Porous polymer materials are essential for a broad range of applications such as automobile parts, medical implants, filtration systems, and catalytic reactors due to a combination of their durability, low weight and cost, and high inner surface. For various of these applications, it is favorable to manufacture microstructures with pores in the range from micrometers to nanometers, also with defined gradients.
In a novel approach, two hitherto separately applied methods, namely hot embossing for microstructuring of polymers and saturation with CO2 under pressure at different temperatures and exposure times are now combined: (i) In a first step, a polymer is microstructured by hot embossing. (ii) In a second step, these microstructures are exposed to CO2 for the pore production. Afterwards they are thermally treated also at different temperatures for different durations.
By the combination of these two methods, with a so far completely different application spectrum, the original material properties of the polymers are modified. Microstructured materials with interconnected pores can be fabricated, but also pore gradients from micr ... mehro to nano size exhibiting improved mechanical and physico-chemical properties. With this method, even the viscoelastic properties of thermoplastic polymers can be tuned by adjusting smoothly graded micro to nano-structures inspired by structural hierarchies and the related excellent mechanical properties of biological materials. Also ultra-thin porous poly-methyl-methacrylate (PMMA) films exhibiting a bright white color, as known from the white beetle of the genus Cyphochilus, can be produced by this saturation method using CO2.