Preparation and Antiscaling Application of Superhydrophobic

Subscriber access provided by UNIV OF MISSISSIPPI

Article

Preparation and Anti-scaling Application of superhydrophobic Anodized CuO nanowires Surface Wei Jiang, Jian He, Feng Xiao, Shaojun Yuan, Houfang Lu, and Bin Liang Ind. Eng. Chem. Res., Just Accepted Manuscript • Publication Date (Web): 19 Jun 2015 Downloaded from http://pubs.acs.org on June 20, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Preparation and Anti-scaling Application of superhydrophobic Anodized CuO nanowires Surface Wei Jiang*, Jian He, Feng Xiao, Shaojun Yuan, Houfang Lu, Bin Liang 1 Multi-phases Mass Transfer and Reaction Engineering Laboratory, College of Chemical Engineering, Sichuan University, Chengdu 610065, China; *Corresponding author: [email protected]

1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Anti-scaling technology is necessary in order to prevent the performance loss and blockage of heat-exchanger. In this research, a superhydrophobic CuO nanowire layer was prepared and utilized for anti-scaling process of CaCO3 on the surface of copper. Modified with 1H,1H,2H,2H-perfluorooctyltriethoxy-silanen (FAS-17) the water contact angle on the CuO surface increased sharply from the 4.5±1° after anodization to 154±2° since the free surface energy decreased from 74.8 mJ/m2 of hydrophilic surface to 0.2 mJ/m2 of superhydrophobic surface. The scale inhibition performance of superhydrophobic CuO nanowires surface was confirmed since the corresponding scaling weight of deposited CaCO3 decreased significantly from 0.6322 mg/cm2 to 0.1607 mg/cm2. This attractive anti-scaling effect of modified superhydrophobic CuO nanowires surface should ascribe to the slow CaCO3 crystal nucleation rate due to the low surface energy, low adhesion strength of CaCO3 crystal and air film retained on the superhydrophobic surface.

Key words: Anti-scaling, Superhydrophobicity, Calcium Carbonate, CuO nanowires, Anodization

2


Page 2 of 49

Page 3 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction Heating and cooling operations are commonplace in modern chemical industry, and heat exchanger is the major device. However, scaling on the surface of heat-exchanger tubes due to the precipitation of dissolved inorganic materials, especially calcium and magnesium salt, will lower the performance of heat-exchanger seriously. Two problems, degradation of thermal conductivity and increase of flow resistance, are due to the occurrence of scale, resulting in the increase of operation and equipment cost1, 2. Garret-Price3 et al estimated that the annual cost of fouling and corrosion for the U.S. industry was about U.S. $ 8–10 billion. In China, the estimated economic penalty per year due to scaling was more than 60 billion4. For the total industrialized in US, the economic loss due to oversized plant, reduced thermal efficiency, increased pressure drop, additional maintenance and loss of production, has been estimated as about $ 5 × 1010 per year5, 6. Therefore, anti-scaling technology is an essential approach to enhance the operation and extend the lifetime of equipment, alleviating such serious pecuniary loss. Calcium carbonate is one of the most common scales in the industrial process, and becomes the hot subject of anti-scaling in the present study. There are three developing routes to retard or prevent scale formation of CaCO3: scaling inhibitors7, 8, water pretreatment9,10,11, and surface treatment12. The former two methods can retard

3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

scaling process effectively, but the cost is relatively high because of the large amount of water for treating and potential water pollution. The cost of the third method is proportionately low since only a small amount of solid surface should be purposefully modified to prevent scaling. The target of surface modification is to lower the surface free energy, which is the key factor in the heterogeneous nucleation and growth of crystals13,14. With the decreasing of heterogeneous nucleation rate of CaCO3, the surface of heat-exchanger pipe can automatically realize the performance of anti-scaling. The modification methods to lower the surface free energy include ion implantation15,16, magnetron sputtering17, chemical deposition18, etc. Among them, molecular self-assembled monolayers (SAMs) technology exhibits a widely potential application in the metal protection field because of simple operation, low cost, high anti-corrosion ability, and thin thickness resulted from the dense, ordered, and hydrophobic self-assembled film on the surface. The surface with low surface free energy is hydrophobic, and the materials with static water contact angle larger than 150° are defined as superhydrophobic materials. Usually the superhydrophobic materials were prepared by creating a rough structure on a hydrophobic surface (CA>90°), or modifying a rough surface with low surface free energy substance16. The main difficulty in preparing superhydrophobic materials is the construction of an appropriate fine structure on the surface. Recent years

4


Page 4 of 49

Page 5 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


superhydrophobic materials have attracted significant attentions because of its extensive potential use, such as self-cleaning19, antifogging20, oil/water separation21,22, drag reduction23, etc. However, utilization of superhydrophobic surfaces as anti-scaling material was not reported before. Promoting an effective anti-scaling layer with superhydrophobicity is a promising research direction for industrial anti-scaling application. Copper is a common material as heat-exchanger thermal conductive material due to its high heat transfer coefficient, but the scaling problem degrades its thermal-conductivity seriously. In recent years, a superhydrophobic copper surface with delicate structure has been reported to be prepared with anodization process in NaOH and KOH solution

24,25,26

. This gives the possibility to achieve an anti-scaling

superhydrophobic copper surface after modified with minimal free energy substance such as silane, which has been widely used to prepare stable superhydrophobic surface on the surface of aluminum and its alloy 23,27. In this study, copper will be anodized in NaOH solution to construct microstructure, modified with 1H,1H,2H,2H-perfluorooctyltriethoxy-silanen (FAS-17) to build superhydrophobic surface, and used for anti-scaling of CaCO3. The anti-scaling effect of superhydrophobic copper surface will be discussed in detail, and the anti-scaling mechanism will be studied systematically.

