Addition-cure silicone rubber forms a three-dimensional crosslinked network through hydrosilylation reaction between vinyl polysiloxane and hydrogen-containing polysiloxane under catalysis. Featuring no by-products during vulcanization, low shrinkage, and tunable curing speed, it has been widely adopted in electronic packaging, biomedical materials, aerospace materials and other fields, especially as LED encapsulants and liquid injection potting adhesives.

Despite its broad application prospects, addition-cure silicone rubber still faces multiple technical bottlenecks in practical use. For one thing, it exhibits poor initial adhesion to most substrates such as metals and plastics, which severely restricts its application in complex component assembly and precision device packaging. Other drawbacks include catalyst poisoning susceptibility, reliance on imported high-grade products, and insufficient mechanical properties of some modified variants. Among these issues, inferior adhesion acts as the primary barrier limiting its expansion into high-end applications. Therefore, enhancing the adhesion capacity of addition-cure silicone rubber is of great significance for promoting its further development and wider utilization.

Root Causes of Poor Adhesion of Addition-Cure Silicone Rubber

Reliable adhesion relies on two sequential critical steps. First, the adhesive fully spreads and wets the substrate surface, filling micro-defects and eliminating interfacial air voids; pressure and heat can further facilitate wetting and gap filling. Second, stable bonding forms at the adhesive-substrate interface via physical adsorption or chemical reactions, delivering durable adhesion. However, restricted by its inherent chemical structure and molecular conformation, addition-cure silicone rubber shows obvious deficiencies in both interfacial wetting and interfacial bonding.

After curing, addition-cure silicone rubber forms a crosslinked polysiloxane network with Si–O–Si backbones and methyl side groups. Its molecular chains tend to adopt low-surface-energy helical conformations dominated by nonpolar surface groups, resulting in low cohesive energy density and a lack of reactive functional groups. Consequently, the rubber poorly wets most substrates and fails to form robust chemical bonds or strong physical adsorption, leading to weak adhesion and limiting its use in composite structures requiring stable interfacial bonding.

Mechanism of Plasma Treatment for Enhancing Adhesion of Addition-Cure Silicone Rubber

Common substrate surface modification approaches include primer coating, plasma treatment, corona discharge and surface roughening. These physical modification methods improve adhesion by altering surface morphology and properties. Primer pretreatment is an effective way to boost silicone adhesion, yet it has notable practical limitations: solvent volatilization occurs during bonding, adhesion degrades under long-term high-temperature and humid conditions, and certain primer systems may hinder the curing reaction of silicone rubber.

As an eco-friendly and high-efficiency surface modification technique, plasma treatment is solvent-free, pollution-free and energy-saving. It effectively raises surface energy, improves wettability, strengthens chemical compatibility between bonded materials, and enables precise tuning of surface properties of various substrates, holding great promise in surface engineering.

Plasma Treatment Technology

Plasma is an ionized gas consisting of electrons, ions and reactive species. Thanks to its high reactivity and adjustable processing parameters, plasma serves as an ideal material modification tool. Unlike conventional high-temperature calcination or wet chemical treatment, plasma modification can be carried out at room temperature and atmospheric pressure, offering flexible control over surface characteristics.

Plasma treatment improves the adhesion of silicone rubber for two main reasons. First, plasma generates reactive functional groups on the silicone surface and alters surface polarity. Second, plasma induces etching and oxidation on the silicone surface, increasing surface roughness.