effect of water absorption on the mechanical properties of poly(vinylidene fluoride-trifluoroethylene) copolymer films. - absorption of water
Introduction of Electroactive Polymer (EAPs)
Is a material that responds to electrical stimulation by showing significant large strain (
From a few hundred percentage points).
When mechanical energy is applied on EAP, electric energy is induced and vice versa.
Since EAPs behaves very similar to biological muscles, EAPs has been nicknamed "artificial muscles" 1].
EAPs has become an alternative material for advanced applications in various technical fields.
Many intelligent materials have been researched and developed for cutting
Cutting-edge technologies such as energy collection systems and robots.
The response of EAPs to electrical stimulation varies significantly in shape and size.
This particular performance, along with other advantages such as light weight and high fracture toughness, increases the potential applicability of these materials in various industrial fields, thus attracting the attention of many different disciplines [1,2].
In this regard, polyethylene (fluori)[P(VDF-TrFE)]
Has been studied extensively [3-9].
According to Zhang and others. , the high-Electronic EnergyirradiatedP(VDF-TrFE)
The polymer shows the typical relaxation of iron and electricity-
Irradiation divides the cohesive polar domain of theP (VDF-TrFE)
The polymer is transformed into a nano-polar region and the material is transformed into a relaxation iron-electron material.
Such a polar region can cause large deformation (5-7%)
Because the grid deformation between polar and non-polar regions varies greatly
Polar phase in which the polarization domain expands and shrinks under an external electric field.
However, the lag is P (VDF-TrFE)
This is due to the energy barrier generated when the polar domain is transferred from one polarization direction to another.
By inserting defects in the polymer chain, the energy barrier of [can be reduced]1]
, In order to enhance the mechanical properties of EAPs, such as the activation strain at the time of electrical stimulation, add any kind of chlorine fluoride (CFE)
Trifluoride (CTFE)to the P(VDF-TrFE)
Two kinds of P (VDF-TrFECFE)or P(VDF-TrFE-CFTE)
Terpolymer has been studied separately .
EAP composite material [11, 12]
Clay particles containing nanoparticles 
Methods to improve electrical parameters such as dielectric constant are also studied. The P(VDFTrFE)
Polymer has been used in applications such as microlenses in electronic equipment 
Thermal power sensor 
Acoustic sensors 
And energy Collection .
In this study, thin P (VDF-TrFE)
The film is manufactured to study its applicability as a sensor or actuator in an environment without degradation of intrinsic properties. Afterthe P(VDF-TrFE)
The movie was drowned in the water at 30degrees]
C. perform a tensile test on it to the maximum of 4 weeks to evaluate changes in its basic mechanical properties, such as elastic modulus and strength.
Test temperature of 30 [degrees]
It is reported that C is the average temperature of the lower half of the human body .
Creep is an important mechanical property of polymer in high temperature or wet environment for a long time.
Creeplimit is defined as the size of the maximum allowable stress that can be applied within a specific environmental condition without damaging the material, usually determined by crawling tests.
The creep test of P (VDF-TrFE)
A movie that simulates the human body-
Just like observing its sticky properties in an in vivo environment.
Our research focuses on P (VDF-TrFE)
Film before adding various fillers.
The expected results will be provided in relation to P (VDF-TrFE)
Polymer, which may expand the use of this material in biomedical devices, such as actuators that can be embedded in humans;
Such as artificial muscles of limbs.
Synthesis of experimental material P (VDF-TrFE)
Polymer was performed in KUREHA, Japan with a mole fraction of vdf 75% and TrFE 25%.
The chemical composition of VDF and TrFE is shown in the figure. 1. Theelectro-
Mechanical properties of P (VDF-TrFE)
Huang and others confirmed the film. 
The biological compatibility of P (VDF-TrFE)
Other researchers have previously confirmed the polymer. 19].
Sample preparation film the sample using 10wt % solution as follows: P (VDF-TrFE)
The powder is dissolved in methyl acetate at 80 [and stirred violently]degrees]C for 2 hr.
Place the surface on a flat glass plate and pull forward to apply the stick with diffusion.
Evaporate the solvent to obtain p (VDF-TrFE)
And then in the film of 145 [annealingdegrees]
C. 12 elimination of residual solvents by hro [20, 21]
And improve the crystal degree of the film.
Therefore, the thickness of P (VDF-TrFE)
The film measured with a digital microscope is about twelve o'clock P. M (
Keyence, VHX1000). The P(VDF-TrFE)
Solvent-containing film samples evaporated during the manufacturing process have been shown to be biologicalcompatible .
Evaluate the basic mechanical properties of theP (VDF-TrFE)
The film, the specimen was made in the dumb.
Bell form based on ASTM D882-10 
As shown in the figure. 2a.
Through mechanical tests and microscopic observations, the mechanical properties of theP are indirectly understood (VDF-TrFE)
Film and its changes in the in vivo environmentVDF-TrFE)
The 30-year-old film specimen was drowned in the water. degrees]
C. use digital water bath for up to 4 weeks (WiseCircu, WCB-22,Germany).
To measure the water absorption, remove the surface moisture from the wet sample and then weigh it with a digital precision balance (
Ohaus, AR2130, Korea).
