8/19/2019 Liu 2015 PDMS

1/31

Accepted Manuscript

Title: Transparent, durable and thermally stablePDMS-derived superhydrophobic surfaces

Author: Xiaojiang Liu Yang Xu Keyang Ben Zao Chen Yan

Wang Zisheng Guan

PII: S0169-4332(15)00484-5

DOI:   http://dx.doi.org/doi:10.1016/j.apsusc.2015.02.157

Reference: APSUSC 29837

To appear in:   APSUSC 

Received date: 29-12-2014

Revised date: 10-2-2015

Accepted date: 23-2-2015

Please cite this article as: X. Liu, Y. Xu, K. Ben, Z. Chen, Y. Wang, Z. Guan,

Transparent, durable and thermally stable PDMS-derived superhydrophobic surfaces,

 Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.02.157

This is a PDF file of an unedited manuscript that has been accepted for publication.

As a service to our customers we are providing this early version of the manuscript.

The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process

errors may be discovered which could affect the content, and all legal disclaimers that

apply to the journal pertain.

http://dx.doi.org/doi:10.1016/j.apsusc.2015.02.157http://dx.doi.org/10.1016/j.apsusc.2015.02.157http://dx.doi.org/10.1016/j.apsusc.2015.02.157http://dx.doi.org/doi:10.1016/j.apsusc.2015.02.157

8/19/2019 Liu 2015 PDMS

2/31

Page 1 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

1

Transparent, durable and thermally stable PDMS-derived

superhydrophobic surfaces

Xiaojiang Liua, Yang Xu

a, Keyang Ben

a, Zao Chen

a, Yan Wang

a, Zisheng Guan*

a

a College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009, China

* Corresponding author: Prof. Zisheng Guan

Tel: +86 025 83587270

E-mail address: zsguan@njtech.edu.cn

Highlights

• Transparent superhydrophobic surfaces were prepared by simple calcination of candle-soot-coated

 polydimethylsiloxane (PDMS) films.

• The resulting surfaces were durable and thermally stable.

• Superhydrophobic fiberglass cotton was prepared for optimized oil-water separation and air filtration.

8/19/2019 Liu 2015 PDMS

3/31

Page 2 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

2

ABSTRACT

We reported a novel, simple, modification-free process for the preparation of transparent

superhydrophobic surfaces by calcining candle-soot-coated polydimethylsiloxane (PDMS) films. Though

a calcination process, a candle soot template was gradually removed while robust fibrous and network

structures were created on glass. Owing to these structures, the glass substrates were durable and highly

transparent with an average transmittance (400- 800 nm) of 89.50%, very closed to the bare glass slides

(89.70%). These substrates exhibited a water contact angle (WCA) of 163° and a sliding angle (SA) of

~1°. Importantly, the superhydrophobicity of these surfaces can thermally recover after oil-contamination

due to their high thermal stability below 500 °C. Based on these, superhydrophobic fiberglass cotton was

also prepared for optimized oil-water separation and air filtration. This method is suitable for large-scale

 production because it uses inexpensive and environmentally friendly materials and gets rids of

sophisticated equipment, special atmosphere and harsh operations.

Keywords: superhydrophobic; transparent; durable; PDMS; template; thermally stable

8/19/2019 Liu 2015 PDMS

4/31

Page 3 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

3

1. Introduction

We all have been attracted by lotus leaves because water droplets can easily roll on their surfaces, take away

contaminants and keep the leaves clean. This phenomenon also gains much interest from researchers during the

 past decades and similar superhydrophobic surfaces with a water contact angle (WCA) larger than 150° and a

sliding angle (SA) less than 10° have been extensively studied due to their potential applications in

water-repellency, self-cleaning, anti-icing, antibacterial, oil-water separation, drag-reduction and optical areas.[1-10]

To prepare this kind of surface, roughness and low surface energy materials are two main factors and organic

materials are essential in nearly every method due to their key roles in constructing structures or providing low

surface energy.[11-18] Polysiloxanes, especially polydimethylsiloxane (PDMS), are good choice because they are

less reactive, less toxic and more inexpensive than fluorosilanes and chlorosilanes and more thermally stable,

durable than many polymers. Using PDMS as main materials, many attempts have been made to prepare

self-cleaning surfaces with special functions, including oil-water separation, durability, thermal stability and

transparency. On one hand, owing to its intrinsic low surface energy and moldability, PDMS was mixed with many

kinds of nano materials such as silica[19-21] and nano carbon materials[22-24] or treated through phase

separation,[25] lithography[26] and pattern[27] methods to prepare superhydrophobic materials. It is easy to get

good performances of oil-water separation and durability based on these low-temperature methods. Zhao et al.[22]

created hierarchical structure on the commercial nickel foam surface by deposition of a soot layer. After being

solidified by PDMS, the as-prepared nickel foam showed both superhydrophobic and superoleophilic properties

simultaneously, which was later applied in oil and water mixture separation. Deng et al.[28] reported an approach

