Measurement of the viscosity of ferroelectric liquid crystals in free-standing films

A new implementation of the technique for the measurement of the Goldstone mode rotational viscosity in the S_c phase is presented. An electric field is applied parallel to the surface of a free-standing liquid crystal film. The optical transmission change of the film is recorded. The viscosity can be calculated from the reorientation time between optically separated positions of the director. A comparison with the viscosity values measured in thin cells is given. The values determined in cells are always higher than the results obtained from free-standing films. This indicates the great influence of the forces of interaction between the liquid crystal molecules and the surface layer in the cells.     

Thin-layer chromatography as a pilot technique for HPLC demonstrated with pesticide samples

The transferability of chromatographic conditions from TLC precoated plates to HPLC columns have been investigated using 62 different pesticides. For the investigation different stationary phases (silica gel, RP-18, RP-8, Diol, NH₂, CN) have been used with standard substances on the one hand and a real sample on the other hand. Rf-values of the pesticides have been converted to k'p, a retention value comparable to HPLC, and have been then compared with k'c values of the HPLC columns with the corresponding chromatographic system. For the evaluation of the results the respective data pairs have been correlated by linear regression. Good results of transfer have been obtained on every stationary phase. In the case of silica gel- and Diol-phases some restrictions have to be made, because of different activity between TLC and HPLC sorbent. In order to show that the transfer of chromatographic conditions is not limited to standards, the experiments have been extended to a spiked real sample (lettuce). The influence of the matrix is shown to be negligible and excellent transfer results are able to be realised.     

Quasi-antichain Chermak–Delgado lattices of finite groups

The Chermak–Delgado lattice of a finite group is a dual, modular sublattice of the subgroup lattice of the group. This paper considers groups with a quasi-antichain interval in the Chermak–Delgado lattice, ultimately proving that if there is a quasi-antichain interval between subgroups L and H with L ≤ H then there exists a prime p such that H/L is an elementary abelian p-group and the number of atoms in the quasi-antichain is one more than a power of p. In the case where the Chermak–Delgado lattice of the entire group is a quasi-antichain, the relationship between the number of abelian atoms and the prime p is examined; additionally, several examples of groups with a quasi-antichain Chermak–Delgado lattice are constructed.     

Ultra-Thin Layer Chromatography (UTLC) — A New Dimension in Thin-Layer Chromatography

JPC – Journal of Planar Chromatography – Modern TLC - Miniaturization is general trend in modern analytical methods, with the main targets of increasing sensitivity, shortening analysis...     

Ground‐state structures of polymers

Two‐ and three‐dimensional structures A_xB_y can be characterized by the numbers T₁ and T₂ of nearest and next‐nearest neighbors of the same kind. A small number of structures at the border of the T₁, T₂ structure map is stabilized by enthalpy compared to an increased number of entropy stabilized structures. About 60 three‐dimensional structures with T₁=2 nearest neighbors of all A atoms are suitable for infinite chains of polymers like (CH)_∞, (CHCH₂)_∞, or (CH₂)_∞. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1944–1955, 2001     

Conoscopic optical method of determining liquid crystal low tilt angles

A simple conoscopic optical method of determining liquid crystal low tilt angles with sufficient accuracy for many practical purposes is described. The similarity between this method and the crystal rotation one is shown. The limits of applicability of the conoscopic optical method are also given.