1. ABOUT THE DATASET -------------------- Title: Direct observation of biaxial nematic order in auxetic liquid crystal elastomers Creator(s): Zhenming Wang[1,2], Thomas Raistrick[1], Aidan Street[1], Matthew Reynolds[1], Yan Jun Liu[2], Helen F. Gleeson[1] Organisation(s): 1. University of Leeds. 2. Southern University of Science and Technology Rights-holder(s):Copyright 2023 University of Leeds Publication Year:2023 Description: A description of the data for auxetic deformations, Raman measurement and figures for biaxial observation. Sufficient to show how the data were collected, what the key characteristics were and their relevance. Cite as: Zhenming Wang, Thomas Raistrick, Aidan Street, Matthew Reynolds, Yan Jun Liu, Helen F. Gleeson (2023) Direct observation of biaxial nematic order in auxetic liquid crystal elastomers. University of Leeds. [Dataset] https://doi.org/10.5518/1263. Related publication: Wang, Z.; Raistrick, T.; Street, A.; Reynolds, M.; Liu, Y. J.; Gleeson, H. F. Materials 2023, 16(1), 393; https://doi.org/10.3390/ma16010393. Contact: h.f.gleeson@leeds.ac.uk 2. TERMS OF USE --------------- This dataset is licensed under a Creative Commons Attribution 4.0 International Licence: https://creativecommons.org/licenses/by/4.0/. 3. PROJECT AND FUNDING INFORMATION ---------------------------------- Title: Stretching the boundaries; new soft matter systems. [title of project] Dates:15 August 2022- 14 August 2027[project start-end] Funding organisation:Engineering and Physical Sciences Research Council (EPSRC EP/V054724/1) Grant no.:RG.PHAS.122862 4. CONTENTS ----------- File listing 1. Data collection.xlsx. This file describes that how the data corresponds to the figures in the paper. 2. Deformation strains.xlsx. This file illustrates the data collected for mechanical deformations of auxetic LCE. 3. Depolarization Ratio Data.xlsx. This file shows the Raman intensity as a function of the laboratory angle. 4. Poisson's ratio.xlsx. This file shows the calculated Poisson's ratio for all the auxetic deformations. 5. Order Parameter Data.xlsx. This files shows the fitted order parameter for auxetic LCE. 5. METHODS ---------- All the samples are fabricated in the lab in the university of Leeds. The planar samples were constructed as described previously as Nat. Commun. 2018, 9, 5095. The process was modified slightly for fabrication of the homeotropic sample where the application of an electric field was required to supplement the homeotropic surface alignment to achieve a uniform monodomain sample. For those samples, the glass substrate was coated with Indium Tin Oxide (ITO) (Xinyan Technology Ltd., China) and the polymer substrate was ITO coated PET film (ITO-PET) (Sigma-Aldrich, Unite States), spin-coated with 0.5 wt.% cetyl trimethyl ammonium bromide (CTAB) (MP Biomedicals, France) solution and left unrubbed. The molds were capillary-filled with the monomer mixture described in the following section. The LCE was created using the method described by Mistry et al. in Nat. Commun. 2018, 9, 5095. All the data are analysis by student version of software Original 2022. For the data of "Deformation strains" and "Poisson's ratio", the mechanical measurements were undertaken using bespoke equipment that was built in-house, comprising two actuators and a load cell enclosed in a tempera-ture-controlled environment in the lab in the university of Leeds. The apparatus is equipped with optics that allows polar-izing microscopy of the LCE under strain. The full specification of the equipment and analysis methodologies, which allow simultaneous optical and mechanical studies of LCEs, are described in previous reports (Nat. Commun. 2018, 9, 5095). For this work, the original gap between the two actuators was 10mm and the LCE samples were loaded at room temperature. The samples were stretched using strain steps of 0.5mm and a waiting time 10 minutes for each step. All the strains are collected by the software ImageJ and the analysis process was described by Mistry et al. (Nat. Commun. 2018, 9, 5095). For the data of "Depolarization Ratio Data" and "Order Parameter Data", the procedure to determine uniaxial and biaxial order parameters in LCEs has been described previously in Phys. Rev. Research 2021, 3, 023191. Conoscopy was performed using a Leica DM 2700P polarizing microscope in transmission mode under cross-polarized conditions. The microscope was equipped with a 0.9 numerical aperture (NA) condensing lens and a 0.95 NA 80x Leitz microscope objective. To study the conoscopic patterns, a Bertrand lens was inserted between the microscope objective and the eyepiece. The conoscopic patterns were captured with a Nikon D3500 camera. The homeotropic sample is held under strain with Kapton tape and allowed to stress relax for two minutes before the image of the conoscopic pattern is recorded. The strain is applied parallel to the analyzer of the cross-polarized microscope and measured with digital calipers. The optical sign of the conoscopic figures was determined by inserting a λ wave-plate and observing the coloration of the grey regions near the melatopes of the acute bisetrix conoscopic figure obtained when the system is rotated to the 45o position. The change in color of the first order ‘grey’ regions of the conoscopic figure indicates whether the system is positive or negative [31, 35]. A positive uniaxial system will produce blue coloration along the direction of the λ wave plate and yellow coloration perpendicular to it [31]. The opposite is true for a negative uniaxial system.