The dynamics of sucessive impacts of water droplets against flat glass surfaces covered by Langmuir-Blodgett films of zinc stearate with 1, 3, 5 and 7 layers was investigated. The structure and resistance of monolayers to the impact was evaluated by using fast images of the drop deformation, Brewster angle microscopy (BAM) and contact angle measurements. Eventual disruption (erosion) of the layers was investigated by using sum-frequency vibrational spectroscopy (SFG).

The effects of ionic strength on ions in aqueous solutions are quite relevant, especially for biochemical systems, in which proteins and amino acids are involved. The teaching of this topic and more specifically, the Debye-Hückel limiting law, is central in chemistry undergraduate courses. In this work, we present a description of an experimental procedure based on the color change of aqueous solutions of bromocresol green (BCG), driven by addition of electrolyte. The contribution of charge product (z+|z-|) to the Debye-Hückel limiting law is demonstrated when the effects of NaCl and Na2SO4 on the color of BCG solutions are compared.

It is very well known that the addition of polymers to a liquid increases the shear viscosity of the solution. In other words, the polymer increases the dissipation of the flow energy. Contrarily, in turbulent flow, some particular macromolecules in very low concentration are able to produce large attenuation in the turbulence and thus, decreasing the dissipation of the energy. This article present a brief revision about macroscopic and molecular models used to explain this dynamic effect. Some of the experimental techniques used to quantify the attenuation of the turbulence and the main active substances are also discussed.

Polímero híbrido derivado de siloxano e b-ciclodextrina (β-CD) foi obtido pela reação de β-CD com g-isocianatopropiltrietoxissilano (IPTS), seguido por reação de hidrólise/condensação, gerando uma resina de polissilsesquioxano modificada por β-CD (PSS-β-CD). PSS-β-CD foi caracterizado por espectroscopia infravermelho e ressonância magnética nuclear de 13C e 29Si. Este híbrido é amorfo e termicamente estável até 180 ºC. PSS-β-CD pode ser obtido também como filme e sua morfologia foi avaliada por microscopia eletrônica de varredura. A capacidade da β-CD ligada ao polímero em formar complexos de inclusão foi avaliada pela formação de um complexo de β-CD-fenolftaleína, utilizando espectroscopia UV-Vis. Mesmo sem mudanças no pH, a forma vermelha da fenolftaleína se converte na forma incolor quando PSS-β-CD é imerso na solução. Cálculos teóricos (métodos AM1 e DFT) mostram que o complexo é formado pela inclusão do anel fenolato na cavidade da β-CD favorecendo a forma incolor da fenolftaleína por mais de 15 kcal mol-1.

A hybrid polymer derived from siloxane and β-cyclodextrin (β-CD) was obtained by reaction of β-CD with g-isocyanatopropyltriethoxysilane (IPTS), followed by hydrolysis/condensation reactions, generating a β-CD-modified polysilsesquioxane resin (PSS-β-CD). PSS-β-CD hybrid was characterized by infrared spectroscopy and 13C and 29Si nuclear magnetic resonance. This hybrid was typically amorphous and thermally stable up to 180 ºC. PSS-β-CD was able to form films and its morphology was evaluated by scanning electron microscopy. The capability of β-CD grafted in the hybrid polymer to form inclusion complex was evaluated by the formation of a β-CD-phenolphthalein complex using UV-Vis spectroscopy. Even without changes in pH, the red form of phenolphthalein converts to the colorless one when PSS-β-CD is immersed in the solution. Theoretical calculations (AM1 and DFT methods) show that the complex is formed through the inclusion of the phenolate ring into β-CD cavity, favoring the colorless form of phenolphthalein by more than 15 kcal mol-1.

A partição de PEO de água para CH2Cl2 e CHCl3 aumenta com a sua massa molar, até se tornar constante em torno de 3 000 g mol-1. Estes resultados revelam que a partição de PEO é bastante sensível à contribuição dos grupos hidroxila, sugerindo a transição de caráter poliglicol para poliéter em torno de 3000 g mol-1.

PEO partitioning from water to CH2Cl2 and CHCl3 increases with its molar mass, leveling off at ca. 3 000 g mol-1. Such a behaviour is related to PEO end-group contributions, suggesting a polyglycol to polyether transition at ca. 3 000 g mol-1.

The microwave oven became a common domestic equipment, due mainly to the short time spent to heat foods. One of the most interesting characteristics of the microwave oven is the selective heating. Different from the conventional oven, where the heating is not selective, the heating by microwave depends on the chemical nature of the matter. Many Students of Chemistry have no knowledge of the principles involved in this selective heating, in spite of the daily microwave oven use. The heating by microwave is feasible for chemistry courses. In discussions about the microwave absorption by the matter it is possible to explore chemical properties like: heat capacity, chemical bound, molecular structure, dipole moments, polarization and dielectric constant. This paper presents the basic principles involved in the microwave heating. It is proposed a simple and inexpensive experiment that could be developed in general chemistry courses, to illustrate the relationship between heating and the chemical properties of some solvents. Experiments to check the power of the microwave oven are also proposed.

The structural characteristics of foams are responsible for a broad range of applications of this system. Foams produced by aqueous solutions of surfactant concentrates are used in fire-fighting due to their special properties as extinguishing agents. In the present paper we discuss the main aspects involved in fire-fighting, based on some properties of foams. Thermal and chemical stability, good wetting of surfaces, cooling effect by water drained from the bubbles, isolation of the air from the burning surface and suppression of flammable vapors are some of the factors involved in the extinguishment of fire by foams.