Temperature-driven elastocaloric enhancement in liquid crystal elastomers

[Description of methods used for collection/generation of data]: Differential scanning calorimetry measurements were performed using DSC Q1000 (TA Instruments) on both the LCE and its precursor. The sample pan utilized for both measurements was the hermetically sealed Tzero aluminum pan (TA Instruments). The heating rate was consistently maintained at 5 °C/min. The temperature modulation parameters were set to a period of 50 seconds and an amplitude of ± 0.663 °C. Before each heating procedure, a 15-minute isothermal interval was applied to allow the equipment to stabilize and reach the designated modulation parameters. Three heat cycles were programmed per measurement with each heat-cool cycle followed by a Newtonian cooling quench. The initial and secondary heat-cool cycles effectively erased the thermal history of the samples. The values presented herein were gathered from the third and final heating cycle. Broadband Dielectric Spectroscopy (BDS) measurement of the prepared LCE material was taken using the Alpha-Beta Impedance Analyzer (Novocontrol). The measurement frequency range was 10^[-1] to 10^[7] Hz. The sample was positioned between 20-mm diameter gold-plated electrodes and subsequently loaded into the Active Sample Cell (Novocontrol) sample stage. The sample was proportioned with a larger diameter than the electrodes to ensure an overhang and prevent short-circuit. The root mean square of the applied AC voltage was 1.0 Vrms. To investigate the polymer dynamics, dielectric measurements were conducted in isothermal mode with a temperature step value of 5 °C/min from -120 to 100 °C/min. The temperature control of each isothermal measurement was maintained by the Quatro Cryosystem (Novocontrol), exhibiting a temperature stability better than ± 0.28$ K. Dynamic mechanical analysis (DMA) measurements were performed using DMA Q800 (TA Instruments) in tension mode. LCE samples were portioned into 25~mm long strips with a width of 2-6 mm. The single-frequency measurement was conducted at a frequency of 1~Hz. The oscillation amplitude was set to 0.37 strain. The sample was initially equilibrated at -100 °C for 5 minutes and then heated up to 70 °C at a heating rate of 2 °C/min. Tensile equipment: A custom-built tensile setup was developed to perform the deformation cycles required for direct measurements of the eC effect. A belt-drive motor provided strain load with an accuracy of ± 0.1 mm. The loading strain rate was set such that the loading strain was reached within 0.2 s, while unloading was performed at the maximum attainable rate of the motor, corresponding to -1200 mm/s. The sample stage was enclosed within a PID-controlled heating chamber to enable precise temperature regulation. The tensile apparatus was housed inside a polystyrene enclosure for temperature regulation, and active cooling was achieved by introducing a controlled nitrogen gas flow into the enclosure. Temperature measurements: Infrared thermography was employed to conduct contact-less temperature measurements. A FLIR A655sc (Teledyne FLIR) with 25°C field of view is pointed towards the thermal window of the polystyrene case. To minimize IR reflections and background noise, the upper surface of the polystyrene enclosure was uniformly covered with black electrical tape. All IR videos were captured at a frame rate of 50 frames per second. The sample temperature was extracted as the mean value of the central third of the visible LCE surface, both in the undeformed and elongated states.

[数据收集与生成所用方法描述]：差示扫描量热法测试采用TA Instruments公司的DSC Q1000设备，分别对液晶弹性体（Liquid Crystal Elastomer，LCE）及其前驱体进行测试。两次测试均使用TA Instruments出品的密封式Tzero铝制样品盘。升温速率恒定为5 °C/min。温度调制参数设置为周期50秒，振幅±0.663 °C。每次升温程序前，均设置15分钟的等温区间，以使设备稳定并达到预设的调制参数。每次测试设置3个热循环，每个热-冷循环后采用牛顿冷却骤冷工艺。初始及第二轮热-冷循环可有效消除样品的热历史。本文所呈现的测试数据均取自第三轮即最终的升温循环。
宽带介电谱（Broadband Dielectric Spectroscopy，BDS）测试采用Novocontrol公司的Alpha-Beta阻抗分析仪，对制备得到的LCE材料进行测试。测试频率范围为10^-1至10^7 Hz。将样品置于直径20 mm的镀金电极之间，随后装入Active Sample Cell（Novocontrol）样品台。样品的直径大于电极直径，以确保边缘悬伸并防止短路。所施加的交流电压的均方根值为1.0 Vrms。为研究聚合物动力学，采用等温模式开展介电测试，以5 °C/min的温度步长在-120 ℃至100 ℃/min区间内进行。每一次等温测试的温度控制均由Novocontrol公司的Quatro Cryosystem实现，该系统的温度稳定性优于±0.28 K。
动态力学分析（Dynamic mechanical analysis，DMA）测试采用TA Instruments公司的DMA Q800设备，测试模式为拉伸模式。将LCE样品裁切成长度25 mm左右、宽度2~6 mm的条状试样。单频测试的频率设置为1 Hz，振荡振幅设定为0.37应变。样品首先在-100 ℃下平衡5分钟，随后以2 °C/min的升温速率加热至70 ℃。
拉伸测试装置：定制的拉伸装置用于开展eC效应直接测量所需的变形循环。该装置采用带驱动电机提供应变载荷，精度可达±0.1 mm。加载应变率设置为使加载应变可在0.2 s内完成，卸载则以电机的最大可达速率进行，对应速率为-1200 mm/s。样品台置于PID控温加热腔体内，以实现精准的温度调节。拉伸装置封装在聚苯乙烯外壳内以调控温度，并通过向外壳内通入受控的氮气气流实现主动冷却。
温度测量：采用红外热成像技术开展非接触式温度测量。使用Teledyne FLIR公司的FLIR A655sc设备，其视场为25 ℃，镜头对准聚苯乙烯外壳的热窗口。为减少红外反射与背景噪声，聚苯乙烯外壳的上表面均匀覆盖黑色电工胶带。所有红外视频均以50帧/秒的帧率采集。样品温度取可见LCE表面中央三分之一区域的平均温度，无论样品处于未变形还是拉伸状态。