Effect of dimensionality of a crystal lattice on the properties of a localized impurity

The changes of electron density due to the presence of a localized impurity in a crystal lattice are examined in dependence on the lattice dimensionality. The Koster–Slater impurity model developed for the case of a three‐dimensional simple cubic lattice has been taken as the basis of examinations. Ordinary bound states, virtual bound states, and delocalized electron states are considered in each lattice case. For the delocalized states extended in a one‐dimensional lattice the amplitude of the oscillatory changes of the electron density due to the impurity perturbation does not decrease with the distance from the impurity position, whereas for a two‐dimensional lattice this amplitude decreases roughly proportionally to the reciprocal value of the square root of the distance from the impurity. Let us note that a well‐known amplitude characterizing the decrease of the oscillatory change of the electron density in a three‐dimensional system is proportional to the reciprocal value of the third power of the distance from the impurity position. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 80: 61–78, 2000     

Thermal properties and morphology of crystal in nylon 1010 formed isothermally at melting peak temperature

Thermal properties and morphology of crystal in NYLON 1010 formed isothermally at melting peak temperature were studied by using DSC, TEM and ED. It turns out that the crystal on the time scale of the DSC experiment is stable, which is not transformed from the crystal with low melting point. Its electron diffraction pattern shows symmetrical and clear electron diffraction spots of single crystal and is proved to be the electron diffraction pattern of single crystal by means of index with parameters of unit cell of Nylon 1010     

微量杂质对苯并三氧化呋咱(BTF)感度影响研究

苯并三氧化呋咱(BTF)是一种由三叠氮三硝基苯(TATNB)经脱氮反应制得的零氧无氢炸药,90℃～120℃温度范围内动力学参数计算外推得到其贮存寿命大约是太安的1．5倍,桥丝感度与太安相当,需要的能量较小,并使发火的电压降低,其起爆性能、输出能量、机械感度、热安定性均     

Effect of surface orientation on the segregation kinetics of Sb from a Cu single crystal

In a previous theoretical study it has been suggested that the bulk vacancy formation energy near a surface depends on the orientation of the surface. It has been suggested also that this dependency of the vacancy formation energy would influence the bulk diffusion coefficient near the surface. The experimental results presented in this paper support this hypothesis. The experimental results were obtained by measuring the bulk‐to‐surface segregation of Sb for a Cu(111) single crystal with 0.088 at.% Sb and for a Cu(110) single crystal with 0.082 at.% Sb. The experimental results were fitted with the vacancy‐modified Darken model and it was clear that the bulk diffusion coefficient beneath the (110) surface is higher than the bulk diffusion coefficient beneath the (111) surface. Copyright © 2003 John Wiley & Sons, Ltd.     

Effects of the fluorinated liquid crystal molecules on the electro-optical properties of polymer dispersed liquid crystal films

The different fluorinated liquid crystal (LC) molecules doped to E8 were used as LC component to prepare polymer dispersed liquid crystal (PDLC) films. The mass fraction of the LC mixture is fixed 50.0 wt%. Results indicate that doping 8.0 wt% fluorinated LC molecule ME3CP to E8 significantly reduced the driving voltage of the PDLC films, and the driving voltage reduced with the rise of mass fraction of ME3CP. Besides, the terminal flexible chain length of the fluorinated LC molecule influenced the LC mixture properties based on E8, such as the dielectric anisotropy, birefringence and viscosity of the LC mixture, and the morphology and the electro-optical properties of PDLC films were controlled not only by the physical properties of the LC mixture, but also by the terminal flexible chain length of the fluorinated LC molecule .     

Effect of a surface charge on the halfwidth and peak position of cluster plasmons in colloidal metal particles

The optical response of colloidal particles depends on a variety of properties of the cluster, e.g., shape, size, size distribution and particle material. Since particles often are charged, also the surface charge may be a parameter which influences their optical properties. In this paper the effect of a surface charge on optical properties of spherical colloidal particles is studied and its magnitude is estimated by extended computations for silver clusters with surface plasmon in aqueous suspension. Two models are presented and discussed. The first model is based on the electrodynamic solution by Bohren and Hunt (Can. J. Phys. 55, 1930 (1977)), where a surface conductivity _S for a free surface charge yield an additional contribution _S to the dielectric constant of the particle material. In the second model, the surface charge contributes to the number density of free electrons in the cluster. Both models lead to a shift of the cluster plasmon peak, while an increase of the plasmon halfwidth could not be derived. The effect is quite small and limited on very small clusters.PACS 61.46+w 73.20.Mf 78.20.Dj     

