Torsional Viscosity Research Articles

Preparation and Study of the Electro-optical Properties of Binary Mixtures of Orthoconic Anti-ferroelectric Esters and Achiral Phenyl Pyrimidine Liquid Crystal

We have prepared three different binary systems by mixing an achiral low viscous phenyl pyrimidine liquid crystalline SmC compound with three different orthoconic antiferroelectric analogous of (S)MHPOBC exhibiting SmA*-SmC*-SmCA* phase sequences. In these binary mixtures, ferroelectric and antiferroelectric phases were induced and their mesomorphic parameters (spontaneous polarization, response time, effective torsional viscosity, and anchoring energy coefficient) were determined by thermo-microscopic and electro-optical study. All the physical parameters show a nonadditive behavior with respect to the concentration of chiral mesogens due to strong dipole-dipole and/or intermolecular interactions between polar fluorinated chiral esters with heterocyclic phenyl pyrimidine compound. Interestingly the achiral mesogen reduces the response time of these binary mixtures at the cost of lower Ps. Therefore, these mixtures can be useful for high speed technological applications where low polarization, long pitch, and very fast switching ferro or anti-ferroelectric liquid crystal mixtures are desirable.

Development and experimental performance validation of torsional viscosity damper for crank shaft system of transporting machine

The purpose of the present study is to deal with the development of a viscosity damper for the crank shaft system of a transporting machine using reverse engineering. A viscosity damper is developed to substitute import product. An engine simulator for performance evaluation has been produced to enable the control of engine speed using a PID controller and to evaluate the performance of several models by reverse engineering. Several prototypes are made according to the mass variation of an inertia ring. To evaluate the reduction effect of torsional vibration by viscosity damper, several sensors are used such as microphone, tri-axis accelerometer and the optical fibre sensor. In addition, order tracking and FFT (Fast Fourier Transform) analysis are performed by FFT analyzer and F/V converter according to speed increase (1,000~4,000 rpm). The viscosity damper for a high performance to reduce torsional vibration has been developed successfully using several designs, structural stability analysis and manufacturing techniques, as well as performance tests.

ELECTRO-OPTICAL STUDIES IN A FERROELECTRIC LIQUID CRYSTAL MIXTURE

Symmetric square and triangular wave pulses have been applied across planar cells of different thickness to a ferroelectric liquid crystal mixture in the SmC* phase. Dynamic processes of molecular reorientation associated with the helix unwinding and winding by applying bias (-10V -0V - +10V) and taking micrographs simultaneously have been studied. The spontaneous polarization (PS), response time (τR) and torsional viscosity (η) have been studied as a function of temperature, sample thickness and bias voltage. PS follows the relation PS = Po(Tc - T)β. η obeys the Arrhenius relation from 35°C to 60°C with an activation energy of 0.89 eV for 5.0 μm sample thickness. The surface switching in the thin cell is more dominant due to the strong surface pinning effect.

Characteristic switching parameters of an antiferroelectric liquid crystal 4H6Bi(S)

Switching study of an antiferroelectric liquid crystal (S)-4-(1-methylheptyloxycarbonyl)phenyl-4′-(6-pentanoyloxyhex-1-oxy)biphenyl-4-carboxylate (4H6Bi(S)) have been carried out for the planar aligned sample as a function of temperature by the polarization reversal current technique. Switching time (t S), spontaneous polarization (P S) and torsional viscosity () of the material have been determined. t S is found to be in the range 2–4 ms in the ferroelectric (SmC*) phase and 0.4–0.7 ms in the antiferroelectric phase. Above the critical electric field E C where the helix unwinds, t S is found to be inversely proportional to E but P S is found to be independent of E. P S lies between 5 and 106 nC cm−2 in the SmC* phase and between 120 and 235 nC cm−2 in the phase. It obeys the power law with nC cm−2, °C and . The activation energies calculated from the Arrhenius plot of are 520 and 41 kJ mol−1 for the SmC* and phases, respectively.

Electro-optical features of antiferroelectric liquid crystal material (S)-(+)-4-(1-methylheptyloxycarbonyl) phenyl 4′-(6-octanoyloxyhex-1-oxy) biphenyl-4-carboxylate in its ferro and antiferroelectric phases

A detailed investigation of the electro-optical switching parameters of an antiferroelectric liquid crystal (S)-(+)-4-(1-methylheptyloxycarbonyl) phenyl 4′-(6-octanoyloxyhex-1-oxy) biphenyl-4-carboxylate (abbreviated as S-7H6Bi) has been carried out. S-7H6Bi has paraelectric (SmA ⁎) and ferroelectric (SmC ⁎) phases in addition to antiferroelectric (SmC ⁎ A) phase. Switching parameters viz. spontaneous polarization and switching time were determined by polarization reversal method. The spontaneous polarization ( P s) is found to be highly temperature dependent and decreases with temperature. The maximum value of P s is found to be ∼90 nC/cm 2 whereas the switching time ( t s) is found to be of the order 1–2 ms. The temperature dependent torsional viscosity ( γ t) is of the order 10 Pa sec. It increases with decrease in temperature.

