Dark, Infrared Reflective, and Superhydrophobic Coatings by

Subscriber access provided by Warwick University Library

Interface Components: Nanoparticles, Colloids, Emulsions, Surfactants, Proteins, Polymers

Dark, Infrared Reflective and Superhydrophobic Coatings by Waterborne Resins Jing Zhang, Weiqiang Lin, Chenxi Zhu, Jian Lv, Weicheng Zhang, and Jie Feng Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b00929 • Publication Date (Web): 23 Apr 2018 Downloaded from http://pubs.acs.org on April 24, 2018

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 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 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.

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 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

Langmuir

Dark, Infrared Reflective and Superhydrophobic Coatings by Waterborne Resins Jing Zhang, Weiqiang Lin, Chenxi Zhu, Jian Lv, Weicheng Zhang, Jie Feng* College of Materials Science & Engineering, Zhejiang University of Technology, Hangzhou 310014, China *Corresponding authors. Prof. Jie Feng, E-mail: [email protected]

ABSTRACT：：Recently, infrared reflective pigments possessing deep colors have attracted much attention. However, in polluted air, the coatings consisting of such pigments are easily contaminated which abates infrared reflectivity. In this work, black and infrared reflective pigments, fluorine silicon sol and a small number of SiO2 nanoparticles were introduced into waterborne epoxy resin emulsion and then coated on an aluminum plate. After drying, black coatings with infrared reflective and superhydrophobic (SH) properties were obtained. The average near infrared (NIR) reflectivity of the coating over wavelength range of 780-2600 nm can reach 68%, which is much larger than that of carbon black coatings and even approaches that of white nano SiO2 coatings. Under the irradiation of a 275-Watt infrared lamp (with height 40 cm), the surface temperature of the coating is 63 oC, which is much lower than that of the carbon black coating (90 oC) and only 7 oC higher than that of the white nano SiO2 coating. Furthermore, the NIR reflective coating exhibited a typical SH property due to its low surface energy and high surface roughness, which may allow for self-cleaning performance in a practical environment, maintaining the coating’s NIR reflective property. KEYWORDS: Dark, Infrared reflective, Superhydrophobic, Coating, Waterborne resins

ACS Paragon Plus Environment

Langmuir 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

INTRODUCTION Following the development of the housing economy, the amount of building energy consumption has increased rapidly, accounting for approximately one-third of total societal energy consumption. Thus, energy saving in buildings has become important for reducing global energy consumption.1-2 Much effort has been devoted to improving the thermal insulation of buildings and increasing energy saving efficiency. For example, thermal insulation coatings consisting of hollow glass beads have been widely applied in the construction market. Heat reflective coatings also play an important role in the field of building thermal insulation due to their high reflectivity of sunlight,3-4 and can be employed in building facades, roofs and other parts in order to reduce the energy consumption of air-conditioning in the summer.5-6 A few centuries ago, humans discovered that white or light colored roofs were cooler than the corresponding black roofs.7 This is because a white coating possesses the highest thermal reflectivity. As a result, more than 90% of thermal reflective coatings on buildings have been designed to be white or light colors. However, the white or light-colored coatings are easily contaminated by environmental pollution. Recently, deeply colored infrared reflective pigments, e.g., black, blue, and red pigments, have been developed.8-9 However, coatings containing such dark pigments are also easily contaminated. The pollutants in the air are readily adsorbed and adhered to the surface of the coating, negatively affecting its NIR-reflectivity.10 A lot of manpower and energy are required to clean the contaminated surface.11-13 Therefore, NIR-reflective coatings need to be further functionalized with self-cleaning properties. Several heat reflective coatings possessing self-cleaning properties have been created. For example, Sriramulu et al. controlled the surface morphology and properties of silica nanoparticles by aggregation-induced segregation of perylene diimide (PDI), obtaining a SH, self-cleaning and NIR-reflective coating.14 Roppolo et al. made an NIR-reflective, hydrophobic, self-cleaning and UV-cured coating by using epoxy resin modified with epoxysiloxane.15 Zhu et al. prepared a superhydrophilic, ACS Paragon Plus Environment

