Effect of surface energy on the removal of supported triglyceride films by a flowing surfactant solution

Abstract

We investigate the role of substrate surface energy on the removal of triacylglycerol (TAG) films by a model surfactant solution under laminar flow conditions. We select a mixture of 0.5:0.3:0.2 triolein:tripalmitin:tristearin mass fraction as a model TAG, yielding a solid ‘fat’ film, and expose it to a micellar aqueous surfactant solution, flowing at rate 250 μLmin−1 (corresponding to a velocity of 1.4 cms−1), within a microfluidic channel. We employ a combination of optical and atomic force microscopy, profilometry, X-ray photoelectron and infrared spectroscopy, and contact angle measurements to characterise a range of model substrates, the TAG films, and their removal over time. Our experimental data show a clear dependence of the TAG removal time with surface energy and, in particular, with the polar component of the surface energy, γSFEP. TAG films on very hydrophilic surfaces, with high γSFEP (>20 mJ/m2), are generally found to delaminate rapidly, while those on lower γSFEP surfaces are progressively eroded over longer timescales. An approximately inverse linear relation is found between γSFEP and removal time τ, which holds for a large range of surfaces including glass, silicon and plastics, and various surface treatments.