Fabrication of Slippery Lubricant-Infused Porous Surface for Inhibition

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Fabrication of slippery lubricant-infused porous surface for inhibition of microbially influenced corrosion Peng Wang, Dun Zhang, Zhou Lu, and Shimei Sun ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b08452 • Publication Date (Web): 30 Nov 2015 Downloaded from http://pubs.acs.org on December 7, 2015

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ACS Applied Materials & Interfaces

Fabrication of slippery lubricant-infused porous surface for inhibition of microbially influenced corrosion Peng Wanga, Dun Zhanga,*, Zhou Lua,b, Shimei Suna,b a

Key Laboratory of Marine Environmental Corrosion and Bio-fouling, Institute of

Oceanology, Chinese Academy of Sciences, 7 Naihai Road, Qingdao 266071, China b

University of the Chinese Academy of Sciences, 19 (Jia) Yuquan Road. Beijing 100039, China.

Abstract: Microbially influenced corrosion (MIC) accelerates the failure of metal in marine environment. In this research, slippery lubricant-infused porous surface (SLIPS) was designed on aluminum; and its great potential for inhibiting MIC induced by sulphate-reducing bacteria (SRB) was demonstrated in simulated marine environment. The inhibition mechanism of SLIPS to MIC was proposed based on its effective roles in the suppression to SRB settlement and isolation effect to corrosive metabolites. The liquid-like property is demonstrated to be the major contributor to suppression effect of SLIPS to SRB settlement. The effects of environmental factors (static and dynamic conditions) and lubricant type to SRB settlement over SLIPS were also investigated. It was indicated that the as-fabricated SLIPS can inhibit the SRB settlement in both static and dynamic marine conditions, and lubricant type presents negligible effect to the SRB settlement. These results will provide a series of foundational data for the future practical application of SLIPS in marine environment, and also a lubricant selecting instruction to construct SLIPS for MIC control.

Key words: Interfaces; Microbially influenced corrosion; Sulphate-reducing bacteria; Slippery lubricant-infused porous surfaces; Aluminum.

1. Introduction Metal corrosion occurs in almost every natural environment, especially in the *

Corresponding author. Tel./Fax:+86 532 82898960. E-mail address: [email protected](Dun Zhang). 1

ACS Paragon Plus Environment


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marine environment. A large number of microorganisms can survive in the ocean. These microorganisms influence the climate, participate in the energy cycle, and provide energy to humans. However, the activity or metabolic products of these microorganisms can accelerate the corrosion process of metal, and this process is generally called microbially influenced corrosion (MIC). According to a previous report, up to 20% of all corrosion losses in the marine environment can be attributed to MIC. 1 Biofilm formation is one of the most common survival strategies of microorganisms in the ocean. This strategy allows microorganisms to form a microenvironment for their defense and food supply. The biofilm can induce or accelerate metal corrosion through numerous mechanisms. Sulphate-reducing bacteria (SRB), a type of corrosive microorganisms typically found in the ocean, were generally utilized as model corrosive bacteria to illuminate the MIC mechanism. Several MIC mechanisms, such as cathodic depolarization theory,

6

2–5

highly reactive

volatile phosphorus compound formation theory, 6 and biopolymer-induced corrosion theory, 7 have been proposed. MIC is a phenomenon that occurs on the metal/solution interface. The surface properties of metal substrates can affect bacterial settlement

8, 9

and their subsequent

corrosion behavior. Superhydrophobic surfaces have attracted intense research interest for their potential applications in MIC control and antibiofouling. These surfaces can inhibit bacterial settlement and consequently reduce MIC. 10, 11 The superhydrophobic properties of a surface originate from the diminished contact of the surface with water via trapping of air pockets within its microstructure. 12, 13 The presence of air pockets is regarded as the main mechanism of antibiofouling.

14

In practical applications, air

pockets can be collapsed by external wetting pressures and microstructure damage. Thus, maintaining stable air pockets remains challenging in industrial applications of superhydrophobic surfaces. 15, 16 As a typical kind of carnivorous plant, Nepenthes utilizes its porous microstructures to lock a layer of liquid, which induces insects to slide into the digestive juice by repelling the oils on their feet.

17-20

2


Inspired by this concept,

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slippery lubricant-infused porous surface (SLIPS) was designed to present anti-wetting properties toward nearly all types of liquid.

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In contrast with

super-hydrophobic surface, the SLIPS can withstand higher external pressure and presents self-healing property. These properties endow SLIPS with advantages in practical application. SLIPS can also prevent the attachment of bacteria, zoospores of the alga Ulva linza in marine environments. 21-25 As such, SLIPS may be expected to suppress bacterial settlement, thereby inhibiting the occurrence of MIC in seawater. In the present study, a simple procedure was utilized to fabricate SLIPS over aluminum. Typical corrosive bacteria (SRB) were used as model bacteria in anti-MIC test. The effects of environmental factor (static and dynamic conditions) and lubricant type on SRB settlement over SLIPS were investigated, to obtain deep insight into the ability of SLIPS to retard SRB settlement. To reveal the major contributors to the suppression effects of SLIPS to SRB settlement, polished silicon wafers with different wettability were utilized as references for comparison. Finally, an anti-MIC mechanism of SLIPS was proposed based on the observed suppression of SRB settlement, and contact inhibition between corrosive metabolites and the substrate. This research provides a theoretical foundation for designing highly effective method for MIC control in marine environment. 2. Experimental 2.1 Materials and reagents Aluminum with purity of ≥ 99.99 wt.% was purchased from Beijing Cuibolin Non-Ferrous

Technology

Developing

Co.,

Ltd.

