Research progress of single/dual network liquid crystal elastomers based on dynamic bonds
-
摘要: 动态键交联的液晶弹性体 (LCEs) 在外界刺激(如光、电、热等)下，能通过改变自身体积或形状执行宏观运动，具有优异的分子协同、自适应等性能，在软体机器人、人工肌肉和微流控等领域具有重要的应用前景。LCEs产生可逆形变的先决条件是实现内部液晶取向的有效控制。动态键的断裂和重组，不仅可以解耦交联网络的构筑和取向调控，还能够改善材料的再加工性能，赋予材料重塑变形、自修复和形状记忆等新的功能。因而交联网络结构(交联剂类型、结构、不同交联网络的协同)的合理设计与构筑对于构建性能优异且多功能集成的LCEs极为重要。本文综述了液晶取向控制和具有单/双动态交联(包括动态非共价键和共价键)网络的LCEs的制备与应用的研究进展，并对该领域的发展前景进行了展望。Abstract: Liquid crystal elastomers (LCEs) containing dynamic cross-linking bonds are capable of undergoing macroscopic motion through alterations in volume or shape in response to external stimuli, including light, electricity, or heat. These materials demonstrate remarkable molecular cooperative effects and adaptive properties, offering considerable potential in the fields of soft robotics, artificial muscles, and microfluidics. Effective control of the internal liquid crystal orientation in LCEs is essential for achieving reversible deformation. The breakage and reformation of dynamic bonds not only decouples the construction of cross-linked networks and orientation control, but also enhances the reprocessing properties of materials, enabling new functionalities like remodeling deformation, self-healing, and shape memory. Therefore, the deliberate design and construction of cross-linked network structures, including the selection of cross-linking agents, their structures, and cooperative effects of various networks, are crucial for producing LCEs with exceptional performance and multifunctional integration. This review comprehensively discusses advancements in the preparation and application of LCEs, encompassing liquid crystal orientation control and single/double dynamic cross-linking networks (involving dynamic non-covalent and covalent bonds), and delineates future prospects for development in this field.
-
图 2 (a) 溶剂蒸发法制备液晶网络(LCN)示意图及其分子结构[12]；(b) 自由溶剂蒸发形成多结构域LCN示意图及其横截面SEM图像和2D大角X射线衍射(WAXD)图像[12]；(c) 定向溶剂蒸发(单轴拉伸)形成单结构域LCN的示意图及其截面SEM图像和2D WAXD图像[12]
Figure 2. (a) Schematic diagram and molecular structure of liquid crystalline network (LCN) prepared by solvent evaporation method[12]; (b) Schematic illustrations of the formation of polydomain LCN via free solvent evaporation and its cross-sectional SEM image and 2D wide angle X-ray diffraction (WAXD) image[12]; (c) Schematic illustrations of the formation of monodomain LCN via aligned solvent evaporation (uniaxial stretching) and cross-sectional SEM image and 2D WAXD image[12]
LC—Liquid crystal; 1, 3-PDT—1, 3-propanedithiol; F—Force
图 4 (a) 聚合物单体和紫外光引发剂的分子结构[22]；(b) 湿敏LCN带的制备示意图[22]；(c) SO2引起的膜表面变化示意图[22]；(d) SO2门控行为的机制示意图[22]
Figure 4. (a) Chemical structures of monomers and UV initiator[22]; (b) Illustration of fabricating humidity-sensitive LCN strip[22]; (c) Schematic illustration of the SO2-induced change of the film surface[22]; (d) Schematic of the mechanism of the SO2-gated behavior[22]
图 6 人工肌肉的纳米复合材料[30]：(a) 具有功能线穿越液晶网络设计结构的复合材料的合成路线示意图；(b) 三步多重刺激响应周期示意图
Figure 6. Multifunctional polymer composite for artificial muscle[30]: (a) Schematic presentation of the synthetic route of composites with the designed structure as a functional thread passing through the liquid crystal network; (b) Schematic diagram of the three-step multiple stimulus-response cycle
NR—Nanorods; PU—Polyurethane; NIR—Near-infrared
