- Physical Review Journals
All JournalsPhysics Magazine
Access Provided by Xinjiang University

Physical Review Materials

Reuse & Permissions

It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

Export citation

Export citation

Choose format for download:

Download Citation
  • Open Access
  • Access by Xinjiang University

Exploration of complex nanostructures in block copolymers

Hojun Lee, Jihoon Kim, and Moon Jeong Park*

  • Department of Chemistry, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongsangbuk-do 37673, Republic of Korea

  • *Corresponding author: moonpark@postech.ac.kr
PDF

Phys. Rev. Materials 8, 020302 – Published 13 February, 2024

DOI: https://doi.org/10.1103/PhysRevMaterials.8.020302

Abstract

The exploration of nanoscale morphologies with three-dimensional spatial arrangements in block copolymers involves the manipulation of compositional fluctuations at interfaces, induction of conformational asymmetry, and design of complex architectures. Despite the abundance of triply periodic minimal surfaces identified to date, the experimental demonstration of thermodynamically stable complex nanostructures with high-packing frustration remains limited. This research update focuses on the importance of molecular interactions for stabilizing complex nanostructures and proposes the use of end-group chemistry as a versatile method for realizing thermodynamically stable network structures with high-packing frustration in simple linear diblock copolymers. The proposed approach substantially alters phase diagrams and reveals unprecedented network structures in block copolymers. Ongoing research has the potential to generate even more diverse and stable nanostructures, thereby advancing nanotechnology and expanding our understanding of polymers and materials science.

View figure in article

Physics Subject Headings (PhySH)

Collections

This article appears in the following collection:

Self-Assembly of Complex Phases in Block Copolymer Materials

The Editors of Physical Review Materials are pleased to present the Collection on Self-Assembly of Complex Phases in Block Copolymer Materials, highlighting one of the most exciting fields in polymer science. Block copolymers offer an excellent model system for comprehending symmetry breaking in soft matter, as well as a unique platform for designing nanostructured materials. This Collection is being guest-edited by Kevin Dorfman from the University of Minnesota and Chris Bates from the University of California - Santa Barbara.

Article Text

References (98)

