Synthesis of monodisperse, highly ordered polymer foams via milli- and microfluidic techniques

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Polymer foams are of great commercial interest in such diverse fields as packaging, insulation or impact protection. Depending on its application a polymer foam has to meet specific requirements which can be tailored via the composition and the structure. In the proposed project we would like to study structure-property relationships. To characterise the foam structure a number of details such as pore size, number of pores, pore size distribution and pore connectivity need to be determined. However, the high complexity of traditional manufacturing processes makes it very difficult, often even impossible, to control the structure and thus the properties of the material. Even processes which allow changing the structure of the foam do not allow manufacturing monodisperse and highly ordered polymer foams. All commercially available foams have a broad size distribution, which means that the properties are just the mean of the respective distribution. It is above all the precise control of the structure which will enable us to tailor the properties of polymer foams. To reach this goal new concepts need to be found.The proposed project aims at developing such a new concept. The focus will be on polystyrene foams, keeping in mind, however, that the long-term aim is to transfer this concept to a broad variety of polymer foams. The concept is based on the polymerisation of monodisperse, highly ordered liquid foams and emulsions which are generated via milli- and microfluidic techniques, respectively. The basic idea is to manufacture the desired materials via templates which are easy to make. In one case this will be a styrene-in-water emulsion with a high styrene content which we will foam via the fluidic technique. The subsequent polymerisation of the foamed emulsion is intended to lead to a polystyrene foam whose pore size corresponds to the bubble size of the templating foam. In the second case we will generate a water-in-styrene emulsion which will directly be polymerized. The polymer foam is expected to have pore sizes which correspond to the water droplet size of the templating emulsion. In both cases a redox-initiator will be used to start the radical polymerisation. Once the concept is established, we will develop a route towards a polymer foam with a clearly defined pore size gradient. Last but not least, the mechanical properties of the resulting polymer foams need to be measured. In order to quantify the relation between structure and properties we will compare (a) monodisperse polymer foams of different pore sizes and connectivities, (b) monodisperse polymer foams without and with a pore size gradient, and (c) monodisperse with polydisperse polymer foams.