CN114806687B - Preparation method of electrorheological material based on carbon quantum dots and electrorheological material - Google Patents
Preparation method of electrorheological material based on carbon quantum dots and electrorheological material Download PDFInfo
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Abstract
The invention provides a preparation method of an electrorheological material with carbon quantum dots and the electrorheological material, and the preparation method comprises the following steps: step S1: synthesizing functionalized carbon quantum dots CDs; step S2: preparation of Co (OH) 2 @ CDs particles comprising the steps of: s21: uniformly mixing cobalt chloride hexahydrate, urea and deionized water to obtain a mixed solution A; adding carbon quantum dots CDs into the mixed solution A, and uniformly mixing to obtain a mixed solution B; s22: adding the mixed solution B into a high-pressure reactor, keeping the temperature at 80-120 ℃ for several hours, and then cooling; s23: taking out the reaction product, centrifuging, cleaning and drying to obtain coupled particles Co (OH) 2 @ CDs, coupling particles Co (OH) 2 @ CDs are three-dimensional radial cobalt hydroxide particles modified by carbon quantum dots; and step S3: coupling particle Co (OH) 2 And mixing the @ CDs with the electrorheological fluid continuous phase to obtain the electrorheological material based on the functionalized carbon quantum dots. The nano particles based on the functionalized carbon quantum dots are used as the disperse phase of the ERF, so that the high-performance electrorheological material is prepared by a simple process.
Description
Technical Field
The invention relates to the technical field of electrorheological materials, in particular to a preparation method of an electrorheological material based on a functionalized carbon quantum dot and the electrorheological material.
Background
Electrorheological fluid (ERF) materials have been applied in the fields of microfluidics, dampers, actuators, soft robots, brakes, damping systems, human muscles, etc. due to their advantages of low energy consumption, fast response speed, etc. However, since the electrorheological fluid is a suspension composed of micro-nano particles (dispersed phase) and an insulating continuous phase (continuous phase), and belongs to a metastable fluid in thermodynamics, the stability, the temperature application range, the high zero field viscosity, the sustainability and the safety of the material and the like of the electrorheological fluid still need to be improved, and especially the problem of poor anti-settling stability limits the practical application of the electrorheological fluid. In addition, for the electrorheological fluid with higher yield strength, a certain amount of polar molecules are contained in the dispersed phase, so that the electrorheological fluid has poor thermal stability and low safety.
Currently, the solid materials selected as the dispersed phase of ERF include mainly inorganic non-metallic, conductive organic and polymeric semiconductor materials. Wherein, the inorganic non-metallic material has good electrorheological effect, but because of the movement of metal cations, the current density of the ERF is relatively high, thereby reducing the safety of the ERF; meanwhile, most of the inorganic materials have higher hardness, so that the devices are greatly damaged; in addition, the density of particles prepared by the material is high, and the prepared ERF has poor sedimentation resistance stability. Compared with inorganic non-metallic materials, conductive organic materials and polymers are easier to disperse in a continuous phase, and ERF with very low apparent viscosity is obtained, but the electrorheological effect of the ERF is relatively weak. Meanwhile, the polymer type ERF particles are easy to agglomerate, so that the current density is relatively high and the dispersion stability is poor.
Therefore, it is becoming increasingly urgent to develop electrorheological fluid materials having high electrorheological efficiency, low zero-field viscosity, low current density, high anti-settling stability, and thermal stability.
Disclosure of Invention
The core-shell structure is the most representative ERF dispersed phase structure, and the ERF generally has higher electrorheological effect, excellent particle dispersibility and anti-settling property. The dielectric properties of core materials of core-shell structure directly influence the electrorheological effect of the corresponding ERF, so materials with high dielectric constants are usually chosen as the core of the particles. However, the synthesis process of the core-shell particles is complex and is not suitable for industrial large-scale production, and the nanoparticles are easy to agglomerate and separate from each other, which causes the stability to be reduced. The invention develops a nano particle based on a functionalized carbon quantum dot as a dispersion phase of ERF, thereby realizing the preparation of the electrorheological material with high performance by a simple process. Carbon quantum dots (CDs) exhibit good semiconductor properties, good stability and low toxicity, and have wide applications in the fields of electrocatalysis, photocatalysis, bioimaging, DNA structure conversion, and the like. The carbon quantum dots are coupled with the cobalt hydroxide nanowires to generate the three-dimensional radial cobalt hydroxide electrorheological particles modified by the carbon quantum dots, so that the novel high-performance electrorheological material is obtained.
The invention aims to provide a preparation method of an electrorheological material based on a functionalized carbon quantum dot, which comprises the following steps:
step S1: synthesizing functionalized carbon quantum dots CDs;
step S2: preparation of Co (OH) 2 @ CDs particles comprising the steps of:
s21: cobalt chloride hexahydrate, urea and deionized water are mixed according to a mass ratio of 1:0.25: (25-30) uniformly mixing to obtain a mixed solution A; according to the weight ratio of cobalt chloride hexahydrate to carbon quantum dots (CDs) of 1: (0.014-0.07), adding the carbon quantum dots CDs into the mixed solution A, and uniformly mixing to obtain a mixed solution B;
s22: adding the mixed solution B into a high-pressure reactor, keeping the temperature at 80-120 ℃ for several hours, and then cooling to room temperature;
s23: taking out the reaction product, centrifuging, and cleaningDrying to obtain coupled particles Co (OH) 2 @ CDs, the coupling particle Co (OH) 2 @ CDs are three-dimensional radial cobalt hydroxide particles modified by carbon quantum dots;
and step S3: coupling the particles Co (OH) 2 And mixing the @ CDs with the electrorheological fluid continuous phase to obtain the electrorheological material based on the functionalized carbon quantum dots.
