Crosslinking gradients of a photopolymerized multifunctional acrylate film control mechanical properties

  • Matthew Hancock
  • Eleanor Hawes
  • Fuqian Yang
  • Eric GrulkeEmail author


Photopolymerization of thin monomer films can be used to manufacture parts rapidly, but can lead to gradients of elastic modulus, particularly when the film is illuminated from only one side. In order to better understand the relationship between film curing (expressed in terms of carbon–carbon double bonds, C=C) and mechanical properties, a model was developed and tested against experimental results. The example system used in this work was a thin film microfluidics chip made from a multifunctional acrylate monomer. An 800-micron monomer film containing a photoinitiator was illuminated from the top surface, producing a solid chip. The C=C content and mechanical properties of the chip were measured at multiple positions over the cross sections. Raman spectroscopy was used to measure local C=C concentrations, and nanoindentation was used to measure local Young’s modulus and hardness. Spatial gradients in monomer conversion, Young’s modulus, and hardness were measured on a series of chips manufactured at different light doses. A photopolymerization model was used to fit the Raman data, providing quantitative predictions of the monomer conversion as a function of film depth and light dose. These data were then correlated with the values of Young’s modulus and hardness. The correlation between the photopolymerization and the mechanical properties can be used to optimize the mechanical properties of thin films within the manufacturing and energy constraints and should be scalable to other multifunctional monomer systems.


Photopolymerization Multifunctional polyacrylate Raman Nanoindentation 



The authors gratefully acknowledge the financial support from Hummingbird Nano, Inc., NSF SBIR Phase II #1555996 (National Science Foundation). Thanks to Freddy Arce and Patrick Marsac for the use of the Raman spectrometer. Also, thanks to Yikai Wang and Yang-Tse Cheng for nanoindentation assistance.