图 7 (a) 超分子液晶聚氨酯复合材料(SMPU-HOBA)的超分子结构和SMPU硬段区域的示意图[31]；(b) SMPU-HOBA复合材料可逆双向形状记忆效应(rbSME)的系列照片[31]；(c) 由SMPU-0.4HOBA制成的夹持装置可逆地捕获和释放硬币[31]
Figure 7. (a) Supramolecular structure of the shape memory polyurethane (SMPU)-4-hexadecyloxybenzoic acid (HOBA) composites and schematic representation of the hard segment region of SMPU[31]; (b) Photograph series showing the reversible bidirectional shape memory effect (rbSME) of SMPU-HOBA composites[31]; (c) A gripper device made from SMPU-0.4HOBA reversibly catches and releases a coin[31]
Treset, Tlow, Thigh—Reset temperature, low temperature, high temperature
图 8 LCE类玻璃体的取向编程机制[32]：(a) 网络重排未激活；(b) 网络重排激活；(c) 取向后LCE的可逆驱动
Figure 8. Orientation programming mechanism of LCE vitrimer[32]: (a) Network rearrangement is not activated; (b) Network rearrangement activation; (c) Reversible driving of LCE after orientation
TV—Topology freezing transition temperature; TNI—Nematic to isotropic phase transition temperature
图 9 液晶环氧树脂3D柔性驱动器[33]：(a) 未取向的液晶环氧树脂固化膜(LCETs)的制备；(b) 基于酯交换将两个未取向的LCET膜压铸在一起；(c) LCET的取向过程；(d) 逐步重新编程LCET创建具有可逆致动的3D虹膜状致动器示意图；(e) 弯曲LCET复合致动器的光触发可逆致动；(f) 螺旋LCET复合致动器的光触发可逆致动
Figure 9. Epoxy resin 3D flexible actuator[33]: (a) Synthesis of unaligned liquid crystalline epoxy thermosets (LCETs); (b) Two unaligned LCET films were compress-moulded together based on the transesterification; (c) Aligning procedure for LCET; (d) Reprogramming LCET stepwise to create a 3D iris-like actuator with reversible actuations; (e) Light-triggered reversible actuation of a bending LCET composite actuator; (f) Light-triggered reversible actuation of a spiral LCET composite actuator
L0—Initial length of the film
图 10 (a) 制备可生长的弹性体的化学组分[34]；(b) 类海葵致动器在冷却和加热时的卷曲/展开运动行为图与致动器倒置后站立与平躺模式实物图片及构造示意图[34]；(c) 聚硫氨基甲酸酯LCE、聚氨酯LCE、环氧树脂LCE、聚硼酸酯LCE和聚肟酯合成路线图[35]
Figure 10. (a) Chemical compositions for the synthesis of the elastomer that can grow[34]; (b) A sea-anemone-like actuator showing curling/uncurling motion upon cooling and heating, and standing up/lying down mode after turning upside down[34]; (c) Synthesis of polythiourethane LCE, polyurethane LCE, epoxy LCE, polyborate LCE, and polyoxime ester[35]
图 12 (a) 聚二硫化物(PDS)基共价适应性(CA)-LCN膜的分子构造与化学组成[42]；(b) PDS基CA-LCN的聚合和解聚可逆循环过程示意图[42]
Figure 12. (a) Molecular design and chemical structures of the polydisulfide (PDS)-based covalent adaptable (CA)-LCN film[42]; (b) Schematic illustration of the reversible polymerization and depolymerization of the PDS-based CA-LCN[42]
图 13 (a) LC单体RM82、扩链剂1 DODT、扩链剂2 OPDSPA和交联剂PETMP的化学结构式[46]；(b) 二硒键复分解示意图[46]；(c) 在热刺激下执行莫比乌斯环的可逆螺旋形状变形、花朵模拟开花运动和包裹变形致动器图片[46]
Figure 13. (a) Chemical structures of LC monomer RM82, chain extender 1 DODT, chain extender 2 OPDSPA, and the crosslinker PETMP[46]; (b) Schematic illustration of the metathesis of diselenide bonds[46]; (c) Photos of the actuators executing reversible helical shape morphing, flower-mimic blooming motion, and enclasping deformation of Mçbius strip under thermal stimulus[46]
图 14 (a) 互穿聚合物网络(IPN)-LCE膜的制备步骤及流程示意图[52]；(b) IPN-LCE材料的LC聚丙烯酸酯(LCPA)和LC聚氨酯(LCPU)体系的化学组成[52]；(c) IPN-LCE膜(20.1 mg)加热/冷却循环中提拉负载(约605.02 g)的实物照片[52]
Figure 14. (a) Schematic illustration of the preparation protocol of interpenetrating polymer network (IPN)-LCE film[52]; (b) Chemical compositions of LC polyacrylate (LCPA) and LC polyurethane (LCPU) systems of the designed IPN-LCE material[52]; (c) Photos of IPN-LCE film (20.1 mg)lifting up a load (ca. 605.02 g) in a heating/cooling cycle[52]
