SCIENCE CHINA Materials, Volume 62 , Issue 12 : 1921-1933(2019) https://doi.org/10.1007/s40843-019-9580-y

Effect of ketyl radical on the structure and performance of holographic polymer/liquid-crystal composites

More info
  • ReceivedJun 27, 2019
  • AcceptedAug 7, 2019
  • PublishedSep 2, 2019


Holographic polymer/liquid-crystal composites, which are periodically ordered materials with alternative polymer-rich and liquid-crystal-rich phases, have drawn increasing interest due to their unique capabilities of reconstructing colored three-dimensional (3D) images and enabling the electro-optic response. They are formed via photopolymerization induced phase separation upon exposure to laser interference patterns, where a fast photopolymerization is required to facilitate the holographic patterning. Yet, the fast photopolymerization generally leads to depressed phase separation and it remains challenging to boost the holographic performance via kinetics control. Herein, we disclose that the ketyl radical inhibition is able to significantly boost the phase separation and holographic performance by preventing the proliferated diffusion of initiating radicals from the constructive to the destructive regions. Dramatically depressed phase separation is caused when converting the inhibiting ketyl radical to a new initiating radical, indicating the significance of ketyl radical inhibition when designing high performance holographic polymer composites.

Funded by

This work was financially supported by the National Natural Science Foundation of China(NSFC,51433002,51773073)

the HUST peak boarding program

the National Science Foundation(NSF)

the Fundamental Research Funds for the Central Universities(2019kfyRCPY089)


We thank the financial supports from the National Natural Science Foundation of China (51433002 and 51773073), HUST peak boarding program, the National Science Foundation (NSF) of Hubei Scientific Committee (2016CFA001) and the Fundamental Research Funds for the Central Universities (2019kfyRCPY089). We also thank the technical assistance from HUST Analytical & Testing Center.

Interest statement

The authors declare no competing financial interest.

Contributions statement

Li MD, Xie X and Peng H gave the direction of the experiments; Zhao X and Sun S conducted the experiments together; Zhao Y participated in the discussion; Liao RZ obtained the DFT calculation results; Liao Y gave suggestions to the experiments and revised the manuscript with Peng H.

Author information

Xiaoyu Zhao received his Master’s degree from Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences in 2016. He is now a PhD candidate at Huazhong University of Science and Technology (HUST) under the supervision of Prof. Xiaolin Xie and Prof. Haiyan Peng. His current interest focuses on photopolymerization mechanism and applications.

Ming-De Li obtained his PhD degree at the University of Hong Kong in 2012. Then he conducted his postdoctoral research at the University of California, Berkeley and The University of Hong Kong. Now, he is a professor at Shantou University. His current interest is in the ultrafast laser spectroscopies.

Haiyan Peng received his PhD degree from HUST in 2014. He visited the University of Colorado Boulder from 2012 to 2014, sponsored by the CSC. Then he did research as an Assistant Professor at Guangzhou Institute of Advanced Technology, Chinese Academy of Sciences, and conducted postdoctoral research at City University of Hong Kong. He has been an Associate Professor at HUST since 2016.


Supplementary information

Supporting data are available in the online version of the paper.


[1] Gabor D. A new microscopic principle. Nature, 1948, 161: 777-778 CrossRef PubMed ADS Google Scholar

[2] Gorkhover T, Ulmer A, Ferguson K, et al. Femtosecond X-ray Fourier holography imaging of free-flying nanoparticles. Nat Photon, 2018, 12: 150-153 CrossRef ADS arXiv Google Scholar

[3] Tikan A, Bielawski S, Szwaj C, et al. Single-shot measurement of phase and amplitude by using a heterodyne time-lens system and ultrafast digital time-holography. Nat Photon, 2018, 12: 228-234 CrossRef ADS Google Scholar

[4] Leite IT, Turtaev S, Jiang X, et al. Three-dimensional holographic optical manipulation through a high-numerical-aperture soft-glass multimode fibre. Nat Photon, 2017, 12: 33-39 CrossRef ADS Google Scholar

