Intense and selective coloration of foams stabilized with functionalized particles

We report a new method for intense and selective coloring of foams stabilized by particles from cellulose derivatives. The addition of pH-sensitive dyes during the process of formation of hydrophobically modified cellulose (HMC) particles by a pH-jump leads to co-precipitation and strong adsorption of the pH-sensitive dyes on the cellulose particle surfaces at low pH. These strongly colored HMC particles not only act as strong stabilizers of the foams, but also allow their intense and selective coloration without any coloring of the solution medium. We characterized quantitatively the color intensity of these foams, analyzed the adsorption behavior of pH-sensitive dyes on the cellulose particles and showed that it follows well the Langmuir isotherm model. Lower pH of the media leads to stronger adsorption of the pH-sensitive dyes on the HMC particles due to the hydrophobic attraction under reduced electrostatic repulsion. The results illustrate how particle stabilizers can be used to impart additional functionality to foams and prepare dispersion systems of unusual properties.