Abstract
Understanding the nanostructure and nanomechanical properties of surface layers of
erucamide, in particular the molecular orientation of the outermost layer is important to its
widespread use as a slip additive in polymer materials. Extending our recent observations of
nanomorphologies of erucamide layers on a hydrophilic silica substrate, here we evaluate its
nanostructure on a more hydrophobic polypropylene surface. Atomic Force Microscopy
(AFM) imaging revealed the molecular packing, thickness and surface coverage of the
erucamide layers, whilst Peak Force Quantitative Nanomechanical Mapping (QNM) showed
that erucamide reduced the adhesive response on polypropylene. Synchrotron X-ray
reflectivity (XRR) was used to probe the out-of-plane structure of the surface layers. Static 2
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contact angle measurements further corroborated on the resulting wettability, also
demonstrating the efficacy of erucamide physisorption in facilitating control over
polypropylene surface wetting. The results show the formation of erucamide monolayers,
bilayers and multilayers, depending on the concentration in the spin-cast solution. Correlation
of AFM, XRR and wettability results consistently points to the molecular orientation in the
outermost layer, i.e. with the erucamide tails pointing outwards for the surface nanostructures
with different morphologies (i.e. bilayers and multilayers). Rare occurrence of monolayers with
exposed hydrophilic headgroups were observed only at the lowest erucamide concentration.
Compared with our previous observations on the hydrophilic surface, the erucamide surface
coverage was much higher on the more hydrophobic propylene surface at similar erucamide
concentrations in the spin-cast solution. Furthermore, the structure, molecular orientation and
nanomechanical properties of the spin-cast erucamide multilayers atop polypropylene were
also similar to those on industrially relevant polypropylene fibres coated with erucamide via
blooming. These findings shed light on the nanostructural features of the erucamide surface
layer underpinning its nanomechanical properties, relevant to many applications in which
erucamide is commonly used as a slip additive.
erucamide, in particular the molecular orientation of the outermost layer is important to its
widespread use as a slip additive in polymer materials. Extending our recent observations of
nanomorphologies of erucamide layers on a hydrophilic silica substrate, here we evaluate its
nanostructure on a more hydrophobic polypropylene surface. Atomic Force Microscopy
(AFM) imaging revealed the molecular packing, thickness and surface coverage of the
erucamide layers, whilst Peak Force Quantitative Nanomechanical Mapping (QNM) showed
that erucamide reduced the adhesive response on polypropylene. Synchrotron X-ray
reflectivity (XRR) was used to probe the out-of-plane structure of the surface layers. Static 2
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contact angle measurements further corroborated on the resulting wettability, also
demonstrating the efficacy of erucamide physisorption in facilitating control over
polypropylene surface wetting. The results show the formation of erucamide monolayers,
bilayers and multilayers, depending on the concentration in the spin-cast solution. Correlation
of AFM, XRR and wettability results consistently points to the molecular orientation in the
outermost layer, i.e. with the erucamide tails pointing outwards for the surface nanostructures
with different morphologies (i.e. bilayers and multilayers). Rare occurrence of monolayers with
exposed hydrophilic headgroups were observed only at the lowest erucamide concentration.
Compared with our previous observations on the hydrophilic surface, the erucamide surface
coverage was much higher on the more hydrophobic propylene surface at similar erucamide
concentrations in the spin-cast solution. Furthermore, the structure, molecular orientation and
nanomechanical properties of the spin-cast erucamide multilayers atop polypropylene were
also similar to those on industrially relevant polypropylene fibres coated with erucamide via
blooming. These findings shed light on the nanostructural features of the erucamide surface
layer underpinning its nanomechanical properties, relevant to many applications in which
erucamide is commonly used as a slip additive.
| Original language | English |
|---|---|
| Pages (from-to) | 6521-6532 |
| Number of pages | 12 |
| Journal | Langmuir |
| Volume | 37 |
| Issue number | 21 |
| Early online date | 20 May 2021 |
| DOIs | |
| Publication status | Published - 1 Jun 2021 |
Bibliographical note
Funding Information:D.G. is supported by the UK Engineering and Physical Sciences Research Council (EPSRC) and Procter and Gamble Industrial Case Award. W.H.B. would like to acknowledge funding from the EPSRC (EP/H034862/1) European Cooperation in Science and Technology (CMST COST) Action CM1101 “Colloidal Aspects of Nanoscience for Innovative Processes and Materials”. We acknowledge the beamline I07 at Diamond Light Source (UK) for beam time (experiment no. SI24392-1) and the staff there for their help during the experiment, as well as EPSRC (EP/K035746/1) for funding for the PeakForce AFM equipment.
Publisher Copyright:
© 2021 American Chemical Society.
Keywords
- Vesicles
- Thin films
- Thermoresponsive polymers
- Layers
- Hydrophobicity