One-Step Fabrication of Composite Hydrophobic Electrically Heated Graphene Surface

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1.      The topic of graphene based hydrophobic surfaces for deicing and anti-icing has been previously fabricated using different techniques and discussed for such purposes. What is the main motivation for creating such a surface? The authors should compare the advantages of their system in terms of performance of the system with others published in the literature (DOI:10.3390/coatings13091559; DOI:10.3390/coatings13091559).

2.     The chemical details of graphene should be given in section 2. Materials and methods.

3.  Please give a detailed explanation of the stability of the surfaces.

Author Response

Response to Reviewer 1 (coatings-3095711)

 

Reviewer 1

1. The topic of graphene based hydrophobic surfaces for deicing and anti-icing has been previously fabricated using different techniques and discussed for such purposes. What is the main motivation for creating such a surface? The authors should compare the advantages of their system in terms of performance of the system with others published in the literature (DOI:10.3390/coatings13091559; DOI:10.3390/coatings13091559).

The author’s answer 1: Thank you for your valuable suggestions. In this study, we employ laser treatment to achieve the deposition of laser-induced graphene(LIG) on  the surface of polyimide films. The primary objective of the study is to fabricate a linear array of LIG for constructing hydrophobic structures, and innovatively improve the hydrophobic properties of graphene surfaces through modulation of laser power. Specifically, our primary focus is to investigate the fundamental macroscopic principle through an exploration of the impact of laser power on the quality of LIG products. This will involve examining variations in surface line width and height morphology resulting from changes in laser power, as well as conducting preliminary research on the development of hydrophobic/electric heating surfaces. Our previous studies have concentrated on micro-level analysis, specifically analyzing the influence of scanning speed and line spacing on the surface structure of LIG. By optimizing and improving the delayed icing/electrothermal de-icing performance, we establish a functional coupling between hydrophobic/superhydrophobic/electrothermal properties to effectively prevent ice formation on the surfaces. (Page 4, lines 156-169, highlighted in green)

 

2. The chemical details of graphene should be given in section 2. Materials and methods.

The author’s answer 2: Thank you for your constructive suggestions. In this revised version of the manuscript, we have added the chemical details in the Figure 1.  (Page 5, line 215, highlighted in green)

 

 

3.  Please give a detailed explanation of the stability of the surfaces.

The author’s answer 3: Thank you for your valuable suggestions. The focus of this study lies in the construction of hydrophobic structures using a linear array of LIG and the innovative enhancement of graphene surfaces’ hydrophobic properties through  laser power modulation. The investigation into surface stability will be address in subsequent research endeavors. Additionally, our previous publication encompasses the experimental content and elucidation of surface stability research, including cyclic icing and cyclic electric heating. (DOI:10.3390/coatings13091559; DOI: 10.3390/mi15020285)

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors! Draft of the article contains interesting information on obtaining graphene-based coatings on the surface of polyimide films by using laser treatment. The authors show the ways of regulating the morphology of the surface layer, surface composition, hydrophobic and electrically conductive properties as a result of control of the laser etching process. The text is easy to read and leaves a good impression.

However, there are a few remarks that would improve the presented material:

1)    In the last paragraph of the introduction, authors should clearly show the scientific novelty (What did the authors do for the first time? What is the main scientific component?) and clearly state the purpose of the work.

2)    In Section 3.3 the authors talk about the formation of air cushion in roughness cavities. You should be careful here: look at the Wenzel and Cassie-Baxter wetting models. You have rather low contact angles, so we cannot talk about a heterogeneous wetting regime (even if you have air bubbles at the initial moment of time, a drop of test liquid will gradually fill the microstructure with the formation of a homogeneous wetting regime).

3)    The title of the paper "One-Step Fabrication of Composite Hydrophobic Electrically Heated Graphene Surface for Anti-Icing" shows the reader that the paper is about the creation of a material for anti-icing, but in the text of the paper it is discussed only in the introduction and there are no experimental data. I recommend that the authors either change the title or add experimental data.

Author Response

Response to Reviewer 2 (coatings-3095711)

 

Reviewer 2

Dear authors! Draft of the article contains interesting information on obtaining graphene-based coatings on the surface of polyimide films by using laser treatment. The authors show the ways of regulating the morphology of the surface layer, surface composition, hydrophobic and electrically conductive properties as a result of control of the laser etching process. The text is easy to read and leaves a good impression.

