Preparation and characterization of side-chain liquid crystalline polymer thin films aligned on PTFE friction-transferred layers

Wittmann, J. C.; Meyer, S.; Damman, Pascal; Dosière, M.; Schmidt, Hans‐Werner

doi:10.1016/s0032-3861(97)10104-5

Cited by 19 publications

(24 citation statements)

References 22 publications

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“…[2][3][4][5][6][7] At a molecular scale, these substrates exhibit large crystallographic ͑010͒ surfaces of perfectly oriented polymer chains, 2,10 while at a mesoscopic scale, AFM examinations of the surface topography reveal ridges and grooves aligned along the sliding direction. 10 Even though the characteristics of the PIA substrates are well known, the mechanisms related to the ability of these substrates to induce the alignment of molecules, liquid crystals ͑LC͒ and crystals are not yet understood.…”

Section: Introductionmentioning

confidence: 99%

“…[2][3][4][5][6][7] The observed lattice mismatches were found to vary typically between 0 and 0.10, which are values commonly accepted to refer as a true epitaxy. In addition, one of us ͑P.D.͒, in collaboration, has recently shown that 2-methyl-4-nitroaniline molecules crystallize on nanostructured PTFE thin films with two different crystalline orientations.…”

Section: Introductionmentioning

confidence: 99%

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Oriented growth of n-alkanes crystals on nanostructured poly(tetrafluoroethylene) substrates

Damman

Fischer

Krüger

2001

The Journal of Chemical Physics

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Articles you may be interested inMicro-structure evolution of wall based crystals after casting of model suspensions as obtained from Bragg microscopy J. Chem. Phys. 137, 094906 (2012); 10.1063/1.4749261 Lamellar nanostructures of silicon heterogeneously solidified on graphite sheets Appl. Phys. Lett. 96, 163113 (2010); 10.1063/1.3407476 Nanoscale domain growth dynamics of ferroelectric poly(vinylidene fluoride-co -trifluoroethylene) thin films Appl. Phys. Lett. 96, 012908 (2010); 10.1063/1.3290247 Orientation and nonlinear optical properties of N-4-nitrophenyl-(L)-prolinol crystals on nanostructured poly(tetrafluoroethylene) substrates Orientation and nonlinear optical properties of 4-(N,N-dimethylamino)-3-acetamidonitrobenzene crystals on nanostructured poly(tetrafluoroethylene) substratesThe growth of n-alkane (C n H 2nϩ2 ) crystals on poly͑tetrafluoroethylene͒ substrates ͑PIA͒ obtained by the friction-transfer method was studied by optical microscopy and grazing incidence x-ray diffraction. The experiments performed on a series of molecules ranging from nϭ21 to nϭ33 reveal the existence of a preferred contact plane with the PIA substrate corresponding to a minimum in lattice mismatch between the two crystallographic systems. Independently of the chain length, the n-alkane crystals tend to orient with their ͑200͒ planes parallel to the substrate, the molecular axis being preferentially aligned along the friction direction of the PTFE substrate. In our study, we demonstrate that the pathways ͑i.e., the orientation mechanisms͒ strongly influence the observed morphology in the low temperature phase.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Oriented growth of n-alkanes crystals on nanostructured poly(tetrafluoroethylene) substrates

Damman

Fischer

Krüger

2001

The Journal of Chemical Physics

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“…Electrondiffraction studies of the friction-transferred PTFE layers showed that the chain axis of the PTFE helixes is oriented parallel to the substrate surface and extended along the sliding direction. 21 The obtained single-crystal-like structure of the PTFE layers over a large surface (several cm 2 ) aligns low and high molecular weight liquid crystalline and crystalline materials from melt, solution, and by epitaxial growth from vapor. [21][22][23][24] VDP was further used to fabricate thin films with intrinsic molecular orientation parallel or perpendicular to the substrate, which can be controlled by the nature of the substrate and the deposition conditions.…”

Section: Introductionmentioning

confidence: 61%

Combinatorial methods for the optimization of the vapor deposition of polyimide monomers and their polymerization

