Functional Films and Fibres based on Liquid Crystal Coatings
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This thesis aims to produce functional polymer fibres and films using liquid crystal networks or photoembossing. The work focuses on visual effects in fibres, optical sensing properties and, actuation and morphing properties. In the first part we focused on changing the perception of textiles by generating structural colours based on diffraction and/or reflection of light. For the former, a micro-structuring technique is combined with a contactless patterning technique: pulsed holography. The results show that diffractive features could be generated on static or moving polymer films allowing for large area patterning. The use of a contactless patterning technique also suggests its potential application for curved surfaces such as fibres. In the second approach, reflective colours are generated using a self-organising cholesteric liquid crystal (CLC) coating. The coating is applied in a one step process though spray coating of a liquid crystal monomer mixture on the polymer substrate followed by photopolymerization. Reflectivity measurements and optical microscopy show that a well-defined liquid crystalline and planar alignment is obtained. In the case of films, a strong angular dependent reflection is obtained. In comparison fibres shown lower reflectivity with an angular dependent colour in a single dimension along the fibre direction which originates from the planar cholesteric alignment on a curved surface. The second part of the project was aimed at detecting strain optically in polymer films and fibres. Here, we used the same process to produce reflective films and studied the optical response to uniaxial deformation. Results showed a colour shift as function of strain that was dependent on the mechanical behaviour of the substrate giving real time information of the deformation in the substrate. In the final part the thesis, we explored shape change in response to light of a bilayer photoresponsive film for adaptive textile applications. Here we showed that bending could be generated by coating a photoresponsive LC layer on an oriented polymer substrate. Bending is attributed to a photo induced contraction that occurs in the coating. The resulting response was strongly dependent on the substrate thickness and stiffness, thermo-mechanical properties and the concentration of chromophore in the LC layer.
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