However, there are a few remarks that would improve the presented material:

• In the last paragraph of the introduction, authors should clearly show the scientific novelty (What did the authors do for the first time? What is the main scientific component?) and clearly state the purpose of the work.

The authors’ answer 1: Thank you for your valuable suggestions. This study employs laser treatment to achieve LIG on the surface of polyimide films. The primary objective of the study is to fabricate a linear array for the construction of hydrophobic structures, while innovatively improve the hydrophobic properties of graphene surfaces through modulation of laser power.

The main innovations and contributions of this study can be summarized as follows:

1. A one-step synthesis method was proposed for the fabrication of composite graphene surfaces with hydrophobicity and electric heating functionality using laser-induced technology. This approach simplifies the traditional multi-step fabrication process and enhances efficiency.
2. By precisely controlling laser power parameters, the microstructure design of the graphene surface has been successfully achieved, thereby imparting not only hydrophobicity but also efficient electric heating performance to the surface.
3. A systematic investigation was conducted to examine the impact of laser power on the quality and surface microstructure of graphene, revealing that optimal hydrophobicity can be achieved while ensuring high-quality graphene production by controlling the laser power at 5W.

(Page 4, lines 170-181, highlighted in yellow)

 

• In Section 3.3 the authors talk about the formation of air cushion in roughness cavities. You should be careful here: look at the Wenzel and Cassie-Baxter wetting models. You have rather low contact angles, so we cannot talk about a heterogeneous wetting regime (even if you have air bubbles at the initial moment of time, a drop of test liquid will gradually fill the microstructure with the formation of a homogeneous wetting regime).

The authors’ answer 2: Thank you for your valuable suggestions. I have reviewed the information regarding the two wetting models, namely Wenzel and Cassie Baxter. The Wenzel model postulates that droplets on rough surfaces exhibit uniform wetting hehavior, wherein they completely occupy the surface microstructure. On the other hand, according to the Cassie Baxter model, droplets on rough surfaces demonstrate non-uniform wetting characteristics as they only partially infiltrate the surface microstructure while retaining some air pockets.

The hydrophobic state investigated in this study bears resemblance to the Cassie Baxter model. Initially, there exist bubbles and a drop of test liquid gradually infiltrates the microstructure, resulting in a uniform wetting state. The graphene surface possess a micro-rough structure, causing water droplets only partially wet the surface while retaining some air trapped between them and the surface. In the case of a small contact angle, it represents completely wetness, whereas for 5W, it signifies partial wetness. During subsequent optimization process, the contact angle further increases, leading to a larger contact angle and exhibiting hydrophobicity. (Page 9, lines 377-385, highlighted in yellow)

 

3)    The title of the paper "One-Step Fabrication of Composite Hydrophobic Electrically Heated Graphene Surface for Anti-Icing" shows the reader that the paper is about the creation of a material for anti-icing, but in the text of the paper it is discussed only in the introduction and there are no experimental data. I recommend that the authors either change the title or add experimental data.

The author’s answer 3: Thank you for your valuable suggestions. The focus of this study is the investigation of graphene surface hydrophobicity. Therefore, the title "One Step febrication of Composite Hydrophobic Electrically Heated Graphene Surface for Anti-Icing" has been revised to "One Step Synthesis of Composite Hydrophobic Electrically Heated Graphene Surface" (Page 1, lines 2-3, highlighted in yellow)

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper describes the surface state and electrical measurement results of laser-induced graphene (LIG) technology. However, there are several parts that are insufficient and difficult for readers to understand. First of all, for example, the following parts need to be revised or added.

 

—What was the PI film placed on? Please show a schematic diagram of the cross-sectional direction.

—Please explain the laser penetration length into the PI film.

—Please also explain the laser scan pitch.

—The units of "95.5 mm" on line 184 and "95.5 µm" in Fig. 1 are different.

—Does Laser focal length mean Working distance?

—In Fig. 1, are the Laser scan path and the SEM image in the same direction?

—The description of the photo in the upper right of Fig. 1 is "Contant angle," so it needs to be revised.

--The photos in Fig. 1 and Fig. 2 should have the same laser scan direction.

—The numbers of each photo in Fig. 3 cannot be distinguished.

—The scale and the numbers of each photo in Fig. 3 cannot be distinguished.

—The numbers on the vertical axis in Fig. 3(f) and 3(g) seem to be in different orders. Is this information correct?

—Why do anomalous values ​​appear when the power is 6 W in Fig. 3(f) and 3(g)?