PTFE—Polytetrafluoroethylene; ca.—Circa
图 15 (a) 双交联网络(U-LCE)薄膜结构示意图[53]；(b) 多孔柔性主链液晶弹性体(PHG-mLCE)/水凝胶的中尺度和微尺度晶格结构以及整体结构[54]
Figure 15. (a) Schematic diagram of the network structure of the double cross-linked network (U-LCE) film[53]; (b) Mesoscale and microscale lattice architecture and overall macrostructure of the porous long chain soft backone based liquid crystal elastomer (PHG-mLCE)/hydrogel[54]
-
[1] WANG Y C, LIU J Q, YANG S. Multi-functional liquid crystal elastomer composites[J]. Applied Physics Reviews, 2022, 9(1): 011301. doi: 10.1063/5.0075471 [2] BISOYI H K, LI Q. Liquid crystals: Versatile self-organized smart soft materials[J]. Chemical Reviews, 2022, 122(5): 4887-4926. doi: 10.1021/acs.chemrev.1c00761 [3] HERBERT K M, FOWLER H E, MCCRACKEN J M, et al. Synthesis and alignment of liquid crystalline elastomers[J]. Nature Reviews Materials, 2022, 7(1): 23-38. [4] SAED M O, GABLIER A, TERENTJEV E M. Exchangeable liquid crystalline elastomers and their applications[J]. Chemical Reviews, 2022, 122(5): 4927-4945. doi: 10.1021/acs.chemrev.0c01057 [5] PANG X L, LYU J A, ZHU C Y, et al. Photodeformable azobenzene-containing liquid crystal polymers and soft actuators[J]. Advanced Materials, 2019, 31(52): 1904224. doi: 10.1002/adma.201904224 [6] BROER D J, FINKELMANN H, KONDO K. In-situ photopolymerization of an oriented liquid-crystalline acrylate[J]. Macromolecular Chemistry and Physics, 1988, 189(1): 185-194. doi: 10.1002/macp.1988.021890117 [7] KUPFER J, FINKELMANN H. Nematic liquid single-crystal elastomers[J]. Makromolekulare Chemie-Rapid Communications, 1991, 12(12): 717-726. doi: 10.1002/marc.1991.030121211 [8] LEI L, HAN L, MA H, et al. Synthesis of well-defined PS-based Azo-liquid crystals with control of phase transitions and photo-behaviors for liquid crystal networks with photomechanical deformation[J]. Polymer, 2020, 203: 122749. doi: 10.1016/j.polymer.2020.122749 [9] YAKACKI C M, SAED M, NAIR D P, et al. Tailorable and programmable liquid-crystalline elastomers using a two-stage thiol-acrylate reaction[J]. RSC Advances, 2015, 5(25): 18997-19001. doi: 10.1039/C5RA01039J [10] AHIR S V, TAJBAKHSH A R, TERENTJEV E M. Self-assembled shape-memory fibers of triblock liquid-crystal polymers[J]. Advanced Functional Materials, 2006, 16(4): 556-560. doi: 10.1002/adfm.200500692 [11] SAED M O, AMBULO C P, KIM H, et al. Molecularly-engineered, 4D-printed liquid crystal elastomer actuators[J]. Advanced Functional Materials, 2019, 29(3): 1806412. doi: 10.1002/adfm.201806412 [12] JIN B J, LIU J Q, SHI Y P, et al. Solvent-assisted 4D programming and reprogramming of liquid crystalline organogels[J]. Advanced Materials, 2022, 34(5): 2107855. doi: 10.1002/adma.202107855 [13] 张宇白, 吉岩. 基于动态共价键的液晶弹性体逆三维结构加工方法研究进展[J]. 液晶与显示, 2022, 37(2): 199-216. doi: 10.37188/CJLCD.2021-0309ZHANG Yubai, JI Yan. Research progress in processing methods of reversible three-dimensional structures of liquid-crystalline elastomers based on dynamic covalent bonds[J]. Chinese Journal of Liquid Crystals and Displays, 2022, 37(2): 199-216(in Chinese). doi: 10.37188/CJLCD.2021-0309 [14] LYU J A, LIU Y Y, WEI J, et al. Photocontrol of fluid slugs in liquid crystal polymer microactuators[J]. Nature, 2016, 537(7619): 179-184. doi: 10.1038/nature19344 [15] XU B, ZHU C Y, QIN L, et al. Light-directed