Preparation and Luminescence Properties of PVDF/ZnS:Mn Flexible Thin-Film Sensors

Round 1

Reviewer 1 Report

Chen and his co-workers present in this paper the preparation of a PVDF/ZnS:Mn composite thin film using an electro-assisted 3D printing technique, and the study of the thin-film’s mechano-luminescence properties. The research is carefully planned and results deserve publication.

Comments:

--- lines 76-77: please clarify if methanol or ethanol was used (text or formula is wrong? “anhydrous ethanol (CH3OH, 99.70%)”); the formula seems to be wrong;

--- lines 77-78: do you mean that ‘Six initial ZnS – MnCO3 mixtures were prepared, containing 1 at.%, 2 at.%, 3 at.%, 4 at.%, 5 at.%, or 6 at.% Mn2+, respectively?’; please make the sentence more clear;

--- lines 87-89: do you mean that ‘A 16%(m/m) polyvinylidene fluoride (PVDF, molecular weight 370000, French Acoma) solution was prepared by dissolving PVDF powder in N,N-dimethylacetamide (DMAC, 99.0%) solvent?’; please simplify the text and make it more clear; use N,N-dimethylacetamide instead of N-dimethylacetamide;

--- line 102: how many layers were printed?

--- line 103: please resolve the meaning of PET, and provide information about how PET layers were prepared, e.g. printing solution, if printing is used;

--- lines 108-117: IR spectrometer and the technique used to record IR spectra, viz. ATR or pellet, are missing;

--- lines 174-189: what is the basis of the assignment of IR bands?; the quality of the spectra is low, therefore conclusions have to be taken with care; band at 763 cm-1 is so weak that conclusion cannot be drawn on the bases of the intensity of this band alone; comparing absolute intensities between different spectra is meaningless, only relative intensities can be compared; authors should tone down their statements based on IR spectra;

--- lines 196-199: S…H hydrogen bonds seems to be very strange in this system, as H is connected to C; a secondary F…H interaction is always stronger than a S…H; dispersion interactions play a key role between polymer chains;

--- Figure 6: wrong and misguiding; the amount of ZnS is negligible compared to the amount of CH2 groups in the polymer; suggesting a S…H hydrogen bond is wrong (see above);

--- lines 216-225: the argument here is not clear; authors should clean up the text;

--- The English of the text should be improved. Spelling mistakes and typically wrong usage of is/are should be cleaned up.

Author Response

Dear reviewer，

Thank you for your comments concerning the manuscript entitled “Preparation and properties of antibacterial PVDF composite thin films”. The comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied comments carefully and have made correction. Revised portions are marked in the paper. The main corrections and the responds to the reviewer’s comments are as follows:

1. lines 76-77: please clarify if methanol or ethanol was used (text or formula is wrong? “anhydrous ethanol (CH3OH, 99.70%)”); the formula seems to be wrong;

Response: Thanks to the reviewer's corrections. we have revised it.

 2. lines 77-78: do you mean that ‘Six initial ZnS – MnCO3 mixtures were prepared, containing 1 at.%, 2 at.%, 3 at.%, 4 at.%, 5 at.%, or 6 at.% Mn2+, respectively?’; please make the sentence more clear;

Response: Yes, we have prepared the MnCO₃-ZnS mixtures, containing 1 at.%, 2 at.%, 3 at.%, 4 at.%, 5 at.%, and 6 at.% Mn²⁺. After solid phase sintering, the ZnS:Mn powders containing different Mn²⁺ doping amounts were obtained. According to your suggestion, we have explained it in the Experiment part. 

3. lines 87-89: do you mean that ‘A 16%(m/m) polyvinylidene fluoride (PVDF, molecular weight 370000, French Acoma) solution was prepared by dissolving PVDF powder in N,N-dimethylacetamide (DMAC, 99.0%) solvent?’; please simplify the text and make it more clear; use N,N-dimethylacetamide instead of N-dimethylacetamide;

Response: Your understanding is correct, and we have modified it in the text as requested.

4. line 102: how many layers were printed?

Response: A 20 mm × 20 mm PVDF/ZnS:Mn composite film with 70 layers was obtained by layer-by-layer printing. we have added it in the Experimental part.

5. line 103: please resolve the meaning of PET, and provide information about how PET layers were prepared, e.g. printing solution, if printing is used;

Response: The PET layers were pasted on the surface of the film by a tape-like PET film.

6. lines 108-117: IR spectrometer and the technique used to record IR spectra, viz. ATR or pellet, are missing;

Response: Thank you for your valuable comments, we have added it.

7. lines 174-189: what is the basis of the assignment of IR bands?; the quality of the spectra is low, therefore conclusions have to be taken with care; band at 763 cm-1 is so weak that conclusion cannot be drawn on the bases of the intensity of this band alone; comparing absolute intensities between different spectra is meaningless, only relative intensities can be compared; authors should tone down their statements based on IR spectra;

Response: Thank you for your suggestion, we modified the content of this section and added a method to calculate the β-phase content of thin film.

8. lines 196-199: S…H hydrogen bonds seems to be very strange in this system, as H is connected to C; a secondary F…H interaction is always stronger than a S…H; dispersion interactions play a key role between polymer chains;

Figure 6: wrong and misguiding; the amount of ZnS is negligible compared to the amount of CH2 groups in the polymer; suggesting a S…H hydrogen bond is wrong (see above);

Response: Thank you very much for the comments. The formation of S-H bond is only a preliminary guess without obvious evidence, and there is no shift or change and no new vibration peak is found in the infrared detection of the composite thin film. After careful consideration, we decided to delete this part of text and Figure 6. When new evidence becomes available, we'll look into it further.

9. lines 216-225: the argument here is not clear; authors should clean up the text;

Response: We modified the Figure5(a), and make the explanation simpler in the text.

10. The English of the text should be improved. Spelling mistakes and typically wrong usage of is/are should be cleaned up.

Response: Thank you for your correction, we have corrected some errors found in the text.

Special thanks to editor and reviewer for your good comments. We appreciate for Editors/Reviewers’ warm work earnestly.

 

Best regards

Caifeng Chen

Reviewer 2 Report

The paper entitled:” Preparation and Luminescence Properties of PVDF/ZnS:Mn 2 Flexible Thin Film Sensors” by Chen et al, treats PVDF/ZnS:Mn flexible thin-film prepared by electro-assisted 3D printing techniques. They investigate the interaction and influence of PVDF thin film and ZnS:Mn.

The results are interesting, and paper is well organized. However, some questions and comments need to be considered by the authors before deciding on the suitability of the paper for publication.

1. Paragraph starting at Line 174 and describing the results of Fig 5: The authors need to justify the attribution of all the wavenumbers (add appropriate references)
2. Fig 7 (a): a schematic presentation of the transition energies is needed to explain the origin of the PL peak’s shift. It would be very helpful to provide the Mn composition of ZnS
3. 1. Fig 7 (b): there’s a huge red shift of the PL energy from Fig 7(a), so why the increase of Mn composition didn’t induce a gradual displacement of the PL peak? May be the author could comment on this point and provide explanation in the text.
   2. Extensive comparative analysis with the work of Sabira et al (https://doi.org/10.1016/j.jlumin.2017.05.014) will be helpful concerning the PL intensity evolution with Mn concentration
4. In section 3.4: the author needs to provide the ML/PL spectra for all the applied forces
5. Typical ML/PL spectrum of the schematic explanation in Fig 9 is also required
6. Typical ML/PL spectrum for low, medium, and high stress will be beneficial for the readers

Author Response

Dear reviewer,

Thank you for your comments concerning the manuscript entitled “Preparation and properties of antibacterial PVDF composite thin films”. The comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied comments carefully and have made correction. Revised portions are marked in the paper. The main corrections and the responds to the reviewer’s comments are as follows:

1. Paragraph starting at Line 174 and describing the results of Fig 5: The authors need to justify the attribution of all the wavenumbers (add appropriate references)

Response: The characteristic peaks of all the wavenunbers have been explained in detail in Fig.5, and the references added are 27, 28, 30 and 31.