Effect of molecular orientation distribution and crystallinity on the measurement of the crystal lattice modulus of nylon 6 by x-ray diffraction

The crystal lattice modulus of nylon 6 (-type) was measured by x-ray diffraction using nylon 6 films drawn up to five times. The measured crystal lattice modulus was 173–175 GPa for all specimens whose crystallinity and the Young's modulus were beyond 46% and 3.75 GPa, respectively. These results indicate that a state of homogenous stress can be achieved. In contrast, the values were scattered for the speciments whose crystallinity and Young's modulus are less than the above values. To study the origin, a numerical calculation of the crystal lattice modulus, as measured by x-ray diffraction, was carried out by considering effects on the orientation factors of molecular chains and crystallinity. In this calculation, a previously introduced model was employed, in which oriented crystalline layers are surrounded by oriented amorphous phases so that the strains of the two phases at the boundary are identical. The theoretical results calculated by the introduced model indicated that the crystal lattice modulus by x-ray diffraction is almost equal to the intrinsic crystal modulus if the morphology of the test specimen can be represented as a series model. In contrast, if a parallel model is more appropriate, the difference between the measured modulus and the intrinsic value can be pronounced. Such morphological dependence was found to be less pronounced with increasing high degree of molecular orientation and crystallinity.     

Dielectric and electro-optical properties of a photosensitive liquid crystal

The temperature dependencies of the dielectric and electro-optical properties of a pure photo-ferroelectric liquid crystal have been investigated, in the chiral smectic C (SmC*) phase, with and without ultraviolet (UV) illumination. The SmC* dielectric Goldstone mode characteristics, the spontaneous polarization, the tilt angle and the rotational viscosity are affected by UV irradiation. Under increasing UV light intensities the dielectric strength Δ?_G increases whereas the relaxation frequency f_G , the spontaneous polarization P _s, the electro-optical rotational viscosity γ_eo and the tilt angle θ decrease. The twist elastic constant K ₃ and the Goldstone mode rotational viscosity γ_G of the studied compound are deduced from dielectric experimental results. Good agreement was found between both viscosities. The observed dielectric behaviours are controlled by the elastic constant and the rotational viscosity variations.     

Effect of low and high concentrations of KCl dopant on ADP crystal properties

The experimental results of the influence of low (1 M%) and high (10 M%) concentrations of potassium chloride (KCl) dopant on ADP crystals are presented. The dopant results in an increase in the metastable zone width leading to an enhanced crystal growth rate, at its low concentrations. In the presence of high concentrations of the dopant in the medium, the growth rate decreases appreciably. Further, low concentrations of dopant improve the crystalline quality with better transparency. The diffraction patterns reveal that there is no change in basic structure except for variation in intensity by doping. Slight broadening is observed in FTIR of ADP in the 3500–3000 cm⁻¹ range in the presence of high [KCl]. It appears that the dopant has not altered much the optical transparency of the crystal. SEM studies of pure and doped samples reveal that structure defect centers are formed in ADP crystals by the dopant. Second harmonic generation (SHG) efficiency measurements indicate that nonlinear optical (NLO) property is enhanced appreciably by [KCl] dopant and the SHG is more pronounced at high concentrations. It seems that the molecular alignment of the crystal facilitates non-linearity in the presence of the dopant.     

Microsolvation effects on the optical properties of crystal violet

We present a joint experimental and theoretical study of the photoabsorption and photodissociation behavior of crystal violet, that is, the tris[p-(dimethylamino)phenyl]methyl cation. The photodissociation spectra of isolated and microsolvated crystal violet have been measured. A single band is observed for the bare cation. This is in good agreement with the calculated vibronic absorption spectrum based on time-dependent density functional theory calculations. The interaction of crystal violet with a single water molecule shifts and broadens the photodissociation spectrum, so that it approaches the spectrum obtained in solution. Theoretical calculations of the structure of the complex suggest that the shift in the absorption spectrum originates from a water molecule bonding with the central carbon atom of crystal violet.     