The role of torsional viscosity in saccadic listing's law

The role of torsional viscosity in saccadic listing's law

Studies on Room Temperature Ferroelectric Liquid Crystal, 12CN5(R*)

Characterization studies are performed on a ferroelectric liquid crystal, 12CN5(R*). Phase sequence and transition temperatures are obtained by polarized thermal microscopy. Temperature variation of spontaneous polarization and tilt angle in the smectic C* phase are found to agree with the mean-field predictions. Results obtained for the variation of the switching time and torsional viscosity with temperature are also presented.

Ferroelectric Characterization of a Room Temperature Liquid Crystal: 2Cl.BAAP.180-BBP by Low Frequency Dielectric and Optical Methods

The isotropic to nematic(IN), nematic to cholesteric(NCh), cholesteric to smectic-A (ChA) and smectic-A to smectic-C* (AC*) phase transition temperatures exhibited by a room temperature ferroelectric liquid crystal RTFLC, viz., 2Cl.BAAP.180-BBP are determined by the observed anomaly in differential permittivity, d l '/dT. The low frequency dielectric dispersion along with the activation energy are detailed in the N, Ch, SmA and SmC* phases. The Soft mode and Goldstone mode relaxation in the vicinity of AC* phase transition are discussed. The trend of distribution parameter h-values for the off-centred Debye relaxation is discussed. Temperature variation of dilectric strength for the soft mode relaxation is estimated through ferrolectric Curie-Weiss law. Observed temperature variation of Spontaneous Polarization P s (T), Tilt angle θ(T), Response Time s (T), and Effective Torsional viscosity m (T) is found to agree with the Mean field expectation. Relative strength of P s among the reported values is discussed as a function of extended conjugation about the chiral centre.

Low Frequency dielectric and optical characterisation of room temperature ferroelectric liquid crystal 2C1. BAAP.120-BBP

Low frequency dielectric relaxation, spontaneous polarization, optical tilt angle, response times and torsional viscosity studies are carried out on a ferroelectric liquid crystal compound (S)-2-Chloro-3-(4-benzamidoacetophenyl)-1-(4'-dodecyloxybenzoyl)-benzoato, (S)-1-[4'-dodecy loxycarbonyl)phenyl]-4-[2-cloro- (4-benzamidoacetyl)phenylpropionato)-benzoate, 2C1. BAAP.120-BBP exhibiting nematic (N), cholesteric (NC ), smectic-A (SA ) and a room temperature smectic-C* phases. Phase transition temperatures are determined from temperature variation of dielectric permittivity 1(T). Dielectric loss spectrum study in N, NC , and SA phases is found to exhibit one relaxation while S*C phase exhibits a goldstone relaxation in addition to soft mode. Dipolar relaxation in N, NC , and SA phases is found to follow Arrhinius shift through their activation energies. The effect of electric field on goldstone mode studied through Curie-Weiss law in phase reflects characteristic ferroelectric nature. Bias variation of goldstone mode relaxation is also reported. Temperature variation of spontaneous polarization, tilt angle in phase agrees with mean field prediction to infer long range transverse dipole interaction. Data of spontaneous polarization and response times exhibited by smectic-C* are discussed on a comparative scale. Temperature variation of computed torsional viscocity in phase agrees with reported values in other compounds

Helix Dynamics and Electro-Optic Switching in Ferroelectric Smectic C Liquid Crystals

The responses of symmetric square and triangular wave pulses have been investigated in planar cells of two ferroelectric liquid crystalline mixtures FLC-6430 and SCE-13 in the SmC*phase. The samples were sandwiched between two parallel polyimide coated substrates. The cells containing SCE-13 and FLC-6430 were considered in the surface stabilised state (p>d) and volume stabilised state (p<d) respectively, (p is the helix pitch and d is the sample thickness). Dynamic processes associated with the helix unwinding and winding by applying bias -10V - 0V - + 10V has been studied. The spontaneous polarisation (Ps), response time (τR) and torsional viscosity (η) have been evaluated in these materials. Materials in surface stabilised configuration show surface switching while in DHF configuration switching is due to bulk and surface effects.

X-ray Diffraction and Torsional Viscosity Investigations of Laterally Linked SC* Liquid Crystal Dimers

The mechanism by which a tristable, laterally linked, SC* liquid crystal dimer reorients under the application of an electric field has been investigated by a combination of X-ray diffraction studies and torsional viscosity measurements. A new experimental liquid crystal cell has been developed that allows direct measurement of layer spacing as a function of applied field at controlled temperature. The distance between smectic layers is consistent with the dimer naturally arranging in a “U” conformation. No significant change in layer spacing of the dimer was observed upon the application of an electric field for all temperatures and field strengths accessible. The torsional viscosity of the tristable phase of the dimer is similar to previously characterized tristable compounds. These results are consistent with the hypothesis that electrically induced switching of the optically pure dimer occurs by conventional, conical Clark−Lagerwall-type switching seen in other ferroelectric and antiferroelectric materials.

