Structural Regulation, Photothermal Conversion, and Interfacial Heat Transfer Mechanisms of Silver Nanoparticle/Wood-Derived Porous Carbon Composite Phase Change Materials

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is currently incomplete, although it shows potential to become a good contribution. 
Substantial revisions are required, as outlined below:

The objective, methodology, and results need to be more clearly described, thoroughly discussed, and properly justified.
Figures 3-4 need clearer justifications in the paper.
A number of review studies are available on this topic please establish your niche.
The literature review is insufficient in its current form. The authors should incorporate additional, up-to-date studies on PCM and ensure the reference list is comprehensive and complete. https://doi.org/10.1016/j.enbuild.2021.111443; https://doi.org/10.1016/j.enbuild.2022.112280.
The discussions should be significantly expanded, with greater emphasis on quantitative analysis.
It is strongly recommended that the authors conduct additional analyses to compare their findings with those of similar studies.

Author Response

Reviewer #1: The manuscript is currently incomplete, although it shows potential to become a good contribution. Substantial revisions are required, as outlined below:

Response to Reviewer #1's General Comment: We would like to express our sincere gratitude to Reviewer #1 for taking the time to rigorously evaluate our manuscript and for recognizing the potential of our work. We highly value your constructive and insightful comments, which have been instrumental in improving the completeness, clarity, and depth of our study.

We have carefully considered all your suggestions and have made substantial revisions throughout the manuscript. Our detailed, point-by-point responses to each of your comments are provided below, and all corresponding modifications have been highlighted in the revised manuscript.

 

Comment 1: The objective, methodology, and results need to be more clearly described, thoroughly discussed, and properly justified.

Response 1: We completely agree with your assessment that the clarity, depth of discussion, and rigorous justification in the original manuscript needed substantial improvement.To address this overarching concern, we have conducted a comprehensive and thorough revision of the entire manuscript. The major improvements can be summarized in the following three aspects:

Clarification of the Objective: We have completely restructured the Introduction (Section 1) to explicitly state our critical scientific objective. Rather than merely reporting macroscopic material performance, we have clearly defined our goal: to quantitatively uncover the atomic-scale mechanisms by which metallic interfacial modification regulates phonon transport and spatial confinement in composite phase change materials (CPCMs).

Elaboration of the Methodology: We have significantly expanded the description of our methods, particularly the Molecular Dynamics (MD) simulations in Section 3.1. We provided exhaustive details regarding the force field (COMPASS III), specific simulation ensembles (NPT/NVT), optimization iterations, and precise simulated annealing protocols, thereby ensuring the full transparency, rigorousness, and reproducibility of our methodology.

Thorough Discussion and Justification of Results: We have deepened the discussion of our results in Section 4.2. We significantly elaborated on the physical significance of the Phonon Density of States (PDOS) and Interfacial Thermal Resistance (ITR) to justify the macroscopically enhanced thermal conductivity. Furthermore, we expanded the discussion on the Mean Square Displacement (MSD) to thoroughly explain the underlying origins of the phase transition behaviors observed in the DSC tests.

We believe these revisions significantly improve the logic and completeness of the entire text. These changes are highlighted in red in the revised manuscript. We are happy to assist with any further adjustments required.

Comment 2: Figures 3-4 need clearer justifications in the paper.

Response 2: We sincerely appreciate the reviewer for highlighting this issue. We agree that the logical connections and justifications for integrating the macroscopic characterizations and microscopic simulations in Figures 3 and 4 were not sufficiently articulated in the original manuscript.

To address this, we have carefully revised Sections 4.2 and 4.3 to provide clearer justifications for the structural composition and analytical purpose of these figures.

For Figure 3: We have added explicit statements in Section 4.2 justifying that Figure 3 is designed to bridge the structural validation (FTIR, XRD) with the underlying heat transfer mechanisms (PDOS, ITR). We clarified that macroscopic thermal conductivity tests alone are insufficient to explain the enhanced performance, which justifies the necessity of incorporating MD simulation panels alongside the experimental data.

For Figure 4: In Section 4.3, we introduced a transitional paragraph to clearly justify the grouping of macroscopic thermal properties (TGA, DSC) and microscopic kinetic behavior (MSD). We explicitly stated that the molecular-level chain mobility restrictions (MSD) are employed to directly justify and explain the macroscopic shifts in phase transition temperatures and latent heat observed in the DSC curves.