Further, in the step S1, a hydrothermal method is adopted to synthesize the functionalized carbon quantum dots CDs, which includes the following steps:
s11: dissolving citric acid in deionized water to obtain 0.45-0.55mol/L citric acid solution;
s12: according to the molar ratio of 1:1, adding an ethylenediamine solution into the citric acid solution to obtain a mixed solution C;
s13: adding the mixed solution C into a high-pressure reactor, keeping the temperature at 180-220 ℃ for several hours, and then cooling to room temperature;
s14: and taking out the reaction product, and carrying out centrifugation, dialysis and freeze drying treatment at the temperature of minus 50-minus 70 ℃ for 24-60 hours to obtain the functionalized carbon quantum dots (CDs).
Further, in step S2, with the increase of the adding amount of the functionalized carbon quantum dots CDs, the prepared coupling particles Co (OH) 2 The microstructure of @ CDs is changed from dumbbell-shaped nano beams to incomplete radial nano beams to complete radial nano beams, wherein the cobalt hydroxide is in a nano-wire shape, and the functionalized carbon quantum dots CDs are in a nano-size and are uniformly coupled on the surface of the cobalt hydroxide nano-wire.
Further, when the coupling particles Co (OH) 2 When the content of the carbon quantum dots CDs in the @ CDs reaches 2.5-5.5 mass percent, the prepared coupling particle Co (OH) 2 The micro-morphology of @ CDs is incomplete radial nanobeams; when the coupling particles Co (OH) 2 When the content of the carbon quantum dots CDs in the @ CDs reaches 5.5-7.5 mass percent, the prepared coupling particle Co (OH) 2 The microtopography of @ CDs is a completely radial nanobeam.
Further, as the addition amount of the functionalized carbon quantum dots CDs is increased, the electrorheological effect of the prepared electrorheological material is enhanced, the apparent viscosity is reduced, the wettability between the coupling particles and the continuous phase of the electrorheological fluid is enhanced, and the shear stress of the electrorheological material is not reduced along with the increase of the shear rate.
An object of an embodiment of the present invention is to provide an electrorheological material based on functionalized carbon quantum dots, including: a dispersed phase of coupled particles Co (OH) 2 @ CDs, the coupling particle Co (OH) 2 @ CDs are three-dimensional radial cobalt hydroxide particles modified by carbon quantum dots; a continuous phase, the continuous phase being an insulating liquid; the dispersed phase is uniformly dispersed in the continuous phase to form a suspension.
Further, the cobalt hydroxide Co (OH) 2 The functionalized carbon quantum dots CDs are in a nanowire shape, have a nanometer size and are uniformly coupled on the surface of the cobalt hydroxide nanowire.
Further, as the content of the functionalized carbon quantum dots CDs in the dispersed phase increases, the coupling particles Co (OH) 2 The micro-morphology of @ CDs gradually changes from dumbbell-shaped nanobeams to incompletely radial nanobeams to completely radial nanobeams.
Further, when the coupling particles Co (OH) 2 When the content of the carbon quantum dots CDs in the @ CDs reaches 2.5-5.5 mass percent, the coupling particles Co (OH) 2 The micro-morphology of @ CDs is incomplete radial nanobeams; when the coupling particles Co (OH) 2 When the content of the carbon quantum dots CDs in the @ CDs reaches 5.5-7.5 mass percent, the coupling particles Co (OH) 2 The microtopography of @ CDs is a completely radial nanobeam.
Further, as the content of the functionalized carbon quantum dots CDs in the dispersed phase increases, the electrorheological effect of the electrorheological material increases, the apparent viscosity decreases, and the wettability between the dispersed phase and the continuous phase increases, and the shear stress of the electrorheological material does not decrease with the increase of the shear rate.
Compared with the prior art, the embodiment of the invention has the following advantages:
1. the cobalt hydroxide nanowire is used as a carrier, the surface of the cobalt hydroxide nanowire is modified by the surface functionalized carbon quantum dots, the carbon quantum dot modified three-dimensional radial cobalt hydroxide electrorheological particles are prepared by a simple hydrothermal method, the preparation process is simple, and the cost is low.
2. The surface of the carbon quantum dot is rich in functional groups such as C = O, N-H, C-NH-C and the like, and has good solution dispersibility and compatibility with other functional materials, so that the carbon quantum dot can be coupled with the cobalt hydroxide nanowire, and the generated nanoparticle has good dispersibility and is suitable for a dispersed phase of ERF.
3. Unlike the conventional polar molecular type ERF, the semiconductor properties of the functionalized carbon quantum dots enable the generation of coupled particles Co (OH) 2 @ CDs has excellent electrorheological effect and lower current density, and the electrorheological efficiency can be as high as 10000 (i.e. the ratio of the yield strength of an applied electric field to the yield strength of no applied electric field). The higher the content of CDs in the dispersed phase particles, the greater the dielectric constant of the corresponding ERF, showing a higher yield strength. This is mainly due to the good semiconductor properties of nano-CDs, which can generate large dipole moment under the action of external electric field, and thus Co (OH) 2 The @ CDs particles can generate dipole moment under the condition of applied electric field, and the high local electric field between adjacent particles is also favorable for generating larger dipole moment on the electrorheological particles, so that larger interaction force can be generated between the particles. With the increase of the intensity of the external electric field, the strong electrostatic interaction between the electrorheological particles can be enhanced, a firmer and stronger fiber structure is formed, and higher yield strength is expressed to the outside.