  1. 1.
    Stuart, MAC, et al., “Emerging Applications of Stimuli-Responsive Polymer Materials.” Nat. Mater., 9 (2) 101–113 (2010)CrossRefGoogle Scholar
  2. 2.
    Armstrong, R, Wright, D, “Polymer Protective Coatings—The Distinction Between Coating Porosity and the Wetted Metal Area.” Electrochim. Acta, 38 (14) 1799–1801 (1993)CrossRefGoogle Scholar
  3. 3.
    Spinks, GM, et al., “Electroactive Conducting Polymers for Corrosion Control.” J. Solid State Electrochem., 6 (2) 85–100 (2002)CrossRefGoogle Scholar
  4. 4.
    Ahn, S-W, et al., “Polymeric Wavelength Filter Based on a Bragg Grating Using Nanoimprint Technique.” IEEE Photonics Technol. Lett., 17 (10) 2122–2124 (2005)CrossRefGoogle Scholar
  5. 5.
    Paloczi, GT, Huang, Y, Yariv, A, “Free-Standing All-Polymer Microring Resonator Optical Filter.” Electron. Lett., 39 (23) 1650 (2003)CrossRefGoogle Scholar
  6. 6.
    Bayer, CL, Peppas, NA, “Advances in Recognitive, Conductive and Responsive Delivery Systems.” J. Control. Release, 132 (3) 216–221 (2008)CrossRefGoogle Scholar
  7. 7.
    Hoffman, AS, “The Origins and Evolution of “Controlled” Drug Delivery Systems.” J. Control. Release, 132 (3) 153–163 (2008)CrossRefGoogle Scholar
  8. 8.
    Jhaveri, SJ, et al., “Release of Nerve Growth Factor from HEMA Hydrogel-Coated Substrates and Its Effect on the Differentiation of Neural Cells.” Biomacromolecules, 10 (1) 174–183 (2008)CrossRefGoogle Scholar
  9. 9.
    Senaratne, W, Andruzzi, L, Ober, CK, “Self-Assembled Monolayers and Polymer Brushes in Biotechnology: Current Applications and Future Perspectives.” Biomacromolecules, 6 (5) 2427–2448 (2005)CrossRefGoogle Scholar
  10. 10.
    Luzinov, I, Minko, S, Tsukruk, VV, “Responsive Brush Layers: From Tailored Gradients to Reversibly Assembled Nanoparticles.” Soft Matter, 4 (4) 714–725 (2008)CrossRefGoogle Scholar
  11. 11.
    Mendes, PM, “Stimuli-Responsive Surfaces for Bio-Applications.” Chem. Soc. Rev., 37 (11) 2512–2529 (2008)CrossRefGoogle Scholar
  12. 12.
    Minko, S, “Responsive Polymer Brushes.” J. Macromol. Sci. C Polym. Rev., 46 (4) 397–420 (2006)CrossRefGoogle Scholar
  13. 13.
    Dong, X, Al-Jumaily, A, Escobar, IC, “Investigation of the Use of a Bio-Derived Solvent for Non-Solvent-Induced Phase Separation (NIPS) Fabrication of Polysulfone Membranes.” Membranes, 8 (2) 23 (2018)CrossRefGoogle Scholar
  14. 14.
    Becker, H, Locascio, LE, “Polymer Microfluidic Devices.” Talanta, 56 (2) 267–287 (2002)CrossRefGoogle Scholar
  15. 15.
    Geng, K, et al., “Nanoindentation Behavior of Ultrathin Polymeric Films.” Polymer, 46 (25) 11768–11772 (2005)CrossRefGoogle Scholar
  16. 16.
    Ellis, G, Claybourn, M, Richards, S, “The Application of Fourier Transform Raman Spectroscopy to the Study of Paint Systems.” Spectrochim. Acta A Mol. Spectrosc., 46 (2) 227–241 (1990)CrossRefGoogle Scholar
  17. 17.
    Wallin, M, et al., “Depth Profiles of Polymer Mobility During the Film Formation of a Latex Dispersion Undergoing Photoinitiated Cross-Linking.” Macromolecules, 33 (22) 8443–8452 (2000)CrossRefGoogle Scholar
  18. 18.
    Nichols, M, et al., “A Simple Raman Technique to Measure the Degree of Cure in UV Curable Coatings.” Prog. Org. Coat., 43 (4) 226–232 (2001)CrossRefGoogle Scholar
  19. 19.
    Marton, B, et al., “A Depth-Resolved Look at the Network Development in Alkyd Coatings by Confocal Raman Microspectroscopy.” Polymer, 46 (25) 11330–11339 (2005)CrossRefGoogle Scholar
  20. 20.
    Oyman, Z, et al., “Oxidative Drying of Alkyd Paints Catalysed by a Dinuclear Manganese Complex (MnMeTACN).” Surf. Coat. Int. B Coat. Trans., 88 (B4) 231–316 (2005)Google Scholar
  21. 21.
    Mirone, G, Marton, B, Vancso, GJ, “Elastic Modulus Profiles in the Cross Sections of Drying Alkyd Coating Films: Modelling and Experiments.” Eur. Polym. J., 40 (3) 549–560 (2004)CrossRefGoogle Scholar
