Dorothee Nonnenmacher

Bio: Dorothee Nonnenmacher is an academic researcher from University of Stuttgart. The author has contributed to research in topics: Liquid crystal & Phase transition. The author has an hindex of 9, co-authored 11 publications receiving 300 citations. Previous affiliations of Dorothee Nonnenmacher include Queen's University.

Microfluidic synthesis of highly shape-anisotropic particles from liquid crystalline elastomers with defined director field configurations.

Abstract: In this article, we present the synthesis of highly shape-anisotropic, micrometer-sized particles from liquid crystalline elastomers, which have the ability to reversibly change their shape in response to a certain external stimulus. For their preparation, we utilized a microfluidic setup. We succeeded in preparing sets of particles with differing degrees of shape anisotropy in their ground state including highly anisotropic fiber-like objects. All samples produced movement during the phase transition from the nematic to the isotropic phase of the liquid crystal. Depending on the direction of this shape change, we classified the samples in two groups. One type showed a contraction, while the other showed an expansion during the actuation, generating displacements of 60% and 80%, respectively. Using X-ray diffraction experiments, we could show that the different actuation properties arise from different director patterns of the liquid crystalline moieties in the microparticles. While the weakly shape-aniso...

Design of Liquid Crystals with “de Vries-like” Properties: Frustration between SmA- and SmC-Promoting Elements

Abstract: According to a new design strategy for “de Vries-like” liquid crystal materials, which are characterized by a maximum layer contraction of ≤1% upon transition from the SmA phase to the SmC phase, we report the synthesis and characterization of two homologous series of organosiloxane mesogens. The design of these new materials is based on a frustration between one structural element that promotes the formation of a SmC phase (a trisiloxane-terminated side-chain) and one that promotes the formation of a SmA phase (either a chloro-terminated side-chain or a 5-phenylpyrimidine core). Measurements of smectic layer spacing d as a function of temperature by small-angle X-ray scattering (SAXS) combined with optical tilt angle measurements revealed that the mesogens 5-(4-(11-(1,1,1,3,3,5,5-heptamethyltrisiloxanyl)-undecyloxy)phenyl)-2-(1-alkyloxy)pyrimidine (3(n)) undergo SmA−SmC phase transitions with maximum layer contractions ranging from 0.5% to 1.4%. A comparison of reduction factors R and f suggests that thi...

Tuning ‘de Vries-like’ properties in siloxane- and carbosilane-terminated smectic liquid crystals

Abstract: Smectic liquid crystals with ‘de Vries-like’ properties are characterized by a maximum layer contraction of ≤1% upon transition from the non-tilted SmA phase to the tilted SmC phase. To expand the current library of ‘de Vries-like’ liquid crystals, we have developed a rational design strategy based on a concept of frustration between two structural elements, one promoting the formation of a SmA phase (chloro-terminated side-chain) and another promoting the formation of a SmC phase (siloxane-terminated side-chain). In this paper, we show that one can tune this apparent frustration—and further improve de Vries-like properties—by substituting the 2-phenylpyrimidine core in our first-generation siloxane-terminated mesogens with one of three cores known to be stronger SmC-promoting elements: 6-phenylpyridazine, 2-phenylpyridine and 2-phenylthiadiazole. We also address a fundamental design flaw of siloxane-terminated mesogens, i.e., the hydrolytic instability of siloxane oligomers, by substituting the siloxane end-group with a chemically inert carbosilane end-group. As a result of this study, we found a carbosilane-terminated 2-phenylthiadiazole mesogen that forms a SmC phase at room temperature with de Vries-like properties that are comparable to those of bona fide de Vries-like liquid crystals.

