Relative performance of several surfactants used for heavy crude oil emulsions as studied by AFM and force spectroscopy

Through force spectroscopy, we use an atomic force microscope (AFM) to compare the forces between two extra heavy crude oil (EHCO) droplets. This is done in various aqueous environments in order to compare said forces in the presence of a variety of surfactants and ionic species. A crude oil droplet is attached to the AFM cantilever and pressed against other droplets placed on a substrate. Differences in the behavior of the forces as a function of surfactant chemistry, concentration and the velocity of the approach and retract of the droplets are observed for droplets with a range of diameters 10 < empty set (mu m) < 70. The surfactant H4 (dodecyl-polyglucoside, designed at the Institut Mexicano del Petroleo) is found to cause the highest forces between the droplets and greatest reduction of drop deformation when pressed together. Qualitative agreement is observed with previous theoretical works with regards to the addition of ionic compounds such as sea-water - the droplets approach more closely and coalescence may be favored in some cases. It is possible to observe structure on the surface of other oil drops by tapping mode AFM imaging. It is believed that this is the first time this has been done on extra heavy crude oil droplets. (C) 2015 Elsevier B.V. All rights reserved.