CN113429784A

CN113429784A - Graphene oxide chiral polypyrrole hybrid material, anti-corrosion wave-absorbing coating and preparation method

Info

Publication number: CN113429784A
Application number: CN202110767493.1A
Authority: CN
Inventors: 孟凡彬; 郭子浩; 任和松; 李天�; 陈谭琳
Original assignee: Southwest Jiaotong University
Current assignee: Southwest Jiaotong University
Priority date: 2021-07-07
Filing date: 2021-07-07
Publication date: 2021-09-24
Anticipated expiration: 2041-07-07
Also published as: CN113429784B

Abstract

The invention discloses a graphene oxide chiral polypyrrole hybrid material, an anticorrosive wave-absorbing coating and a preparation method thereof, wherein the preparation method comprises the following steps: step 1: adding N-myristoyl-L-glutamic acid and pyrrole monomer into a solvent, and fully and uniformly dispersing to obtain a mixed solution A; wherein the mass ratio of the N-myristoyl-L-glutamic acid to the pyrrole monomer is 1: 1-5; step 2: dispersing graphene oxide in the solution to form a solution B; and step 3: fully mixing the mixed solution A and the solution B to form a mixed solution C, and slowly dropwise adding an initiator into the mixed solution C under the stirring condition; the mass ratio of the graphene oxide to the pyrrole monomer in the mixed solution C is 1: 20-50; and 4, step 4: after full reaction, filtering, cleaning, drying and grinding to obtain the required graphene oxide/chiral polypyrrole hybrid material; the hybrid material obtained by the invention has excellent wave-absorbing performance and also has good environment adaptability, namely corrosion resistance.

Description

Graphene oxide chiral polypyrrole hybrid material, anti-corrosion wave-absorbing coating and preparation method

Technical Field

The invention relates to the technical field of functional materials, in particular to a graphene oxide chiral polypyrrole hybrid material, an anticorrosive wave-absorbing coating and a preparation method thereof.

Background

The conductive polymer is compounded with other materials, so that the method is an effective method for improving the comprehensive performance of microwave absorption, corrosion protection and the like of the materials. The conductive polymer has the advantages of simple preparation process, low density, corrosion resistance, stable chemical performance and the like, and after the conductive polymer is compounded with the magnetic loss substance, the material has better conductivity and magnetism, and the attenuation of electromagnetic waves is changed from the original single electric loss into the dielectric loss and the magnetic loss. The carbon materials such as graphene and graphene oxide have the characteristics of low density, good mechanical properties, good conductivity and the like, and thus can be widely applied to the field of electromagnetic wave absorption. The absolute barrier property to molecules makes it well applicable in the field of corrosion protection. However, the large specific surface area and high conductivity of carbon materials such as graphene may reduce the dispersibility and impedance matching degree thereof.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a graphene oxide/chiral polypyrrole hybrid material, a composite coating, a coating and a preparation method, wherein the graphene oxide/chiral polypyrrole hybrid material has the integrated functions of microwave absorption and corrosion protection.

The technical scheme adopted by the invention is as follows:

a preparation method of a graphene oxide/chiral polypyrrole hybrid material comprises the following steps:

step 1: adding N-myristoyl-L-glutamic acid and pyrrole monomer into a solvent, and fully and uniformly dispersing to obtain a mixed solution A; wherein the mass ratio of the N-myristoyl-L-glutamic acid to the pyrrole monomer is 1: 3-5;

step 2: dispersing graphene oxide in the solution to form a solution B;

and step 3: fully mixing the mixed solution A and the solution B to form a mixed solution C, and slowly dropwise adding an initiator into the mixed solution C under the stirring condition; the mass ratio of the graphene oxide to the pyrrole monomer in the mixed solution C is 1: 20-50;

and 4, step 4: after full reaction, filtering, cleaning, drying and grinding to obtain the required graphene oxide/chiral polypyrrole hybrid material.

Further, the preparation method of N-myristoyl-L-glutamic acid in the step 1 is as follows:

s11: adding L-glutamic acid and sodium hydroxide into a solvent, and fully stirring and uniformly mixing;

s12: dropwise adding an aqueous solution of N-myristoyl chloride and sodium hydroxide into the solution obtained in the step S11, and sufficiently stirring;

s13: after full reaction, adjusting the pH value to 1 under the ice bath condition, and separating out white crystals in the system;

s14: cleaning, freeze drying and grinding to obtain the required N-myristoyl-L-glutamic acid.

Further, the concentration of sodium hydroxide in the solution formed in S11 is 5-6g/mL, and the concentration of sodium hydroxide in S12 is 0.001 mol/mL; the molar ratio of L-glutamic acid in S11 to N-myristoyl chloride in S12 was 1: 1.

Further, the molar ratio of the L-glutamic acid to the sodium hydroxide in the S11 is 1: 2; the molar ratio of N-myristoyl chloride to sodium hydroxide in S12 was 1: 1.

Further, the initiator in the step 3 is ammonium persulfate, and the molar ratio of the initiator to the pyrrole monomer is 1: 1.

Further, both the step 1 and the step 2 adopt an ultrasonic method for dispersion; in the step 3, the stirring speed is 1000-1500 rpm.

The graphene oxide/chiral polypyrrole hybrid material is a sheet structure or a sheet and fiber blended structure.

A method for preparing a composite coating from a graphene oxide/chiral polypyrrole hybrid material comprises the following steps:

adding the graphene oxide/chiral polypyrrole hybrid material into a solvent, and uniformly dispersing by ultrasonic;

fully mixing the solution with epoxy resin, and stirring under a vacuum-pumping condition; adding a curing agent, and continuously stirring under a vacuum-pumping condition to obtain the required composite coating; wherein the mass fraction of the graphene oxide/chiral polypyrrole hybrid material in the composite coating is 0.3-1 wt.%.

The composite coating prepared by the composite coating is coated on a substrate and cured to obtain the required coating.

