Precision engineering of molecular orientation in amorphous polymer via thermal nanoimprint lithography: From flow mechanics to optical encryption

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Abstract
Thermal nanoimprint lithography (T-NIL) offers a compelling route for simultaneously patterning polymer surfaces and manipulating internal molecular order. However, the fundamental mechanisms governing flow-induced orientation in amorphous polymers and their functional exploitation remain underexplored. This study investigates molecular chain alignment in polycarbonate films during T-NIL, elucidating the link between processing rheology and optical functionality. We demonstrate that the geometry of imprinted structures, specifically gratings and square pillars, strictly dictates local flow fields, resulting in distinct, programmable orientation patterns confirmed by birefringence mapping. Critically, we reveal that the directionality of demolding dictates the interfacial shear stress, which induces a localized shear-aligned surface layer. This interfacial effect can reorient molecular chains at the polymer surface, potentially compromising both structural integrity and programmed optical properties. Furthermore, quantitative analysis reveals that the degree of orientation is tunable via nanoconfinement effects, scaling inversely with feature linewidth and proportionally with aspect ratio. Harnessing this tunable anisotropy, we demonstrate a novel polarization-responsive anticounterfeiting interface. Through the spatial engineering of local optical axes, the fabricated label conceals information under unpolarized ambient light while revealing dynamic, high-contrast patterns under polarized illumination. This study provides a mechanistic framework for nanoimprint-induced molecular alignment in amorphous polymers and demonstrates its potential application in optical anticounterfeiting.
Funding Information
  • Science, Technology and Innovation Commission of Shenzhen Municipality (RCJC20200714114436046)

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