Alignment behaviour and molecular dynamics of liquid crystalline side-chain polymers

Williams, Graham

doi:10.1080/02678292.2015.1016736

Cited by 4 publications

(3 citation statements)

References 41 publications

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“…A devia-tion from this response occurred at high voltage amplitudes (U > 50 V) that might be caused by LC realignment effects under influence of the strong electric field due to two-frequency addressing, thereby suppressing the electrothermal effect. [37,38] Figure 4b shows that ΔT can be divided into three regions upon enhancing the frequency: a linear response (f = 0-3 MHz), a flattening (f = 3-10 MHz) and a decrease (f = 10-20 MHz) of ΔT with respect to the applied frequency. At 10 MHz, the highest temperature was recorded, corresponding to the maximum blue shift (Figure 3b) that was attained at the same frequency.…”

Section: Resultsmentioning

confidence: 99%

Electrothermal Color Tuning of Cholesteric Liquid Crystals Using Interdigitated Electrode Patterns

Froyen

Wübbenhorst

Liu

et al. 2020

Adv Elect Materials

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A transparent color‐tunable device is presented based on an electrothermal response by using interdigitated electrode patterns. The response is generated by applying an in‐plane AC electric field that heats up a thermosensitive cholesteric liquid crystal mixture. The induced temperature elevations cause band gap shifting (Δλ > 350 nm) up until a colorless state is reached, corresponding to the isotropic phase. Color shifting can be tuned manually by varying the electric field or autonomously by the surrounding temperature. Broadband dielectric spectroscopy reveals that the electrothermal response originates from resistive heating of the transparent electrode pattern in conjunction with the cell capacitance and is therefore largely dependent on the electrode configuration. Hence, the electrothermal response can be easily modified by changing the electrode pattern, frequency and/or voltage, dependent on the user's requirements. Therefore, the ability of this technique to manipulate the autonomous thermal response by an electric field, using only one conductive substrate, shows promise in the field of optoelectronics, sensors, and smart windows.

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Section: Resultsmentioning

confidence: 99%

Electrothermal Color Tuning of Cholesteric Liquid Crystals Using Interdigitated Electrode Patterns

Froyen

Wübbenhorst

Liu

et al. 2020

Adv Elect Materials

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“…We adopted a value of γ = 2 × 10 –9 J cm –2 , on the basis of literature data. − The molar volume of the nucleating nematic phase, V mol , is semiarbitrarily set equal to 100 cm 3 mol –1 , approximately 5 times that of water and therefore reasonably consistent with the selected axial ratio. Figures and show the relative rates of anisotropic phase nucleation, calculated from the free energy results by the FW and MS methods, respectively.…”

Section: Resultsmentioning

confidence: 99%

Rate of Lyotropic Nematic Phase Formation: Derivation and Application of Time–Concentration–Temperature–Transformation Diagrams

