In high-temperature superconducting (HTS) cable terminations, stress-buffering encapsulation is a critical challenge for ensuring the long-term reliable operation of the system. These terminations must withstand severe thermal cycling—ranging from room temperature down to cryogenic temperatures (specifically the liquid nitrogen range at -196°C)—during which vast disparities in the coefficients of thermal expansion among different materials generate significant mechanical stress. Traditional encapsulation materials tend to become brittle and crack at extreme cryogenic temperatures, or fail to effectively buffer stress due to excessively high elastic moduli; this leads to damage to the insulation layer, seal failure, and can even trigger a "quench" (loss of superconductivity) accident. Phenyl silicone, with its unique characteristics of "retained low-temperature elasticity" and "tunable modulus," serves as a "low-temperature stress buffering shield" for cable terminations, achieving a seamless transition—at the microscopic level—from a "rigid connection" to a "flexible transition."

The core mechanism by which phenyl silicone resolves the challenge of low-temperature stress buffering lies in its "regulation of free volume via phenyl side groups" and its inherent "low-temperature flexibility." In ordinary silicone, molecular chain segment motion becomes frozen at -196°C; with a glass transition temperature (Tg) typically hovering around -120°C, it is highly susceptible to brittle fracture. In phenyl silicone, while the introduction of phenyl groups does increase the rigidity of the molecular chains, precise control over the phenyl content (typically maintained between 5–15 mol%) allows for the optimization of molecular chain packing density, thereby lowering the Tg to below -130°C. This signifies that within the liquid nitrogen temperature range, phenyl silicone retains its highly elastic, rubber-like state; its elastic modulus can drop to below 1 MPa, enabling it to effectively absorb and dissipate the stresses generated by thermal cycling, thereby preventing stress concentrations from being transmitted to the fragile superconducting tapes or insulation layers.

Furthermore, phenyl silicone's exceptional "low-temperature sealing performance" ensures the insulation reliability of the cable termination. The Si-O bonds within its molecular chains possess high bond energy, and the hydrophobic nature of the phenyl groups ensures that the material maintains an extremely low permeability to gases and moisture, even at cryogenic temperatures. In thermal cycling tests consisting of 50 cycles ranging from -200°C to room temperature, the phenyl silicone potting layer exhibited neither cracking nor delamination; its volume resistivity remained above 10¹⁴ Ω·cm, and its dielectric strength exceeded 20 kV/mm. These results fully satisfy the stringent requirements for insulation and sealing demanded by superconducting cable terminations.

Ranging from the molecular-level design of chain segment flexibility to macroscopic low-temperature stress buffering, phenyl silicone resolves the complex potting challenges associated with high-temperature superconducting cable terminations through a synergistic mechanism characterized by "low-temperature flexibility and high elasticity." It serves not only as a critical material for ensuring the safe operation of superconducting power transmission systems but also acts as the invisible safeguard enabling the realization of highly efficient and compact superconducting cable terminations.