4. The oleophylic group on the surface of the functionalized carbon quantum dot and the three-dimensional radial cobalt hydroxide particle structure. That is, on one hand, since the surface of the carbon quantum dot has a large number of functional groups (e.g., -NH bond and-C-NH-C bond), they can form weak hydrogen bonds with the continuous phase siloxane to improve wettability; on the other hand, the addition of the carbon quantum dots changes the shape of the nanowire-shaped cobalt hydroxide particles into the shape of radial nanowires, and Co (OH) 2 Nanowire phase ratio, radial Co (OH) 2 The @ CDs nanowire particles have larger specific surface area, so that the dispersed phase formed after the coupling of the cobalt hydroxide particles and the surface functionalized carbon quantum dots and the continuous phase have good wettability, and the electro-rheological material based on the functionalized carbon quantum dots has excellent anti-settling performance, good thermal stability, low zero field viscosity and higher safety.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention.
FIG. 1 shows Co (OH) in an embodiment of the present invention 2 Nanowire and three coupled particles of Co (OH) with different CDs content 2 SEM image of @ CDs, where (a) Co (OH) 2 SEM image of nanowires, (b) Co (OH) 2 SEM images of @ CDs-20 dumbbell-shaped particles; (c) Co (OH) 2 SEM picture of incompletely radial particles @ CDs-50; (d) Co (OH) 2 @ CDs-100 SEM image of fully radial particles;
FIG. 2 shows Co (OH) 2 @ CDs-100 TEM images of fully radial particles at different magnifications;
FIG. 3 shows Co (OH) 2 The EDS overlay image and element mapping image of the @ CDs-100 particle, where (a) and (b) are Co (OH) 2 EDS overlay images of @ CDs-100 particles, (c) Co (OH) 2 Carbon element mapping image of the @ CDs-100 particles, (d) Co (OH) 2 Cobalt elemental mapping image of the @ CDs-100 particles, (e) Co (OH) 2 Oxygen element mapping image of @ CDs-100 particles, (f) Co (OH) 2 The nitrogen element map image of the @ CDs-100 particles;
FIG. 4 shows Co (OH) 2 、Co(OH) 2 @CDs、Co(OH) 2 @CDs-20、Co(OH) 2 @CDs-50、Co(OH) 2 The XRD patterns of @ CDs-100 and CDs;
FIG. 5 shows Co (OH) 2 、Co(OH) 2 @CDs-20、Co(OH) 2 @CDs-50、Co(OH) 2 The TG curves of @ CDs-100 and pure CDs materials, and Co (OH) 2 @CDs-20、Co(OH) 2 @ CDs-50 and Co (OH) 2 Carbon quantum dots in @ CDs-100The content;
FIG. 6 shows Co (OH) 2 The yield strength test result chart of the @ CDs electrorheological fluid is shown in the specification, wherein (a) the mass fractions of the dispersed phases of Co (OH) are respectively 20%, 30% and 40% 2 Yield strength (Yield stress) of the @ CDs-100 electrorheological fluid under different strength external Electric field strengths (Electric fields); (b) Co (OH) with the mass fraction of dispersed phase being 40 percent 2 Suspension, co (OH) 2 @ CDs-50 and Co (OH) 2 @ CDs-100 electrorheological fluid has yield strength under electric fields with different strengths;
FIG. 7 (a) shows Co (OH) 2 、Co(OH) 2 @CDs-20、Co(OH) 2 @CDs-50、Co(OH) 2 The contact angle of the @ CDs-100 particles with dimethicone; FIG. 7 (b) shows Co (OH) 2 And Co (OH) 2 N of @ CDs-100 particles 2 Adsorption isotherm;
FIG. 8Co (OH) 2 Colloid (left) and Co (OH) 2 @ CDs-100 electrorheological fluid (right) real object photo;
FIG. 9 shows Co (OH) with a dispersed phase mass fraction of 40% 2 The curve of the dynamic shear stress of the @ CDs-100 electrorheological fluid under the electric field intensity of 0,1,2,3kV/mm along with the change of the shear rate;
FIG. 10 shows 20% by mass of Co (OH) in the dispersed phase 2 @ CDs-100 electrorheological fluid and Co (OH) 2 The change curve of the anti-settling rate of the @ CDs-50 electrorheological fluid along with time and the macroscopic settling condition of the sample after 30 days of testing;
FIG. 11 (a) shows the yield strength of Co (OH) 2@ CDs-100 electrorheological fluid with dispersed phase mass fraction of 40% at different temperatures with applied electric field strength of 5kV/mm, and (b) shows the yield strength of Co (OH) with different mass fractions with different applied electric field strengths 2 @ CDs-100 electrorheological fluid.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, it will be appreciated by those of ordinary skill in the art that numerous technical details are set forth in order to provide a better understanding of the present application in various embodiments of the present invention. However, the technical solution claimed in the present application can be implemented without these technical details and various changes and modifications based on the following embodiments. The following embodiments are divided for convenience of description, and should not constitute any limitation to the specific implementation manner of the present invention, and the embodiments may be mutually incorporated and referred to without contradiction.
Example 1
The embodiment of the invention provides a preparation method of an electrorheological material based on functionalized carbon quantum dots. The method comprises the following steps: step S1 is the synthesis of functionalized carbon quantum dots (CDs); step S2 is Co (OH) 2 Synthesis of @ CDs electrorheological particles; step S3 is Co (OH) 2 The preparation of @ CDs-ERF electrorheological fluid material.
Step S1: synthesis of functionalized carbon quantum dots (CDs)
CDs were synthesized in this example by a hydrothermal method. Firstly, 40mmol of citric acid is dissolved in 80ml of deionized water, ultrasonic stirring is carried out to ensure that the citric acid is fully dissolved, and then 2.8ml of ethylenediamine is added into the citric acid solution and fully stirred. The mixed solution was then transferred to a 200ml stainless steel autoclave lined with polytetrafluoroethylene and heated in an oven at 200 ℃ for 6 hours. And taking out the reaction product after the stainless steel autoclave is cooled to room temperature, centrifuging the reaction product to remove impurities settled at the bottom, and pouring the reaction product into a centrifugal tube to centrifuge at the rotating speed of 10000rpm (revolutions per second) for 5 minutes. The brown liquid product was then subjected to dialysis, in this example the pure water used for dialysis was replaced every two hours during dialysis, for a total duration of 48 hours. And (3) putting the dialyzed solution into a freeze dryer for freeze drying, wherein the temperature of a cold well of the freeze dryer is 50 ℃ below zero, and the drying time is 50 hours. And freeze-drying to obtain black CDs powder.
Step S2: co (OH) 2 Synthesis of current-variable particles of @ CDs
Firstly, 6mmol of cobalt chloride hexahydrate and 6mmol of urea are uniformly dispersed in 40ml of deionized water, 20mg of functionalized carbon quantum dots CDs are added into the deionized water, and then the mixed solution is transferred into a 100ml stainless steel autoclave with a polytetrafluoroethylene lining and heated in an oven at 100 ℃ for 6 hours. To be treatedAfter the stainless steel autoclave was naturally cooled to room temperature, the reaction product was transferred to a centrifugal tube and centrifuged at 10000rpm for 5 minutes. The pink powder that fell to the bottom of the centrifuge tube was then washed several times with absolute ethanol and centrifuged repeatedly. Washing, centrifuging for 3 times, filtering to obtain particles, oven drying in 80 deg.C oven for 48 hr, and completely removing water to obtain Co (OH) 2 Coupled particles of quantum dots CDs, noted Co (OH) 2 @CDs-20。
The addition amounts of the functionalized carbon quantum dots CDs are changed to be 50mg and 100mg respectively, and other preparation processes and parameters are not changed, so that the coupled particles with different CDs contents can be prepared and recorded as Co (OH) respectively 2 @ CDs-50 and Co (OH) 2 @CDs-100。
And step S3: co (OH) 2 Preparation of @ CDs electrorheological liquid
Mixing the above three kinds of Co (OH) with different CDs contents 2 The @ CDs particles are respectively mixed with an electrorheological fluid continuous phase (such as dimethyl silicone oil) according to a certain proportion, and fully ground at room temperature to prepare uniform mixed fluid or colloid. By adjusting the mass ratio of the electrorheological particles to the dimethyl silicone oil, the electrorheological fluid with the mass fraction of 10-50% can be synthesized.
Example 2
The embodiment of the invention provides an electrorheological material based on functionalized carbon quantum dots. The method comprises the following steps: a dispersed phase and a continuous phase. The dispersed phase is coupled particles Co (OH) 2 @ CDs, coupling particles Co (OH) 2 @ CDs is three-dimensional radial cobalt hydroxide Co (OH) modified by carbon quantum dots CDs 2 Particles; the continuous phase is an insulating liquid, in this example, dimethicone; the dispersed phase is dispersed homogeneously in the continuous phase to form suspension, i.e. electrorheological fluid.
Example 3
Co (OH) was prepared by adjusting the amounts of CDs added to 20mg, 50mg and 100mg, respectively, by the preparation method of example 1 2 @CDs-20、Co(OH) 2 @ CDs-50 and Co (OH) 2 @ CDs-100 three electrorheological particles with different CDs contents. The mass fraction of 40 is prepared by adjusting the mass ratio of the electrorheological particles to the dimethyl silicone oil% of Co (OH) 2 The electric rheologic liquid contains @ CDs-20/50/100 and Co (OH) 2@ CDs-100 in 20% and 30% separately. The prepared electrorheological fluid samples are subjected to property and performance tests such as particle morphology, microstructure, electrorheological property, rheological property, wettability, stability, safety and the like.
(1)Co(OH) 2 And Co (OH) 2 Characterization of the morphology of the @ CDs particles
FIG. 1 shows Co (OH) according to an embodiment of the present invention 2 Nanowire and three coupled particles of Co (OH) with different CDs content 2 SEM (scanning Electron microscope) image of @ CDs. Co (OH) prepared without addition of CDs 2 A fibrous structure is present as shown in fig. 1 (a). Co (OH) prepared when the amount of CDs added during the preparation was 20mg 2 The @ CDs-20 particles are dumbbell-shaped, as shown in FIG. 1 (b). When the amount of CDs added is 50mg, incomplete radial morphology particles are obtained, and the particle size is about 10 μm, as shown in FIG. 1 (c). Co (OH) prepared when the amount of CDs added was increased to 100mg 2 The @ CDs-100 particle has a complete 3D radial geometry, as shown in FIG. 1 (D).
