Silicone rubber is inherently an excellent electrical insulator, with a volume resistivity as high as 10¹⁴–10¹⁶ Ω·cm. However, through ingenious material design, scientists have endowed it with conductivity, creating a composite functional material that combines elasticity, sealing capability, and conductivity—known as conductive silicone rubber (CSR). Though not metals or ordinary wires, CSRs play indispensable roles in fields such as electromagnetic interference (EMI) shielding, electrostatic discharge (ESD) protection, and flexible sensing.

1. Mechanism of Conductivity: From Insulation to Conduction

Conductive silicone rubber itself does not conduct electricity; its conductivity originates from the formation of a percolation network created by adding conductive fillers. When the concentration of these fillers exceeds a critical threshold (the percolation threshold), particles either come into contact or form continuous pathways through tunneling effects, allowing electrons to migrate.

Commonly used conductive fillers include:

Metals: Silver (Ag), nickel (Ni), copper (Cu)—excellent conductivity (volume resistivity can be as low as 10⁻³ Ω·cm), but expensive and dense.

Carbon-based materials: Carbon black, carbon nanotubes (CNTs), graphene—cost-effective and lightweight, but with lower conductivity (10⁰–10³ Ω·cm) and potential impact on mechanical properties.

Composite fillers: Such as silver-coated glass spheres, nickel-coated graphite—balancing conductivity, density, and cost.

Silver-filled silicone rubber, due to its anti-oxidation properties, high conductivity, and ease of processing, is often chosen for high-end EMI shielding applications. Carbon black-filled types are more commonly used for anti-static purposes.

2. Key Performance Characteristics

Performance Description

Volume Resistivity      10⁻³ – 10⁵ Ω·cm (depending on filler type and content)

Shielding Effectiveness (SE)      Silver-based can reach 80–120 dB (30 MHz–10 GHz)

Elasticity Retention     Maintains good resilience under moderate filler loading (hardness 40A–80A)

Weather Resistance    Inherits advantages of silicone rubber, resistant to temperature extremes, UV, and ozone

Compressibility    Used as EMI gaskets, maintains conductive paths even at 50% compression

3. Major Application Fields

Electromagnetic Interference (EMI): In 5G base stations, military radars, and medical device enclosures, CSR gaskets provide continuous conductive paths, reflecting/absorbing electromagnetic waves to prevent internal signals from leaking out or external interference from entering, meeting standards like FCC and MIL-STD-461.

Electrostatic Discharge Protection (ESD): In semiconductor manufacturing cleanrooms or explosive environments, conductive silicone floors, gloves, or tool handles safely dissipate static charges to ground, preventing sparks that could cause accidents.

Flexible Electrodes and Sensors: Soft, skin-conforming electrodes for ECG/EEG reduce motion artifacts; pressure/strain sensors utilize piezoresistive effects to monitor deformation; stretchable conductive interfaces for smart textiles.

Heating Elements: Upon electrification, Joule heating causes CSR to generate heat, used in applications like automotive rearview mirror defogging and medical heating pads, offering uniform temperatures and high safety.

4. Challenges and Optimization Directions

Filler Sedimentation: High-density metal powders tend to settle in liquid rubber, requiring surface modification or thickening agents.

Compression Set: High filler loads can reduce elasticity, affecting long-term sealing.

Cost Control: The high price of silver drives research into nickel/carbon alternatives.

Anisotropic Conductivity (ACF): Using magnetic/electric fields to align fillers achieves Z-axis conductivity while maintaining insulation along the XY axes.

Methyl vinyl silicone Gum MY 3110 series-Mingyi Silicone