  1. F. H. Schacher, P. A. Rupar, and I. Manners, Functional block copolymers: Nanostructured materials with emerging applications, Angew. Chem., Int. Ed. Engl. 51, 7898 (2012).
  2. L. Martín-Moreno, F. J. García-Vidal, and A. M. Somoza, Self-assembled triply periodic minimal surfaces as molds for photonic band gap materials, Phys. Rev. Lett. 83, 73 (1999).
  3. J. B. Pendry, A. J. Holden, W. J. Stewart, and I. Youngs, Extremely low frequency plasmons in metallic mesostructures, Phys. Rev. Lett. 76, 4773 (1996).
  4. D. R. Smith, W. J. Padilla, D. C. Vier, S. C. Nemat-Nasser, and S. Schultz, Composite medium with simultaneously negative permeability and permittivity, Phys. Rev. Lett. 84, 4184 (2000).
  5. F. S. Bates, M. A. Hillmyer, T. P. Lodge, C. M. Bates, K. T. Delaney, and G. H. Fredrickson, Multiblock polymers: Panacea or Pandora's box?, Science 336, 434 (2012).
  6. C. Nowak and F. A. Escobedo, Optimizing the network topology of block copolymer liquid crystal elastomers for enhanced extensibility and toughness, Phys. Rev. Mater. 1, 035601 (2017).
  7. R. P. Collanton and K. D. Dorfman, Interfacial geometry in particle-forming phases of diblock copolymers, Phys. Rev. Mater. 6, 015602 (2022).
  8. F. S. Bates, Polymer-polymer phase behavior, Science 251, 898 (1991).
  9. F. S. Bates and G. H. Fredrickson, Block copolymer thermodynamics: Theory and experiment, Annu. Rev. Phys. Chem. 41, 525 (1990).
  10. E. Helfand, Block copolymer theory. III. Statistical mechanics of the microdomain structure, Macromolecules 8, 552 (1975).
  11. E. Helfand, Block copolymers, polymer-polymer interfaces, and the theory of inhomogeneous polymers, Acc. Chem. Res. 8, 295 (1975).
  12. L. Leibler, Theory of microphase separation in block copolymers, Macromolecules 13, 1602 (1980).
  13. C. Sinturel, F. S. Bates, and M. A. Hillmyer, High χ-low N block polymers: How far can we go?. ACS Macro Lett. 4, 1044 (2015).
  14. L. Kumar, S. Singh, A. Horechyy, A. Fery, and B. Nandan, Block copolymer template-directed catalytic systems: Recent progress and perspectives, Membranes 11, 318 (2021).
  15. Y. C. Lu, P. C. Tseng, M. J. Yang, C. J. Wang, Y. C. Ling, C. F. Lin, and H. Y. Hsueh, Fabrication of gyroid-structured metal/semiconductor nanoscaffolds with ultrasensitive SERS detection via block copolymer templating, Adv. Opt. Mater. 11, 2202280 (2023).
  16. H.-Y. Hsueh, Y.-C. Ling, H.-F. Wang, L.-Y. C. Chien, Y.-C. Hung, E. L. Thomas, and R. -M. Ho, Shifting networks to achieve subgroup symmetry properties, Adv. Mater. 26, 3225 (2014).
  17. E.-L. Lin, W.-L. Hsu, and Y.-W. Chiang, Trapping structural coloration by a bioinspired gyroid microstructure in solid state, ACS Nano 12, 485 (2018).
  18. R. Dehmel, A. Nicolas, M. R. J. Scherer, and U. Steiner, 3D nanostructured conjugated polymers for optical applications, Adv. Funct. Mater. 25, 6900 (2015).
  19. Y. La, C. Park, T. J. Shin, S. H. Joo, S. Kang, and K. T. Kim, Colloidal inverse bicontinuous cubic membranes of block copolymers with tunable surface functional groups, Nat. Chem. 6, 534 (2014).
  20. H. Sai, K. W. Tan, K. Hur, E. Asenath-Smith, R. Hovden, Y. Jiang, M. Riccio, D. A. Muller, V. Elser, L. A. Estroff, S. M. Gruner, and U. Wiesner, Hierarchical porous polymer scaffolds from block copolymers, Science 341, 530 (2013).
  21. H.-Y. Hsueh, H.-Y. Chen, M.-S. She, C.-K. Chen, R.-M. Ho, S. Gwo, H. Hasegawa, and E. L. Thomas, Inorganic gyroid with exceptionally low refractive index from block copolymer templating, Nano Lett. 10, 4994 (2010).
