Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

Gvozdovskyy, Igor; Kurioz, Yu.; Reznikov, Yuriy

doi:10.2478/s11772-008-0065-5

Cited by 13 publications

(6 citation statements)

References 8 publications

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“…In this case all the measurements of geometrical dimension of droplets were carried out along direction of rubbing. In the case of ODAPI, a certain correlation between the contact angle β (Figure 15a, curve 2) and calculated value of AAE W φ [62] for the number of rubbing N rubb is observed, similarly to the case of the photosensitive PVCN-F surface [40]. Consequently, for the ODAPI layers possessing a strong AAE W φ (when N rubb = 10 -15), small contact angles β were found.…”

Section: Contact Angle Of the Droplets On Rubbed Polymer Filmsmentioning

confidence: 70%

“…To measure the contact angle β of isotropic liquid (glycerol) or two nematic LCs (E7 and MLC-6609), the simple method has been used [40]. It is based on the measurement of linear dimensions of the droplet placed to the aligning layer by means of the horizontal microscope, as shown in Figure 4a.…”

Section: Determination Of the Contact Angle βmentioning

confidence: 99%

“…shown that on the one hand, there has been certain exposure dependence of the contact angle of the nematic droplet E7 at the photosensitive PVCN-F surface [40] and on the other hand, the irradiation time dependence of the AAE W φ of PVCN-F surfaces was found [36]. It is important to note that the influence of the laser power on both the adhesion, surface free energy graphene treated by nonlinear laser lithography (NLL) [41], and contact angle of the water droplets deposited on the various treated graphene surfaces was studied [42].…”

Section: Introductionmentioning

confidence: 99%

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Azimuthal and polar anchoring energies of aligning layers structured by nonlinear laser lithography

et al. 2020

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In spite of the fact that there are different techniques in the creation of the highquality liquid crystals (LCs) alignment by means of various surfaces, the azimuthal and polar anchoring energies as well as the pre-tilt angle are important parameters to all of them. Here, the modified by a certain manner aligning layers, previously formed by nonlinear laser lithography (NLL), having high-quality nano-periodic grooves on Ti surfaces, recently proposed for LC alignment was studied. The change of the scanning speed of NLL in the process of nano-structured Ti surfaces and their further modification by means of ITO-coating, and deposition of polyimide film has enabled different aligning layers, whose main characteristics, namely azimuthal and polar anchoring energies, were measured. For the modified aligning layers, the dependencies of the twist and pre-tilt angles for LC cells filled by nematic E7 (Δε > 0) and MLC-6609 (Δε < 0) were obtained. Also the contact angle for droplets of isotropic liquid (glycerol), and nematic LCs was measured for the various values of the scanning speed during the laser processing.

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Section: Contact Angle Of the Droplets On Rubbed Polymer Filmsmentioning

confidence: 70%

Section: Determination Of the Contact Angle βmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Azimuthal and polar anchoring energies of aligning layers structured by nonlinear laser lithography

et al. 2020

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“…The contact angle values of PVCN-F coated surfaces are slightly higher than those with PVA coating on respective surfaces (Table 1). However, wettability of such films can be tuned either by temperature or by varying the irradiation time of the UV light (Gvozdovskyy et al 2009)…”

Section: Anchoring Characterization Of Functionalized Substratesmentioning

confidence: 99%

Functionalization of microfluidic devices for investigation of liquid crystal flows