et al. 2006

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A combinatorial study on the synthesis and in situ orientation of thin films of aromatic polyimides on different aligning surfaces was carried out. Monomer and polyimide libraries prepared by using a combinatorial approach consisting of step gradients with different thicknesses, sectors with different compositions, and sectors with or without alignment layers were investigated. As aligning surfaces, friction deposited layers of PTFE, rubbed polyimide films, and highly oriented polyimide layers prepared by a shearing technique were used. In addition to 3,39,4,49-biphenyldianhydride (BPDA), only para-linked dianhydrides and diamines with different aspect ratios were utilized.Vapor deposition was performed first with individual monomers, then sequentially or by coevaporation of two or more monomers. By using this combinatorial approach, the monomer and polyimide orientation can be optimized by variation of monomer composition, film thickness, and deposition sequence. The resulting films were characterized regarding their thickness and the achieved degree of orientation by polarized FTIR and UV-vis spectroscopy. The highest degree of orientation indicated by a dichroic ratio of nine to ten was observed for 4,40-diamino-p-terphenyl on PTFE surfaces. For other monomers, dichroic ratios of around two were determined irrespective of the aligning surface, indicating low orientation. It was found that coevaporation of both monomers yields isotropic polyimide films in good quality, whereas sequential evaporation of monomer pairs yields polyimide films with anisotropic properties.

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“…Therefore, they show the entropy elasticity of elastomers as well as the anisotropic characteristics of liquid crystals. Mesogens are either incorporated into the polymer backbone (main‐chain LCE) or linked to it via flexible spacers (side‐chain LCE) . They cause the molecular self‐organization in liquid crystalline (LC) phases (mesophases).…”

Section: Introductionmentioning

confidence: 99%

Influences of Ortho‐Fluoroazobenzenes on Liquid Crystalline Phase Stability and 2D (Planar) Actuation Properties of Liquid Crystalline Elastomers

Ditter

Braun

Zentel

2019

Macro Chemistry & Physics

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In general, LCEs have gained great interest as stimuli-responsive and actuator materials in the last decades. [7-16] They consist of shape anisotropic molecules (mesogens) that are incorporated in a weakly crosslinked polymeric network (an elastomer). Therefore, they show the entropy elasticity of elastomers as well as the anisotropic characteristics of liquid crystals. Mesogens are either incorporated into the polymer backbone (main-chain LCE) or linked to it via flexible spacers (side-chain LCE). [17-20] They cause the molecular selforganization in liquid crystalline (LC) phases (mesophases). In nematic phases, for example, rod shaped mesogens align with their long axis roughly parallel to a common director and thus have directional but no positional order. [21,22] Integrated in a polymeric network, they act as an anisotropic environment for the polymer chains and stretch them to some extent in the mesophase. [7,13-16,23] On the other hand, in the isotropic state the order is lost and polymers can adopt their favored isotropic coil conformation. Switching between these states results in a macroscopic shape change if the LC state is present as a monodomain within the LCE sample. Shrinkage parallel to the director and expansion in the perpendicular direction are observed while the volume is kept constant. [13-16,24] These actuation properties had already been predicted by de Gennes in 1975. [25,26] So far, actuations up to 400% [27] could be observed for main-chain LCEs while side-chain LCEs could achieve actuations of up to 70% [26,28] corresponding to the increase in length. [7] To obtain a monodomain, LCE samples need to be pretreated to align mesogens before crosslinking. This is usually done in magnetic [29,30] or electric fields, [31] with the help of photoalignment layers [32,33] or by mechanical stretching of prepolymerized samples. [7,10] After alignment, crosslinking can occur via covalent or physical netpoints. [7,8,34] To investigate actuation properties of LCEs, it is necessary to switch between the liquid crystalline and the isotropic state. This requires an external stimulus. Such stimulus can be, for example, a change of temperature, [35] irradiation with light, [36,37] a pH change, [38] or the use of electric or magnetic fields. [39,40] Most attention has been paid to temperature changes. This often requires temperatures far beyond ambient temperature and mostly the whole actuator device has to be heated which results in high energy consumption. In contrast, light as a Actuation Systems In this article, the influences of ortho-fluoroazobenzenes (o-Fbs) on liquid crystalline (LC) phase stability and actuation properties of liquid crystalline elastomers (LCEs) are presented. Such o-Fbs find interest because they allow full photoswitching with visible light (no ultraviolet (UV) radiation). Novel o-Fb monomers and crosslinkers are synthesized and characterized. Different amounts of an LC mixture are replaced with synthesized o-Fbs successively and their influences on the LC phase stability in the cis...

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Preparation and characterization of side-chain liquid crystalline polymer thin films aligned on PTFE friction-transferred layers

Cited by 19 publications

References 22 publications

Oriented growth of n-alkanes crystals on nanostructured poly(tetrafluoroethylene) substrates

Oriented growth of n-alkanes crystals on nanostructured poly(tetrafluoroethylene) substrates

Combinatorial methods for the optimization of the vapor deposition of polyimide monomers and their polymerization

Influences of Ortho‐Fluoroazobenzenes on Liquid Crystalline Phase Stability and 2D (Planar) Actuation Properties of Liquid Crystalline Elastomers

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