Fabrication of a Simultaneous Highly Transparent and Highly Hydrophobic Fibrous Films

Round 1

Reviewer 1 Report

The reviewer could not understand the following sentence in the Introduction:

"If we obtain the transparent surface more than 80 % on the surface of solar cell, the solar cell could save power more than 40% of energy consumption [4]."

In reference [4], reviewer could not find the reason of the value 40%.
Also, reviewer could not find the reason of the vslue80%.

For solar cells, we should think the light absorbance of the solar cells at first.
An then discuss the condition.
Otherwise, the word BIPV must be removed from the paper title.

English corrections and small corrections must be performed by specialist, for example

P1L25 grearer ->greater
P1L27 highly highly ->highly

Author Response

Reviewer”s comments

Reviewer-1

Open Review

Comments and Suggestions for Authors

The reviewer could not understand the following sentence in the Introduction:

1. Does the introduction provide sufficient background and include all relevant references? Not applicable.

Answer: We add sentence and references to supplement the background in introduction (page 2 line 3-17).

Recently, building integrated photovoltaics (BIPV) are received great attention as a renewable and non-polluting energy, together with energy efficiency, are ever increasing, zero energy and zero emission buildings. To become a zero energy or zero emission building, solar cells are integrated within the climate envelopes of buildings and utilizing solar radiation to produce electricity. BIPV offer an economical and technical solution to integrate solar cells harvesting solar radiation to produce electricity within the climate envelopes of buildings. Self-cleaning property receives attention in applications such as building walls. The most commonly used concepts for self-cleaning surfaces are hydrophobicity. The hydrophobicity for self-cleaning comes from the assumption that rolling water droplets down the hydrophobic surface will pick dirt on it and gets washed away. One of the tools to realize self-cleaning includes textiles and fabrics. Electrospinning is an effective process for fabrication of high surface-to-volume ratio and the generation of rough surface. Several researches have been able to produce electrospun surfaces with hydrophobicity. Such property comes about from a combination of surface texture and material used [1-12].

 

2. Are the methods adequately described? Must be improved

Answer: We add sentence to explain the characterization process in introduction (page 2, line 26-31).

The transmission characteristics of the randomly distributed fibers and the aligned fibers were measured using UV-Visible transmission spectroscopy. Surface roughness of the randomly distributed fibers and the aligned fibers was analyzed based on atomic force microscope (AFM) images. The distributions in the fiber diameter of the randomly distributed fibers and the aligned fibers were investigated with scanning electron microscopy (SEM) micrographs.

 

3. Are the results clearly presented? Must be improved

Answer: We add the figure 9 and the explanatory sentence in Discussion to characterize the results by quantitative data of the contact angle and surface roughness, and fiber diameter, etc.

(page 12, line 1-14/ page 13, Figure 9).

Figure 9 showed the surface morphology obtained by AFM images. The mean roughness values of the aligned fibers ranged from 360 ± 35 nm to 560 ± 130 nm. And the mean roughness values of the randomly distributed fibers ranged from 175 ± 15 nm to 262 ± 90 nm. The average fiber diameter of the aligned fibers was 178 ± 25 nm as shown in Figure S1 (supplementary information). And the average fiber diameter of the randomly distributed fibers was 250 ± 50 nm as shown in Figure S2 (supplementary information). The roughness values of the aligned fibers are higher than that of the random distributed fibers. Recently, Daniel et al. observed that the water contact angle depends on the surface roughness [25-29]. And Iren et al. described when air is entrapped inside the surface roughness (grooves) underneath the liquid drop, is termed the heterogeneous wetting, and is described by the Cassie-Baxter contact model. The volume of air packets underneath the liquid drop is increases as the surface roughness increases. Therefore, the contact angles (hydrophobicity) of the aligned fibers are increased due to the increase in the surface roughness. And the contact angle of the aligned fiber was higher than that of the random distributed fibers due to the higher surface roughness value [30-35].

 

4. Are the conclusions supported by the results? Must be improved Answer: We add the sentence to explain that conclusion supported by the results (page 14, line 2-17).