8/19/2019 Liu 2015 PDMS

5/31

Page 4 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

4

for the production of durable superhydrophobic and photocatalytic hybrid films fabrics with TiO2 –SiO2 sol-gel and

PDMS. The as-prepared films on glass slides could present superhydrophobicity below 250 °C. However, almost

all of the above products are unable to endure a higher temperature (> 400 °C). On the other hand, when combined

with some suitable methods, PDMS can be applied in preparing transparent superhydrophobic surfaces with high

thermal stability. Wang et al.[29] used a liquid polysiloxane containing Si–H and Si–CH=CH2  groups as the

 precursor and methyl-terminated PDMS as porogens, successfully fabricating highly transparent and durable

superhydrophobic coatings through a simple solidification phase-separation method under an argon atmosphere at

550 °C. The as-prepared coatings have an average transmittance (AT) > 85% at the wavelength range of 400-780

nm, a WCA of 155° and a SA < 1°. Li and his co-workers[30] prepared superhydrophobic coating through spraying

the mixture of PDMS and hydrophobic nanosilica on the slide glass. After a calcination process at 400 °C, the

coating kept superhydrophobic and became transparent with the visible light transmittance at about 80%. Inspired

 by Deng’s templating methods[11], we have prepared antireflective superhydrophobic surfaces on a small scale via

a CVD process with PDMS as raw materials.[31] However, although these three kinds of superhydrophobic

surfaces are transparent and thermally stable, some challenges still exist either in not high enough transparency,

harsh preparation condition or small-scale production. So, it is necessary to confer high transparency, durability and

thermal stability on the PDMS-derived superhydrophobic surfaces through a more convenient approach.

In this paper, we develop a facile and novel method to prepare transparent, durable and superhydrophobic

surfaces in air by calcination of candle-soot-coated PDMS. High transparency was easily obtained due to the

nano-sized structures after the removal of candle soot template. Compared to the existing templating methods in

 preparing transparent superhydrophobic surfaces, this templating method did not involve any additional

modification process, which means the operations have been greatly simplified and the cost has been reduced.

Because these superhydrophobic surfaces are thermally stable below 500 °C, they can thermally recover from

oil-contamination. What’s more, employing the same method, we have also firsty prepared superhydrophobic

8/19/2019 Liu 2015 PDMS

6/31

Page 5 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

5

fiberglass cotton for potential application such as oil-water separation and air filtration. This method is suitable for

large-scale production because the materials were inexpensive and environmentally friendly and the operations

were very simple.

2. Experimental

2.1.Materials

Commercial used wax and cotton threads were employed to fabricate candles. 7101 slides (25.4 mm × 76 mm

× 1.2 mm), whose WCA is 5.5 ± 0.5° were used as substrates. α, ω- dihydroxypolydimethylsiloxane (Sylgard 107)

with a viscosity of 5 000 cps was purchased from Jiangxi Xinghuo Organic Silicone Plant (China). TEOS was

obtained from Sinopharm Chemical Reagent Co., LTD (China). Dibutyltindilaurate (DBTDL) was obtained from

Shanghai Lingfeng Chemical Reagent CO., LTD (China). Ethanol and n-hexane were got from Wuxi Yasheng Che

Co., LTD (China). n-dodecane was obtained from Jintong Letai Chemical Product Co., LTD (Beijing, China). All

of the reagents were used as received. The water in this experiment was high pure with a resistivity of 18.25

MΩ·cm-1. The dust particles used in the test of air filtration were commonly used cement powder.

2.2. Creation of Transparent Superhydrophobic Surfaces on glass slides

The PDMS were created through mixing TEOS, α, ω- dihydroxypolydimethylsiloxane and DBTDL into

n-hexane under stirring, in which DBTDL was adopted as a catalyst to accelerate the curing reaction. The mass

ratio of α, ω- dihydroxypolydimethylsiloxane, TEOS, DBTDL and n-hexane was 50: 10: 1: 1500. The mixture was

stirred for 30 min to get a PDMS solution. Glass slides were dip-coated in this solution at a speed of 40 mm/s to get

PDMS films. Different glass slides were dip-coated for different times and the interval between each dip-coating

was about 8 s for the evaporation of n-hexane. After dip-coating, the glass slides with PDMS were moved

horizontally through the middle of the candle flame until the glass slides became black. The candle-soot-coated

substrates were later subjected to a heat treatment in a muffle furnace (300 mm × 200 mm × 120 mm) including a

heating speed of 5 °C/min and a holding time for 1 h in air. After the heat treatment, the samples were cooled to

8/19/2019 Liu 2015 PDMS

7/31

Page 6 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

6

room temperature naturally.

