Products Cited in Publications Worldwide Cholesteric Liquid Crystals in Additive Manufacturing

Cholesteric Liquid Crystals in Additive Manufacturing

Jeroen Sol

DOI:

Abstract

The perception of colour has played a critical role in human development, helping the earliest peoples to judge the ripeness of food, vital for their safety (1, 2). For this reason, human vision has evolved to be most sensitive in the range of 380 to 780 nm (3). Visible colours result from light absorbance, luminescence by pigments, or photonic systems that generate vivid colours via selective reflection of the electromagnetic spectrum as a result of nanoscale arrangement of their constituent materials (4). Using structural rather than pigmental or luminophore-generated colour has some key advantages. First is that structural colour is generally less susceptible to degradation. Secondly, the structured materials may also be made dynamic: when the material is swelled or contracted by exposure to environmental factors, the result may be dramatic colour changes, which could be harnessed for use as sensors (5). As discussed in Chapter 1, liquid crystals (LCs) are positioned to be the basis of many responsive structurally coloured materials. Addition of a chiral dopant to a nematic LC leads to the formation of a light-reflecting chiral nematic phase, inwhich the depth spanned by a 360° rotation of the directors of the LC planes is labelled the “pitch”, p. The product of p, average refractive index ⟨n⟩, and the angle of observation θ yields the wavelength of maximum reflection: λmax = p⟨n⟩ cos (θ). By polymerizing the reactive ChLC monomers into a ChLC network (ChLCN), one makes a step towards materials applicable as photonic plastics. Almost always described in thin-film format, these materials have served as visual security features (6), and indicators for temperature (7, 8), medical conditions (hypo- or hypercalcaemia) (9) or chemical analytes, such as for volatile low molecular weight amines (10). Furthermore, owing to their vibrant, angle-dependent colour, ChLC materials have been used in the decorative coatings industry as effect pigments (11), and recently as organic solvent-responsive coatings (12). An alternative to a fully cholesteric coating is based on spherical cholesteric particles embedded in a non-LC binder, although high concentrations of the particles are required (13).

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4-((6-(Acryloyloxy)hexyl)oxy)benzoic acid

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