Study of Brush-Painted Ag Nanowire Network on Flexible Invar Metal Substrate for Curved Thin Film Heater
Round 1
Reviewer 1 Report
The presented manuscript is related to the study of brush painted Ag nanowires network on flexible invar metal substrate for curved thin film heaters. The presented work is novel and original and has technological value in the applications of Ag NW’s for curved thin film heaters. Despite clear benefits, manuscript needs major improvements before publishing:
Introduction part: instead of part related to the applicability of brush painting technologies for variety of applications would be more useful to discuss current state of art of materials used for flexible heaters applications, such as conducting polymers, carbon nanotubes, graphene, and metal nanowires. Would be useful to show benefits of Ag NW for thermal heaters and to discuss main challenges related to deposition (Why brush painting is better in comparison to other methods?) and properties (for example stability of Ag NWs at high temperatures at atmospheric conditions etc.). Talking about methodology it is not justified why heating was done till 110 0C? What about higher temperatures, let’s say up to 200 0C and stability at atmospheric conditions close to it? The need and added value of theoretical calculations related to saturation temperature of Ag NWs remains not enough justified, because it did not influenced Conclusion properly. Instead of calculations would be more useful to present experimental observations on Ag NW aging at high temperatures for prolonged time in atmospheric conditions. Figure 5 presents brush-painted AgNW results. Is it twice brush-painted? Or other samples? The description of Figure 5 is incomplete (lines 190-191; what about “(d)”?). The manuscript needs essential review by native English speaker. For example lines 23 – “satruration”, 33 – “However, However”, 72 – “invar sbustrate”, 75-“subsrrate”, “paining”; 96 – “sovelnt” etc.Author Response
Manuscript ID : metals-602136
Reviewer 1
Question 1) instead of part related to the applicability of brush painting technologies for variety of applications would be more useful to discuss current state of art of materials used for flexible heaters applications, such as conducting polymers, carbon nanotubes, graphene, and metal nanowires.
Answer) As reviewer suggested, we added about a state of art of material used for flexible heater application in introduction part like below. (Line 31~34)
Joule heat based thin film heater(TFH)s have been investigated for various device applications. For successful manufacturing of TFHs, it demand a high quality electrode with a low resistivity and outstanding mechanical flexibility[1,2]. To meet the requirements of the TFHs, many electrode materials such as graphene, carbon nanotube, metal nanowire, conductive oxide, and hybrid electrodes have been employed [3–9].
Question 2) Would be useful to show benefits of Ag NW for thermal heaters and to discuss main challenges related to deposition (Why brush painting is better in comparison to other methods?) and properties (for example stability of Ag NWs at high temperatures at atmospheric conditions etc.).
Answer) As review suggested, we added main advantages of Ag nanowire electrode and the advantages of brush painting over other methods already were mentioned in introduction like below (Line 35~40) (Line 50~55)
Among them, Ag nanowire(NW) network was extensively employed as an electrode material due to its merits such as solution-based simple coating process, a low resistivity, a high optical transmittance, and outstanding mechanical properties[10]. Although the Ag NW network electrode was used as a Joule heating layer for TFHs which fabricated on polymer or glass substrates[11–14], flexible or curved TFHs fabricated on Ag NW coated metal foil substrate was not reported until now.
Recently, simple printing processes such as spin-coating, bar-coating, ink-jet, and brush-painting are attracting great attention because those processes are easy, fast, and cheap[26,27]. Among them, brush-painting process is the most simple printing process because it requires only painting brush and functional ink [28]. Specially, it can control film thickness from ~10 nm to a few hundred nanometers and form polymer chain or 1-dimensional nanostructure layer by shear stress. In addition, it can be and applied onto various flat and textured substrates [28].
Question 3) Talking about methodology it is not justified why heating was done till 110 0C? What about higher temperatures, let’s say up to 200 oC and stability at atmospheric conditions close to it? The need and added value of theoretical calculations related to saturation temperature of Ag NWs remains not enough justified, because it did not influenced Conclusion properly. Instead of calculations would be more useful to present experimental observations on Ag NW aging at high temperatures for prolonged time in atmospheric conditions.
Answer) Temperature detector of our laboratory cannot measure of the temperature above 120 oC due to limit of power supply. Therefore, we cannot carry out the stability test at high saturation temperature at this moment. Considering evaporation or melting temperature of ice, saturation temperature of 120oC is enough for flexible or curved TFHs.