2.3. Creation of Superhydrophobic Fiberglass Cotton

To get a PDMS solution, the mass ratio of α, ω- dihydroxypolydimethylsiloxane, TEOS, DBTDL and n-hexane

was 50: 10: 1: 3000 and the mixture was stirred for 30 min. Superfine fiberglass cotton (thickness= 1 mm), which

was commercially used as air filtration, was firstly immersed in the PDMS solution for 1 min. The fiberglass cotton

was later dried before deposition of candle soot on both sides. Then, this PDMS and candle-soot-coated fiberglass

cotton was calcined at 450 °C for 1 h to obtain superhydrophobic fiberglass cotton.

2.4. Characterization

WCA (4 µL Milli-Q water droplet) and SA (12.5 µL Milli-Q water droplet) were measured with the JC2000CS

measuring instrument equipped with a CCD camera at room temperature. Thermogravimetry/Differential Scanning

Calorimetry (TG/DSC) was performed with a thermal analysis system (PERKIN-ELMER, USA) and the samples

were heated from room temperature to 800 °C at a heating rate of 10 °C·min -1  in air with a gas flow rate of 20

mL·min-1. The morphologies of the as-prepared samples and EDS spectra were investigated by field emission

scanning electron microscopy (FE-SEM, Hitachi, S-4800) equipped with EDS unit. Fourier Transform Infrared

Spectroscopy (FT-IR) measurements of the samples were carried out on a FT-IR spectrometer (Nicolet Nexus 670).

The transmittance of the samples was measured on a UV-VIS-NIR spectrophotometer (UV-3600, SHIMADZU).

3. Results and discussion

3.1. Fabrication procedure of the superhydrophobic surfaces

Fig. 1 shows the schematic illustration of the fabrication procedure of the superhydrophobic surfaces on glass

slides. Through a curing reaction of TEOS and α, ω- dihydroxypolydimethylsiloxane, the PDMS films were

 prepared on the glass slides. These PDMS films were first coated by the deposition of candle soot and the coated

films were later calcined in a muffle furnace to obtain superhydrophobic surfaces.

8/19/2019 Liu 2015 PDMS

8/31

Page 7 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

7

Si   SiOO

OSi   Si

x Si   O Si   + D x+1

x=2,3,4...

 

(1)

Si   Si

Me

Me

Me

Me

O2Si   Si

Me Me

CH2OOH CH2OH

O   O   Si   Si

Me Me

O

O   O

 

(2)

When heated in air, a series of decomposition and oxidization reactions occurred to the PDMS, mainly

including degradation (Eq. 1) and oxidization reaction (Eq. 2), where  D  represents cyclosiloxanes.[32, 33] The

cyclosiloxanes can be oxidized to form hydrophobic SiO2  particles with candle soot as a template.[31] These

reactions occurred both during the deposition of candle soot and the calcination processes. It is notable that the hot

candle soot with a temperature of 300-400 °C can also etch the PDMS films during the deposition process. As

calcination proceeds in a muffle furnace, the residues from PDMS and the hydrophobic PDMS-derived SiO2

 particles can connect to each other directionally to form fibrous and network structures while the candle soot is

oxidized gradually. By controlling the heating temperature, the template of candle soot is removed through an

oxidization reaction without complete oxidization of the alkyl groups on the hydrophobic SiO2 particles. As a result,

surfaces with low surface energy and rough structures were obtained, which led to the formation of

superhydrophobic surfaces.

The candle-soot-coated PDMS films (Fig. 2a and 2e) have a WCA of 163° and a SA less than 1°, similar to

earlier report.[34] However, these surfaces suffer from a low transmittance. After 400 °C heat treatment, both of 

PDMS-derived SiO2 particles with size of ~50 nm and part of the unoxidized candle soot exist on the surfaces (Fig.

2b and 2e). When calcined at 420 °C for 1 h, no black candle soot can be observed on the substrates by naked eye.

At this stage, porous and network structures begin to appear with accompany of very small amount of candle soot

(Fig. 2c). When the heating temperature is up to 460 °C, most candle soot has been oxidized (Fig. 2e) and the

 porous and network structures are finally created (Fig. 2d). The formation of this kind of structures means chemical

 bonds have been created through the heat treatment. These surfaces after 400 °C and 460 °C treatment are all

superhydrophobic with a WCA of > 160° and the latter exhibits excellent transparency. EDS date (Table 1) show

8/19/2019 Liu 2015 PDMS

9/31

Page 8 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

8

that the weight % of the element C has greatly decreased as temperature increases due to the gradually removed

candle soot. These candle soot template was essential because a relatively flat surface with a smaller WCA of 109°

was created without the candle soot template (Fig. S1).