The invention has the beneficial effects that:

(1) the coating prepared from the graphene oxide/chiral polypyrrole hybrid material has higher epsilon 'and epsilon' values through tests, and the coating has the strongest electromagnetic wave polarization and conductivity loss capability; and has a low μ "value, meaning a weak magnetic loss capability to electromagnetic waves; so that excellent microwave absorption performance can be exhibited;

(2) the composite coating prepared by the invention has stronger seawater corrosion resistance, and the graphene oxide/chiral polypyrrole hybrid material is uniformly dispersed in the epoxy matrix, so that the inherent defects and holes of the pure epoxy matrix can be well filled, and the protection capability of the coating is improved.

Drawings

Fig. 1 is an infrared spectrum (a) and a raman spectrum (b) of a graphene oxide/chiral polypyrrole hybrid material obtained in example 1 of the present invention.

Fig. 2 is an SEM image of the graphene oxide/chiral polypyrrole hybrid material obtained in

embodiments

1 and 2 of the present invention.

Fig. 3 is a three-dimensional graph and a two-dimensional graph of RL values of graphene oxide/chiral polypyrrole hybrid materials obtained in

embodiments

1 and 2 of the present invention.

Fig. 4 is an electromagnetic parameter diagram of the graphene oxide/chiral polypyrrole hybrid material obtained in

embodiments

1 and 2 of the present invention.

Fig. 5 is a graph showing the variation of the attenuation constant of the graphene oxide/chiral polypyrrole hybrid material obtained in

embodiments

1 and 2 of the present invention.

Fig. 6 shows the RL value of a coating prepared from the graphene oxide/chiral polypyrrole hybrid material obtained in example 1 of the present invention before and after 21 days of immersion in a NaCl solution.

Fig. 7 is an EIS diagram of composite coatings with different contents prepared from the graphene oxide/chiral polypyrrole hybrid material obtained in example 1 of the present invention and a comparative example obtained after being soaked in an aqueous NaCl solution for different times.

FIG. 8 is an equivalent circuit model of EIS data fitting.

Fig. 9 is a potentiodynamic polarization curve of composite coatings with different contents prepared by using the graphene oxide/chiral polypyrrole hybrid material obtained in example 1 of the present invention and comparative examples after being soaked in NaCl aqueous solution for 21 days.

Fig. 10 is a sectional SEM image of composite coatings with different contents prepared by using the graphene oxide/chiral polypyrrole hybrid material obtained in example 1 of the present invention and a comparative example coating after being soaked in a 3.5% NaCl solution for 21 days.

Fig. 11 is a schematic illustration of the corrosion protection mechanism of a pure EP coating (a) and a coating (b) of the present invention.

Detailed Description

The invention is further described with reference to the following figures and specific embodiments.

step 1: adding N-myristoyl-L-glutamic acid and pyrrole monomer into a solvent, and fully and uniformly dispersing to obtain a mixed solution A; wherein the mass ratio of the N-myristoyl-L-glutamic acid to the pyrrole monomer is 1: 3-5; the preparation method of the N-myristoyl-L-glutamic acid comprises the following steps:

s11: adding L-glutamic acid and sodium hydroxide into a solvent, and fully stirring and uniformly mixing; the concentration of sodium hydroxide in the solution formed in S11 is 5-6g/mL, and the concentration of sodium hydroxide in S12 is 0.001 mol/mL; the molar ratio of L-glutamic acid in S11 to N-myristoyl chloride in S12 was 1: 1.

Step 2: dispersing graphene oxide in the solution to form a solution B;

and step 3: fully mixing the mixed solution A and the solution B to form a mixed solution C, and slowly dropwise adding an initiator (APS ammonium persulfate) into the mixed solution C under the stirring condition; the stirring speed is 1000-1500 rpm. The molar ratio of the initiator to the pyrrole monomer is 1: 1; the mass ratio of the graphene oxide to the pyrrole monomer in the mixed solution C is 1: 20-50;

The graphene oxide/chiral polypyrrole hybrid material is of a sheet structure or a sheet and fiber blended structure.

The method for preparing the composite coating by adopting the graphene oxide/chiral polypyrrole hybrid material comprises the following steps:

The composite coating is coated on a substrate and cured to obtain the required coating.

Example 1

Preparing a graphene oxide/chiral polypyrrole hybrid material according to the following steps:

step 1: 30mg of N-myristoyl-L-glutamic acid and 2mmol of pyrrole monomer (Py) after distillation and purification are added into 15mL of absolute ethyl alcohol under the condition of room temperature, and 100W ultrasound is carried out for 30 min.

The preparation method of the N-myristoyl-L-glutamic acid comprises the following steps:

s11: adding L-glutamic acid and sodium hydroxide into an acetone solution at room temperature, and mechanically stirring for 30min to uniformly mix the system; wherein the concentration of the L-glutamic acid in the mixed solution is 0.001mol/mL, and the concentration of the sodium hydroxide is 5-6 g/mL.

S12: to the solution obtained in step S11, an aqueous solution of N-myristoyl chloride and sodium hydroxide was added dropwise with mechanical stirring during the addition to allow the system to react sufficiently. After dropwise addition, the concentration of N-myristoyl chloride in the solution was 0.001mol/mL, and the concentration of sodium hydroxide was 0.001 mol/mL.

S13: after the dropwise addition is finished, keeping the reaction condition unchanged, after full reaction, adjusting the pH value to 1 under the ice bath condition, and separating out white crystals in the system; the pH value of the system is adjusted by adopting 6mol/L hydrochloric acid, and a large amount of white crystals are separated out from the system along with the acidification process.

S14: and alternately cleaning the obtained white crystal by using petroleum ether and deionized water for several times, freezing, drying and grinding to obtain the required N-myristoyl-L-glutamic acid (L-MGA).

Step 2: 7mg of graphene oxide is dispersed in 20mL of deionized water, and the GO is uniformly dispersed by 200W ultrasonic wave for 30 min.

And step 3: and (3) mixing the two component systems in the step (1) and the step (2), adding 30mL of deionized water after uniformly stirring, and stirring at 1500rpm for 30min to uniformly mix the systems. Under the ice-bath condition, 10mL of aqueous solution containing 2mmol of ammonium persulfate is slowly dripped into the solution system while stirring, and the dripping process lasts for 30min at the rotating speed of 1500 rpm.

