Growing ZnO crystals on magnetite nanoparticles

We report herein on the oriented growth of ZnO crystals on magnetite nanoparticles. The ZnO crystals were grown by hydrolyzing a supersaturated aqueous solution of zinc nitrate. The seeds for the growth were magnetite nanoparticles with a diameter of 5.7 nm and a narrow size distribution. Hollowed ZnO hexagons of 0.15 microm width and 0.5 microm length filled with Fe(3)O(4) particles were obtained. HR-TEM (high-resolution transmission electron microscopy) and selected-area EDS (energy-dispersive spectroscopy) show that the nanoparticles are homogenously spread in the ZnO tubes. Zeta potential measurements were employed to understand the relationship between the nanoparticles and the oriented growth of the ZnO crystals. The results show that the surfactants induced the directional growth of the ZnO crystals.     

Single-molecule single crystals

Various approaches to the preparation and verification of single-molecule single crystals are discussed for polyethylene and poly (oxyethylene). Analytic tools are electron microscopy, electron diffraction, and differential scanning calorimetry. The main difficulty in producing a single-molecule single crystal is to keep crystals from joining during growth.     

Single-chain single crystals

Single-chain single crystals of isotactic polystyrene and poly(ethylene oxide) were studied by using transmission electron microscopy, high resolution electron microscopy, electron diffraction. Single-chain single crystals were prepared by spreading a dilute solution of polymers on a water surface and collecting the resulting single-chain particles on copper grids, followed by isothermal crystallization. A statistical analysis of the sizes of single-chain crystals was found to match with the known molecular weight distribution of original sample, indicating the particles to be composed of single chain. Observation of the morphology and electron diffraction gave evidence of the single crystal nature. Regular-shaped single-chain crystals were obtained after isothermal crystallization for a longer time. By close observation, several types of morphologies were found for single-chain crystals of isotactic polystyrene and poly(ethylene oxide); in addition to the conventional morphologies observed for multi-chain crystals, new morphologies were observed in both cases. The morphologies of poly(ethylene oxide) were explained according to the crystal structure and twin modes. Tent-like single-chain crystals were often observed. Because of the small size of the crystals, they can avoid collapse on the substrate. The crystalline c-axis of single-chain crystals were found to orient preferably in the direction normal to the substrate. The investigation of electron diffraction and high resolution electron microscopy revealed that the structure of the single-chain crystals of isotactic polystyrene is the same as for multi-chain crystals. A reasonable explanation is given for the unusual resistance to electron irradiation and the missing of lower-index reflections. Regular periodic stripes were found on the top surface of single-chain crystal of isotactic polystyrene with an average periodic length in accordance with (220) spacing. In addition, a statistical thermodynamics theory was developed for single-chain crystal. It is found that the equilibrium dimensions are related to molecular weight and annealing temperature, while the equilibrium melting temperature depends on molecular weight.     

Molecular orientation in tetraiodoethylene single crystals

Crystals of C₂I₄ have been grown, and their unit cell, twinning, optics and vibrational spectra examined, using precession camera, polarising microscopy, laser Raman and polarised infrared techniques. Vibrational assignments permitted the calculation of force constants for the molecule. It was deduced that the C-C bond directions are at least partially ordered in the crystal, and lie approximately parallel to a the reciprocal lattice direction.     

Exciton self-trapping in tetrafluoro-dimethyl-aminoacridine single crystals

The UV-visible optical spectra of 1,2,3,4-tetrafluoro-7-(N,N)dimethyl-amino-acridine single crystals are reported. The results are discussed on the basis of the molecular transitions and crystal packing in the framework of the theory of molecular excitons under a fluctuating potential field due to dynamic disorder. A strong local geometry distortion is demonstrated by applying the Urbach rule to the absorption tails, which is the amplitude of the local potential fluctuation being larger than the intermolecular transfer energy. The lineshape and linewidth of the emission band and its temperature dependence give further evidence of exciton self-trapping.     

Twinning in macroscopic polymer single crystals

Twinning in macroscopic single crystals of poly(TSHD) has been investigated using scanning electron microscopy. Two particular chain-axis rotation twins have been identified unambiguously. They have K₁ twinning planes of (012) and (212). It is also thought that twins with K₁ planes of (21 2) and (202) may possibly occur. The possible mechanisms of twinning in polymer crystals have been discussed and chain-axis rotation twinning in poly(TSHD) has been compared with a similar type of deformation that has been suggested to take place in polyethylene crystals.     

NH2 radicals trapped in NH3 single crystals and various polycrystalline ammonia matrices

?H₂ radical trapped in various ammonia matrices has been investigated by ESR spectroscopy. From the study of the coupling tensors of the ?H₂ radical in a single crystal of NH₃, and taking into account the motions of this radical, it is shown that for all these matrices the spectra can be interpreted on the basis of coupling tensors which give for all cases the same isotropic coupling constants: a_N = 11.3 G, a_H = 24.6 G. Nitrogen and hydrogen coupling tensors for the motionless ?H₂ radical are also discussed     

Photochromism of diarylethene single molecules in polymer matrices

Robust fluorescent photoswitching molecules, having perylene bisimide as the fluorescent unit and diarylethene as the switching unit, were prepared, and their photochromic reactions were measured at the single-molecule level in various polymer matrices. The histograms of the fluorescent on and off times were found to deviate from normal exponential distribution and showed a peak when the molecules are embedded in rigid polymer matrices, such as Zeonex or poly(methyl methacrylate) (PMMA). In soft polymer matrices, such as poly(n-buthyl methacrylate) (PnBMA), exponential distribution was observed for the on and off times. The abnormal distribution suggests that the quantum yields of the photoreactions are not constant and the molecules undergo the reactions after absorbing a certain number of photons. A multilocal minima model was proposed to explain the environmental effect.     