liquid manipulation in flexible bilayer microtubes[J]. Small, 2019, 15(24): 1901847. doi: 10.1002/smll.201901847 [16] CHEN M S, YAO B J, KAPPL M, et al. Entangled azobenzene-containing polymers with photoinduced reversible solid-to-liquid transitions for healable and reprocessable photoactuators[J]. Advanced Functional Materials, 2020, 30(4): 1906752. doi: 10.1002/adfm.201906752 [17] LUGGER S J D, HOUBEN S J A, FOELEN Y, et al. Hydrogen-bonded supramolecular liquid crystal polymers: Smart materials with stimuli-responsive, self-healing, and recyclable properties[J]. Chemical Reviews, 2022, 122(5): 4946-4975. doi: 10.1021/acs.chemrev.1c00330 [18] FAN Y X, LIU T, LI Y Z, et al. One-step manufacturing of supramolecular liquid-crystal elastomers by stress-induced alignment and hydrogen bond exchange[J]. Angewandte Chemie-International Edition, 2023, 62(37): e202308793. doi: 10.1002/anie.202308793 [19] ZHAO X, CHEN Y, PENG B, et al. A facile strategy for the development of recyclable multifunctional liquid crystal polymers via post-polymerization modification and ring-opening metathesis polymerization[J]. Angewandte Chemie-International Edition, 2023, 62(21): e202300699. doi: 10.1002/anie.202300699 [20] VERPAALEN R C P, DEBIJE M G, BASTIAANSEN C M, et al. Programmable helical twisting in oriented humidity-responsive bilayer films generated by spray-coating of a chiral nematic liquid crystal[J]. Journal of Materials Chemistry A, 2018, 6(36): 17724-17729. doi: 10.1039/C8TA06984K [21] WANI O M, VERPAALEN R, ZENG H, et al. An artificial nocturnal flower via humidity-gated photoactuation in liquid crystal networks[J]. Advanced Materials, 2019, 31(2): 1805985. doi: 10.1002/adma.201805985 [22] LAN R C, SUN J, SHEN C, et al. Reversibly and irreversibly humidity-responsive motion of liquid crystalline network gated by SO2 gas[J]. Advanced Functional Materials, 2019, 29(23): 1900013. doi: 10.1002/adfm.201900013 [23] LEWIS K L, HERBERT K M, MATAVULJ V M, et al. Programming orientation in liquid crystalline elastomers prepared with intra-mesogenic supramolecular bonds[J]. ACS Applied Materials & Interfaces, 2023, 15(2): 3467-3475. doi: 10.1021/acsami.2c18993 [24] WANG L, ZHOU Y, MA S K, et al. Reprocessable and healable room temperature photoactuators based on a main-chain azobenzene liquid crystalline poly(ester-urea)[J]. Journal of Materials Chemistry C, 2021, 9(38): 13255-13265. doi: 10.1039/D1TC03064G [25] MAMIYA J I, YOSHITAKE A, KONDO M, et al. Is chemical crosslinking necessary for the photoinduced bending of polymer films?[J]. Journal of Materials Chemistry, 2008, 18(1): 63-65. doi: 10.1039/B715855F [26] FU S Y, ZHANG H, ZHAO Y. Optically and thermally activated shape memory supramolecular liquid crystalline polymers[J]. Journal of Materials Chemistry C, 2016, 4(22): 4946-4953. doi: 10.1039/C6TC00718J [27] LIU M J, LIU P, LU G, et al. Multiphase-assembly of siloxane oligomers with improved mechanical strength and water-enhanced healing[J]. Angewandte Chemie-International Edition, 2018, 57(35): 11242-11246. doi: 10.1002/anie.201805206 [28] YU H T, FENG Y Y, GAO L, et al. Self-healing high strength and thermal conductivity of 3D graphene/PDMS composites by the optimization of multiple molecular interactions[J]. Macromolecules, 2020, 53(16): 7161-7170. doi: 10.1021/acs.macromol.9b02544 [29] NI B, XIE H L, TANG J, et al. A self-healing