5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 49

2. Experiments 2.1 Materials Commercially Cu foils (0.1 mm thick; purity ≥ 99.8%)were purchased from Shenzhen Jiusheng copper & aluminum stainless steel material Co. LTD (China). 1H, 1H,

2H,

2H-Perfluorodecyltriethoxysilane

(FAS-17)

was

purchased

from

Sicongprotect Chemicals Corp. (China). The other chemical reagents were analytical-grade and obtained from Kelong Chemicals Corp. (Chengdu, China). All reagents were used without further treatment unless otherwise specified. 2.2 Synthesis of CuO nanowire films The copper foil was mechanically polished with 1000#, and 1200# metallographic sand paper, in succession, and then ultrasonically cleansed with acetone, isopropyl alcohol, ethanol, and deionized water sequentially. After that, the copper foil was chemically polished in 0.1 mol/L HCl solution for 40 min. Hereafter the anodization of polished copper foil was carried out in 1M NaOH aqueous solution, which has been deaerated with a dry nitrogen stream for 1h without stirring. The copper foil served as anode while platinum as cathode electrode. The distance between the two electrodes was 3 cm and the current density was kept constant value of 0.06 mA/cm2. The total anodization time was 5 min at temperature of 25 ºC. Finally the anodized copper foil was cleaned with deionized water and annealed in tubular furnace with nitrogen protection. 6


Page 7 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2.3 Preparation of superhydrophobic films The FAS-17 solution was pre-made by mixing 1g of FAS-17 and 99 g of ethanol for 3 h under continuous stirring at the rate of 100 round/min. The as-prepared anodized copper foil was immersed into the FAS-17 solution at ambient temperature for 12 h. After that, the copper foil was washed with ethanol and dried in a drying chamber at 100 ºC for 1 h. 2.4 Process of the Crystallization on the Cu and CuO films The Cu foil samples (1×1 cm2) after anodization and modification were immersed into a 100 ml beaker with a solution mixed with 50 mL CaCl2 solution of 0.02 mol/L and 50 ml NaHCO3 solution of 0.02 mol/L. Then the beaker was placed into an oil pan (DF-101S), heated to 90 ºC and maintained for specified time. After termination of crystallization process, the samples were taken out from the solution and the residual liquid on the surface of samples was washed with deionized water carefully. Then the samples were hung in an empty beaker to drop the residual water by gravity for 4 h, hereafter dried in a vacuum drying chamber under 30 ºC. The amount of CaCO3 deposited on the surface of the sample was determined by dissolving the crystals with 0.1 mol/L HCl solution and detecting the concentration of Ca2+ in solution with AAS (SpectrAA, 220Z ). The weight of the CaCO3 deposited on

7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the surface of the samples was calculated through the determined amount of Ca2+ indirectly. 2.5 Characterization Static contact angles were measured with a contact angle meter (Powereach, JC2000C1) at room temperature. Water or CH2I2 droplets of approximately 5 µL were dropped gently onto the surface of a sample. Three points of each sample were tested and the average value of the three left and right contact angles was calculated as the determined static contact angle. The surface morphology of Cu film and deposited CaCO3 was observed with a scanning electron microscope (SEM, JEOL JSM-5900LV) and polarizing microscope (Eclipse Lv100pol, Nikon). The growth process of the calcium carbonate was monitored through polarizing microscope. The crystal structure was tested with an X-ray diffraction (XRD, DX2700). The existence of FAS-17 was identified by judging the absorption spectra obtained from Fourier transform infrared spectroscopy (FTIR, Spectrum Two, L1600300 ).

8


Page 8 of 49

Page 9 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3. Results and Discussion 3.1 Preparation of the superhydrophilic anodized Cu surface The polished copper foil was anodized in 1M NaOH solution for 5 min and annealed in N2 atmosphere for 6 h. The obtained samples after anodization and after annealing were characterized with SEM and XRD to determine the corresponding morphology and crystal structure, respectively. The results were shown in Fig. 1, and the photos of measured static water contact angle were attached accordingly to exhibit the wettability of varied samples. The change of the voltage in anodization process was studied (shown in Fig. S1 in the Supporting Information) through the electrochemical workstation (CHI660E, Shanghai,China). The surface of pure Cu foil in Fig. 1-a was appeared to be smooth with some shallow grooves, which should ascribe to the polished process. XRD results in Fig. 1-b confirmed that only the characteristic peak of pure copper could be observed. Water contact angle testing result confirmed that the surface of pure Cu foil was hydrophilic with angle of 87.4±1°. The appearance of the anodized sample showed that the surface of Cu foil was covered with a kind of blue substance. The top SEM images of such as-prepared Cu foil after anodizing were shown in Fig. 1-c, and confirmed that this blue substance was nano-wires with a length of more than 4 µm and diameter of 0.1 µm. These

9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

observed nano-wires grew together to form clusters like the grass, which was overlapped and interlaced each other, constructing a complicated microstructure. The superficial area of Cu foil was increased greatly because of the existence of such intensive nano-wires. The XRD result of the anodized Cu foil shown in Fig. 1-d confirmed that the crystal structure of anodized Cu foil surface should be assigned to the orthorhombic Cu(OH)2 phase with cell parameters of a = 2.947 Å, b = 10.59 Å, and c = 5.256 Å28,29. The water contact angle of anodized Cu foil was about 3±1 °, which confirmed the superhydrophlicity of the anodized Cu foil surface. Fig. 1-e was the morphology of anodized Cu foil after annealing. The microstructure of annealed nanowires was seemed similar to the Cu(OH)2 nano-wires with a slight change on, the dimension and morphology of the nanostructure. The appearance of the annealed sample surface was transformed into black, the typical color of CuO. The determined XRD pattern of the annealed Cu foil in Fig. 1-f confirmed that Cu(OH)2 on Cu foil surface has dehydrated and converted to CuO. The wettability of annealed Cu foil kept superhydrophilic with the static water contact angle keeping of 4.5±1°. 3. 2 Preparation of the superhydrophobic modified Cu surface Since the superhydrophilic Cu foil surface with fine CuO microstructure has been obtained with anodization process, the modification of the surface with low surface

10


Page 10 of 49

Page 11 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


free energy substance should be conducted to prepare the superhydrophobic Cu surface. FAS-17, a typical fluoroalkyl silane commonly used in the surface hydrophobic modification, was chosen to perform the molecular self-assembly process by silanizing the surface of CuO nanowires. Ethanol was added to protect FAS-17 from hydrolyze and auto-agglutination because FAS-17 was easy to hydrolyze in water existed atmosphere. In this way, FAS-17 can realize self-assembly on CuO surface21. Morphology of modified Cu foil surface with FAS-17 was shown in Fig. 2-a. A great amount of surface wolf-bane can be observed on the nanowire clusters, even covering the whole grass-like structure completely. However, the photomicrograph with high magnification in Fig. 2-b confirmed that the shape of nanowires still kept unchanged. Surface modifier FAS-17 only changed the appearance not the structure of CuO nanowires.

