Article pubs.acs.org/Langmuir
Interaction of Oil Drops with Surfaces of Different Interfacial Energy and Topography Joseph C. Cremaldi,† Tushar Khosla,† Kejia Jin,†,‡ David Cutting,†,§ Kristen Wollman,† and Noshir Pesika*,† †
Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, United States Intralox, New Orleans, Louisiana 70123, United States § Koch International, Witchita, Kansas 67220, United States ‡
S Supporting Information *
ABSTRACT: During a marine oil spill, the oil can interact with and potentially wet a variety of surfaces such as corals, skin/shells of marine animals, and bird feathers. We present both qualitative and quantitative data for the interaction of a dodecane droplet submerged in water with surfaces varying in both surface energy and roughness. Flat, unstructured silicon surfaces with water in air contact angles of 0°, 43°, 66°, 87°, 96°, and 108° were tested first to obtain base readings, after which photolithography was used to introduce structured surfaces representative of marine biological systems. We find that the more hydrophilic a surface, the less prone it is to oil contamination. Also, the Cassie−Baxter approximation holds up for submerged oil in water systems and can be used to predict contact angles of oil on solid rough surfaces submerged in an aqueous environment. Furthermore, the addition of surface structure, even on strongly hydrophobic (oleophilic) surfaces, greatly reduced (≈75% reduction in Fadhesion) a surface’s affinity for oil.
■
INTRODUCTION The interaction (i.e., spreading or wetting) of oil with any surface is dependent on surface topography and chemistry. Surface topography encompasses the physical shape of the surface and can be present on many scales and several levels of hierarchy, while surface chemistry encompasses the material or materials that make up the surface. During an oil spill, oil (in the form of an oil slick or dispersed oil droplets) may cause economic loss and environmental damage to the affected region. Despite the fast-acting biodegradation of petroleum hydrocarbons,1,2 environmental damage comes in a variety of forms encompassing marine life and costal ecologies. This includes but is not limited to fouling and deterioration of deepwater coral communities3,4 and population loss in sea dwelling mammals5,6 fish7,8 and birds9,10,11 through exposure or ingestion. Additionally, coastal damage to plant life in wetlands and marshes causes plant death while also disrupting nesting and migration areas.12,13,14 Long term studies have shown that these adverse effects are unbalancing to the ecosystem and long lasting,6,15,16 showing the need for an understanding of the most basic principles and mechanisms in which oil interacts with and coats surfaces. Understanding these complex interactions will help to both prevent and minimize damage, while also allowing one to capture the beneficial attributes of these surfaces through biomimicry and its wide range of applications. To demonstrate the variation in oil−surface interactions during a spill, two representative biological samples have been © 2015 American Chemical Society
characterized: saltmarsh cordgrass, Spartina alternif lora, and the applesnail, Pomacea canaliculata (Figure S1). Spartina alternif lora has stomata present on the adaxial surface and an epicuticular, hydrophobic wax coating over the entirety. Pomacea canaliculata displays macrolevel roughness on the outer shell and is hydrophilic. The interactions with water/air (W/A) systems and submerged oil/water (O/W) systems display the effects of roughness on biological samples. Spartina alternif lora displays a superhydrophobic interaction with a water droplet due to the ridges whereas Pomacea canaliculata is wetting to a water drop with a contact angle below 90°. When submerged in deionized water (DI H2O), the adaxial surface of Spartina alternif lora is superoleophilic (completely wetting to oil) due to the wax coating, whereas that of the Pomacea canaliculata is superoleophobic. With an end goal of quantifying the relationship between oil and these types of surfaces, we aim to quantify and characterize their interactions. Because surface testing on biological samples may be difficult to experiment on reliably, however, we have modeled these types of surfaces using surface patterning and treatment. In doing so, oil−surface interactions are more quantifiable and reproducible. In order to quantify the interaction of an oil drop with a surface, oil bridging has proven to be a reliable approach previously in terms of both experimental and modeling Received: January 9, 2015 Revised: February 26, 2015 Published: February 27, 2015 3385
DOI: 10.1021/acs.langmuir.5b00051 Langmuir 2015, 31, 3385−3390
Article
Langmuir
A typical maximum contact angle of a water drop on a flat, fully hydrophobic surface in air ranges from 110° to 115°35,36 but this limit may be far surpassed when roughness is introduced in the surface.37 This effect is commonly seen in nature on surfaces that are self-cleaning (due to extremely small roll-off tilt angles