UV-Visible transmission spectroscopy showed an increased transmittance of up to 91.8% of aligned electrospun PS scaffolds, which was the key to enhancing the light absorption of solar cell. The water contact angle measurement by a contact angle meter showed an increased contact angle from 126° (randomly distributed fibers) to 142° (aligned fibers) at the same deposition time. The scanning electron microscope (SEM) images showed that the average fiber diameter of the aligned fibers was 178 ± 25 nm. And the average fiber diameter of the randomly distributed fibers was 250 ± 50 nm. The atomic force microscope (AFM) images showed that the mean roughness values of the aligned fibers ranged from 360 ± 35 nm to 560 ± 130 nm. And the mean roughness values of the randomly distributed fibers ranged from 175 ± 15 nm to 262 ± 90 nm.

 

5. "If we obtain the transparent surface more than 80 % on the surface of solar cell, the solar cell could save power more than 40% of energy consumption [4]." In reference [4], reviewer could not find the reason of the value 40%. Also, reviewer could not find the reason of the value 80%. For solar cells, we should think the light absorbance of the solar cells at first. And then discuss the condition. Otherwise, the word BIPV must be removed from the paper title.

Answer: We removed the sentence “"If we obtain the transparent surface more than 80 % on the surface of solar cell, the solar cell could save power more than 40% of energy consumption [4]”.

 

6. English corrections and small corrections must be performed by specialist, for example, P1L25 grearer -> greater and P1L27 highly highly -> highly.

Answer: We received the English corrections by native speaker. We removed the sentence in the title

“Potential for the development of hydrophobic and transparent building integrated photovoltaics”.

We removed the sentence in the introduction from line-34 to line-37

 If we obtain the transparent surface more than 80 % on the surface of solar cell, the solar cell could save power more than 40% of energy consumption [4]. Therefore, the focus of this research is to obtain the simultaneous highly hydrophobic (> 120°) and highly transparent (> 80 %) surfaces to be mounted on the surface of solar cell.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript presents development and characterization of electrospun polymer material (fiber scaffold/film of Polystyrene) with hybrid functionality –simultaneously transparent and hydrophobic. Its fabrication is achieved via optimization of electrospinning parameters and processes in order to control fiber orientation up to aligning polymer fibers predominantly in one direction. Similar multifunctional materials are widely studied in the last two decades and highly perspective for applications for sells surface coatings in photovoltaistics.

The proposed article properly exemplifies previously published papers on original self-made electrospinning setup and operational approaches for electrospinnig of nano-/micro-fibers with various alignment-angle configurations. The article is in line with the journal scope and aim. However, the proposed manuscript has a number of flaws that need revision in order to enhance its readability, acceptability and quality. Following the manuscript parts, here are my comments and suggestions:

1. The novelty claim in the Abstract (Rows 12, 13) should be reconsidered and/or removed. In fact, there are such reports and articles.
2.  It would be beneficial to include in the Abstract exact values of fabrication parameters, which enable achievement of optimal WCA and transparency (> 120°; > 80 %).
3.  The used materials should be characterized by source, molecular weight, and purity grade. (It concerns the analysis of results and their reproducibility).
4.  The instrument used for WCA measurements should be noted. The way of roughness measurement/estimation should be clearly explained.
5.  The proposed material characterization lacks for important quantitative data, such as fibers diameters and average (or range of) aspect ratio, polymer film/scaffold thickness and roughness, average distance between fibers, fibers shape (morphology), degree of alignment, etc. These characteristics are measurable and needed for correct analysis and discussion of results, as well as to make credible conclusions.
6.  The data about both measured characteristics (transparency and WCA) are given without statistics/errors. The term "Averaged transmittance" (Row. 93) should be explained and/or revised.

Comments for author File: Comments.docx

Author Response

Reviewer-2

Open Review

(x) I would not like to sign my review report
( ) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
(x) Moderate English changes required
( ) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style

 

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	( )	(x)	( )	( )
Is the research design appropriate?	( )	( )	(x)	( )
Are the methods adequately described?	( )	( )	(x)	( )
Are the results clearly presented?	( )	(x)	( )	( )
Are the conclusions supported by the results?	( )	(x)	( )	( )

Comments and Suggestions for Authors

The manuscript presents development and characterization of electrospun polymer material (fiber scaffold/film of Polystyrene) with hybrid functionality –simultaneously transparent and hydrophobic. Its fabrication is achieved via optimization of electrospinning parameters and processes in order to control fiber orientation up to aligning polymer fibers predominantly in one direction. Similar multifunctional materials are widely studied in the last two decades and highly perspective for applications for sells surface coatings in photovoltaistics.