The surface composition of the CuO films before and after FAS-17 modified was determined with FT-IR and results were shown in Fig. 3-a and Fig. 3-b, respectively. No significant peaks were observed in the range of wavenumber from 450 cm-1 to 1500 cm-1 in Fig. 3-a. However, the significant peaks belonging to the fluoroalkyl silane, including the dominant IR bands at 1200 cm-1 and bands at 715 cm-1 of different modes

11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of C-F2 groups30 were observed in Fig. 3-b. The peaks in 1070 cm-1, 810 cm-1 are corresponding to Si-O-Si asymmetric stretching vibration absorption peak and symmetric stretching vibration absorption peak. The presence of additional new peaks of C-F2, Si-O-Si confirmed that FAS-17 molecules were loaded on the surface of the CuO layer. As to the peaks appeared in the 1150 cm-1 belongs to C-O-Si. This maybe the FAS-17 has not been hydrolyzed completely. The wettability of the modified Cu foil was determined and shown in Fig. 4-a. The static water contact angle of modified Cu foil increased sharply from 4.5±1° to 154±2°, which can be judged as superhydrophobic surface. The stability of this superhydrophobicity can maintain more than one month in air at room temperature. The contact angle after one month is shown in Fig. 4-b confirmed this superb stability of superhydrophobicity of modified Cu foil. 3.3 Anti-scaling performance of the modified Cu foil The thermal conductivity of the untreated, anodized, and modified Cu foil samples was determined and shown in Support Information Tab. S1. The result confirmed that the influence of anodization of Cu and modification with FAS-17 on the thermal conductivity of Cu foil was small enough to be ignored. The application of modified Cu foil on the heat-exchanger was feasible.

12


Page 12 of 49

Page 13 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


A contrasting experiment was carried out to confirm the anti-scaling effect of superhydrophobic Cu surface by selecting the Cu foil samples with different wettability, including pure Cu foil which was polished with 1200# metallographical sand paper (1#), pure Cu foil which was chemical polished in 0.1 mol/L hydrochloric acid for 40 min (2#), pure Cu foil directly modified in FAS -17 solution for 12 h (3#), anodized Cu foil (4#), and anodized Cu foil modified in FAS-17 solution for 12 h (5#). 3.3.1 The measurement of the surface free energy The corresponding wettability and surface energy of different samples was characterized with the H2O and CH2I2 static contact angle on the surface. Solid–liquid interfacial tension (γSL) was expressed as Young’s equation32 in the absence of spreading pressure as Eq.1. + cos = (1) Equation(1) can be express as following two forms33,34,15

+ 2( ) + 2( ) = + (2)

(cos + 1) = 2( ) + 2( ) (3) Here γS was the surface free energy of the solid and γL was the surface tension of the liquid in equilibrium with the vapor of the liquid. θ was the contact angle formed

13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

by the liquid on the solid. γd was the dispersive component of surface free energy and γnd the polar component. = +

(4)

According to Eq.2, Eq.3 and Eq.4, the surface energy was obtained: For H2O: = 72.8 mJ/m2,

= 21.8 mJ/m2,

For CH2I2: = 50.8 mJ/m2,

= 48.5 mJ/m2,

= 51.0 mJ/m2 = 2.3 mJ/m2

The contact angle determined and corresponding surface free energy calculated of five samples were presented in the Tab. 1, and the corresponding optical images were shown in Fig. S2. It can be found that the wettability and surface free energy of five samples were gradually varied from the super-hydrophilic anodized Cu foil of 74.8 mJ/m2 to the superhydrophobic modified anodized Cu foil of 0.2 mJ/m2. The high surface free energy of anodized Cu foil was decreased sharply to low surface free energy surface after modification with FAS-17. 3.4.2 Nucleation rate on different surface The above five samples were immersed into the solution mixed with CaCl2 and NaHCO3 at 90 °C.

The time of scaling process was set at 120 minutes. The weight

of CaCO3 grew on the surface of different Cu foils was determined and plotted against the surface free energy, shown in Fig. 5. It can be observed that there was 0.6322 mg/cm2 CaCO3 deposited on the super-hydrophilic surface of the anodized Cu foil

14


Page 14 of 49

Page 15 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(4#). After treated with FAS-17 solution, the weight of CaCO3 was reduced sharply to 0.1607 mg/cm2 on the superhydrophobic surface. This dramatic drop of CaCO3 deposition should be ascribed to the superhydrophobicity of the modified surface resulted from the low surface free energy. Based on the theory of heterogeneous35, 36 nucleation process, the crystallization process of CaCO3 on the surface of Cu foil should be significantly influenced by the surface energy of the substrate. The lower surface energy of the modified Cu foil should result in the slower heterogeneous nucleation rate. The nucleation rate of CaCO3 on the superhydrophobic Cu foil surface and superhydrophilic Cu foil surface was calculated and show in Fig.6 different surface was determined, and contrasted with the calculated value based on the Eq.5 and Eq.6 introduced by Melia37, 38. = − f(θ) =

! "# ($%) (&')

( ( ))

(,-./ 0)(- -./ 0) 2

(5) (6)

The parameters needed in calculate the nucleation rate by Eq.(5), (6) are show as follows: Frequency factor A is 1025, Gas constant R is 8.3194×107 ergs/g‧mol‧k, Crystal surface energy σ is 38.62 ergs/cm2, Molar volume Vm=M/ρ, Density ρ is 2.71 g/cm3, Avogadro's constant N is 6.0222×1023 molecular/g‧mol, Super saturation ratio S=C0/C*. C0 represent the real concentration, C* is the super saturation, Temperature T is 363 K, θ is the contact angle.

15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Based on the calculation, it was observed that the nucleation rate of CaCO3 on the superhyophobic surface was always less than on the superhydrophilic surface. The nucleation rate of CaCO3 on the modified CuO film was close to zero when the super saturation of CaCO3 was ranged from 1.0 to 1.4. On the contrary, the nucleation rate of CaCO3 on the superhydrophilic CuO surface had reached to 5.67×1024 s-1. When super saturation was greater than 2.0, the nucleation rate of CaCO3 on modified CuO film increased dramatically, but still far less than on the superhydrophilic surface at the same super saturation. The nucleation rate of CaCO3 on the superhydrophilic CuO surface had reached to 1025 s-1, whereas on the superhydrophobic CuO surface only reached to 1022 s-1. It can be affirmed that under such circumstances, the surface free energy of the superhydrophobic CuO surface still influence the nucleation rate seriously. Therefore, it is reasonable to deduce that the modification can improve the anti-scaling performance of Cu foil. This theory was confirmed by the series polarization microscope photos of different samples against time in Fig. 7. It can be observed that the number of the crystals on the super-hydrophilic surface against time in Fig. 7-a was considerably more than on the superhydrophobic surface in Fig. 7-b. However, the actual nucleation density observed in the photos was far less than the calculated value in Fig.6. This decreasing

16


Page 16 of 49

Page 17 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


should ascribe to the frequent and quick extinction of the formed nucleus in the crystallization process. The projection area of CaCO3 crystals deposited on the superhydrophilic and superhydrophobic Cu surface was counted. The total area of the images is 0.541 mm2 and the result was shown in Tab. 2. It can be observed that the coverage of the crystals on the suerhydrophobic surface is always less than on the superhydrophilic surface, which confirmed the results in calculation. 3.4.3 Space restriction effect of CuO nanowires The different Cu foil samples with CaCO3 deposition were analyzed with SEM, and shown in Fig. 8. On the surface of polished pure Cu foil in Fig. 8-a, only well-distributed rhombohedrum CaCO3 crystals were observed. These crystals with size of about 8µm can be regarded as the typical geometrical shape of calcite CaCO3. In Fig. 8-b, there were two widely different main shapes of CaCO3 deposition grew on the super-hydrophilic surface from the roots of nanowire cluster: needlelike crystals with length of less than 150 µm and

diameter of about 5 µm, and hexagonal

flakiness with diagonal of about 9.5 µm, side length of about 6 µm, and thickness of about 0.5 µm. In the scope, a small number of rhombohedrum crystals were observed, growing on the top of the nanowires cluster.

17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

On the surface of superhydrophobic surface shown in Fig. 8-c a similar situation can be observed. Almost no rhombohedron crystals were found, and a great number of needlelike and maple leaves-shaped crystals grew from the roots of CuO nanowire clusters. Needlelike hexagonal prism crystals tended to grew in cluster with the length ranged from 10 µm to 150 µm, and the diameter of about 3~4 µm. Some crystals looked like to be broken and fall in the nanowires cluster. The giant maple-leaf-like crystals stood or lay on the nanowire layer, with the maximum length from the center to the farthest edge of 40 µm and the thickness of about 0.5 µm. The average size of CaCO3 crystals on the superhydrophobic surface was much greater than on pure Cu foil or super-hydrophilic surface, but the density was significantly sparser. However, although the appearance of these CaCO3 crystals seemed significantly different, the XRD results shown in Fig. 9 confirmed that only one crystallographic form of CaCO3 calcite was constructed whatever it grew on the hydrophilic or hydrophobic Cu surface. This fact elucidated that the change of the surface feature and wettability of Cu foil only resulted in the change of crystal shape appearance not the crystal type itself. This remarkable difference of CaCO3 crystal shape on the different surface could be ascribed to the cooperative effect of surface free energy and the space restriction

18


Page 18 of 49

Page 19 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


effect of the nanowires on the nucleation stage and growth stages of CaCO3 deposition. In the nucleation stage, the CaCO3 solute was adsorbed on any position of the smooth surface with the same probability, and formed nucleus with am even distribution. On the super-hydrophilic surface with nanowires, the CaCO3 solute tended to enter the interval of nanowires due to the capillary phenomenon of the hydrophilic surface, nucleating at the root of the nanowire cluster. Only a few nucleuses can be formed at the tip of the nanowires. However, the stable nucleus formed at the tip should be larger than at the root because the sharp shape with relatively high surface area resulted in larger critical radius and low nucleation rate according to the Eq.7 39 and Eq.5. 34 =

256 (7) 789:;

In addition, the shear force caused by the water turbulence at the tip to detach the adhered nucleus was stronger than at the root. Therefore, the density of the nucleus at the tip should be far smaller than at the root. If the surface were covered by the low surface with low free surface energy free energy substance, the nucleation situation was different. The capillary phenomenon of the hydrophobic surface prevented the entry of CaCO3 solute, causing the decrease in the number of the nucleus formed at the root of nanowire cluster. At the tip of the nanowires, the decrease of the surface

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

free energy of hydrophobic surface would result in the smaller critical radius and higher nucleation rate than on the hydrophilic surface according to the Eq. 7 and Eq. 5. The total nucleation amount should increase as the result. However, such phenomenon was not observed since almost no nucleus grew at the tip of the nanowires on the superhydrophobic surface. This should ascribe to the weak adhesion strength between the tiny nucleus and the superhydrophobic surface. It was known that the adhesive strength between nucleus and surface had a maximum when the surface free energy of the adhesive was equal to that of the substrate 40. In this study, the measured value of superhydrophobic surface free energy was 0.2 mJ/m2, super-hydrophilic surface of 74.8 mJ/m2, and polished pure Cu surface of 34.1 mJ/m2. The surface free energy of calcite reported 41 was 38.62 mJ/m2 according to the Lifshitz-van der Waals/acid-base (van Oss) approach, the calculate method is shown in Eq.8

42,43

, This value was close to the surface free energy of

polished pure Cu surface, 34.1 mJ/m2. = = => + ?=@ =,

(8)

@ γB is the surface free energy, γCD B represent Lifshitz-Van der Waals component, =

is the Lewis Acid component, =, is the Lewis Alkali component. It can be judged that the adhesion of CaCO3 scaling on the pure Cu surface was the strongest, and weakest on superhydrophobic surface based on the conclusion of Dyckerhoff 44.

20


Page 20 of 49

Page 21 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The stable tiny nucleus with weak adhesion were easy to depart from the superhydrophobic surface under the action of shear force, and became unstable in solution because its size was smaller than the larger critical radius caused by the high surface energy itself without the influence of solid wall according to the Eq. 7. Therefore, the vast majority of detached nucleus faded away, and only the fortunate nucleus formed at the root of nanowires can survive and grow up. In the growing stage of crystal, the growth of the CaCO3 calcite also was seriously influenced by the space effect of the nanowires cluster. As known to all, calcite was a typical trigonal system with space group of R3Ec, cell parameter of a = b = 4.990 Å, c = 17.061 Å, α = β = 90°, γ = 120 ° 45. For rhombohedral calcite, the six crystal planes all belonged to the {104} crystal plane, which was of the most thermodynamic stability and lowest surface free energy 46. There were two periodic bond chain (PBC) directions in the {104} crystal plane, which was flat face (F face). A two-dimensional nucleus formed on the complete {104} crystal plane firstly at the growing process of crystal. All the four edges of the nucleus were of one PBC as stepped face(S face), growing in priority with fast speed to cover the {104} crystal plane completely and consequently waiting for

to the formation of new nucleus47. According to this

growing mechanism, the calcite on the different surface can be described as the below. The detailed growth mechanism sketch was described in Fig. 10.