We believe these additions significantly strengthen the internal logical flow of the manuscript. The specific revisions have been highlighted in the updated text.

Comment 3: A number of review studies are available on this topic please establish your niche.

Response 3: We sincerely appreciate the reviewer’s insightful comment. We fully acknowledge that the field of composite phase change materials (CPCMs)－particularly those utilizing porous carbon skeletons－has been extensively documented and reviewed.

However, a careful survey of the existing reviews and literature reveals that the vast majority of current studies predominantly focus on the macroscopic engineering aspects, such as screening different support matrices, maximizing PCM loading capacity, or tracking bulk thermal conductivity and leakage prevention. The intricate atomic-level interactions at the heterogeneous interfaces are often treated as a "black box."

Therefore, the unique niche of our study lies in bridging macroscopic thermodynamic behaviors with microscale atomic physics. Unlike conventional experimental reports, our work does not merely stop at observing that silver nanoparticles enhance thermal conductivity or shift the phase transition temperature. Instead, we establish our niche by introducing non-equilibrium molecular dynamics (NEMD) simulations to quantitatively decode the underlying mechanisms in a ternary heterogeneous system (Carbon/Silver/PEG).

Specifically, our niche is defined by:

Quantitatively visualizing how the metallic interface smooths the phonon vibration frequency mismatch (via PDOS analysis) to physically explain the reduction in Interfacial Thermal Resistance (ITR).

Revealing how the spatial confinement of the nano-pores fundamentally restricts the kinetic mobility of polymer chains (via MSD analysis), directly correlating with the macroscopic DSC thermal shifts.

To ensure our specific niche is immediately apparent to the readers, we have explicitly articulated this distinctive positioning in the revised Introduction (Section 1).

Comment 4: The literature review is insufficient in its current form. The authors should incorporate additional, up-to-date studies on PCM and ensure the reference list is comprehensive and complete.

https://doi.org/10.1016/j.enbuild.2021.111443; https://doi.org/10.1016/j.enbuild.2022.112280.

Response 4: We sincerely thank the reviewer for pointing out the insufficiency in our literature review and for recommending these highly relevant and insightful studies. We completely agree that a comprehensive discussion of recent advancements is essential for establishing a solid background, especially regarding the broader applications of PCMs in thermal management and energy efficiency.

We have carefully read the suggested papers and found them extremely valuable to our study. Consequently, we have significantly expanded the Introduction (Section 1) to incorporate these up-to-date studies. Specifically, we highlighted the profound potential of advanced PCMs in building thermal management and sustainable energy savings, which perfectly aligns with the ultimate application goals of our prepared wood-derived CPCMs.

The reference list has been updated to include these critical works (now added as Ref. [2] and Ref. [3]), and the corresponding discussions have been highlighted in the revised manuscript. We believe this addition has greatly enriched the comprehensiveness of our literature review.

Comment 5: The discussions should be significantly expanded, with greater emphasis on quantitative analysis.

Response 5: We sincerely thank the reviewer for this constructive feedback. We completely agree that a robust scientific paper requires deep quantitative analysis rather than merely qualitative descriptions. In the original manuscript, we fell short of adequately quantifying the performance enhancements and correlating the macroscopic data with the microscopic simulation results.

To address this, we have comprehensively reviewed all our data and significantly expanded the discussions in Section 4 by incorporating rigorous quantitative analyses. The major quantitative enhancements include:

Quantitative Correlation of Heat Transfer (Section 4.2): Instead of merely stating that thermal conductivity improved, we now explicitly calculate the enhancement percentages. We quantitatively correlate the macroscopic thermal conductivity increase (an impressive 185.8% enhancement relative to pure PEG) with the microscopic simulation data, specifically highlighting the 32.8% numerical reduction in Interfacial Thermal Resistance (ITR) driven by the silver modification.