2. Fig 7 (a): a schematic presentation of the transition energies is needed to explain the origin of the PL peak’s shift. It would be very helpful to provide the Mn composition of ZnS

Response: Thank you for your suggestion. After deleting Figure 6, Figure 7 is renamed Figure 6 in the manuscript. we modified the Figure 6(a), and explain the origin of the PL peak’s shift.

3. Fig 7 (b): there’s a huge red shift of the PL energy from Fig 7(a), so why the increase of Mn composition didn’t induce a gradual displacement of the PL peak? May be the author could comment on this point and provide explanation in the text.Extensive comparative analysis with the work of Sabira et al (https://doi.org/10.1016/j.jlumin.2017.05.014) will be helpful concerning the PL intensity evolution with Mn concentration

Response: In Fig.6 (a), the luminescent waves of λ₁=530 nm and λ₂=580 nm correspond to two energy release ways respectively. Luminescence of Mn composition is the second way of energy release, The Mn electron transition process(⁴T₁ to ⁶A₁) is accompanied by the release of energy in the form of light(λ₂=580 nm). Mn is a luminescent center, and the increase of Mn content only increases the number of luminescent centers. But it has no significant effect on the way of energy release. Therefore, the PL spectrogram only shows the change of light intensity without red shift, as shown in Figure 6(b).

 4. In section 3.4: the author needs to provide the ML/PL spectra for all the applied forces. Typical ML/PL spectrum of the schematic explanation in Fig 9 is also required. Typical ML/PL spectrum for low, medium, and high stress will be beneficial for the readers

Response: Thanks to the reviewer for this very constructive suggestion, the PVDF/ZnS:Mn composite thin film is highly sensitive and emits visible light when applied with very little forces. Therefore, currently only 0-20N loading force have been done. We will improve the instrument and working conditions, and further work will be carried out on this proposal.

Special thanks to editor and reviewer for your good comments. We appreciate for Editors/Reviewers’ warm work earnestly.

 

Best regards

Caifeng Chen

Reviewer 3 Report

The work "Preparation and Luminescence Properties of PVDF/ZnS:Mn Flexible Thin Film Sensors" is, overall, sound and well-written except for some parts (see my comments below) but still requires some major revision. Once the authors revise the manuscript, I think that the work might become publishable.

- Abstract: use "photoluminescence" (instead of photo-luminescence)

- Line 25: "voltage" instead of electricity seems more precise.

- Lines 23-29 (first part of the introduction): when talking about luminescence-based sensors, it shall be said that luminescence is a transduction parameter of importance in chemical (i.e. gas) sensing, so that - among the fields mentioned in line 26 ("biomedical detection, structural health detection,..") air quality monitoring shall also be mentioned, being it a vast and important subject I think it shall at least be mentioned. At the same time, I would add some additional and general references dealing also with this latter topic. Being metal-organic frameworks and metal oxides the two major "players", I'd suggest to add references dealing on these class of materials, some examples are: 10.1002/advs.201500434 (Lin et al, Advanced sciences), 10.1021/acssensors.6b00432 (Pallotti et al, ACS Sensors); 10.1186/s11671-017-1891-5 (Zhyrovetsky et al, Nanoscale research letters). I'd suggest that authors cite these works together with those already mentioned in the original manuscript in a same group of references, and add to this same group the work by Mahata work (the one on rare-earth doped MOFs for luminescence-based chemical sensing).

The reason why I suggest doing that is that placing it outside the initial block of general references seems a bit arbitrary, as it does not deal with mechano-responsive luminescence (MRL)(or, if author prefer, ML) which is the topic of the manuscript. All the non-MRL related references shall be placed together. Then, the introduction can deal with the actual work by Candra on ML materials and by Kim on torque-based luminescence sensors.

