Scientists looked at dry paint – the chaotic shapes revealed a world of movement and mystery

Researchers have found that the shape of dried paint is affected by pigment concentration and the temperature at which it is dried. A study in ACS Langmuir Drops with less pigment or those placed on cooler surfaces resembled „fried eggs” when dried, while those with more pigment or dried at higher temperatures appeared more uniform. The findings suggest that by adjusting the pigment concentration and drying temperature, one can control the final appearance of dried paint.

The drying process of paint is affected by its pigment concentration and drying temperature, and adjustments in these factors control the final appearance of the paint.

A coffee spill leaves a dark stain on the edge of the puddle when it dries. But as the paint drops dry, some look like „fried eggs,” surrounded by beautiful white halos of „yellow” color, while others appear uniform. To understand this variation, researchers report in the ACS. Langmuir The paint actually dried. Pigment concentration and temperature affected how the liquid gelled and evaporated, information that helped control patterns in dried paint.

Paint consists of a mixture of ingredients including resins, pigments, additives and a solvent such as water. Due to the complex composition of the paint, various chemical interactions play out when the paint drops evaporate, which sometimes lead to undesirable patterns or small cracks. Generally, painters and house painters prefer uniform pigment distribution after the paint is applied to the surface. But it’s not really clear how to avoid patterns once the liquid dries. Therefore, Stella Ramos, Catherine Parentin and colleagues wanted to investigate the factors that affect the evaporation of water-based paint.

Drying paint patterns

Once the paint dries, they may look like a „fried egg” (left image, scale bar is one millimeter) or create a heavy pigment distribution (right image). Credit: Adapted from Langmuir 2023, DOI: 10.1021/acs.langmuir.3c01605

The researchers prepared five mixtures of water-based acrylic paint and water, then dropped the solutions onto heated glass slides. As the liquid evaporated, they analyzed and photographed the deposits, and observed three phenomena:

  • Initially, there were inward and outward flows of fluid: inward flow from the hot substrate to the cooler surface of the droplet and outward drag from the capillary flow.
  • Ultimately, gelation of the paint suspension increased viscosity and decreased pigment mobility.
  • A final drying step locks the pigments onto the surface of the slide.

Both the amount of pigment and the surface temperature of the glass affected the size, shape, and form of the dried paint drops. The researchers observed that drops with lower pigment concentrations or 86 degrees lower temperatures placed on the surface. Fahrenheit Colored molecules concentrated in the center, giving a „fried egg” appearance. With high pigment and high temperature, up to 176 degrees Fahrenheit, the dry pattern was very uniform and had color distribution throughout the entire circle.

The researchers say that pigment concentration and surface temperature can be adjusted to control the appearance of dried paint, depending on the desired final shape.

Note: Stella MM. From “fried eggs” to semi-homogeneous shapes in “Drying Drops of Paint Suspension,” by Ramos, Damien Chauperand, Rémi Fulgrand, and Catherine Parentin, 14 September 2023. Langmuir.
DOI: 10.1021/acs.langmuir.3c01605

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