3.2. Transparency and wettability

The calcination temperature is a key parameter to control the transparency and wettability of the surfaces. As

the temperature increases, the transmittance changes (Fig. 3) and when the temperature is 460 °C, the AT of the

samples in visible wavelength (400-800 nm) is up to 89.49%, very closed to the bare glass slide (89.70%). If the

temperature is lower or higher, the transmittance decreases because of the small amount of unoxidized candle soot

at lower temperature or small fusion of the SiO2  structures at higher temperature.[35, 36] On the other hand, the

wettability is also dependent on the temperature (Fig. 4a). When the temperature is below 480 °C, the WCAs are

larger than 160°, indicating a good thermal stability. The WCA rapidly decreases to 0 if the temperature is up to 540

°C. This phenomenon can be explained by the FT-IR spectra (Fig. 4b) and TG/ DSC curves (Fig. 4c). There are

four exothermic peaks at 348 °C, 411 °C, 464 °C and 522 °C in the DSC curve, which could be attributed to the

oxidization reactions of the PDMS. When the temperature is 460 °C, besides the emerging absorption peak of -OH

around 3440 cm-1

, the peak of C-H around 2960 cm-1

still exist in the FT-IR, meaning the oxidization reaction is not

complete at this temperature and this is why the as-prepared surfaces are still superhydrophobic. When the

temperature is higher than 522 °C, the surfaces have become superhydrophilic with a WCA of 0. There is no

exothermic peak in the DSC curve and no peak of C-H around 2960 cm-1 can be observed in the FT-IR., indicating

the coatings have been thoroughly oxidized.

The transmittance of the superhydrophobic substrates is also influenced by the dip-coating times. Because the

size of the structure diameters is within 100 nm and the thickness of the coatings is within the range from several

hundred nanometers to several micrometers (Fig. S2), these substrates are of high transmittance that the ATs in

visible wavelength are all higher than 86% (Fig. 5). With the increasing dip-coating times, the transmittance of the

8/19/2019 Liu 2015 PDMS

10/31

Page 9 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

9

samples has a slightly tendency to decrease. This is due to the increased light scattering caused by the enhanced

structure and coverage of the rough structures on the glass substrates (Fig. 6a-b). When the sample is dip-coated for

5 times, the AT in the visible wavelength range is as high as 89.50%, which means these superhydrophobic coatings

cause only very small decrease to the transparency. On the other hand, the wettability is not obviously determined

 by the dip-coating times because the surfaces always keep stable superhydrophobicity with the increasing

dip-coating times (Fig. 7). These transparent superhydrophobic surfaces exhibit very low adhesion to water droplets.

As demonstrated in Fig. 6c and Movie S1, it is very hard for a water droplet to adhere to the surfaces even by

additional force. Meanwhile, the SAs of these superhydrophobic surfaces are near 0 and the droplets are extremely

unstable on the horizontal superhydrophobic surfaces that very small kinetic energy is enough to make the droplets

roll off (Fig. 6d and Movie S2). These results imply that the surfaces are within the range of stable Cassie Model.

3.3. Durability of the transparent superhydrophobic surfaces

We conducted three tests to confirm the durability of the superhydrophobic surfaces, including water drop test,

ultrasonic treatment and water immersion. Firstly, a water drop test was conducted to study the relationship

 between the coverage and the durability. Water droplets with volume of ~12.5 µL are impacted on the

superhydrophobic surfaces continuously from a height (h) of 10 cm (the impacting velocity is about 1.4 m/s) and

the substrates are placed by a title angle of 45° against the horizontal plane (insert in Fig. 8a). It is observed that as

the dip-coating times increased from 1 to 7, the total volume of impacted water to damage the superhydrophobicity

increased from 10 mL to 4 500 mL (Fig. 8a). This result shows that a higher coverage of the fibrous and network

structures led to a higher durability. However, as mentioned above, the increased robustness was slightly at the cost

of the transparency. To further study the adhesion and structure robustness of the superhydrophobic surfaces, we

 put the substrates into an anhydrous ethanol solution which was later subjected to an ultrasonic treatment at 40 KHz,

100 W for 4 h (insert in Fig. 8b). After this process, the surfaces still kept a WCA > 160° and a SA < 2°. SEM

images show that the surface structures were almost not affected after ultrasonic treatment (Fig. S3). UV-visible

8/19/2019 Liu 2015 PDMS

11/31

Page 10 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

10

spectra results (Fig. 8b) indicated that no significant change in the transmittance was observed. Because

ultrasonication can generate shock waves that dislodge contaminants and other soils on the surface of materials,[37]

this result is useful to confirm the good adhesion and structure robustness of the superhydrophobic surfaces.