Tensile and creep tests using a universal testing machine (
Instron, 5565A, United States)
Ultra-precision load cell (
Honeywell, 31, United States of America)
And one more person.
Simulation Environment (seeFig. 2b)
Follow the standard test procedure (ASTM D882-10 andASTM D2990-09 ).
Because the soft film specimen is very thin (around 12 pm)
Excessive elongation (
Much bigger than 3%)contact-
Type equipment cannot be used to measure true strain, especially under water conditions (see Fig. 2b).
Conversely, nominal strain defined by elongation divided by length is used to compare the mechanical behavior of the film that experiences different environmental conditions.
In the tensile test, five samples were used for each test condition according to the water exposure time (0, 2, 4 weeks).
The test speed is 1. 5 mm/min.
Three loads of 3. 71 MPa, 5. 31 MPa, and 6. 46 MPa at 0. 5%, 0. 7%, and 0.
9% strain from the elastic region of stress
Strain curve of P (VDF-TrFE)dry film (see Fig. 3)
Was selected for Creep test for 10,000 seconds , An X-
Ray diffraction (Bruker-AXS, New D8-
Used to observe changes in crystal and microstructure
Structure of P (VDF-TrFE)
According to the time of water exposure, the film formed due to water absorption.
The scanning speed and range are 2. 4[degrees]/min and2[theta]= 10[degrees]-30[degrees], respectively.
Water absorption results and discussion of P (VDF-TrFE)
The film Table 1 shows that P (VDFTrFE)
The documentation depends on the time the water is exposed.
In fact, P (VDF-TrFE)
As we all know, the fact that polymer is basically not dissolved in water does not mean that there is no interaction with water [at all]26]
Crystal polymers such as polydiammonium can absorb a small amount of water (
A few percent)
By inserting or occupying water molecules at the Gap position between the layers of the material, not just water molecules filling gaps and defects [26-29].
The maximum water absorption rate of 4-1 is about 5%
30 [soak in water for a weekdegrees]C. The P(VDF-TrFE)
The film interacts physically with water rather than chemically.
10 hours after 50 [annealing]degrees]
C. completely eliminate istoisture from P (VDF-TrFE)
The weight obtained is 0.
217 grams, similar to the original movie.
According to Jacobson and others. , the X-Ray diffraction (XRD)
The film is almost the same as the original film, and the diffraction intensity and specific lattice constants are the same as the original film.
Therefore, water absorption is reversible and does not cause any permanent changes in P (VDF-TrFE)films.
Basic mechanical properties of P (VDF-TrFE)
Films taken according to water exposure time represent pressure-
Figure 1 shows the strain curve based on the water exposure time. 3.
In addition, changes in mechanical properties such as elastic modulus, tensile strength, and the relationship between strain and water exposure time, as shown in Fig. 4a-cand Table 1.
As shown in the figure.
All the pressure-
The strain relationship shows the initial linear elastic state and then is
The linear state, and finally the failure state.
It is well known that the interaction between the polymer chain through hydrogen bonds can lead to changes in polymer properties [30, 31].
Generally speaking, at room temperature and above, the absorbed water may be the main factor in reducing the modulus and increasing the failure strain and impact strength [32, 33]
, This can be explained by assuming that water acts as an interval between polymer chains.
However, the results of the wetP tensile test (VDF-TrFE)
The film is completely different from previous reports. 32, 33].
Young model and strength of WetP (VDF-TrFE)
The film is increased compared to the dry film, and the increment is almost proportional to the water exposure time.
In addition, there is an increase in the number of failed strains.
The elastic modulus, strength and fracture strain were increased by 9, respectively. 33%, 36. 66%,and 66.
23%, respectively in the water.
Physical bonding between high negative fluorine atoms of P (VDF-TrFE)
The hydrogen atom of water limits the fluidity of the polymer chain and ultimately leads to some improvement in mechanical properties, especially the tensile strength of P (VDF-TrFE)films [34, 35]
Hot entangled polymer chains of P (VDF-TrFE)
The water part of the membrane absorbed is stretched, which leads to pre-stretchingstrain effect 
Therefore, the polymer chain is in P (VDFTrFE)
Membrane is affected to induce polymer crystals in tensile tests .
Through the way before
Strain effect, P (VDF-TrFE)
Films can effectively support the initial tensile load, thus increasing their elastic modulus (see Fig. 4a). X-
X-ray diffraction analysis Figure 5a shows P (VDF-TrFE)films.
Layer spacing [d. sub. 110](see Fig. 5b)
Calculate from the peak position using the Bloggs law (, Eq. 1). 2d sin [theta]= n[lambda](1)where [lambda]is the X-
Radiation wavelength of the radiation line (CuK[alpha])
, The spacing between the diffraction lattice planes, and [theta]
It's half a corner.
In the case of dry film, in theta]=20. 05[degrees]
The corresponding grid layer spacing is observed to be 4. 46 [Angstrom].