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

On the smooth surface, the CaCO3 solute can approach the nucleus formed in nucleation stage from all directions except the bottom plane with the same probability by diffusion, and grow evenly to form perfect rhombohedron crystal after the formation of the initial nucleus. This growth process was marked as route 1 in Fig.10. On the contrary, if the surface was sheltered with a great number of nanowires, the solute only approached the nucleus from the top direction with the smallest diffusion resistance, and therefore, the orientation of crystal growth would be upward. This growth mechanism of CaCO3 was marked as route 2 in Fig.10. If the nucleus was surrounded tightly by the high density nanowires, the growth of crystal was confined upward, and finally needlelike crystal shape with rhomb plane was constructed, as shown in Fig.10-a. However, if the density of nanowires was not uniform, the rhombohedron crystals maybe expanded along the direction with relatively sparse nanowires, accumulating on the stepped face (S face) and kinked face (K face), and finally constructing a thin and hexagonal flakiness, as shown in Fig. 10-b. Meanwhile the nucleus survived at the tip of nanowires still grew into perfect rhombohedron shape without the space restriction effect of nanowires, as shown in Fig. 10-c. On the superhydrophobic surface, the growth process of calcite crystal was similar to the super-hydrophilic surface because of the existence of the nanowires, and was marked as route 3 in Fig.10. The nucleus formed at the root of the nanowire clusters

22


Page 22 of 49

Page 23 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


had the same tendency to construct needlelike and flakiness crystals due to the space restriction effect, as shown in Fig. 10-d and Fig. 10-e. However, the low surface free energy would impact the crystal growth process seriously, and transform the original simple hexagonal flakiness into final complicated dendritic crystal. Such transformation effect of low surface free energy substance was confirmed by the morphology of CaCO3 crystal deposited (see Support Information Fig. S3) on the smooth Cu foil surface which was modified with FAS-17 directly.

Because the

anisotropy of calcite was great, the maple-leaf-like dendritic crystals with clear backbone were built as shown in Fig. 10-e. Because the surface free energy difference between superhydrophobic surface and calcite {104} plane was great48, 49, the CaCO3 solute tended to grow on the calcite surface not on the superhydrophobic surface, promoting to achieve overlong needlelike rhombohedrum crystals and mammoth maple-leaf-like dendritic crystals. Scant surviving CaCO3 nucleus at the tip of superhydrophobic nanowires still to form a small number of perfect rhombohedron crystals as shown in Fig. 10-f. 3.4.4 The influence of air film on the superhydrophobic surface There was the third advantage to reinforce the anti-scaling performance of superhydrophobic surface. A silver gas film existed on the surface of modified Cu foil shown in Fig. 11-a can be observed clearly while immersing the foil into liquid. Such

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

gas film covered a considerable portion of surface. Scaling phenomenon only happened along the outside of the gas film, which was shown in Fig.11-b. The formation of such gas film should ascribe to the low surface free energy. Based on the Cassie-Wenzel model

50, 51

, the hydrophobic nanowires on the surface

can trap the air and built the bubbles when the modified Cu foil was immersed into the water. The mechanism was exhibited in Fig. 11. Because of the existence of the air trapped on the superhydrophobic surface, the contact state between the solid surface and liquid should be in Cassie-Baxter state 52. With the rising of temperature, the gas volume would expand, and the partial pressure of steam would increase, which resulted in the transformation to the suspending state. With the rising of temperature, the gas volume would expand, and the partial pressure of steam would increase, which resulted in the transformation to suspending state. Air bubbles are generated quickly and escape from the hydrophilic surface easily. However air bubbles are generated slowly and prefer to stick on the hydrophobic surface for a longer time53. This gas film isolated the liquid from hydrophobic surface, introducing an insurmountable giant diffusion resistance for CaCO3 solute. The occurrence of scaling process was exiled to the edge of the gas film. Hence, the anti-scaling performance of superhydrophobic surface was reinforced. 3.5 Crystal kinetics

24


Page 24 of 49

Page 25 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For further understanding the anti-scaling performance of superhydrophobic surface for application, the crystallization kinetic of different surface was determined, and shown in Fig. 12. The weight of CaCO3 grew on modified Cu foil and annealed Cu foil all increased with time. However, the mass increasing speed of CaCO3 on the superhydrophobic surface was significantly lower than on the super-hydrophilic surface. The average mass increasing rate of CaCO3 was calculated with Eq. 9. FG =

FH (9) FI

dw is the weight of CaCO3 deposited on the Cu, θ is the deposit rate of CaCO3 on the Cu surface. On the superhydrophilic surface, the growth of crystal can be divided into two stages based on the Fig. 12. The start time of crystallization was set at the time when the temperature of the solution reached 90 ºC for avoiding the homogeneous nucleation in solution. This caused the initial weight of CaCO3 at the starting time. At first stage from starting to 1.5 h, the weight of CaCO3 linearly increased from 0.1263 mg/cm2 to 0.6013 mg/cm2 against time with average scaling rate of 0.3167 mg/cm2·h. After that, the growth rate of CaCO3 tended to be slow, and the CaCO3 weight slightly increased from 0.6013 mg/cm2 to 0.6322 mg/cm2. The second stage with slow CaCO3 growth rate of 0.0618 mg/cm2·h should ascribe to the significant decreasing of super-saturation of CaCO3 in solution since the solution was seemed to be clear.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

On the superhydrophobic surface, the linear increasing tendency of CaCO3 weight from 0.039 mg/cm2 to 0.1806 mg/cm2 against time rang from starting to 1.5 h also can be observed in Fig. 12. The average scaling rate of CaCO3 was 0.0944 mg/cm2·h, far less than the CaCO3 scaling rate in the first stage on superhydrophilic surface. However, in the second stage, the weight of scaling CaCO3 was fluctuated between 0.1607 mg/cm2 and 0.2174 mg/cm2. The average CaCO3 scaling rate turned negative, -0.0398 mg/cm2·h, which meant the decrease of scale mass on the superhydrophobic surface. This mass decrement should ascribe to the detaching of CaCO3 scaled on the superhydrophobic surface. As shown in Fig.8(c), the dimension of the CaCO3 crystals on superhydrophobic surface was much greater than on the superhydrophilic surface. The scale on the superhydrophobic surface had big surface area, but with relatively small anchored area with the nanowires, it was of high probability to detached from the surface on the erosion of the flow. Furthermore, according to calculation shown in Fig. 6 and SEM pictures in Fig. 7, the numbers of CaCO3 crystal nucleus formed on the superhydrophobic surface are inherently much less than on the superhydrophilic surface, and such scaling only happened on the surface which was not occupied by the bubble shown in Fig. 11. These two effects also intensified the decreasing of the scales on superhydrophobic surface. Such detachment effect of CaCO3 resulted from the damage effect of perturbance in solution on heating to giant CaCO3 crystals with