Rectangular single crystals of polyacrylonitrile

Rectangular single, multilayered and twinned crystals of polyacrylonitrile have been grown from the fractionated samples in propylene carbonate at different temperatures (140–150°) using Film Formation Method of crystal growth.     

Periodic precipitation of lanthanum molybdate crystals in silica gel

Formation of Liesegang rings on the growth of La₂(MoO₄)₃·XH₂O in silica gel by single diffusion technique is discussed. The nature of the periodic precipitation is found to depend on the concentration of inner and outer electrolytes, gel medium and its pH. The ‘time law’, ‘spacing law’ and ‘the law relating diffusion depth and width’ are found obeyed in this system. The one-dimensional Liesegang phenomena is thus investigated quantitatively making use of the simple laws of diffusion.     

Chain folding in single crystals of polytetrafluoroethylene

Potential-energy calculations are performed in order to obtain satisfactory models for folding in single crystals of polytetrafluoroethylene crystallized in the phase stable below 19°C. The folds are assumed to be tight with adjacent reentry. Folds with a variable number of bonds are analyzed. Their conformation is deduced by a method which obtains closure between two semifolds into which each fold is decomposed. The allowed models are subsequently investigated by using an energy minimization program. Some possible models are proposed. The calculations show that the folds must be described by a number of rotational isomeric states higher than is usually assumed.     

Simultaneous immunoblotting analysis with activity gel electrophoresis in a single polyacrylamide gel

We describe here that a simple diffusion blotting method can couple immunoblotting analysis with another biochemical technique in a single polyacrylamide gel. The efficiency of protein transfer was evaluated by serial dilutions of nephrosin, a metalloproteinase of the astacin family, and by immunodetection. It is estimated that diffusion blotting produces 25-50% of the signal intensity compared to the classical electrophoretic transfer method. However, with diffusion blotting it is possible to generate several replicas from a single gel. In addition, a protein blot can be obtained from a sodium dodecyl sulfate (SDS)-polyacrylamide gel for zymography assay or from a native polyacrylamide gel for electrophoretic mobility shift assay (EMSA). In this regard, a particular signal in zymography or EMSA can be confirmed by simultaneous immunoblotting analysis with a corresponding antiserum. Therefore, diffusion blotting allows a direct comparison of signals between gels and replicas in zymography assay and EMSA. These advantages make diffusion blotting desirable when partial loss of transfer efficiency can be tolerated or be compensated by a more sensitive immunodetection reaction using enhanced chemiluminescence substrates.     

Determination of oxygen in bismuthate single crystals

An improved procedure for determining oxygen in single crystals was developed. The procedure was tested on samples prepared from stoichiometric BaBiO₃ by thermal treatment in a controlled medium. The error of the procedure is about 0.5 mol%.     

Thermotropic liquid crystals embedded in a high water gel system

An emulsion was formed when the thermotropic liquid crystal (LC) mixture E5 was added to an aqueous polyvinylalcohol (pva) solution and shaken. This emulsion was gelled by addition of an aqueous borax solution. The pva polymer functioned not only as the gelling agent but also appeared to act as a polymeric surfactant which stabilised the LC droplets. This high water gel-liquid crystal (HWG-LC) system contained nearly 80 wt % water and more LC wt % than polymer. The system was thermally reversible, undergoing a gel to sol transition upon heating to 70°C and reforming a gel upon cooling. The HWG-LC showed electrooptical behaviour dependent upon a switched electric field when constrained between transparent electrodes. The pressure required to form a thin film between these electrodes induced a structural emulsion in the dispersion causing LC droplet disruption and the formation of an LC network in the gel.     

Statistical thermodynamics of single-chain single crystals

A simple statistical mechanical theory is developed assuming a chain-folded crystal. Taking account of the side-surface energy of the single-chain single crystal, the partition function and the free energy are calculated. Also, the expressions for equilibrium thickness l_e and melting temperature T_{m, e} of the single-chain single crystal are obtained, and they are similar to that given by a thermodynamic analysis of the single-chain single crystal. It is shown that l_e depends on temperature and on the molar mass of the single-chain single crystal, while T_{m, e} depends on the molar mass. Furthermore, it is found that the side-surface and the fold-surface free energies γ and γ_e can be explained on a molecular basis.     

Vibrational spectra of CsNCS single crystals

Single crystal i.r. and Raman spectra are reported for CsNCS. The main spectral features are in accord with the factor group predictions. Many of the polarisation sensitive multiphonon modes can be accounted for by k = 0 frequencies but for others k ≠ 0 critical points are implicated.     

Polarized absorption of quaterthiophene single crystals

Polarized optical spectra of quaterthiophene single crystals are reported over a wide spectral range for different planes and angles of incidence corresponding to either transverse or mixed longitudinal/transverse wave propagation. From the absorbance and reflectance spectra the corresponding absorption coefficients are deduced. In the region of the first molecular transition, polarized exciton states of Frenkel origin are found to be responsible for a strong optical anisotropy and for the modification of the state of polarization during light propagation in the crystal. Transmission measurements with crossed polarizer and analyzer allow to clearly identify Frenkel replica of the principal transition.