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The ongoing trend toward high-power and miniaturized electronic devices has raised increasingly stringent requirements for the high-temperature electrical properties of epoxy encapsulating materials. In this study, epoxy-terminated phenyltrisiloxane (ETS) is used as a functional monomer to incorporate Si-O bonds into bisphenol-A epoxy resin through crosslinking reactions, thereby systematically investigating the influence and modulation effects of ETS on the structure and high-temperature electrical characteristics of epoxy composites. Gel content measurements indicate that as the concentration of ETS increases, the gel content of the epoxy resin composite decreases accordingly, suggesting that higher ETS content reduces the crosslinking density of the epoxy network. Experimental test results demonstrate that compared with pure epoxy resin, the composite with 2.5% ETS exhibits superior performance: the glass transition temperature increases to 129 ℃ with thermal decomposition temperature rising, while showing optimal high-temperature (70 ℃) electrical properties including significantly reduced conductivity, markedly suppressed space charge accumulation, deepened trap energy level (from 0.834 eV to 0.847 eV), reduced dielectric loss (0.005 at 50 Hz), and improved breakdown strength (74.2 kV/mm). Notably, as the ETS content increases, the electrical properties of epoxy composite follow a non-monotonic concentration dependence, initially enhancing then deteriorating, exhibiting evolutionary characteristics similar to those of nanoparticle-modified systems. Herein, a competitive mechanism between the epoxy network structure and intrinsic properties of ETS is proposed to explain this phenomenon: at low concentrations, the original C—C network dominates, where the intrinsic properties of ETS are constrained by the host matrix, leading to improved thermal stability. Simultaneously, the bandgap difference between ETS and DGEBA establishes charge barriers that can enhance insulation performance. However, at higher concentrations, the reduced crosslinking density and increased free volume caused by reactivity and structural mismatch between ETS and DGEBA ultimately lead to performance degradation. This study offers crucial theoretical insights into and produces the design strategies for developing high-performance siloxane-modified epoxy encapsulants.
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Keywords:
- epoxy resin /
- siloxane /
- crosslinked network /
- high-temperature insulation
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图 1 ETS单体的化学分子式
Figure 1. Molecular structure of ETS monomer.
图 2 环氧树脂单体的分子轨道能级分布 (a) DGEBA; (b) ETS
Figure 2. Energy level distribution of epoxy monomers: (a) DGEBA; (b) ETS.
图 3 Pure EP, 2.5% Si-EP, 5% Si-EP和10% Si-EP复合材料的凝胶含量
Figure 3. The gel content of Pure EP, 2.5% Si-EP, 5% Si-EP, and 10% Si-EP composites.
图 4 (a)—(d) Pure EP, 2.5% Si-EP, 5% Si-EP和10% Si-EP的SEM照片; (e), (f) 2.5% Si-EP表面C, O, Si元素分布及含量; (g), (h) 10% Si-EP表面C, O, Si元素分布及含量
Figure 4. (a)–(d) SEM of Pure EP, 2.5% Si-EP, 5% Si-EP and 10% Si-EP samples; (e), (f) distribution of C, O and Si elements and content on the surface of 2.5% Si-EP; (g), (h) distribution of C, O and Si elements and content on the surface of 10% Si-EP.
图 5 Pure EP, 2.5% Si-EP, 5% Si-EP和10% Si-EP的XPS图谱以及Si-EP对应的Si 2p的放大图谱
Figure 5. XPS spectra of Pure EP, 2.5% Si-EP, 5% Si-EP和10% Si-EP samples, with insets showing enlarged Si 2p spectra for the Si-EP samples.
图 6 Pure EP, 2.5% Si-EP, 5% Si-EP 和10% Si-EP的FTIR图谱
Figure 6. FTIR spectra of Pure EP, 2.5% Si-EP, 5% Si-EP and 10% Si-EP samples.
图 7 Pure EP, 2.5% Si-EP, 5% Si-EP 和10% Si-EP的DSC曲线
Figure 7. DSC curves of Pure EP, 2.5% Si-EP, 5% Si-EP and 10% Si-EP samples.
图 8 Pure EP, 2.5% Si-EP, 5% Si-EP和10% Si-EP的热失重曲线
Figure 8. TGA curves of Pure EP, 2.5% Si-EP, 5% Si-EP and 10% Si-EP samples.
图 9 Pure EP, 2.5% Si-EP, 5% Si-EP和10% Si-EP在不同场强下的电导率
Figure 9. Conductivity of Pure EP, 2.5% Si-EP, 5% Si-EP and 10% Si-EP samples at different applied electric fields.
图 10 (a) Pure EP, (b) 2.5% Si-EP, (c) 5% Si-EP和(d) 10% Si-EP在不同场强下空间电荷分布随时间的变化
Figure 10. Space charge distribution of (a) Pure EP, (b) 2.5% Si-EP, (c) 5% Si-EP and (d) 10% Si-EP samples at different applied electric fields.
图 11 Pure EP, 2.5% Si-EP, 5% Si-EP和10% Si-EP平均电荷密度随时间的衰减
Figure 11. Decay of average charge density with time for Pure EP, 2.5% Si-EP, 5% Si-EP and 10% Si-EP samples.
图 12 Pure EP, 2.5% Si-EP, 5% Si-EP和10% Si-EP的陷阱能级
Figure 12. Trap energy levels of Pure EP, 2.5% Si-EP, 5% Si-EP and 10% Si-EP samples.
图 13 Pure EP, 2.5% Si-EP, 5% Si-EP 和10% Si-EP的宽频介电常数实部ε'
Figure 13. Broadband dielectric spectroscopy real part ε' of Pure EP, 2.5% Si-EP, 5% Si-EP and 10% Si-EP samples.
图 14 (a) Pure EP, (b) 2.5% Si-EP, (c) 5% Si-EP和(d) 10% Si-EP的宽频介电虚部ε''弛豫响应分解
Figure 14. Broadband dielectric spectroscopy imaginary part ε'' of (a) Pure EP, (b) 2.5% Si-EP, (c) 5% Si-EP and (d) 10% Si-EP samples.
图 15 Pure EP, 2.5% Si-EP, 5% Si-EP和10% Si-EP交流击穿场强的韦布尔分布
Figure 15. Weibull distribution of AC breakdown field strength for Pure EP, 2.5% Si-EP, 5% Si-EP and 10% Si-EP samples.
图 16 Pure EP, 5% Si-EP, 5% Si-EP, 10% Si-EP 环氧树脂交联网络随着ETS含量增大的演变示意图
Figure 16. Schematic diagram of the evolution of Pure EP, 2.5% Si-EP, 5% Si-EP, and 10% Si-EP cross-linked network with increasing ETS content.
表 1 Pure EP, Si-EP韦布尔概率分布参数
Table 1. Weibull distribution parameters for Pure EP and Si-EP samples.
Pure EP 2.5% Si-EP 5% Si-EP 10% Si-EP β 68.3 74.2 72.6 67.2 σ 14.5 16.1 11.1 12.5 
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