  22. K. Hur, Y. Francescato, V. Giannini, S. A. Maier, R. G. Hennig, and U. Wiesner, Three-dimensionally isotropic negative refractive index materials from block copolymer self-assembled chiral gyroid networks, Angew. Chem., Int. Ed. 50, 11985 (2011).
  23. K. D. Dorfman, Frank–Kasper phases in block polymers, Macromolecules 54, 10251 (2021).
  24. L. Yan, C. Rank, S. Mecking, and K. I. Winey, Gyroid and other ordered morphologies in single-ion conducting polymers and their impact on ion conductivity, J. Am. Chem. Soc. 142, 857 (2020).
  25. S. Choudhury, M. Agrawal, P. Formanek, D. Jehnichen, D. Fischer, B. Krause, V. Albrecht, M. Stamm, and L. Ionov, Nanoporous cathodes for high-energy Li-S batteries from gyroid block copolymer templates, ACS Nano 9, 6147 (2015).
  26. D. A. Hajduk, P. E. Harper, S. M. Gruner, C. C. Honeker, G. Kim, L. J. Fetters, and G. Kim, The gyroid: A new equilibrium morphology in weakly segregated diblock copolymers, Macromolecules 27, 4063 (1994).
  27. E. W. Cochran, C. J. Garcia-Cervera, and G. H. Fredrickson, Stability of the gyroid phase in diblock copolymers at strong segregation, Macromolecules 39, 2449 (2006).
  28. S. Cui, B. Zhang, L. Shen, F. S. Bates, and T. P. Lodge, Core–shell gyroid in ABC bottlebrush block terpolymers, J. Am. Chem. Soc. 144, 21719 (2022).
  29. M. W. Matsen, Effect of architecture on the phase behavior of AB-type block copolymer melts, Macromolecules 45, 2161 (2012).
  30. P. Padmanabhan, F. Martinez-Veracoechea, and F. A. Escobedo, Computation of free energies of cubic bicontinuous phases for blends of diblock copolymer and selective homopolymer, Macromolecules 49, 5232 (2016).
  31. M. W. Matsen and M. Schick, Stable and unstable phases of a linear multiblock copolymer melt, Macromolecules 27, 7157 (1994).
  32. Q. Du, Z. Wang, S. Zhou, J. Zhao, and V. Kumar, Searching for cluster Lego blocks for three-dimensional and two-dimensional assemblies, Phys. Rev. Mater. 5, 066001 (2021).
  33. A. Travesset, Nanoparticle superlattices as quasi-Frank-Kasper phases, Phys. Rev. Lett. 119, 115701 (2017).
  34. M. W. Matsen and F. S. Bates, Origins of complex self-assembly in block copolymers, Macromolecules 29, 7641 (1996).
  35. A. J. Meuler, M. A. Hillmyer, and F. S. Bates, Ordered network mesostructures in block polymer materials, Macromolecules 42, 7221 (2009).
  36. R. Roy, J. K. Park, W. S. Young, S. E. Mastroianni, M. S. Tureau, and T. H. Epps, Double-gyroid network morphology in tapered diblock copolymers, Macromolecules 44, 3910 (2011).
  37. J. R. Brown, S. W. Sides, and L. M. Hall, Phase behavior of tapered diblock copolymers from self-consistent field theory, ACS Macro Lett. 2, 1105 (2013).
  38. B. Yu, R. Li, and R. A. Segalman, Tuning the double gyroid phase window in block copolymers via polymer chain conformation near the interface, Macromolecules 54, 5388 (2021).
  39. N. A. Lynd and M. A. Hillmyer, Influence of polydispersity on the self-assembly of diblock copolymers, Macromolecules 38, 8803 (2005).
  40. N. A. Lynd, A. J. Meuler, and M. A. Hillmyer, Polydispersity and block copolymer self-assembly, Prog. Polym. Sci. 33, 875 (2008).
  41. A. J. Meuler, C. J. Ellison, M. A. Hillmyer, and F. S. Bates, Polydispersity-induced stabilization of the core–shell gyroid, Macromolecules 41, 6272 (2008).
  42. M. W. Matsen, Phase behavior of block copolymer/homopolymer blends, Macromolecules 28, 5765 (1995).
  43. K. I. Winey, E. L. Thomas, and L. J. Fetters, The ordered bicontinuous double-diamond morphology in diblock copolymer/homopolymer blends, Macromolecules 25, 422 (1992).
