Giovanni Polito

Template-Assisted Preparation of Micrometric Suspended Membrane Lattices of Photoluminescent and Non-Photoluminescent Polymers by Capillarity-Driven Solvent Evaporation: Application to Microtagging

In this work, the bottom-up template-assisted preparation of high-density lattices (up to 11 · 106 membranes/cm2) of suspended polymer membranes with micrometric size (in the order of few μm2) and sub-micrometric thickness (in the order of hundreds of nm) is demonstrated for both photoluminescent and non-photoluminescent polymers by capillarity-driven solvent evaporation. Solvent evaporation of low concentration polymer solutions drop-cast on an array of open-ended micropipes is shown to lead to polymer membrane formation at the inlet of the micropipes thanks to capillarity. The method is proven to be robust with high-yield (>98%) over large areas (1 cm2) and of general validity for both conjugated and non-conjugated polymers, e.g. poly(9,9-di-n-octylfluorene-alt-benzothiadiazole (F8BT), poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV), polystyrene (PS), thus breaking a new ground on the controlled preparation of polymer micro and nanostructures. Angle dependence and thermal stability of photoluminescence emission arising from F8BT membrane lattices was thorough investigated, highlighting a non-Lambertian photoluminescence emission of membrane lattices with respect to F8BT films. The method is eventually successfully applied to the preparation of both photoluminescent and non-photoluminescent micro Quick Response (μQR) codes using different polymers, i.e. F8BT, MDMO-PPV, PS, thus providing micrometric-sized taggants suitable for anti-counterfeiting applications.

Synergic Integration of Conjugated Luminescent Polymers and Three-Dimensional Silicon Microstructures for the Effective Synthesis of Photoluminescent Light Source Arrays

In this work, a novel and straightforward technology for the fabrication of two-dimensional (2D) photoluminescent light source arrays by selective infiltration of conjugated luminescent polymers into three-dimensional (3D) silicon microstructures is presented. Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) integration into 3D silicon microstructures is investigated by means of three different deposition techniques, namely, spin-coating, dip-coating and drop-casting/slow solvent evaporation. The microstructure is fabricated by electrochemical micromachining (ECM) technology and integrates 2D arrays of square holes with different sizes (about 40 and 4 μm), spatial periods (about 70 and 10 μm), and aspect ratios (ARs) (about one and ten). Notably, square holes with higher AR can be selectively filled with polymer using spin-coating and drop-casting techniques, whereas dip-coating technique allows selective polymer filling of square holes with lower AR. Independently of size, period and AR, each polymer-infiltrated hole behaves as a single light source, thus enabling the effective synthesis of 2D photoluminescent light source arrays.