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Heads or tails: Nanostructure and molecular orientations in organised erucamide surface layers

DOI: 10.1016/j.jcis.2021.01.087 DOI Help

Authors: Dajana Gubala (University of Bristol) , Laura Fox (University of Bristol) , Robert Harniman (University of Bristol) , Hadeel Hussain (Diamond Light Source) , Eric Robles (Procter & Gamble Newcastle Innovation Centre) , Meng Chen (Procter & Gamble Beijing Innovation Centre) , Wuge H. Briscoe (University of Bristol)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Journal Of Colloid And Interface Science , VOL 590 , PAGES 506 - 517

State: Published (Approved)
Published: May 2021
Diamond Proposal Number(s): 22176

Abstract: Hypothesis: Despite the widespread industrial usage of erucamide as a slip additive to modify polymer surface properties, a controversy appears to have persisted regarding the nanostructure of erucamide surface layers, particularly the molecular orientation at the outermost layer. The erucamide nanostructure and molecular orientation, along with its surface coverage, hydrophobicity, and adhesive response, can be tuned by simply varying the erucamide concentration in the solution from which the spin coated layer is prepared. Experiments: Synchrotron X-ray reflectivity (XRR) allowed a comprehensive characterisation of the out-of-plane structural parameters (e.g. molecular packing and thickness) of the erucamide layers prepared via spin coating from nonaqueous solution on silica. Complementary Atomic Force Microscopy (AFM) imaging with high lateral resolution revealed localised in-plane structures. Contact angle measurements provided information on the wettability of erucamide-coated surfaces. Peak Force Quantitative Nanomechanical Mapping (QNM) allowed a correlation between the erucamide nanostructure with the surface nanomechanical properties (i.e. adhesive response). Findings: Our results reveal erucamide surface nanostructures on silica as patchy monolayers, isolated circular bilayers/rounded rectangle-like aggregates and overlapping plate-like multilayers as the erucamide concentration in the spin coating solution was varied. In all the cases, XRR and AFM results were consistent with the picture that the erucamide tails were oriented outwards. The QNM adhesion force mapping of all the observed morphologies also supported this molecular orientation at the outermost erucamide monolayer. The wettability study further confirmed this conclusion with the observed increase in the surface hydrophobicity and coverage upon increasing erucamide concentration, with the macroscopic water contact angle θ = 92.9° ± 2.9° at the highest erucamide concentration of 2 wt%.

Journal Keywords: Erucamide; Slip additives; Interfacial structure; XRR; AFM imaging; Multilayers

Subject Areas: Biology and Bio-materials, Physics, Chemistry

Instruments: I07-Surface & interface diffraction

Discipline Tags:

Physical Chemistry Life Sciences & Biotech Chemistry

Technical Tags:

Diffraction X-ray Reflectivity (XRR)