[5] Vyas S, Chia YH, Luo Y. Conventional volume holography for unconventional airy beam shapes. Opt Express, 2018, 26: 21979-21991 CrossRef PubMed ADS Google Scholar

[6] Melde K, Mark AG, Qiu T, et al. Holograms for acoustics. Nature, 2016, 537: 518-522 CrossRef PubMed ADS Google Scholar

[7] van den Heuvel M, Prenen AM, Gielen JC, et al. Patterns of diacetylene-containing peptide amphiphiles using polarization holography. J Am Chem Soc, 2009, 131: 15014-15017 CrossRef PubMed Google Scholar

[8] Kobayashi Y, Abe J. Real-time dynamic hologram of a 3D object with fast photochromic molecules. Adv Opt Mater, 2016, 4: 1354-1357 CrossRef Google Scholar

[9] Blanche PA, Bablumian A, Voorakaranam R, et al. Holographic three-dimensional telepresence using large-area photorefractive polymer. Nature, 2010, 468: 80-83 CrossRef PubMed ADS Google Scholar

[10] Ozaki M, Kato J, Kawata S. Surface-plasmon holography with white-light illumination. Science, 2011, 332: 218-220 CrossRef PubMed ADS Google Scholar

[11] Chen G, Ni M, Peng H, et al. Photoinitiation and inhibition under monochromatic green light for storage of colored 3D images in holographic polymer-dispersed liquid crystals. ACS Appl Mater Interfaces, 2017, 9: 1810-1819 CrossRef Google Scholar

[12] Xie XL, Peng HY, Zhou XP, et al. Visible Light Photoinitiating System for Preparing High Diffraction Efficiency Hologram Optical Polymer Material. USA Patent, US 9753431 B2, 2017-09-05. Google Scholar

[13] Peng H, Bi S, Ni M, et al. Monochromatic visible light “photoinitibitor”: Janus-faced initiation and inhibition for storage of colored 3D images. J Am Chem Soc, 2014, 136: 8855-8858 CrossRef PubMed Google Scholar

[14] Ni M, Peng H, Liao Y, et al. 3D image storage in photopolymer/ZnS nanocomposites tailored by “photoinitibitor”. Macromolecules, 2015, 48: 2958-2966 CrossRef ADS Google Scholar

[15] Li X, Ren H, Chen X, et al. Athermally photoreduced graphene oxides for three-dimensional holographic images. Nat Commun, 2015, 6: 6984 CrossRef PubMed ADS Google Scholar

[16] Luo Y, Gelsinger PJ, Barton JK, et al. Optimization of multiplexed holographic gratings in PQ-PMMA for spectral-spatial imaging filters. Opt Lett, 2008, 33: 566-568 CrossRef PubMed ADS Google Scholar

[17] Yu R, Li S, Chen G, et al. Monochromatic “photoinitibitor”-mediated holographic photopolymer electrolytes for lithium-ion batteries. Adv Sci, 2019, 6: 1900205 CrossRef PubMed Google Scholar

[18] Shen W, Wang L, Chen G, et al. A facile route towards controllable electric-optical performance of polymer-dispersed liquid crystal via the implantation of liquid crystalline epoxy network in conventional resin. Polymer, 2019, 167: 67-77 CrossRef Google Scholar

[19] Shen W, Wang L, Zhong T, et al. Electrically switchable light transmittance of epoxy-mercaptan polymer/nematic liquid crystal composites with controllable microstructures. Polymer, 2019, 160: 53-64 CrossRef Google Scholar

[20] Zhao D, Zhou W, Cui X, et al. Alignment of liquid crystals doped with nickel nanoparticles containing different morphologies. Adv Mater, 2011, 23: 5779-5784 CrossRef PubMed Google Scholar

[21] Hu X, de Haan LT, Khandelwal H, et al. Cell thickness dependence of electrically tunable infrared reflectors based on polymer stabilized cholesteric liquid crystals. Sci China Mater, 2017, 61: 745-751 CrossRef Google Scholar