26


Page 26 of 49

Page 27 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


low adhesion was remarkable, and was conducive to the final purpose of anti-scaling. 4. Conclusion In this research, CuO nanowire film and modified CuO nanowire film with FAS-17 on the Cu foil are prepared and used for anti-scaling of CaCO3. The as-prepared CuO nanowire film after anodizing and annealing exhibits superhydrophilic property with static water contact angle of 4.5±1°, and the surface free energy of 74.8 mJ/m2. After modified with FAS-17 for 12h, the superhydrophilic CuO nanowire film turns to superhydrophobic with the static water contact angle of 154±2°, and the surface free energy of 0.2 mJ/m2. This superhydrophobic film exhibits a promising anti-scaling property for CaCO3. All the CaCO3 deposited is determined to be calcite. The scaling weight of CaCO3 crystals deposited on the superhydrophilic films reaches to 0.6322 mg/cm2, but on the superhydrophobic surface the scaling weight of CaCO3 drops to 0.1607 mg/cm2. This anti-scaling performance should ascribe to three reasons resulted from the fine nanowire micro-structure modified with low surface free energy substance. The CaCO3 crystal nucleation rate is retarded because of the low surface energy. The CaCO3 nucleus grows vertically to form long needle-like crystal or thin hexagonal/maple-leaf-like flakiness with relatively low mechanical strength because of the space restriction effect of nanowires. The air film retained on the superhydrophobic surface due to the low surface free energy covers the surface and

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 49

prevents the approaching of solution. Such attractive anti-scaling property of superhydrophobic surface is worth for studying further and industrial application in future.

Acknowledgements We appreciated the financial support from the National Natural Science Foundation of China (NO. 21176157, and No. 21476146).

Associated Content Supporting Information In the Supporting Information there are four figures. The first one is the thermal conductivity of samples. The second one is the anodization potential. The third one is the corresponding optical images of five samples tested with H2O and CH2I2. The last one is the pictures of CaCO3 deposited on modified pure Cu surface. This information is available free of charge via the Internet at http://pubs.acs.org/.

Author Information Corresponding Author Address:

College

of

Chemical

Engineering,

Sichuan

No.24 South Section 1, Yihuan Road, Chengdu , China, 610065. Fax: 86-28-85460557;

28


University,

Page 29 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Tel : 86-28-85990133; E-mail: [email protected]

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Reference

(1) Cho, Y. I.; Liu, R. Control of fouling in a spirally-ribbed water chilled tube with electronic anti-fouling technology. Int. J.Heat.Mass.Tra. 1999, 42, 3037. (2) Suitor, J. W.; Marner, W. J.; Ritter, R. B.; The History and Status of Research in Fouling of Heat Exchanger in Cooling Water Service. Can. J. Chem. Eng. 1977, 55, 374. (3) Garrett-Price, B. Fouling of heat exchangers: Characteristics, costs, prevention, control and removal. Noyes Publications. 1985, 417. (4) Haibo, L.; Yumei, L.; Jianming, L.; Chuntao, Y.; Danping, H. Fouling and Cleaning of Heat Exchanger. Journal of

Sichuan University of Science & Engineering (Natural Science

Edition). 2006, 19, 2. (5) Master, B.I.; Chunangad, K.S.; Pushpanathan, V.; Fouling Mitigation Using Helixchanger Heat Exchangers. Heat Exchanger Fouling and Cleaning: Fundamentals and Applications, Art. 2003, 43, 7. (6) Macchietto, S.; Hewitt, G. F.; Coletti1, F.; Crittenden, B.D.; Dugwell, D.R.; Galindo,A.; Jackson, G.; Kandiyoti, R.; Kazarian, S.G.; et.al. Fouling in crude oil preheat trains: a systematic solution to an old problem. Proceedings of International Conference on Heat Exchanger Fouling and Cleaning VIII. 2009. (7) Ketrane, R.; Saidani, B.; Gil, O.; Leleyter, L.; Baraud, F. Efficiency of five scale inhibitors on calcium carbonate precipitation from hard water: Effect of temperature and concentration. Desalination. 2009, 249, 1397. (8) Butt, F.; Rahman, F.; Baduruthamal, U. Evaluation of SHMP and advanced scale inhibitors for control of CaSO3, SrSO3, and CaCO3 scales in RO desalination. Desalination. 1997, 109, 323. (9) Cowan, J. C.; Weintritt, D. J. Water-formed scale deposits. Gulf Publishing Company, Book Division: 1976. (10) Nishida, I.; Precipitation of calcium carbonate by ultrasonic irradiation. Ultrason. Sonochem. 2004, 11, 423. (11)He, K.; Chen, Y.; Feng, J.; Mo, S.; Investigation on the Thermal Conductivity and Anti-Fouling Property of Ni-P-PTFE Electroless Composite Coating. Mater Rev B: research paper. 2013, 27, 4. (12) Tijing, L. D.; Yu, M. H.; Kim, C. H.; Amarjargal, A.; Lee, Y. C.; Lee, D. H.; Kim, D. W.; Kim, C. S. Mitigation of scaling in heat exchangers by physical water treatment using zinc and tourmaline. Appl. Therm. Eng. 2011, 31, 2025. (13) Zhao, Q.; Liu, Y.; Muller-Steinhagen, H.; Liu, G. Graded Ni-P-PTFE coatings and their potential applications. Surf. Coat. Tech. 2002, 155, 6. (14) Zhao, Q. Effect of surface free energy of graded Ni-P-PTFE coatings on bacterial adhesion. Surf. Coat. Tech. 2004, 185,199.

30


Page 30 of 49

Page 31 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(15) Michalski, M. C.; Hardy, J.; Saramago, B. J. On the surface free energy of PVC/EVA polymer blends: comparison of different calculation methods. J. Colloid. Interf. Sci. 1998, 208, 319. (16) Drábik, M.; Polonskyi, O.; Kylián, O.; Čechvala, J.; Artemenko, A.; Gordeev, I.; Choukourov, A.; Slavínská, D.; Matolínová, I.; Biederman, H. Superhydrophobic Coatings Prepared by RF Magnetron Sputtering of PTFE. Plasma. Process. Polym. 2010, 7, 544. (17) Onda, T.; Shibuichi, S.; Satoh, N.; Tsujii, K. Super-water-repellent fractal surfaces. Langmuir. 1996, 12, 2125. (18) Song, J.; Xu, W.; Liu, X.; Wei, Z.; Lu, Y. Fabrication of superhydrophobic Cu surfaces on Al substrates via a facile chemical deposition process. Mater. Lett. 2012, 87, 43. (19)

Kang,

C.;

Lu,

H.;

Yuan,

S.;

Hong,

D.;

Yan,

K.;

Liang,

B.