The proposed article properly exemplifies previously published papers on original self-made electrospinning setup and operational approaches for electrospinnig of nano-/micro-fibers with various alignment-angle configurations. The article is in line with the journal scope and aim. However, the proposed manuscript has a number of flaws that need revision in order to enhance its readability, acceptability and quality. Following the manuscript parts, here are my comments and suggestions:

1. The novelty claim in the abstract (Rows 12, 13) should be reconsidered and/or removed. In fact, there are such reports and articles. Answer: We removed the sentence (page 1, line 12-13).
2. It would be beneficial to include in the abstract exact values of fabrication parameters, which enable achievement of optimal WCA and transparency (> 120°; > 80 %).

Answer: We add the sentence in abstract (line 14-23). The correlation between the water contact angles and surface roughness of the aligned electrospun fibers was investigated. From this analysis the water contact angle was increased as the surface roughness was increased. Therefore, the hydrophobic properties of the aligned electrospun fibers was enhanced by increasing the surface roughness. The change in the electrospinning mode from the randomly distributed fibers to the aligned fibers, the transmittance of the aligned electrospun fibers was increased. The increase in the porous area where the light transmittance of the aligned electrospun fibers enhanced the transmission. Through the above investigation of electrospinning parameters, we obtained the simultaneous transparent (> 80%) and hydrophobic (θ_W > 140°) electrospun fiber scaffold.

3.The used materials should be characterized by source, molecular weight, and purity grade. (It concerns the analysis of results and their reproducibility).

Answer: We revised the sentence in materials and solution synthesis. (page 5, line 9-16). Polystyrene (PS) with molecular weight of 104.1 g/mol and density of 1060 kg/m³ was purchased from Aldrich. The PS was dissolved in a solution of dimethylformamide (DMF) solvents. N-N-dimethylformamide (DMF)) mixed with de-ionized water in a ratio of 100 and 10 by weight (10 w%) gave consistent electrospun nanofiber scaffolds. The solvents were purchased from Aldrich. Strong stirring was performed to obtain uniform solutions. A voltage of 25 kV was applied between the nozzle tip (blue) and the collecting plate (pink). Polysyrene (PS) powder was solved using a dimethylformamide (DMF) with 10 weight percent (wt%). The solution feed rate was maintained at 0.1 ml/h for stable electrospinning. The thickness of the electrospun fibers were controlled by increasing the deposition time from 10 s to 40 s.

 

4. The instrument used for WCA measurements should be noted. The way of roughness measurement/estimation should be clearly explained.

Answer: We revised the sentence in characteristics and measurements (page 5, line 8-24/ page 6, line 1-25).

2.3.1. Materials and solution synthesis.

Polystyrene (PS) with molecular weight of 104.1 g/mol and density of 1060 kg/m³ was purchased from Aldrich. The PS was dissolved in a solution of dimethylformamide (DMF) solvents. N-N-dimethylformamide (DMF)) mixed with de-ionized water in a ratio of 100 and 10 by weight (10 w%) gave consistent electrospun nanofiber scaffolds. The solvents were purchased from Aldrich. Strong stirring was performed to obtain uniform solutions. A voltage of 25 kV was applied between the nozzle tip (blue) and the collecting plate (pink). Polysyrene (PS) powder was solved using a dimethylformamide (DMF) with 10 weight percent (wt%). The solution feed rate was maintained at 0.1 ml/h for stable electrospinning. The thickness of the electrospun fibers were controlled by increasing the deposition time from 10 s to 40 s.

2.3.2. Contact angle measurements

The water contact angle of electrospun fibers was measured by a contact angle meter (Phoenix 300 Touch (S.E.O), Seoul, Korea) at room temperature (22–25 °C). The volume of the droplets on the surface of electrospun scafollds was 3~4 µL volume on the surfaces using deionized (DI) water. The contact angle measurements were carried over a 1 min period with a 1 or 2 s step to capture the time-dependent shaper of the drop. The contact angle measured range was 10 ~ 180 °. Experiments were carried out at a temperature of 22 ◦C and a humidity of 50 %. Immediately, after the liquid deposition, the images of droplets were taken.

