Dynamic Water Transport in a Pigmented Porous Coating Medium: Novel Study of Droplet Absorption and Evaporation by Near-Infrared Spectroscopy

Abstract

The dynamic wetting of, and absorption into, model porous coatings in the form of compressed particulate pigment tablets by monocomponent, dual-component, and multicomponent liquid droplets has been studied by observation of apparent contact angle and near-infrared spectroscopy to identify the liquid water/moisture content. The absorption of the liquids was studied in a corresponding vapor-saturated environment. Liquid evaporation was determined for the tablets at both equilibrium starting pore saturation and under limited volume-filling conditions as evaporation proceeds. The changes in water and moisture content within the coatings as a function of time were also determined gravimetrically to relate the water uptake and evaporation being observed to changes in the near-infrared spectral data. Model and commercial offset printing fountain solutions were compared with respect to both absorption and evaporation. For the solutions containing isopropyl alcohol in water, a nonlinear behavior in the water response in the near-infrared spectra during absorption is observed as a function of time, which can be related to the fast evaporation of the alcohol. The nonlinear region was followed by a decline in water and moisture content as the penetration/evaporation of the water phase proceeded. Comparing the near-infrared water volume dependency in the upper layers of the structure with weight loss during evaporation showed that the mechanism of liquid transport to the surface−air interface reflected the logarithmic volume distribution of pore sizes, as might be expected from capillarity considerations and pore condensation hysteresis.

Mechanism of adsorption of actives onto microporous functionalised calcium carbonate (FCC)

“…As FCC is a composite of both of these materials, the FCC will also be hydrophilic. Direct observation of the contact angle of water onto FCC is not possible because water adsorbs onto the microporous surface so quickly (Tåg et al, 2010). FCC is likely to have at least a monolayer of physically adsorbed water when exposed in ambient air (Misra, 1988).…”

Determination of dynamic surface tension and viscosity of non-Newtonian fluids from drop oscillations

“…Its solubility in water is 0.032 wt%, 25 corresponding to a solution concentration of about 1 mM. It does not form micelles.…”

“…It does not form micelles. 25 The amount of Dynol 607 (0.06%) in the formulation exceeds the solubility limit, but some of the surfactant will be used to stabilise the PEDOT:PSS particles. For a nonionic surfactant with two branched chains, the maximum surface excess (corresponding to the minimum surface tension) is estimated to be Γ max ≈ 2 × 10 -6 mol m -2 .…”

Lifetime Prediction of Sessile Droplet Evaporation with Coupled Fields

“…Evaporation of sessile droplets on a substrate is a fundamental phenomenon, which is widely encountered in various industrial applications and scientific analysis, including the surface coating technique, inkjet printing, and efficient cooling. , Therefore, it is crucial to predict the temporal evolution behaviors of evaporative droplets. Picknett and Bexon found two extreme modes of sessile droplet evaporation: the constant contact radius (CCR) mode and the constant contact angle (CCA) mode.…”