A ferroelectric material capable of continuously generating recoverable pseudo plastic deformation and a method for preparing the same

Abstract

The application discloses a ferroelectric material capable of continuously generating recoverable pseudo plastic deformation and a preparation method thereof, and the method comprises the following steps: mixing a ferroelectric polymer and N,N-dimethylformamide (DMF), stirring, pouring on a plate, drying, heat treatment, and obtaining a film; cutting the film into a strip and performing a "programming" process; after the "programming" is completed, a recovery process is performed: firstly, the temperature of the film is raised, and it can be observed that the shape of the film is gradually recovered to the initial shape through rising to different temperatures from a complex shape. The application provides a ferroelectric polymer capable of continuously generating recoverable pseudo plastic deformation under temperature regulation, and the preparation operability is high and the process is relatively simple; the shape of the ferroelectric polymer is regulated in a one-way heating process, and is expected to be applied to some switches which need to be opened in two or N sections or some places which need to release substances step by step.

Description

Technical Field

[0001] This invention belongs to the field of functional materials application, and mainly relates to a ferroelectric material that can continuously generate recoverable pseudo-plastic deformation and its preparation method. Background Technology

[0002] Shape memory materials have potential applications in many fields, such as sensors, artificial muscles, and soft robots, due to their ability to change shape in response to external stimuli. Polymers, with their high flexibility and ease of processing, have a wider range of applications compared to shape memory alloys and ceramics. In recent decades, the triggering mechanisms of shape memory polymers have been extensively studied, including thermal triggering, optical triggering, and electrical triggering, with thermal triggering being the most common: its triggering temperature is typically the polymer's glass transition temperature or melting point.

[0003] However, recent studies have shown that the ferroelectric phase transition of ferroelectric polymers can also achieve shape memory effects. For example, in patent CN114369270B, P(VDF-TrFE) ferroelectric polymers are heated to the Curie temperature T. C Above, apply external force for a period of time (or continue to apply external force during the heating process), then cool down, and under the action of external stress, pass through the Curie temperature T. C Upon cooling from a high temperature, the transformation from the paraelectric phase to the ferroelectric phase involves relatively significant deformation. This is partly due to the differences in lattice parameters and crystal structures between the ferroelectric and paraelectric phases, and partly because the ferroelectric phase possesses several equivalent orientations, some of which preferentially form under stress. Therefore, stress-induced orientation of the ferroelectric phase occurs during its formation at T0. C Even after stress is removed (after the formation of the ferroelectric phase), the preferred orientation can still be maintained.

[0004] However, this shape memory effect can usually only remember one shape at a time. If ferroelectric polymers can remember two or more shapes during deformation, that is, the shape can be controlled during use, its applications may become more diversified. Summary of the Invention

[0005] This invention discloses a ferroelectric material capable of continuously generating recoverable pseudo-plastic deformation and its preparation method. A third component, such as CFE or CTFE, is introduced into a P(VDF-TrFE) copolymer with a primary ferroelectric-paraelectric phase transition to form trimers or even tetramers. This is equivalent to introducing defective units, which disrupts the long-range ferroelectric order of the copolymer, causing it to exhibit a certain degree of relaxation. This results in a wide phase transition temperature range for the ferroelectric polymer, i.e., a dispersed phase transition occurs. Within this wide phase transition temperature range, the orientation of the crystal phase gradually changes, thus enabling the memorization of multiple shapes during the process. The shape recovery can be controlled by adjusting the triggering conditions, thereby achieving the effect of continuous material deformation.

[0006] The present invention adopts the following technical solution:

[0007] Ferroelectric polymer films with dispersed phase transitions were prepared using solution casting. A "programming" process followed: a certain external stress was applied to the initially shaped relaxor ferroelectric polymer film, causing deformation, denoted as shape 1. While maintaining this stress, the temperature was increased, with the highest temperature exceeding the highest value of the phase transition temperature range from low-symmetry to high-symmetry phases (ferroelectric phase to paraelectric phase), denoted as temperature T1. The film was then cooled to a temperature within the phase transition temperature range (designated as near the peak dielectric constant temperature, denoted as temperature T2), held for a period, and then the external force was removed. At this point, the film shape was very close to shape 1. Subsequently, the external force conditions were changed at this temperature, causing deformation to shape 2. While maintaining this stress, the film was further cooled to a temperature below the lowest value of the phase transition temperature range, denoted as temperature T3. After holding this temperature for a period, the external force was removed, and the film shape was again very close to shape 2. After the "programming" is completed, the recovery process is carried out: First, the temperature of the film is raised to T2, and the shape of the film can be observed to change from shape 2 to shape 1. Then, the temperature is raised to T1, and the shape of the film is restored to the initial shape.