And 4, step 4: keeping the conditions unchanged, continuing to react and polymerize for 2h, alternately filtering and washing the cleaning product with water and absolute ethyl alcohol until the solution is colorless to obtain a black filter cake, drying and grinding to obtain a black powder sample, namely the graphene oxide/chiral polypyrrole hybrid material, which is marked as GO₁@CPPy₂₀。

Example 2

step 1: 30mg of N-myristoyl-L-glutamic acid and 5mmol of pyrrole monomer (Py) purified by distillation are added into 15mL of absolute ethyl alcohol under the condition of room temperature, and 100W ultrasound is carried out for 30 min.

And 4, step 4: keeping the conditions unchanged, continuing to react and polymerize for 2h, alternately filtering and washing the cleaning product with water and absolute ethyl alcohol until the solution is colorless to obtain a black filter cake, drying and grinding to obtain a black powder sample, namely the graphene oxide/chiral polypyrrole hybrid material, which is marked as GO₂@CPPy₅₀。

Taking 120mg of prepared GO₁@CPPy₂₀The sample was added to 20mL of acetone,performing 400W ultrasonic treatment for 60min to ensure that GO is subjected to ultrasonic treatment₁@CPPy₂₀The sample was uniformly dispersed in acetone. Then 10g of epoxy E51 was weighed out with homogeneously dispersed GO₁@CPPy₂₀The acetone solution was mixed together and stirred while applying vacuum (500rpm, 15 min). Finally obtaining the composite coating with moderate and uniform viscosity and marked as 0.6 percent GO @ CPPy-EP composite coating (namely GO)₁@CPPy₂₀The proportion in the composite coating material was 0.6 wt%). The same method is adopted to prepare pure epoxy coating (EP), 0.6% PPy-EP (polypyrrole monomer accounts for 0.6 wt% of the composite coating, additive accounts for polypyrrole monomer), 0.6% GO-EP (graphene oxide accounts for 0.6 wt% of the composite coating, additive accounts for graphene oxide), 0.3% GO @ CPPy-EP (GO) ("CPPy-EP")₁@CPPy₂₀The ratio of the composite coating to the paint is 0.3wt percent) and 1 percent of GO @ CPPy-EP composite coating (GO)₁@CPPy₂₀The proportion in the composite coating material is 1 wt%).

Comparative example

The other preparation procedure was as in example 1, except that step 2 was not included, and the resulting material, HPPy, was prepared. The corresponding coating is obtained according to the preparation method of the composite coating.

GO, HPPy and GO @ CPPy were structurally characterized using a Tensor type II Fourier transform infrared (FT-IR) transmission mode from Bruker, Germany. The scanning precision is 4cm^-1The scanning range is 4000-400 cm^-1. Before testing, the sample and potassium bromide are ground and mixed uniformly according to a proper proportion, and the infrared sample is tabletted under the pressure of 10MPa by a tabletting mold. And performing structural characterization on GO, HPPy and GO @ CPPy by using a confocal Raman spectrometer (Saimeri fly Dxi). Subjecting GO (graphene oxide), HPPy (comparative example), GO to field emission scanning electron microscope (FE-SEM, JEOL, JSM-7001F)₁@CPPy₂₀(graphene oxide/chiral polypyrrole hybrid material obtained in example 1) and GO₁@CPPy₅₀(graphene oxide/chiral polypyrrole hybrid material obtained in example 2) sample was subjected to morphological structure characterization.

Fig. 1 is an infrared spectrum (a) and a raman spectrum (b) of a graphene oxide/chiral polypyrrole hybrid material obtained in example 1 of the present invention. WhereinA is GO₁@CPPy₂₀B is HPPy (comparative) and C is GO. Due to the addition of GO, pyrrole monomers grow on a GO sheet layer in an in-situ polymerization manner, and the GO @ CPPy hybrid material is finally obtained under the induction of L-MGA chiral acid. The infrared spectrum is shown in FIG. 1a at 1636cm for the HHPy sample^-1The characteristic peak at (A) is due to stretching vibration of C ═ C bond in aromatic ring, and at 1561 and 1461cm^-1The characteristic peak at (A) is related to the stretching vibration of C-C bond and C-N bond in pyrrole ring. In addition, at 1318 and 1051cm^-1The characteristic peaks at (A) correspond to the C-N and C-H bond plane conjugate vibration absorption peaks. For the infrared spectrum of the GO @ CPPy sample, a characteristic peak representing stretching vibration of a C-C bond in a pyrrole ring has a red shift of 13 wave numbers relative to HPPpy, which is caused by the fact that an electron cloud on the pyrrole ring shifts due to electrostatic adsorption between an amino group on the pyrrole and an oxygen-containing functional group on GO. In addition, in the infrared spectrum of the GO @ CPPy sample, the plane conjugate vibration absorption peaks representing C-N and C-H bonds in the pyrrole rings are red-shifted by 6 wave numbers and 12 wave numbers relative to HPPy respectively, which is caused by the enhancement of the pi-pi conjugate effect between polypyrrole and GO. Indicating that an interaction occurred between GO, PPy and L-MGA.

Raman spectra As shown in FIG. 1b, the Raman spectra of GO were at 1351, 1580 and 2916cm^-1Three characteristic peaks are shown, corresponding to D band (representing defect condition), G band (representing sp)²In-plane vibration of carbon atoms) and 2D bands (representing stacking mode). HPPy at 925, 974, 1054, 1229, 1328, 1380 and 1578cm^-1And (3) shows obvious Raman characteristic peaks respectively attributed to ring deformation vibration between the dicationic unit and the radical cation, symmetrical C-H in-plane bending between the dicationic unit and the radical cation, asymmetrical C-H deformation vibration, C-N stretching vibration and C ═ C stretching vibration. For the Raman spectrum of the GO @ CPPy hybrid material, the position of the characteristic peak is consistent with that of GO and HPPy, and certain peak movement is accompanied. Further, the D-band to G-band strength ratio (I) is generally adopted_D/I_G) To evaluate the degree of disorder of GO in different systems.

