Apparatus for “on-the-fly” sample preparation of aerosol-grown block copolymer microdroplets

Abstract

The morphology of phase separated amorphous A/B block copolymers depends not only on the relative volume fraction of the A and B components but also on external shape constraints imposed on the sample. Whereas it is well established that thin planar of microstructured copolymers differ considerably from the bulk materials, the influence of roughness and curvature, which are of practical importance in coating technology, are presently unknown. Because the simplest curved surface is a sphere, the effect of surface curvature on block copolymer microdomains can be conveniently studied by TEM observations of spherical microdroplets prepared with the apparatus described here.Samples for microscopy are prepared by the “gunshot” technique: an atomized solution of the copolymer in a homogeneous solvent is allowed to fall onto carbon coated grids. During fall the solvent evaporates, leaving small spheres of the copolymer that continue falling. By means of a special set of tubes along the fall path, the spheres are annealed (by heating in a nitrogen atmosphere) and stained/fixed (by exposure to osmium tetroxide vapors).