Silicone rubbers for dielectric elastomers with improved dielectric and mechanical properties as a result of substituting silica with titanium dioxide

Figures & data

Figure 1. Tensile stress–strain, breakdown strength and actuation measurements.

Figure 2. Thermal degradation analysis of the LSR and RTV films.

Table 1. Thermal properties of the LSR and RTV films.

Silicone	Formulation	Td2%(°C)	Tmax(°C)	Inorganic residue (wt.%)
LSR	LR 3043	406	683	72
	XLR	389	671	37
	MJK 5/13	349	643	21
	MJK 4/13	303	639	18
RTV	RT 625	365	665	27

Figure 3. Breakdown strength versus filler content as determined from the TGA of LSR and RTV films. All films are of similar thickness (60–80 μm).

Table 2. Weibull analysis parameters for LSR and RTV samples.

Silicone	Formulation	β	η	r^2
LSR	ELASTOSIL® LR 3043 A/B	35	123	0.90
	POWERSIL® XLR A/B	46	132	0.92
	MJK® 135 5/13 A/B	33	125	0.96
	MJK® 135 4/13 A/B	25	94	0.92
RTV	ELASTOSIL® RT 625 A/B	32	88	0.87

Figure 4. Tear strength of the LSR and RTV films. The results are summarized in Table 3.

Table 3. The mechanical properties of LSR and RTV films.

Formulation	Sample thickness (μm)	Young’s modulus (MPa)	Tensile strength (MPa)	Tear strength (MPa)	Elongation at break in tear experiment (%)	Permittivity (εr) @ 0.1 Hz
LR 3043	73 ± 2	0.80 ± 0.02	8.8 ± 0.2	3.96 ± 0.09	235 ± 6	2.70 ± 0.01
XLR	80 ± 2	0.76 ± 0.02	7.0 ± 0.2	2.82 ± 0.07	145 ± 4	3.06 ± 0.01
RT 625	74 ± 2	0.56 ± 0.01	6.5 ± 0.2	1.01 ± 0.02	206 ± 5	2.97 ± 0.01

Figure 5. Dynamic viscosity of the XLR–TiO₂ mixtures at 23°C.

Figure 6. Frequency-dependent relative permittivity spectra of the pure XLR and XLR–TiO₂ elastomers at 23°C.

Figure 7. Frequency-dependent dielectrical loss tangent spectra of the pure XLR and XLR–TiO₂ elastomers at 23°C. The observed relaxations are Maxwell relaxations.

Figure 8. Tear strength of the pure XLR and XLR–TiO₂ elastomers.

Figure 9. Stress and elongation at breaking in the tear experiment on the pure XLR and XLR–TiO₂ elastomers.

Figure 10. SEM images of R420 TiO₂ filler (a), pure XLR film (b) and XLR+35 wt.% R420 TiO₂ film (c).

Table 4. Mechanical properties and breakdown strength of the XLR–TiO₂ films. The optimum of a given property is marked in gray.

Formulation	Sample thickness (μm)	Young’s modulus (MPa)	Tear strength (MPa)	Elongation at break (%)	Breakdown strength (V/μm)
XLR	80 ± 2	0.76 ± 0.02	2.82 ± 0.07	145 ± 4	130 ± 3
XLR + 30 wt.% TiO2	65 ± 1	0.80 ± 0.02	3.98 ± 0.08	151 ± 4	144 ± 4
XLR + 32.5 wt.% TiO2	45 ± 1	0.82 ± 0.02	4.77 ± 0.1	173 ± 4	146 ± 3
XLR + 35 wt.% TiO2	62 ± 1	0.85 ± 0.02	5.30 ± 0.09	189 ± 5	158 ± 4
XLR + 37.5 wt.% TiO2	57 ± 1	0.88 ± 0.02	5.03 ± 0.1	177 ± 4	160 ± 5
XLR + 40 wt.% TiO2	53 ± 1	0.90 ± 0.03	2.67 ± 0.1	113 ± 3	163 ± 5

Figure 11. 3D plot of breakdown strength as a function of the Young’s modulus and filler amount for the XLR–TiO₂ (R420) films and the pure LSRs.

Figure 12. 3D plot of breakdown strength as a function of the Young’s modulus and filler amount for the MJK 4/13-TiO₂ (T805) films.

Table 5. Weibull analysis parameters for XLR–TiO₂ and RTV–TiO₂ samples.

Formulation	β	η	r^2
XLR	46	132	0.92
XLR + 30 wt.% TiO2	37	146	0.97
XLR + 32.5 wt.% TiO2	50	148	0.96
XLR + 35 wt.% TiO2	48	160	0.89
XLR + 37.5 wt.% TiO2	36	162	0.97
XLR + 40 wt.% TiO2	35	165	0.97
LR3043 + 35 wt.% TiO2	33	116	0.93
RT625 + 35 wt.% TiO2	16	91	0.92

Table 6. Dielectric and mechanical performances and figures of merit (F_om) of the LSR–TiO₂ and RTV–TiO₂ formulations. Optimal properties are marked in gray.

Formulation	Sample thickness (μm)	Young’s modulus (MPa)	Tear strength (MPa)	Elongation at break (%)	Breakdown strength (V/μm)	Permittivity (εr) @ 0.1 Hz	Fom(DEA)@ 0.1 Hz	Fom(DEG)@ 0.1 Hz
XLR + 35 wt.% TiO2	62 ± 1	0.85 ± 0.02	5.30 ± 0.09	189 ± 5	158 ± 4	4.92 ± 0.02	3.60 ± 0.04	5.46 ± 0.05
LR3043 + 35 wt.% TiO2	64 ± 1	1.30 ± 0.03	2.90 ± 0.07	200 ± 5	114 ± 4	4.69 ± 0.02	1.17 ± 0.01	2.71 ± 0.03
RT625 + 35 wt.% TiO2	68 ± 1	0.80 ± 0.02	2.25 ± 0.06	180 ± 5	87.9 ± 6	4.03 ± 0.02	0.97 ± 0.01	1.39 ± 0.02
RT625 ^a)	74 ± 1	0.56 ± 0.01	1.01 ± 0.03	206 ± 4	87.0 ± 3	2.97 ± 0.01	1 ± 0.01 *	1 ± 0.01 *

Note: ^a) Benchmark material, which is used for normalization, such that a value of 1 for both F_om(DEA) @ 0.1 Hz and F_om(DEG) @ 0.1 Hz of RT625 elastomer.

Figure 13. Actuation curves for pure XLR and XLR+35 wt.% TiO₂ films at 23°C.