Komadina

Watt²,

McEwen

et al. 2015

Crystal Growth & Design

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The effect of both temperature and composition on the rate of transformation of a nematic phase from an isotropic solution is examined from a theoretical standpoint. The kinetics of the transformation are presented as a time− concentration−temperature−transformation (TCTT) diagram, analogous to the time−temperature−transformation (TTT) diagrams commonly used in metallurgical process design. The transformation is regarded as a nucleated process in which the transformation rate is proportional to the number of stable nuclei, and this in turn depends on a balance between the energy gained by nematic ordering and the energy expended in forming the nematic−isotropic interface. The nematic ordering term is estimated as a function of both concentration and temperature via two different approaches: (i) the lattice theory as described by Flory and Warner and (ii) the Maier−Saupe theory of nematic ordering. Although there are differences in detail, both approaches yield the same qualitative result. The present work provides the details necessary for developing a specific example application of our recently reported generalized system-independent model of nucleation and growth. The TCTT diagram is in essence a phase diagram augmented by kinetic information for nematic ordering, and thus is expected to be a powerful graphical tool in liquid crystal process engineering and other applications. ■ INTRODUCTIONNucleation and growth theory has been applied to a broad range of phase transformation phenomena that exhibit a competition between favorable transformation energy and unfavorable surface energy. Indeed, classical nucleation theory, originally derived for condensation of vapor to liquid, 1,2 is now commonly taught in introductory materials science courses in terms of the heat treatment of steels. 3−8 Classical nucleation and growth theory applies equally well to crystallization (of ice, 9 proteins from solution, 6,10−13 and colloids 13,14 ), liquid crystalline phase formation, 15−17 and even fields outside of the physical sciences, such as epidemiology. 18 In the case of metallurgical, 3,19,20 ceramic, 21 and mineral 22 phase transformations, the kinetic behavior that results from nucleation and growth is commonly represented on a time−temperature− transformation (TTT) diagram. Such diagrams display contours, often "C" shaped, of constant transformed fraction plotted on the temperature−time plane and are valuable graphical tools for process engineering.An analogous example is found in the transformation from an isotropic solution to a lyotropic nematic liquid crystalline phase, discussed in McEwen 23 and in the present work. The nematic phase becomes thermodynamically favored at a critical mesogen concentration, with the overall free energy becoming more negative as the concentration of the mesogen is further increased. Given this increasing thermodynamic "drive", the number of nuclei and the rate of nematic phase growth should be an increasing function of concentration. However, since increased concentration also reduces m...

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“…Depending on the mesogenic units in the polymer, liquid crystalline polymers are divided into main-and side-chain liquid crystalline polymers [21][22][23][24][25]. The side-chain liquid crystalline polymers are further divided into 'side-on' and 'end-on' types depending on whether the mesogenic groups are attached laterally or terminally to the polymer backbone via a flexible spacer [26,27].…”

Section: Introductionmentioning

confidence: 99%

Synthesis, liquid crystalline mesophases and morphologies of diblock copolymers composed of a poly(dimethylsiloxane) block and a nematic liquid crystalline block

Wei

Ma²,

Zhang

et al. 2016

Liquid Crystals

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In this study, a series of liquid crystalline diblock copolymers, composed of a soft poly(dimethylsiloxane) (PDMS) block with a defined length and a side-on liquid crystalline poly(3ʹʹ-acryloyloxypropyl 2,5-di(4ʹ-butyloxybenzoyloxy) benzoate) (P3ADBB) block with different lengths, are synthesised by the atom transfer radical polymerisation. The macromolecular structures, liquid crystalline properties and the microphase-separated morphologies of the diblock copolymer are investigated by 1 H NMR, FT-IR, GPC, POM, DSC and TEM. The results show that the well-defined diblock copolymers (PDMS n -b-P3ADBB m ) possess four different soft/rigid ratios (n = 58, m = 10, 25, 42, 66) and relatively narrow molecular distributions (PDI ≤ 1.30). P3ADBB blocks of the copolymers show nematic sub-phases, which are identical to the mesomorphic behaviour of the homopolymer P3ADBB. After being annealed at 90°C in a vacuum oven for 48 h, the copolymers form a lamellar morphology when m = 10 and morphologies of PDMS spheres embedded in P3ADBB matrix when m = 25, 42 and 66. ARTICLE HISTORY

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Alignment behaviour and molecular dynamics of liquid crystalline side-chain polymers

Cited by 4 publications

References 41 publications

Electrothermal Color Tuning of Cholesteric Liquid Crystals Using Interdigitated Electrode Patterns

Electrothermal Color Tuning of Cholesteric Liquid Crystals Using Interdigitated Electrode Patterns

Rate of Lyotropic Nematic Phase Formation: Derivation and Application of Time–Concentration–Temperature–Transformation Diagrams

Synthesis, liquid crystalline mesophases and morphologies of diblock copolymers composed of a poly(dimethylsiloxane) block and a nematic liquid crystalline block

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