  22. 22.
    Belaroui, F, et al., “Depth Profiling of Small Molecules in Dry Latex Films by Confocal Raman Spectroscopy.” Polymer, 41 (21) 7641–7645 (2000)CrossRefGoogle Scholar
  23. 23.
    Sammon, C., et al., “Materials Analysis Using Confocal Raman Microscopy.” In: Macromolecular Symposia. Wiley Online Library (1999)Google Scholar
  24. 24.
    Rodríguez, R, et al., “Drying Kinetics and Segregation in a Two-Component Anti-Adherent Coating Studied by Photoluminescence and Raman Spectroscopies.” J. Non-Cryst. Solids, 354 (30) 3623–3629 (2008)CrossRefGoogle Scholar
  25. 25.
    Sturdy, LF, et al., “Quantitative Characterization of Alkyd Cure Kinetics with the Quartz Crystal Microbalance.” Polymer, 103 387–396 (2016)CrossRefGoogle Scholar
  26. 26.
    Comte, C, Von Stebut, J, “Microprobe-Type Measurement of Young’s Modulus and Poisson Coefficient by Means of Depth Sensing Indentation and Acoustic Microscopy.” Surf. Coat. Technol., 154 (1) 42–48 (2002)CrossRefGoogle Scholar
  27. 27.
    Geng, K, et al., “Nanoindentation-Induced Delamination of Submicron Polymeric Coatings.” Polymer, 48 (3) 841–848 (2007)CrossRefGoogle Scholar
  28. 28.
    Geng, K, Yang, F, Grulke, EA, “Nanoindentation of Submicron Polymeric Coating Systems.” Mater. Sci. Eng. A, 479 (1) 157–163 (2008)CrossRefGoogle Scholar
  29. 29.
    Geng, K., Mechanical Evaluation of Nanocomposite Coatings, University of Kentucky Doctoral Dissertations, 395, 2006 Google Scholar
  30. 30.
    Carswell, T, et al., “Kinetic Parameters for Polymerization of Methyl Methacrylate at 60 C.” Polymer, 33 (1) 137–140 (1992)CrossRefGoogle Scholar
  31. 31.
    Decker, C, “Kinetic Study of Light-Induced Polymerization by Real-Time UV and IR Spectroscopy.” J. Polym. Sci. A Polym. Chem., 30 (5) 913–928 (1992)CrossRefGoogle Scholar
  32. 32.
    Decker, C, Jenkins, AD, “Kinetic Approach of Oxygen Inhibition in Ultraviolet-and Laser-Induced Polymerizations.” Macromolecules, 18 (6) 1241–1244 (1985)CrossRefGoogle Scholar
  33. 33.
    Decker, C, Moussa, K, “Real-Time Kinetic Study of Laser-Induced Polymerization.” Macromolecules, 22 (12) 4455–4462 (1989)CrossRefGoogle Scholar
  34. 34.
    Zetterlund, PB, Yamauchi, S, Yamada, B, “High-Temperature Propagation and Termination Kinetics of Styrene to High Conversion Investigated by Electron Paramagnetic Resonance Spectroscopy.” Macromol. Chem. Phys., 205 (6) 778–785 (2004)CrossRefGoogle Scholar
  35. 35.
    Fouassier, J-P, Lalevée, J, Photoinitiators for Polymer Synthesis: Scope, Reactivity, and Efficiency. Wiley, New York (2012)CrossRefGoogle Scholar
  36. 36.
    Albino, LGB, et al., “Knoop Microhardness and FT-Raman Evaluation of Composite Resins: Influence of Opacity and Photoactivation Source.” Braz. Oral Res., 25 (3) 267–273 (2011)CrossRefGoogle Scholar
  37. 37.
    Rocks, J, et al., “The Kinetics and Mechanism of Cure of an Amino-Glycidyl Epoxy Resin by a Co-anhydride as Studied by FT-Raman Spectroscopy.” Polymer, 45 (20) 6799–6811 (2004)CrossRefGoogle Scholar
  38. 38.
    Oliver, WC, Pharr, GM, “An Improved Technique for Determining Hardness and Elastic Modulus Using Load and Displacement Sensing Indentation Experiments.” J. Mater. Res., 7 (6) 1564–1583 (1992)CrossRefGoogle Scholar
  39. 39.
    Macosko, CW, Miller, DR, “A New Derivation of Average Molecular Weights of Nonlinear Polymers.” Macromolecules, 9 (2) 199–206 (1976)CrossRefGoogle Scholar
  40. 40.
    Chiu, WY, Carratt, GM, Soong, DS, “A Computer Model for the gel Effect in Free-radical Polymerization.” Macromolecules, 16 (3) 348–357 (1983)CrossRefGoogle Scholar

Copyright information

© American Coatings Association 2019

Authors and Affiliations

  1. 1.Department of Chemical and Materials EngineeringUniversity of KentuckyLexingtonUSA
  2. 2.NicholasvilleUSA

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