高分子纳米复合材料的受限动力学与流变学

尤伟; 俞炜

doi:10.14028/j.cnki.1003-3726.2024.24.230

您当前的位置：

首页 >

文章列表页 >

高分子纳米复合材料的受限动力学与流变学

专论 | 更新时间：2025-01-23

- 高分子纳米复合材料的受限动力学与流变学
- Confined Dynamics and Rheology of Polymer Nanocomposites
- 高分子通报 2025年38卷第2期页码：169-182
- 作者机构：
  
  上海交通大学化学化工学院，流变学研究所，上海 200240
- 作者简介：
  
  *尤伟，E-mail: weiyou13@sjtu.edu.cn；俞炜，E-mail: wyu@sjtu.edu.cn
- 基金信息：
  
  国家自然科学基金(22341303;21790344;21903053)
- DOI：10.14028/j.cnki.1003-3726.2024.24.230
  中图分类号：
- 收稿日期：2024-08-10，
  
  录用日期：2024-09-01，
  
  网络出版日期：2024-09-25，
  
  纸质出版日期：2025-02-20
- 稿件说明：
移动端阅览
尤伟, 俞炜. 高分子纳米复合材料的受限动力学与流变学. 高分子通报, 2025, 38(2), 169–182.

You, W.; Yu, W. Confined dynamics and rheology of polymer nanocomposites. Polym. Bull. (in Chinese), 2025, 38(2), 169–182.
尤伟, 俞炜. 高分子纳米复合材料的受限动力学与流变学. 高分子通报, 2025, 38(2), 169–182. DOI： 10.14028/j.cnki.1003-3726.2024.24.230.

You, W.; Yu, W. Confined dynamics and rheology of polymer nanocomposites. Polym. Bull. (in Chinese), 2025, 38(2), 169–182. DOI： 10.14028/j.cnki.1003-3726.2024.24.230.

摘要

高分子纳米复合材料(PNCs)以其优异的机械性能和多功能性等特点，在众多领域展现出巨大的应用潜力和发展前景。但是，由于对PNCs受限动力学和流变学缺乏充分理解，PNCs同时也存在性能调控难度大和加工制备技术不成熟等不足。本文旨在总结近年来PNCs在受限动力学与流变学方面的最新研究进展，从多尺度分子动力学与流变学、多尺度粒子动力学与流变学两方面阐述PNCs中受限动力学与线性流变学的关系，探讨其研究方法、理论基础以及未来发展方向。

Abstract

Polymer nanocomposites (PNCs) have demonstrated significant potential and promising development prospects in numerous fields

owing to their exceptional mechanical properties and multifunctionality. However

the inadequate understanding of the confined dynamics and rheology of PNCs poses challenges in manipulating their properties and results in immature processing and preparation technologies. This monograph aims to summarize the recent advancements in the confined dynamics and rheology of PNCs and explain the relationship between confined dynamics

including multiscale molecular dynamics and multiscale particle dynamics

with linear rheology in PNCs. It also discusses the research methods

theoretical foundations

and future directions.

关键词

Keywords

references

Kumar, S. K. ; Benicewicz, B. C. ; Vaia, R. A. ; Winey, K. I . 50th anniversary perspective: are polymer nanocomposites practical for applications ? Macromolecules , 2017 , 50 ( 3 ), 714 − 731 .

Lin, Y. ; Li, P. L. ; Liu, W. J. ; Chen, J. ; Liu, X. Y. ; Jiang, P. K. ; Huang, X. Y . Application-driven high-thermal-conductivity polymer nanocomposites . ACS Nano , 2024 , 18 ( 5 ), 3851 − 3870 .

Yang, M. Z. ; Guo, M. F. ; Xu, E. X. ; Ren, W. B. ; Wang, D. Y. ; Li, S. A. ; Zhang, S. J. ; Nan, C. W. ; Shen, Y . Polymer nanocomposite dielectrics for capacitive energy storage . Nat. Nanotechnol. , 2024 , 19 , 588 − 603 .

Wu, D. ; Feng, Y. ; Li, R. H. ; Ozisik, R. ; Akcora, P . Entanglement density and particle dynamics in rigid interfacial layers of polymer nanocomposites . J. Appl. Phys. , 2021 , 130 ( 6 ), 064701 .

Cui, W. Z. ; Liu, J. ; You, W. ; Yu, W . Mechanical reinforcement by bridging chains in polymer nano-composites . Polymer , 2024 , 306 , 127208 .

Cui, W. Z. ; You, W. ; Yu, W . Mechanism of mechanical reinforcement for weakly attractive nanocomposites in glassy and rubbery states . Macromolecules , 2021 , 54 ( 2 ), 824 − 834 .

Zhang, H. ; You, W. ; Bian, F. G. ; Yu, W . Hetero-geneous percolation in poly(methylvinylsiloxane)/silica nanocomposites: the role of polymer-particle interaction . Macromolecules , 2022 , 55 ( 19 ), 8834 − 8845 .

Li, B. K. ; You, W. ; Peng, L. ; Huang, X. B. ; Yu, W . Revealing the shear effect on the interfacial layer in polymer nanocomposites through nanofiber reori-entation . Macromolecules , 2023 , 56 ( 8 ), 3050 − 3063 .

Yu, W. ; Wang, J. ; You, W . Structure and linear visco-elasticity of polymer nanocomposites with agglomerated particles . Polymer , 2016 , 98 , 190 − 200 .

Ondreas, F. ; Lepcio, P. ; Zboncak, M. ; Zarybnicka, K. ; Govaert, L. E. ; Jancar, J . Effect of nanoparticle organization on molecular mobility and mechanical properties of polymer nanocomposites . Macromolecules , 2019 , 52 ( 16 ), 6250 − 6259 .

Song, Y. H. ; Zheng, Q . Concepts and conflicts in nanoparticles reinforcement to polymers beyond hydrodynamics . Prog. Mater. Sci. , 2016 , 84 , 1 − 58 .

Cui, W. Z. ; You, W. ; Sun, Z. Y. ; Yu, W . Decoupled polymer dynamics in weakly attractive poly(methyl methacrylate)/silica nanocomposites . Macromolecules , 2021 , 54 ( 12 ), 5484 − 5497 .

Ma, M. C. ; Cui, W. Z. ; Guo, Y. L. ; Yu, W . Adsorption-desorption effect on physical aging in PMMA-silica nanocomposites . Polymer , 2022 , 255 , 125124 .

Dai, L. J. ; Fu, C. L. ; Zhu, Y. L. ; Li, Z. W. ; Sun, Z. Y . Probing intermittent motion of polymer chains in weakly attractive nanocomposites . Chinese J. Polym. Sci. , 2020 , 38 ( 6 ), 620 − 628 .

Dai, L. J. ; Fu, C. L. ; Zhu, Y. L. ; Sun, Z. Y . Hetero-geneous dynamics of unentangled chains in polymer nanocomposites . J. Chem. Phys. , 2019 , 150 ( 18 ), 184903 .

Liu, X. ; Cui, W. Z. ; Yu, W . Interfacial chain entan-glements induced melt memory effect in poly(ε-caprolactone)/silica nanocomposites . Chinese J. Polym. Sci. , 2022 , 40 ( 11 ), 1451 − 1465 .

You, W. ; Yu, W. ; Zhou, C. X . Cluster size distribution of spherical nanoparticles in polymer nanocomposites: rheological quantification and evidence of phase separation . Soft Matter , 2017 , 13 ( 22 ), 4088 − 4098 .

Lin, S. S. ; Li, B. K. ; Chen, T. T. ; Yu, W. ; Wang, X. H . Mechanical reinforcement in poly(propylene carbonate) nanocomposites using double percolation networks by dual volume exclusions . Compos. Sci. Technol. , 2018 , 167 , 364 − 370 .

Lin, S. S. ; You, W. ; Yu, W. ; Wang, X. H . Key factors in mechanical reinforcement by double percolation network: particle migration and shear stability of filler network . Polymer , 2019 , 182 , 121820 .

Wang, Y. M. ; Sun, M. H. ; Zhang, H. ; Lu, Y. D. ; You, W. ; Bian, F. G. ; Yu, W . Quantitative correlation between hierarchical nanofiller structure and rheology of polymer/fumed silica nanocomposites . Macromolecules , 2023 , 56 ( 3 ), 934 − 946 .

You, W. ; Yu, W . Slow linear viscoelastic relaxation of polymer nanocomposites: contribution from confined diffusion of nanoparticles . Macromolecules , 2019 , 52 ( 23 ), 9094 − 9104 .