I of GO calculated by fitting_D/I_GValue of 1.67While GO @ CPPy hybrid materials show higher I_D/I_GThe value is 2.73, since the in situ growth of polypyrrole introduces more defects to GO. And the successful preparation of the GO @ CPPy hybrid material is proved by combining the characterization analysis of infrared spectrum and Raman spectrum.

embodiments

1 and 2 of the present invention. a is GO, b is PPy, and c is GO₁@CPPy₂₀D is GO₁@CPPy₅₀. As can be seen from the figure, the pure GO sheets are smooth without other foreign materials, show more wrinkles, indicating its less flexible layer properties. When GO is not added into the chiral microemulsion system, the prepared HPPy shows a better helical structure and is in a uniform fiber shape, as shown in figure 2 b. After GO is added into the system, the flaky GO can be used as a template to adsorb pyrrole monomers Py through electrostatic interaction, so that the pyrrole monomers can be polymerized into flaky polypyrrole on the surface in situ. On the other hand, the existence of the chiral micromolecule L-MGA can dope pyrrole monomers and endow Py chiral characteristics, so that the lamellar GO @ CPPy hybrid material is obtained.

Comparing fig. 2c and fig. 2d, it can be seen that the obtained hybrid material micro-morphology changes with the change of the GO to Py mass ratio. When the mass ratio of GO to Py is 1:20, the obtained GO is₁@CPPy₂₀The hybrid material exhibits a full-scale platelet-like microstructure (2c) of uniform size. When the mass ratio of GO to Py is 1:50, the obtained GO is₁@CPPy₅₀The hybrid material exhibits a platelet-like and fibrous blended micro-morphology (2 d). This is mainly because after excess Py has consumed the oxygen-containing functional groups on the GO sheets, the remaining Py monomer is combined with the chiral acid L-MGA to produce a fibrous PPy. The L-MGA is influenced to induce Py to form HPPy due to the existence of GO, so that the fibrous PPy does not have an obvious spiral structure.

In order to measure the wave absorbing performance of the graphene oxide @ chiral polypyrrole, the obtained graphene oxide @ chiral polypyrrole is prepared into a wave absorbing ring.

Taking 7.2mg of prepared GO₁@CPPy₂₀Mixing the sample with 112.8mg paraffin, heating to melt, mixing uniformly, cooling, pouring into a mould, and press-forming to obtain the final productCoaxial rings with a diameter of 3.04mm and an outer diameter of 7mm, i.e. GO₁@CPPy₂₀Wave absorbing ring, denoted GO₁@CPPy₂₀-6％(GO₁@CPPy₂₀The mass ratio of the sample to the absorber ring was 6 wt.%). GO was prepared in the same manner₁@CPPy₂₀-x% and GO₁@CPPy₅₀-x% absorber ring (x ═ 3, 6, 9).

Calculating GO₁@CPPy₂₀-x% and GO₁@CPPy₅₀-a reflection loss RL value of x%. Generally, a lower RL value indicates a stronger absorption of electromagnetic waves of a corresponding frequency band by the absorber. The wider the effective absorption band (the bandwidth corresponding to the RL less than-10 dB), the wider the frequency band for the electromagnetic wave of the material to be effectively absorbed. In general, a proper filler ratio has an important influence on the wave-absorbing performance of the wave-absorbing ring, and too little or too much filler ratio is not favorable for preparing the wave-absorbing material with strong absorption because of agglomeration caused by insufficient and excessive fillers. The optimal filler ratio of the GO @ CPPy wave-absorbing ring is 6%, and in the ratio, the GO @ CPPy can be uniformly dispersed in paraffin and shows strong and wide wave-absorbing characteristics. When the filler ratio is 3%, the GO @ CPPy cannot completely fill paraffin, and a blank area without the filler exists in the wave absorbing ring, so that the wave absorbing performance is poor, and the minimum RL value is not lower than-20 dB. When the filler ratio is 9%, although the GO @ CPPy can be completely filled with paraffin, the excessive GO @ CPPy filler is easy to agglomerate due to large specific surface area and strong pi-pi action, which is also not favorable for the wave absorbing performance of the wave absorbing ring.

embodiments

1 and 2 of the present invention. HPPy-1500rpm (a, a'), GO₁@CPPy₂₀(b, b') and GO₁@CPPy₅₀(c, c'), the filler ratio of all tested samples was 6%. From the figure, it can be seen that all three samples have strong and wide wave-absorbing characteristics. The best microwave absorption performance was achieved when the HPPy-1500 rpm-6% absorbing ring thickness was 3.6mm, which exhibited the lowest RL value of-44.5 dB at 11.5GHz, and the widest effective bandwidth of 5.4GHz at that thickness (as shown in FIG. 4 a'). After GO is added, when GO and Py are addedThe mass ratio of the GO to the wave absorbing ring is 1:20, and when the thickness of the wave absorbing ring is 3.8mm, the GO is coated on the surface of the metal substrate₁@CPPy₂₀6% of the samples had the lowest RL value of-55.5 dB at 8.55 GHz; when the thickness of the wave-absorbing ring is 3.0mm, the wave-absorbing ring has the widest effective bandwidth of 8.4GHz (as shown in figure 4 b'). When the mass ratio of GO to Py is 1:50 and the thickness of the wave-absorbing ring is 2.5mm, the GO is in contact with the wave-absorbing ring₁@CPPy₅₀The sample had the lowest RL value of-46.4 dB at 16.08 GHz; when the thickness of the wave-absorbing ring is 3.0mm, the wave-absorbing ring has the widest effective bandwidth of 6.8GHz (as shown in figure 4 c'). GO (graphene oxide)₁@CPPy₂₀The 6% wave-absorbing ring has the lowest RL value and the widest effective bandwidth, which means that the wave-absorbing ring has the best microwave absorption performance.