(China).

The

1H,1H,2H,2H-perfluorodecyl-triethoxysilane (PFTEOS, 97%) was purchased from Sigma-Aldrich. Perfluoropolyether (PFPE, NascentTM FX-5200, FX-7200, FX-8205, Switzerland) was used as received. Other chemical reagents employed in this work were of analytical grade and used as received. Milli-Q water with a resistivity of 18.2 MΩ·cm was used in all experiments. 2.2 Fabrication of SLIPS Aluminum samples were cut into dimensions of 1.2 cm × 2 cm × 0.1 cm, and polished using the same electrochemical method described in our previous report. 3


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After electropolishing, anodization was carried out in a two-electrode cell at room temperature. In the two-electrode cell, the polished aluminum and stainless steel were respectively used as working and counter electrodes. A voltage of 80 V was applied between the two electrodes during anodization, and the anodization time was set to 30, 60, or 120 s. After anodization, the aluminum samples were immersed in ethanol solution with 1 vol.% PFTEOS for 5 min at room temperature and then transferred into an oven for heating (120 °C, 10 min). After modification, lubricant was poured onto the modified samples. The samples were tilted at an angle of about 20°for more than 2 h to allow the excess lubricant to flow off. Unless otherwise specified, SLIPS infused with lubricant FX-5200 was utilized for characterization and evaluation. 2.3 Characterization 2.3.1 Morphology and composition characterizations A field emission scanning electron microscope (Hitachi S4800, Tokyo, Japan) was utilized to monitor micro-morphological changes to the aluminum layer with anodization time, and X-ray photoelectron spectroscopy (XPS) (Thermo Escalab 250, USA) was utilized to analyze the surface chemical composition of samples. Atomic force microscopy (AFM) (Agilent 5400, USA) was used to characterize the topography of silicon wafers and the negative replicate (resin layer) of SLIPS. Fluorescence microscope (Olympus BX-51, Tokyo, Japan) was utilized for the observation of SRB settlement. The static contact angle and sliding angle of water droplets (volume, 3 μL) on the sample surfaces were measured by a contact angle meter (Powereach, JC2000C1, Shanghai, China). They were determined from three droplets at three different locations per sample, and the mean value ± standard deviation of three replicates was reported. 2.3.2 Electrochemical experiment Potentiodynamic polarization experiments were performed in a conventional three-electrode cell using an electrochemical instrument (CHI760C, Shanghai, China). Test specimens with an exposed area of 0.5 cm2 were used as the working electrode. A platinum wire and silver–silver chloride (Ag/AgCl, 3 M KCl) reference electrode were used as the counter electrode and reference electrode, respectively. Before 4


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polarization measurements, the test specimens were immersed in the test electrolyte (seawater with SRB at 30 °C) at the open circuit potential until a steady state was achieved. Polarization curves were recorded with a potential sweep rate of 1 mV·s−1. 2.4 Microorganism cultivation and toxicity test 2.4.1 Microorganism cultivation The model SRB (Desulfovibrio sp.) samples were isolated from Bo Sea, China. They were grown in sterilized seawater with addition of Na2SO4 and MgSO4. 200 mL of fresh seawater with 0.4 g of Na2SO4 and 0.1 g of MgSO4 was injected into an Erlenmeyer flask and autoclaved at 121 °C for half hour. After cooling down to 25 °C, the sterilized seawater was then inoculated with SRB, sparged with nitrogen for 60 min, and then stored in incubator at 30 °C. The as-obtained seawater with SRB was used for the SRB settlement and electrochemical experiments in this research. 2.4.2 Toxicity assessment of lubricant The toxicity of the lubricant to SRB was evaluated by analyzing its impact on the SRB biofilm. In details, the viability of SRB biofilms in physical contact with the sterilized SLIPS and a sterilized slide glass was compared. Figure S1 shows schematic representations of the test procedure. 2.4.3 SRB settlement analysis After sterilization by ultraviolet radiation for 30 min, bare aluminum and SLIPS samples were immersed into seawater inoculated with SRB to initiate SRB settlement analysis and electrochemical measurement. The SRB settlement experiment was performed in both static and dynamic environments. To achieve SRB settlement analysis in a static environment, the sterilized samples were immersed vertically in seawater with SRB at 30 ± 2 °C. For SRB settlement analysis in a dynamic environment, samples were attached to the inner surface of an Erlenmeyer flask filled with seawater with SRB. Figure S2 shows a schematic of the simulation device. The Erlenmeyer flask was shaken using an orbital shaker at 30 °C with a shaking speed of 120 rpm. The movement speed of seawater over the samples can be estimated to be 40 cm/s. During immersion in both environments, 100 mL of sterile fresh seawater with addition of 0.2 g of Na2SO4 and 0.05 g of MgSO4 was injected into the system every 3 5



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days to replace an equivalent volume of the old seawater with SRB; this step ensures sufficient energy to maintain bacteria activity. Samples after settlement experiments were immersed into acridine orange solution with concentration of 10 μg/mL for 0.5 h. After being washed with sterile seawater, the stained samples were observed with a fluorescence microscope, and the coverage of the SRB biofilm over the samples was determined by using Image J software. 2.5 Statistical Analysis The statistical results in this research were represented as mean ± standard deviation, and they were assessed statistically using one-way analysis of variance with Tukey post hoc test. A P value of

Fabrication of Slippery Lubricant-Infused Porous Surface for Inhibition

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