Interaction of Oil Drops with Surfaces of Different Interfacial Energy and Topography Joseph C. Cremaldi,† Tushar Khosla,† Kejia Jin,†,‡ David Cutting,†,§ Kristen Wollman,† and Noshir Pesika*,† †
Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana 70118, United States Intralox, New Orleans, Louisiana 70123, United States § Koch International, Witchita, Kansas 67220, United States ‡
S Supporting Information *
ABSTRACT: During a marine oil spill, the oil can interact with and potentially wet a variety of surfaces such as corals, skin/shells of marine animals, and bird feathers. We present both qualitative and quantitative data for the interaction of a dodecane droplet submerged in water with surfaces varying in both surface energy and roughness. Flat, unstructured silicon surfaces with water in air contact angles of 0°, 43°, 66°, 87°, 96°, and 108° were tested first to obtain base readings, after which photolithography was used to introduce structured surfaces representative of marine biological systems. We find that the more hydrophilic a surface, the less prone it is to oil contamination. Also, the Cassie−Baxter approximation holds up for submerged oil in water systems and can be used to predict contact angles of oil on solid rough surfaces submerged in an aqueous environment. Furthermore, the addition of surface structure, even on strongly hydrophobic (oleophilic) surfaces, greatly reduced (≈75% reduction in Fadhesion) a surface’s affinity for oil.
■
INTRODUCTION The interaction (i.e., spreading or wetting) of oil with any surface is dependent on surface topography and chemistry. Surface topography encompasses the physical shape of the surface and can be present on many scales and several levels of hierarchy, while surface chemistry encompasses the material or materials that make up the surface. During an oil spill, oil (in the form of an oil slick or dispersed oil droplets) may cause economic loss and environmental damage to the affected region. Despite the fast-acting biodegradation of petroleum hydrocarbons,1,2 environmental damage comes in a variety of forms encompassing marine life and costal ecologies. This includes but is not limited to fouling and deterioration of deepwater coral communities3,4 and population loss in sea dwelling mammals5,6 fish7,8 and birds9,10,11 through exposure or ingestion. Additionally, coastal damage to plant life in wetlands and marshes causes plant death while also disrupting nesting and migration areas.12,13,14 Long term studies have shown that these adverse effects are unbalancing to the ecosystem and long lasting,6,15,16 showing the need for an understanding of the most basic principles and mechanisms in which oil interacts with and coats surfaces. Understanding these complex interactions will help to both prevent and minimize damage, while also allowing one to capture the beneficial attributes of these surfaces through biomimicry and its wide range of applications. To demonstrate the variation in oil−surface interactions during a spill, two representative biological samples have been © 2015 American Chemical Society
characterized: saltmarsh cordgrass, Spartina alternif lora, and the applesnail, Pomacea canaliculata (Figure S1). Spartina alternif lora has stomata present on the adaxial surface and an epicuticular, hydrophobic wax coating over the entirety. Pomacea canaliculata displays macrolevel roughness on the outer shell and is hydrophilic. The interactions with water/air (W/A) systems and submerged oil/water (O/W) systems display the effects of roughness on biological samples. Spartina alternif lora displays a superhydrophobic interaction with a water droplet due to the ridges whereas Pomacea canaliculata is wetting to a water drop with a contact angle below 90°. When submerged in deionized water (DI H2O), the adaxial surface of Spartina alternif lora is superoleophilic (completely wetting to oil) due to the wax coating, whereas that of the Pomacea canaliculata is superoleophobic. With an end goal of quantifying the relationship between oil and these types of surfaces, we aim to quantify and characterize their interactions. Because surface testing on biological samples may be difficult to experiment on reliably, however, we have modeled these types of surfaces using surface patterning and treatment. In doing so, oil−surface interactions are more quantifiable and reproducible. In order to quantify the interaction of an oil drop with a surface, oil bridging has proven to be a reliable approach previously in terms of both experimental and modeling Received: January 9, 2015 Revised: February 26, 2015 Published: February 27, 2015 3385
DOI: 10.1021/acs.langmuir.5b00051 Langmuir 2015, 31, 3385−3390
Article
Langmuir
A typical maximum contact angle of a water drop on a flat, fully hydrophobic surface in air ranges from 110° to 115°35,36 but this limit may be far surpassed when roughness is introduced in the surface.37 This effect is commonly seen in nature on surfaces that are self-cleaning (due to extremely small roll-off tilt angles