Superhydrophilicity/superhydrophobicity of nickel micro-arrays fabricated by electroless deposition on an etched porous aluminum template. Chem. Eng. J. 2012, 203, 1-8. (20) Hyomin Lee, M. L. A., Michael F. Rubner, and Robert E. Cohen. Zwitter-Wettability and Antifogging Coatings with Frost-Resisting Capabilities. Nano. 2013, 7, 11. (21) Pan, Q.; Wang, M.; Wang, H. Separating small amount of water and hydrophobic solvents by novel superhydrophobic copper meshes. Appl. Surf. Sci. 2008, 254, 6002. (22) Lee, C. H.; Johnson, N.; Drelich, J.; Yap, Y. K. The performance of superhydrophobic and superoleophilic carbon nanotube meshes in water–oil filtration. Carbon. 2011, 49, 669. (23) Bhushan, B.; Jung, Y. C. Natural and biomimetic artificial surfaces for superhydrophobicity, self-cleaning, low adhesion, and drag reduction. Prog. Mater. Sci. 2011, 56, 1. (24) Chen, X.; Kong, L.; Dong, D.; Yang, G.; Yu, L.; Chen, J.; Zhang, P. Synthesis and characterization of superhydrophobic functionalized Cu(OH)2 nanotube arrays on copper foil. Appl. Surf. Sci. 2009, 255, 4015. (25) Chen, X.; Yang, G.; Kong, L.; Dong, D.; Yu, L.; Cheng, J.; Zhang, P. Direct Growth of Hydroxy Cupric Phosphate Heptahydrate Monocrystal with Honeycomb-Like Porous Structures on Copper Surface Mimicking Lotus Leaf. Cryst. Growth. Des. 2009, 9, 6. (26) Chen, X.; Yang, G.; Kong, L.; Dong, D.; Yu, L.; Chen, J.; Zhang, P. Different wetting behavior of alkyl- and fluorocarbon-terminated films based on cupric hydroxide nanorod quasi-arrays. Mater. Chem. Phys. 2010, 123, 309. (27) Hu, J.M.; Liu, L.; Zhang, J. Q.; Cao, C. N. Electrodeposition of silane films on aluminum alloys for corrosion protection. Prog. Org. Coat. 2007, 58, 26. (28) Xufeng Wu, H. B., Jiaxin Zhang, Fengen Chen, and Gaoquan Shi. Copper Hydroxide Nanoneedle and Nanotube Arrays Fabricated by Anodization of Copper. J. Phys. Chem. B. 2005, 109, 7. (29) La, D. D.; Nguyen, T. A.; Lee, S.; Kim, J. W.; Kim, Y. S. A stable superhydrophobic and superoleophilic Cu mesh based on copper hydroxide nanoneedle arrays. Appl. Surf. Sci. 2011, 257, 5705.

31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 49

(30) Mihály, J.; Sterkel, S.; Ortner, H.; Kocsis, L.; Hajba, L.; Furdyga, É.; Minka, J. FTIR and FT-Raman Spectroscopic Study on Polymer Based High Pressure Digestion Vessels. Croatica Chemica Acta Ccacaa. 2006, 79, 5. (31) Jongwook, k. Correlation Study on the Low-dielectric Characteristics of SiOC(-H) Thin Film from a BTMSM/O2 Precursor. J. Korean. Phys. Soc. 2010, 56, 89. (32) Young, T. An Essay on the Cohesion of Fluids. Philosophical Transactions of the Royal Society of London. 1805, 95, 65. (33) Shalel-Levanon, S.; Marmur, A. Validity and accuracy in evaluating surface tension of solids by additive approaches. J. Colloid. Interf. Sci. 2003, 262, 489. (34) Owens, D. K.; Wendt, R. Estimation of the surface free energy of polymers. J. Appl. Polym. Sci. 1969, 13, 1741. (35) Markus Förster, M. B. Influence of the interfacial free energy crystal/heat transfer surface on the induction period during fouling. Int. J. Therm. Sci. 1999, 38. (36) Liua, X. Y. Heterogeneous nucleation or homogeneous nucleation? J. Chem. Phys. 2000, 112, 7. (37) Melia, T. Crystal nucleation from aqueous solution. J. Appl. Chem. 1965, 15, 345. (38) Mullin, J. W., Crystallization. Butterworth-Heinemann: 2001. (39) Chan, S. H, Ghassemi, K. F. Analytical modeling of calcium carbonate deposition for Laminar

falling

film

sand

turbulent

flow

in

annuli:

Part

I-Formulation

and

single-speciesmodel. Journal of Heat Transfer. 1991,113,735 (40) Förster, M.; Bohnet, M. Influence of the interfacial free energy crystal/heat transfer surface on the induction period during fouling. Int. J. Therm. Sci. 1999, 38, 944. (41) Wang, H.; Gu, G. Surface free energy of solid matter and its hydrophilic/hydrophobic. Chemistry Online. 2009, 72, 1091.

(42) Van Oss, C. J.; Chaudhury, M. K.; Good, R. J. Interfacial Lifshitz-van der Waals and polar interactions in macroscopic systems. Chem. Rev. 1988, 88, 927. (43) Van-Oss, C.; Chaudhury, M.; Good, R. The mechanism of partition in aqueous media. Separ. Sci. Technol. 1987, 22, 1515. (44) Dyckerhoff, V. G.; Sell, P. J. Über den Einfluß der Grenzflächenspannung auf die Haftfestigkeit. Die Angewandte Makromolekulare Chemie. 1972, 21, 169. (45) Wu, C.; Wang. X.; Zhao, K.; Cao, M.; Xu, Hai; Lü, J. AFM Study of Calcite Growth and Dissolution on the (104) Face. Prog. Chem. 2011, 1, 012. (46) Sommerdijk, N. A.; With, G. d. Biomimetic CaCO3 mineralization using designer molecules and interfaces. Chem. Rev. 2008, 108, 4499. (47) Li Jie, Z. G., Xu Jing. Study on Soft Scale Mechanism of CaCO3. Journal of Tongji Uninversity(Natural Science). 2007, 35, 626. (48) Ben-Jacob, E.; Garik, P. The formation of patterns in non-equilibrium growth. Nature. 1990, 343, 523.

32


Page 33 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(49) Nittmann, J. and dendritic growth patterns arising from molecular anisotropy. Nature. 1986, 321, 12. (50) Wenzel, R. N. Resistance of solid surfaces to wetting by water. Ind. Eng. Chem. 1936, 28, 988. (51) Cassie, A. Contact angles. Discuss. Faraday Soc. 1948, 3, 11. (52) Cassie, A.; Baxter, S. Wettability of porous surfaces. Transactions of the Faraday Society. 1944, 40, 546. (53) Zhang, T.; Wang, J.; Chen, L.; Zhai, J.; Song, Y.; Jiang, L. High-temperature wetting transition on micro- and nanostructured surfaces. Angew. Chem. 2011, 50, 5311.

