Interlayers

An interlayer is a material layer placed between two other layers in a composite, laminate, coating, glaze, or geological sequence. Its purpose is to improve adhesion or bonding, reconcile differences in mechanical behavior, control diffusion or moisture, and sometimes provide a functional property such as damping, insulation, or ion exchange. Interlayers can be organic or inorganic, thin films, foils, sheets, or gels, and may be static or reactive.

In laminated glass and composites, interlayers hold components together after fracture and enhance safety by keeping shards bonded (for example, polyvinyl butyral or ionoplast between glass panes). In fiber-reinforced laminates, interlayers between plies can improve delamination resistance and energy absorption.

In geology and mineralogy, interlayers occur in layered minerals such as clays, where spaces between tetrahedral and octahedral sheets host water molecules and exchangeable cations. The interlayer region governs swelling, rheology, and stability, affecting soil behavior, drilling, and sediment transport.

In civil engineering and construction, interlayers are used between structural layers to distribute load, reduce crack propagation, and improve bonding and drainage. Examples include asphalt-treated interlayers, geosynthetic sheets, and bonding agents designed to mitigate stress and vibration.

In electronics and coatings, interlayers act as diffusion barriers, adhesion promoters, or buffer layers between substrates and functional films. They help control interface reactions, improve film integrity, and accommodate thermal or mechanical mismatch.

Overall, interlayers are versatile components that tailor the interaction between adjacent layers to enhance performance, durability, and functionality across multiple disciplines.