Transition from Spin Dewetting to continuous film in spin coating of Liquid Crystal 5CB

Dhara, Palash; Bhandaru, Nandini; Das, Anuja; Mukherjee, Rabibrata

doi:10.1038/s41598-018-25504-7

Cited by 24 publications

(20 citation statements)

References 80 publications

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“…21 The droplets remain stable approximately 12 to 14 hours, aer which they start to slowly spread over the substrate, which is attributed to the absorption of the -CN end group of 5CB on polar PMMA. 48,49 The gradual healing of a fully dewetted 5CB lm, is shown in Fig. S2 of ESI.…”

Section: Resultsmentioning

confidence: 99%

Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate

Dhara

Mukherjee

2019

RSC Adv.

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Section: Resultsmentioning

confidence: 99%

Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate

Dhara

Mukherjee

2019

RSC Adv.

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“…The influence of the concentration of inorganic precursor in the starting solution, together with aging time, was also investigated ( Figure ). Some films made with fresh low‐concentration solutions were observed to dewet during the spin‐coating process, either partially (0.7 m ) or completely (0.3 m ) . An increase in the concentration of the solution or in the time of aging avoided this problem, since the solutions became more viscous because of the higher degree of condensation, allowing the deposition of thicker films at a fixed spin speed.…”

Section: Resultsmentioning

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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“…Polymer dispersed liquid crystals (PDLCs) are one such example and are an important class of materials * b.chakrabarti@sheffield.ac.uk with applications ranging from novel bulk phenomena in electro-optic devices [7] to very rich and unique surface phenomena like tunable surface roughness [8] and electric field driven meso-patterning on soft surfaces [9,10]. These soft materials can be termed multi-responsive as they can be controlled by electro-magnetic fields, the presence of interfaces or substrates and temperature or concentration-gradients etc.…”

Section: Introductionmentioning

confidence: 99%

Canonical Simulation Methodology to Extract Phase Boundaries of Liquid Crystalline Polymer Mixtures

Fall¹,

Kolli²,

Mukherjee³

et al. 2021

Preprint

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We report a novel multi-scale simulation methodology to quantitatively predict the thermodynamic behaviour of polymer mixtures, that exhibit phases with broken orientational symmetry. Our system consists of a binary mixture of oligomers and rod-like mesogens. Using coarse-grained molecular dynamics (CGMD) simulations we infer the topology of the temperature-dependent free energy landscape from the probability distributions of excess volume fraction of the components. The mixture exhibits nematic and smectic phases as a function of two temperature scales, the nematic-isotropic temperature TNI and the Tc, the transition that governs the polymer demixing. Using a mean-field free energy of polymer-dispersed liquid crystals (PDLCs), with suitably chosen parameter values, we construct a mean-field phase diagram that semi-quantitatively match those obtained from CGMD simulations. Our results are applicable to mixtures of synthetic and biological macromolecules that undergo phase separation and are orientable, thereby giving rise to the liquid crystalline phases.

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Transition from Spin Dewetting to continuous film in spin coating of Liquid Crystal 5CB

Cited by 24 publications

References 80 publications

Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate

Phase transition and dewetting of a 5CB liquid crystal thin film on a topographically patterned substrate

Fabrication of Biomimetic Micropatterned Surfaces by Sol–Gel Dewetting

Canonical Simulation Methodology to Extract Phase Boundaries of Liquid Crystalline Polymer Mixtures

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