The effect of lactate unit number in compounds with azo group in the molecular core

Abstract: A liquid crystalline compound with the azo group in the molecular core and three lactic acid units in the chiral chain (n = 3) was synthesised and its mesomorphic properties established. Spontaneous polarisation and tilt angle were determined in the ferroelectric and antiferroelectric smectic C phases. Dielectric spectroscopy in the frequency range of 1 Hz–10 MHz was performed within the temperature range of smectic phases showing the characteristic modes in each phase. Small-angle X-ray diffraction was performed and temperature dependences of layer spacing value calculated. Comparison with previously studied compounds with one (n = 1) and two lactate units (n = 2) is presented to establish the effect of lactate unit number on the liquid crystalline properties.

Elucidating the smectic A-promoting effect of halogen end-groups in calamitic liquid crystals

Abstract: Two isometric series of chloro-terminated 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine mesogens QL8-m/n and QL9-m/n (m + n = 16), with the chloro-terminated alkoxy chain tethered to either the pyrimidine ring or the phenyl ring, were synthesized and their liquid crystalline properties characterized by polarized optical microscopy and differential scanning calorimetry. Based on the analysis of mesogenic properties and correlations to electrostatic potential isosurfaces calculated at the B3LYP/6-31G* level, we present evidence suggesting that the SmA-promoting effect of chloro end-groups is not due to strong polar interactions at the layer interfaces, as previously postulated in the literature. Instead, the evidence suggests that the SmA-promoting effect is due to the electron-withdrawing effect of the chloro end-group, which should reduce electrostatic repulsion between alkoxy chains and, consequently, increase van der Waals interactions between aromatic cores in the orthogonal SmA phase.

Ionic Liquid Crystals: Versatile Materials.

Abstract: This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

Liquid-crystalline ordering as a concept in materials science: from semiconductors to stimuli-responsive devices.

Abstract: While the unique optical properties of liquid crystals (LCs) are already well exploited for flat-panel displays, their intrinsic ability to self-organize into ordered mesophases, which are intermediate states between crystal and liquid, gives rise to a broad variety of additional applications. The high degree of molecular order, the possibility for large scale orientation, and the structural motif of the aromatic subunits recommend liquid-crystalline materials as organic semiconductors, which are solvent-processable and can easily be deposited on a substrate. The anisotropy of liquid crystals can further cause a stimuli-responsive macroscopic shape change of cross-linked polymer networks, which act as reversibly contracting artificial muscles. After illustrating the concept of liquid-crystalline order in this Review, emphasis will be placed on synthetic strategies for novel classes of LC materials, and the design and fabrication of active devices.

Current status and future developments in preparation and application of colloidal crystals

Abstract: Colloidal crystals (CCs) are ordered arrays of monodisperse colloidal particles. Because of the presence of a periodic superlattice of colloids and voids, CCs bear many unique structures and fascinating properties which are distinctly different from those of standard crystals with atoms, ions or molecules as repeating subunits. The research on CCs has surprisingly blossomed during recent decades, and many practical materials based on CCs with potential applications in photonic devices, material science and biomedical engineering have been generated. In this review, we give a systematic, balanced and comprehensive summary of the main aspects of CCs related to their preparation and application, and propose perspectives for the future developments of CCs.

A Facile Synthesis of Dynamic, Shape‐Changing Polymer Particles

Abstract: We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles that exhibit a pH-triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) in dispersed droplets. In a second step, the dynamic shape change is realized by cross-linking the P2VP domains, thereby connecting glassy PS discs with pH-sensitive hydrogel actuators.

Photomobile polymer materials with crosslinked liquid-crystalline structures: molecular design, fabrication, and functions.

Abstract: Crosslinked liquid-crystalline polymer materials that macroscopically deform when irradiated with light have been extensively studied in the past decade because of their potential in various applications, such as microactuators and microfluidic devices. The basic motions of these materials are contraction–expansion and bending–unbending, which are observed mainly in polysiloxanes and polyacrylates that contain photochromic moieties. Other sophisticated motions such as twisting, oscillation, rotation, and translational motion have also been achieved. In recent years, efforts have been made to improve the photoresponsive and mechanical properties of this novel class of materials through the modification of molecular structures, development of new fabrication methods, and construction of composite structures. Herein, we review structures, functions, and working mechanisms of photomobile materials and recent advances in this field.