Question 4) Figure 5 presents brush-painted AgNW results. Is it twice brush-painted? Or other samples? The description of Figure 5 is incomplete (lines 190-191; what about “(d)”?).
Answer) As reviewer suggested we added Figure caption for Figure 5(d). (now Figure 5d is Figure 6 d)
The brush-painted Ag NW for thin film heaters is twice brush-painted. In accordance with your thankful advice, we revised it to clarify the content.
Figure 6 shows a promising application of brush painted optimized (twice brush-painted) Ag NW network electrode on SiO2 coated invar metal substrate in curved TFHs.
Figure 6(d) Thermal stability test of Ag NWs/SiO2/invar heater.
Question 5) The manuscript needs essential review by native English speaker. For example lines 23 – “satruration”, 33 – “However, However”, 72 – “invar sbustrate”, 75-“subsrrate”, “paining”; 96 – “sovelnt” etc.
Answer) As reviewer suggested, we corrected all typo in manuscript.
Reviewer 2 Report
In this paper, the authors report Ag nanowires applied to a metal foil using a brush. The films are characterized and used as a heater. Whilst it is important to study new ways of applying electronic thin films such as brush painting, the paper only adds incrementally to the field. I recommend to reject it. I have the following comments that might help for a resubmission:
A major motivation of using the metal substrate is that polymer substrates cannot withstand high temperatures in a heater. However, the heater is only demonstrated up to about 100C, which would work for many polymer substrates such as PEN or PI. The heater should be demonstrated for higher temperatures or there should be another motivation for the metal substrate. The authors should also comment on the cost of the metal substrate vs polymers.
The main motivation for using brushing compared with vacuum techniques (or even more controlled printing techniques such as gravure or screen) is low-cost and ease. But the SiO2 layer is deposited by PECVD. This doesn’t fit with the brushing. The authors should motivate this better or use a solution-processed insulator.
A more thorough study of the brushing process would make the paper much more impactful. For example, what is the variability? What is the effect of processing parameters such as brushing velocity and force? What about brush parameters like density or bristle size?
For many of the photos it is hard to make out details, especially when printing the paper in black and white. The authors should improve image quality. E.g. Fig 1d, Fig 2a, Fig 4c.
More details should be included on suppliers and exact products used e.g. for the Ag NWs or the brush.
Line 225: hc is calculated. Describe how. What assumptions are used?
What is the temperature coefficient of resistance for the Ag NW film? Should it be included in the model?
The manuscript contains many spelling errors and language issues. It should be carefully edited before submitting it again.
Author Response
Reviewer 2
Question 1) A major motivation of using the metal substrate is that polymer substrates cannot withstand high temperatures in a heater. However, the heater is only demonstrated up to about 100C, which would work for many polymer substrates such as PEN or PI. The heater should be demonstrated for higher temperatures or there should be another motivation for the metal substrate. The authors should also comment on the cost of the metal substrate vs polymers.
Answer) Temperature detector of our laboratory cannot measure of the temperature above 120 oC due to limit of power supply. Therefore, we cannot increase the temperature above120 oC at this moment. However, we believe the higher saturation temperature of invar-based TFHs than polymer-based TFHs. Although the cost of invar substrate is higher than polymer substrate, it is better choice considering reliability and thermal stability of invar metal substrate.
Question 2) The main motivation for using brushing compared with vacuum techniques (or even more controlled printing techniques such as gravure or screen) is low-cost and ease. But the SiO2 layer is deposited by PECVD. This doesn’t fit with the brushing. The authors should motivate this better or use a solution-processed insulator.
Answer) As reviewer suggested, low cost fabrication of insulator is necessary. However, at this moment, we cannot carry out the printing of insulating layer on the invar substrate due to absence of coating system. However, as we start the coating process of insulator, we will employ the solution processed insulating layer on the invar substrate.
Question 3) A more thorough study of the brushing process would make the paper much more impactful. For example, what is the variability? What is the effect of processing parameters such as brushing velocity and force? What about brush parameters like density or bristle size?
Answer) In our previous work, we investigated the effect of brush velocity. To achieve low sheet resistance, the optimized brush velocity is necessary. The change of sheet resistance as a function of brush velocity is not linear [1]. Although the study of force, bristle density or size were not performed here, detailed study was reported in our previous work [1].
[1] Lim, J.E.; Lee, S.M.; Kim, S.S.; Kim, T.W.; Koo, H.W.; Kim, H.K. Brush-paintable and highly stretchable Ag nanowire and PEDOT:PSS hybrid electrodes. Sci. Rep. 2017, 7, 1–12.
