Peer review of: Direct observation of desorption of a melt of long polymer chains (2020)

REVIEWER COMMENTS

Reviewer #1 (Remarks to the Author): 

This manuscript reports the first direct measurement of desorption thermodynamics of a polymer from 
a solid substrate. The temperature of desorption can be a high value. The value reported in this 
manuscript is ~ 660K. As a result, assessing desorption thermodynamics, i.e., enthalpy of desorption, 
is challenging as material degradation can occur. To overcome this challenge, the authors used fast 
scanning calorimetry to "by pass" degradation to measure desorption. The results systematically show 
how annealing time impacts the desorption enthalpy. The manuscript presents a well articulated story 
of novel experiments. The manuscript should be published in Nature Communications. I have two 
additional comments: 

1. I found the comparison (analogy) to crystallization not necessary. For instance, the manuscript 
estimates Tm for PTBS even thought it does not crystallize, as the authors pointed out. (Also from 
calorimetry is it confirmed that the desorption observed in this manuscript is first order.) 

2. On page 12, the manuscript cites reference 18 in the context of changing solvent quality. In ref 18, 
only one solvent was used. Hence, the quality of the solvent was unchanged. 



Reviewer #2 (Remarks to the Author): 

The authors propose the new thermodynamic concept about polymer desorption. They utilize the novel 
approach, fast scanning calorimetry (FSC), and studied the adsorption/desorption behavior of poly(4-
tert-butylstyrene) (PtBS) chains deposited on the solid coated with a silicon oxide layer. The results 
are informative and the discussions behind the phenomenon are thoughtful. I believe the work offers 
an important aspect in the field. However, my major concern is that the authors used only one 
polymer with a fixed molecular weight, one heating rate, and one substrate to draw the conclusion: 
polymer adsorption/desorption is the first-order phase transition. It is known that results obtained 
with calorimetric methods strongly depend on heating rates. In fact, according to their data shown in 
Fig. 1a, the Tg value obtained from the FSC is about 30C higher than the bulk. So the question is 
whether the transition they claim is inherent. Can the authors show systematic FSC data with different 
heating rates to validate the statement? Also, I understand the choice of PtBS as the model, but 
polystyrene (PS) would be a better system since the degradation temperature is much lower than 
PtBS, monodisperse PS with different molecular weights are cheaply available commercially, and the 
mechanism of polymer adsorption has been extensively studied by the authors and other groups. In 
addition, depending on the interactions between a polymer and substrate as well as chain flexibility, 
the conformations of an adsorbed polymer chain and the desorption mechanism should be different. 
Moreover, the comparison between polymer adsorption/desorption and crystallization/melting with 
PtBS (on Page 10) is not convincing. For that purpose, it would be interesting to use semicrystalline 
polymers, such as PET where the adsorption behavior is well characterized (Macromolecules 2017, 50, 
6804) or syndiotactic (or isotactic) PS, and to study the melting/crystallization transition as well as 
adsorption/desorption transition with FCS. Without such additional experimental supports/evidence, 
their conclusion may not be justified and the manuscript may not be fully extended yet to merit a 
publication in the journal. 



Reviewer #3 (Remarks to the Author):
Referee report on First direct observation of desorption of a melt of long polymer chains
by Xavier Monnier, Simone Napolitano & Daniele Cangialosi


The authors report on a direct observation (using fast scanning calorimetry) of a desorp-
tion transition for a polymer melt from a solid wall. Such a thermodynamic transition is
very difﬁcult to observe as normally the polymer chains are degraded before the transition
occurs. Fast scanning calorimetry allows the measurement to be faster than degradation.
Overall, the manuscript is well written, the realisation of the experiment and its analysis
are well explained, and the results are interesting. Explanations and conclusions are
instructive. I have a number of individual points that should be changed to make the
manuscript more accessible for a readership that consists of experimentalists and theoreticians in the wider ﬁeld of soft matter.
Then I believe, the manuscript can be published.

1. Title: Many journals prefer not to have self-assessments as “ﬁrst” or “novel” in a
text. The referee is of the same opinion. If a “direct observation” is novel then the
informed reader will recognise and value it, and for the non-informed reader it does
not matter. So dropping the “ﬁrst” does not diminish the impact, but spares the au-
thors the embarrassment if it is later found that someone else had done something
similar before.

2. Intro, p.2: I understand sentence 1, 2 and 4, but the role of “The related changes
in particle density in proximity of the transition zone between two or more phases
determines the stability of the whole system.” is not clear. Please explain better
what is meant. Does “stability” here relate to instability in relation to possible pattern
formation?

3. Intro, p.2, ﬁnal sentence of paragr.2: something is amiss in the sentence.

4. p.3, l.4: It is stated that the argument against desorption is based on kinetics. But
isn’t the kinetic argument itself at the core an energetic one, as ∆E determines the
probability via a Boltzmann factor?

5. On pg. 3, adsorption is nicely introduced as a phase transition depending on control 
parameters concentration and temperature.
It would be instructive to give a
phase diagram in these parameters and sketch what are the paths taken by sam-
ple preparation, annealing and during the fast scanning. It would be, in particular,
useful to discuss in this context which preparation steps are actually nonequilibrium
processes and which are phase transitions in the ’quasi-equilibrium’ sense.

6. pg.5: If the mentioned glass transition mentioned (at 433K) is visible in Fig.1b, it
should be mentioned how, and if not this also should be mentioned and brieﬂy
explained. As the run passes through the 433K some readers could expect to see
it there.

7. p.5, bottom: gsample should be explained.
8. Fig.1: be kind to the casual reader: Mention in the caption what is actually seen on
the y-axis, add ticks and tick labels (there are none at all) - also for the inset. Is the
inset of (b) at a particular temperature? What means “Endo up”? The curious lines
going to the inset are not needed, barely visible, confusing and should be dropped
as they are not needed if plot and inset have proper axes ticks and labels.

9. Fig.2: same as Fig.1

10. p.10, l2: “ustmost”?

11. As on p.10 crystallization/melting and adsorption/desorption are classiﬁed as ﬁrst
order transitions, the question arises how important hysteresis effects are in the
performed experiments. Please add a short comment.

12. Fig.4: The scheme is overall ﬁne, but the rational behind the various colourings of
the beads remains elusive to me. If there is a rational, please explain. If there is
none, make it less confusing.
E.g., why when melting, a single long chain breaks in 6 different ones; or why does
a desorbing chain become shorter.

13. p.12, bottom: why is “varying the quality of the solvent” termed “artiﬁcial” but fast
heating not? Are these not only experiments using different control parameters?
Why is one “better” than the other?

14. p.13, l.2: what is meant by “way far from”?; further down on line 16 “desorption” is
misspelled.

15. Intro and conclusion: I stumbled over statements that seem to contradict each other:
On the one hand it is said that degradation normally preempts desorption, there-
fore fast scanning calorimetry is needed. On the other hand, it is emphasised in
the introduction and conclusion that desorption can be used to “ﬁnely tune the per-
formance of nanomaterials” and is “tremendously relevant for the performance and
stability of thin polymer coatings”, respectively. Somehow, these statements seem
to contradict each other. Would not degradation be the practically more important
issue?

16. Above critique of ﬁgures also applies to ﬁgures in the Supplement.

17. Final point: It becomes increasingly good practise to provide the community and
wider society with the original data. Will the original data for the ﬁgures be available
on a data repository like zenodo or ﬁgshare (even if still embargoed)? Then a
remark with a doi link would be helpful.