 

- The introduction does not make completely clear which was the purpose of the present work, given that the approach is not completely original: was it to compare their results (based on Mn doping) with those obtained by Subira et al based on ZnS:Cu? Also, I'd recommend that the author dedicate part of the discussion (before the conclusion) to compare their results with those based on differently doped ZnS embedded in flexible matrixes. The sensing performances appear to be good but at least one reference point shall be given to the readers.

 

- The experimental details on how the photoluminescence apparatus works shall be given, in order to give to the reader suggestion on possible repeatability of the experiment and on the PL efficiency of the sample. The authors mention that a "steady-state transient fluorescent system": here, steady-state AND transient seem to be mutually in contradiction. It shall be explained : which was the excitation source? (a laser? incoherent light?) was it a steady-state or pulsed excitation? or maybe modulated periodic excitation? which was the excitation wavelength? can the author give an estimation of the excitation power on the sample surface?

 

- Figure 7: are the PL peaks normalized or it happens by chance that the samples show almost exactly the same PL intensity?

 

- Figure 8: It seems that the PL spectra also present a wide minor band centered at 400 nm (also evident in Figure 7). Authors shall mention this point, suggesting and giving literature reference for a possible cause for the corresponding optical transitions. I'd suggest that this may originate from the ZnS matrix, based on a possible interpretation that the authors can check: Sanz et al, J. Phys. Chem. C, 2011, 115 (8), pp 3203–3211 (DOI: 10.1021/jp108489k)- Other suggestions might be found in the references therein.

 

- I am not totally convinced by the model sketched in Figure 9. Usually, defect levels also vary their energy (i.e. shift or bend) in presence of an electrostatic field. Is the model supported by additional references?

 

- Maybe I missed it, but is there any evidence that the use of dopant improves the strain-related sensing performances? In principle, I might expect similar phenomena also for undoped ZnS, is that correct? Is there any experimental finding (by authors of in literature) about that? I'd suggest the author to comment on this point.

Efter giving my comments, I however would like to say that the work is not bad and is well-written, so that the authors shall consider my observation as a way to improve their work and not as a hard criticism. Unfortunately, I have to evaluate my observations as "major" points and recommend a re-evaluation of the revised work, but I guess that it shall become publishable after the revisions.

   

Author Response

Dear reviewer,

Thank you for your comments concerning the manuscript entitled “Preparation and properties of antibacterial PVDF composite thin films”. The comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our research. We have studied comments carefully and have made correction. Revised portions are marked in the paper. The main corrections and the responds to the reviewer’s comments are as follows:

1. Abstract: use "photoluminescence" (instead of photo-luminescence)

Response: We have revised it in the abstract.

 2. Line 25: "voltage" instead of electricity seems more precise.

Response: we have revised it in the text.

 3. Lines 23-29 (first part of the introduction): when talking about luminescence-based sensors, it shall be said that luminescence is a transduction parameter of importance in chemical (i.e. gas) sensing, so that - among the fields mentioned in line 26 ("biomedical detection, structural health detection,..") air quality monitoring shall also be mentioned, being it a vast and important subject I think it shall at least be mentioned. At the same time, I would add some additional and general references dealing also with this latter topic. Being metal-organic frameworks and metal oxides the two major "players", I'd suggest to add references dealing on these class of materials, some examples are: 10.1002/advs.201500434 (Lin et al, Advanced sciences), 10.1021/acssensors.6b00432 (Pallotti et al, ACS Sensors); 10.1186/s11671-017-1891-5 (Zhyrovetsky et al, Nanoscale research letters). I'd suggest that authors cite these works together with those already mentioned in the original manuscript in a same group of references, and add to this same group the work by Mahata work (the one on rare-earth doped MOFs for luminescence-based chemical sensing).The reason why I suggest doing that is that placing it outside the initial block of general references seems a bit arbitrary, as it does not deal with mechano-responsive luminescence (MRL)(or, if author prefer, ML) which is the topic of the manuscript. All the non-MRL related references shall be placed together. Then, the introduction can deal with the actual work by Candra on ML materials and by Kim on torque-based luminescence sensors.