Page 2 of 17

Page 3 of 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

Langmuir

anti-infrared, self-cleaning coating using a two-layer structure of SiO2 (top)/TiO2 (bottom) on the substrate.16 Unfortunately, these reports only mention light-colored coatings, thus are unable to meet the demands of modern architecture where a variety of different colors are desired.17-19 Therefore, the development of heat reflective coatings possessing SH property as well as various dark colors, such as black, gray, brown and so on, is highly desired. In this work, we propose a facile method for the preparation of a dark colored, NIR-reflective

and

SH

coating,

by

simply

mixing

SiO2

nanoparticles,

perfluorodecyltriethoxysilane (FAS), waterborne epoxy resin (EP) and dark NIR-reflective pigments at room temperature, then coating and drying. The obtained coating is not only environmentally friendly but also possesses the desired self-cleaning performance and good energy saving effects. The reason for selecting SiO2 nanoparticles and FAS is that they are general substance in fabricating SH surface. EP was selected because it can ensure coating excellent mechanical property.

EXPERIMENTAL SECTION

Materials. Waterborne epoxy emulsion (AB-EP-51) and water-based epoxy curing agent (AB-HGA) were purchased from Zhejiang Anbang New Material Co., Ltd. (China). Nano-SiO2 (SP30) was purchased from Zhejiang Wanjing New Material Co., Ltd. (China). Infrared reflective pigment ("cool cold" pigment-Black 30C941) was obtained

from

Shepherd

Color

Company

(USA).

1H,

1H,

2H,

2H-Perfluorodecyltriethoxysilane (FAS) was purchased from Sicong New Material Ltd (Quanzhou, China). γ-aminopropyltriethoxysilane (KH-550) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (China). All other chemicals were general sale products. Preparation of Coatings. 0.4 g nano-SiO2 was added into 60 mL ethanol and 10 mL deionized water, 0.8 mL FAS and 1 mL KH-550 were added with stirring. Then 10 drops (∼0.3 mL) of 1 mol/L dilute hydrochloric acid were used to adjust the pH value of the suspension to ∼4. The FAS modified nano-SiO2 suspension was obtained after magnetic stirring for 2 h at room temperature. Subsequently, 0.6 g AB-EP-51 and 0.48 ACS Paragon Plus Environment

Langmuir 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 4 of 17

g AB-HGA were added into the FAS modified nano-SiO2 suspension and further stirred for 15 min. Then 7 g "cool cold" black pigment was added and stirred for a further 15 min. The resulting mixture was sprayed on an aluminum plate, which was cleaned with ethanol and acetone in advance. Then the coat was dried at 120 oC for 1 h. As control samples, coatings only containing carbon black or white SiO2 nanoparticles were prepared by using the above method but replacing 0.4 g nano-SiO2 with 4 g nano-SiO2 or 4 g carbon black, respectively (both without further addition of "cool cold" black pigment). Scheme 1 shows the preparation process for the coatings. SiO2, ethanol, and deionized water

FAS and KH550

Stir

Substrate Epoxy resins

Epoxy resins

“Cool cold” black pigment

Stir

Superhydrophobic coatings

Stir Spraying

Stir

SiO2 “Cool cold” black pigment

Water Scheme 1. Scheme outlining the preparation process of the coatings.

Characterization. The infrared reflective property of the coating was tested by UV-Visible-Infrared Spectrophotometer (UV-3150, Shimadzu, Japan). For simulating practical applications, the coatings were placed on a polystyrene (PS) foam board under a 275-Watt infrared lamp radiation (Scheme 2) or under sunshine radiation, recording changes in their surface temperatures. The surface morphology was characterized by field emission scanning electron microscopy (F-SEM, NovaNano450, FEI). The wettability of the coating was studied by measuring the contact angle (CA) and sliding angle (SA) using a contact-angle system (OCA35, German Dataphysics) with 4 µL deionized water droplets at room temperature. Either CAs or SAs, they were


