# Influence of DMSO Non-Toxic Solvent on the Mechanical and Chemical Properties of a PVDF Thin Film
## 3 Results and Discussion
### Chemical Characterization  
FTIR-ATR analysis allowed us to obtain the vibrational absorption band characteristics of each phase (\(\alpha\) and EA phases) and the transmittance values needed to calculate the phase content in the sample. Figure 5 shows a peak at 766 cm\({}^{-1}\), which is representative of \(\alpha\) phase, while the peak 840 cm\({}^{-1}\) validates the presence of EA phases. These results are in agreement with previous studies [32; 34] on this type of material. From Equation (1), the content of each phase is calculated. The samples of 12/88% PVDF/DMSO with IL contained approximately 80% EA phase, which is believed to be enough to perform a good piezoelectric response when externally stimulated by electrical inputs. Considering other ratios of PVDF/DMSO (using IL), such as 15/85% \(w/w\), the EA content increased to approximately 86%. Without IL, those values decreased to 69% and 70%, respectively. The samples with a PVDF/DMSO ratio of 12/88% \(w/w\) were also analysed with XRD and DSC techniques. XRD analysis allows us to identify and distinguish the \(\beta\) phase from the other phases: mainly from the \(\gamma\) EA phase. Despite the peak around 2\(\theta\) = 20\({}^{\circ}\) being characteristic of both EA phases of PVDF (\(\beta\) and \(\gamma\)), the absence of clear peaks before that value is an indicator of the main presence of \(\beta\) phase instead of \(\gamma\) phase (Figure 6) [34; 66]. This result is expected for enhanced piezoelectric characteristics of the samples, since the beta phase being the prevalent EA phase is an advantage for piezoelectric materials. DSC analysis (Figure 7) quantifies the crystallinity of the sample and investigates the response of the polymer to heat. From Equation (2), a degree of crystallinity of approximately 30% was achieved, meaning that 30% of the polymer's mass formed crystalline regions, which directly interfere with some properties, such as the stiffness and piezoelectric behaviour [67]. Higher crystallinity means higher alignment of the polymer chains, which increases the stiffness of the material. The remaining polymer percentage, i.e., 70%, represents the amorphous regions. Moreover, it was possible to determine the melting (T\({}_{m}\)  
Figure 5: FTIR\(-\)ATR analysis of the composite material. The peaks corresponding to \(\alpha\) and EA phases are represented in the graph and are marked with the dotted rectangles. and the onset (T\({}_{onset}\)) temperatures as 159.1 \({}^{\circ}\)C and 144.68 \({}^{\circ}\)C, respectively. At the end of this analysis, no mass loss was observed. Other authors such as [PERSON] et al. [32] and [PERSON] et al. [68] also characterized PVDF films prepared with DMF solvent in terms of chemical properties regarding EA phases. [PERSON] et al. [32] reported a \(\beta\) content from 59% to 89% using different types of IL and maintaining the IL/PVDF ratio at 40%. Compared with the results from this study, the values obtained match the range obtained by [PERSON] et al. [32] even though different solvents were used. [PERSON] et al. [68] obtained a \(\beta\) content higher than 93% by using the IL ([C2 min][BF4]), which is higher than the results obtained in this study. Nevertheless, they also concluded that the polymer phases and their content were influenced by PVDF/solvent ratios and by the presence of IL. Considering the solvent and the presence of IL, a higher concentration of PVDF increased the percentage of electroactive phases. In addition to the \(\beta\) content, [PERSON] et al. [32] also measured the crystallinity and the melting and onset temperatures. They obtained a \(\chi\) result varying between 28% and 56% depending on the type of IL used. Regarding the melting temperature, the result obtained via DSC was between 154 \({}^{\circ}\)C and 173 \({}^{\circ}\)C, while the onset temperature was between 371 \({}^{\circ}\)C and 407 \({}^{\circ}\)C as measured by thermal gravimetric analyser (TGA). [PERSON] et al.