—The font size in Fig. 4 is too small for readers to read.

—Why does excessive heat accumulate when the laser power exceeds 6 W in Fig. 4?

—Why does anomalous values ​​appear when the power is 6 W in Fig. 5? Please explain.

—In Fig. 6, please explain why processing with a laser power of 6 W has low resistance.

—Please provide specific figures for the emissivity in Fig. 7(d).

Author Response

Response to Reviewer 3 (coatings-3095711)

Reviewer 3

1. What was the PI film placed on? Please show a schematic diagram of the cross-sectional direction.

The authors’ answer 1: Thank you for your valuable suggestions. The laser processing procedure involves placing the PI onto the stainless steel plate using PET and clamping it onto the three-dimensional moving axis. The laser light source is directed onto the surface of the PI through the reflector and galvanometer, resulting in photothermal action and chemical reaction on the irradiated area. The laser processing flow diagram, LIG surface, edge, cross-section SEM figure are presented below, sourced from our previous published articles ((DOI: 10.3390 / coatings13091559).

 

2. Please explain the laser penetration length into the PI film.

The authors’ answer 2: Thank you for your valuable suggestions. During the experiment, the laser defocus parameter is set to 0, meaning that the laser’s minimum spot scans the surface of the PI film, including a photothermal effect and resulting in the formation of a new substance called LIG. It should be noted that throughout this process, there is no penetration of the film by the laser.

 

3. Please also explain the laser scan pitch.

The authors’ answer 3: Thank you for your valuable suggestions. The laser scanning distance refers to the spacing between adjacent scanning tracks, with the laser serving as the center point in the process. (In the text, the periodic line spacing is patterned due to its alignment with aser spacing.)

 

4. The units of "95.5 mm" on line 184 and "95.5 µm" in Fig. 1 are different.

The authors’ answer 4: Thank you for your valuable suggestions. The units should be 95.5mm, as indicated in Figure 1. (Page 5, Line 211, Highlight in Blue)

 

5. Does Laser focal length mean Working distance?

The authors’ answer 5: Thank you for your valuable suggestions. The laser focal length indicates the working distance between the PI film and the lens, i.e., ensuring that the laser focus (the smallest spot) precisely aligns with the PI film.

 

6. In Fig. 1, are the Laser scan path and the SEM image in the same direction?

The authors’ answer 6: Thank you for your valuable suggestions. The scanning path direction shown in FIG. 1 is exactly not consistent with the SEM direction of the presented sample and has been rectified.

 

Revised Figure 1

7. The description of the photo in the upper right of Fig. 1 is "Contant angle," so it needs to be revised.

The authors’ answer 7: Thank you for your valuable suggestions. The term “Contact Angle” has been revised as follows.

 

8. The photos in Fig. 1 and Fig. 2 should have the same laser scan direction.

The authors’ answer 8: Thank you for your valuable suggestions. The laser scan direction has been revised, as shown in revised Figure 1 .

 

9. The numbers of each photo in Fig. 3 cannot be distinguished.The scale and the numbers of each photo in Fig. 3 cannot be distinguished.

The authors’ answer 9: Thank you for your valuable suggestions. The Figure 3, including numbers, scale, and axis, has been revised as follows.(Page 7, Line 261, Highlight in Blue)

 

Original Figure 3 Revised Figure 3

10. The numbers on the vertical axis in Fig. 3(f) and 3(g) seem to be in different orders. Is this information correct?

The authors’ answer 10: Thank you for your valuable suggestions. The line roughness on the vertical axis is illustrates in Figure 3 (f). The measurement results of line roughness are obtained by randomly intercepting perpendicular to the direction of the graphene line array. Figure 3 (g) shows the surface roughness on the vertical axis, primarily investigating the impact of laser power on the surface structure. The variation trends of these two parameters exhibits remarkable similarity. From a macroscopic perspective, this congruence between local and global variation trends proves evidence for a relatively complete periodic structure in the surface.

 

11. Why do anomalous values appear when the power is 6 W in Fig. 3(f) and 3(g)?

The authors’ answer 11: Thank you for your valuable suggestions. In combination of the changing trend of line height, line width, and line spacing in Figure 5a indicates that at higher laser power, the surface of the PI film experience overheating, resulting in intensified thermal decomposition and structural alterations, consequently resulting in an increase in surface roughness. Wider lines may contribute to increased surface roughness due to reduced gap between them, thereby diminishing surface smoothness. Increased line height can also elevate surface roughness as it creates more pronounced irregularities on the surface. Furthermore, a reduction in line spacing enhances overlap between lines and subsequently raises surface roughness by concentrating more heat within a smaller area and intensifying thermal decomposition. However, based on experiment results, it observed that 6W may be a critical threshold, exceeding this power level could trigger sudden changes in material properties that affect the surface structure. Consequently, when operating at 6W power level or below it, the sample exhibits lowest degree of surface roughness.

