# Influence of DMSO Non-Toxic Solvent on the Mechanical and Chemical Properties of a PVDF Thin Film
## 3 Results and Discussion
### Mechanical Characterization  
The mechanical properties--yield stress, strain and stiffness--were obtained through uniaxial tensile tests. Figure 4 shows the linear elastic behaviour of PVDF samples of 12/88% \(w/w\) (PVDF/DMSO) from 20 valid tests (gray lines), the mean curve (black full line) and standard error of the mean (SEM) (gray area). Through the mean curve, a \(\sigma_{Yield}\) of 9 MPa and a corresponding \(\varepsilon_{Yield}\) of 0.06 were estimated. Moreover, a Young's modulus (\(E\)) of 144 MPa could be obtained from the slope of the linear elastic region. To evaluate the influence of the concentration of PVDF on the mechanical properties, another percentage of PVDF was analysed. Maintaining the proportion of IL/PVDF but changing the ratio of PVDF/DMSO to 15/85% \(w/w\), the result of \(\sigma_{Yield}\) was 9.8 MPa, and the corresponding \(\varepsilon_{Yield}\) was 0.17: both results being higher for this ratio. The value of \(E\) was smaller at 118 MPa. This indicates that by increasing the percentage of PVDF, the yield stress and yield strain increase, but the Young's modulus decreases.  
The same relation between the increase of stiffness with the decrease in the percentage of PVDF has also been observed by other authors and has been reported in the literature [62]. [PERSON] et al. [32; 46], using DMF as solvent, obtained an \(E\) ranging from 75 MPa to 184 MPa and a \(\sigma_{Yield}\) varying from 2.53 MPa to 6.4 MPa, with the range of values dependent on the IL used. Comparing the results from [PERSON] et al. [32] with those obtained in this study for 12/88% \(w/w\) PVDF/DMSO, it is worth pointing out that \(E\) is similar and \(\sigma_{Yield}\) is on the same order of magnitude. However, the last parameter is higher in the present study, which might be due to different solvents and conditions used in the experimental protocols.  
[PERSON] et al. [63] studied a PVDF/IL piezo-active composite film to be used for highly sensitive pressure sensors. The samples were prepared with 1-Ethyl-3-methyl- imidazolium Chloride ([EMIM]Cl), were dissolved in DMF and were tensile tested, and the stress-strain relation was determined. They reported that the Young's modulus decreased with the IL content. However, [PERSON] et al. [64] studied the mechanical properties of a composite material based on PVDF and reinforced with conductive black carbon and silicon dioxide, since damage severely limits the applications of polymer membranes. The samples were  
Figure 4: Mechanical tensile results of 12/88% \(w/w\) samples. Grey lines—20 individual specimens; black full line—mean curve; gray area—SEM.  
prepared using DMF as solvent and were tested referring to the ASTM D 882-2012 standard [56]. They conclude that the tensile strength of PVDF increases with the content of the additive.  
The results of this study show that the mechanical properties are influenced by the PVDF/DMSO ratio and decrease with the addition of fillers, as reported by [PERSON] et al. [65]. Nevertheless, the use of a different solvent, when compared to the literature, seems not to have a significant impact on the mechanical properties. Despite the property variations in comparison with PVDF, the piezoelectric material exhibits mechanical properties suitable for real-world applications. Its resistance to plastic deformation at low stress levels can be a potential advantage for applications in rehabilitation scenarios.