  44. F. J. Martinez-Veracoechea and F. A. Escobedo, Bicontinuous phases in diblock copolymer/homopolymer blends: Simulation and self-consistent field theory, Macromolecules 42, 1775 (2009).
  45. T. H. Epps, E. W. Cochran, C. M. Hardy, T. S. Bailey, R. S. Waletzko, and F. S. Bates, Network phases in ABC triblock copolymers, Macromolecules 37, 7085 (2004).
  46. Y. Masushita, J. Suzuki, and M. Seki, Surfaces of tricontinuous structure formed by an ABC triblock copolymer in bulk, Phys. B: Condens. Matter 248, 238 (1998).
  47. T. A. Shefelbine, M. E. Vigild, M. W. Matsen, D. A. Hajduk, M. A. Hillmyer, E. L. Cussler, and F. S. Bates, Core−shell gyroid morphology in a poly(isoprene-block-styrene-block-dimethylsiloxane) triblock copolymer, J. Am. Chem. Soc. 121, 8457 (1999).
  48. T. S. Bailey, C. M. Hardy, T. H. Epps, and F. S. Bates, A noncubic triply periodic network morphology in poly(isoprene-b-styrene-b-ethylene oxide) triblock copolymers, Macromolecules 35, 7007 (2002).
  49. M. Takenaka, T. Wakada, S. Akasaka, S. Nishitsuji, K. Saijo, H. Shimizu, M. I. Kim, and H. Hasegawa, Orthorhombic Fddd network in diblock copolymer melts, Macromolecules 40, 4399 (2007).
  50. S. Lee, M. J. Bluemle, and F. S. Bates, Discovery of a Frank-Kasper σ phase in sphere-forming block copolymer melts, Science 330, 349 (2010).
  51. J. Zhang and F. S. Bates, Dodecagonal quasicrystalline morphology in a poly(styrene-b-isoprene-b-styrene-b-ethylene oxide) tetrablock terpolymer, J. Am. Chem. Soc. 134, 7636 (2012).
  52. S. Chanpuriya, K. Kim, J. Zhang, S. Lee, A. Arora, K. D. Dorfman, K. T. Delaney, G. H. Fredrickson, and F. S. Bates, Cornucopia of nanoscale ordered phases in sphere-forming tetrablock terpolymers, ACS Nano 10, 4961 (2016).
  53. S. T. Milner, Chain architecture and asymmetry in copolymer microphases, Macromolecules 27, 2333 (1994).
  54. P. D. Olmsted and S. T. Milner, Strong segregation theory of bicontinuous phases in block copolymers, Macromolecules 31, 4011 (1998).
  55. G. M. Grason, B. A. DiDonna, and R. D. Kamien, Geometric theory of diblock copolymer phases, Phys. Rev. Lett. 91, 058304 (2003).
  56. G. M. Grason and R. D. Kamien, Interfaces in diblocks:  A study of miktoarm star copolymers, Macromolecules 37, 7371 (2004).
  57. N. Xie, W. Li, F. Qiu, and A.-C. Shi, σ Phase formed in conformationally asymmetric AB-type block copolymers, ACS Macro Lett. 3, 906 (2014).
  58. Q. Dong and W. Li, Effect of molecular asymmetry on the formation of asymmetric nanostructures in ABC-type block copolymers, Macromolecules 54, 203 (2021).
  59. Y. Seo, D. Woo, L. Li, W. Li, and J. K. Kim, Phase behavior of PS-(PS−b−P2VP)3 miktoarm star copolymer, Macromolecules 54, 7822 (2021).
  60. M. W. Matsen and F. S. Bates, Block copolymer microstructures in the intermediate-segregation regime, J. Chem. Phys. 106, 2436 (1997).
  61. G. M. Grason and R. D. Kamien, Self-consistent field theory of multiply branched block copolymer melts, Phys. Rev. E 71, 051801 (2005).
  62. M. Watanabe, Y. Asai, J. Suzuki, A. Takano, and Y. Matsushita, Frank-Kasper A15 phase formed in ABn block-graft copolymers with large numbers of graft chains, Macromolecules 53, 10217 (2020).
  63. M. W. Bates, J. Lequieu, S. M. Barbon, R. M. Lewis, K. T. Delaney, A. Anastasaki, C. J. Hawker, G. H. Fredrickson, and C. M. Bates, Stability of the A15 phase in diblock copolymer melts, Proc. Natl. Acad. Sci. USA 116, 13194 (2019).
  64. C. Y. Chu, W. F. Lin, J. C. Tsai, C. S. Lai, S. C. Lo, H. L. Chen, and T. Hashimoto, Order–order transition between equilibrium ordered bicontinuous nanostructures of double diamond and double gyroid in stereoregular block copolymer, Macromolecules 45, 2471 (2012).