An immersion test was carried out to study the corrosion resistant ability of the superhydrophobic surfaces by

 putting the substrates into the aqueous solutions with pH of 3, 7 and 11 (Fig. 8c). After 15 days immersion in

aqueous solution with pH 7, the surfaces are still superhydrophobic with a WCA > 150°. Besides, the transmittance

was not obviously influenced by the water immersion (Fig. S4). However, the surfaces have WCAs >120° and

about 50° after immersion in acid and basic solution, respectively. This phenomenon is explained that in aqueous

solution, hydrolyzation and reconstruction can occur to the surfaces, and in acid or basic solutions these reactions

would be increased.[38] Fig. 8d-f show the SEM images of the surfaces after 15 days immersion in different

aqueous solutions. It is observed that aggregates begin to appear on the surfaces in acid and neutral solutions and

the aggregates in acid solution are much bigger. However, the fibrous and network structures on the surfaces have

 been destroyed in basic solution, which make the surfaces become hydrophilic.

3.4. Thermally recoverable superhydrophobicity

Besides water impact and immersion, oil contamination is also a threat to the superhydrophobic surfaces, which

can led an obvious decrease of the WCA. So, it will be very important to remove the oil without damaging the

superhydrophobicity. To many organic solvents such as hexane and ethanol which can volatilize easly, the

immersed superhydrophobic surfaces are able to recover soon after being taken out (Fig. 9a). However, many

mineral oils are of high boiling point, making it hard to remove them. Herein, we immersed the as-prepared

transparent superhydrophobic glass substrates into n-dodecane for 10 min. The substrates after immersion in

n-dodecane showed a WCA of ~96°, which was very small compared to the original 163°. Because the n-dodecane

has a boiling point of 215~217 °C, these slides were later put in a muffle furnace for heat treatment at 250 °C to

remove the n-dodecane. We observed that due to the thermal stability, the superhydrophobicity recovered to the

8/19/2019 Liu 2015 PDMS

12/31

Page 11 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

11

original state immediately. This cycle was repeated for 8 times and almost no change occurred to the wettability of

the substrates (Fig. 9b), meaning these oil-contaminated surfaces can be thermally recoverable through a heat

treatment at some temperature that is slightly higher than the boiling point.

3.5. Superhydrophobic fiberglass cotton for optimized oil-water separation and air filtration

Owing to the thermal recovery of these superhydrophobic surfaces, we can design superhydrophobic fiberglass

cotton for potential application such as optimized oil-water separation and air filtration. The glass fibers of the

fiberglass cotton have diameters ranging from several hundred nanometers to several micrometers (Fig. 10a).

Different from the smooth glass fibers of the original fiberglass cotton (insert in Fig. 10a), the glass fibers of the

superhydrophobic fiberglass cotton are covered by nano-sized particles (Fig. 10b and insert). Because the glass

fibers were loose and non-planar, these nano-sized particles are unable to directionally form fibrous and network

structures like the superhydrophobic glass slides mentioned above. Fortunately, the as-prepared superhydrophobic

fiberglass cotton still has excellent superhydrophobicity and superoleophilicity. Water droplet can keep perfect

sphere (Fig. 10c) and roll off easily on the superhydrophobic fiberglass cotton while the n-dodecane can quickly

 penetrate into it (Fig. 10d). When a mixture of n-dodecane and water dropped on this surface, the n-dodecane was

absorbed thoroughly and the water still keeps ellipsoidal on the surface (Fig. 10e). This result means our

superhydrophobic fiberglass cotton is able to effectively absorb oil from the mixture of oil and various aqueous

solutions like early reported superhydrophobic materials.[39, 40]

Fig. 11a and Movie S3 demonstrate the the process of oil-water separation using superhydrophobic fiberglass

cotton as a tool. It is shown that n-dodecane can be quickly absorbed by the superhydrophobic fiberglass cotton

within several seconds. The absorption capacity of the superhydrophobic fiberglass cotton for n-dodecane is 5

times its own weight and absorption rate of the n-hexane is more than 99%, indicating a high level of separation

efficiency. Compared to many reported superhydrophobic carriers for oil-water separation, such as metal,[41]

foam[42] and candle soot,[22] our superhydrophobic fiberglass cotton is thermally stable and can be thermally

8/19/2019 Liu 2015 PDMS

13/31

Page 12 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

12

recoverable from oil-immersion. Thus, when used in oil-water separation, the oil can be collected through an

evaporation condensation operation and the fiberglass cotton can be recycled. This kind of superhydrophobic

fiberglass cotton might be for collection of oil from a large area of oil-polluted seas or waters.

 Nowadays, air filtration has been a hot topic due to the increasingly serious air pollution.[43] For traditional

fiberglass cotton used in air filtration, one most effective way to remove the dust particles is blowback. However,

 because the traditional fiberglass cotton is hydrophilic, once wetted by water the dust particles will aggregate and

 block the pores. It is very hard to remove these wetted dusts even by drying and blowback (Fig. 11b-c).

Consequently, the separation efficiency will be greatly reduced. Herein, using our superhydrophobic fiberglass

cotton to replace the traditional hydrophilic fiberglass cotton for air filtration can perfectly solve this problem. It is

shown in Fig. 11d that most of the dust particles can be taken away by water flow without wetting the fiberglass

cotton. For the very small amount of the rest dust particles, gentle blowback is enough to remove them (Fig. 11e).

