Mechanism of Pressure-Sensitive Adhesion in Nematic Elastomers

Nematic liquid crystal elastomers (LCEs) have anomalouslyhighvibration damping, and it has been assumed that this is the causeof their anomalously high-pressure-sensitive adhesion (PSA). Here,we investigate the mechanism behind this enhanced PSA by first preparingthin adhesive tapes with LCE of varying cross-linking densities, characterizingtheir material and surface properties, and then studying the adhesioncharacteristics with a standard set of 90 & DEG; peel, lap shear, andprobe tack tests. The study confirms that the enhanced PSA is onlypresent in (and due to) the nematic phase of the elastomer, and thestrength of bonding takes over 24 h to fully reach its maximum value.Such a long saturation time is caused by the slow relaxation of localstress and director orientation in the nematic domains after pressingagainst the surface. We confirm this mechanism by showing that freshlypressed and annealed tape reaches the same maximum bonding strengthon cooling, when the returning nematic order is forming in its optimalconfiguration in the pressed film.

Automated summary

The abnormal high adhesion strength of nematic liquid crystal elastomers is due to the slow relaxation process of stress and director orientation in the nematic domains after contacting with the surface. The bonding strength reaches its maximum value after more than 24 hours of saturation time. Freshly pressed and annealed tapes demonstrate the same maximum bonding strength upon cooling, indicating the formation of optimal nematic order in the pressed film.