Validation of the poke-flow technique combined with simulations of fluid flow for determining viscosities in samples with small volumes and high viscosities

Viscosity in particles consisting of secondary organic material (SOM) has recently become an area of research focus, since information on viscosity is needed to predict the environmental impacts of SOM particles. Recently Renbaum-Wolff et al. (2013a) developed a poke-flow technique that was combined with simulations of fluid flow to constrain the viscosities of SOM samples of 1-5 mg mass, roughly the maximum that may be collected from environmental chambers or flow tubes on a reasonable timescale. The current manuscript expands on the initial validation experiments carried out by Renbaum-Wolff et al. First, the poke-flow technique combined with simulations of fluid flow was used to determine the viscosity of sucrose-water particles over a relatively wide range of relative humidities (RHs). The lower and upper limits of viscosity at 59% RH were 1.0 × 10¹ and 1.6 × 10⁴ Pa s, whilst at 37% RH the corresponding values were 7.2 × 10⁴ and 4.7 × 10⁶ Pa s, respectively. The results are in good agreement with recent measurements by Quintas et al. (2006) and Power et al. (2013). Second, the approach was used to determine the viscosity of two polybutene standards. The simulated lower and upper limits of viscosity for standard #1 was 2.0 × 10² and 1.2 × 10⁴ Pa s, whilst for standard #2 the corresponding values were 3.1 × 10² and 2.4 × 10⁴ Pa s. These values are in good agreement with values reported by the manufacturer. The results for both the sucrose-water particles and the polybutene standards show that the poke-flow technique combined with simulations of fluid flow is capable of providing both lower and upper limits of viscosity that are consistent with literature or measured values when the viscosity of the particles are in the range of ≈ 5 × 10² to ≈ 3 × 10⁶ Pa s.