  65. C.-H. Lin, T. Higuchi, H.-L. Chen, J.-C. Tsai, H. Jinnai, and T. Hashimoto, Stabilizing the ordered bicontinuous double diamond structure of diblock copolymer by configurational regularity, Macromolecules 51, 4049 (2018).
  66. C. Y. Chu, X. Jiang, H. Jinnai, R. Y. Pei, W. F. Lin, J. C. Tsai, and H. L. Chen, Real-space evidence of the equilibrium ordered bicontinuous double diamond structure of a diblock copolymer, Soft Matter 11, 1871 (2015).
  67. M. W. Bates, S. M. Barbon, A. E. Levi, R. M. Lewis III, H. K. Beech, K. M. Vonk, C. Zhang, G. H. Fredrickson, C. J. Hawker, and C. M. Bates, Synthesis and self-assembly of ABn miktoarm star polymers, ACS Macro Lett. 9, 396 (2020).
  68. M. J. Park and N. P. Balsara, Phase behavior of symmetric sulfonated block copolymers, Macromolecules 41, 3678 (2008).
  69. C. E. Sing, J. W. Zwanikken, and M. Olvera de la Cruz, Electrostatic control of block copolymer morphology, Nat. Mater. 13, 694 (2014).
  70. S. Y. Kim, S. Kim, and M. J. Park, Enhanced proton transport in nanostructured polymer electrolyte/ionic liquid membranes under water-free conditions, Nat. Commun. 1, 88 (2010).
  71. O. Kim, K. Kim, U. H. Choi, and M. J. Park, Tuning anhydrous proton conduction in single-ion polymers by crystalline ion channels, Nat. Commun. 9, 5029 (2018).
  72. O. Kim, S. Y. Kim, H. Ahn, C. W. Kim, Y. M. Rhee, and M. J. Park, Phase behavior and conductivity of sulfonated block copolymers containing heterocyclic diazole-based ionic liquids, Macromolecules 45, 8702 (2012).
  73. O. Kim, S. Y. Kim, J. Lee, and M. J. Park, Building less tortuous ion-conduction pathways using block copolymer electrolytes with a well-defined cubic symmetry, Chem. Mater. 28, 318 (2016).
  74. H. Y. Jung, O. Kim, and M. J. Park, Ion transport in nanostructured phosphonated block copolymers containing ionic liquids, Macromol. Rapid Commun. 37, 1116 (2016).
  75. J. Min, H. Jung, S. Jung, B. Lee, C. Y. Son, and M. J. Park, Enhancing ion transport in charged block copolymers by stabilizing low symmetry morphology: Electrostatic control of interfaces, Proc. Natl. Acad. Sci. USA 118, e2107987118 (2021).
  76. M. W. Matsen and F. S. Bates, Conformationally asymmetric block copolymers, J. Polym. Sci., Part B: Polym. Phys. 35, 945 (1997).
  77. K. Kim, M. W. Schulze, A. Arora, R. M. Lewis, M. A. Hillmyer, K. D. Dorfman, and F. S. Bates, Thermal processing of diblock copolymer melts mimics metallurgy, Science 356, 520 (2017).
  78. T.-Y. Lo, C.-C. Chao, R.-M. Ho, P. Georgopanos, A. Avgeropoulos, and E. L. Thomas, Phase transitions of polystyrene-b-poly(dimethylsiloxane) in solvents of varying selectivity, Macromolecules 46, 7513 (2013).
  79. C. Y. Chang, G. M. Manesi, C. Y. Yang, Y. C. Hung, K. C. Yang, P. T. Chiu, A. Avgeropoulos, and R. M. Ho, Mesoscale networks and corresponding transitions from self-assembly of block copolymers, Proc. Natl. Acad. Sci. USA 118, e2022275118 (2021).
  80. X. Zeng, G. Ungar, and M. Impéror-Clerc, A triple-network tricontinuous cubicliquid crystal, Nat. Mater. 4, 562 (2005).
  81. Y. Cao, M. Alaasar, L. Zhang, C. Zhu, C. Tschierske, and F. Liu, Supramolecular meso-trick: Ambidextrous mirror symmetry breaking in a liquid crystalline network with tetragonal symmetry, J. Am. Chem. Soc. 144, 6936 (2022).
  82. S. Poppe, C. Chen, F. Liu, and C. Tschierske, A skeletal double gyroid formed by single coaxial bundles of catechol based bolapolyphiles, Chem. Commun. 54, 11196 (2018).
  83. X. Zeng, M. Prehm, G. Ungar, C. Tschierske, and F. Liu, Formation of a double diamond cubic phase by thermotropic liquid crystalline self-assembly of bundled bolaamphiphiles, Angew. Chem., Int. Ed. 55, 8324 (2016).