Page 5 of 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

Langmuir

the averaged values of five different measuring points on each surface. The water impact

resistance of the SiO2-"cool cold" coating was observed under splashing water and in a rainstorm (75.1 mm/24 h). The coating was placed horizontally, and its stability was observed. The rain resistance was also judged by measuring the coating's CA and SA after certain raining time. For studying the mechanism of the formation of the SH coating, the contents of the coating surface elements, such as F, O, N and their distribution along the depth of coating, were characterized by X-ray Photoelectron Spectroscopy (XPS, AXIS Ultra DLD, Shimadzu-Kratos, Japan) at different measuring angles (from 0° to 90°, corresponding 0 to 10 nm depth). The adhesive strength between the coating and substrate was tested using the cross-cut method. The distance between adjacent parallel horizontal cuttings was 1 mm. The cutting depth completely penetrated the substrate. The adhesive strength of the coatings was separated into six grades (0B to 5B, with 0B being complete detachment of the crosscut patterns and 5B being no detachment of the crosscut patterns) (ASTM D3359-09). The scratch resistance of the coating was measured by a pencil scratch test with pencils bearing different hardness grades from HB to 9H (hardest). 1. Infrared lamp 2. Coatings

1

40 cm

3. PS foam box

2

3

Scheme 2. Homemade device for measuring the infrared-reflective properties of the coatings.

RESULTS AND DISCUSSION NIR-reflective properties of the coating. Since the wavelengths of solar radiation are concentrated between 200 nm and 2600 nm, the infrared reflectivity of the


Langmuir

coatings was measured by a UV-Visible-Near Infrared Spectrophotometer at a wavelength range from 220 nm to 2600 nm. We prepared three dark coatings with differing amounts of "cool cold" black pigment (5 wt%, 10 wt%, 20 wt%, all named SiO2-"cool cold" coatings). As shown in Figure 1, compared with the carbon black coating, the SiO2-"cool cold" coatings possessed much higher reflectivity in the infrared region. Because the coatings were black, the reflectivity in the visible region of 400 nm to 780 nm was not high, and only approximately 5% higher than that of the carbon black coating. However, in the band from 780 nm to 1200 nm, the reflectivity of the SiO2-"cool cold" coatings increased sharply to 70%. Furthermore, when the content of the "cool cold" black pigment in the coating exceeded 10 wt%, the coating had an average reflectivity of 68 % at the NIR band (780 nm to 2600 nm) (Table 1). Its NIR-reflectivity was 80% in the range between 1300 nm and 2600 nm, even higher than that of the SiO2 white coating.

100 80

Reflectivity (%)

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 17

60 SiO2 white coating

40

carbon black coating SiO2-"cool cold" coating (5 wt%)

20

SiO2-"cool cold" coating (10 wt%) SiO2-"cool cold" coating (20 wt%)

0 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600

Wavelength (nm)

Figure 1. The UV-visible-infrared reflectivity of different coatings.

In contrast, the maximum and average reflectivity of the carbon black coating at the band from 220 nm to 2600 nm were only 7.3% and 4.5%, respectively. This demonstrated

that

the

SiO2-"cool

cold"

black

coatings

have

excellent

infrared-reflective properties. Additionally, there is no significant difference between


Page 7 of 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

Langmuir

the infrared reflectivity of the SiO2-"cool cold" coating (20 wt%) and that of the SiO2-"cool cold" coating (10 wt%). Therefore, with regards to its low cost, the SiO2-"cool cold" coating (10 wt%) is the best formula and was used to carry out subsequent experiments. Table 1. The average reflectivity (from 780 nm to 2600 nm) and wettability of the coatings. Sample

Average reflectivity (%)

CA (°)

SA (°)

SiO2 white coating

73.3

153.4±0.4

3.0±1.1

Carbon black coating

4.5

152.2±0.6

3.9±0.9

SiO2-"cool cold" coating (5 wt%)