[22] Bunning TJ, Natarajan LV, Tondiglia VP, et al. Holographic polymer-dispersed liquid crystals (H-PDLCs). Annu Rev Mater Sci, 2000, 30: 83-115 CrossRef ADS Google Scholar

[23] White TJ, Natarajan LV, Tondiglia VP, et al. Monomer functionality effects in the formation of thiol−ene holographic polymer dispersed liquid crystals. Macromolecules, 2007, 40: 1121-1127 CrossRef ADS Google Scholar

[24] Peng H, Yu L, Chen G, et al. Liquid crystalline nanocolloids for the storage of electro-optic responsive images. ACS Appl Mater Interfaces, 2019, 11: 8612-8624 CrossRef Google Scholar

[25] Ni M, Chen G, Wang Y, et al. Holographic polymer nanocomposites with ordered structures and improved electro-optical performance by doping POSS. Compos Part B-Eng, 2019, 174: 107045 CrossRef Google Scholar

[26] Yagci Y, Jockusch S, Turro NJ. Photoinitiated polymerization: Advances, challenges, and opportunities. Macromolecules, 2010, 43: 6245-6260 CrossRef ADS Google Scholar

[27] Dadashi-Silab S, Doran S, Yagci Y. Photoinduced electron transfer reactions for macromolecular syntheses. Chem Rev, 2016, 116: 10212-10275 CrossRef PubMed Google Scholar

[28] Aguirre-Soto A, Lim CH, Hwang AT, et al. Visible-light organic photocatalysis for latent radical-initiated polymerization via 2e/1H+ transfers: Initiation with parallels to photosynthesis. J Am Chem Soc, 2014, 136: 7418-7427 CrossRef PubMed Google Scholar

[29] Xi W, Pattanayak S, Wang C, et al. Clickable nucleic acids: Sequence-controlled periodic copolymer/oligomer synthesis by orthogonal thiol-X reactions. Angew Chem Int Ed, 2015, 54: 14462-14467 CrossRef PubMed Google Scholar

[30] Zhang J, Xiao P. 3D printing of photopolymers. Polym Chem, 2018, 9: 1530-1540 CrossRef Google Scholar

[31] Michalek L, Barner L, Barner-Kowollik C. Polymer on top: Current limits and future perspectives of quantitatively evaluating surface grafting. Adv Mater, 2018, 30: e1706321 CrossRef PubMed Google Scholar

[32] Zhang J, Zivic N, Dumur F, et al. N-[2-(dimethylamino)ethyl]-1,8-naphthalimide derivatives as photoinitiators under LEDs. Polym Chem, 2018, 9: 994-1003 CrossRef Google Scholar

[33] Yu J, Gao Y, Jiang S, et al. Naphthalimide aryl sulfide derivative norrish type I photoinitiators with excellent stability to sunlight under near-UV LED. Macromolecules, 2019, 52: 1707-1717 CrossRef ADS Google Scholar

[34] Yang H, Li G, Stansbury JW, et al. Smart antibacterial surface made by photopolymerization. ACS Appl Mater Interfaces, 2016, 8: 28047-28054 CrossRef Google Scholar

[35] Deng J, Wang L, Liu L, et al. Developments and new applications of UV-induced surface graft polymerizations. Prog Polymer Sci, 2009, 34: 156-193 CrossRef Google Scholar

[36] Zhang L, Du W, Nautiyal A, et al. Recent progress on nanostructured conducting polymers and composites: Synthesis, application and future aspects. Sci China Mater, 2018, 61: 303-352 CrossRef Google Scholar

[37] Fouassier JP, Allonas X, Burget D. Photopolymerization reactions under visible lights: Principle, mechanisms and examples of applications. Prog Org Coatings, 2003, 47: 16-36 CrossRef Google Scholar

[38] Grotzinger C, Burget D, Jacques P, et al. Photopolymerization reactions initiated by a visible light photoinitiating system: Dye/amine/bis(trichloromethyl)-substituted-1,3,5-triazine. Macromol Chem Phys, 2001, 202: 3513-3522 CrossRef Google Scholar

[39] Peng H, Yu L, Chen G, et al. Low-voltage-driven and highly-diffractive holographic polymer dispersed liquid crystals with spherical morphology. RSC Adv, 2017, 7: 51847-51857 CrossRef Google Scholar

[40] Stoll S, Schweiger A. Easyspin, a comprehensive software package for spectral simulation and analysis in EPR. J Magn Reson, 2006, 178: 42-55 CrossRef PubMed ADS Google Scholar

[41] Peng H, Ni M, Bi S, et al. Highly diffractive, reversibly fast responsive gratings formulated through holography. RSC Adv, 2014, 4: 4420-4426 CrossRef Google Scholar

[42] Peng H, Nair DP, Kowalski BA, et al. High performance graded rainbow holograms via two-stage sequential orthogonal thiol–click chemistry. Macromolecules, 2014, 47: 2306-2315 CrossRef ADS Google Scholar

[43] Winter HH, Chambon F. Analysis of linear viscoelasticity of a crosslinking polymer at the gel point. J Rheology, 1986, 30: 367-382 CrossRef ADS Google Scholar

[44] Scott TF, Kowalski BA, Sullivan AC, et al. Two-color single-photon photoinitiation and photoinhibition for subdiffraction photolithography. Science, 2009, 324: 913-917 CrossRef PubMed ADS Google Scholar

[45] Frisch MJ, Trucks GW, Schlegel HB, et al. Gaussion, D.01. Wallingford CT: Gaussion, Inc. 2013. Google Scholar

[46] Yamaji M, Oshima J, Hidaka M. Verification of the electron/proton coupled mechanism for phenolic H-atom transfer using a triplet π,π carbonyl. Chem Phys Lett, 2009, 475: 235-239 CrossRef ADS Google Scholar

[47] Christensen SK, Chiappelli MC, Hayward RC. Gelation of copolymers with pendent benzophenone photo-cross-linkers. Macromolecules, 2012, 45: 5237-5246 CrossRef ADS Google Scholar

[48] Li MD, Du Y, Chuang YP, et al. Water concentration dependent photochemistry of ketoprofen in aqueous solutions. Phys Chem Chem Phys, 2010, 12: 4800-4808 CrossRef PubMed ADS Google Scholar

[49] McIntire GL, Blount HN, Stronks HJ, et al. Spin trapping in electrochemistry. 2. Aqueous and nonaqueous electrochemical characterizations of spin traps. J Phys Chem, 1980, 84: 916-921 CrossRef Google Scholar

[50] Odian G. Radical Chain Polymerization. In Principles of Polymerization, 4th ed. Hoboken, New Jersey: John Wiley & Sons, Inc. 2004. P198–349. Google Scholar

[51] Church DF. Substituent effects on nitroxide hyperfine splitting constants. J Org Chem, 1986, 51: 1138-1140 CrossRef Google Scholar

[52] Sargent FP, Gardy EM. Spin trapping of radicals formed during radiolysis of aqueous solutions. Direct electron spin resonance observations. Can J Chem, 1976, 54: 275-279 CrossRef Google Scholar

[53] Ni ML, Peng HY, Xie XL. Structure regulation and performance of holographic polymer dispersed liquid crystals. Acta Polym Sin, 2017, 48: 1557–1573. Google Scholar

[54] Peng H, Chen G, Ni M, et al. Classical photopolymerization kinetics, exceptional gelation, and improved diffraction efficiency and driving voltage in scaffolding morphological H-PDLCs afforded using a photoinitibitor. Polym Chem, 2015, 6: 8259-8269 CrossRef Google Scholar

[55] Ni M, Chen G, Sun H, et al. Well-structured holographic polymer dispersed liquid crystals by employing acrylamide and doping ZnS nanoparticles. Mater Chem Front, 2017, 1: 294-303 CrossRef Google Scholar

[56] Kabatc J, Czech Z, Kowalczyk A. The application of halomethyl 1,3,5-triazine as a photoinitiator or co-initiator for acrylate monomer polymerization. J Photochem Photobiol A-Chem, 2011, 219: 16-25 CrossRef Google Scholar

[57] He M, Huang X, Zeng Z, et al. Phototriggered base proliferation: A highly efficient domino reaction for creating functionally photo-screened materials. Macromolecules, 2013, 46: 6402-6407 CrossRef ADS Google Scholar

  • Figure 1

    Ground state absorptions of KCD, NPG and TA in acetonitrile. NPG was recrystallized before use.

