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.
Heterogeneous polymer brushes on surfaces can be easily formed from a binary initiator on a silicon oxide substrate where two different types of polymers can be grown side-by-side. Herein, we designed a new Y-shaped binary initiator using straightforward chemistry for "grafting from" polymer brushes. This initiator synthesis takes advantage of the Passerini reaction, a multicomponent reaction combining two initiator sites and one surface linking site. This Y-shaped binary initiator can be synthesized in three steps with a higher yield than other similar initiators reported in the literature, and can be performed on a multigram scale. We were able to attach the initiator to a silicon oxide substrate and successfully grow polymer brushes from both initiators (separately and in combination), confirmed by NEXAFS, AFM, and contact angle.
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...
LCE films can be patterned in the micrometer range with standard MEMS techniques.
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