Intrinsic Torsional Viscosity in a Narrow Tube of Nematic Liquid Crystal†

We dcscribe two phenomena which can occur in crystalline liquids and which are analogues of effects that occur in superconductors. The first concerns the acquisition of torsional viscosity. rather ...

Intrinsic torsional viscosity of nematic liquid crystals.

A nematic liquid-crystal cylinder may exhibit metastable cholesteric-type twisted states in which the director uniformly rotates along the sample in the plane orthogonal to the cylinder axis. If a constant torque is maintained by strongly anchoring end plates, thermal fluctuations can produce rotation, leading to torsionally viscous behavior. We present a theory for the fluctuation-induced intrinsic torsional viscosity of narrow cylinders of nematic, based on the Frank free energy and constructed by analogy with the work of Langer and Ambegaokar on the resistance of superconducting channels.

The Second Viscosity Coefficient in Rheological Systems

Viscosity in liquids may be regarded as that property which corresponds to elasticity in solid systems, and the coefficient of viscosity is expected to show as many independent components as the modulus of elasticity. For isotropic systems two components are expected. These two components are denoted by η and ξ. The Stokes relationship between the two coefficients, viz. ζ=-⅔η is compared with the Cauchy-Poisson relationship between the two moduli of elasticity of an isotropic solid, and is claimed as of no more general application. Indeed, experience in sound absorption leads to the conclusion that ζ�η and many measurements on the viscosity of plastic materials appear tacitly to assume that ζ=∞. ζ, however, has a finite value for systems which undergo a progressive change in density at constant pressure. For such systems it is shown that the coefficient of viscosity, as determined by a tensile testing method, while always less than that as determined by torsion testing methods is greater than two-thirds of the latter value. The bulk viscosity, measured by the bulk stress required to produce a progressive density change, is shown to be related to the difference between the shear (or torsional) and the tensile (or flexural) viscosities. Measurements of all three viscosities carried out on a specimen of solid carbon dioxide gives a satisfactory agreement with the theory of small deformations. The values recorded are : Coefficient of viscous traction 10.5 x 101� poises, Torsional viscosity 4.2 x lof0 poises, Bulk viscosity 5.4 x 1010 poises (measured), or 7.0 x 10lU poises (computed). Both flexural and torsional flow curves are of the Bingham type. Corrected yield points are 6.9 x 106 baryes for tensile stress and 4.8 x 106 baryes for shear stress.

Scientific Serials

American Journal of Science, July.—The viscosity of steel and its relations to temperature, by Carl Barus. In this paper the author's studies are mainly restricted to a discussion of the relation between torsional viscosity and temperature as observed with steel in different states of hardness. Reference is also made to the effect of stress on the amount of viscous motion in solids, and to a more general method by which the instantaneous deformation and the gradual deformation produced by stress may be co-ordinated. It is shown that imperceptible gradations lead from the purely viscous deformation which follows strains within the elastic limits to the sudden permanent set which follows strains beyond those limits.—Kilauea in 1880, by William T. Brigham. A detailed account is given of the results of the outbreak of May I, 1880, with a description of the changes that had taken place since the author's previous visit in 1865. The trigonometrical survey then made was found to be already antiquated, the whole boundary perceptibly changed, and Kilauea apparently 5 per cent. larger than eighteen years previously.—Recent explorations in the Wappinger Valley lime stone of Dutchess County, New York (continued), by W. B. Dwight. In this paper (No. 6 of the series) the author deals with the discovery of additional fossiliferous Potsdam strata and pre-Potsdam strata of the Olenellus group near Poughkeepsie. This review of the latest palæontological facts makes it evident that the strata in Dutchess County are simply the continuation of the strata characterizing the Taconic and adjoining series lying northward. But while proving a grand unity, they indicate also an interesting and unexpected variety of rock structure.—Image transference, by M. Carey Lea. By image transference are here denoted curious effects produced on sensitive films, and specially interesting in connexion with the subjects of papers which appeared in the May and June numbers of the journal. In supplement to those papers the possibility is here shown of developing on a film of silver haloid a complete image, a print from a negative for example, without either exposing the silver haloid to light, or to the action of hypo-phosphite, or subjecting it to any treatment whatever, between the moment of its formation and that of its development. The film of silver haloid comes into existence with the image already impressed upon it.—The theory of the wind vane, by George E. Curtis. The author's theoretical studies lead to the inference that the oscillations of both spread and straight vanes are smaller as the vanes are longer and larger; that the spread is always more stable than the straight vane; and that this advantage in stability is greater for long than for short vanes, and is independent of the wind velocity.—On the manner of deposit of the glacial drift, by O. P. Hay. The author's studies of this great geological problem lead to the following conclusions: (1) an ice-sheet moving over a nearly level surface would possess far less abrading power than it would have while descending at a higher angle; (2) through subsidence of the glacial mass by the earth's heat and other causes a constantly increasing proportion of inert matter would collect in the lower-layers of the moving ice; (3) this accumulated material would tend to retard and finally arrest the motion of the lower portions of the glacier, and a permanent deposit would then be gradually made; (4) other detritus might accumulate at the foot of the glacier as a terminal moraine, and still other masses on the top of the already formed deposit when the glacier finally melted.