STUDY ON THE COLLOIDAL STABILITY MECHANISMS OF ACETAL-FUNCTIONALIZED LATEXES

In this work the colloid stability mechanisms of polystyrene latexes o f acetal functionality are studied. These acetal latexes were prepared by two-step emulsion polymerization.. The core was a seed of polystyr ene, and the shell was synthesized by terpolymerization of styrene (St ), methacrylic acid (MAA), and (methacrylamido)acetaldehyde dimethyl a cetal (MAAMA) termonomers. The results were three latexes with differe nt surface characteristics and with charged (carboxyl) and uncharged ( acetal) surface groups provided by the MAA and MAAMA monomers, respect ively. The anomalous electrokinetic behavior of the acetal latex was a consequence of their electric double layer structure, especially for one of the latexes with a significant highly charged ''hairy'' surface . The high colloidal stability of the acetal latexes was not explained by the classical Derjaguin-Landau-Verwey-Overbeck theory, and some co rrection factors, such as the Stern layer thickness (ionic size) and e lectrosteric stabilization mechanisms, were included in this theory. T he last mechanism may be due to the existence of a hairy layer formed during the synthesis method. The stability factor was measured in orde r to obtain quantitative information about some parameters related to the interfacial properties of the colloidal particles, such as the Ham aker constant and diffuse potential. These parameters and the steric s tabilization theory were used to calculate the total interaction energ y at several electrolyte concentrations. By using the electrosteric me chanism to explain the stability results, it was possible to find a se t of parameters that provide critical coagulation concentration values that were in accordance with the experimental one.