Background
The surface and interface regions of organic polymers play a
vital role in many aspects of modern everyday life. In areas such
as biotechnology, electronic devices, composite materials,
corrosion protection, packaging and decorative coatings, the
properties of polymer surfaces and interfaces have an important
influence on the performance of technology.
Polymers are amenable to controlled surface modification
processes such as flame or plasma treatment or the use of a surface
segregating chemical component, thus allowing surface properties to
be optimised while retaining desirable bulk properties.
The Challenge
| Scientists from the National Centre for Electron Spectroscopy
and Surface Analysis (NCESS) at Daresbury Laboratory, set out to
characterise the uppermost surface regions (1 - 5 nm) of a wide
range of technologically important polymers, using x-ray
photoelectron spectroscopy (XPS), specifically using the NCESS
ESCA300 XPS spectrometer. |
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The solution
For poly(ethylene terephthalate) (PET), widely used in bottles,
packaging and film, the high energy resolution of the ESCA300
spectrometer was used to discover that the shape of the polymer
chains subtly influences the XPS spectrum thus providing a
diagnostic for the crystalline/amorphous nature of the polymer
surface.
The benefits
The high energy resolution of the ESCA300 was also used to show
that thermal treatment of PET causes the surface chains to
rearrange more quickly than those in the bulk. For poly(ethylene
glycol) (PEG) the high intensity of the spectrometer was used to
demonstrate that the chain shape influences the XPS spectrum, again
providing a diagnostic for the crystalline/amorphous nature of the
surface.
The blending of polymers is an important way of modifying both
bulk and surface properties. However polymer blends are complex and
require a multi-technique characterisation approach. Polymer blend
thin films often behave very differently from the bulk materials.
Current work at NCESS uses XPS and AFM (Atomic Force Microscopy) to
investigate polymer blends as a function of molecular weight and
film thickness. This will ultimately feed into an improved
understanding of polymer blend thin film devices such transistors
and displays.
Other applications
Polymers are often reinforced with fibres (e.g. carbon fibre,
glass fibre) or powders to generate stronger and tougher composite
materials and there is currently much interest in using nanoscale
reinforcement to produce nanocomposites with improved properties.
The surface chemistry of the nanomaterial is crucial as this
provides interfacial bonding between the polymer and the
nanoparticles. Scientists from NCESS and the Universities of
Liverpool and Florida State have characterised the surfaces of
carbon nanotubes (CNT), nanodiamonds (ND) and silica nanoparticles
for use in polymer composites. It has been found, for example, that
CNTs coated with ND considerably improve the ballistic resistance
of composites for body armour applications.
The future
The NCESS research programme into polymer surfaces is set to
continue into the future and interested parties are encouraged to
contact the
Unit either directly or via Daresbury SIC.
Click here to view the full case
study detailing NCESS' x-ray photoelectron spectroscopy
characterization of technological polymer surfaces.