Plastic fingerprint replica: solvent-assisted 3D molding and motion-promoted nano-spherulite formation

Fingerprinting is an essential form of identification for both biometric security and forensics today. Herein, we describe the procedure and principle of creating highly resolved, chemically robust, 3D fingerprint physical replicas, which is based on the solvent-assisted molding of transparent plastics and motion-promoted growth of semi-crystalline polymeric nanostructures. Prior to fingerprinting atop, polycarbonate, a commercial polymer with excellent durability and optical transparency, is first swelled and softened with a mild solvent (acetone). The molding motion conforms polymer chains between fingerprint ridges, which facilitates the formation of semi-crystalline spherulites and results in greater opacity between ridges than underneath ridges. Besides being more enduring than digital scanning and ink printed counterparts, the plastic fingerprint replicas can provide additional morphological information (depth of the ridge) and high-level details (distribution of sweat pores).

AFM Studies on the Effect of Crystalline Interphase on Adhesion of Polyurethane Thin Film to Al Substrate

Polyurethanes crystallized at the aluminum surface, but the crystalline interphase varied with polyol OH number. Early stage of spherulite formation was characterized using AFM after removing amorphous polyurethane. The crystallite shapes of polyurethanes were correlated with the bond strength measured from indentation debonding. Interestingly, the samples involving non-specific shape of crystallites displayed high bond strength, while the polyurethanes with rod-like crystallite poorly adhered to aluminum substrate. Although crystallite shape did not unequivocally relate to bond strength, the results propose that there is a probable correlation.