119402-91-4Relevant academic research and scientific papers
Design of liquid crystals with 'de Vries-like' properties: Carbosilane-terminated 5-phenylpyrimidine mesogens suitable for chevron-free FLC formulations
Schubert, Christopher P.J.,Bogner, Andreas,Porada, Jan H.,Ayub, Khurshid,Andrea, Tamer,Giesselmann, Frank,Lemieux, Robert P.
, p. 4581 - 4589 (2014/06/09)
Smectic liquid crystals with 'de Vries-like' properties are characterized by a maximum layer contraction of ≤1% upon transition from the orthogonal SmA phase to the tilted SmC phase. In an effort to expand the library of 'de Vries-like' liquid crystals required for the formulation of chevron-free ferroelectric liquid crystal mixtures, we report the synthesis of a homologous series of tricarbosilane 5-phenylpyrimidine liquid crystals QL16-n using an improved synthetic route, and the characterization of their liquid crystalline and 'de Vries-like' properties. Measurements of orientational order parameters S2 and effective molecular lengths Leff by monodomain 2D X-ray scattering suggest that 'de Vries-like' behavior in series QL16-n is due to the combined effect of an increase in S2 and a decrease in bilayer interdigitation, thus causing a smectic layer expansion that compensates for the molecular tilt in the SmC phase. We also show how the optical tilt angle in the SmC phase may be optimized for SSFLC displays - without compromising 'de Vries-like' properties - by shortening the tricarbosilane end-group to a dicarbosilane. Two of the new materials reported herein, 5-[4-(12,12,14,14,16, 16-hexamethyl-12,14,16-trisilaheptadecyloxy)phenyl]-2-hexyloxypyrimidine (QL16-6) and 2-hexyloxy-5-[4-(12,12,14,14-tetramethyl-12,14-disilapentadecyloxy) phenyl]pyrimidine (QL24-6) rank among the best 'de Vries-like' materials reported heretofore, with broad SmC phases and reduction factors R of 0.17 and 0.18, respectively, at a reduced temperature T - TAC = -10 K. We also show that inverting the orientation of the 5-phenylpyrimidine core in the homologous series QL17-n causes a suppression of 'de Vries-like' properties. These results suggest that non-covalent core-core interactions in the intercalated smectic bilayers formed by these mesogens may influence 'de Vries-like' behavior.
Design of liquid crystals with de Vries-like properties: Frustration between SmA- and SmC-promoting elements
Roberts, Jeffrey C.,Kapernaum, Nadia,Song, Qingxiang,Nonnenmacher, Dorothee,Ayub, Khurshid,Giesselmann, Frank,Lemieux, Robert P.
supporting information; experimental part, p. 364 - 370 (2010/03/25)
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 this behavior is due in part to a pronounced negative thermal expansion in the SmC phase that counterbalances the layer contraction caused by increasing tilt. SAXS measurements also revealed that compounds 3(n) are characterized by low orientational and high translational order, which is consistent with theoretical predictions that such materials should exhibit de Vries-like properties. The R values for series 3(n) are comparable to, and even lower than, those reported for established de Vries-like materials such as the perfluorinated 2-phenylpyrimidine material 3M 8422.
Design of liquid crystals with de Vries-like properties: Organosiloxane mesogen with a 5-phenylpyrimidine core
Roberts, Jeffrey C.,Kapemaum, Nadia,Giesselmann, Frank,Lemieux, Robert P.
supporting information; experimental part, p. 13842 - 13843 (2009/02/07)
According to a new design strategy for de Vries-like liquid crystal materials, we report the synthesis and characterization of an organosiloxane mesogen with a 5-phenylpyrimidine core that forms SmA and SmC liquid crystal phases. This new material is characterized by a maximum layer contraction of 1.2% upon SmA-SmC phase transition and is comparable to the best de Vries-like materials reported heretofore. Copyright