FIG. 2 shows Co (OH) in an embodiment of the present invention 2 @ CDs-100 particles TEM (Transmission Electron microscope) images at different magnifications. As can be seen from FIG. 2 (a), co (OH) 2 The nano wires outside the @ CDs-100 particles are uniformly fixed on the surface of the microsphere and present a three-dimensional radial shape. TEM images of the Co (OH) 2@ CDs-100 particles at larger magnification, as shown in FIGS. 2 (b) and 2 (c), clearly show the morphology of the nanowires and the good binding of CDs to the nanowires. Good binding of CDs to cobalt hydroxide is more clearly observed by FIG. 2 (d). Wherein, the cobalt hydroxide is in a nanowire shape, and CDs are uniformly distributed on the surface of the nanowire and have a nanometer size. FIG. 3 shows Co (OH) 2 The EDS overlay image and element map image of the @ CDs-100 particle. FIG. 3 shows cobalt, oxygen, carbon and nitrogen elements in Co (OH) 2 The uniform distribution of the surface of the particles of @ CDs-100, which also demonstrates the interaction of CDs with Co (OH) 2 Good bonding.
(2)Co(OH) 2 And Co (OH) 2 XRD (X-ray diffraction) and X-ray diffraction of the @ CDs particlesTG (thermogravimetric) characterization
FIG. 4 shows Co (OH) 2 、Co(OH) 2 @CDs、Co(OH) 2 @CDs-20、Co(OH) 2 @CDs-50、Co(OH) 2 The XRD patterns of @ CDs-100 and CDs. As shown in FIG. 4, co (OH) can be seen from the XRD test curve 2 And Co (OH) 2 The sharp reflection peaks for the @ CDs sample are 17.4 °, 33.4 °, 34.9 °, 36.4 °, 39.1 °, 46.5 °, 53.3 °, 55.4 ° and 61.3 °, respectively, according to Co (CO) 3 ) 0.35Cl0.20 (OH) 1.10NWs (JCPDS: 38-0547) standard card, 0.25 and 0.235nm lattice fringes due to 36.4 DEG and 39.1 DEG corresponding XRD peaks, and 0.21nm interplanar spacing due to the (100) face of CD, demonstrating Co (OH) 2 @ CDs formation of the coupling structure.
The content of CDs in the coupled particles can be estimated by TG measurements. FIG. 5 shows Co (OH) 2 、Co(OH) 2 @CDs-20、Co(OH) 2 @CDs-50、Co(OH) 2 TG curves of @ CDs-100 and pure CDs materials, and Co (OH) 2 @CDs-20、Co(OH) 2 @ CDs-50 and Co (OH) 2 The carbon quantum dot content in @ CDs-100. As shown in FIG. 5, co (OH) 2 、Co(OH) 2 @CDs-20、Co(OH) 2 @ CDs-50 and Co (OH) 2 The sharp drop in quality occurred at around 250 ℃ for both @ CDs-100, due to the removal of structural water and carbon dioxide. Co (OH) 2 @CDs-20、Co(OH) 2 @ CDs-50 and Co (OH) 2 Weight loss minus Co (OH) for @ CDs-100 2 The mass fractions after weight loss of (a) were 1.01%,2.74% and 6.09%, respectively, and were close to the addition amount of CDs.
(3)Co(OH) 2 Electro-rheological Properties of @ CDs-ERF
FIG. 6 shows Co (OH) 2 The yield strength test result chart of the @ CDs electrorheological fluid. FIG. 6 (a) shows Co (OH) 2 The relationship between the yield strength and the mass fraction of the particles of @ CDs-100-ERF, and the variation of the yield strength with the increase of the applied electric field strength. Co (OH) 2 The yield strength of @ CDs-100-ERF shows a nearly linear relationship with the electric field strength. In addition, under the action of the same external electric field intensity, co (OH) 2 The yield strength of @ CDs-100-ERF increases with increasing mass fraction of the dispersed phase. Quality of dispersed phaseCo (OH) with a fraction of 40% 2 The @ CDs-100-ERF has excellent electrorheological property, and the yield strength reaches 3kPa when the external electric field strength is 6 kV/mm. FIG. 6 (b) shows Co (OH) 2 Suspension and Co (OH) 2 @ CDs-50-ERF yield strength under different strength applied electric field conditions. Co (OH) 2 The suspension has almost no electrorheological effect under the action of an external electric field, and the yield strength value of the suspension is not changed along with the increase of the electric field strength. Co (OH) 2 The yield strength of @ CDs-50-ERF increases with increasing applied electric field strength, and the two also satisfy substantially linear relationships. But Co (OH) under the condition of an external electric field with the same strength 2 The yield strength of @ CDs-50-ERF is significantly lower than that of Co (OH) 2 @ CDs-100-ERF. Thus, as can be seen from the data in FIG. 6 (b), CDs are given Co (OH) 2 Particle Current Effect, the higher the CDs content, co (OH) 2 The better the electrorheological properties of @ CDs-ERF. This is mainly due to the good semiconductor properties of nano-CDs, which can generate larger dipole moment under the action of external electric field, and thus Co (OH) 2 The @ CDs particles can generate dipole moment under the condition of applied electric field, and the high local electric field between adjacent particles is also favorable for generating larger dipole moment on the electrorheological particles, so that larger interaction force can be generated between the particles. With the increase of the intensity of the external electric field, the strong electrostatic interaction between the electrorheological particles can be enhanced, a firmer and stronger fiber structure is formed, and higher yield strength is expressed to the outside.