33



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 49

Tables Tab. 1 The surface free energy and contact angle of different surface Average Contact

Average Contact

Samples

γS (mJ/m2)

CuO film

74.8

4.5

0

Pure Cu

47.7

61.8

34.4

Chemical polished Cu

34.1

87.4

50.6

Modified pure Cu

18.1

102.5

79.2

Modified CuO film

0.2

154.1

133.1

angle (H2O)

angle (CH2I2)

Tab.2 The coverage of the crystals on superhydropbobic/superhydrophilic surface tested with Polarizing Microscope Superhydrophobic

Superhydrophilic

Time(min)

Projected Area(mm2)

Time(min)

Projected Area(mm2)

0

0

0

0

10

0.0178

10

0.0266

30

0.0473

30

------

60

0.0654

60

------

90

0.105

90

0.113

120

0.0779

120

0.149

Annotation：The crystals deposited on the superhydrophilic at 30 min and 60 min can not be readed by the software.

34


Page 35 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure captions Fig.1 Typical SEM images (a,c,e) and XRD analysis (b,d,f) for different samples: (a,b) Pure Cu foil polished with HCl solution. (c,d) Cu(OH)2 nanowires obtained through anodization in a 1.0 mol/L NaOH solution at an constant current densities for 0.006 A/cm-2 (X 5000). (e,f) CuO nanowires after annealed in tubular furnace (X 5000) Fig.2 SEM images of the surfaces (a) modified CuO nanowire films with 1wt% FAS-17 solution (X 5000), (b) the modified CuO nanowires magnitude of (X 10,000) Fig. 3 Differential FTIR absorption spectra of (a) CuO nanowires and (b) modified CuO nanowires with 1wt% FAS-17 solution Fig.4 The contact angle profile of a water droplet on the FAS-17 modified (a) CuO nanowires film and (b) the same CuO nanowires film exposed in atmosphere for one month Fig.5 The CaCO3 deposited on the different surfaces which own different surface free energy were dissolved with 0.1M HCl solution and the concentration of the Ca2+ was tested with AAS Fig.6 The nucleation rate with different super saturation on the superhydrophobic CuO nanowires film and superhydrophilic CuO nanowires film was calculated under the idealism condition Fig.7 the serial photos of the CaCO3 scaling against time with polarizing microscope (a) CuO nanowires, (b) modified CuO nanowires Fig.8 The typical SEM images of CaCO3 crystals after 1h crystallization in a mixed solution of 0.01 mol/L CaCl2 and 0.01 mol/L NaHCO3 with diffeeent samples of (a,b) pure Cu foil, (c,d) CuO nanowires film and (e,f) the modified CuO nanowires film Fig.9 XRD analysis of the scaled surfaces (a) pure Cu foil, (b) CuO nanowires film and (c) the modified CuO nanowires film

35



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig.10 The schematic diagram of specific crystallization mechanism (a)on the smooth pure Cu surface shown as the route 1, (b) on the superhydrophilic CuO nanowires surface shown as the route 2, (c) on the superhydrophobic CuO nanowires surface shown as the route 3, Fig.11 The schematic diagram and photograph explained the mechanism of air film sized between the nanowires and bubbles generated during the scaling process influence on the superhydrophobic surface scaling process Fig.12 the CaCO3 weight changed with time on the superhydrophilic and superhydrophobic CuO nanowires film

36


Page 36 of 49

Page 37 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 1 Typical SEM images (a,c,e) and XRD analysis (b,d,f) for different samples: (a,b) Pure Cu foil polished with HCl solution. (c,d) Cu(OH)2 nanowires obtained through anodization in a 1.0 mol/L NaOH solution at an constant current densities for 0.006 A/cm-2 (X 5000). (e,f) CuO nanowires after annealed in tubular furnace (X 5000) 143x166mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 2 SEM images of the surfaces (a) modified CuO nanowire films with 1wt% FAS-17 solution (X 5000), (b) the modified CuO nanowires magnitude of (X 10,000) 145x58mm (300 x 300 DPI)


Page 38 of 49

Page 39 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 3 Differential FTIR absorption spectra of (a) CuO nanowires and (b) modified CuO nanowires with 1wt% FAS-17 solution 287x201mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 4 The contact angle profile of a water droplet on the FAS-17 modified (a) CuO nanowires film and (b) the same CuO nanowires film exposed in atmosphere for one month 140x57mm (300 x 300 DPI)


Page 40 of 49

Page 41 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 5 The CaCO3 deposited on the different surfaces which own different surface free energy were dissolved with 0.1M HCl solution and the concentration of the Ca2+ was tested with AAS 201x141mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 6 The nucleation rate with different super saturation on the superhydrophobic CuO nanowires film and superhydrophilic CuO nanowires film was calculated under the idealism condition 287x201mm (300 x 300 DPI)


Page 42 of 49

Page 43 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 7 the serial photos of the CaCO3 scaling against time with polarizing microscope (a) CuO nanowires, (b) modified CuO nanowires 106x73mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 7 the serial photos of the CaCO3 scaling against time with polarizing microscope (a) CuO nanowires, (b) modified CuO nanowires, 166x115mm (300 x 300 DPI)


Page 44 of 49

Page 45 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 8 The typical SEM images of CaCO3 crystals after 1h crystallization in a mixed solution of 0.01 mol/L CaCl2 and 0.01 mol/L NaHCO3 with diffeeent samples of (a,b) pure Cu foil, (c,d) CuO nanowires film and (e,f) the modified CuO nanowires film 144x235mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 9 XRD analysis of the scaled surfaces (a) pure Cu foil, (b) CuO nanowires film and (c) the modified CuO nanowires film 201x141mm (300 x 300 DPI)


Page 46 of 49

Page 47 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 10 The schematic diagram of specific crystallization mechanism (a)on the smooth pure Cu surface shown as the route 1, (b) on the superhydrophilic CuO nanowires surface shown as the route 2, (c) on the superhydrophobic CuO nanowires surface shown as the route 3, 443x284mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Fig. 11 The schematic diagram and photograph explained the mechanism of air film sized between the nanowires and bubbles generated during the scaling process influence on the superhydrophobic surface scaling process 248x198mm (300 x 300 DPI)


Page 48 of 49

Page 49 of 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 12 the CaCO3 weight changed with time on the superhydrophilic and superhydrophobic CuO nanowires film 287x201mm (300 x 300 DPI)


Preparation and Antiscaling Application of Superhydrophobic

Recommend Documents