photoinduced-deformable material fabricated by liquid crystalline elastomers using multivalent hydrogen bonds as cross-linkers[J]. Chemical Communications, 2016, 52(67): 10257-10260. doi: 10.1039/C6CC04199J [30] CHEN C, LIU Y Y C, HE X M, et al. Multiresponse shape-memory nanocomposite with a reversible cycle for powerful artificial muscles[J]. Chemistry of Materials, 2021, 33(3): 987-997. doi: 10.1021/acs.chemmater.0c04170 [31] MO F N, BAN J F, PAN L L, et al. Liquid crystalline polyurethane composites based on supramolecular structure with reversible bidirectional shape memory and multi-shape memory effects[J]. New Journal of Chemistry, 2019, 43(1): 103-110. doi: 10.1039/C8NJ05451G [32] LU X L, ZHANG H, FEI G X, et al. Liquid-crystalline dynamic networks doped with gold nanorods showing enhanced photocontrol of actuation[J]. Advanced Materials, 2018, 30(14): 1706597. [33] YANG Y, TERENTJEV E M, ZHANG Y B, et al. Reprocessable thermoset soft actuators[J]. Angewandte Chemie-International Edition, 2019, 58(48): 17474-17479. doi: 10.1002/anie.201911612 [34] LIANG H, WU Y H, ZHANG Y B, et al. Elastomers grow into actuators[J]. Advanced Materials, 2023, 35(12): 2209853. doi: 10.1002/adma.202209853 [35] LIANG H, ZHANG S, LIU Y W, et al. Merging the interfaces of different shape-shifting polymers using hybrid exchange reactions[J]. Advanced Materials, 2023, 35(1): 2202462. doi: 10.1002/adma.202202462 [36] YAO Y J, HE E J, XU H T, et al. Fabricating liquid crystal vitrimer actuators far below the normal processing temperature[J]. Materials Horizons, 2023, 10(5): 1795-1805. doi: 10.1039/D3MH00184A [37] UBE T, TSUNODA H, KAWASAKI K, et al. Photoalignment in polysiloxane liquid-crystalline elastomers with rearrangeable networks[J]. Advanced Optical Materials, 2021, 9(9): 2100053. doi: 10.1002/adom.202100053 [38] MA J Z, YANG Y Z, VALENZUELA C, et al. Mechanochromic, shape-programmable and self-healable cholesteric liquid crystal elastomers enabled by dynamic covalent boronic ester bonds[J]. Angewandte Chemie-International Edition, 2022, 61(9): e202116219. doi: 10.1002/anie.202116219 [39] SEAD M O, GABLIER A, TERENTEJV E M. Liquid crystalline vitrimers with full or partial boronic-ester bond exchange[J]. Advanced Functional Materials, 2020, 30(3): 1906458. doi: 10.1002/adfm.201906458 [40] TANG D, ZHANG L, ZHANG X Y, et al. Bio-mimetic actuators of a photothermal-responsive vitrimer liquid crystal elastomer with robust, self-healing, shape memory, and reconfigurable properties[J]. ACS Applied Materials & Interfaces, 2022, 14(1): 1929-1939. [41] RIM M W, JUNG D Y, YU D M, et al. Multifunctional liquid crystal polymer networks: Azobenzene based monoacrylate molecules impart a photothermal effect to polymer networks[J]. ACS Applied Polymer Materials, 2023, 5(2): 1325-1333. [42] HUANG S, SHEN Y K, BISOYI H K, et al. Covalent adaptable liquid crystal networks enabled by reversible ring-opening cascades of cyclic disulfides[J]. Journal of the American Chemical Society, 2021, 143(32): 12543-12551. doi: 10.1021/jacs.1c03661 [43] JI S B, CAO W, YU Y, et al. Dynamic diselenide bonds: Exchange reaction induced by visible light without catalysis[J]. Angewandte Chemie-International Edition, 2014, 53(26): 6781-6785. doi: 10.1002/anie.201403442 [44] IRIGOYEN M, FERNÁNDEZ A, RUIZ A, et al. Diselenide bonds as an alternative to outperform