Toward Programmed Complex Stress-Induced Mechanical Deformations of Liquid Crystal Elastomers
Round 1
Reviewer 1 Report
Report on MS crystals-769463 (Mistry and Gleeson)
This is a fine paper studying the anisotropic and locally varying strain response to an LCE sheet with patterned circular director field subject to an externally imposed stress. I am happy to recommend it for publication after the following minor issues have been addressed.
1. All equations have also been typeset incorrectly. The LaTex code precedes each equation.
2. Page 1, Content: "isotropic liquid crystal phase"
Comment: This seems to be a contradiction in terms. Don’t the authors mean “isotropic phase of a liquid crystal-forming material”?
3. Page 2, Content: "only two studies that consider the mechanical properties of director patterned LCEs.[11,23]"
Comment: When I first read this, I was very surprised, as in my opinion the actuation of LCEs belongs to their mechanical properties, a very broadly (or even vaguely) defined term. As I read on, I finally understood that the authors restrict their discussion to mechanical deformation under _externally applied stress_. This is an extremely important distinction, and adding it (also to the title of the paper!) will avoid confusion and misunderstanding. The vast majority of the LCE community is concerned with the deformations induced by the LCEs themselves when they are actuate, hence the small number of papers looking at the passive response that the authors focus on. This means that many authors might fall in the same misunderstanding pit as I did, and get confused. I believe it is essential that the authors are very clear about this issue; that they are _not_ considering actuation, but passive response to externally imposed stress.
4. Page 3, Content: "substrates were coated with a poly(vinyl alcohol) alignment layer which was rubbed circularly "
Comment: How were the substrates positioned with respect to each other? I guess the overall effect will be very sensitive to mismatch, at least near the defect.
5. Page 3, Content: "precursor"
Comment: I would write something like “The reactive components of the precursor mixture”, to emphasize that a significant fraction (56%) is unreactive.
6. Page 3, Content: "ensure complete polymerisation)."
Comment: This is in contradiction with your washing away unreacted components in the next sentence.
7. Page 3, Content: "anisotropically deswell."
Comment: I think this needs better specification. Along which direction(s) does the LCE deswell? If it’s like Finkelmann’s anisotropic deswelling (his group coined the term), then I don’t see why a saddle shape arises. With a clearer definition, this confusion should disappear.
8. Page 3, Content: "259 ± 4 px - equivalent to 2.00 ± 0.03 mm."
Comment: Why not stick to millimeter and micrometer? The pixel count seems not so interesting.
9. Page 3, Content: "complexly aligned"
Comment: I find this attribute slightly inappropriate. Is circular really complex? And why use a vague term when you can use more precise and descriptive terms?
10. Page 5, equations. Avoid vector product for regular multiplication, i.e., use \cdot, not \times.
11. Page 5, Content: "engineering strain,"
Comment: Since many readers may be chemists and physicists interested in LCEs, who may not have the different engineering definitions in mind, it would be helpful to briefly remind the reader of the distinction between strain and engineering strain.
12. Page 5, Content: "Δϵ is"
Comment: This is a potentially misleading choice of notation, considering that \Delta \epsilon in LCs is almost synonymous with dielectric anisotropy. The authors might think about choosing a different letter.
13. Page 6, Content: "the prominence region"
Comment: For clarity, it would be good to clearly indicate in the figure what is considered the prominence region.
14. Page 7, figure 3. What do the particle trajectories mean in the unstrained state? Is the circle the end or the beginning of a trajectory?
15. Page 8, figure 5. I think this graphic deserves a few comments more. Is is obtained on reference samples cut along different directions from a uniformly aligned LCE?
16. Page 8, Content: " mechanical shape deformations of LCEs"
Comment: Again: it would be good to emphasize better that you refer to the response to an externally imposed stress. Often when you hear “shape deformation” in the context of LCEs, you think of the LCE actuating and thus changing its shape on its own. To avoid misinterpretations, the authors may wish to clarify that this is not what is meant.
17. Page 12, line 397, Content: "... director profiles."
Comment: For clarity, I suggest to end this sentence with "... director profiles, subject to externally applied stress.".
18. Page 12, Content: "FEA"
Comment: What is FEA? Please spell out the abbreviation the first time it is used.
19. Considering that the paper is written by two native English speakers, it contains surprisingly many typos and grammatical errors, especially towards the end. Below follows a list of issues that I picked up, but there may be others. Many errors would have been detected by standard grammar and spell checkers such as those installed in Word. For future manuscripts, I warmly recommend the authors to add a final proofreading stage prior to submission, engaging the tools of the software, thus sparing the reviewers from this task.
Page 1, Content: " functionailty."
Comment: Typo.
Page 4, Content: "particles"
Comment: Typo (should not be plural).
Page 5, \beta has become B in the table.
Page 6, Content: "extended"
Comment: was extended?
Page 6, Content: "maximally"
Comment: maximally strained
Page 6, Content: "comparatively"
Comment: Repetition (the sentence begins with "Comparatively").
Page 9, Content: "similar"
Comment: similar to
Page 9, Content: "varies"
Comment: Already stated in "a spatially varying difference"; this is a confusing repetition.
Page 10, Content: "localised"
Comment: Duplicate
Page 11, line 374, Content: "as"
Comment: at?
Page 11, line 375, Content: "the initial"
Comment: where the initial?
Page 11, line 379, Content: "the fact"
Comment: by the fact?
Page 11, line 380, Content: "comparatively"
Comment: is comparatively?
Page 11, line 385, Content: "we had "
Comment: delete this or the "were" before "available".
Page 12, line 391, Content: "those"
Comment: with those
Page 12, line 412, Content: "we "
Comment: that we
Page 12, line 414, Content: "the model"
Comment: that the model
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors present a study of director rotations and deformations in liquid crystal elastomers (LCEs) with complex director patterns. They use a combination of methods to track both sample deformation and director reorientation simultaneously. These studies produce impressive heat maps of the director reorientation throughout the sample and strain maps across the sample under deformation. They furthermore apply an empirical model that produces predictions that compare favorably with measured engineering stresses. Overall, this is an excellent study of deformation of LCEs and analysis of their strain and director reorientation response. I recommend acceptance for publication.
However, I do have several suggestions for the authors to consider to improve the study. Most importantly, the authors claim they developed design rules for LCE deformations. However, this was not clear to me on reading the manuscript - what exactly are these design rules? are they quantitative, or qualitative? The authors should more explicitly identify and explain the design rules they have been able to develop in their study.
The authors also claim that their results will be useful to making real-world LCE devices. This implies (I believe) being able to program a desired shape-change. This again is unclear to me on reading the article. How can their model be used to program a desired shape change in the LCE? Or, if I am misunderstanding the text, how does this model help advance LCEs towards applications?
Author Response
Please see the attachement
Author Response File: Author Response.docx
