Ice nucleation by smectites: the role of the edges

Kumar, Anand; Klumpp, Kristian; Barak, Chen; Rytwo, Giora; Plötze, Michael; Peter, Thomas; Marcolli, Claudia

doi:https://doi.org/10.5194/acp-23-4881-2023

Articles | Volume 23, issue 8

https://doi.org/10.5194/acp-23-4881-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-23-4881-2023

© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 23, issue 8

Research article

|

25 Apr 2023

Research article |

| 25 Apr 2023

Ice nucleation by smectites: the role of the edges

Anand Kumar, Kristian Klumpp, Chen Barak, Giora Rytwo, Michael Plötze, Thomas Peter, and Claudia Marcolli

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Final revised paper (published on 25 Apr 2023)
Preprint (discussion started on 17 Aug 2022)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-526', Gabor Vali, 06 Sep 2022

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-526/egusphere-2022-526-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2022-526-RC1
- AC1: 'Reply on RC1', Anand Kumar, 19 Dec 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-526/egusphere-2022-526-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-526-AC1
RC2:
'Comment on egusphere-2022-526', Anonymous Referee #3, 03 Dec 2022

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-526/egusphere-2022-526-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2022-526-RC2
- AC2: 'Reply on RC2', Anand Kumar, 19 Dec 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-526/egusphere-2022-526-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-526-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Anand Kumar on behalf of the Authors (19 Dec 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (29 Dec 2022) by Hinrich Grothe

RR by Gabor Vali (13 Jan 2023)

Suggestions for revision or reasons for rejection

Although it may be marginal to the specific topic of this paper, it seems worthwhile to pursue futher points raised in my previous comment about how DSC results may be viewed with a sharper focus on the nucleation events which are to be studied. DSC data make important contributions to ice nucelation studies and the opportunity arose with this paper to discuss some aspects of those measurements with a view toward better exchange of information between different researchers.

1. The paper is consistent with the terminology it uses (as defined on lines 287-290 and in Fig. A) in accord with previous publications. To this reviewer, that terminology has some unfortunate aspects. Strictly speaking, there is no 'heterogeneous and homogeneous freezing' and it is not a good shorthand for indicating heterogeneous and homogeneous nucleation events. Similarly, 'freezing peak' is an awkward shorthand designation. It is understandable, when describing DSC data, that freezing is used in many contexts since that is the source of the detected signal. However, since the goal of the measurements is to diagnose and understand nucleation, that usage is distracting. Reference to freezing diverts attention and looses the sharpness that nucleation implies as a near-instantenous process at a very specific location.

The foregoing point comes into focus with respect to Thet. I raised questions about the phycial meaning of this parameter in my previous comment. The authors responded by saying that they do not mean it to be a threshold or onset of nucleation, as I referred to it, but a 'freezing onset temperature'. Since there is no freezing without nucleation this response eludes the real issue of the interpretation of what Thet stands for. Onset is not a good way to characterize the nucleating abilities of samples in general, because it arises from a small number of events highly dependent on particle concentration (loading) and chance. With Thet the meaning of onset is even more fuzzy are there are evident DSC signals beyond Thet indicating some nucleation activity of the sample at higher temperatures. So, while Thet is a convenient reference temperature, calling it something else than 'onset' temperature would avoid questions about its meaning. By determining Thet by extrapolation from the slope of the thermal signature, the problem of dependence on a small fraction of the nucleation events is avoided but the ambiguity of the physical meaning is not resolved.

Perhaps consideration has been already given to using the point of steepest slope of the thermal signal as the reference tenperature. That temperature, say Ts corresponds to large numbers of nucleation events, albeit not necessarily a maximum, and it seems easier to relate to than to Thet. Neglecting droplet size variations, or in cases where uniform droplets are used, Ts would corerspond to a peak in the differential nucleus spectrum. The use of Ts would avoid awkward situations such as having Thet appear on a totally flat part of the curve displayed, e.g. SHCa-1. 5% in Fig. 1. which is probably due to the normalization of the curves to a uniform height making the first pulse inappreciable.

The other parameter used to characterize nucleation activity in a sample is Fhet. This parameter is a measure of the mass loading of the sample and the size distribution of particles in the droplets with the nucleating material. Beyond comparisons, it provides little quantitative information on the nucleating ability of the material being tested.

In essence, the foregoing comments are aimed at shifting focus in the descriptions of the results on nucleation rather than the freezing that results from it. No specific recommendations is made here on how to achieve that. The authors and the editor may decide that this is not the time to reconsider how DSC data are presented.

2. On a more specific aspect of the paper, the arguments in Section 4.5 should perhaps consider more than size as influencing nucleating ability of a site. Ice nucleation literature abounds in discussions about the roles of unique sites (crystal steps, specific molecular arrangements, etc.) versus the general properties of a substrate surface. This paper considers the size necessary for embryo formation on the basis of CNT, thus implicitly asssuming that average surface properties form the criteria for nucleation. It would increase the value of the paper if the authors included some discussion about the possible role of unique sites.

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RR by Anonymous Referee #3 (12 Feb 2023)

ED: Publish subject to minor revisions (review by editor) (13 Feb 2023) by Hinrich Grothe

AR by Anand Kumar on behalf of the Authors (17 Mar 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (30 Mar 2023) by Hinrich Grothe

AR by Anand Kumar on behalf of the Authors (30 Mar 2023) Manuscript

Short summary

Smectites are a major class of clay minerals that are ice nucleation (IN) active. They form platelets that swell or even delaminate in water by intercalation of water between their layers. We hypothesize that at least three smectite layers need to be stacked together to host a critical ice embryo on clay mineral edges and that the larger the surface edge area is, the higher the freezing temperature. Edge sites on such clay particles play a crucial role in imparting IN ability to such particles.