Developing of a jujube cake structured composite filler SiO₂@PHT-1 for preparing a pH-indicating film with high pH measurement precision and strong reusability

Phenolphthalein (PHT) is always applied as an acid-base indicator but suffers from too wide a range of characterization and uneven dispersion in thin films. To solve this problem, in this work, a composite filler SiO₂@PHT-1 with a jujube cake structure was designed. The size of phenolphthalein particles was effectively regulated by intervening in the growth process of phenolphthalein nuclei through silica (SiO₂). This also improved the dispersion of PHT in fluororubber (FKM) films, as well as the indicator film's tensile strength (57.1%) and initial decomposition temperature (201.6 °C), resulting in the pH indicator film with excellent tensile properties and thermal stability. The FKM/SiO₂@PHT-1 film is also capable of determining the pH value of a solution based on color and phenomena. In addition, the dense protective layer formed by the silica retards the release of PHT in the sample solution, which contributes to the reusability of the film. This method shows great promise and can be applied to laboratory and swimming pool alkalinity testing.