By calculating the mass fraction of the dispersed phase to be 20% of Co (OH) 2 The electrorheological efficiency of @ CDs-100-ERF can be quantitatively evaluated by Co (OH) 2 @ CDs-100-ERF electrorheological Properties. Co (OH) with the mass fraction of the dispersed phase being 20 percent 2 @ CDs-100-ERF has a yield strength τ E of about 1kPa when an applied electric field having a strength of 5kV/mm is applied. The yield strength τ 0 is about 0.1Pa without the application of an electric field. The current change efficiency e is equal to 10,000 through the current change efficiency calculation formula. Compared with the electrorheological fluid of the same type and the same mass fraction, co (OH) 2 The electrorheological efficiency of @ CDs-100-ERF is highest and exceeds that of many ERFs containing polar molecules, e.g. giant electrorheological efficiencyLiquid (GERF).
(4)Co(OH) 2 Rheological Properties of @ CDs-ERF
Research Co (OH) 2 、Co(OH) 2 @CDs-20-ERF、Co(OH) 2 @CDs-520-ERF、Co(OH) 2 After the viscosity of @ CDs-100-ERF trended with shear rate, co (OH) was found to be present in greater amounts of CDs 2 The lower the apparent viscosity of @ CDs-ERF, especially Co (OH) 2 The apparent viscosity of @ CDs-100-ERF is 0.46 Pa.s, which is significantly lower than other ERFs of the same type. Co (OH) with reduced CDs content 2 @ CDs-20-ERF and Co (OH) 2 The apparent viscosity of @ CDs-50-ERF is much higher, being about 1.8 pas. And Co (OH) 2 The viscosity of the colloid hardly reached a stable value and changed greatly with the increase in shear rate, indicating that Co (OH) 2 The particles in the colloid bind poorly to the continuous phase. Co (OH) was also found 2 The viscosity of @ CDs-100-ERF leads to a stable viscosity value, which also indicates that the ERF undergoes little shear thinning.
TABLE 1 dynamic yield stress τ of different ERFs by Herschel-Bulkley rheology model fitting 0 And shear thinning coefficient (n)
(5)Co(OH) 2 Wettability of @ CDs with continuous phase
Co (OH) with increasing CDs content in the dispersed phase 2 The dynamic yield strength and apparent viscosity of @ CDs-ERF gradually decrease and the shear-thinning phenomenon weakens. Co (OH) 2 The rheological behaviour of @ CDs-ERF depends on the nature of the dispersed phase particles and the interaction between the dispersed and continuous phases. The wettability between the dispersed phase particles and the continuous phase can be directly reflected by the contact angle test. FIG. 7 (a) shows Co (OH) 2 、Co(OH) 2 @CDs-20、Co(OH) 2 @CDs-50、Co(OH) 2 The contact angle of the @ CDs-100 particles with dimethicone; FIG. 7 (b) shows Co (OH) 2 And Co (OH) 2 N of @ CDs-100 particles 2 Adsorption isotherms. As shown in FIG. 7 (a), co (OH) 2 The contact angle between the particles of @ CDs-100 and silicone oil is only 11.01 DEG, and the contact angle is changed along with Co (OH) 2 The increasing content of CDs in the @ CDs particles, the contact angle gradually decreased. Indicating that CDs in the dispersed phase is beneficial in increasing the wettability between the dispersed phase particles and the continuous phase. The improvement of wettability has positive effects on improving the dynamic yield strength and apparent viscosity of ERF and improving the shear thinning performance. The main reasons for the improved wettability of particles by CDs are two: co (OH) 2 The CDs surfaces in the @ CDs particles have a large number of-NH and-C-NH-C bonds that can form weak hydrogen bonds with the continuous phase siloxane to improve wettability; in addition, with Co (OH) 2 Nanowire phase contrast, radial Co (OH) 2 The @ CDs-100 nanowire particles have a larger specific surface area, while the large specific surface area of the dispersed phase is advantageous for improving the wettability between the dispersed phase and the continuous phase. Therefore, the CDs in the dispersed phase have a large number of multifunctional groups, so that the wettability of the electrorheological particles is improved, and the appearance of the electrorheological particles can be changed by adding the CDs, so that the particles have larger specific surface area, and the electrorheological fluid has better rheological property. As a result, co (OH) containing no carbon quantum dots 2 The colloid is clay-shaped, and the fluid property is in accordance with the characteristics of Bingham fluid, but the content of Co (OH) in CDs is higher 2 @ CDs-100-ERF has significant fluidity, exhibiting Newtonian fluid behavior, as shown in FIG. 8.
(6)Co(OH) 2 @ CDs-ERF dynamic shear stress stability
Co(OH) 2 The @ CDs particles have good wetting with the continuous phase, which also has a positive effect on the dynamic shear stress stability of the ERF. The dynamic shear stress stability of the ERF refers to the fluctuation condition of the shear stress of the ERF after an external electric field is applied under the condition of higher shear rate, and if the shear stress can not be reduced along with the change of the shear rate, the ERF has good dynamic shear stress stability. Dynamic shear stress is dominated by electrostatic interactions induced by electric fields and hydrodynamic interactions induced by shear fields. Under high shear rate conditions, the hydrodynamic interaction is enhanced and the electrostatic interaction is gradually overcome, the electrorheological particles extend along the direction of the electric fieldThe arranged chain-like structures are broken and when the rate of breakage is greater than the rate of recombination, the shear stress is reduced. In addition, as the shear rate is increased in the test process, the dispersed phase can migrate to the outer edge of the electrode under the action of centrifugal force, so that the two phases of the dispersed phase and the continuous phase are separated, the electro-rheological effect is weakened, and the shear stress is reduced. The dynamic shear stress of most ERFs therefore decreases with increasing shear rate, which is detrimental to practical applications of ERFs.
As shown in FIG. 9, the dispersed phase mass fraction was 40% of Co (OH) 2 @ CDs-100-ERF exhibits excellent dynamic shear stress stability under applied electric fields of strengths 1,2 and 3 kV/mm. Co (OH) when the applied electric field strength is 3kV/mm 2 The dynamic shear stress of @ CDs-100-ERF can be stabilized substantially at around 300Pa, and the shear stress does not decrease with increasing shear rate. This is mainly due to Co (OH) 2 The @ CDs-100 particles have good wetting to the continuous phase and the dimethylsilicone oil can be tightly wrapped around the particles, making it less prone to two-phase separation even at higher shear rates. Meanwhile, since Co (OH) 2 The @ CDs-100-ERF has high dielectric constant, and can generate large electrostatic force action among particles under the condition of applying an external electric field, so that the formed chain structure is not easy to damage. And the bionic radial structure has a larger specific surface area, so that the contact area among particles is increased, and polarization enhancement is facilitated. In addition, due to the shape structure of the bionic radial particles, the radial particles are tightly gathered together under an external electric field, and the bionic radial particles have strong inter-particle friction and mechanical cohesion and form a firm chain-shaped structure.
(7)Co(OH) 2 Stability and safety of @ CDs-ERF
Because the ERF is a suspension liquid and a solid-liquid interface exists between a dispersed phase and a continuous phase, the ERF is unstable in thermodynamics and belongs to a metastable system. Therefore, the electrorheological particles are easy to agglomerate, thereby causing the weakening of ERF electrorheological effect, and even causing the phenomena of solid-liquid separation and hardening at the bottom when the agglomeration is serious. In addition, the density mismatch between the dispersed phase particles and the continuous phase can cause sedimentation, which leads to poor stability of the ERF, and is not beneficial to the practical application of the ERF. Therefore, the high anti-settling stability is an important index for evaluating the high-performance ERF. The macroscopic anti-settling rate method is often used to evaluate the rank of the ERF stability performance and is calculated by the formula shown in FIG. 10. The lower the height of the clear liquid portion, the more excellent the settling resistance of the sample.
In a 30-day standing test, the mass fraction of Co (OH) in the dispersed phase was found to be 20% 2 @ CDs-100-ERF has excellent anti-settling properties. The sample still maintained the anti-settling rate above 90% after 30 days of testing, as shown in figure 10. And Co (OH) 2 The anti-settling performance of @ CDs-50-ERF is slightly inferior to that of Co (OH) 2 @ CDs-100-ERF, which showed about 85% sedimentation resistance after 30 days of testing. It can also be seen from the time-dependent curve of the anti-settling rate of the sample that the rapid settling time of the two ERFs was 5 days before the test, and the samples were substantially in a stable state after that, and the tendency of the anti-settling rate decreasing with time became very slow.
The test characterizes Co (OH) 2 Thermal stability and safety of @ CDs-100-ERF. The thermal stability is characterized by the testing of Co (OH) over a temperature range of 20 ℃ to 100 ℃ 2 @ CDs-100-ERF yield strength at an applied electric field strength of 5kV/mm, as shown in FIG. 11 (a). Co (OH) 2 The yield strength of @ CDs-100-ERF at various temperatures was substantially stabilized at 2kPa, with no decrease occurring with increasing test temperature. Co (OH) compared to the apparent fluctuation in yield strength of ERF containing polar molecules when tested at high temperature 2 The thermal stability of @ CDs-100-ERF was more excellent. This is mainly because polar molecules on the surface of polar molecule type ERF particles are desorbed or decomposed with the temperature rise, thereby causing the attenuation of the electrorheological effect, and the macroscopic performance is expressed as yield strength fluctuation. From the thermogravimetric data, co (OH) 2 @ CDs particles in place of polar molecules CDs are less affected by temperature, and therefore Co (OH) 2 @ CDs-100-ERF has excellent thermal stability.
Furthermore, co (OH) 2 The @ CDs coupled particles not only have excellent thermal stability, but also have extremely high current density under a direct current fieldLow, with a lower risk of breakdown. As shown in FIG. 11 (b), co (OH) of different mass fractions of dispersed phase 2 @ CDs-100-ERF has a current density that increases with increasing applied DC field strength and, under the same field conditions, increases with increasing mass fraction of ERF. But even under a DC electric field of 6kV/mm, the mass fraction of Co (OH) is 40% 2 The current density of @ CDs-100-ERF is also only 0.33. Mu.A/cm 2 . Thus, co (OH) 2 @ CDs-100-ERF has better safety.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (9)
1. A preparation method of an electrorheological material based on carbon quantum dots is characterized by comprising the following steps:
step S1: the method for synthesizing the carbon quantum dots CDs comprises the following steps:
s11: dissolving citric acid in deionized water to obtain 0.45-0.55mol/L citric acid solution;
s12: according to the molar ratio of 1:1, adding an ethylenediamine solution into the citric acid solution to obtain a mixed solution C;
s13: adding the mixed solution C into a high-pressure reactor, keeping the temperature at 180-220 ℃ for several hours, and then cooling to room temperature;
s14: taking out the reaction product, and carrying out centrifugation, dialysis and freeze drying treatment at the temperature of minus 50-minus 70 ℃ for 24-60 hours to obtain the carbon quantum dots CDs;
step S2: preparation of Co (OH) 2 @ CDs particles comprising the steps of:
s21: cobalt chloride hexahydrate, urea and deionized water are mixed according to the mass ratio of 1:0.25: (25-30) uniformly mixing to obtain a mixed solution A; according to the weight ratio of cobalt chloride hexahydrate to carbon quantum dots CDs of 1: (0.014-0.07), adding the carbon quantum dots CDs into the mixed solution A, and uniformly mixing to obtain a mixed solution B;
s22: adding the mixed solution B into a high-pressure reactor, keeping the temperature at 80-120 ℃ for several hours, and then cooling to room temperature;
s23: taking out the reaction product, centrifuging, cleaning and drying to obtain coupled particles Co (OH) 2 @ CDs, the coupling particle Co (OH) 2 @ CDs are three-dimensional radial cobalt hydroxide particles modified by carbon quantum dots;
and step S3: coupling the particles Co (OH) 2 And mixing the @ CDs with the electrorheological fluid continuous phase to obtain the electrorheological material based on the carbon quantum dots.
2. The method for preparing an electrorheological material based on carbon quantum dots according to claim 1, wherein in step S2, the coupling particles Co (OH) are prepared with the increase of the addition amount of the carbon quantum dots CDs 2 The microstructure of the @ CDs is changed from dumbbell-shaped nano beams to incomplete radial nano beams gradually until the complete radial nano beams, wherein the cobalt hydroxide is in a nano-wire shape, and the carbon quantum dots CDs are in nano-size and are uniformly coupled on the surface of the cobalt hydroxide nano-wires.
3. The method for preparing an electrorheological material based on carbon quantum dots according to claim 2,
when the coupling particle Co (OH) 2 When the content of the carbon quantum dots CDs in the @ CDs reaches 2.5-5.5 mass percent, the prepared coupling particle Co (OH) 2 The micro-morphology of @ CDs is incomplete radial nanobeams;
when the coupling particles Co (OH) 2 When the content of the carbon quantum dots CDs in the @ CDs reaches 5.5-7.5 mass percent, the prepared coupling particle Co (OH) 2 The microtopography of @ CDs is a completely radial nanobeam.
4. The method for preparing an electrorheological material based on carbon quantum dots according to claim 1, wherein the prepared electrorheological material has an enhanced electrorheological effect and a reduced apparent viscosity as the addition amount of the carbon quantum dots CDs increases, and the wettability between the coupling particles and the continuous phase of the electrorheological fluid increases, and the shear stress of the electrorheological material does not decrease as the shear rate increases.
5. The carbon quantum dot-based electrorheological material prepared by the preparation method of the carbon quantum dot-based electrorheological material according to any one of claims 1 to 4, which is characterized by comprising the following steps of:
a dispersed phase of the coupled particles Co (OH) 2 @ CDs, the coupling particle Co (OH) 2 @ CDs are three-dimensional radial cobalt hydroxide particles modified by carbon quantum dots;
a continuous phase, the continuous phase being an insulating liquid;
the dispersed phase is uniformly dispersed in the continuous phase to form a suspension.
6. The carbon quantum dot-based electrorheological material of claim 5, wherein the cobalt hydroxide Co (OH) 2 The carbon quantum dots CDs are in a nanowire shape, are in a nanometer size and are uniformly coupled on the surface of the cobalt hydroxide nanowire.
7. The carbon quantum dot-based electrorheological material of claim 6, wherein the coupling particles Co (OH) increase with an increase in the content of the carbon quantum dots CDs in the dispersed phase 2 The micro-morphology of @ CDs gradually changes from dumbbell-shaped nanobeams to incompletely radial nanobeams to completely radial nanobeams.
8. The carbon quantum dot-based electrorheological material of claim 7,
when the coupling particle Co (OH) 2 When the content of the carbon quantum dots CDs in the @ CDs reaches 2.5-5.5% by mass, the coupling particles Co (OH) 2 The micro-morphology of @ CDs is incomplete radial nanobeams;
when said coupling is effectedParticle Co (OH) 2 When the content of the carbon quantum dots CDs in the @ CDs reaches 5.5-7.5 mass percent, the coupling particles Co (OH) 2 The microtopography of @ CDs is a fully radial nanobeam.
9. The carbon quantum dot-based electrorheological material of claim 5, wherein as the content of the carbon quantum dot CDs in the dispersed phase increases, an electrorheological effect of the electrorheological material increases, an apparent viscosity decreases, wettability between the dispersed phase and the continuous phase increases, and a shear stress of the electrorheological material does not decrease with an increase in a shear rate.
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