As a result, the high separation efficiency can be kept and the service life can be extended. On the other hand, oil

contamination sometimes can reduce the efficiency of air filtration by blocking the pores structures. Heating the

oil-contaminated superhydrophobic fiberglass cotton will be a convenient way to remove the oil and continue to

use it for next air filtration.

4. Conclusions

We have successfully developed transparent superhydrophobic surfaces through calcination of

candle-soot-coated PDMS films. The prepared substrates have a WCA > 160° and a SA~ 1° as well as an AT of

89.50% in visible wavelength, almost the same as the pristine glass (89.70%). Tests of water-droplet impact,

ultrasonic treatment and water immersion show that the superhydrophobic surfaces are of good durability. The

oil-contaminated surfaces can easily regain superhydrophobicity through a heat treatment. Superhydrophobic

fiberglass cotton was prepared at the first time for optimized oil-water separation and air filtration. This method is

very novel, simple, low-cost and environmentally friendly in preparing transparent superhydrophobic surfaces

8/19/2019 Liu 2015 PDMS

14/31

Page 13 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

13

which makes it available for large-scale production.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (21071081) and a project

funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions of China. We

greatly thank State Key Laboratory of Materials-Oriented Chemical Engineering for help during experiments.

References

[1] W. Barthlott, C. Neinhuis, Planta 202 (1997) 1-8.

[2] Y. Wang, J. Xue, Q. Wang, Q. Chen, J. Ding, Acs Appl. Mater. Interfaces 5 (2013) 3370-3381.

[3] T. Sun, L. Feng, X. Gao, L. Jiang, Acc. Chem. Res. 38 (2005) 644-652.

[4] T. J. Wood, G. A. Hurst, W. C. E. Schofield, R. L. Thompson, G. Oswald, J. S. O. Evans, G. J. Sharples, C.

Pearson, M. C. Petty, J. P. S. Badyal, J. Mater. Chem. 22 (2012) 3859-3867.

[5] Q. Zhu, Q. Pan, ACS Nano 8 (2014) 1402-1409.

[6] B. Bhushan, Y. C. Jung, Prog. Mater. Sci. 56 (2011) 1-108.

[7] X. T. Zhu, Z. Z. Zhang, G. Ren, X. H. Men, B. Ge, X. Y. Zhou, J. Colloid Interface Sci. 421 (2014) 141-145.

[8] J. B. Lin, H. L. Chen, T. Fei, C. Liu, J. L. Zhang, Appl. Surf. Sci. 273 (2013) 776-786.

[9] S. A. Mahadik, D. B. Mahadik, M. S. Kavale, V. G. Parale, P. B. Wagh, H. C. Barshilia, S. C. Gupta, N. D.

Hegde, A. V. Rao, J. Sol-gel. Sci. Techn. 63 (2012) 580-586.

[10] T. Fei, H. Chen, J. Lin, Colloids Surf., A 443 (2014) 255-264.

[11] X. Deng, L. Mammen, H. J. Butt, D. Vollmer, Science 335 (2012) 67–70.

[12] X. Deng, L. Mammen, Y. Zhao, P. Lellig, K. Mullen, C. Li, H. J. Butt, D. Vollmer, Adv. Mater. 23 (2011)

2962-2965.

[13] G. D. Bixler, B. Bhushan, Nanoscale 6 (2014) 76-96.

8/19/2019 Liu 2015 PDMS

15/31

Page 14 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

14

[14] S. H. Lee, K. S. Han, J. H. Shin, S. Y. Hwang, H. Lee, Prog. Photovoltaics 21 (2013) 1056-1062.

[15] J. H. Kong, T. H. Kim, J. H. Kim, J. K. Park, D. W. Lee, S. H. Kim, J. M. Kim, Nanoscale 6 (2014)

1453-1461.

[16] R. Scheffler, N. S. Bell, W. Sigmund, J. Mater. Res. 25 (2011) 1595-1600.

[17] X. Li, G. Chen, Y. Ma, L. Feng, H. Zhao, L. Jiang, F. Wang, Polymer 47 (2006) 506-509.

[18] J. Liu, X. Xiao, Y. Shi, C. Wan, Appl. Surf. Sci. 297 (2014) 33-39.

[19] K. Li, X. Zeng, H. Li, X. Lai, C. Ye, H. Xie, Appl. Surf. Sci. 279 (2013) 458-463.

[20] E. J. Park, J. K. Sim, M. G. Jeong, H. O. Seo, Y. D. Kim, RSC Adv. 3 (2013) 12571-12576.

[21] Z. He, M. Ma, X. Xu, J. Wang, F. Chen, H. Deng, K. Wang, Q. Zhang, Q. Fu, Appl. Surf. Sci. 258 (2012)

2544-2550.

[22] F. Zhao, L. L. Liu, F. J. Ma, L. Liu, RSC Adv. 4 (2014) 7132–7135.

[23] Y. Gao, Y. S. Zhou, W. Xiong, M. Wang, L. Fan, H. Rabiee-Golgir, L. Jiang, W. Hou, X. Huang, L. Jiang, J. F.

Silvain, Y. F. Lu, Acs Appl. Mater. Interfaces 6 (2014) 5924-5929.

[24] H. O. Seo, K. D. Kim, M. G. Jeong, Y. D. Kim, K. H. Choi, E. M. Hong, K. H. Lee, D. C. Lim,

Macromolecular Research 20 (2011) 216-219.

[25] N. Zhao, Q. D. Xie, L. H. Weng, S. Q. Wang, X. Y. Zhang, J. Xu, Macromolecules 38 (2005) 8996-8999.

[26] M. Im, H. Im, J. H. Lee, J. B. Yoon, Y. K. Choi, Soft Matter 6 (2010) 1401-1404.

[27] G. Davaasuren, C. V. Ngo, H. S. Oh, D. M. Chun, Appl. Surf. Sci. 314 (2014) 530-536.

[28] Z. Deng, W. Wang, L. Mao, C. Wang, S. Chen, J. Mater. Chem. A 2 (2014) 4178.

[29] D. Wang, Z. Zhang, Y. Li, C. Xu, Acs Appl. Mater. Interfaces 6 (2014) 10014-10021.

[30] K. Li, X. Zeng, H. Li, X. Lai, H. Xie, Colloids Surf. A 445 (2014) 111-118.

[31] X. Liu, Y. Xu, Z. Chen, K. Ben, Z. Guan, RSC Adv. 5 (2015) 1315-1318.

[32] G. Camino, S. M. Lomakin, M. Lazzari, Polymer 42 (2001) 2395-2402.

8/19/2019 Liu 2015 PDMS

16/31

Page 15 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

15

[33] G. Camino, S. M. Lomakin, M. Lazzari, Polymer 43 (2002) 2011-2015.

[34] L. Shen, W. Wang, H. Ding, Q. Guo, Appl. Surf. Sci. 284 (2013) 651-656.

[35] G. Helsch, A. Mös, J. Deubener, M. Höland, Sol. Energ. Mater. Sol. C. 94 (2010) 2191-2196.

[36] X. Lu, Z. Wang, X. Yang, X. Xu, L. Zhang, N. Zhao, J. Xu, Surf. Coat. Technol. 206 (2011) 1490-1494.

[37] W. Huang, C. Lin, Appl. Surf. Sci. 305 (2014) 702-709.

[38] J. Zimmermann, G. R. J. Artus, S. Seeger, Appl. Surf. Sci. 253 (2007) 5972-5979.

[39] J. Li, L. Shi, Y. Chen, Y. Zhang, Z. Guo, B. Su, W. Liu, J. Mater. Chem. 22 (2012) 9774-9781.

[40] Z. Xue, Y. Cao, N. Liu, L. Feng, L. Jiang, J. Mater. Chem. A 2 (2014) 2445-2460.

[41] B. Wang, Z. G. Guo, Appl. Phys. Lett. 103 (2013) 063704.

[42] X. Y. Zhang, Z. S. Li, K. Liu, L. Jiang, Adv. Funct. Mater. 23 (2013) 2881-2886.

[43] H. Wan, N. Wang, J. Yang, Y. Si, K. Chen, B. Ding, G. Sun, M. El-Newehy, S. S. Al-Deyab, J. Yu, J. Colloid

Interface Sci. 417 (2014) 18-26.

Appendices:

Fig. 1. Schematic illustration of the fabrication procedure of the superhydrophobic surfaces on glass slides.

Fig. 2. SEM images of the surfaces after calcination at 25 °C (a), 400 °C (b), 420 °C (c) and 460 °C (d). The

substrates were dip-coated for 5 times. (e) Digital photographs of the candle-soot-coated PDMS films and the

samples after 400 °C and 460 °C treatment. The inserts in (e) show the WCAs of the corresponding surfaces.

Table 1.

The weight % of the element C, O, Si of the the candle-soot-coated surfaces without heat treatment and the surfaces

after 400 °C, 420 °C and 460 °C (c) treatment, respectively.

Fig. 3. Dependence of AT (400-800 nm) on the calcination temperature.

Fig. 4. (a) Dependence of the WCAs on the temperature. (b) FT-IR spectra of the cured PDMS and the coatings

 prepared at 460 °C and 540 °C. (c) TG/ DSC curves of the cured PDMS.

8/19/2019 Liu 2015 PDMS

17/31

Page 16 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

16

Fig. 5. Dependence of AT (400-800 nm) on the dip-coating times.