Flooding bag 30 in wet film [degrees]
C. 2 and 4 weeks, peak angle from [theta]= 20. 05[degrees]to 2[theta]= 19. 92[degrees]and 2[theta]=19. 84[degrees]
With the corresponding grid spacing ([d. sub. 110])of4. 49 [Angstrom]and 4. 51 [Angstrom], respectively.
This may be due to water molecules and P (VDF-TrFE)
By inserting layers in the gap sites between the materials [layers], the polymer chain at the crystalline stage26-29].
Creep Properties of P (VDF-TrFE)
Observing the viscous properties of P with wet film (VDF-TrFE)
In the in vivo environment, the creep test of the film under three stress conditions (3. 71 MPa, 5. 31 MPa, and 6. 46 MPa at0. 5%, 0. 7%, and 0. 9% strains)
Lasts 10,000 seconds in a simulated human body.
Like the environment.
Figure 1 shows the creep strain curve based on the water exposure time. 6a-c.
With the increase of stress, the creep stress increased significantly.
As mentioned earlier, P (VDF-TrFE)
With the increase of water exposure time, the modulus and strength of the film increase, which in turn increases the film's ability to resist external stress.
This feature of P (VDF-TrFE)
Wet film was also observed in creep tests.
In addition, the results of tensile and creep tests showed similar deformation trends.
Under the same load conditions, the induced creep strain decreases with the increase of water absorption.
In addition, no samples were cracked under the loading of the fomsec.
Usually, polymer creep occurs due to the yield of secondary bonding .
Therefore, P (VDF-TrFE)
There may be more than 6 movies in this movie. 26 MPa.
Considering the tensile strength of apiezo electric polymer (PVDF)is 4. 8 MPa , the P(VDF-TrFE)
The film can be used as an artificial muscle actuator.
And the continuity of P (VDF-TrFE)film for bio-
Other researchers have demonstrated relevant and mechanical applications [1, 40].
Conclusion in this study, P (VDF-TrFE)
An EAP with a dielectric.
Stretching and crawling tests using the dry and wet film of P (VDF-TrFE)
Observe the changes in the mechanical properties of the simulated human body --
Like the environment.
The damp film is submerged in water degrees]
C is 0, 2, 4 weeks.
We find the weight of P (VDF-TrFE)
Wet membranes soaked in water for 2 weeks and 4 weeks increased by 2.
Compared with dry film, 31% and 5% respectively.
In other words, the water absorption in the film is proportional to the time of water exposure.
In addition, after annealing of the wet film, the weight is restored to its original value, indicating that P (VDF-TrFE)
The physical action of the film with water, not the chemical action.
Tensile test results of dry and wet P (VDF-TrFE)
The films show that the maximum increments of Young's modulus, strength and strain are 9%, 36% and 66%, respectively.
The properties of the material are enhanced by water absorption.
Physical bonding between high negative fluorine atoms of P (VDF-TrFE)
The hydrogen atom of water limits the fluidity of the polymer chain, which ultimately results in some improvement in the mechanical properties of P (VDF-TrFE)films.
X-ray analysis showed that after 2 weeks and 4 weeks of water absorption, water molecules and P (VDF-TrFE)
The polymer chain in the crystal phase, and insert the layer in the gap between the material layers.
In the case of dry film, in theta]= 20. 05[degrees]
It was observed that it reflected d-spacing ([d. sub. 110])was 4. 46 [Angstrom].
For wet film, peak (2[theta]= 20. 05[degrees])
Go to the lower angles2 [theta]= 19. 92[degrees](
2 weeks flooded)and 2[theta]=19. 84[degrees](
4 weeks flooded)
And the corresponding d-spacing ([d. sub. 11]0)increased to 4. 49 [Angstrom]and4. 51 [Angstrom], respectively.
Creep strain of wet P (VDF-TrFE)
Under the same load conditions, the film soaked in water for 4 weeks is smaller than the film soaked in dry film and wet film for 2 weeks in water.
This result is consistent with the above conclusion: the mechanical properties of P are enhanced by water absorption (VDF-TrFE)films. The P(VDF-TrFE)
The creep limit of the film may exceed 6. 26 MPa.
After 4 weeks of flooding, we expect P (VDF-TrFE)
Increasing the water content will improve the mechanical properties of the film.
Therefore, in the future experimental work, it is necessary to study the maximum water content absorbed by the film and the corresponding changes in the mechanical properties of the material.
Features and changes of mechanical properties of P (VDF-TrFE)
By flooding the film in the water of 30 [, indirectly observing the film in the in vivo environment]degrees]
C up to 4 weeks.
We have P (VDF-TrFE)
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Young Li of Chengdong
Zhong Wan Chang School of Mechanical Engineering-
Hook Su Keang University 221-Dong, Dongjak-Gu, Seoul 156-
756 letter from the Republic of Korea to S. H. Chang; e-
Email: phigs4 @ cauac.
Scholarship for outstanding students in university.
Contracted funding unit: Basic scientific research project of Korea National Research Foundation (NRF)
Funded by the Ministry of Education, Science and technology;
Contract award No. : 20I2R1 AlA204I883. DOI 10. 1002/pen.
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