Application of the negative staining technique to both aqueous and organic solvent solutions of polymer particles

Abstract

Transmission electron microscopy (TEM) imaging of several different polymers in aqueous and organic solutions using the negative staining technique is demonstrated, to emphasise the possibilities of this specimen preparation technique for polymer science. Negative stains can readily be prepared in both water and organic solvents (e.g. dimethyl formamide (DMF), dimethyl sulfoxide (DMSO) and tetrahydrofurane (THF)). Polymer particle size, size distribution and shape seen in negative stain correlates well with those of unstained materials. The particle surface and smaller particles (e.g. 10–20 nm) are more clearly defined in the presence of a negative stain. The inherent problems of sample overload, anomalous double-sided sample spreading of the sample on the carbon support film and rapid drying of polymer and negative stain from organic solvents, do not prevent the production and selection of satisfactory specimen regions for TEM study. The presence of metallic clusters within polymer particles is not masked by negative stain and assessment of the number of metallic clusters entrapped within the polymer and/or free in the solvent can be readily made. The cationic negative stain, uranyl actetate (UA), is widely used as the stain of choice for polymer solutions, but the anionic negative stains (phosphotungstic acid (PTA) and ammonium molybdate (AM)) have also been successfully employed in this work.