SPECTROSCOPY
Figure 1: 3D heatmaps of polarisation-resolved Raman spectra in PE foil before (left) and after stretching (right). Labelled Raman peaks: (1) asymmetrical C-C
stretching, (2) symmetrical C-C stretching, (3) CH2 twisting, (4) CH2
bending, (5) C-H stretching
ORIENTATIONS MOLECULAR VISUALISING
Thomas Meyer, Ute Schmidt, Stefan Kreißl and Judith Beer from Oxford Instruments present polarisation-resolved Raman analyses that reveal the structural organisation in polymer and geological samples
R
esolving the organisation and orientation of molecules in a material is essential in various research fields. From
retracing the formation of naturally occurring structures to tailoring the chemical and physical properties in synthetics, structural analyses are the basis for many applications in geology, biology, pharmacology and material sciences. Polarisation- resolved Raman spectroscopy is a powerful tool to unveil these structural characteristics in a non- destructive and efficient way.
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POLARISATION- RESOLVED RAMAN SPECTROSCOPY Polarisation is a property of light that describes the directionality of the electric field vector in a light wave. Polarisation-resolved Raman spectroscopy uses this feature, as certain vibrational modes of molecular bonds detected in Raman spectroscopy are sensitive to the light’s polarisation angle. If these molecular bonds are oriented similarly in a sample, the Raman signal intensities vary with
changing polarisation angles of the excitation light. This can provide profound information on the sample’s molecular structure and organisation of different domains.
TECHNICAL REQUIREMENTS For polarisation-resolved Raman analyses, it is necessary to have suitable instrumentation that enables stable and precise control of the polarisation angle in the beam paths. A polarisation module can rotate incident linearly polarised light to the desired orientation. Polarisation filters in the detection beam path allow for the selection of the polarisation state of the scattered light. In the presented measurements, an Oxford Instruments WITec alpha300 Raman microscope with an automated polarisation module was used to record a 360° polarisation rotation series.
FIBER ALIGNMENT IN POLYETHYLENE FOIL STRETCHING Polyethylene (PE), a versatile synthetic polymer used for the creation of plastics with diverse
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