The Multi-Layered Structure of Novel Cellulose-Coated Oil-in-Water Emulsions Revealed by Contrast Variation Neutron Scattering*

Amphiphilic cellulose chains dissolve molecularly in the ionic-liquid 1-ethyl-3-methylimidazolium acetate. When the solution is mixed vigorously with oil and water a stable oil-in-water emulsion is formed, as water regenerates an amorphous cellulose coating on the oil droplets. Imaging by cryo-transmission electron microscopy indicated a unique multilayered structure of the cellulose coating. Small-angle neutron scattering from these emulsions was measured at three contrasts: full contrast (protiated oil and cellulose in D₂O), shell contrast (oil matched to D₂O) and core contrast (water matched to cellulose). The fitted model describes a spherical core with two concentric shells. The fitted parameters were the core diameter and thicknesses of the two shells, and the scattering length densities of the inner and outer shells, to account for their cellulose content. Particular attention was focused on whether the inner shell is imbibed by water or oil. It was concluded that the oil core (diameter 67±17 nm) is surrounded by a water-imbibed cellulose hydrogel (~3% cellulose), of thickness 34.5 nm an outer coating of a dense cellulose layer 3.5 nm thick. This novel structure may be utilized as a microreactor for cascade enzymatic reactions