Application of flow field-flow fractionation (FlFFF) for size characterization of carbon black particles in ink

Abstract

The size and distribution of the carbon black particles play important roles with respect to application in diverse areas. When used in inks, the smaller the particle size, the better the carbon black particles are dispersed, and thus the glossiness of ink increases. Asymmetrical flow field-flow fractionation (AsFlFFF) has shown to be applicable for size characterization of various types of colloidal particles. In the present study, AsFlFFF was employed to analyze the size of carbon black particles used in ink. Carbon black suspensions were prepared by dispersing carbon black powder in aqueous media containing various types of copolymeric dispersing agents of hydrophobic (styrene) and hydrophilic (acrylic or maleic acid) monomers. Experimental parameters of AsFlFFF including the type of the surfactant added to the carrier liquid, the channel and the cross flow rates, and the ionic strength were varied to find an optimum condition for analysis of the carbon black particles. It was found that the use of FL-70 as an additive to the carrier liquid resulted in the best elution profile among the tested surfactants (cationic, anionic, and nonionic surfactant). Although the mean sizes obtained by AsFlFFF and dynamic light scattering (DLS) were generally in good agreements, DLS failed to distinguish between the carbon black suspensions having different size distributions, whereas AsFlFFF was able to differentiate easily. Results indicated that the carbon black particles were dispersed better with the copolymeric dispersing agents having the hydrophobic content of 2 to 3 times higher than the hydrophilic molecules. At the styrene:acrylic acid of 1:1, the carbon black particles tend to have larger mean sizes and the size distributions tend to become broader, probably due to poor dispersion. Furthermore, it was observed that as the mean size of the carbon black particles decreased and the size distribution became narrower, the ink became clearer and glossier.