Steerable mass transport in a photoresponsive system for advanced anticounterfeiting

Assembly‐Induced Dynamic Structural Color in a Host‐Guest System for Time‐Dependent Anticounterfeiting and Double‐Lock Encryption

“…It is well known that cis-azo groups often undergo cis-to-trans back-isomerization upon heating and the recov- ered trans-azo moieties may form mesogenic phase. [19] As we reported earlier, [18] the 5 : 1 sample has a glass-transition temperature (T g ) at 45 °C and a transition temperature from liquid-crystalline phase to isotropic phase (T i ) at around 100 °C. Therefore, surface morphing has been conveniently manipulated by heating the film with tunable surface relief gratings (SRGs) at different temperatures, then variations of structural color can be observed by naked eye.…”

“…Previous work has demonstrated that the region where the value of scale bar � 0.10 is cis-rich, the region where the value of scale bar � 0.06 is trans-rich, and the initial state is a periodic distribution of trans-azo groups and their cis-isomers. [18] As shown in Figure S5a, the transrich region and cis-rich region can be distinguished in Raman microscopy, where the dark green area was cis-rich and the light area was trans-rich. Upon heating the film at 100 °C until 1 st DA, the value of scale bar in the entire film was less than 0.06 (Figure S5b), indicating that the film was in the trans-rich state and cis-to-trans thermal recovery was almost completed, consistent with the result of UV/Vis absorption spectra (Figure 2a).…”

“…The mixture solution was spin-coated on the substrate, and then after pre-illumination and photo-patterning using a photomask with a periodic pattern, the film was exposed to methanol vapor for a period of time to fabricate micro/nanostructures on film surface (Figure S1). The best host-guest molar ratio for fabricating micro/nanostructures on film surface is 5 : 1 ([the repeated unit of PM6AZC4] : [5CB]) according to previous work, [18] so the 5 : 1 film sample was used in this work except for cases where the host-guest ratio was changed. It is well known that cis-azo groups often undergo cis-to-trans back-isomerization upon heating and the recov- ered trans-azo moieties may form mesogenic phase.…”

“…Our previous work has demonstrated that the host-guest system can generate periodic micro/nanostructures on film surface by mass transport upon exposure to solvent vapor, exhibiting vivid angle-dependent structural color. [18] Usually, cis-azo groups can thermally recover to their trans-isomers, and trans-azo moieties often act as mesogenic moieties undergoing assembly processes. These can be utilized to design an anticounterfeiting material with multiple switchable states of structural color.…”

Manipulation of photoresponsive liquid-crystalline polymers and their applications: from nanoscale to macroscale

“…Essentially, this flow from the flowing fluid ( cis -rich PM6AZC4) to the glassy plastic ( trans -rich PM6AZC4) is the capillary flow induced by the flow of the solvent on the film surface with wettability gradients. 110 Therefore, combining this unique phenomenon with the traditional Marangoni flow, a steerable mass transport direction was successfully realized. 110 To obtain well-controlled bidirectional mass transport, one commercial small-molecule nematic LC, 4-cyano-4′-pentylbiphenyl (5CB), was introduced into the azopolymer as a functional additive to build a host–guest system (half-life: 7.8 h).…”