Fluorescently Labelled Latex Particles to Monitor Film Formation

Latex film formation has been of commercial importance for many years, particularly in the paint industry. Since the 1960s latex paints have largely replaced oil-based paints, which have been known to contain hazardous amounts of lead. The film formation process begins with latex particles in an aqueous dispersion. As the water evaporates, the particles come into close contact and start deforming before they coalesce and the polymer chains interdiffuse. The interparticle polymer diffusion (IPD) undergone by the polymer chains leads to the formation of a homogenous film with good mechanical properties. Several methods have been investigated in the past to probe IPD, but all have significant drawbacks. A new method recently proposed to probe IPD involves the introduction of pyrene labels into the latex particles. Pyrene is a fluorescent molecule, widely used because of its good quantum yield and high molar extinction coefficient, which makes it possible to acquire noise-free fluorescence spectra at low pyrene concentrations. Pyrene is typically excited in the UV region, and fluoresces with a lifetime τM. If an excited pyrene molecule encounters a ground-state pyrene, an excimer is formed which emits with a lifetime τE. The reaction scheme for pyrene excimer formation is depicted in Figure 1 along with the corresponding fluorescence spectrum.