陈诗依 , 尤伟 , 俞炜 . 纳米粒子交联类玻璃高分子材料的动力学行为和流变行为研究 . 高分子学报 , 2020 , 51 , 670 − 678 .

Li, B. K. ; Guo, Y. ; Steeman, P. ; Bulters, M. ; Yu, W . Shear-induced breakdown and agglomeration in nanoparticles filled polymer: the shift of phase boundary and kinetics . J. Rheol. , 2021 , 65 ( 3 ), 291 − 309 .

Zhang, H. ; You, W. ; Bian, F. G. ; Yu, W . Percolation to jamming in polymethylvinylsiloxane/silica nano-composites . Polymer , 2024 , 303 , 127107 .

Wang, J. ; Guo, Y. ; Yu, W. ; Zhou, C. X. ; Steeman, P . Linear and nonlinear viscoelasticity of polymer/silica nanocomposites: an understanding from modulus decomposition . Rheol. Acta , 2016 , 55 ( 1 ), 37 − 50 .

You, W. ; Cui, W. Z. ; Yu, W . Decoupling hydrodynamic and entanglement effects on the modulus reinforcement of grafted silica filled nanocomposites through thermal and rheological features . Polymer , 2021 , 213 , 123323 .

王一名 , 尤伟 , 俞炜 . 聚甲基丙烯酸甲酯/聚醋酸乙烯酯/纳米二氧化硅体系的相分离行为研究 . 高分子学报 , 2022 , 53 , 962 − 972 .

Cui, W. Z. ; You, W. ; Yu, W . Interplay of grafted and adsorbed chains at the polymer-particle interface in tuning the mechanical reinforcement in polymer nanocomposites . ACS Appl. Polym. Mater. , 2024 , 6 ( 3 ), 1843 − 1852 .

Schneider, G. J . Dynamics of nanocomposites . Curr. Opin. Chem. Eng. , 2017 , 16 , 65 − 77 .

戴利均 , 孙昭艳 . 聚合物纳米复合体系中聚合物结构及动力学研究进展 . 高等学校化学学报 , 2020 , 41 ( 5 ), 924 − 935 .

Bailey, E. J. ; Winey, K. I . Dynamics of polymer segments, polymer chains, and nanoparticles in polymer nanocomposite melts: a review . Prog. Polym. Sci. , 2020 , 105 , 101242 .

Sattar, M. A . Interface structure and dynamics in polymer-nanoparticle hybrids: a review on molecular mechanisms underlying the improved interfaces . ChemistrySelect , 2021 , 6 ( 20 ), 5068 − 5096 .

Cheng, S. ; Carroll, B. ; Bocharova, V. ; Carrillo, J. M. ; Sumpter, B. G. ; Sokolov, A. P . Focus: Structure and dynamics of the interfacial layer in polymer nanocomposites with attractive interactions . J. Chem. Phys. , 2017 , 146 ( 20 ), 203201 .

Cheng, S. W. ; Carroll, B. ; Lu, W. ; Carrillo, J. M Y. ; Martin, H. ; Holt, A. P. ; Kang, N. G. ; Bocharova, V. ; Mays, J. W. ; Sumpter, B. G. ; Dadmun, M. ; Sokolov, A. P . Interfacial properties of polymer nanocomposites: role of chain rigidity and dynamic heterogeneity length scale . Macromolecules , 2017 , 50 ( 6 ), 2397 − 2406 .

Popov, I. ; Carroll, B. ; Bocharova, V. ; Genix, A. C. ; Cheng, S. W. ; Khamzin, A. ; Kisliuk, A. ; Sokolov, A. P . Strong reduction in amplitude of the interfacial segmental dynamics in polymer nanocomposites . Macromolecules , 2020 , 53 ( 10 ), 4126 − 4135 .

Holt, A. P. ; Griffin, P. J. ; Bocharova, V. ; Agapov, A. L. ; Imel, A. E. ; Dadmun, M. D. ; Sangoro, J. R. ; Sokolov, A. P . Dynamics at the polymer/nanoparticle interface in poly(2-vinylpyridine)/silica nanocomposites . Macromolecules , 2014 , 47 ( 5 ), 1837 − 1843 .