57.0

152.0±0.5

3.5±0.5


67.6

152.6±0.6

2.8±0.9


68.9

152.1±0.8

4.0±1.1

To study the heat reflective property of SiO2-"cool cold" coatings, we monitored the surface temperature of the coatings under infrared lamp radiation, and the data for which is presented in Figure 2. Firstly, compared to the black carbon coating, the black "cool cold" coating can significantly reflect heat. The surface temperature of the "cool cold" coating was approximately 20 oC lower than that of the carbon black coating (90 oC). Additionally, the white SiO2 coating has the best heat reflective property. This is consistent with the result of Figure 1, where the white SiO2 coating has the highest NIR-reflectivity. Combining advantages of the dark "cool cold" coating and white SiO2 coating, the SiO2-"cool cold" coating was not only color adjustable, but also exhibited the desired heat reflective effect. The average surface temperature of the SiO2-"cool cold" coating was 7 oC lower than that of the "cool cold" coating and only 6 oC higher than that of the white SiO2 coating. Although dark coatings inherently appear much worse with regards to heat reflective performance than white coatings do, the heat insulating performance of the SiO2-"cool cold" coating we prepared here was much better than that of ordinary black coating, and even close to that of the white coating.


Langmuir

100 90 80 70

o

Temperature ( C)

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 8 of 17

60 50 SiO2 white coating

40

carbon black coating "cool cold"coating SiO2-"cool cold"coating

30 20 0

5

10

15

20

25

30

Time (min)

Figure 2. Surface temperatures of coatings as function of infrared lamp radiation time. The lamp was turned off after 20 min radiation, thus the surface temperatures all decreased soon.

To further investigate the actual heat reflective effect of the coatings, the coatings were placed under outdoor sunlight between 10:00 am to 3:00 pm in August (summer). The highest air temperature was 38 oC and the wind was a gentle breeze. The results are shown in Figure 3. The overall trend of the curves is like that seen for indoor infrared lamp radiation. The white SiO2 coating possesses the best heat reflective effect. The average surface temperature of the "cool cold" coating was 5 oC lower than that of the carbon black coating. The average surface temperature of the SiO2-"cool cold" coating was 3.5 oC lower than that of the "cool cold" coating. The addition of a small amount of SiO2 to the "cool cold" coating formula did not affect the black color of the coating but significantly enhanced the coating’s heat reflectivity. However, there were significant variations between the results of the outdoor and indoor heat reflective measurements. The results of the outdoor experiment appeared to be less obvious than that of the indoor experiments. This is because the sun emits light with a full wavelength range, including UV, visible and infrared light. Among all solar energy, infrared light only accounts for 50% (45% from visible light and 5% from UV light). In the outdoor experiment, the black SiO2-"cool cold" coating reflected most of the infrared radiation but also absorbed almost all the visible light (Figure 1). The temperature difference between that of the carbon black coating was


Page 9 of 17

only 7 oC. At the same time, the white SiO2 coating reflected most of the solar energy, thus has a lowest surface temperature. However, the outdoor results still prove that the SiO2-"cool cold" coating was good at reflecting solar energy. 75 70 65 60

o

Temperature ( C)

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

Langmuir

55 50 45 40 35

SiO2 white coating carbon black coating "cool cold"coating SiO2-"cool cold"coating

30 10:00 10:30 11:00 11:30 12:00 12:30 13:00 13:30 14:00 14:30 15:00

Time (h)

Figure 3. Surface temperature changes of coatings as a function of solar radiation time.

Morphology and wettability of the coating. As the coatings contained nanoparticles and a fluorine silicon sol mixture, they may possess rough surface structures and SH properties.20 As shown in Figure 4A and 4B, the white SiO2 coating consists of micro- and nanostructures formed by SiO2 nanoparticles, and exhibits excellent SH properties with CA 153.4±0.4° and SA 3.0±1.1° (Table 1). Figure 4C and 4D show the morphology of the carbon black coating, which also has obvious micro- and nanostructures, showing SH properties with CA 152.2±0.6° and SA 3.9±0.9°. However, the surface of the "cool cold" coating only consists of smooth submicro-structures (Figure 4E, F), and the CA is 130±3.5°, showing no SH property. Therefore, to fabricate dark coating with SH and NIR-reflective properties, a certain amount of nano-SiO2 was added to the dark "cool cold" coating formula to form a micro and nano multi-structure, while at the same time retaining its infrared reflective performance. Figure 4G, 4H show our design. The as-prepared SiO2-"cool cold" coating possesses micro and nano multi-structures and a static CA and SA of 152.6±0.6° and 2.8±0.9°, respectively, exhibiting an excellent SH property, which generally means a self-cleaning capability.


