Repositionable pressure-sensitive adhesive possessing thermal-stimuli switchable transparency

Described is the formulation for a repositionable pressure-sensitive adhesive (PSA) capable of reversibly switching between opaque and transparent via a thermal trigger. The smart adhesive is generated by casting films from a solution of polydimethylsiloxane (PDMS), its organometallic crosslinker and a paraffin wax/dodecane solution on poly(ethylene terephthalate) (PET) sheets. Once cured, the PDMS/paraffin wax composite films demonstrate characteristics consistent with commercial repositionable PSAs. Properties were found to be dependent on the paraffin wax content and degree of crosslinking in the PDMS. Performance of the developed adhesive films is highly stable remaining unchanged subsequent to extended use and repeated repositioning. The appearance of the films can be switched between opaque at room temperature to transparent for temperatures above 53 °C. The change in optical properties is nearly instantaneous and there appears to be no limitation on how many times the cycle can be repeated. The mechanism involved is unique involving the melting of the paraffin wax, which appears to allow for the formation of a more homogeneous composite structure. This adhesive formulation may be well suited for use as a low-cost, convenient smart window coating.