Quantitative Assessment of Energy Storage Efficiency (Section 4.3): We expanded the quantitative discussion on the thermal storage capabilities by calculating both the actual mass loading fraction (via TGA) and the enthalpy efficiency (via DSC). We quantitatively demonstrated that while the actual PEG loading fraction reaches 80.7%, the effective enthalpy efficiency stands at an impressive 72.4% (133.9 J/g compared to 184.8 J/g of pure PEG). This rigorous numerical comparison further allowed us to quantitatively elucidate the nanoconfinement effect of the porous skeleton.

Quantitative Analysis of Phase Transition Kinetics (Section 4.3): We quantitatively linked the temperature offset of the dynamic transition points in the MSD curves (a microscale delay of 1.2-2.0 °C) directly to the macroscopic phase transition temperature shifts observed in the DSC curves.

These expanded quantitative discussions rigorously substantiate our conclusions. All corresponding revisions have been distinctly highlighted in the updated manuscript.

Comment 6: It is strongly recommended that the authors conduct additional analyses to compare their findings with those of similar studies.

Response 6: We sincerely thank the reviewer for this highly constructive recommendation. We completely agree that benchmarking our results against recent state-of-the-art studies is essential to clearly demonstrate the competitive edge and practical value of our prepared composite phase change materials.

To address this, we have conducted an extensive literature review of recently reported PEG-based form-stable phase change materials, specifically focusing on porous carbon skeletons and metal-modified support matrices. We systematically extracted their core thermophysical parameters—including melting latent heat, thermal conductivity, and leakage resistance—and compiled a comprehensive comparison table (Table 1) in the revised manuscript.

In the newly added discussion within Section 4.3, we performed a detailed comparative analysis. The comparison clearly reveals that while some purely carbon-based materials achieve high latent heat, their thermal conductivity remains severely limited. Conversely, heavily metal-loaded networks often sacrifice a massive amount of energy storage density. Our optimally prepared DAP800 composite stands out by achieving an exceptional balance: it delivers a highly competitive thermal conductivity of 0.683  W/(m·K) while retaining an outstanding melting latent heat of 133.9  J/g, along with excellent leakage resistance over 100 thermal cycles.

We believe this robust comparative analysis significantly elevates the practical significance of our work. The corresponding text and Table 1 have been added to the revised manuscript.

Table 1. Comparison of thermophysical properties between the prepared DAP800 and reported PEG-based and other typical composite phase change materials.

Material	PCM	Latent Heat (J/g)	Thermal Conductivity (W/(m·K))	Leakage Resistance	Reference
GF@PPy	PEG	158.5	0.415	Excellent	[32]
BPC@Ag	PEG	134.1	0.68	Excellent	[9]
Cu@rGO-CMF	PEG	149.8	0.45	Excellent	[33]
Ag@rGO-CMF	PEG	154~157.7	0.49	Excellent	[15]
PVA/graphene	PW	165.3	0.486	Excellent	[34]
Wood-derived porous carbon	PEG	133.9	0.683	Excellent (100 cycles)	This work

 

Reviewer 2 Report

Comments and Suggestions for Authors

1. The leakage test was only performed at 90°C for 30 min. Could the authors provide long-term leakage tests or repeated melting-cooling tests?
2. Could the authors provide DSC results after more thermal cycles, such as 50 or 100 cycles?
3. Please add a comparison table with similar reported PEG-based composite PCMs, including thermal conductivity, latent heat, leakage resistance, and other relevant properties.
4. The melting latent heat of CPCM is 133.9 J/g, which is lower than that of pure PEG. What about the PEG loading fraction and enthalpy efficiency of DAP800?
5. Please provide error bars or standard deviations for the key data, such as thermal conductivity and latent heat. The number of repeated measurements should also be stated.

Author Response

Reviewer #2:

Response to Reviewer #2: We would like to express our sincere gratitude to Reviewer #2 for dedicating time to rigorously evaluate our manuscript. Your highly constructive comments and specific questions are extremely valuable, and addressing them has significantly helped us improve the quality, accuracy, and clarity of our research.

We have carefully studied each of your comments and made the corresponding revisions throughout the text. Our point-by-point responses are detailed below, and all modifications have been clearly highlighted in the revised manuscript.

 

Comment 1: The leakage test was only performed at 90°C for 30 min. Could the authors provide long-term leakage tests or repeated melting-cooling tests?

Comment 2: Could the authors provide DSC results after more thermal cycles, such as 50 or 100 cycles?