Liquid crystal properties of a self-assembling viral coat protein

Monomers of the fd bacteriophage major coat protein, g8p, interact to form a helical bent-core structure surrounding the viral deoxyribonucleic acid (DNA). It was hypothesised that g8p has mesophasic characteristics guiding viral coat assembly. Atomic force and scanning electron microscopy reveal that g8p monomers organise to form films that wrap around a central axis to form birefringent fibres. These fibres resemble the filament structure of bent-core thermotropic B7 liquid crystals. These results offer insight into the g8p self-assembly mechanism that results in the formation of new viral particles in vivo.     

Optical properties of electron beam- and UV-cured polypropyleneglycoldiacrylate/liquid crystal E7 systems

This contribution focuses on a detailed investigation of the relationship between the method of polymerisation/cross-linking, such as slow and rapid UV radiation, and high voltage accelerated electron beam (EB), and the obtained physical properties including phase diagrams, polymerisation and phase separation kinetics, morphologies and electro-optic responses of polypropyleneglycoldiacrylate (PPGDA) monomers, in the presence of the nematic liquid crystal E7. The longer the spacing between double bonds, the more rapid was the photopolymerisation under both UV systems; however, the reverse was proved under EB. More homogenous and regular morphologies were obtained under EB curing.

The electro-optical responses of various polymer dispersed liquid crystals (PDLCs) systems exhibited remarkable differences between the UV-cured samples and those cured by the EB technique. It was found that the threshold and saturation voltages considerably increased in the case of the UV-cured systems. Other results involving the contrast ratio, which is higher for EB-cured systems, confirm their higher quality, although the rapid photopolymerisation UV source was employed, which slightly improved the electro-optical responses. Moreover, EB curing leads to high enough conversions without a photoinitiator, which may act as an impurity that might have a strong impact on the electro-optical performance of the obtained PDLCs.     

Effect of oligomeric surface modifying agent on electro-optical properties of polymer dispersed liquid crystal

In order to lower the driving voltage of polymer dispersed liquid crystal (PDLC), an oligomeric surface modifying agent (SMA) which is a fluoroalkyl terminated polyurethane (PU) oligomer has been synthesized and added to polyurethane acrylate (PUA) resin. With the addition of SMA, contact angle of the resin surface with an LC drop increased and domain size decreased significantly due to the enrichment of SMA molecules at the surfaces. Operating voltage decreased up to 5 phr SMA and increased beyond this content. Regarding the effect of SMA molecular weight, lower molecular weight drove the shutter at lower operating voltage, indicative of more enrichment of the SMA molecules at the surfaces.     

Nanostructure and dielectric properties of a twist-bend nematic liquid crystal mixture

We present freeze-fracture transmission electron microscopy (FF-TEM), dielectric spectroscopy and electro-optic measurements on a dimeric liquid crystal mixture, which previously was proposed to form the twist-bend nematic (N_tb) phase. Our FF-TEM studies provide a direct image of a 10.5 nm periodic structure, consistent with the expected nanoscale, heliconical twist-bend modulation of the molecular orientation. Dielectric measurements in the 100 Hz to 10 MHz range reveal three nearly Debye-type dispersion processes in the nematic and the twist-bend phase. Low frequency 8 V/µm electric fields applied on planar cells cause the optical-scale stripe texture (another characteristic feature of the N_tb phase) to disappear. Higher (>16 V/µm) fields gradually realign the heliconical axis along the electric field; it relaxes back after the field removal.     

Synthesis and liquid crystal properties of a novel family of oligothiophene derivatives

In order to develop novel oligothiophene-based liquid crystals capable of hydrogen bonding, new terthiophene derivatives containing an alkylamide group, N,N′-dialkyl-5,5″-dichloro-2,2′:5′,2″-terthiophene-4,4″-dicarboxamide (DNC_nDCl3T, n=8, 18), N,N′-dialkyl-5,5″-dibromo-2,2′:5′,2″-terthiophene-4,4″-dicarboxamide (DNC_nDBr3T, n=5, 8, 16, 18), or N,N′-dialkyl-5,5″-diiodo-2,2′:5′,2″-terthiophene-4,4″-dica-rboxamide (DNC_nDI3T, n=8, 18), were designed and synthesized, and their thermal behaviour was examined. It was found that DNC₁₈DCl3T, DNC₁₈DI3T and DNC_nDBr3T (n=8, 16, 18) form a smectic A phase and that the alkyl chain length greatly affects liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester derivatives suggests that intermolecular hydrogen bonding also plays a role in the formation of a liquid crystal phases in the DNC_nDBr3T system.     