Langmuir 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

Page 10 of 17

B

500 nm

2 µm

C

D

500 nm

2 µm

E

F

500 nm

2 µm

G

H

2 µm

500 nm

Figure 4. SEM images of white nano-SiO2 coating (A/B), carbon black coating (C/D), black "cool cold" coating (E/F) and black SiO2-"cool cold" coating (G/H). B/D/F/H are maginified images of A/C/E/G, respectively. The insets were profiles of 4 µL water drops on coatings, showing CAs all larger than 150° except for that on the black "cool cold" coating.


Page 11 of 17

In addition to the micro-nano rough structure, surface energy is another factor that determines the wettability of a surface. To analyze the elemental composition of the SiO2-"cool cold" coating, we measured the elemental distribution of F, O and N within a depth of 10 nm from the surface of the coating. As shown in Figure 5, fluorine can be seen to be concentrated on the surface of the coating, and following an increase in depth, the amount of F decreases while the content of O and N increase. This indicated that the hydrolyzed FAS moves towards the surface and the hydrophilic groups migrate to the bottom of the surface during solidification of the coating. Therefore, the coating has a low surface energy, helping it to possess a SH property.

80 The content of F, O, N (wt%)

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

Langmuir

F O N

70 20

10

0 0

2

4

6 Depth (nm)

8

10

Figure 5. F, O and N elements distribution of SiO2-"cool cold" coating in 10 nm depth.

Mechanical Property and Superhydrophobicity Stability. From the cross-cut test and pencil scratch test, the adhesive strength of the coatings on the aluminum plate was found to be 5B. The hardness of the coating was 5H, which shows that the coating has good mechanical properties. However, compared with general coatings, SH coatings appear to be much weaker in practical applications [21]. One of the main obstacles limiting application of SH surfaces is stability, especially resistance to water impact. High impact velocity may cause Cassie-Wenzel transition of SH surface. The following section describes the water impact resistance of the SiO2-"cool cold" coating in a laboratory environment and in the rain.


Langmuir

The coating was placed under tap water and its stability was observed (see Supporting Information, Movie S1). The results show that the coating can resist water splashing. We then placed the coating horizontally in the rain to test its outdoor rain-resistance ability. A significant bounce phenomenon was observed, e.g., most of the raindrops bounced off the surface of the coating (representative impact velocity is ∼2.1 m/s, bouncing velocity is ∼0.5 m/s, see Supporting Information, Figure S1). Although a few small water droplets failed to bounce off the coating surface, most of them were removed by subsequent raindrops (see Supporting Information, Movie S2). The remaining water droplets on the coating surface could be rolled away by slightly sloping the coating to an angle less than 10°. No significant differences were observed within 6 hours, except for a large water drop forming at the corner of the coating after 5 h and becoming larger at 6 h. Nevertheless, when the coating was sloped to an angle of ∼5°, the drop rolled away. Additionally, we also measured the coating's CA and SA at certain time intervals in raining process and found that the CA of the coating remains above 150° and the SA does not exceed 10° (Figure 6). This implies that the coating can maintain its SH property when exposed to continuous heavy rain for at least 6 hours, and thus possesses excellent resistance to rain. 180 160

152.1

152.0

152.4

151.8

152.0

140

151.7 CA SA

120

Angle (°)

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 12 of 17

100 80 60 40 20 3.4

4.1

4.0

3.8

4.4

4.3

0 1

2

3

4

5

6

Time (h) Figure 6. The CA and SA of SiO2-"cool cold" coating after being subjected to rain with different time.