Response to Comments 1 and 2: We sincerely thank the reviewer for these highly constructive comments. Because your concerns in Comment 1 and Comment 2 are closely related—both pointing to the crucial need for evaluating the long-term cyclic reliability and encapsulation stability of the composite phase change materials (CPCMs)—we have addressed them comprehensively together here.

We completely agree that the initial 30-minute heating test was insufficient. To thoroughly address your requests for both repeated melting-cooling tests and extended cyclic DSC results, we subjected the optimal DAP800 sample to an accelerated thermal reliability test comprising 100 consecutive melting-cooling cycles using a Differential Scanning Calorimeter (DSC). We have updated Figure 5 to include the 100-cycle 3D DSC waterfall plot (Figure 5b) and significantly expanded the discussion in Section 4.4 of the revised manuscript.

As explicitly shown in the newly added Figure 5b, the endothermic and exothermic peaks from the 1st cycle all the way to the 100th cycle highly overlap without any observable baseline drift. The phase transition temperatures and specific latent heat enthalpy exhibit no significant degradation. This highly stable 100-cycle DSC result perfectly addresses both comments simultaneously:

Addressing Comment 1 (Repeated melting-cooling test & Leakage resistance): The absence of latent heat degradation over 100 cycles serves as robust thermodynamic evidence that the liquid PEG is effectively locked within the carbon/silver heterogeneous skeleton. If macroscopic liquid leakage or exudation had occurred during these repeated thermal cycles, a corresponding precipitous drop in the effective PCM mass and the latent heat enthalpy would have been inevitably recorded.

Addressing Comment 2 (DSC results after more thermal cycles): The perfectly overlapping 100-cycle DSC curves directly fulfill your request for extended cyclic data, convincingly proving that the rigid spatial confinement effect effectively suppresses the thermal degradation of PEG molecular chains during prolonged phase transition cycles.

We believe this single, comprehensive 100-cycle thermodynamic experiment perfectly resolves both of your related concerns with rigorous data. The detailed discussions have been highlighted in the revised text.

 

Figure 5. (a) Infrared thermal imaging and leak prevention performance testing process of pure PEG and various composite phase change materials on a 90 ℃ constant temperature heating stage; (b) DSC curves of the optimal DAP800 composite phase change material over 100 repeated melting-cooling cycles.

 

Comment 3: Please add a comparison table with similar reported PEG-based composite PCMs, including thermal conductivity, latent heat, leakage resistance, and other relevant properties.

Response 3: We sincerely appreciate the reviewer’s constructive recommendation. We completely agree that a comprehensive comparison with recent state-of-the-art PEG-based composite PCMs is highly necessary to clearly highlight the competitive advantages of our prepared materials.

To address this, we have extensively reviewed recently published literature and added a detailed comparison table (Table 1) in Section 4.3 of the revised manuscript. As requested, this table systematically benchmarks our optimal DAP800 composite against other similar porous support matrices, specifically comparing their core properties including:

Phase change material type (PEG and other organic PCMs)

Melting latent heat (J/g)

Thermal conductivity (W/(m·K))

Leakage resistance / Shape stability

The comparison explicitly demonstrates that while many existing composites struggle to balance high energy storage density with efficient thermal transport, our DAP800 composite achieves a superior synergy. It delivers a highly competitive thermal conductivity of 0.683  W/(m·K) and retains an outstanding melting latent heat of 133.9  J/g, while demonstrating excellent leakage resistance even after 100 severe melting-cooling cycles.

We believe this added table fully addresses your comment and significantly enhances the practical value of our manuscript.

Table 1. Comparison of thermophysical properties between the prepared DAP800 and reported PEG-based and other typical composite phase change materials.

Material	PCM	Latent Heat (J/g)	Thermal Conductivity (W/(m·K))	Leakage Resistance	Reference
GF@PPy	PEG	158.5	0.415	Excellent	[32]
BPC@Ag	PEG	134.1	0.68	Excellent	[9]
Cu@rGO-CMF	PEG	149.8	0.45	Excellent	[33]
Ag@rGO-CMF	PEG	154~157.7	0.49	Excellent	[15]
PVA/graphene	PW	165.3	0.486	Excellent	[34]
Wood-derived porous carbon	PEG	133.9	0.683	Excellent (100 cycles)	This work

 

Comment 4: The melting latent heat of CPCM is 133.9 J/g, which is lower than that of pure PEG. What about the PEG loading fraction and enthalpy efficiency of DAP800?

