Microfluidic-Assisted Fabrication of Monodisperse Core–Shell Microcapsules for Pressure-Sensitive Adhesive with Enhanced Performance

Microcapsule-based adhesives hold special properties offered by encapsulation via an interfacial shell. Microencapsulation provides the possibility of combining the materials with opposite properties for which co-existence is commonly difficult. In this work, we report on a high performance pressure-sensitive adhesive (PSA) based on monodisperse and size-controllable core–shell microcapsules, which are prepared from double-emulsion droplets constructed using microfluidic devices. Monodisperse microcapsules containing oxalic acid are prepared with a coefficient of variation (CV) size of <5% and the core-material encapsulation efficiency of >90%. The microcapsules and urea-formaldehyde resin are mixed to obtain capsules-based PSA. The overall size uniformity achieved from droplet microfluidics and the rigid interfacial shells from photopolymerized materials ensure high rupture efficiency and sufficient curing reaction during the process. The microcapsules with proper shell thickness can well encapsulate the core material with an even distribution in the center, separating the curing agent from the matrix resin to form a latent adhesive, which is released at the right place and the right time. The bonding strength of >0.7 MPa has been achieved for plywood boards bonding using the prepared PSAs. The capsule-based PSA could encapsulate active components to achieve an extended lifetime for storage, controlled release to achieve on-demand operation, and pressurized mechanical rupture for ease of use. These would be expected to promote the use of PSAs in modern industries such as micro- and nano-optoelectronic devices by further tuning the size and materials of the microcapsules.