The general behavior of Newtonian, shear-thinning, shear-thickening, thixotropic, negative thixotropic, and viscoelastic fluids is characterized and briefly discussed in terms of existing theoretical models. Whenever possible, examples of these types of fluids taken from everyday life are given for better understanding. This theoretical introduction is the basis for same, simple, and inexpensive laboratory work employing no special glassware and generally done by pairs of students. The work involves the synthesis of two well-known viscoelastic materials displaying unique properties: poly(vinyl alcohol) (PVA) and white glue, a poly(vinyl acetate)-based emulsion. The students are asked to perform a series of representative mechanical tests on both gels and to describe their observations in full detail. In particular, they are expected to recognize and identify the origin of the intriguing behaviors found (elasticity, spinability, self-siphoning effect, die-swell effect, Weissenberg effect). The tests include the preparation of fibers by extrusion, introducing concepts such as water solubility, hydrogen bonding, and glass transition temperature. The long list of questions, which ideally should be answered at the end of the laboratory work, allows the students to apply the new concepts acquired.
A novel synthesis of aminosquarylium cyanine dyes, based on the methylation of readily available squarylium dyes with methyl triflate, followed by nucleophilic substitution with appropriate aliphatic amines, was disclosed. By this procedure several new aminosquarylium cyanine dyes bearing benzothiazole, benzoselenazole and quinoline nuclei were prepared.
Cyanine and polymethine dyesCyanine and polymethine dyes T 1300New Synthetic Approach to Aminosquarylium Cyanine Dynes. -Based on the methylation of the squarylium cyanine dyes (III), a simple preparative procedure for the production of aminosquarylium cyanine dyes (VII) is developed. -(REIS, L. V.; SERRANO, J. P. C.; ALMEIDA, P.; SANTOS*, P. F.; Synlett 2002, 10, 1617-1620; Dep. Quim., Univ. Tras-os-Montes, P-5000 Vila Real, Port.; Eng.) -Mais 05-195
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