Comparison of the Diffusion Coefficients Obtained for Latex Film Formation Studied by FRET and Pyrene Excimer Formation Remi Casier Profs. Jean Duhamel and Mario Gauthier University of Waterloo, Waterloo, Ontario 1

Latex: o Stable dispersion of polymer particles in an aqueous solution Applications: o Products: gloves and tires o Additives: adhesives and paper coatings o Films: paints and coatings 2Introduction Tire tread,. Painted boards,.

Film Formation from a Latex Dispersion 3 The minimum film formation temperature (MFT) must be reached before polymer chains can interdiffuse (MFT ≈ T g ) 1 Interparticle polymer diffusion (IPD) during the coalescence of latex particles produces a homogeneous film Mechanical properties are highly dependent on the extent of IPD 2 1.Zhao, C., Wang, Y., Hruska, Z., Winnik, M. Molecular Aspects of Latex Film Formation: An Energy-Transfer Study; Macromolecules 1990, 23, Gauthier, C.; Guyot, A.; Perez, J.; Sindt, O. Film Formation and Mechanical Behavior of Polymer Laticies. Film Formation in Waterborne Coatings, Chapter 10, 1996, Washington, DC: American Chemical Society. Good Mechanical Properties Poor Mechanical Properties T > MFT Stage 1: Water Evaporation Stage 2: Particle Deformation Stage 3: Coalescence

4 Background Previous studies of latex film formation by the Winnik group have primarily used fluorescence resonance energy transfer (FRET) to probe IPD 1-2 Two dyes used: Phenanthrene as a donor (D) and anthracene as an acceptor (A) Time resolved fluorescence decays are obtained for various annealing times 1.Zhao, C.; Wang, Y.; Hruska, Z.; Winnik, M. A. Molecular Aspects of Latex Film Formation: An Energy-Transfer Study; Macromolecules 1990, 23, Wang, Y.; Winnik, M. A. Energy-Transfer Study of Polymer Diffusion in Melt-Pressed Films of Poly(methyl methacrylate); Macromolecules 1993, 26, D D D D D D A A A A D A A A IPD T > MFT

Develop a simpler method to probe the minimum film formation temperature (MFT) and the degree of interparticle polymer diffusion (IPD) in latex films Using a fluorescently-labeled latex with an emission that changes depending on the degree of IPD A single fluorophore pyrene (Py) can be used, thus only a single fluorescently-labeled latex must be prepared 5 Objective

Pyrene Fluorescence IMIM IEIE Excimer Monomer I E /I M – a measure of the amount of excimer formed 6 Monomer EmissionExcimer Emission

7 Interparticle Polymer Diffusion Using Pyrene t=0 t˃0 High C py Low C Py High excimer formation Low excimer formation High I E /I M ratio Low I E /I M ratio T > MFT Py

8 Pyrene Labeled Latex PyEG 3 MA Hydrophobicity of the monomer was tuned by varying the length of the oligo(ethylene glycol) unit 3 x1-x 3 Semi-batch emulsion process Copolymerized with n-butyl methacrylate (BMA) to yield a poly(n-butyl methacrylate) randomly labeled with pyrene (Py-PBMA) Py-PBMA Latex

9 SamplePyLMPyLM Incorporated (mol%) Particle Size (nm) PSDM w (kg/mol) Ð Py-PBMA-Latex-1PyEG 3 MA Py-PBMA-Latex-2PyEG 3 MA GPC: Py-PBMA-Latex-1

A film was prepared from a mixture of 5 wt% Py-PBMA-latex in 95 wt% PBMA-latex The films were dried overnight under nitrogen, then: 1.Annealed at a constant temperature 2.Rapidly cooled to room temperature on an aluminum block 3.Analysed by steady-state fluorescence 4.Steps 1 – 3 repeated for increasing annealing time 10 Film Composition FilmLatex Latex Pyrene Content (mol%) Particle Size (nm) PSD M w (kg/mol) Đ Weight Fraction 1 Py-PBMA-Latex PBMA-Latex , Py-PBMA-Latex PBMA-Latex

11 Steady-State Fluorescence: Film 1 Annealing Time (min.) I E /I M t∞t∞ 0.04 Increasing Annealing Time T an = 102 °C

12 Fraction of Mixing: Film ° C 112 ° C 111 ° C 102 ° C 94 ° C 88 ° C 84 ° C 75 ° C 98 ° C M w = 820 kg/mol

Fraction of Mixing: Film ° C 84 ° C 75 ° C 98 ° C 94 ° C 102 ° C 111 ° C 112 ° C119 ° C M w = 360 kg/mol

Fraction of Mixing: Molecular Weight Dependence 14 FilmLatex Latex Pyrene Content (mol%) Particle Size (nm) PSD M w (kg/mol) Đ Weight Fraction 1 Py-PBMA-Latex PBMA-Latex , Py-PBMA-Latex PBMA-Latex T an = 75 °C T an = 119 °C Film 1: M w = 820 kg/mol Film 2: M w = 360 kg/mol Film 1: M w = 820 kg/mol Film 2: M w = 360 kg/mol

Concentration profile of molecules diffusing out of a spherical particle of radius R using Fick’s law: 3 15 Polymer Diffusion Coefficients (D) Increasing Annealing Time 3. Crank, J. The Mathematics of Diffusion, 2 nd ed. Oxford: Clarendon Press, 1975, pp R

16 Polymer Diffusion Coefficients (D)

Diffusion Coefficients: f m 17 Film 1: M w = 820 kg/molFilm 2: M w = 360 kg/mol

Apparent Activation Energy Following the procedure outlined in previous FRET studies, E a was found by comparing D at different temperatures at a fixed f m. 1,2,6-8 Using an Arrhenius type plot, E a = R·Slope Zhao, C., Wang, Y., Hruska, Z., Winnik, M. Macromolecules 1990, 23, Wang, Y., Winnik, M. Macromolecules 1993, 26, Oh, J. K., Tomba, P., Ye, X., Eley, R., Rademacher, J., Rarwaha, R., Winnik, M. A. Macromolecules 2003, 36, Wang, Y. C., Winnik, M. A. J. Phys. Chem. 1993, 97, Ye, X., Farinha, J. P. S., Oh, J. K, Winnik, M. A., and Wu, C. Macromolecules, 2003, 36 (23), 8749–8760 fmfm MethodPy: Film 1Py: Film 2FRET 1 FRET 7 M w (kg/mol) E a (kJ/mol)180 ± 8160 ± Film 1: M w = 820 kg/mol Film 2: M w = 360 kg/mol fmfm fmfm PBMA Film probed by FRET M w = 420 kg/mol

Master Curves Using E a Master curves (left) were constructed by shifting D(T) using the E a values found in the previous slide T 0 = 75 °C 19 Comparison with a master curve (right) of a PBMA film using FRET 8 T 0 = 57 °C M w = 38 kg/mol 8. Ye, X., Farinha, J. P. S., Oh, J. K, Winnik, M. A., and Wu, C. Macromolecules, 2003, 36 (23), 8749– °C 74 °C 56 °C 90 °C PBMA Film probed by FRET (M w = 38 kg/mol ) 8 Film 1: M w = 820 kg/mol Film 2: M w = 360 kg/mol

Why Use Pyrene Excimer Formation? 20 RequirementFRETPyrene Excimer Formation Instrumentation Time-resolved fluorometer (complex and expensive) Steady-state fluorometer (simple and inexpensive) Data Acquisition~ 10 minutes per decay~ 30 seconds per spectrum Fluorescence Analysis Decay must be modeled, fitted, and then integrated I E /I M ratio Fluorescently-Labeled Latex 2 (donor labeled, acceptor labeled) 1 (pyrene labeled) Film Composition100 wt% labeled-latex ≤ 5 wt% labeled-latex ≥ 95 wt% native-latex Latex NanoparticlesSymmetricalSymmetrical or Asymmetrical

Future Work Probe the diffusion between asymmetric latex nanoparticles: Particle size Molecular weight Different Polymers 21 Py

Supervisors: Prof. Jean Duhamel Prof. Mario Gauthier All members of the Duhamel and Gauthier groups. Thank you for your attention! 22Acknowledgements

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24 WLF: Doolittle: Linear free volume: