We utilize quartz crystal resonators operating at multiple resonant harmonics to measure the high-frequency rheological properties of materials with a broad range of viscoelastic properties. The technique is demonstrated with poly(t-butyl acrylate) films in the vicinity of the calorimetrically determined glass transition and with rubbery polyisoprene films. The technique is a noncontact technique that can be used to quantify the temperature or time-dependent viscoelastic response in homogeneous films with thicknesses in the micrometer range. This work complements the ability of the resonators to quantify the viscoelastic behavior of viscoelastic polymer solutions and simple Newtonian liquids. For each material we obtain the density-shear modulus product and the viscoelastic phase angle at frequencies of 5 and 15 MHz. A standardized analysis protocol is described that enables this information to be obtained reliably and accurately. The polyisoprene data are found to be in good agreement with measurements obtained by dynamic mechanical analysis using extrapolated temperature shift factors.

The quartz crystal microbalance (QCM) was used to measure the time-dependent mechanical properties of an alkyd resin throughout the transition from its application as a liquid to the formation of a solid film. Three different regions of curing were observed, corresponding to solvent evaporation; early stage curing, where the mass increases as oxygen is incorporated into the film; and long-term curing, where the mass decreases as volatile compounds are released. Mechanical property changes obtained at 15 MHz with the QCM were correlated with measurements at much lower frequencies utilizing traditional dynamic mechanical analysis. These mechanical property changes were in turn correlated to chemical changes tracked with Raman spectroscopy. From the temperature dependence of the curing process we obtain an effective activation energy of 4.1 kcal/mol.

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The utility of the quartz crystal microbalance (QCM) as a high-frequency rheometer operating at 15 MHz was demonstrated. High-frequency data obtained from a series of rubbery materials were compared with results obtained from traditional dynamic mechanical analysis (DMA) at much lower frequencies.The high-frequency data enable meaningful shift factors to be obtained at temperatures much further above glass-transition temperature (T g ) than would otherwise be possible, giving a more complete picture of the temperature dependence of the viscoelastic properties. The QCM can also be used to quantify mass uptake and changes in viscoelastic properties during sample oxidation. The viscoelastic response spanning the full range of behaviors from the rubber to glassy regimes was found to fit well with a six-element model consisting of three power-law springpot elements. One of these elements is particularly sensitive to the behavior in the transition regime where the phase angle is maximized. The value of this quantity is obtained from the maximum phase angle, which can be obtained from a temperature sweep at fixed frequency, proving a means for more detailed frequency-dependent rheometric information to be obtained from a fixed-frequency measurement at a range of temperatures.

Please cite this article as: L.F. Sturdy, M.S. Wright, A. Yee et al., Effects of zinc oxide filler on the curing and mechanical response of alkyd coatings, Polymer (2020), doi: https://doi. AbstractThe mechanical properties of an alkyd resin filled with zinc oxide pigment were studied at different concentrations over a wide range of time scales using dynamic mechanical analysis, quartz crystal rheometry and nanoindentation. The motivation for this work stems from the interest in accessing the long-term properties of paint coatings by studying the mechanical properties of historic paints. In this foundational work, we compare three different modalities of mechanical measurements and systematically determine the effect of pigment filler loading on the measured properties. Quantitative agreement between the methods is obtained when the characteristic time scales of each of the methods is taken into account. While nanoindentation is the technique most readily applied to historic paint samples, the rheometric quartz crystal microbalance (rheo-QCM) is the best suited for obtaining mechanistic information from measurements of paint properties over time, provided that appropriate thin-film samples can be produced. In these studies we find that ZnO increases the rate of oxidation of the alkyd during the initial stages of cure by an amount that depends on the ZnO content. J o u r n a l P r e -p r o o f Journal Pre-proof 2. Materials and Methods 2.1. Materials The alkyd films were prepared from Gamblin Artists Colors (Portland, OR) Galkyd mixed with Fischer Z50 zinc oxide ranging from 0.05 to 0.60 wet weight fraction. When necessary to change 2 J o u r n a l P r e -p r o o f Journal Pre-proof J o u r n a l P r e -p r o o f Journal Pre-proof J o u r n a l P r e -p r o o f Journal Pre-proof 7 J o u r n a l P r e -p r o o f Journal Pre-proof Thermogravimetric (TGA) experiments were conducted on naturally aged 5-month-old alkyd samples for four of the zinc oxide filler loadings listed in Table 1 to confirm the amount of zinc oxide pigment present relative to the binder after solvent evaporation. These results are shown in Figure 8 J o u r n a l P r e -p r o o f Journal Pre-proof J o u r n a l P r e -p r o o f Journal Pre-proof J o u r n a l P r e -p r o o f Journal Pre-proof J o u r n a l P r e -p r o o f Journal Pre-proof J o u r n a l P r e -p r o o f Journal Pre-proof -Zinc oxide accelerates the oxidative curing of alkyd paints. -Consistent results obtained with nanoindentation, dynamic mechanical analysis and high frequency rheometry. J o u r n a l P r e -p r o o f Journal Pre-proof J o u r n a l P r e -p r o o f Journal Pre-proof Declaration of interest: none J o u r n a l P r e -p r o o f Journal Pre-proof