摘要:

A simple model for stiff polymers is here proposed to describe the flow behavior in the nematic phase. The model relaxes the usual assumption of a complete rigidity of the rodlike molecule. The dynamical equation is tractable if the molecular bending motion is much faster than rotation of the molecular axis.

ISSN:1058-725X    

DOI:10.1080/10587259508033627

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Rigid rod epoxy compounds can be cured in liquid crystalline structure. The so obtained networks exhibit better mechanical properties with respect to the isotropic ones. The mesogenic character of the epoxy compounds appears more crucial than the molecular geometry of the curing agent in developing liquid crystallinity. The curing temperature plays an important role in affecting the state of order of the thermosets.

ISSN:1058-725X    

DOI:10.1080/10587259508033628

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The phase behaviour of two polymer/liquid crystal blends has been investigated by DSC and optical microscopy. In one case, blends of poly(octadecylethylene) (POE) and p-azoxyanisole (PAA) are found almost immiscible below the isotropization temperature of the liquid crystal. The crystallization process of PAA in the blends takes place with a sporadic growth of dendritic structures determined by the dispersion of the nematic phase in the molten polymer. In the other case, blends of poly(biphenylyloxyexylacrylate) (PBHA) and PAA display a different phase behaviour indicating partial miscibility of the two components at temperatures above the melting point of the polymer. At high concentrations of PAA a nematic phase dispersed in a isotropic liquid mixture of polymer and liquid crystal is observed. These results are accounted for by the different side-chain structure of the polymer components.

ISSN:1058-725X    

DOI:10.1080/10587259508033629

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this Paper we report optical dichroism and polarized resonance Raman scattering measurements on Langmuir-Blodgett layers of tetra tertiary butyl monosulphonic acid of phthalocyanine (tBPcSA). These measurements were performed to determine molecular alignment and local ordering in our samples, using surface enhanced optical and Raman spectroscopy. Thus our L-B layers were deposited on rough thin (50 Å) Ag island films. We found that the surface enhancement effects dominated the optical behaviour of our samples, making it more difficult to extract the desired information on molecular orientation. At the same time, we found that tBPcSA L-B layers can be a good system to study resonance effects and to test the reliability of the structural information obtainable by optical spectroscopic techniques.

ISSN:1058-725X    

DOI:10.1080/10587259508033630

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The orientational distribution function for the C-CD3bond on the perdeuterated polymethacrylate chain of a liquid-crystalline side group polymer was determined in the frozen SAphase by solid-state2H NMR. The results are compared with the ones of two similar systems recently reported. The slow chain dynamics above the glass transition was studied via 2D2H NMR, which indicates a diffusive motion constrained by the partial orientational order of the mesophase.

ISSN:1058-725X    

DOI:10.1080/10587259508033631

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Blends of poly(phenylene sulfide) and a semiflexible liquid-crystalline polymer have been prepared, in the whole range of concentration, by melt mixing. The effect of the LCP phase on the crystallization of PPS has been studied by non-isothermal and isothermal calorimetry. It has been found that the addition of only 2-5% LCP into PPS strongly increases the crystallization rate of the latter polymer. This effect has been interpreted as the result of an increased nucleation density. The morphology of the blends, studied by scanning electron microscopy, has shown that the two polymers are incompatible, although the phase dispersion is good. Under elongational flow, the dispersed phase shows a distinct tendency toward fibrillation.

ISSN:1058-725X    

DOI:10.1080/10587259508033632

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The reorientation process of a probe molecule in a supercooled polymeric liquid crystal has been studied by non linear Electron Spin Resonance. The temperature dependence of the correlation time of the spinning motion of the probe τ∥and the collective viscoelastic relaxation, as given by dynamic-mechanical measurements, have been compared. In amorphous samples the Williams-Landel-Ferry law is observed, which in annealed samples is replaced by a dual Arrhenius law broken at the glass transition. A scaling law τ∥∝ ηξ, η being the polymer viscosity, is found in both amorphous (ξ = 4.7 10−2± 2.8 10−3) and partly crystalline samples (ξ = 5.9 10−2± 6.5 10−3).

ISSN:1058-725X    

DOI:10.1080/10587259508033633

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In this letter we report on the turbulence to turbulence transition, which occurs in a homogeneously oriented nematic liquid crystal (NLC) film under the action of an external alternate voltage. Our observation show that the transition is characterized by a NLC-substrate anchoring breaking, which results in the on set of the twist distortion of the molecular director field. We give the characterization of the different dynamic regimes in terms of the probability distribution functions (PDF's) of the director field curvature energy. The PDF's, which are undoubtedly non-gaussian, indicate that, in both turbulent regimes, the curvature energy is highly intermittent.

ISSN:1058-725X    

DOI:10.1080/10587259508033634

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The synthesis of some crosslinked polymers based on a segmented-chain polymeric mesogen containing variable amounts of a side chain substituent is reported. The unswollen networks show thermotropic mesomorphism of nematic character whose stability decreases with increasing substitution and crosslink density. Depending on the same parameters, the swollen networks may show optical anisotropy at room temperature whose origin is attributed to phase separation

ISSN:1058-725X    

DOI:10.1080/10587259508033635

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Liquid crystalline textures exhibited by aqueous solutions of hydroxypropylcellulose were investigated by video-enhanced contrast polarized light microscopy. For the first time in this particular system, typical cholesteric structures, such as oily streaks and fingerprint lines, were resolved in close detail by light microscopy. Biphasic separation was observed even in samples of concentration well above the critical value generally accepted for mesophase formation at room temperature (∼40% wt). The dependence of the helical pitch on polymer concentration was also studied, by Fourier transforming images of the cholesteric textures.

ISSN:1058-725X    

DOI:10.1080/10587259508033636

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor