The twist–bend nematic (NTB) phase is a liquid crystal (LC) phase with a heliconical structure that typically forms below the temperature of the conventional nematic (N) phase. By contrast, the direct transition between the NTB and isotropic (Iso) phases without the intermediation of the N phase rarely occurs. Herein, we demonstrate the effects of linkage type (i.e., methylene, ether, and thioether) on the typical Iso–N–NTB and rare direct Iso–NTB phase-transition behaviors of cyanobiphenyl (CB) dimers CB3CB, CB2OCB, and CB2SCB bearing three-atom-based propane, ethoxy, and ethylthio spacers, respectively. In our previous study, CB2SCB exhibited the monotropic direct Iso–NTB phase transition. In this study, we report that CB3CB also shows the direct Iso–NTB phase transition, whereas CB2OCB exhibits the typical Iso–N–NTB phase sequence with decreasing temperature. The Iso–LC (Iso–NTB or Iso–N) phase-transition temperatures upon cooling show the order CB2OCB (108 °C) > CB3CB (49 °C) > CB2SCB (43 °C). The thioether-linked CB2SCB is vitrifiable, whereas CB3CB and CB2OCB exhibit strong crystallization tendencies. The phase-transition behaviors are also discussed in terms of the three bent homologous series with different oligomethylene spacers n: CBnCB, CBnOCB, and CBnSCB.
In recent years, needs for micro drilling are increasing, accompanying the development of higher wiring density of printed circuit board (PCB). When drilling PCB for the purpose of making the electric through holes, it has been said that the drill breakage is caused by being filled the chips of GFRP and copper of PCB in the drill flutes. The aim of this study is to clarify the effect of PCB drilling using DLC coated drill on tool wear, chip evacuation and cutting torque. Series of drilling tests of PCB have been carried out to investigate the amount of drill wear, the chips evacuation behavior out of drilled hole with the drill, the shape of chips produced and the cutting torque using DLC-coated drill and non-coated drill. The chips evacuation behavior out of drilled hole with the drill is filmed by a high-speed motion camera and the shape of chips produced is observed by a microscope. The cutting torque is measured by a dynamometer; Kistler 9329A. The amounts of drill flank wear and margin wear using DLC-coated drill and non-coated drill are almost the same. The chips of GFRP using DLC-coated drill are shorter and smaller than those using non-coated drill. The chips evacuation out of drilled hole with the drill using DLC-coated drill is better than those using non-coated drill, and cutting torque using DLC-coated drill is lower than those using non-coated drill.
Synthesis of COOnSynthetic procedures of COO3 are representatively described below. Other COOn homologues were synthesised with corresponding α,ω-dibromoalkanes in a manner similar to the synthesis of COO3.
Methyl 4'-cyano-[1,1'-biphenyl]-4-carboxylateMethyl 4-bromobenzoate (4.69 g, 21.8 mmol), 4-cyanophenylboronic acid pinacol ester (5.00 g, 21.8 mmol), Cs2CO3 (14.5 g, 44.5 mmol), and Pd(PPh3)4 (0.759 g, 0.657 mmol)were put in a double-necked flask purged with argon gas. THF (20 mL) degassed by bubbling argon gas was added into the prior flask and the mixture was stirred at reflux temperature for 22 h. The mixture was extracted with dichloromethane and washed with water and brine. The organic phase was dried over MgSO4 and the volatiles were evaporated under reduced pressure. The residue was purified via column chromatography on silica gel with a mixed solvent of dichloromethane/hexane (1/1, v/v). Yield: 87.7%. 1 H
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