Sengupta

Schulz

Ouskova

et al. 2012

Microfluid Nanofluid

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Systematic studies of thermotropic liquid crystals in confinement, such as liquid crystals in microfluidic channels, require control of the anchoring conditions on the surfaces. Especially for the case of uniform planar anchoring, the standard method involves a mechanical treatment (rubbing) of the surface that is not applicable to microfluidic devices. In the present study, we report methods for the achievement of well-defined anchoring conditions for liquid crystals in microfluidic channels consisting of polydimethylsiloxane and glass. Various physico-chemical techniques enable to establish homeotropic, degenerate planar, uniform planar, and hybrid anchoring conditions on the surface of the channel walls. We characterize the treated surfaces in terms of wettability and liquid crystal anchoring and determine the director field in the microchannels for the different anchoring configurations using polarizing optical microscopy and fluorescence confocal polarization microscopy. The relevance of the surface anchoring for the flow behavior of the liquid crystal in the microchannel is demonstrated by studying the onset of defect-mediated chaoticlike flow at high Ericksen numbers for the different anchoring cases.

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“…The contact angle values of PVCN-F coated surfaces are slightly higher than those with PVA coating on respective surfaces (Table 4.1). However, wettability of such films can be tuned either by temperature or by varying the irradiation time of the UV light [173].…”

Section: Anchoring Characterization Of Functionalized Substratesmentioning

confidence: 99%

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

Sengupta

Herminghaus

Bahr

2011

Molecular Crystals and Liquid Crystals

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Where the mind is without fear and the head is held high;Where knowledge is free;Where the world has not been broken up into fragments by narrow domestic walls;Where words come out from the depth of truth;Where tireless striving stretches its arms towards perfection;Where the clear stream of reason has not lost its way into the dreary desert sand of dead habit;Where the mind is led forward by thee into ever-widening thought and actionInto that heaven of freedom, my Father, let my country awake.Rabindranath Tagore (1861Tagore ( -1941 To my parents, my brother, and all the sacrifices they made for me AbstractThe doctoral thesis presented here is one of the first systematic attempts to unravel the wonderful world of liquid crystals within microfluidic confinements, typically channels with dimensions of tens of micrometers. The present work is based on experiments with a roomtemperature nematic liquid crystal, 5CB, and its colloidal dispersions within microfluidic devices of rectangular cross-section, fabricated using standard techniques of soft lithography. To begin with, a combination of physical and chemical methods was employed to create well defined boundary conditions for investigating the flow experiments. The walls of the microchannels were functionalized to induce different kinds of surface anchoring of the 5CB molecules: degenerate planar, uniform planar, and homeotropic surface anchoring. Channels possessing composite anchoring conditions (hybrid) were additionally fabricated, e. g. homeotropic and uniform planar anchoring within the same channel. On filling the microchannels with 5CB in the isotropic phase, different equilibrium configurations of the nematic director resulted, as the sample cooled down to nematic phase. For a given surface anchoring, the equilibrium director configuration varied also with the channel aspect ratio. The static director field within the channel registered the initial conditions for the flow experiments. The static and i ii dynamic experiments have been analyzed using a combination of polarization, and confocal fluorescence microscopy techniques, along with particle tracking method for measuring the flow speeds. Additionally, dual-focus fluorescence correlation spectroscopy is introduced as a generic velocimetry tool for liquid crystal flows.The flow of nematic liquid crystals is inherently complex due to the coupling between the flow and the nematic director. The presence of the four confining walls and the nature of surface anchoring on them complicate the flow-director interactions further. In microchannels possessing degenerate planar anchoring, four different flow-induced defect textures were identified with increasing Ericksen number: π-walls, disclination lines pinned to the channel walls, disclination lines with one pinned and one freely suspended end, and disclination loops freely flowing in a chaotic manner. However, such textures and sequence of defects were not observed for flows within channels with homogeneous anchoring.Using experiments and numerical modeling...

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Exposure and temperature dependences of contact angle of liquid crystals on photoaligning surface

Cited by 13 publications

References 8 publications

Azimuthal and polar anchoring energies of aligning layers structured by nonlinear laser lithography

Azimuthal and polar anchoring energies of aligning layers structured by nonlinear laser lithography

Functionalization of microfluidic devices for investigation of liquid crystal flows

Nematic Liquid Crystals and Nematic Colloids in Microfluidic Environment

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