Self-assembled polystyrene/xyloglucan nanospheres from spin coating evaporating mixtures

Thin polystyrene-polysaccharide films were deposited on mica by spin coating evaporating mixtures. Solutions of PS (polystyrene) in chloroform (15, 30 and 60 mg/L) and XG (xyloglucan) in water (15 mg/L) were prepared and mixed by stirring in different proportions. After evaporation by spin coating, a low order array of nanospheres was observed by AFM on top of a homogeneous layer, contingent on the proportion of the components in the original mixtures. A XG nanosphere array formed on top of a polystyrene layer was obtained from mixtures containing from 5 to 30% (v/v) of a 15 mg/L XG solution and 95-70% (v/v) of a 15 mg/L PS solution. XPS results showed that equal amounts of XG and PS were adsorbed on the mica substrate for 50% (v/v) XG as well as for 10% (v/v) XG mixtures. PS adsorption was not detected when the XG proportion was 90% (v/v). PS nanospheres were only obtained on top of the XG layer when the PS concentration was increased to four times the original solution. Furthermore, for a constant spin coating speed, the nanosphere diameter was found to be independent of the component proportion within the investigated range. We also found that the nanosphere diameter is correlated to the inverse square-root of the spin coating speed.