The electromagnetic parameters of the prepared coaxial ring are tested by a vector network analyzer (Agilent PNA E5071C) through a coaxial method, and the frequency range of the tested electromagnetic waves is 2.0-18.0 GHz. FIG. 4a shows HPPy-1500 rpm-6%, GO₁@CPPy₂₀6% and GO₁@CPPy₅₀-6% (sample preparation method as described above for the sucker ring) change in real part of dielectric constant (. epsilon.') of the sucker ring versus frequency of electromagnetic wave. It is evident from the figure that the epsilon' curves of the samples all show a decreasing trend with increasing frequency, and this dispersion behavior occurs because the polarization behavior of the material shows an increasing hysteresis in response to changes in the electric field at higher frequencies. At 2GHz frequency, with respect to the value of ε' of HPPy-1500 rpm-6% 5.5, GO₁@CPPy₂₀6% and GO₁@CPPy₅₀The epsilon' values of 6% of the samples are obviously increased, namely 6.2 and 7.8 respectively, which represents that the samples have stronger polarization storage capacity for electromagnetic waves. FIG. 4b shows the change of the imaginary part (. epsilon. ") of the dielectric constant of the sample with frequency. GO (graphene oxide)₁@CPPy ₂₀6% and GO₁@CPPy₅₀The-6% sample has a higher epsilon' value for the electromagnetic wave of 2-18GHz full frequency band, which shows the strong polarization relaxation capability and conductivity loss capability for the electromagnetic wave. And GO₁@CPPy₂₀The-6% wave-absorbing ring has the highest epsilon 'and epsilon', which shows that the wave-absorbing ring has the strongest electromagnetic wave polarization and conductivity loss capability.

FIG. 4c shows the variation of the μ' relative frequency of the sample. In the full wave band range of 2-18GHzAll samples were kept above 0.95 μ' value, where GO₁@CPPy₂₀6% and GO₁@CPPy₅₀The-6% sucker ring shows a higher μ' value, which indicates its better magnetic storage loss capability. The HPPy-1500 rpm-6% wave absorption ring has a strong magnetic polarization formant at 11.8GHz, which shows that the HPPy-1500 rpm-6% wave absorption ring has strong magnetic polarization capability to the electromagnetic wave in the frequency band. FIG. 4d shows the magnetic loss properties of different wave-absorbing materials, wherein the HPPy-1500 rpm-6% wave-absorbing ring has the highest μ "value, which shows that it has the strongest magnetic loss capability to electromagnetic waves, which is due to the strong cross polarization of electromagnetic field brought by its obvious helical structure. GO (graphene oxide)₁@CPPy ₂₀6% and GO₁@CPPy₅₀The 6% sample shows a lower μ "value because there is no significant helical structure, meaning a weaker magnetic loss capability to electromagnetic waves.

A wave-absorbing material with good microwave absorption properties must have two basic characteristics: firstly, more electromagnetic waves enter the wave-absorbing material as much as possible, namely the wave-absorbing material is required to have good impedance matching degree; secondly, more loss is performed on the electromagnetic waves entering the wave-absorbing material as far as possible, namely, the wave-absorbing material is required to have strong loss capacity on the electromagnetic waves. To better explain the problem of why GO @ CPPy has excellent microwave absorption properties, impedance matching and attenuation constants serve as two important factors that affect the absorption properties of the material. Calculating to obtain an impedance matching value | Z_in/Z₀I, when I Z_in/Z₀When the value of | is closer to 1, better impedance matching is shown, which means that more electromagnetic waves can enter the wave-absorbing material. On the contrary, if | Z_in/Z₀The farther the value of | is from 1, the more mismatched the impedance is, which will cause a large amount of electromagnetic waves to be strongly reflected on the surface of the wave-absorbing material and not enter the wave-absorbing material to be further attenuated by loss. Therefore, we consider that when | Z_in/Z₀When the value of | is within the range of 0.8-1.2, the impedance matching degree of the wave-absorbing material is better, and more electromagnetic waves can enter the wave-absorbing material. In general, | Z in the range of 0.8-1.2_in/Z₀The larger the area formed by the | value, the better the impedance matching of the material.Tests show that HPPy-1500 rpm-6% and GO₁@CPPy₂₀-6% wave absorbing ring | Z in the range of 0.8-1.2_in/Z₀The area formed by the | value is compared with GO₁@CPPy₅₀And larger, which indicates that they have better impedance matching degree and can allow more electromagnetic waves to enter the interior of the wave-absorbing material.

The wave-absorbing material with excellent microwave absorption performance not only requires good impedance matching degree, but also requires strong loss capability, thereby greatly losing the energy of electromagnetic waves. The attenuation constant of the sample is calculated to quantitatively characterize the attenuation effect on the incident electromagnetic wave. As shown in figure 5, a higher alpha value can cause stronger electromagnetic wave loss of the wave-absorbing material, and GO is arranged in a 2-18GHz frequency band₁@CPPy₂₀The 6% wave-absorbing material has the highest attenuation constant, which shows that the wave-absorbing material has the strongest electromagnetic wave loss capability. In conjunction with impedance matching and attenuation constant analysis of the wave absorbing material, it can be concluded that: GO (graphene oxide)₁@CPPy₂₀The sample of-6% has not only a good impedance matching degree but also the highest attenuation constant, which makes it exhibit excellent microwave absorption performance. When the thickness is 3.8mm, GO₁@CPPy₂₀The 6% absorber ring has the lowest RL value of-55.5 dB at 8.55 GHz; when the thickness is 3.0mm, it shows the widest effective bandwidth of 8.4 GHz.

The essential feature of chiral materials is the cross-polarization of the electromagnetic field. For chiral materials with a helical structure, in addition to the self-polarization of the electromagnetic field, there is also cross-polarization of the electromagnetic field. First, a special spiral structure is similar to a conductor coil, and when electromagnetic waves are incident on a chiral material having such a spiral structure, electromagnetic wave energy is transferred in the spiral coil in the form of micro-current through electromagnetic cross polarization and debye polarization. Secondly, the electromagnetic wave is subject to conductive losses during transmission and is dissipated as heat. Finally, after the electromagnetic wave is incident on the material with the spiral chiral structure, an induced electric field and an induced magnetic field are generated, and the energy of the induced electric field and the induced magnetic field is further attenuated. In addition, the existence of the spiral structure can also increase the impedance matching degree of the wave absorber material, so that more electromagnetic waves can enter the wave absorber and then be lost by the material. Therefore, the hybrid material prepared by adding the chiral material has excellent wave-absorbing performance.

The wave-absorbing coating is prepared according to the following method.