  • Scheme 1

    Schematic illustration on the conversion of the ketyl radical with an inhibition function to a new initiating radical and the corresponding ordered structures.

  • Scheme 2

    Chemical structures of KCD, NPG, TA, 6361-100, EHA and DMAA.

  • Figure 2

    (a–c) Nanosecond transient absorption of pure KCD (175 μmol L−1) in toluene upon a 400 nm pulse laser excitation. (d) Comparison between the experimental spectra (black line) and TD-DFT calculations (red and blue lines). The calculated spectra are scaled by 1.23 times with a half-width of 700 cm−1.

  • Scheme 3

    Schematic illustration on the diffraction efficiency measurement.

  • Figure 3

    (a–c) Nanosecond transient absorption when irradiating the KCD/NPG “photoinitibitor” (175 μmol L−1 for each in toluene) by a 400 nm pulse laser. (d) Spectra comparison between the experimental result (black line) and TD-DFT calculation (red line). The calculated spectrum is scaled by 1.23 times with a half-width of 700 cm–1.

  • Scheme 4

    Simplified structures of KCD and the radical coupling product of ketyl radical for calculations.

  • Figure 4

    (a) Chemical structures of radicals 1, 2 and 3. (b) Experimental and simulated EPR signals of the KCD/NPG “photoinitibitor” upon visible light irradiation.

  • Scheme 5

    Proposed radical diffusion during holographic photopolymerization.

  • Figure 5

    Comparison between the experimental and calculated absorptions of KCD and KCD’ (the radical coupling product). DMF is the solvent during characterization. All alkyl chains are replaced with the methyl group during DFT calculations to save the computation resource. The calculated spectra are scaled by 1.23 times with a half-width of 2500 cm−1.

  • Figure 6

    (a–c) Nanosecond transient absorption when irradiating the KCD/NPG/TA mixture (175 μmol L−1 for each in toluene) by a 400 nm pulse laser. (d) The transitent decay of KCD/NPG and KCD/NPG/TA mixtures at 528 nm. Pseduo-biexponential fitting is implemented to give the lifetime.

  • Figure 7

    (a) Chemical structures of radicals 3 and 4. (b) Experimental and simulated EPR signals of the KCD/NPG/TA system.

  • Figure 8

    Polymerization rate (a) and modulus (b) of the holographic mixture against the irradiation time upon a 460 nm light irradiation (3.0 mW cm−2). The concentration of KCD is 6 mmol L−1, while that of NPG and TA are 60 mmol L−1, respectively.

  • Figure 9

    (a) Electro-optic response of holographic polymer composites with the LC fabricated with the KCD/NPG “photoinitibitor” and KCD/NPG/TA system. SEM (b) and AFM (c) images of the holographic polymer composites with the KCD/NPG “photoinitibitor” (left) and KCD/NPG/TA system (right) after removing the LC. The dark holes in the SEM images and dark channels in the AFM images represent the orginal location of the LC. AFM scanning is hard to give the hole morphology because of the limited tip resolution. The grating ordered structure depth in the AFM images is 128.1±5.9 and 60.4±1.9 nm, respectively. The grating pitch is measured to be 840±10 and 830±40 nm from the SEM and AFM images, respectively, which is slightly smaller than the predesigned (889 nm).

  • Figure 10

    Holographic images reconstructued with the KCD/NPG “photoinitibitor” (a) and KCD/NPG/TA system (b). The images are viewed at the identical angle.

Copyright 2020 Science China Press Co., Ltd. 《中国科学》杂志社有限责任公司 版权所有

京ICP备17057255号       京公网安备11010102003388号