[0008] A method for preparing ferroelectric materials capable of continuously generating recoverable pseudo-plastic deformation includes the following steps:

[0009] (1) Mix the relaxor ferroelectric polymer and organic solvent, stir, pour onto a plate, dry to evaporate the solvent, then remove the film from the plate and vacuum heat treat to obtain the sample film;

[0010] (2) Cut the sample film into strips, which is the original shape. Then, perform the "programming" process: apply external stress to the strip sample film to deform it and form the first shape. While maintaining this stress, raise the temperature or apply external stress at a high temperature. Hold the temperature for the first time, then lower the temperature, hold the temperature for the second time, and then remove the external force. At this time, the film shape is fixed as the first shape. Then change the external force conditions to deform and fix the film into the second shape. Hold the temperature for the third time at different temperatures, then lower the temperature, hold the temperature for the fourth time, and then remove the external force. At this time, the film shape is fixed as the second shape. Preferably, by operating in the same steps, the material can "memorize" N shapes while controlling the holding temperature.

[0011] (3) After completing the “programming”, the recovery process is carried out: First, the temperature of the film is raised, and the shape of the film can be observed to change from the second shape to the first shape. Then, the temperature is raised again, and the shape of the film is restored from the first shape to the initial shape (i.e., strip). Preferably, the same process is used to control the recovery of the film from the Nth shape to the initial shape.

[0012] Furthermore, the ferroelectric polymer is P(VDF-TrFE-CTFE) powder or P(VDF-TrFE-CFE) powder.

[0013] Furthermore, in step (1), the organic solvent is N,N-dimethylformamide (DMF).

[0014] Further, in step (2), an external force (above 0.01N) is applied to the strip-shaped thin film sample to deform it into a first shape. Under the condition of maintaining this stress, the temperature is raised to above the dielectric peak temperature T1 and held for more than 1 second. Then, the temperature is lowered to below the dielectric peak temperature T2 and held for more than 1 second. The external force is then removed, and the shape of the thin film is fixed as the first shape. Then, the external force conditions are changed at this temperature to deform the thin film into a second shape, which is recorded as the second shape. After holding for more than 1 second, the temperature is lowered to room temperature, and after holding for more than 1 second, the external force is removed. At this time, the shape of the thin film is the second shape. Preferably, by performing the same steps, the material can "memorize" N shapes while controlling the heat preservation temperature.

[0015] Further, in step (3), after completing the "programming", the recovery process is carried out: first, the temperature of the film is raised to T2, and it can be observed that the shape of the film changes from the second shape to the first shape. Then, the temperature is raised to T1, and the shape of the film is restored from the first shape to the initial shape. Preferably, the same process is used to control the recovery of the film from the Nth shape to the initial shape.

[0016] Furthermore, the first shape is a "√" shape, and the second shape is an "N" shape.

[0017] Ferroelectric materials capable of recovering pseudoplastic deformation are prepared by the method described in any of the preceding methods.

[0018] Advantages and positive effects:

[0019] The ferroelectric polymer with diffuse phase transition that can continuously generate recoverable pseudoplastic deformation described in this invention has the following advantages: (1) It proposes a ferroelectric polymer that can continuously generate recoverable pseudoplastic deformation under temperature control, which is highly operable and relatively simple in preparation; (2) It realizes the control of the shape of the ferroelectric polymer in a unidirectional heating process (direct heating or indirect heating such as light or electricity), which is expected to be applied to some switches that need to be opened in two or N stages or places that need to release substances gradually. Attached Figure Description

[0020] Figure 1 Dielectric temperature spectrum of ferroelectric polymer P(VDF-TrFE-CTFE);

[0021] Figure 2 The results of fitting the dielectric temperature spectrum of the ferroelectric polymer P(VDF-TrFE-CTFE) using the Curie-Weiss law yielded γ = 1.66034, which is close to 2.

[0022] Figure 3 The shape fixation-recovery process of relaxor ferroelectric polymer P (VDF-TrFE-CTFE) at 80℃-45℃-20℃;

[0023] Figure 4 The shape fixation-recovery process of relaxor ferroelectric polymer P (VDF-TrFE-CTFE) at 80℃-55℃-20℃;

[0024] Figure 5 The shape fixation-recovery process of relaxor ferroelectric polymer P (VDF-TrFE-CFE) at 80℃-25℃-0℃. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0026] The present invention proposes a ferroelectric polymer with a dispersed phase transition obtained by introducing other units into the ferroelectric copolymer P(VDF-TrFE), which can achieve continuous and recoverable pseudoplastic deformation. Here, the present invention uses P(VDF-TrFE-CTFE) and P(VDF-TrFE-CFE) as examples to illustrate the feasibility.

[0027] The temperature dependence of the dielectric constant of P(VDF-TrFE-CTFE) is as follows: Figure 1 As shown, the phase transition temperature range is approximately 30℃ to 70℃. The results of linear fitting using the Curie-Weiss formula are as follows: Figure 2 As shown, the value of γ is 1.66034, which is close to 2. According to the Curie-Weiss law, P(VDF-TrFE-CTFE) has a certain degree of relaxation.