Taking a certain amount of GO₁@CPPy₂₀The sample was added to acetone and sonicated at 400W for 60min to allow uniform dispersion in acetone. Then weighing a certain amount of epoxy resin E51 and uniformly dispersed GO₁@CPPy₂₀The acetone solution was mixed together with stirring under vacuum (500rpm, 15 min). Then, a certain amount of polyamide 650 curing agent is weighed and added into the system, and the system is stirred (500rpm, 15min) while vacuumizing is carried out, and finally the composite coating (wherein GO) with moderate and uniform viscosity is obtained₁@CPPy₂₀6% by mass in the epoxy curing agent system). And then, coating the prepared composite coating on a plate, and curing and forming to obtain the 6% GO @ CPPy-EP wave-absorbing coating.

The RL values of the coatings before and after 21 days immersion in 3.5% NaCl solution were tested by the bow test system and the test data are shown in fig. 6. As can be seen from the figure, the wave-absorbing coating before soaking shows better microwave absorption performance, the lowest RL value is-31.9 dB at 15.17GHz, and the effective bandwidth is 5.04 GHz. After the wave-absorbing coating is soaked in 3.5% NaCl solution for 21 days, the RL value of the wave-absorbing coating is reduced to a certain extent, but the wave-absorbing coating still shows good wave-absorbing performance, the lowest RL value is-27.5 dB at 12.38GHz, and the effective bandwidth is 4.89 GHz. The phenomenon that the RL value is increased and the frequency corresponding to the lowest RL value is shifted to low frequency is probably caused by that during the soaking process in a 3.5 percent NaCl solution, salt water and corrosive media diffuse into the coating, so that the impedance mismatch and the attenuation capability of the coating are reduced on one hand, and the thickness of the coating is increased on the other hand. The experimental result shows that the prepared 6% GO @ CPPy-EP composite coating not only has excellent microwave absorption performance, but also has strong seawater corrosion resistance, so that the composite coating still can show good microwave absorption performance after being soaked in 3.5% NaCl solution for 21 days.

Using a German tanner electrochemical workstation, using a classical three-electrode mode of pairingThe obtained working electrode is subjected to Electrochemical Impedance Spectroscopy (EIS) and potentiodynamic polarization curve tests, in the test process, the surface of the working electrode with the coating is in contact with 3.5% NaCl solution, and the contact area is 1cm². Wherein the working electrode is a Q235 steel sheet coated with composite coating, the reference electrode is a saturated silver chloride electrode, and the auxiliary electrode is a platinum mesh electrode (2cm multiplied by 2 cm). Before testing, the working electrode needs to be tested for Open Circuit Potential (OCP), and EIS testing can be carried out after the open circuit potential is stable. The tested alternating current of EIS has amplitude of 10mV and frequency range of 10^-2－10⁵Hz. Potential range of potentiodynamic polarization curve test of the working electrode: the scan rate was 1mV/s, relative to OCP, from-250 mV to 250 mV.

The preparation method of the working electrode comprises the following steps:

a Q235 steel sheet with the specification of 20mm multiplied by 5mm is sequentially polished by 80, 200, 400, 800 and 1200 meshes of sand paper, and then is respectively treated with alcohol and acetone to remove stains on the surface of the steel sheet. And then, the prepared composite coating is timely coated on the processed Q235 steel sheet in a spinning way, the steel sheet is placed in a ventilation position and is cured for 7 days at normal temperature, working electrodes for electrochemical tests are obtained, and 3 groups of parallel working electrodes are prepared from each composite coating.

The working electrode was immersed in 3.5% NaCl solution to simulate the marine environment and the corrosion resistance of the coating was examined by electrochemical measurement techniques of a typical three-electrode system. The results of the tests are shown in FIG. 7, which shows the Electrochemical Impedance Spectroscopy (EIS) of the samples during 21 days of immersion in 3.5% NaCl solution. Fig. 7a is a graph of pure EP resin test results, fig. 7b is a PPy-EP (polypyrrole-epoxy coating), fig. 7c is 0.6% GO-EP (graphene oxide content in epoxy coating is 6 wt.%), fig. 7d is (0.3% GO @ CPPy-EP, i.e., a composite coating obtained by using the graphene oxide/chiral polypyrrole hybrid material prepared in example 1 of the present invention and an epoxy resin according to a coating preparation method, wherein the mass ratio of the graphene oxide/chiral polypyrrole hybrid material in the composite coating is 0.3 wt.%), and fig. 7e is 0.6% @ CPPy-EP, i.e., a composite coating obtained by using the graphene oxide/chiral polypyrrole hybrid material prepared in example 1 of the present invention and an epoxy resin according to a coating preparation method, wherein the mass ratio of the graphene oxide/chiral polypyrrole hybrid material in the composite coating is 0.6 wt.%) Fig. 7f is 1% GO @ CPPy-EP, that is, a composite coating obtained by using the graphene oxide/chiral polypyrrole hybrid material prepared in example 1 of the present invention and an epoxy resin according to a coating preparation method, wherein the mass ratio of the graphene oxide/chiral polypyrrole hybrid material in the composite coating is 1 wt.%).