Response: Thank you very much for your valuable suggestions. We have revised the introduction part. 

 4. The introduction does not make completely clear which was the purpose of the present work, given that the approach is not completely original: was it to compare their results (based on Mn doping) with those obtained by Subira et al based on ZnS:Cu? Also, I'd recommend that the author dedicate part of the discussion (before the conclusion) to compare their results with those based on differently doped ZnS embedded in flexible matrixes. The sensing performances appear to be good but at least one reference point shall be given to the readers.

Response: Thanks to the reviewer for this very constructive suggestion. The purpose of the present work is to improve the β-phase of PVDF matrix by using 3D printing method, so as to improve the piezoelectric properties of the composite thin film, and on the basis of studying the luminescence properties of PVDF/ZnS:Mn composite film, the possible contribution of piezoelectric properties of PVDF and ZnS:Mn to the influence of ML luminescence was explored. Some experimental phenomena are similar to PVDF/ZnS:Cu reported by Subira et al., which has been added in the text.

 5. The experimental details on how the photoluminescence apparatus works shall be given, in order to give to the reader suggestion on possible repeatability of the experiment and on the PL efficiency of the sample. The authors mention that a "steady-state transient fluorescent system": here, steady-state AND transient seem to be mutually in contradiction. It shall be explained: which was the excitation source? (a laser? incoherent light?) was it a steady-state or pulsed excitation? or maybe modulated periodic excitation? which was the excitation wavelength? can the author give an estimation of the excitation power on the sample surface?

Response: In the work, an advanced steady-state transient fluorescence measurement system(PTI QuantaMaster^TM 4CW, USA) was used to examinate the photo-luminescence(PL) properties of the sensors. The instrument is called a fluorescence steady-state measurement system, but it can not only measure steady-state spectra, but also perform transient (fluorescence lifetime) measurements, so it is also called a fluorescence steady-state/transient measurement system. In the steady-state spectrum measurement, the photon counting technology is used to detect the signal. In the transient measurement, the system adopts advanced stroboscopic time-division measurement technology and nonlinear time-scale data acquisition technology, and the excitation light source of the system is laser, which is a pulsed excitation. However, it is a pity that our laboratory has not yet possessed such advanced testing and experimental instruments. The PL test data is obtained by sending out samples and paying for the test. We are sorry that we cannot give more detailed answers to your questions.

6. Figure 7: are the PL peaks normalized or it happens by chance that the samples show almost exactly the same PL intensity?

 Response: The PL peaks of PVDF/ZnS:Mn composite film are normalized when excited by a light source with a wavelength of 320 nm. The experimental phenomenon is repeatable. Only when the doping amount of Mn changes, the intensity of the peak at 580nm will change.

7. Figure 8: It seems that the PL spectra also present a wide minor band centered at 400 nm (also evident in Figure 7). Authors shall mention this point, suggesting and giving literature reference for a possible cause for the corresponding optical transitions. I'd suggest that this may originate from the ZnS matrix, based on a possible interpretation that the authors can check: Sanz et al, J. Phys. Chem. C, 2011, 115 (8), pp 3203–3211 (DOI: 10.1021/jp108489k)- Other suggestions might be found in the references therein.

Response: Thank you very much for the comments. We have added the analysis of PL peaks at 400nm band in the text. 

8. I am not totally convinced by the model sketched in Figure 9. Usually, defect levels also vary their energy (i.e. shift or bend) in presence of an electrostatic field. Is the model supported by additional references?

Response: The model sketched in Figure 9 is only a conjecture to explain the excellent luminescence of the PVDF/ZnS:Mn composite thin film, and there is no relevant direct evidence or literature to confirm it.

Special thanks to editor and reviewer for your good comments. We appreciate for Editors/Reviewers’ warm work earnestly.

 

Best regards

Caifeng Chen

Round 2

Reviewer 2 Report

The provided feedback from the authors and changes introduced to the revised version seems convincing. The paper can be accepted for publication

Reviewer 3 Report

Based on the revisions made, I evaluate the manuscript as publishable.