that the volatilization-gelation mechanism can play a role in preparing uniform films with different thicknesses and different sizes.For the prepared CNF films,the U value of thickness uniformity was less than 10%,and the U value of electrical uniformity was less than 13%.Finally,we prepared the corresponding IGZO-TFT device based on the printed CNF dielectric film.The I_on of TFT was about 10^-4 A,and the on-off current ratio was greater than 5×10⁴,indicating that the obtained CNF dielectric film had the potential to be applied to electronic devices.