Response 4: We sincerely thank the reviewer for this highly professional and insightful question. We completely agree that providing a quantitative distinction between the actual physical loading fraction and the effective enthalpy efficiency is essential for fully understanding the interfacial confinement effects within the composite phase change materials (CPCMs).

 To thoroughly address your comment, we have systematically calculated these two critical parameters based on different characterization methods (TGA and DSC) for the optimal DAP800 composite, and incorporated deep mechanistic discussions into Section 4.3 of the revised manuscript.

Actual Mass Loading Fraction (R): The actual physical mass fraction of PEG encapsulated within the DAP800 composite is precisely determined from the major weight loss platform in the thermogravimetric analysis (TGA) curve. The calculation shows that the actual loading fraction of PEG is 80.7%.

Enthalpy Efficiency (η): The enthalpy efficiency reflects the effective utilization rate of the latent heat of the loaded PEG. It is calculated from the DSC results using the formula: .For DAP800, the enthalpy efficiency is calculated to be 72.4%.

Scientific Insight (The Nanoconfinement Effect): As the data reveals, the effective enthalpy efficiency (72.4%) is slightly lower than the actual mass loading fraction 80.7%. In the revised manuscript, we have explicitly explained that this discrepancy is a classic manifestation of the nanoconfinement effect. Within the highly confined three-dimensional carbon/silver heterogeneous microchannels, the strong surface tension, capillary forces, and interfacial interactions severely restrict the free mobility of the PEG molecular chains located in close proximity to the pore walls. Consequently, a thin layer of PEG segments is "frozen" into a non-crystallizable layer (dead layer). These molecules are physically loaded within the pores (detected by TGA) but fail to arrange into an ordered crystal lattice during the cooling phase, thus not contributing to the macroscopic latent heat (undetectable by DSC).

Nevertheless, achieving a high enthalpy efficiency of 72.4% within a rigid, highly thermally conductive skeleton rigorously validates the excellent encapsulation architecture of our DAP800 carrier. We believe these precise calculations and the accompanying physical explanations thoroughly address your concern.

 

Comment 5: Please provide error bars or standard deviations for the key data, such as thermal conductivity and latent heat. The number of repeated measurements should also be stated.

Response 5: We sincerely thank the reviewer for this rigorous suggestion. We completely agree that providing error bars and standard deviations is essential to demonstrate the reliability, accuracy, and reproducibility of our experimental data.To fully address this comment, we have carefully reviewed our raw experimental records and updated the revised manuscript to explicitly include the standard deviations and the number of repeated measurements:

Number of Repeated Measurements: In Section 2.4 (Characterization Methods), we have added an explicit statement that all key quantitative thermophysical measurements—including the transient plane source thermal conductivity tests and the differential scanning calorimetry (DSC) measurements—were independently repeated three times for each sample.

Standard Deviations in Text and Figures: We have updated the data descriptions in Section 4.2 and Section 4.3 to express the key values in the format of "Average  Standard Deviation". Additionally, we have updated the caption of Figure 3 to explicitly state that the error bars represent the standard deviation of the three independent measurements.

We believe these additions significantly enhance the scientific rigor of our reported results. The corresponding modifications have been clearly highlighted in the revised manuscript.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All comments have been addressed. 

Author Response

Reviewer #1:

Comment: All comments have been addressed.

Response: We sincerely thank the reviewer for the positive evaluation and for confirming that all comments have been properly addressed. We are deeply grateful for your rigorous review and constructive suggestions throughout the review process, which have significantly elevated the scientific quality and rigor of our manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have addressed my comments well.

Author Response

Reviewer #2:

Comment: The authors have addressed my comments well.

Response: We sincerely thank the reviewer for your positive feedback and for confirming that our revisions have met your expectations. We deeply appreciate the time, effort, and highly constructive suggestions you have dedicated to evaluating our work. Your insightful comments were instrumental in improving the comprehensiveness and overall quality of our manuscript.