Page 13 of 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

Langmuir

CONLUSIONS In summary, a dark coating, fabricated using a waterborne epoxy resin emulsion, and consisting of a nano SiO2/fluorine silicon sol mixture and "cool cold" infrared reflective pigment, has been prepared. Due to the addition of the "cool cold" pigment, the as-prepared SiO2-"cool cold" coating showed favorable heat reflective performance. Although only the "cool cold" black pigment was demonstrated here, this study provides greater color choice for meeting the needs of new building designs and decorations by simply replacing the color of the "cool cold" pigments. Moreover, due to the presence of a small amount of nano SiO2 and concentration of the fluorine silicon sol on the outer surface of the coating, the SiO2-"cool cold" coating possessed excellent SH properties. Furthermore, the superhydrophobicity was stable to continuous heavy rain for at least 6 hours. We believe that this color adjustable, NIR-reflective, SH and inexpensive coating has great potential for use in practical applications to help reduce building energy consumption and allows for self-cleaning of the external walls of buildings.


Langmuir 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

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: XXX. Splashing of tap water on the SiO2-"cool cold" SH coating (Movie S1); Impacting of rain drops on the SiO2-"cool cold" SH coating (Movie S2); Time-lapse optical images of impacting and bouncing rain drops on the SiO2-"cool cold" SH coating surface. The inset data showing corresponding velocities calculated by snapshot images from Movie S2 (Figure S1).

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

Notes The authors declare no competing financial interest.

AKNOWLEDGEMENTS We gratefully acknowledge financial support from the National Natural Science Foundation of China (No. 51172206) and the Public Welfare Foundation from Zhejiang Province (2016C31G2020062).


Page 14 of 17

Page 15 of 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

Langmuir

REFERENCES (1) Zhao, H. X.; Magoulès, F. A Review on The Prediction of Building Energy Consumption. Renew. Sust. Energ. Rev. 2012, 16, 3586−3592. (2) Dounis, A. I. Artificial Intelligence for Energy Conservation in Buildings. Adv. Build. Energ. Res. 2010, 4, 267−299. (3) Karatasou, S.; Santamouris, M.; Geros, V. Modeling and Predicting Building's Energy Use with Artificial Neural Networks: Methods and Results. Energ. Building. 2005, 38, 949−958. (4) Xing, Z.; Tay, S. W.; Ng, Y. H.; Hong, L. Porous SiO2 Hollow Spheres as A Solar Reflective Pigment for Coatings. ACS. Appl. Mater. Interfaces 2017, 9, 15103−15113. (5) Santamouris, M.; Synnefa, A.; Karlessi, T. Using Advanced Cool Materials in The Urban Built Environment to Mitigate Heat Islands and Improve Thermal Comfort Conditions. Sol. Energy 2011, 85, 3085−3102. (6) Xing, Z.; Tay, S. W.; Liu, Y.; Hong, L. Solar Heat Reflective Coating Consisting of Hierarchically Assembled Polystyrene Nanoparticles. Surf. Coat. Tech. 2015, 265, 99−105. (7) Akbari, H.; Pomerantz, M.; Taha, H. Cool Surfaces and Shade Trees to Reduce Energy Use and Improve Air Quality in Urban Areas. Sol. Energy 1998, 70, 295−310. (8) Ianoş, R.; Muntean, E.; Păcurariu, C.; Lazău, R.; Bandas, C.; Delinescu, G. Combustion Synthesis of A Blue Co-Doped Zinc Aluminate Near-Infrared Reflective Pigment. Dyes. Pigments 2017, 142, 24−31. (9) Yang, R.; Han, A.; Ye, M.; Chen, X.; Yuan, L. Synthesis, Characterization and Thermal Performance of Fe/N Co-Doped MgtiO3 as A Novel High Near-Infrared Reflective Pigment. Sol. Energ. Mat. Sol. C. 2017, 160, 307−318. (10) Han, L.; Li, H.; Lei, Y.; Cao, D. Preparation and Transparent Heat Insulating Properties of Aqueous Acrylic–Amino–Alkyd Coatings with Cus Nanoplates. J. Mater. Sci-Mater. El. 2017, 28, 14596−14604. (11) Lee, Y.; You, E. A.; Ha, Y. G. Transparent, Self-Cleaning and Waterproof Surfaces with Tunable Micro/Nano Dual-Scale Structures. Nanotechnology 2016, 27, 355701−355707. (12) Lin, H.; Wang, Y.; Gan, Y.; Hou, H.; Yin, J.; Jiang, X. Simultaneous Formation of A Self-Wrinkled Surface and Silver Nanoparticles on A Functional Photo-Curing Coating. Langmuir 2015, 31, 11800−11808. (13) Ruan, M.; Wang, J. W.; Liu, Q. L.; Ma, F. M.; Yu, Z. L.; Feng, W.; Chen, Y. Superhydrophobic and Anti-Icing Properties of Sol–Gel Prepared Alumina Coatings. Russ. J. Non-Ferr. Met+. 2016, 57, 638−645. (14) Sriramulu, D.; Reed, E. L.; Annamalai, M.; Venkatesan, T. V.; Valiyaveettil, S. Synthesis and Characterization of Superhydrophobic, Self-Cleaning NIR-Reflective Silica Nanoparticles. Sci. Rep-UK. 2016, 6, 35993−36002. (15) Roppolo, I.; Shahzad, N.; Sacco, A.; Tresso, E.; Sangermano, M. Multifunctional NIR-Reflective and Self-Cleaning UV-Cured Coating for Solar Cell Applications Based on Cycloaliphatic Epoxy Resin. Prog. Org. Coat. 2014, 77, 458−462. (16) Zhu, W.; Tong, D.; Xu, J.; Liu, Y.; Ma, J. Multifunctional Composite Multilayer Coatings on Glass with Self-Cleaning, Hydrophilicity and Heat-Insulating Properties. Thin Solid Films 2012, 526 (1), 201−211. (17) Gao, Q.; Wu, X.; Fan, Y.; Meng, Q. Color Performance and Near Infrared Reflectance


