Lithographic Alignment of Discotic Liquid Crystals: A New Time–Temperature Integrating Framework

Cavallini, Massimiliano; Calò, Annalisa; Stoliar, Pablo; Kengne, Jean Crispin; Martins, Sandrine; Matacotta, F.C.; Quist, Florence; Gbabode, Gabin; Dumont, Nicolas; Geerts, Yves; Biscarini, Fabio

doi:10.1002/adma.200901258

Cited by 56 publications

(51 citation statements)

References 41 publications

(24 reference statements)

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“…However, the large‐area uniform molecular alignment of DLCs is the key issue for the improvement of charge transport properties, thus influencing their application in such devices. Hitherto, the self‐organized alignment of DLC molecules can be induced by different techniques, including mechanical shearing, Langmuir–Blodgett thin films, zone‐casting technique, zone melting, template growth, applying aligned polytetrafluoroethylene layers, micro‐ and nanoconfinement, magnetic and electric field alignment, and lithographically wetting technique . These methods are good examples to align DLC materials into homogeneous thin film with high quality (uniformity of macroscopic orientation of DLC molecules).…”

Section: Introductionmentioning

confidence: 99%

Patterning of Discotic Liquid Crystals with Tunable Molecular Orientation for Electronic Applications

Zou

Wang

et al. 2018

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The large-area formation of functional micropatterns with liquid crystals is of great significance for diversified applications in interdisciplinary fields. Meanwhile, the control of molecular alignment in the patterns is fundamental and prerequisite for the adequate exploitation of their photoelectric properties. However, it would be extremely complicated and challenging for discotic liquid crystals (DLCs) to achieve the goal, because they are insensitive to external fields and surface chemistry. Herein, a simple method of patterning and aligning DLCs on flat substrates is disclosed through precise control of the formation and dewetting of the capillary liquid bridges, within which the DLC molecules are confined. Large-area uniform alignment occurs spontaneously due to directional shearing force when the solvent is slowly evaporated and programmable patterns could be directly generated on desired substrates. Moreover, the in-plane column direction of DLCs is tunable by slightly tailoring their chemical structures which changes their self-assembly behaviors in liquid bridges. The patterned DLCs show molecular orientation-dependent charge transport properties and are promising for templating self-assembly of other materials. The study provides a facile method for manipulation of the macroscopic patterns and microscopic molecular orientation which opens up new opportunities for electronic applications of DLCs.

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Section: Introductionmentioning

confidence: 99%

Patterning of Discotic Liquid Crystals with Tunable Molecular Orientation for Electronic Applications

Zou

Wang

et al. 2018

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“…While these approaches offer a precise control of the size and spatial distribution of the features, the techniques are often complex and not suitable to upscaling. Recently, research in material science has focused on biomimetic approaches based on integrating physical and chemical methods that combine soft matter structures and processes to yield materials with a variety of textures and shapes at different length scales . Among these, film dewetting is an attractive patterning approach, which combines low cost and straightforward procedures with the possibility of control over large pattern areas …”

Section: Introductionmentioning

confidence: 99%

“…When the polymer film is brought below its T g , the pattern is frozen in and preserved . Spatially controlled alignment of the droplets or confinement of the dewetted areas can be induced by external stimuli such as stamp or probe, or by using pre‐patterned substrates …”