 

12. The font size in Fig. 4 is too small for readers to read.

The authors’ answer 12: Thank you for your valuable suggestions. The Figure 4 has been revised as follows.

 

13. Why does excessive heat accumulate when the laser power exceeds 6 W in Fig. 4?

The authors’ answer 13: Thank you for your valuable suggestions. The laser power serves as the primary influencing factor in the process of laser-induced graphene formation. At higher power levels, the duration of laser beam interaction with the material surface increases, resulting in enhanced heat transfer. The cumulative thermal effect rapidly elevates the material’s surface temperature, thereby facilitating material decomposition and graphene formation. XPS test results demonstrated in Figure 4 show that at a laser power of 6W, carbon saturation is observed, signifying complete conversion of PI film into graphene. Consequently, when the laser power exceeds 6W, excessive heat accumulation occurs which becomes counterproductive.

 

14. Why does anomalous values appear when the power is 6 W in Fig. 5? Please explain.

The authors’ answer 14: Thank you for your valuable suggestions. The primary objective of this study is to construct a hydrophobic structure through the generation of line array graphene. Generally, augmenting surface roughness can enhance hydrophobicity to a certain extent. It can be concluded from Figure 3 that when the power ranges between 3W and 5W, the prominence pf the surface roughness structure becomes more pronounced. However, as the power increase to 6W, the roughness diminishes. The protrusion of graphene’s surface microstructure proves counterproductive, and should ideally be in an ablative state at this juncture, thereby resulting in an outlier at is 6 W in Figure 5.

 

15. In Fig. 6, please explain why processing with a laser power of 6 W has low resistance.

The authors’ answer 15: Thank you for your valuable suggestions.The surface resistance is influenced by laser power, with insufficient heat accumulation observed at 3W and 4W powers, resulting in the generation of graphene with small dimensions and poor quality within the gaps of the graphene wire array. Consequently, this compromises the overall quality of graphene, leading to higher resistance. However, a laser power of 5W minimizes the square resistance, while a power of 6W minimizes the connection resistance. The connection resistance measures the expansion of graphene wire onto the graphene surface. With higher power levels, there is reduced spacing between the graphene lines which leads to increased heat accumulation within their gaps during laser action and induces additional formation of graphene paths. This ultimately results in lower connection resistance when using a laser power of 6W.

 

16. Please provide specific figures for the emissivity in Fig. 7(d).

The authors’ answer 16: Thank you for your valuable suggestions.The objective of this study is to investigate the hydrophobic effect of graphene surface through patterning design, and explore the potential of de-icing by examining the main factor that influences the surface morphology and quality of graphene - laser power. Currently, emissivity has not been considered in the experiment, but it will be addressed in future research.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This manuscript presents interesting work on constructing super-hydrophobic surfaces for aviation applications. Overall, the experiements seem to be pretty thorough and well-described, but I'll admit this is outside my area of expertise. 

Author Response

Response to Reviewer 4 (coatings-3095711)
Reviewer 4

This manuscript presents interesting work on constructing super-hydrophobic surfaces for aviation applications. Overall, the experiements seem to be pretty thorough and well-described, but I'll admit this is outside my area of expertise. 

The author’s answer: Thank you for your recognition of our work, we shall persist in upholding a scientific and rigorous approach to conduct further research work. 

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript has been improved, but please add more information to help readers understand.

 

-Answer 1

Add this content to the text.

 

-Answer 2

The laser light and PI interact with each other, which means that the laser light penetrates into the PI. Therefore, please estimate the penetration depth of the laser light. Also, please use specific values ​​to describe whether the LIG structure is higher or lower than the PI surface before the laser light irradiation.

 

-Answer 3

Please provide specific values ​​for the period  to the text.

 

-Answer 5

Add this content to the text.

 

-Answer 10

It is (generally) unnatural for the surface roughness to be 10 times larger than the roughness scanned by the line. Please recheck the measurement results. If the surface roughness is 10 times more uneven than the line roughness, it means that the in-plane uniformity is significantly poor.

