Supporting Information

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1 Supporting Information Multi-temperature Memory Actuation of a Liquid Crystal Polymer Network over a Broad Nematic-Isotropic Phase Transition Induced by Large Strain Rong Yang a,b and Yue Zhao b* a Jiangsu Key Laboratory of Environmentally Friendly Polymeric Materials, School of Materials Science and Engineering, Jiangsu Collaborative Innovation Center of Photovolatic Science and Engineering, Changzhou University, Changzhou, , P. R. China b Département de chimie, Université de Sherbrooke, Sherbrooke, Québec, J1K 2R1, Canada. yue.zhao@usherbrooke 1) Experimental Materials. The liquid crystal polymer was synthesized by polycondensation from 4,4 -bis(6-hydroxyhexyloxy)biphenyl, 2-phenylsuccinic acid and 4-(6-Hydroxyhexyloxy)cinnamic acid. The used sample has M n =36,700 g/mol, and PDI=2.25 (from differential scanning calorimetry). The detailed synthesis was fully described in our previous report. [1] Preparation of LCN Actuators. Unless otherwise stated, for all LCN actuators, the film was stretched at 51 o C (in the nematic phase) to % elongation. The external force was then removed and the film with the monodomain retained was exposed to UV light ( nm filter, 80 mw cm -2 ) at 47 o C for the photocrosslinking, i.e., the fixation of the actuation domains. All specimens were thick films prepared by compression-molding (200 µm in thickness prior to stretching). For LCN actuators presented in Figure 4, one side of the elongated film was irradiated by UV light for 60 min, then, the LCN film under constant strain was heated in the isotropic phase for thermal equilibrium, which was followed by flood photocrosslinked for 60 min on the other side; finally, it was cooled to the LC phase. For LCN actuators presented in Figure 5 ( bloom upon heating), one side of the elongated film was irradiated by UV light for 60 min, the elongated LCP film was heated to 80 o C in the isotropic phase for stress release while being kept flat, then subjected to flood photocrosslinking for 60 min on the other side and cooled to the LC phase. The actuator for bloom upon cooling was prepared as actuators in Figure 4. After the preparation, the film was cut to a petaloid shape, then all the petals weld on a piece of round LCP film at 80 o C by compression molding. Finally, the welded round LCP film was subjected to flood photocrosslinking. 1

2 Characterizations. Thermal transition temperatures of all samples were measured using a differential scanning calorimetry (DSC TA Q200) with about 5 mg of sample under a nitrogen atmosphere (flow rate of 50 ml min -1 ) at a heating and cooling rate of 10 o C min -1. Small angle X-ray scattering (SAXS) measurements were carried out on a Bruker AXS Nanostar system equipped with a Microfocus Copper Anode at 45 kv / 0.65 ma, MONTAL OPTICS and a VANTEC D detector at 90 mm from the samples calibrated with a Silver Behenate standard. Azimuthal scans of 360 deg. were recorded at 2θ= (for smectic layers) and 2θ = (for nematic order). The collection exposure times were 10 minutes. Stress-strain behavior of LCP and LCN were measured by using a universal material testing machine (Instron 5965, UK) equipped with a heating chamber at a crosshead speed of 1000 mm min -1. Thermal mechanical analysis (TMA) of the specimens (3 mm 2 mm 0.08 mm, the two sides of the film were each exposed to UV light for 120 min, reaching essentially uniform crosslinking) were performed on a dynamic mechanical analyser (PerkinElmer 8000) at a heating/cooling rate of 3 C min -1 from 25 to 80 C under tension clamp by TMA mode. 2) Unstretched Liquid Crystal Polymer before and after Photocrosslinking Figure S1. DSC thermograms of unstretched LCP (polymer prior to photocrosslinking) and LCN (after photocrosslinking) 2

3 Figure S2. 1D XRD and 2D XRD patterns of unstretched LCP and LCN. Figure S3. Stress-strain curves of LCP and LCN in the LC state at 50 C. Figure S3 shows the stress-strain behavior of the LCP and LCN. Up to 25%, display a sharp increase in stress linear stress-strain relation with a high slope; then the stress increases slowly with a constant slope (higher for LCN) up to 340% strain for LCN and over the entire tested strain range (550%) for LCP. Finally, the stress increases swiftly again for LCN over larger strains. The stress-strain curve of LCN can be divided into three regions: region I (elastic deformation of polydomain), region Ⅱ (polydomain monodomain transition) and region Ⅲ (elastic deformation of monodomain). [2,3] The polydomain-monodomain transition is completed when the strain reaches around 340%. For LCP, there are only two regions. While the first belongs to elastic deformation (up to 25%), the stress remains almost constant for larger strains up to 550%. In region II, oriented polymer chains can relax after polydomain-monodomain transition because physical crosslinking is not as strong as chemical crosslinking, resulting in the apparent absence of region III. 3

4 3) Stretched Liquid Crystal Polymer Actuators Figure S4. Azimuthal diffraction profiles (black lines: 2θ= for smectic layers; red lines: 2θ= for nematic order) for LCP stretched to different strains and their corresponding LCN. The results show unambiguously the disappearance of the smectic order in LCP500 and the retention of the mechanically suppressed smectic phase in the actuator LCN500. Figure S5. DSC thermograms (second heating scan) for LCNs prepared with different initial strains, showing a broad nematic-isotropic phase transition in the actuator LCN500 as a result of the mechanically suppressed smectic phase. 4

5 4) Supporting Movie Captions Movie S1. Comparison of two polymer actuators prepared using specimens stretched to 300% and 500% (LCN300 and LCN500), respectively: they both roll upon heating in a temperature-controlled chamber, but the one with 500% strain proceeds faster due to a lower actuation temperature and greater actuation force. Movie S2. Right-handed helix to left-handed helix upon temperature switch from 45 to 50 to 55 and 60 C in a water bath, showing the multi-temperature memory actuation of LCN500. Movie S3. Artificial flower: closure upon heating inside an oven blooming upon cooling outside the oven. Movie S4 and Movie 5. Artificial flower: closure upon cooling and blooming upon heating on a hot plate set to low and high temperature, respectively. Reference [1] R. Yang, Y. Zhao, Non-uniform Optical Inscription of Actuation Domains in Liquid Crystal Polymer of Uniaxial Orientation: An Approach to Complex and Programmable Shape Changes. Angew. Chem. Int. Ed. 2017, 56, [2] R. Ishige, K. Osada, H. Tagawa, H. Niwano, M. Tokita, J. Watanabe, Elongation Behavior of a Main-Chain Smectic Liquid Crystalline Elastomer. Macromolecules 2008, 41, [3] H. P. Patil, D. M. Lentz, R. C. Hedden, Necking Instability during Polydomain-Monodomain Transition in a Smectic Main-Chain Elastomer. Macromolecules 2009, 42: