Supporting Information. Crosslinked network development in compatibilized alkyd/acrylic. hybrid latex films for the creation of hard coatings

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1 Supporting Information Crosslinked network development in compatibilized alkyd/acrylic hybrid latex films for the creation of hard coatings Tao Wang, Carolina de las Heras Alarcón, Monika Goikoetxea, Itxaso Beristain, Maria Paulis, Maria J. Barandiaran, José M. Asua, and Joseph L. Keddie * Department of Physics and Surrey Materials Institute, University of Surrey, Guildford GU2 7XH, UK Institute of Polymer Materials (POLYMAT), Grupo de Ingeniería Química, University of the Basque Country, Centro Joxe Mari Korta, Avenida Tolosa 72, Donostia- San Sebastián, Spain These authors contributed equally to this work. Current address: Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK. *Corresponding author. j.keddie@surrey.ac.uk Tel.: Fax:

2 1. The dependence of H eff and E eff on the indentation depth (applied force) The applied force and the consequent indentation depth into the polymer film are known to influence the as-measured film hardness. 1 There is no general agreement on exactly how the hardness will depend on the indentation depth so far. Different conclusions have been drawn from studying different materials. 2,3,4 The optimization of the applied force to minimize any potential errors needs to be based on the systematic investigation of the specific materials. Fig. S1A illustrates the indentation curves on one type of alkyd/acrylic hybrid latex film with varying applied forces. The indentation depth increases with an increasing applied force. The calculated hardness from Figure S1A is plotted in Figure S1B as a function of indentation depth. Surface roughness and a low precision in the force will have a greater effect during indentation when a small force is applied. It has been found in previous work that hardness can be dramatically high with a very small applied force. 5 In this experiment, when an applied force is lower than N, it is found that the hardness of the alkyd-acrylic hybrid film is much higher. It has been suggested elsewhere that the mechanical response of the hard substrate will contribute to the measured hardness and modulus when the indentation depth reaches 10~25 % of the film thickness. 6 However, in this study hardness is found to be constant regardless of indentation depth when the applied force increases from N through 4 N. Since the measured hardness is independent of the applied force when it is higher than N in this specific case, there are no apparent substrate effects. Drawing from these results, an indentation force of N will be employed in the following experiments. 2

3 4 (a) 7 6 (b) F= N F/ N Hardness/MPa h /mm Indentation depth / mm Figure S1. (a) Force-displacement curves of micro-indentation on an alkyd-acrylic latex film with increasing applied loads. (The film thickness was 350 µm.). (b) Dependence of the measured hardness value on the indentation depth. 3

4 2. GARField profiling of alkyd/acrylic blends GARField profiling studies were carried out on alkyd/acrylic blends (or admixtures) in a 50:50 weight ratio, for both hydrophobic (HB) and hydrophilic (HL) alkyd resin, with or without the presence of drier. Thus, the effects of the resin type and the effect of drier addition were investigated. Profiles obtained over times up to 74 hours are shown in Fig. S2. In all four systems, the NMR signal continues to decrease after the water has left the films. The signal decreases are attributed to the crosslinking of the alkyd. By comparing (a) with (b) and (c) with (d) it is evident that the addition of the drier speeds up the crosslinking of the alkyd. The rate of the NMR signal loss is fastest at the top of the film (on the right side of the profiles), which indicates a faster crosslinking there. The profiles decrease linearly with depth into the film in a way that has been seen previously in alkyd films, as a result of oxygen diffusion from the film surface. 4

5 (a) 0h 1.3h 12h 30h 48h 66h 74h Height (µm) (b) Intensity (a.u.) 6h Height (µm) 2h 4h 0h h 1.3h 12h 30h 48h 74h 66h Intensity (a.u.) (c) (d) Intensity (a.u.) 0.6 Intensity (a.u.) Height (µm) 74h 66h48h 1.3h 0h 12h 30h Height (µm) 0h 1.3h 12h 30h 48h 74h 66h Figure S2. GARField profiles obtained over time during the drying of (a) a blend (admixture) of acrylic latex and HB resin without drier; (b) a blend of acrylic latex and HB resin with 2 wt.% drier; (c) a blend of acrylic latex and HL resin without drier; and (d) a blend of acrylic latex and HL resin with 2 wt.% drier. Profiles were taken from 0 up to 74 hours. 5

6 3. Latex films cast from blends of alkyd emulsions and acrylic latex (a) (b) (c) (d) Figure S3. Photographs of dried latex films cast from (a) acrylic latex blended with HB alkyd emulsion; (b) acrylic latex blended with HL alkyd emulsion, (c) HB-alkyd/acrylic hybrid latex; and (d) HL alkyd/acrylic latex. All films have 2 wt.% drier. Blends of latex dispersions and alkyd emulsions produced wrinkled films, whereas the hybrid latex dispersion produced smooth films. 6

7 4. Glass transition temperatures in GMA-alkyd/acrylic hybrid latex films The glass transition temperatures (T g ) of crosslinked GMA-alkyd/acrylic films were determined using a differential scanning calorimeter (Q1000, TA Instruments). Thermograms were obtained by scanning through heat-cool-heat cycles from -100 C to 100 C at a rate of 10 C/min. The second heating cycles were chosen to determine the T g and consequently to analyze the changes after crosslinking of the alkyd component in the hybrid films. Results are presented in Figure S4. After crosslinking, the T g of the hybrid increases by ca. 10 C. T g study also indicates that alkyd is in its rubbery state at room temperature, even after crosslinking. Heat flow (W/g) T g =-21.9 o C T g = o C T g = o C T g = o C A B C D Temperature ( o C) Figure S4. Glass transition temperatures (T g ) of alkyd component in the GMA-alkyd/acrylic hybrids with different crosslinking conditions. A) Freshly dried GMA-alkyd/acrylic hybrid (GMA-HB) with minimal crosslinking. The observed T g is C. B) The GMA-alkyd/acrylic hybrid after crosslinking over 60 days without the presence of drier (GMA-HB0). The T g is C. C) Crosslinked GMA-alkyd/acrylic hybrid with 1 wt.% drier (GMA-HB1) after 60 days. The T g is C. D) Crosslinked GMA-alkyd/acrylic hybrids with 2 wt.% drier (GMA-HB2) 7

8 after 60 days. The T g is C. 5. Glass transition temperature in cross-linked GMA-alkyd-acrylic latex films by DMA The specimens for dynamic mechanical analysis are the same as those used for tensile deformation. Dynamic mechanical analysis (DMA, Q800, TA Instruments, New Castle, DE, USA) was performed with a strain of 5% and a frequency of 1 Hz over a temperature range from -100 C to 100 C at a rate of 3 C/min. The T g of the crosslinked hybrid is 14 C according to the analysis in Figure S5 (determined by the peak temperature of the loss tangent, tanδ). The values of E and E are approximately equal at room temperature. Prior to crosslinking, E is higher, and the hybrid material is in its rubbery state at room temperature. Modulus (MPa) E' E" 14 o C Tan delta 0.1 tanδ Temperature ( o C) Figure S5. DMA of the functionalized alkyd hybrid latex film with 2 wt% drier (GMA-HB2) after crosslinking for 60 days, showing that the T g is 14 C. 8

9 6. Tensile cycling of crosslinked GMA-alkyd/acrylic hybrid latex films Tensile cycling of crosslinked GMA-alkyd/acrylic latex films was performed with a loading and unloading speed of 5 mm/sec. The unloading was started when the extension ratio reached The specimens had dimensions that were the same as for the tensile deformation and were dried over 12 days at room temperature. Figure S6 shows that more than 80% of the strain is recovered even when the specimen has been strained with an extension ratio of 1.33 and under a high loading and unloading speed of 5 mm/sec. Leaving the strained free-standing specimen for a longer time (more than 10 min.) with no load, it was found that 100% of the strain is recovered. This result confirms that there is mainly viscoelastic deformation rather than plastic deformation during tensile deformation to moderate extensions. Film dried 12 days Stress (MPa) GMA-HB2 5mm/sec GMA-HB 5mm/sec Strain 0.5 Figure S6. Tensile cycling of GMA-alkyd/acrylic hybrid latex films. Both specimens demonstrate recovery, which is indicative of viscoelastic deformation. 9

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