Klonos, P. ; Kulyk, K. ; Borysenko, M. V. ; Gun’ko, V. M. ; Kyritsis, A. ; Pissis, P . Effects of molecular weight below the entanglement threshold on interfacial nanoparticles/polymer dynamics . Macromolecules , 2016 , 49 ( 24 ), 9457 − 9473 .

Holt, A. P. ; Sangoro, J. R. ; Wang, Y. Y. ; Agapov, A. L. ; Sokolov, A. P . Chain and segmental dynamics of poly(2-vinylpyridine) nanocomposites . Macromolecules , 2013 , 46 ( 10 ), 4168 − 4173 .

Carroll, B. ; Cheng, S. W. ; Sokolov, A. P . Analyzing the interfacial layer properties in polymer nanocomposites by broadband dielectric spectroscopy . Macromolecules , 2017 , 50 ( 16 ), 6149 − 6163 .

Yang, J. ; Melton, M. ; Sun, R. K. ; Yang, W. ; Cheng, S. W . Decoupling the polymer dynamics and the nanoparticle network dynamics of polymer nanocomposites through dielectric spectroscopy and rheology . Macromolecules , 2020 , 53 ( 1 ), 302 − 311 .

Senses, E. ; Akcora, P . An interface-driven stiffening me-chanism in polymer nanocomposites . Macromolecules , 2013 , 46 ( 5 ), 1868 − 1874 .

Lin, Y. ; Liu, L. P. ; Xu, G. M. ; Zhang, D. G. ; Guan, A. G. ; Wu, G. Z . Interfacial interactions and segmental dynamics of poly(vinyl acetate)/silica nanocomposites . J. Phys. Chem. C , 2015 , 119 ( 23 ), 12956 − 12966 .

Xia, Z. ; Wang, Y. ; Gong, K. ; Chen, W . An in situ stretching instrument combined with low field nuclear magnetic resonance (NMR): rheo-spin NMR . Rev. Sci. Instrum. , 2022 , 93 ( 3 ), 033905 .

Golitsyn, Y. ; Schneider, G. J. ; Saalwächter, K . Reduced-mobility layers with high internal mobility in poly(ethylene oxide)-silica nanocomposites . J. Chem. Phys. , 2017 , 146 ( 20 ), 203303 .

Fernández-de-Alba, C. ; Jimenez, A. M. ; Abbasi, M. ; Kumar, S. K. ; Saalwächter, K. ; Baeza, G. P . On the immobilized polymer fraction in attractive nano-composites: T g gradient versus interfacial layer . Macromolecules , 2021 , 54 ( 22 ), 10289 − 10299 .

Jouault, N. ; Crawford, M. K. ; Chi, C. ; Smalley, R. J. ; Wood, B. ; Jestin, J. ; Melnichenko, Y. B. ; He, L. ; Guise, W. E. ; Kumar, S. K . Polymer chain behavior in polymer nanocomposites with attractive interactions . ACS Macro Lett. , 2016 , 5 ( 4 ), 523 − 527 .

Kim, J. ; Thompson, B. R. ; Tominaga, T. ; Osawa, T. ; Egami, T. ; Förster, S. ; Ohl, M. ; Senses, E. ; Faraone, A. ; Wagner, N. J . Suppression of segmental chain dynamics on a particle's surface in well-dispersed polymer nanocomposites . ACS Macro Lett. , 2024 , 13 ( 6 ), 720 − 725 .

Cheng, S. ; Bocharova, V. ; Belianinov, A. ; Xiong, S. ; Kisliuk, A. ; Somnath, S. ; Holt, A. P. ; Ovchinnikova, O. S. ; Jesse, S. ; Martin, H. ; Etampawala, T. ; Dadmun, M. ; Sokolov, A. P . Unraveling the mechanism of nanoscale mechanical reinforcement in glassy polymer nanocomposites . Nano Lett. , 2016 , 16 ( 6 ), 3630 − 3637 .

Liang, X. B . Visualization of nanomechanical properties of polymer composites using atomic force microscopy . Polym. J. , 2023 , 55 , 913 − 920 .

Sargsyan, A. ; Tonoyan, A. ; Davtyan, S. ; Schick, C . The amount of immobilized polymer in PMMA SiO 2 nanocomposites determined from calorimetric data . Eur. Polym. J. , 2007 , 43 ( 8 ), 3113 − 3127 .

Long, D. ; Sotta, P . Stress relaxation of large amplitudes and long timescales in soft thermoplastic and filled elastomers . Rheol. Acta , 2007 , 46 ( 8 ), 1029 − 1044 .

Chen, Q. ; Gong, S. S. ; Moll, J. ; Zhao, D. ; Kumar, S. K. ; Colby, R. H . Mechanical reinforcement of polymer nanocomposites from percolation of a nanoparticle network . ACS Macro Lett. , 2015 , 4 ( 4 ), 398 − 402 .

Baeza, G. P. ; Dessi, C. ; Costanzo, S. ; Zhao, D. ; Gong, S. S. ; Alegria, A. ; Colby, R. H. ; Rubinstein, M. ; Vlassopoulos, D. ; Kumar, S. K . Network dynamics in nanofilled polymers . Nat. Commun. , 2016 , 7 , 11368 .

Liu, A. Y. ; Emamy, H. ; Douglas, J. F. ; Starr, F. W . Effects of chain length on the structure and dynamics of semidilute nanoparticle-polymer composites . Macromolecules , 2021 , 54 ( 7 ), 3041 − 3051 .

Zhou, Y. X. ; Schweizer, K. S . PRISM theory of local structure and phase behavior of dense polymer nanocomposites: improved closure approximation and comparison with simulation . Macromolecules , 2020 , 53 ( 22 ), 9962 − 9972 .

Zarybnicka, K. ; Ondreas, F. ; Lepcio, P. ; Kalina, M. ; Zboncak, M. ; Jancar, J . Thermodynamic parameters controlling nanoparticle spatial packing in polymer solutions . Macromolecules , 2020 , 53 ( 19 ), 8704 − 8713 .

Zhu, Z. Y. ; Thompson, T. ; Wang, S. Q. ; von Meerwall, E. D. ; Halasa, A . Investigating linear and nonlinear viscoe-lastic behavior using model silica-particle-filled polybuta-diene . Macromolecules , 2005 , 38 ( 21 ), 8816 − 8824 .

Mujtaba, A. ; Keller, M. ; Ilisch, S. ; Radusch, H. J. ; Beiner, M. ; Thurn-Albrecht, T. ; Saalwächter, K . Dete-ction of surface-immobilized components and their role in viscoelastic reinforcement of rubber-silica nanocomposites . ACS Macro Lett. , 2014 , 3 ( 5 ), 481 − 485 .

Yavitt, B. M. ; Salatto, D. ; Zhou, Y. X. ; Huang, Z. X. ; Endoh, M. ; Wiegart, L. ; Bocharova, V. ; Ribbe, A. E. ; Sokolov, A. P. ; Schweizer, K. S. ; Koga, T . Collective nanoparticle dynamics associated with bridging network formation in model polymer nanocomposites . ACS Nano , 2021 , 15 ( 7 ), 11501 − 11513 .

de Gennes, P. G . Polymers at an interface; a simplified view . Adv. Colloid Interface Sci. , 1987 , 27 ( 3-4 ), 189 − 209 .

Sprakel, J. ; van der Gucht, J. ; Cohen Stuart, M. A. ; Besseling, N. A . Brownian particles in transient polymer networks . Phys. Rev. E , 2008 , 77 , 061502 .

Liu, S. Q. ; Senses, E. ; Jiao, Y. ; Narayanan, S. ; Akcora, P . Structure and entanglement factors on dynamics of polymer-grafted nanoparticles . ACS Macro Lett. , 2016 , 5 ( 5 ), 569 − 573 .

Sorichetti, V. ; Hugouvieux, V. ; Kob, W . Structure and dynamics of a polymer-nanoparticle composite: effect of nanoparticle size and volume fraction . Macromolecules , 2018 , 51 ( 14 ), 5375 − 5391 .

Egorov, S. A . Anomalous nanoparticle diffusion in polymer solutions and melts: a mode-coupling theory study . J. Chem. Phys. , 2011 , 134 ( 8 ), 084903 .

Cai, L. H. ; Panyukov, S. ; Rubinstein, M . Mobility of nonsticky nanoparticles in polymer liquids . Macromolecules , 2011 , 44 ( 19 ), 7853 − 7863 .