2.3.3 Scanning electron microscopy

Samples with the size of 9 x 9 mm were installed onto the stage of the scanning electron microscope (SEM). Platinum (Pt) was coated at the thickness of 30 nm before scanning using Eiko IB3 sputter coater (Japan). The surface morphology of the electrospun fibers were analyzed using the TM3000 (Hitachi, Japan) at 15 kV accelerating voltage.

2.3.4 Atomic Force Microscope

The nanofibers’ topography was further identified with AFM (AFM Workshop, USA) in an intermittent tapping mode of 10 μm × 10 μm area with a back-side aluminium-coated rectangular cantilever. The acquired topography AFM images were then subjected to post-analyses of surface roughness. Within the area of 10 m x 10 m, we measure 5 points to obtain root-mean-square (R_q, RMS) roughness. The 2D images from profilometry analysis of all electrospun samples and thickness measurements are provided in Figure 9.

2.3.5. Optical transmittance measurement.

The light transmittance transparency of the nanofiber scaffold was measured by a UV-Visible transmission spectroscopy (Rambda 750 model). The electrospun fiber scaffolds with different electrospinning times of 10, 20, 30, and 40 s with a time interval of 10 s were used. The light transmitted area was 5 mm x 25 mm and the scanned sample area of the electrospun fibers on glass was 25 mm by 30 mm.

 

5. The proposed material characterization lacks for important quantitative data, such as fibers diameters and average (or range of) aspect ratio, polymer film/scaffold thickness and roughness, average distance between fibers, fibers shape (morphology), degree of alignment, etc. These characteristics are measurable and needed for correct analysis and discussion of results, as well as to make credible conclusions.

Answer: We add the figure 9 and the explanatory sentence in Discussion part to characterize the results by quantitative data of the contact angle and surface roughness, and fiber diameter, etc. (page 12, line 1-14/ page 13, Figure 9).

Figure 9 showed the surface morphology obtained by AFM images. The mean roughness values of the aligned fibers ranged from 360 ± 35 nm to 560 ± 130 nm. And the mean roughness values of the randomly distributed fibers ranged from 175 ± 15 nm to 262 ± 90 nm. The average fiber diameter of the aligned fibers was 178 ± 25 nm as shown in Figure S1 (supplementary information). And the average fiber diameter of the randomly distributed fibers was 250 ± 50 nm as shown in Figure S2 (supplementary information). The roughness values of the aligned fibers are higher than that of the random distributed fibers. Recently, Daniel et al. observed that the water contact angle depends on the surface roughness [25-29]. And Iren et al. described when air is entrapped inside the surface roughness (grooves) underneath the liquid drop, is termed the heterogeneous wetting, and is described by the Cassie-Baxter contact model. The volume of air packets underneath the liquid drop is increases as the surface roughness increases. Therefore, the contact angles (hydrophobicity) of the aligned fibers are increased due to the increase in the surface roughness. And the contact angle of the aligned fiber was higher than that of the random distributed fibers due to the higher surface roughness value [30-35].

6. The data about both measured characteristics (transparency and WCA) are given without statistics/errors. The term "averaged transmittance" (Row. 93) should be explained and/or revised.

Answer: We revised the measured data with statistics/errors as follows. (page 12, line 1-14).

1. A) The mean roughness values of the aligned fibers ranged from 360 ± 35 nm to 560 ± 130 nm. And the mean roughness values of the randomly distributed fibers ranged from 175 ± 15 nm to 262 ± 90 nm. B) The average fiber diameter of the aligned fibers was 178 ± 25 nm as shown in Figure S1 (supplementary information). And the average fiber diameter of the randomly distributed fibers was 250 ± 50 nm as shown in Figure S2 (supplementary information). C) The term "averaged transmittance" changed to “The transmittance of the randomly distributed fibers was measured” (page 7, line 10-11). The light transmitted data in Figure 4 and Figure 5 were measured values from the sample area of the electrospun fibers on glass was 25 mm by 30 mm. Therefore, it is no necessary statistics/errors.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

This manuscript describes the the fabrication  of electrospun polystyrene nano fiber films. This film may be used for the surface coating of the photovoltaics.

Referee think this manuscript meets the criteria of the jounral, applied sciences.

 

Reviewer 2 Report

The new version of manuscript follows my comments and suggestions. Almost all of my concerns are widely addressed and the paper is significantly improved.