[0028] Example 1: P(VDF-TrFE-CTFE) (Chinese name: poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene)) film sample was prepared by solution casting: 0.4 g of P(VDF-TrFE-CTFE) powder (molar ratio of 66.4 / 27.1 / 6.5, purchased from Arkema, France) was weighed into a glass bottle, 5 ml of N,N-dimethylformamide (DMF) solution was added, stirred at room temperature for 12 h, poured onto a clean glass plate, placed in an oven and treated at 70 °C for 2 h to evaporate the solvent, and then the film was gently peeled off the glass plate and placed in a vacuum oven and heat-treated at 120 °C for 5 h to obtain the sample film with a thickness of about 50 μm.

[0029] The P(VDF-TrFE-CTFE) sample film was cut into strips (50×5×0.05mm) and a "programming" process was performed: an external force of 0.01N was applied to the strip of P(VDF-TrFE-CTFE) film to deform it into a "√" shape, denoted as shape 1. Under this stress condition, the temperature was raised to T1 = 80℃ and held for 2 minutes, then lowered to T2 = 45℃ and held for 2 minutes. The external force was then removed, and the film shape was basically fixed as a "√" shape. Subsequently, the external force conditions were changed at 45℃, causing the film to deform into an "N" shape, denoted as shape 2. After holding for 2 minutes, the temperature was lowered to T3 = 20℃ and held for another 2 minutes before the external force was removed. The film shape was now an "N" shape. After completing the "programming," a recovery process was performed: first, the film temperature was raised to 45℃, and the film shape was observed to change from an "N" shape to a "√" shape. Then, the temperature was raised further to 80℃, and the film shape returned from the "√" shape to its initial shape. A schematic diagram of the entire process is shown below. Figure 3 As shown.

[0030] The P(VDF-TrFE-CTFE) sample film was cut into strips and subjected to the same "programming" process as described above, except that the temperature T2 in the phase transition temperature region was changed to 55℃. Then, the same recovery process was performed. A schematic diagram of the entire process is shown below. Figure 4 As shown.

[0031] Example 2: The P(VDF-TrFE-CFE) (Chinese name: poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)) film sample was prepared by solution casting. The only difference from Example 1 is that P(VDF-TrFE-CFE) powder (molar ratio of 62 / 31 / 7, purchased from Poly-K Company, USA) was used instead of P(VDF-TrFE-CTFE) powder in Example 2. All other aspects are the same. For details, please refer to Example 1.

[0032] The P(VDF-TrFE-CFE) sample film was cut into strips (50×5×0.05mm) and subjected to the same "programming" process as described above. The temperature T2 in the phase transition temperature region was changed to 25℃, which was determined based on the dielectric temperature spectrum results of P(VDF-TrFE-CFE). The minimum temperature T3 was set to approximately 0℃. Then, the same recovery process was performed. A schematic diagram of the entire process is shown below. Figure 5 As shown.

[0033] The parts of this invention not described in detail are well-known to those skilled in the art. The embodiments described above are merely preferred embodiments of the invention, and do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Various modifications and improvements to the technical solutions of this invention made by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of this invention.

Claims

1. A method for continuously generating recoverable pseudo-plastic deformation in a ferroelectric material, characterized in that, Includes the following steps: (1) Mix the relaxor ferroelectric polymer and organic solvent, stir, pour onto a plate, dry to evaporate the solvent, then remove the film from the plate and vacuum heat treat to obtain the sample film; (2) Apply external force to the strip-shaped thin film sample to deform it into a first shape. Under the condition of maintaining this stress, heat it to a temperature above the dielectric peak temperature T1 and hold it for more than 1 second. Then cool it down to a temperature below the dielectric peak temperature T2 and hold it for more than 1 second. Remove the external force. At this time, the shape of the thin film is fixed as the first shape. Then change the external force conditions at this temperature to deform the thin film into a second shape, which is recorded as the second shape. Hold it for more than 1 second and then cool it down to room temperature. Hold it for more than 1 second and then remove the external force. At this time, the shape of the thin film is fixed as the second shape. (3) After completing the "programming", the recovery process is carried out: First, the temperature of the film is raised, and it can be observed that the shape of the film changes from the second shape to the first shape. Then, the temperature is raised again, and the shape of the film is restored from the first shape to the initial shape of strip. The ferroelectric polymer is P(VDF-TrFE-CTFE) powder or P(VDF-TrFE-CFE) powder.

2. The method according to claim 1, characterized in that, In step (1), the organic solvent is N,N-dimethylformamide.

3. The method according to claim 1, characterized in that, In step (3), after completing the "programming", the recovery process is carried out: first, the temperature of the film is raised to T2, and it can be observed that the shape of the film changes from the second shape to the first shape. Then, the temperature is raised to T1, and the shape of the film is restored from the first shape to the initial shape.

4. The method according to claim 1, characterized in that, In step (2), the same steps are performed, and the material can "memorize" N shapes while controlling the heat preservation temperature; In step (3), the same process is used to control the recovery of the film from the Nth shape to the initial shape.

5. The method according to claim 4, characterized in that, The first shape is a "√" shape, the second shape is an "N" shape, and the Nth shape can be a more complex shape.

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