Dell, Z. E. ; Schweizer, K. S . Theory of localization and activated hopping of nanoparticles in cross-linked networks and entangled polymer melts . Macromolecules , 2014 , 47 ( 1 ), 405 − 414 .

Mangal, R. ; Srivastava, S. ; Narayanan, S. ; Archer, L. A . Size-dependent particle dynamics in entangled polymer nanocomposites . Langmuir , 2016 , 32 ( 2 ), 596 − 603 .

Bailey, E. J. ; Griffin, P. J. ; Composto, R. J. ; Winey, K. I . Multiscale dynamics of small, attractive nanoparticles and entangled polymers in polymer nanocomposites . Macromolecules , 2019 , 52 ( 5 ), 2181 − 2188 .

Carroll, B. ; Bocharova, V. ; Carrillo, J. M Y. ; Kisliuk, A. ; Cheng, S. W. ; Yamamoto, U. ; Schweizer, K. S. ; Sumpter, B. G. ; Sokolov, A. P . Diffusion of sticky nanoparticles in a polymer melt: crossover from suppressed to enhanced transport . Macromolecules , 2018 , 51 ( 6 ), 2268 − 2275 .

Grabowski, C. A. ; Mukhopadhyay, A . Size effectof nano-particle diffusion in a polymer melt . Macromolecules , 2014 , 47 ( 20 ), 7238 − 7242 .

Wang, C. ; Lv, B. W. ; Hou, J. ; Wang, P. F. ; Miao, L. Z. ; Ci, H. L . Quantitative measurement of aggregation kinetics process of nanoparticles using nanoparticle tracking analysis and dynamic light scattering . J. Nanopart. Res. , 2019 , 21 ( 5 ), 87 .

Lurio, L. B. ; Lumma, D. ; Sandy, A. R. ; Borthwick, M. A. ; Falus, P. ; Mochrie, S. G. J. ; Pelletier, J. F. ; Sutton, M. ; Regan, L. ; Malik, A. ; Stephenson, G. B . Absence of scaling for the intermediate scattering function of a hard-sphere suspension: static and dynamic X-ray scattering from concentrated polystyrene latex spheres . Phys. Rev. Lett. , 2000 , 84 ( 4 ), 785 − 788 .

Cai, L. H. ; Panyukov, S. ; Rubinstein, M . Hopping diffusion of nanoparticles in polymer matrices . Macromolecules , 2015 , 48 ( 3 ), 847 − 862 .

Einstein, A . Eine neue bestimmung der moleküld-imensionen . Ann. Der Phys. , 1906 , 324 ( 2 ), 289 − 306 .

Batchelor, G. K . The stress generated in a non-dilute suspension of elongated particles by pure straining motion . J. Fluid Mech. , 1971 , 46 ( 4 ), 813 − 829 .

Batchelor, G. K. ; Green, J. T . The determination of the bulk stress in a suspension of spherical particles to order c 2 . J. Fluid Mech. , 1972 , 56 ( 3 ), 401 .

Krieger, I. M. ; Dougherty, T. J . A mechanism for non-Newtonian flow in suspensions of rigid spheres . Trans. Soc. Rheol. , 1959 , 3 ( 1 ), 137 − 152 .

Song, Y. H. ; Zheng, Q . A guide for hydrodynamic reinforcement effect in nanoparticle-filled polymers . Crit. Rev. Solid State Mater. Sci. , 2016 , 41 ( 4 ), 318 − 346 .

Song, Y. H. ; Zheng, Q . Linear viscoelasticity of poly-mer melts filled with nano-sized fillers . Polymer , 2010 , 51 ( 14 ), 3262 − 3268 .

Rishi, K. ; Beaucage, G. ; Kuppa, V. ; Mulderig, A. ; Narayanan, V. ; McGlasson, A. ; Rackaitis, M. ; Ilavsky, J . Impact of an emergent hierarchical filler network on nanocomposite dynamics . Macromolecules , 2018 , 51 ( 20 ), 7893 − 7904 .

浏览量

514

下载量

CSCD

文章被引用时，请邮件提醒。

提交

工具集

关联资源

瞬时纳米沉淀法制备壳聚糖/三聚磷酸钠纳米粒子及其siRNA递送性能评价

受限态高分子的微观动力学与流变学行为研究进展

类玻璃高分子流变学研究进展

机械互锁聚合物的流变学研究