Stabilizing contact angle hysteresis of paraffin wax surfaces with nanoclay

Colloid Polym Sci (2013) 291:383389

DOI 10.1007/s00396-012-2754-3

ORIGINAL CONTRIBUTION

Stabilizing contact angle hysteresis of paraffin wax surfaces with nanoclay

Gang Pu & Steven J. Severtson

Received: 20 July 2012 /Accepted: 28 July 2012 /Published online: 31 August 2012 # Springer-Verlag 2012

Abstract The addition of montmorillonite clay modified with an alkylammonium salt surfactant (i.e., organoclay) to paraffin wax is found to reduce the decay in wetting properties associated with its heating in the melt. It was previously shown that holding wax in its molten form prior to characterization reduces crystallinity when the solid forms. This results in the development of microscale amorphous regions at wax surfaces, which appear to be more polar given the abundance of methylene linkages versus methyl groups. These regions are believed to impact the receding angles for more polar liquids almost exclusively. It is known that the introduction and exfoliation of a small amount of the organoclay greatly enhances the stiffness, strength, and toughness of paraffin wax. Here, it is shown that the organo-clay also promotes the formation of coatings possessing fewer thermal cracks and helps maintain higher crystallinity levels. Fresh wax surfaces containing the clay are slightly rougher than those without, which produces a slight increase in hysteresis. However, the significant drops in receding angles found for paraffin wax samples cast from the melt subsequent to heating are absent.

Keywords Contact angle . Hysteresis . Nanoclay

Introduction

Paraffin wax, which is isolated from petroleum crudes, consists mainly of C18 to C45 normal alkanes [1, 2].

Due to its ability to repel water, low cost, and ease of handling, paraffin wax has found use as a moisture barrier for agricultural products and packaging, protective coatings against corrosion for metal components, and as an insulator in electrical systems [3]. A key property that makes paraffin wax attractive for these and other similar applications is its surface energy which is about 25 mJ/m2 and almost entirely from dispersion contributions [4]. This allows wax to easily spread on and/or saturate most materials. The disadvantage of using wax is that it is a soft and weak material with typical tensile strength and modulus values of approximately 0.8 and 60 MPa, respectively. Furthermore, it is quite brittle with an elongation at break on the order of...