MEMS analogous micro-patterning of thermotropic nematic liquid crystalline elastomer films using a fluorinated photoresist and a hard mask process

Ditter, David; Chen, Wei‐Liang; Best, A.; Zappe, Hans; Koynov, Kaloian; Ober, Christopher K.; Zentel, Rudolf

doi:10.1039/c7tc03958a

Cited by 19 publications

(13 citation statements)

References 65 publications

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“…The thermal actuation of the LCE without azochromophore (first line of Table ) is in the same range as observed for similar systems . The maximal thermal actuation decreases then, at first, slightly with increasing azobenzene component up to 5 mol%.…”

Section: Resultssupporting

confidence: 73%

“…The thermal actuation of the LCE without azochromophore (first line of Table 1) is in the same range as observed for similar systems. [26,30,33] The maximal thermal actuation decreases then, at first, slightly with increasing azobenzene component up to 5 mol%. When increasing the azobenzene content further to 7 and 10 mol% the thermal actuations decrease drastically.…”

Section: Investigation Of Thermal and Photochemical Actuation Propertmentioning

confidence: 97%

“…To obtain a monodomain, LCE samples need to be pretreated to align mesogens before crosslinking. This is usually done in magnetic or electric fields, with the help of photoalignment layers or by mechanical stretching of prepolymerized samples . After alignment, crosslinking can occur via covalent or physical netpoints …”

Section: Introductionmentioning

confidence: 99%

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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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Section: Resultssupporting

confidence: 73%

Section: Investigation Of Thermal and Photochemical Actuation Propertmentioning

confidence: 97%

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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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“…They consist of mesogenic groups, which are incorporated in an elastomer network and thus combine the orientational order of the LC phase with rubber elasticity . For synthesis, often a LC monomer, a crosslinker and an initiator are mixed as a LCE precursor, aligned as a monodomain with photoalignment layers, shear flow (for example with the help of a microfluidic device), electric or magnetic fields and polymerized and crosslinked in the LC state . The mesogenic groups are thereby either incorporated directly into the polymer main‐chain (main‐chain LCE) or linked to it via flexible spacers (side‐chain LCE) .…”

Section: Introductionmentioning

confidence: 99%

Microfluidic Synthesis of Liquid Crystalline Elastomer Particle Transport Systems which Can Be Remote‐Controlled Magnetically

Ditter

Blümler

Klöckner

et al. 2019

Adv Funct Materials

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Here, the microfluidic synthesis of liquid crystalline elastomer (LCE) particles, which can be remote-controlled magnetically and used as transport systems, is presented for the first time. Ferri-magnetic, rod-shaped Fe 3 O 4 nanoparticles are functionalized with poly(methyl methacrylate) to make them compatible with organic LCE precursor compounds. Their influence on the LCE precursor alignment is studied and thermoresponsive as well as photoresponsive LCE microparticles containing 0-6 wt% Fe 3 O 4 are synthesized with a microfluidic device. Thermal and photochemical actuations of these particles are investigated. Their magnetic addressability is studied with a recently developed magnetic setup, by which the particles can be guided on liquid surfaces in the centimeter range-but with a precision in the submillimeter range. This allows the performance of reversible light-or heat-controlled actuations at desired positions. The potential of synthesized LCE particles as transport systems is demonstrated by the transport of plastic, textiles or copper, which can be pushed just due to magnetic forces or transported in general by taking advantage of the phase dependent "stickiness" of LCEs. These studies open doors to novel applications of LCEs as microrobots using magnetism as a control.

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“…In order to obtain a strong deformation, it is necessary that the sample either forms a monodomain or features at least a preferred orientation of the single domain's directors during the crosslinking step 20 . For the production of LCE films, this is often achieved by the stretching of a pre-polymerized sample, via the orientation of the domains in an electric or magnetic field, with the aid of photo-alignment layers or via 3Dprinting 21,22,23,24,25,26 .…”

Section: Introductionmentioning

confidence: 99%

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

Hessberger

Braun

Serra

et al. 2018

JoVE

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This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

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MEMS analogous micro-patterning of thermotropic nematic liquid crystalline elastomer films using a fluorinated photoresist and a hard mask process

Abstract: LCE films can be patterned in the micrometer range with standard MEMS techniques.

Cited by 19 publications

References 65 publications

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

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

Microfluidic Synthesis of Liquid Crystalline Elastomer Particle Transport Systems which Can Be Remote‐Controlled Magnetically

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

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