Question 4) For many of the photos it is hard to make out details, especially when printing the paper in black and white. The authors should improve image quality. E.g. Fig 1d, Fig 2a, Fig 4c.
Answer) When the paper in black and white, in case of Fig 1d, 2a(now Fig 1d is Fig 2b and Fig 2a is Fig 3a), the original color of the sample are gray so it is hard to express more clearly. Likewise, Fig 4c is difficult to express clearly because it is a FESEM image. However, as reviewer suggested, we improved the quality of image.
Question 5) More details should be included on suppliers and exact products used e.g. for the Ag NWs or the brush.
Answer) We added exact products of Ag NWs and bristle.
Question 6) Line 225: hc is calculated. Describe how. What assumptions are used?
Answer) Qr is assumed negligible compared to convective heat power. And A and Ti are also assumed exactly 2.5 â…¹ 1.5 cm2 and 298K, respectively. The measured average resistance is 20.078 Ohm
, If voltage is 8V hc is 9.9 W/cm2-K
We repeated upper calculation and averaged out each result. But we had a one mistake. When we calculated hc at 4V. we wrongly substituted T for 41.9 oC. Therefore, the hc have to recalculate at 47.2. the recalculated average hc is 9.2 W/cm2-K
Question 7) What is the temperature coefficient of resistance for the Ag NW film? Should it be included in the model?
Answer) The temperature coefficient of resistance for Ag NW is not consider in the model. Because the temperature coefficient of resistance of Ag NWs is not studied in this paper.
Question 8) The manuscript contains many spelling errors and language issues. It should be carefully edited before submitting it again.
Answer) As reviewer suggested, we corrected all typo in manuscript.
Reviewer 3 Report
Issues to be addressed:
The entire manuscript should be checked for English spelling and grammar errors. The entire manuscript should be checked for missing/extra letters often found at word level, which generates confusions and tampered reading. A clear and detailed distinction between investigated samples should be provided in the Materials and Methods section. In figure 1, the font size should be increased for a clearer view. Also, it should be divided, as to insert the b) and c) parts in Results and Discussion section. Accordingly, the interpretation of these results provided on lines 87-99 should be reorganized as part of Results and Discussion section. In figure 2a) the contrast/brightness of images should be improved. Also the acquisition method should be mentioned. Figure 2 should be enlarged. The scale bar for SEM micrographs is missing. In figure 1, the font should be modified according to the article. Overall, references are missing from Results and Discussion section. In figure 6, font and size should be compatible with all the other provided figures.Author Response
Reviewer 3
Question 1) The entire manuscript should be checked for English spelling and grammar errors. The entire manuscript should be checked for missing/extra letters often found at word level, which generates confusions and tampered reading. A clear and detailed distinction between investigated samples should be provided in the Materials and Methods section.
Answer) As reviewer suggested, we entirely checked for miss spelling and grammar errors. And we modified Figure in Material and Method section.
Question 2) A clear and detailed distinction between investigated samples should be provided in the Materials and Methods section. In figure 1, the font size should be increased for a clearer view. Also, it should be divided, as to insert the b) and c) parts in Results and Discussion section. Accordingly, the interpretation of these results provided on lines 87-99 should be reorganized as part of Results and Discussion section
Answer) As reviewer suggested, we modified the font size of Figure 1. Figure 1a and b are inserted to result and discussion section. Therefore, we reorganized lines 87-99 as part of Result and discussion section.
Question 3) In figure 2a the contrast/brightness of images should be improved. Also the acquisition method should be mentioned. Figure 2 should be enlarged. The scale bar for SEM micrographs is missing.
Answer) To solve the mentioned problem, Figure 2a(now Figure 2a is Figure 3a) is adjusted. And Figure 2a were enlarged. Figure 2a is just sample photo image by commercial camera. And scale bar is not missing.
Question 4) In figure 1, the font should be modified according to the article. Overall, references are missing from Results and Discussion section. In figure 6, font and size should be compatible with all the other provided figures
Answer) As reviewer suggested, Figure 1 and 6(now figure 6 is figure 7) were modified. And we added reference to Result and discussion.
Round 2
Reviewer 1 Report
As Ag NWs/SiO2/invar sample were developed using brush processing (by hand?) at room temperature, would be useful to add some information about repeatability in samples preparation.
It would be also useful to add information why water-IPA mixing ratio 1:2 were chosen (lines 122-124; for example, why not 1:1 or other)?
Reviewer 2 Report
The authors have addressed my concerns and it can be published.
