Janus optical clear adhesive with tunable crosslinking density gradient for foldable display

With the rapid advancement of flexible electronic technology, foldable displays have emerged as a leading application requiring highly reliable optical clear adhesives (OCAs). However, conventional OCAs lead to crease formation and interfacial failure on the screen under repeated folding. Here, a novel, flexible bilayer OCA with Janus feature in crosslinking density (v) is proposed, balancing high interfacial adhesion and high internal cohesion. The bilayer design enables a gradient v along the thickness direction, which is directly quantified by advanced unilateral NMR (UNMR). The optimized Janus OCA achieves comparable optical performance but superior mechanical properties compared to conventional OCA, effectively mitigating screen creases during dynamic folding test. Such enhanced performance originates from its asymmetric architecture, in which the low-v layer accommodates deformation on the compressive side, while the high-v layer maintains integrity on the tensile side. This design strategy offers a promising pathway toward next-generation flexible and foldable display technologies.