the efficiency of disulfides in self-healing materials[J]. The Journal of Organic Chemistry, 2019, 84(7): 4200-4210. doi: 10.1021/acs.joc.9b00014 [45] VALENZUELA C, CHEN Y H, WANG L, et al. Functional liquid crystal elastomers based on dynamic covalent chemistry[J]. Chemistry—A European Journal, 2022, 28(70): e202201957. doi: 10.1002/chem.202201957 [46] CHEN L, BISOYI H K, HUANG Y L, et al. Healable and rearrangeable networks of liquid crystal elastomers enabled by diselenide bonds[J]. Angewandte Chemie-International Edition, 2021, 60(30): 16394-16398. doi: 10.1002/anie.202105278 [47] BLANKE M, POSTULKA L, D'ACIERNO F, et al. Manipulation of liquid crystalline properties by dynamic covalent chemistry—En route to adaptive materials[J]. ACS Applied Material Interfaces, 2022, 14(14): 16755-16763. [48] LIN X Y, GABLIER A, TERENTJEV E M. Imine-based reactive mesogen and its corresponding exchangeable liquid crystal elastomer[J]. Macromolecules, 2022, 55(3): 821-830. [49] HUANG X, QIN L, WANG J L, et al. Multiple shape manipulation of liquid crystal polymers containing diels-alder network[J]. Advanced Functional Materials, 2022, 32(51): 2208312. doi: 10.1002/adfm.202208312 [50] JIANG Z C, XIAO Y Y, YIN L, et al. "Self-lockable" liquid crystalline diels-alder dynamic network actuators with room temperature programmability and solution reprocessability[J]. Angewandte Chemie-International Edition, 2020, 59(12): 4925-4931. doi: 10.1002/anie.202000181 [51] 李蒙. 高强度自修复液晶弹性体材料的合成及性能研究 [D]. 常州: 常州大学, 2022.LI Meng. Synthesis and performance study of high-strength self-healing liquid crystal elastomer materials[D]. Changzhou: Changzhou University, 2022(in Chinese). [52] LU H F, WANG M, CHEN X M, et al. Interpenetrating liquid-crystal polyurethane/polyacrylate elastomer with ultrastrong mechanical property[J]. Journal of the American Chemical Society, 2019, 141(36): 14364-14369. doi: 10.1021/jacs.9b06757 [53] LI M, DAI S P, DONG X, et al. High-strength, large-deformation, dual cross-linking network liquid crystal elastomers based on quadruple hydrogen bonds[J]. Langmuir, 2022, 38(4): 1560-1566. doi: 10.1021/acs.langmuir.1c03010 [54] JIANG Y Y, DONG X, ZHU S J, et al. Skin-friendly and antibacterial monodomain liquid crystal elastomer actuator[J]. Colloids and Surfaces B: Biointerfaces, 2023, 222: 113110. doi: 10.1016/j.colsurfb.2022.113110 [55] LIN X Y, ZOU W K, TERENTJEV E M. Double networks of liquid-crystalline elastomers with enhanced mechanical strength[J]. Macromolecules, 2022, 55(3): 810-820. doi: 10.1021/acs.macromol.1c02065 [56] LU X L, AMBULO C P, WANG S T, et al. 4D-printing of photoswitchable actuators[J]. Angewandte Chemie-International Edition, 2021, 60(10): 5536-5543. doi: 10.1002/anie.202012618 [57] YUAN S J, RONG Z M, ZHANG M Q, et al. Enhancement of intrinsic thermal conductivityof liquid crystalline epoxy through the strategyof interlocked polymer networks[J]. Materials Chemistry Frontiers, 2022, 6(9): 1137-1149. doi: 10.1039/D2QM00090C [58] YUAN S J, RONG Z M, ZHANG M Q, et al. Increasing strengths of liquid crystalline polymers while minimizing anisotropy via topological rearrangement assisted Bi-directional stretching of reversibly interlocked macromolecular networks[J]. Applied Materials Today, 2022, 29: 101643. doi: 10.1016/j.apmt.2022.101643 -
下载:
点击查看大图
计量
- 文章访问数: 397
- HTML全文浏览量: 223
- PDF下载量: 28
- 被引次数: 0