 

-Answer 11, 13, 14, 15

The reviewer asked about the reason why the data at 6W was unusual. The authors' answer is a qualitative explanation of the results at 6W. Why does this phenomenon not occur at 5W or 7W? Please explain "why it occurs at 6W" by showing the physical reason.

Author Response

Review 3（Round2）

-Answer 1

Add this content to the text.

The authors’ answer 1: Thank you for your valuable suggestions. This section has been added to the main text. (Page 4-5, lines 204-208, highlighted in pink)

 

-Answer 2

The laser light and PI interact with each other, which means that the laser light penetrates into the PI. Therefore, please estimate the penetration depth of the laser light. Also, please use specific values to describe whether the LIG structure is higher or lower than the PI surface before the laser light irradiation.

The authors’ answer 2: Thank you for your valuable suggestions. The process of LIG is highly efficient, with the laser energy effectively triggering photochemical reactions in the irradiated PI film. This leads to recombination between the C elements within the PI film and diffusion of elements like N/O into the surrounding air as gas. The SEM images below depict the edges and cross-sections of graphene generated through this method, sourced from our previous research(DOI: 10.3390/coatings 13091559). Base on the trend chart illustrating variation in line height, width, and spacing within the text, it can be inferred that when using laser ranging from 3-7W on PI material, the resulting graphene exhibits an approximately height of 60-130 μ m.

 

 

-Answer 3

Please provide specific values for the period  to the text.

The author’s answer 3: Thank you for your valuable suggestions. The scanning spacing is 100 μ m and is specified in the subsequent flowchart.

(Page 5, Figure 1,highlighted in pink)

 

 

-Answer 5

Add this content to the text.

The author’s answer 4: Thank you for your valuable suggestions. This section has been added to the main text.

(Page 5, lines 215-217, highlighted in pink)

 

-Answer 10

It is (generally) unnatural for the surface roughness to be 10 times larger than the roughness scanned by the line. Please recheck the measurement results. If the surface roughness is 10 times more uneven than the line roughness, it means that the in-plane uniformity is significantly poor.

The author’s answer 5: Thank you for your valuable suggestions. The results have been retested and are shown in the following figure.

(Page 7, Figure 3, lines 268-269, highlighted in pink)

 

 

-Answer 11, 13, 14, 15

The reviewer asked about the reason why the data at 6W was unusual. The authors' answer is a qualitative explanation of the results at 6W. Why does this phenomenon not occur at 5W or 7W? Please explain "why it occurs at 6W" by showing the physical reason.

The author’s answer 6:Thank you for your valuable suggestions. The schematic diagram in the following figure illustrates the measurement of surface pore size on graphene at different powers: (a) 3 W; (b)4 W; (c)5 W； (d)6 W； (e)7 W；  (f) Trend of pore size variation on graphene surface. The aperture size of the scanning area shows a decreasing trend within the range of 3-5 W, reducing from 2.67 µ m to 1.84 µ m. This phenomenon can be attributed to an enhanced decomposition process of PI film with increasing laser power levels. At lower power levels such as 3 W, there is a slower thermal accumulation process that hinders timely discharge of gas generated during PI-to-graphene conversion and decomposition into the external environment. Consequently, liquid PI forms on the surface, expanding and saturating the gas wall before exploding and resulting in larger pores on the graphene surface. As the laser power gradually increases, the gas accumulation process accelerates progressively, leading to a more complete decomposition of the PI film. The rate of film decomposition surpasses that of liquid PI inflation saturation, resulting in a gradual reduction in pore size on the graphene surface. At laser powers of 6 W and 7 W, the aperture increases from 1.84 µ m to 2.25 µ m and 2.17 µ m respectively. This phenomenon is attributed to sufficient and intense decomposition of the PI film, accompanied by rapid gas generation. The saturation rate of gas exceeds that of the film decomposition, giving rise to explosive gas holes and thorny residual walls on the graphene surface. When the power increases to 6W, there is a decrease in roughness, while the protrusion of the graphene surface microstructure exhibits a counteractive effect. At a laser power of 6W, the C element tends to saturate, indicating complete decomposition of the PI film into graphene. Consequently, exceeding 6W in laser power leads to excessive heat accumulation. The combined effect of pore accumulation, surface roughness, and thermal energy contribute to abnormal data at 6W.

(Page 7-8, Figure 3, lines 273-305, highlighted in pink)

 

 

Author Response File: Author Response.pdf