Preparation And Properties Of Keratin Gel Based Flexible Pressure Sensor

In recent years,the construction of flexible devices is attracting more and more attention.Among these devices,flexible pressure sensors are widely used in many fields,such as robots,electronic skin,electronic consumer products,displays and medical monitoring equipment because of their excellent flexibility and sensing ability in complex environmental conditions.For pressure sensors,elastic dielectric material is the key to sensor sensitivity measurement.As a typical soft elastic material,polymer gel material can produce large deformation under low modulus,and the preparation of raw materials and methods are varied.Therefore,polymer gel is the best choice for the dielectric layer of pressure sensor.In this thesis,we report a facile strategy for preparing keratin gel by reacting a cross-linker(PEG-4VS)with wool keratin solution under the alkaline conditions through Michael addition.In addition,the keratin gel can be further assembled into a flexible pressure sensor by sandwiching it between two stainless steel foils.The main contents and results of this paper are as follows:1.The keratin solution were extracted from wool under the reduction method through breaking disulfide bond.The effects of different quality reductants on the molecular weight and the thiol content of as-prepared keratin solution were also investigated.The experimental results showed that the molecular weight of keratin was smaller as increasing the reductants,but more Na2S results in a higher thiol content.2.The effects of different keratin types,different cross-linker concentrations and different mass fractions on the gel properties were investigated.Rheological experiments showed that all the obtained gel materials had very good elasticity.In addition,the amount of reducing agent in the preparation of keratin solution had a great influence on the performance of the gel.More Na2S results in a higher content of covalent cross-linking sites(i.e,free thiol groups).However,the amount of reductant cannot be too high since this also leads to the reduction of keratin molecular weight and suppression of gel formation.Meanwhile,the stiffness of keratin gels could also be easily tuned by changing the concentrations of protein and cross-linker.3.Compared with the mechanical properties of the keratin gel and silica gel,the recovery time of the sensor is faster to 0.1 s.And,und the strain of 80%,the internal structure kept stable during compression.Moreover,our as-prepared gel exhibited good anti-fatigue behavior.After 10,000 cycles,only 17%the energy loss was observed at a strain:magnitude of 50%.4.The flexible pressure sensor could output two kinds of electrical signal(capacitance and resistance),and have a wide range of mechanical response.It not only could detect the waveform of the human pulse,and the high frequency physiological signals of the sound,but also it could be respond for the large amplitude low frequency activities such as the finger or arm bending.Furthermore,it is suitable for the signal detection of different pressure range.Therefore,our work provides an alternative choice for the construction of flexible pressure sensors in the medical health field.