  84. X. Zeng, S. Poppe, A. Lehmann, M. Prehm, C. Chen, F. Liu, H. Lu, G. Ungar, and C. Tschierske, A self-assembled bicontinuous cubic phase with a single-diamond network, Angew. Chem., Int. Ed. 58, 7375 (2019).
  85. S. Poppe, X. Cheng, C. Chen, X. Zeng, R. B. Zhang, F. Liu, G. Ungar, and C. Tschierske, Liquid organic frameworks: The single-network “Plumber's Nightmare” bicontinuous cubic liquid crystal, J. Am. Chem. Soc. 142, 3296 (2020).
  86. C. Tschierske, Development of structural complexity by liquid-crystal self-assembly, Angew. Chem., Int. Ed. 52, 8828 (2013).
  87. Z. Su, C.-h. Hsu, Z. Gong, X. Feng, J. Huang, R. Zhang, Y. Wang, J. Mao, C. Wesdemiotis, T. Li, S. Seifert, W. Zhang, T. Aida, M. Huang, and S. Z. D. Cheng, Identification of a Frank-Kasper Z phase from shape amphiphile self-assembly, Nat. Chem. 11, 899 (2019).
  88. K. Yue, M. Huang, R. L. Marson, J. He, J. Huang, Z. Zhou, J. Wang, C. Liu, X. Yan, K. Wu, Z. Guo, H. Liu, W. Zhang, P. Ni, C. Wesdemiotis, W.-B. Zhang, S. C. Glotzer, and S. Z. D. Cheng, Geometry induced sequence of nanoscale Frank–Kasper and quasicrystal mesophases in giant surfactants, Proc. Natl. Acad. Sci. USA 113, 14195 (2016).
  89. J. Huang, Z. Su, M. Huang, R. Zhang, J. Wang, X. Feng, R. Zhang, W. Shan, X.-Y. Yan, Q.-Y. Guo, T. Liu, Y. Liu, Y. Cui, X. Li, A.-C. Shi, and S. Z. D. Cheng, Spherical supramolecular structures constructed via chemically symmetric perylene bisimides: Beyond columnar assembly, Angew. Chem., Int. Ed. 59, 18563 (2020).
  90. F. Ishiwari, G. Okabe, H. Ogiwara, T. Kajitani, M. Tokita, M. Takata, and T. Fukushima, Terminal functionalization with a triptycene motif that dramatically changes the structural and physical properties of an amorphous polymer, J. Am. Chem. Soc. 140, 13497 (2018).
  91. V. Schädler, J. Spickermann, H. J. Räder, and U. Wiesner, Synthesis and characterization of α,ω-macrozwitterionic block copolymers of styrene and isoprene, Macromolecules 29, 4865 (1996).
  92. V. Schädler and U. Wiesner, Salt-controlled lamellar spacing in ionically end-capped symmetric diblock copolymers, Macromolecules 30, 6698 (1997).
  93. G. Jo, H. Ahn, and M. J. Park, Simple route for tuning the morphology and conductivity of polymer electrolytes: One end functional group is enough, ACS Macro Lett. 2, 990 (2013).
  94. H. Y. Jung, P. Mandal, G. Jo, O. Kim, M. Kim, K. Kwak, and M. J. Park, Modulating ion transport and self-assembly of polymer electrolytes via end-group chemistry, Macromolecules 50, 3224 (2017).
  95. A. Reddy, M. S. Dimitriyev, and G. M. Grason, Medial packing and elastic asymmetry stabilize the double-gyroid in block copolymers, Nat. Commun. 13, 2629 (2022).
  96. M. S. Dimitriyev, A. Reddy, and G. M. Grason, Medial packing, frustration, and competing network phases in strongly segregated block copolymers, Macromolecules 56, 7184 (2023).
  97. A. Reddy, X. Feng, E. L. Thomas, and G. M. Grason, Block copolymers beneath the surface: Measuring and modeling complex morphology at the subdomain scale, Macromolecules 54, 9223 (2021).
  98. H. Lee, S. Kwon, J. Min, S.-M. Jin, J. H. Hwang, E. Lee, W. B. Lee, and M. J. Park, Thermodynamically stable plumber's nightmare structures in block copolymers, Science 383, 70 (2024).

Outline

Information

Phys. Rev. Materials 8, 020302– Published 13 February, 2024
  • Received 20 November 2023
  • Accepted 16 January 2024
Crossmark - Check for updates button
Creative Commons Logo

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation