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Open Access Research

A study of photothermal laser ablation of various polymers on microsecond time scales

Ralf S Kappes12*, Friedhelm Schönfeld3, Chen Li1, Ali A Golriz14, Matthias Nagel5, Thomas Lippert6, Hans-Jürgen Butt1 and Jochen S Gutmann24

Author Affiliations

1 Max Planck Institute for Polymer Research, D-55128 Mainz, Germany

2 Deutsches Textilforschungszentrum Nord-West gGmbH, D-47798 Krefeld, Germany

3 Hochschule RheinMain University of Applied Sciences, Faculty of Engineering, D-65428 Rüsselsheim, Germany

4 Center for Nanointegration Duisburg-Essen (CENIDE), University Duisburg-Essen, D-45141 Essen, Germany

5 Functional Polymers, EMPA Swiss Federal Lab. for Materials Science and Technology, CH-8600 Dübendorf, Switzerland

6 Materials Group, Paul Scherrer Institute, CH-5232 Villigen, PSI, Switzerland

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SpringerPlus 2014, 3:489  doi:10.1186/2193-1801-3-489

Published: 30 August 2014

Abstract

To analyze the photothermal ablation of polymers, we designed a temperature measurement setup based on spectral pyrometry. The setup allows to acquire 2D temperature distributions with 1 μm size and 1 μs time resolution and therefore the determination of the center temperature of a laser heating process. Finite element simulations were used to verify and understand the heat conversion and heat flow in the process. With this setup, the photothermal ablation of polystyrene, poly(α-methylstyrene), a polyimide and a triazene polymer was investigated. The thermal stability, the glass transition temperature Tg and the viscosity above Tg were governing the ablation process. Thermal decomposition for the applied laser pulse of about 10 μs started at temperatures similar to the start of decomposition in thermogravimetry. Furthermore, for polystyrene and poly(α-methylstyrene), both with a Tg in the range between room and decomposition temperature, ablation already occurred at temperatures well below the decomposition temperature, only at 30–40 K above Tg. The mechanism was photomechanical, i.e. a stress due to the thermal expansion of the polymer was responsible for ablation. Low molecular weight polymers showed differences in photomechanical ablation, corresponding to their lower Tg and lower viscosity above the glass transition. However, the difference in ablated volume was only significant at higher temperatures in the temperature regime for thermal decomposition at quasi-equilibrium time scales.

Keywords:
Temperature measurement; Laser heating; Finite element simulation; Polystyrene; Molecular weight; Poly(α-methylstyrene); Polyimide; Triazene polymer; Ablation threshold