Effect of organic solvent on the crystal structure of Concanavalin A

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Melting,volatilisation and crystal lattice enthalpies of acridin-9(10H)-ones

The enthalpies and temperatures of melting and sublimation of acridin-9(10H)-one, 10-methylacridin-9(10H)-one, 2,10-dimethylacridin-9(10H)-one, 10-methyl-2-nitroacridin-9(10H)-one, 10-ethylacridin-9(10H)-one and 10-phenylacridin-9(10H)-one were measured by DSC. Enthalpies and temperatures of volatilisation were also obtained by fitting TG curves to the Clausius-Clapeyron relationship. Complementary investigations for anthracene showed the extent to which the thermodynamic characteristics thus obtained compare with those determined by means of other techniques. For compounds whose crystal structures are known, experimental enthalpies of sublimation correspond reasonably well to crystal lattice enthalpies predicted theoretically as the sum of electrostatic, dispersive and repulsive interactions. Analysis of crystal lattice enthalpy contributions indicates that dispersive interactions always predominate. Interactions are enhanced in acridin-9(10H)-one where intermolecular hydrogen bonds occur: this is reflected in the relatively high enthalpy of sublimation. This revised version was published online in July 2006 with corrections to the Cover Date.     

The physical properties of alkene-terminated liquid crystal molecules/E8 mixture and the electro-optical properties as they doped in polymer-dispersed liquid crystal systems

Effects of the content of fluorinated alkene-terminated liquid crystal (LC) molecules on the physical properties of the fluorinated alkene-terminated LC/E8 mixture were studied. The morphology and electro-optical properties as they doped in polymer-dispersed liquid crystal (PDLC) films were investigated. The detailed discussion of the obtained results is given. As a result, comparing with the physical properties of the series of LC mixtures with the same content of the analogous fully saturated compounds doped with E8, we find that the birefringence is significantly larger for the LC mixture with the alkene-terminated materials. Both fluorinated alkene-terminated LC molecules and the analogous fully saturated compounds doped with E8 reduce the driving voltage of PDLC films. Moreover, PDLC films with the fluorinated alkene-terminated LC molecules possessed higher contrast ratio and faster response time than that of the PDLC films prepared by adding the same mass fraction of the analogous fully saturated compounds. Thus, the ability to manipulate physical properties of LC mixture and electro-optical properties of PDLC films by changing the LC molecular structures may have future relevance for new LC structures design and applications of PDLC films.     

A facile preparation, the crystal structure, the chemical and electrochemical properties of [4-(dimethylamino)phenyl]-3-guaiazulenylmethylium tetrafluoroborate

Reaction of guaiazulene (1) with p-dimethylaminobenzaldehyde in methanol in the presence of tetrafluoroboric acid gives the title monocarbocation compound, [4-(dimethylamino)phenyl]-3-guaiazulenylmethylium tetrafluoroborate (2), in 90% yield. The title investigations of compound 2 compared with those of two other monocarbocations stabilized by a 3-guaiazulenyl group (i.e. phenyl-3-guaiazulenylmethyl and [4-(isopropyl)phenyl]-3-guaiazulenylmethyl cations) are reported.     

六烷氧基取代的苯并菲和六氮杂苯并菲盘状液晶中的电荷转移

用电子转移的半经典模型在量子化学B3LYP/6-31G(d)水平(对单体)和B3LYP/STO-3G水平(对二聚物)对六烷氧基取代的苯并菲和六烷氧基取代的六氮杂苯并菲组成的盘状晶体系的电荷转移性质进行了研究,发现在用量子化学方法研究电荷转移反应时,不能简单地用氢氧基代替长链烷氧取代基。由于在电荷转移反应中,要考虑参与反应的分子之间前线轨道的细微差别,所以将长链取代基用氢氧基取代,可能得不到定性正确的结果。