Determination of the nano and microstructures of self assembled block copolymer is normally accomplished by a combination of transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). With more complex polymer architectures and the addition of more block components (A, B, C…) the types of periodic BCP phases has grown markedly including many new multi continuous tubular network phases (double gyroid, double diamond, O52 and O70). A relatively new technique, slice and view scanning electron microscopy (SVSEM), is highly suitable for investigation of complex morphologies since it can directly generate a high resolution 3D tomogram of the nanoscale structure. The particular material studied is a polystyrene (PS) – polydimethylsiloxane (PDMS) diblock copolymer that exhibits the cubic double gyroid network morphology with a lattice parameter of ~ 130 nm, with feature sizes on the 20 nm scale, typical of many soft matter assemblies. By combining thin slices via gallium ion milling with secondary electron imaging using low voltage incident electron beam, the voxel size is approximately 4 nm^3. SVSEM allows analysis of a host of sub-unit cell morphological descriptors and critical comparison to theoretical models of the structure. For example, the network dihedral angles, the network skeletal graph, the distance distribution between the BCP interface and the skeletal graph and the distance distribution between the BCP interface and the gyroid minimal surface are measured and compared to self consistent field calculations.
Ned Thomas’ research interests include polymer
physics and engineering of the mechanical and optical properties of block
copolymers, liquid crystalline polymers, and hybrid organic-inorganic