Programming Thermochromic Liquid Crystal Hetero-Oligomers for Near-Infrared Reflectors: Unequal Incorporation of Similar Reactive Mesogens in Thiol-ene Oligomers

Abstract

Cholesteric liquid crystal oligomers are widely researched for their interesting thermochromic properties. However, structure−property relationships to program the thermochromic properties of these oligomers have been rarely reported. In this work, we use the versatile thiol-ene click reaction to synthesize a series of hetero-oligomers and study the impact of different compositions on the thermochromic behavior of the resulting material. Characterization of the oligomers shows significantly different rates of reaction for the monomers despite their very similar structures, which leads to oligomer compositions that do not match the original reaction feed. The oligomers are then used to produce thin near-infrared reflecting coatings. The best-performing thermochromic reflector has a room-temperature reflection band that shifts a total of 510 nanometers upon heating to 120 °C. The shift is repeatable for up to 10 times with no appreciable degradation. The room temperature reflection of the coatings is shown to be tunable not only by adjusting the chiral dopant concentration but also by the ratio of the monomers. Finally, we show that the oligomers can be chemically modified by making their reactive end groups undergo a reaction with monothiol compounds. These modifications allow for further fine-tuning of liquid crystal oligomers for heat-regulating window films, for example.

Sticky Multicolor Mechanochromic Labels

“…1 H-nuclear magnetic resonance ( 1 H NMR) measurements were performed on a Bruker Avance Core III 400 MHz spectrometer using deuterated chloroform as the solvent; the average length was calculated using the relative integrals of the remaining acrylate groups and the aromatic hydrogens of the liquid crystal units. 32 The glass transition (T g ) and cholesteric to isotropic transition (T Ch,I ) temperatures were determined by differential scanning calorimetry (DSC) with a TA Instruments Q2000 apparatus; samples were placed on aluminum hermetic crucibles and scanned during heating and cooling cycles from −50 to 150 °C at a 10 °C/min rate. The transition temperatures were obtained from the second and third heating cycles.…”

Recent advances in solar infrared light regulating smart windows based on organic materials

“…By adding a diacrylate with a relatively short alkyl chain to a baseline oligomer mixture, roomtemperature reflection can be improved without hindering the total reflection band shift (Figure 12). [60] Conversely, adding a diacrylate with a relatively long alkyl chain to the same baseline oligomer results in a greater shift of the reflection, albeit at a cost to reflector performance and transparancy. [61] Transparency in the visible region remains >80% for all cases.…”

“…Where no data are shown, no reflection band was observed. [60] F I G U R E 1 3 Modulation of visible light transmission in a Hele-Shaw cell. (a) Reversible injection and collapse of air bubble within a Hele-Shaw cell, including minute:second timestamps.…”

“…(b) Shifting position of the reflection band peak of the five coatings. Where no data are shown, no reflection band was observed [60] …”

Impact of Endcap Molecules on Temperature‐Responsive Cholesteric Liquid Crystal Oligomers in Structural Color Stability and Hypsochromic Shift

“…[13] Oligomerization of reactive LCs has been shown to result in versatile, responsive materials that change color as a response to various stimuli, [14][15][16] while being wellsuited for 3D-printing [17][18][19][20] or coating techniques. [21][22][23] Of particular note are temperature responsive CLC oligomers with hypsochromic properties, i. e. where the color shifts to shorter wavelengths upon heating. While the color of a cholesteric phase is ordinarily only dependent on the composition of the mixture, CLC oligomers experience a pre-transitional effect.…”