In the Bode graph, the impedance modulus (| Z! Y at the lowest measurement frequency_0.01Hz) Can be used as a semi-quantitative index of the corrosion resistance of the coating. (ii) Z non-woven cells with the increase of soaking time_0.01HzThe value of (a) tends to decrease, indicating a decrease in the corrosion protection capability of the coating. 0.3%, 0.6% and 1% GO @ CPPy-EP | Z | (R) cells after 6 days of immersion in 3.5% NaCl solution_0.01HzThe values are respectively as high as 1.94 multiplied by 10⁵Ωcm²、1.28×10⁶Ωcm²And 4.51X 10⁵Ωcm²| Z Ycells well above pure EP, 0.6% PPy-EP and 0.6% GO-EP coatings_0.01Hz. With the exception of pure EP and 0.6% GO-EP coatings, all other coating samples had an | Z! Z-E when immersed in 3.5% NaCl solution for 16 days_0.01HzValue relative to | Z tintwhen soaked for 11 days_0.01HzThere is a large increase in value. The reason is that the existence of the electroactive polypyrrole can react with the metal substrate to generate a compact passivation layer, so that a corrosion medium is prevented from reaching a protected substrate, the corrosion resistance of the substrate is improved, and the | Z_0.01HzThe case of an increase in value. For EIS spectra (7e) of 0.6% GO @ CPPy-EP, higher | Z & lt & gt cells were shown during early soaking_0.01HzValue of 1.28X 10 at the maximum⁶Ωcm²(ii) Y & ltZ & gt after 21-day soaking_0.01HzThe value is still higher than 1.28 multiplied by 10⁵Ωcm². The reason is that the crosslinking and curing of amino groups in polypyrrole and epoxy resin are promoted by a proper amount of filler ratio, so that the crosslinking network degree of the epoxy resin is increased, and meanwhile, the molecular barrier property of GO is greatly increased to inhibit corrosive media, so that the corrosion resistance of the GO @ CPPy-EP composite coating is further improved. Too little filler fraction did not completely fill the inherent defects and gaps of pure epoxy, 0.3% GO @ CPPy-EP showed slightly lower | Z_0.01HzThe value was 1.94X 10⁵Ωcm²(FIG. 7 d). Too high filler fraction can also cause the agglomeration of GO @ CPPy, adversely affecting the corrosion resistance of the coating, 1% of the | Z! Y of GO @ CPPy-EP_0.01HzThe value is only 4.51 × 10⁵Ωcm²As shown in fig. 7 f.

The equivalent circuit of the Bode plot was fitted using ZView software, as shown in fig. 8. The equivalent circuit includes R_s、R_pore、C_c、R_ctAnd Q_dlThese five elements represent solution resistance, pore resistance, coating capacitance, charge transfer resistance and bilayer constant phase, respectively. The constant phase element (Q) is used to compensate for the deviation behavior from the ideal value capacitance, and the index (n) thereof represents the degree of deviation from the ideal dielectric properties^[161,162]. Ideal capacitance (Q ═ C), n ═ 1. If when n is 0, it is an ideal resistor.

Potentiodynamic polarization curve measurements and electrochemical parameter statistics were performed on the coating samples after 21 days immersion in 3.5% NaCl solution, as shown in fig. 9. Extrapolation of the anode and cathode lines to corrosion potential (E) using electrochemical analysis software_corr) To calculate the corrosion current density (I)_corr) Anodic tafel slope (b)_a) And cathode tafel slope (b)_c). Polarization resistance (R)_p) Is determined from the potentiodynamic polarization curve over a narrow potential range of 20mV relative to the corrosion potential. Annual corrosion rate v_corr(mm/year) and protection efficiency (IE,%) were calculated.

As can be seen in FIG. 9, E of pure epoxy (-433.0mV) compared to bare steel (-425.0mV)_corrHigher values indicate that the epoxy coating has certain barrier properties. The GO @ CPPy-EP composite coating has higher E_corrValues (0.3% GO @ CPPy-EP of-291.0 mV, 0.6% GO @ CPPy-EP of-197.0 mV and 1% GO @ CPPy-EP of-282.0 mV) because a large number of imine groups on the polypyrrole framework can adsorb Fe through²⁺And Fe³⁺Ions are converted into Fe-NH-chelating functional groups to stabilize the passivation potential of the metal, and the existence of GO can also increase the barrier property to corrosive media, so that the corrosion potential of the coating can be further improved. In addition, higher b_a/b_cThe ratio shows that the application of external current makes the anode strongAnd (4) polarizing strongly. Notably, the addition of GO @ CPPy makes b_aThe value increased greatly, indicating a decrease in the rate of dissolution of the cation. Corrosion current density (I)_corr) As an important index for indicating the severity of the corrosion behavior, a lower value indicates that the corrosion behavior occurs less. 0.6% GO @ CPPy-EP has the lowest I_corrValue (1.35X 10)^-7A/cm²) I of bare steel_corrValue (5.05X 10)^-5A/cm²) 2 orders of magnitude lower. At the same time, the 0.6% GO @ CPPy-EP corrosion protection coating showed the lowest annual corrosion rate (1.56 х 10)^-3mm/year) and the highest IE (99.73%). The 0.3% GO @ CPPy-EP and 1% GO @ CPPy-EP coating samples had lower IEs of 98.32% and 99.19%, respectively. This shows that only a proper amount of GO @ CPPy can be uniformly dispersed in the epoxy matrix, and thus the inherent defects and holes of the pure epoxy matrix can be well filled, and the protective capability of the coating is improved.

TABLE 1 electrochemical parameters of different coated electrodes after 21 days immersion in 3.5% NaCl solution

Fig. 10 is a sectional SEM image of composite coatings with different contents prepared by using the graphene oxide/chiral polypyrrole hybrid material obtained in example 1 of the present invention and a comparative example coating after being soaked in a 3.5% NaCl solution for 21 days. a is EP, b is 0.6% PPy-EP (composite coating prepared by taking polypyrrole as filler), c is 0.6% GO-EP (composite coating prepared by taking graphene oxide as filler), d is 0.3% GO @ CPPy-EP, e is 0.6% GO @ CPPy-EP, and f is 1% GO @ CPPy-EP.

It can be seen from the figure that the pure EP coating has a flat smooth cross section, since the epoxy resin is brittle. However, the inherent lamellar spacing and defects of epoxy resins favor corrosive media (H)₂O、O₂、Cl^-Etc.) and thus exhibits poor corrosion protection. After 21 days of immersion in 3.5% NaCl solution, the pure EP coating had been completely destroyed and corrosion products were exposed on the surface of the coatingThis indicates that the coating has lost its corrosion protection capability completely (as shown in 10 a). When GO @ CPPy is added into pure EP as a filler, the inherent defect gap of the epoxy resin is filled, and a corrosive medium can be effectively blocked, so that the corrosion resistance of the coating is improved to a certain extent. From the SEM image of the cross section of the 0.6% GO @ CPPy-EP coating (fig. 10e) it can be seen that the whole cross section is complete and free of defects, meaning a strong barrier to corrosive media.

