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(a) optical indicatrix of a uniaxial liquid crystal where the semi axes correspond to the extraordinary (ne) and ordinary (no) refractive index with the incident light parallel to the extraordinary axis. This models a homeotropically aligned liquid crystal. (b) optical indicatrix of a uniaxial liquid crystal with a tilt towards the direction of shear with incident light oblique to the ordinary and extraordinary axes

(a) optical indicatrix of a uniaxial liquid crystal where the semi axes correspond to the extraordinary (ne) and ordinary (no) refractive index with the incident light parallel to the extraordinary axis. This models a homeotropically aligned liquid crystal. (b) optical indicatrix of a uniaxial liquid crystal with a tilt towards the direction of shear with incident light oblique to the ordinary and extraordinary axes

Source publication
Technical Report
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A novel experimental project adapted from my undergraduate thesis investigating the uses of polarised light microscopy techniques and single-wavelength ellipsometry for understanding the structure of smectic/lamellar liquid crystal structures in an EHD contact. The layered, lamellar phase of lyotropic liquid crystals (LLCs) display promising trib...

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Context 1
... is the optical property of a material that has a refractive index that depends on the propagation direction of the incident light and is measured as the maximum difference between the refractive indices of the material. Figure 3(a) shows a prolate spheroid model of a uniaxial liquid crystal molecule, birefringence of an LC sample is due to the index of refraction along the long axis (extraordinary axis, ne) being different to the index of refraction perpendicular to the short axis (ordinary axis, no). The birefringence (B) is expressed by: í µí°µí µí±–í µí±Ÿí µí±’í µí±“í µí±Ÿí µí±–í µí±›í µí±”í µí±’í µí±›í µí±í µí±’ (í µí°µ) = |í µí±› − í µí±› | Plane polarised light incident on a birefringent sample is split into two mutually perpendicular planes. ...
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... λ is the wavelength of plane polarised light [13]. Figure 3(a) shows that plane polarised light incident on the axis corresponding to ne. The wavefront only coincides with this refractive index and no birefringence will be observed, the light beam only interacts with no. Figure 3(b) shows how light incident on a LC molecule tilted in a shear flow will interact with two refractive indices, both the ordinary and extraordinary indices. ...
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... wavefront only coincides with this refractive index and no birefringence will be observed, the light beam only interacts with no. Figure 3(b) shows how light incident on a LC molecule tilted in a shear flow will interact with two refractive indices, both the ordinary and extraordinary indices. This light will be subject to a birefringent effect and produce an image at the analyser demonstrating an anisotropic effect, and hence LC structure in the sample. ...
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... Figure 12 faint Newton rings can be observed below the contact but this detail is lost at speeds above 50 mms -1 . Figure 13 shows TEOL behaviour in a range of speeds with a 20 N load and 50% SRR. At low speeds [Figures 13(a) and 13(b)] show the inlet pool contains separated domains of alignment with only some of the LC structure appearing light blue along the slow axis of the QWP. ...
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... low speeds [Figures 13(a) and 13(b)] show the inlet pool contains separated domains of alignment with only some of the LC structure appearing light blue along the slow axis of the QWP. As speed is increased to 20 mms -1 [Fig 13(c)] the LC in the inlet pool align homogenously in the entrainment direction with a much more stable flow. Figure 14 shows an enlarged image of the of the inlet at 5 mms -1 and 20 mms -1 . ...
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... higher speeds [Figures 13(d) and 13(e)] the entrainment direction dominates the LC alignment in the inlet pool up to speeds of around 200 mms -1 at which point the homogenous alignment began to break down at the entry of the inlet pool [Fig 13(f)]. This is characterised by dark spikes appearing demonstrating a definite change in LC structure in this region, a gradient of colour is seen indicating that this feature is still birefringent and therefore structured. ...
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... a speed of 500 mms -1 the measured film thickness using optical interferometry was approximately 102 nm, which would give an optical path length of approximately 288 nm (í µí±¡ = () = 288 í µí±›í µí±š, í µí±¤ℎí µí±’í µí±Ÿí µí±’ ℎ = 102 í µí±›í µí±š). If the LC structure was homeotropically aligned in the contact, as suggested by the previous experiments [ Fig 13] with the microscope normal to the contact, a noticeable birefringent effect would be expected. This leaves two cases (i) there is no structure at the contact or (ii) the optical anisotropy of the sample is sufficiently small that the phase shift of the light is small. ...