Langmuir 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

Property of Novel Yellow Pigment Based on Fe2TiO5 Nanorods Decorated Mica Composites. Dyes. Pigments 2017, 146. 537−542. (18) Zheng, X.; Tay, S. W.; Ng, Y. H.; Liang, H. Solar Heat Reflective Coating Formed of Polystyrene Chains Bearing 4-Vinylpyridine-Rich End Segments. Polymer 2016, 87, 170−180. (19) Choi, J.; Han, K.; Kim, J. H. Enhanced Near Infrared Reflectance of TiO2/SiO2/TiO2 Multilayer Structure Using A Base-Catalyzed SiO2 Film. Thin Solid Films 2014, 569, 100−103. (20) Zhu, L.; Shi, P.; Xue, J.; Wang, Y.; Chen, Q.; Ding, J.; Wang, Q. Superhydrophobic Stability of Nanotube Array Surfaces Under Impact and Static Forces. ACS. Appl. Mater. Interfaces 2014, 6, 8073−8079. (21) Cheng, M. J.; Zhang, S. S.; Dong, H. Y.; Han, S. H.; Wei, H.; Shi, F. Improving the Durability of a Drag-Reducing Nanocoating by Enhancing Its Mechanical Stability. ACS. Appl. Mater. Interfaces 2015, 7, 4275-4282.


Page 16 of 17

Page 17 of 17

Table of Contents Graphic:

Dark, Infrared Reflective and Superhydrophobic Coatings by Waterborne Resins Jing Zhang, Weiqiang Lin, Chenxi Zhu, Jian Lv, Weicheng Zhang, Jie Feng*

100 80

Reflectivity (%)

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

Langmuir

60 40 20

SiO2 white coating carbon black coating SiO2-"cool cold" coating (5 wt%) SiO2-"cool cold" coating (10 wt%) SiO2-"cool cold" coating (20 wt%)

0 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600

Wavelength (nm)

Heat reflective coatings especially those with superhydrophobic and colorful surface play an important role in the field of building thermal insulation due to their high infrared reflectivity and self-cleaning ability. In this work, black and infrared reflective pigments, fluorine silicon sol and a small number of SiO2 nanoparticles were introduced into waterborne epoxy resin emulsion and then coated on an aluminum plate. After drying, black coatings with infrared reflective and superhydrophobic properties were obtained. Furthermore, the superhydrophobicity was stable to continuous heavy rain for at least 6 hours. Such coating has great potential for use in practical applications to help reduce building energy consumption and allows for self-cleaning of the external walls of buildings.


Dark, Infrared Reflective, and Superhydrophobic Coatings by

Recommend Documents