Fig. 6. (a,b) SEM images of the superhydrophobic surfaces, which are dip-coated for 1 and 7 times, respectively. (c)

Photographs of the anti-adhesive behavior of the transparent superhydrophobic surfaces by squeezing the droplet.

(d) Photographs of the sliding behavior of the droplet (12.5 µL) dropped on the horizontal superhydrophobic

surfaces.

Fig. 7. WCAs and SAs of the superhydrophobic surfaces prepared with different dip-coating times.

Fig. 8. (a) The total volume of impacted water to damage the superhydrophobicity of the samples prepared with

different dip-coating times. (b) Transmittance of the superhydrophobic surfaces (dip-coating time = 5) before and

after ultrasonic treatment. (c) WCAs and SAs of the surfacs immersed in solutions of different pH values for

different days. (d-f) SEM image of the superhydrophobic surfaces after immersion in solutions with pH of 3, 7 and

11for 15 days.

Fig. 9. (a) Illustration of the recovering routes of the superhydrophobicity for the glass slides. (b) The cycles of

WCAs of the oil-immersed superhydrophobic surfaces and the oil-immersed sufaces after heat treatment at 250 °C

for 10 min.

Fig. 10. SEM images of the glass fibers on the original fiberglass cotton (a,b) and superhydrophobic fiberglass

cotton (c,d). (e-g) Photographs of water, n-dodecane and their mixture dropped on superhydrophobic fiberglass

cotton. The water was dyed with CuSO4 for discrimination.

Fig. 11. (a) Photographs of the process of oil-water separation. (b-c) Photographs of the dust-contaminated

untreated fiberglass cotton after water syringe and drying/ blowback treatment. (d-e) Photographs of the

dust-contaminated superhydrophobic fiberglass cotton after water syringe and blowback treatment. The regions in

red circle show the dust-contaminated place after water syringe and gentle drawback (e).

8/19/2019 Liu 2015 PDMS

18/31

Page 17 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

17

Room

temperature

400 °C 420 °C 460 °C

C 72.70 49.76 22.88 16.89

O 10.98 30.76 46.93 52.30

Si 16.31 19.49 30.20 30.81

Total 100.00 100.00 100.00 100.00

8/19/2019 Liu 2015 PDMS

19/31

Page 18 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

aphical Abstract (for review)

8/19/2019 Liu 2015 PDMS

20/31

Page 19 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475257&guid=16da0cb5-6395-4a4b-aa56-8c7f8d94d9f0&scheme=1

8/19/2019 Liu 2015 PDMS

21/31

Page 20 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475258&guid=ba738280-1f19-4874-ab1c-fd846765a6be&scheme=1

8/19/2019 Liu 2015 PDMS

22/31

Page 21 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475272&guid=31030fd0-682f-4a12-a05f-661cf9eddc88&scheme=1

8/19/2019 Liu 2015 PDMS

23/31

Page 22 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475290&guid=addc5e0a-8bcc-4aa6-b314-b8237c7c615e&scheme=1

8/19/2019 Liu 2015 PDMS

24/31

Page 23 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475291&guid=c3a04e7e-848b-45ba-bb57-e5dd05760ea3&scheme=1

8/19/2019 Liu 2015 PDMS

25/31

Page 24 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475292&guid=73096c34-4eaf-4fc5-a8ec-e7182a992349&scheme=1

8/19/2019 Liu 2015 PDMS

26/31

Page 25 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475295&guid=2db78bec-a5cb-4a08-8ac7-9ab6fa0ff6d9&scheme=1

8/19/2019 Liu 2015 PDMS

27/31

Page 26 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475297&guid=7ec79932-86a7-4127-8c7a-2d0427aa792e&scheme=1

8/19/2019 Liu 2015 PDMS

28/31

Page 27 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475300&guid=1e4a354b-b20d-4352-a77e-2977f5b74f3d&scheme=1

8/19/2019 Liu 2015 PDMS

29/31

Page 28 of 30

   A  c  c  e   p

   t  e  d    M  a

  n   u  s  c  r

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475301&guid=6159e295-593c-4086-b6d0-b0e074c5471a&scheme=1

8/19/2019 Liu 2015 PDMS

30/31

Page 29 of 30

   A  c  c  e   p   t  e

  d    M  a  n   u

  s  c  r   i   p   t

gure

http://ees.elsevier.com/apsusc/download.aspx?id=1475303&guid=04838885-eb6e-4552-aad9-b38407ad676a&scheme=1

8/19/2019 Liu 2015 PDMS

31/31

   A  c  c  e   p   t  e  d

    M  a  n   u  s

  c  r   i   p   t

 

Room

temperature

400 °C 420 °C 460 °C

C 72.70 49.76 22.88 16.89

O 10.98 30.76 46.93 52.30

Si 16.31 19.49 30.20 30.81

Total 100.00 100.00 100.00 100.00

ble