The exploitation of spinodal decomposition in the two-dimensional confinement of nanopores and micropores is an elegant strategy for the synthesis of tubes and rods with an internal fine structure. At first, a homogeneous mixture is infiltrated into the pores. Decomposition is induced by thermal quenching or by evaporation of a solvent. The initially fine phase structure coarsens in order to minimize the interfacial area within the system. The presence of the pore walls influences the structure formation, as the component with higher affinity to the wall material segregates to the pore walls. Finally, a layered structure is to be expected (Fig. 1).
Figure 1. Schematic diagram of spinodal decomposition inside nanopores. A homogeneous mixture (green) is infiltrated. Thermal quenching or evaporation of a solvent induces decomposition and the formation of an initially fine phase structure. Ripening occurs driven by the reduction of the internal interface area and by preferential segregation of one of the components to the pore walls. In the end, a layered structure is to be expected.
As example in case, we investigated the decomposition of a polymer/metal precursor mixture. Pyrolysis yielded metal tubes with a fine structure determined by the ripening stage of the phase morphology. Fig. 2a and b show palladium tubes with a fine structure corresponding to an early ripening stage, and Fig. 2 c and d palladium tubes having a morphology corresponding to a late ripening state. Other systems being investigated include, for example, mixtures of polymers and liquid crystals.
Figure 2. Palladium nanotubes having a fine structure generated by decomposition of a polymer/metal precursor mixture. a) Scanning electron microscopy image and b) transmission electron microscopy image of palladium tubes having a morphology corresponding to an early ripening stage. c) Scanning electron microscopy image and d) transmission electron microscopy image of palladium tubes having a morphology corresponding to a late ripening stage.