Journal of Colloid and Interface Science 305 (2007) 286–292 www.elsevier.com/locate/jcis Interfacial interactions between hydrocarbon liquids and solid surfaces used in mechanical oil spill recovery Victoria Broje, Arturo A. Keller ∗ Donald Bren School of Environmental Science and Management, University of California, Santa Barbara, CA, USA Received 2 August 2006; accepted 30 September 2006 Available online 5 October 2006 Abstract The goal of this research was to study wetting and adhesion processes between various petroleum products and solid surfaces. When a liquid interacts with a solid surface, wetting, spreading and adhesion processes determine its behavior. These processes are of great importance for understanding oil spill response as well as oil spill behavior on land and in near shore environments, and oil extraction from the reservoir rock. The current study aimed at analyzing oil affinity and adhesion to surfaces used in the mechanical recovery of oil spills. A number of crude oils and petroleum products were tested with the surface materials that are used or may potentially be used to recover oil spills. Through the study of contact angles and recovered mass, it was found that the behavior of the oils at the solid surface is largely determined by the roughness of the solid. For smooth solids, contact angle hysteresis is a good indicator of the ability of the solid to retain oil. For rougher elastomers, the advancing contact angle can be used to predict wetting and adhesion processes between oil and solid. This study showed that oleophilic elastomers (e.g., Neoprene and Hypalon) have higher oil recovery potential than smooth polymers.  2006 Elsevier Inc. All rights reserved. Keywords: Contact angle; Adhesion; Oil; Mechanical recovery; Spreading; Wilhelmy plate; Skimmer 1. Introduction Mechanical recovery is the most commonly used oil spill response technique [1]. This technique physically removes oil from the water surface. The main disadvantage of mechanical cleanup is the recovery rate. When employed on a large scale, it may be very time consuming and expensive. It may require a large amount of personnel and equipment, and every additional hour of cleanup time can significantly increase the cost of re- covery. A more efficient recovery device can thus reduce the cost significantly and reduce the risk of oil reaching the shore- line. An adhesion (oleophilic) skimmer is one of the most com- mon types of mechanical recovery equipment. It is based on the adhesion of oil to the skimmer surface. The rotating sur- face lifts the oil out of the water to an oil removal device (e.g., scraper, roller, etc.). The adhesion surface is the most critical element of the recovery equipment as it largely determines its * Corresponding author. Fax: +1 805 456 3807. E-mail address: keller@bren.ucsb.edu (A.A. Keller). efficiency. Aluminum and common use plastics are currently being used on recovery units. This original material selection was not based on the adhesion properties, but rather on price, availability and historical practice. This research aimed to study the interfacial processes between various oils and solid surfaces in order to identify methods and criteria that would help to se- lect the most efficient material for the recovery unit. Contact angles of liquids on solid surfaces are widely used to predict wetting and adhesion properties through calculation of the solid–vapor surface tension. This method has been dis- cussed in the earlier literature [2–6]. When a drop of liquid is deposited on the solid surface, a contact angle θ is formed. The affinity of a solid for a liquid increases with decreasing θ . The size of this angle is determined by the equilibrium of sur- face forces including liquid surface tension (γ lv ), solid surface energy (γ sv ) and surface tension at liquid–solid interface (γ sl ). This relationship is described by Young’s equation [7]: (1) γ lv cos θ = γ sv − γ sl . The theory of contact angle measurements is based on the equilibrium of an axisymmetric sessile drop on a flat, hori- 0021-9797/$ – see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2006.09.078