Both 0.3% GO @ CPPy-EP (FIG. 10d) and 1% GO @ CPPy-EP (FIG. 10f) coating sections exhibited some hole defects that facilitated the diffusion of corrosive media due to too little or too much filler loading, and exhibited somewhat poor corrosion protection. As a control, the cross-sections of both the 0.6% PPy-EP (FIG. 10b) and 0.6% GO-EP (FIG. 10c) coatings exhibited poor corrosion protection due to the large number of pores resulting from the non-uniform filler dispersion. By comparing optical photographs of the different coatings after 21 days immersion in 3.5% NaCl solution, the 0.6% GO @ CPPy-EP coating surface was most fully preserved with essentially no corrosion products. Both the 0.3% GO @ CPPy-EP and 1% GO @ CPPy-EP coatings remained intact with a small amount of corrosion products appearing on the coating surface. Pure EP, 0.6% GO-EP and 0.6% PPy-EP coatings all show signs of damage and high amounts of corrosion products, meaning poor corrosion protection. This phenomenon is consistent with previous conclusions from analysis of electrochemical impedance spectroscopy and potentiodynamic polarization curves, and the 0.6% GO @ CPPy-EP coating shows the most excellent corrosion resistance.

Fig. 11 is a schematic illustration of the corrosion protection mechanism of a pure EP coating (a) and a coating (b) of the present invention. Corrosive medium (H)₂O、O₂Cl-, etc.) penetrate to the coating/metal interface through defects and pores of the coating and cause corrosion of the metal. In the case of pure EP coatings (fig. 11a), they can be considered as single element barriers and corrosive agents will penetrate the coating in its thickness direction without any barrier effect, following the redox reaction at the coating/metal interface.

Fe→Fe²⁺+2e^-

Fe→Fe³⁺+e^-

H₂O+(¹/₂)o₂(g)+2e→2OH^-

2Fe²⁺(aq)+O₂(g)+2H₂O→FeOOH+2H⁺

The redox reaction causes pitting on the metal substrate and the coating falls off, leaving the metal substrate unprotected. However, GO @ CPPy-EP nanocomposite coatings have a longer term protective effect than pure EP coatings. This is because the molecular barrier property of GO can prevent the diffusion of corrosive media, and at the same time, it can cause labyrinth effect to prolong or even block the diffusion path of corrosive media^[165]. Furthermore, as a conducting polymer, PPy is able to accept electrons released by dissolution of the metal and reduce from an oxidized state (doped form) to a reduced state (dedoped form), in a neutral environment, increased Fe ions (Fe)²⁺And Fe³⁺) As oxide layer converted into passivation layer Fe₂O₃And Fe₃O₄。

From the above tests, GO can be seen₁@PPy₂₀The samples exhibited a uniform sheet-like morphology with optimal MA performance. When the thickness is 3.8mm, GO₁@CPPy₂₀6% of the samples had a low RL value of-55.5 dB at 8.55 GHz; when the thickness is 3.0mm, it shows the widest effective bandwidth of 8.4 GHz. After the coating is soaked in a 3.5% NaCl aqueous solution for 21 days, the epoxy coating (0.6% GO @ CPPy-EP) with the filler proportion of 0.6% has the best anticorrosion performance, and the protection efficiency can reach 99.73%. The wave-absorbing coating before soaking has the lowest RL value of-31.9 dB at 15.17GHz, the effective bandwidth is 5.04GHz and shows better microwave absorption performance. After the wave-absorbing coating is soaked in 3.5% NaCl solution for 21 days, the RL value of the wave-absorbing coating is reduced to a certain extent, the lowest RL value at 12.38GHz is-27.5 dB, and the effective bandwidth is 4.89 GHz. The 6% GO @ CPPy-EP composite coating has excellent microwave absorption performance and strong seawater corrosion resistance, so that the composite coating still can show good microwave absorption performance after being soaked in 3.5% NaCl solution for 21 days.

The composite material prepared by the invention grows chiral polypyrrole by in-situ polymerization on graphene oxide to prepare the graphene oxide @ chiral polypyrrole hybrid material (GO @ CPPy). The hybrid material has excellent wave-absorbing performance and also has good environment adaptability, namely corrosion resistance. Has the functions of microwave absorption and corrosion protection.

Claims

1. A preparation method of a graphene oxide/chiral polypyrrole hybrid material is characterized by comprising the following steps:

step 2: dispersing graphene oxide in the solution to form a solution B;

2. The method for preparing a graphene oxide/chiral polypyrrole hybrid material according to claim 1, wherein the method for preparing N-myristoyl-L-glutamic acid in step 1 is as follows:

3. The method for preparing a graphene oxide/chiral polypyrrole hybrid material according to claim 2, wherein the concentration of sodium hydroxide in the solution formed in S11 is 5-6g/mL, and the concentration of sodium hydroxide in S12 is 0.001 mol/mL; the molar ratio of L-glutamic acid in S11 to N-myristoyl chloride in S12 was 1: 1.

4. The preparation method of the graphene oxide/chiral polypyrrole hybrid material according to claim 2, wherein the molar ratio of L-glutamic acid to sodium hydroxide in S11 is 1: 2; the molar ratio of N-myristoyl chloride to sodium hydroxide in S12 was 1: 1.

5. The preparation method of the graphene oxide/chiral polypyrrole hybrid material according to claim 1, wherein the initiator in the step 3 is ammonium persulfate, and the molar ratio of the initiator to the pyrrole monomer is 1: 1.

6. The preparation method of the graphene oxide/chiral polypyrrole hybrid material according to claim 1, wherein the step 1 and the step 2 are dispersed by an ultrasonic method; in the step 3, the stirring speed is 1000-1500 rpm.

7. The graphene oxide/chiral polypyrrole hybrid material obtained by any one of the preparation methods of claims 1 to 5 is characterized in that the graphene oxide/chiral polypyrrole hybrid material is of a sheet structure or a sheet and fiber blended structure.

8. The method for preparing the composite coating by using the graphene oxide/chiral polypyrrole hybrid material as claimed in claim 7, is characterized by comprising the following steps:

9. A composite coating prepared using the composite coating material obtained in claim 8, wherein the desired coating layer is obtained by applying the composite coating material to a substrate and curing the coating material.