Surfactant-polymer interactions: an investigation to understand surfactant behaviour in ink formulation

Abstract

The requirement for greener, safer, and non-hazardous components in formulations including inkjet ink is one driving factor for the need to continually improve formulations. From a consumer’s perspective, the other is the demand for better print quality. As such generating knowledge surrounding component interactions and their influence on stability, ink-printhead and ink-media is key to advancing ink formulation for a specified printhead. One of the important formulant components that can be substituted is the primary surfactant. Currently, the Surfynol® series of surfactants are known to work well in ink formulations for use with thermal inkjet printheads. However, there is risk that they become obsolete, or their use is restricted. Several alternative surfactants with similar hydrophilic lipophilic balance values have been chosen to evaluate their suitability as alternatives. The baseline surfactant along with alternative surfactants have been investigated by determining their critical micelle concentration and surface-active properties in water. Their interaction with an acrylic polymer was studied via dynamic surface tension, using methods from literature and then via dynamic light scattering and nuclear magnetic resonance. These techniques confirmed the interaction and formation of larger surfactant-polymer complexes. They may associate through hydrogen bonds from the alcohol group in the surfactant head portion with alcohol groups on the acrylic polymer and hydrophobic interactions of methyl and ethyl groups. The degree of interaction in the bulk was found to decrease with increasing ethoxylation units for surfactants in the same family and were enhanced by cosolvents. Polymer saturation with surfactants was identified to be a slow process. Low solubility surfactants caused swelling or contraction of polymer chains, with visible aggregation precipitates. Soluble surfactants formed worm like micelles to continually increase polymer-surfactant complex size. Of the investigated alternative surfactants, one promising alternative was identified to meet the requirements for which it is intended to replace. The print quality and physical properties of the identified surfactant in black formulation was shown to be promising and comparable to the baseline formulation. Further component optimisation of the alternative surfactant formulation can result in the development of a commercially viable printing ink.