How do van der Waals forces contribute to dyeing cotton with direct dyes?

In the context of dyeing cotton, van der Waals forces act as a critical mechanism for dye retention by facilitating the attraction between the fibre's molecular units and the direct dyes.1

These forces are defined as the attractive interactions between the atoms or molecules of all substances. In the specific case of cellulosic fibres like cotton, which possess relatively large, planar areas, these interactions become particularly effective when the separation between the dye molecules and the fibre is small. Because direct dyes typically feature linear, extended molecular structures, they are well-suited to align with these planar regions of the cellulose, allowing van der Waals forces to contribute to the adsorption and retention of the dye within the fibre's microstructure.12