Section: Introductionmentioning

confidence: 99%

Fabrication of Biomimetic Micropatterned Surfaces by Sol–Gel Dewetting

Colusso

Martucci

Neto

2019

Adv Materials Inter

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Dewetting is a spontaneous phenomenon that occurs when unstable thin liquid films break apart on a non-wettable substrate, driven by unfavorable intermolecular forces at the interface. The Neto group has used dewetting of polymer films extensively in the last decade to generate patterned surfaces for a range of applications, including atmospheric water capture and cell patterning. [16][17][18][19][20][21] Dewetting of metastable thin polymer films (≈100 nm) occurs when the polymer is brought above its glass transition temperature (T g ), by either thermal or solvent annealing, to enable sufficient mobility of the polymer chains. During dewetting, holes appear in the initially uniform film, then grow with time, until eventually all the polymer is accumulated in isolate droplets on the substrate. When the polymer film is brought below its T g , the pattern is frozen in and preserved. [22][23][24][25][26] Spatially controlled alignment of the droplets or confinement of the dewetted areas can be induced by external stimuli such as stamp or probe, or by using prepatterned substrates. [14,[27][28][29] Sol-gel films are much more robust than polymer films as they are mostly inorganic in nature, so can withstand high working temperature and UV irradiation, are harder, and their refractive index and electronic properties can be modulated. [30][31][32][33] In the sol-gel process, inorganic polymers and ceramics are obtained starting from liquid precursors though hydrolysis and condensation reactions that lead the formation of a network structure called "gel.". This gel is then converted into a dense "xerogel" during the drying through expulsion of solvent and collapse of the porous network and eventually converted into a dense ceramic through calcination at high temperature (if required). [34,35] So far, the dewetting of sol-gel films has been studied only in a couple of papers. [36,37] In this paper, we investigated for the first time the dewetting of bilayers of sol-gel films: the top film is hydrophilic (silica) and the bottom one hydrophobic (CH 3silica), with the objective of producing silicate patterns that are both chemical and topographical in nature. The control of the wettability of the surface is obtained by chemical modification of the sol-gel network by using organic-modified silicon precursors with hydrophobic groups. [38,39] The produced patterns, hydrophilic bumps on a hydrophobic background, mimic the exoskeleton of the Namib desert beetle (which has ≈500 µm hydrophilic bumps on a waxy background), [17,40] and could facilitate the nucleation of water droplets via condensation Dewetting of thin polymer films has been extensively investigated as a way to generate patterned surfaces. In this paper, the controlled dewetting of sol-gel thin films induced by solvent annealing is reported. The key factors that control the dewetting process are identified and patterns with tunable diameter between 5 and 80 µm and tunable height between 1 and 10 µm are fabricated on a large scale. By changing the chemistry of the s...

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“…Discotic liquid crystals (DLCs) [1] are a class of liquid crystals proposed for many applications in organic electronics [2][3][4][5], including organic field effect transistors (OFETs) [6,7], in photovoltaics [8][9][10], as sensors [11,12] and in information storage [12]. DLCs are formed by a rigid aromatic core and highly flexible peripheral chains, which provide solubility and drive self-organizing properties of these materials in columns forming different mesophases [13,14].…”

Section: Introductionmentioning

confidence: 99%

Doping and photo-induced current in discotic liquid crystals thin films: Long-time and temperature effects

Calò¹,

Stoliar²,

Cavallini³

et al. 2011

Organic Electronics

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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. b s t r a c tHere we address the problem of time and temperature instability of the electrical current related to parasitic doping effects in discotic liquid crystals (DLCs). We investigated the electrical transport in thin films of a phthalocyanine-based DLC in-dark and upon laser irradiation during long thermal cycles. Measuring the electrical transport between two electrodes we observed that in-dark the current is mostly due to doping levels while, upon laser irradiation, the photocurrent reflects the diffusion length of the photogenerated charge carriers and it is limited by the coherence length of a column. We prove here that the two contributions are completely independent. Our result experimentally supports the theoretical studies performed at the molecular level on discotic liquid crystals.

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Lithographic Alignment of Discotic Liquid Crystals: A New Time–Temperature Integrating Framework

Cited by 56 publications

References 41 publications

Patterning of Discotic Liquid Crystals with Tunable Molecular Orientation for Electronic Applications

Patterning of Discotic Liquid Crystals with Tunable Molecular Orientation for Electronic Applications

Fabrication of Biomimetic Micropatterned Surfaces by Sol–Gel Dewetting

Doping and photo-induced current in discotic liquid crystals thin films: Long-time and temperature effects

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