Thermotropic Behavior of the Silica−Alkyltrimethylammonium Chloride Mesostructured Materials

Abstract

The characteristics of the thin films of silica-alkyltrimethylammonium chloride mesostructured materials have been investigated by means of the fluorescence of pyrene as well as the infrared spectra at variable temperatures. Pyrene molecules were incorporated in the hydrophobic part of the silica-surfactant mesostructured materials without aggregation even at a high loading amount. The temperature dependence of the luminescence of pyrene revealed that the microviscosity of the probe microenvironments decreased gradually with decreasing temperature. The infrared absorption bands of the mesostructured materials confirmed the thermotropic change in the state of the surfactant aggregates.

Alcóxidos como precursores na síntese de novos materiais através do processo sol-gel

“…Com esta estrutura formada, pode-se trabalhar quimicamente no sentido de incrustar novos derivados na superfície inorgânica do material sintetizado, através de agentes sililantes adequados, que estão acompanhados de funções químicas, para se atingir uma determinada finalidade na utilização do novo material preparado [13][14][15][16] . Um dos recentes usos dos alcóxidos de silício tem sido na obtenção de sílica lamelar [17][18][19][20][21][22][23][24][25] , cuja divulgação do tema 26 mostra o inegável progresso laboratorial, na descoberta de propriedades de hidrólise controlada, para se atingir o objetivo desejado. Neste aspecto é bastante explorado o processo sol-gel, através da chamada rota da diamina neutra 27 .…”

Preparation of Self-Standing Transparent Films of Silica-Surfactant Mesostructured Materials and the Conversion to Porous Silica Films

“…[4±8] We have reported the photomodulation of LC phases using ªchirop-tical molecular switchesº. [5,8] Photochemical interconversion of two opposite helices of cis and trans isomers of overcrowded alkenes doped in nematic LCs resulted in switching between two cholesteric phases, depending on the irradiation wavelength employed. As the isomers of the chiral dopant were pseudoenantiomers the pitches of the two phases were opposite in sign.…”

“…[5] When enantiomers were used instead (racemic mixture), circular polarized light was necessary in order to achieve a small enantiomeric excess, which was amplified by doping the chiral overcrowded alkene photoswitch in a nematic LC phase, which resulted in a chiral nematic phase. [8] It is also conceivable that switching between nematic and cholesteric phases can be achieved by doping with a chiral photoswitch that exhibits large difference in twisting power in its two photostates.…”

Dispersion of Organic Dyes in n-Hexadecylamine-Intercalated Vanadium Xerogel Thin Films

“…Layered materials have been studied extensively as matrices for photofunctional molecules [1][2][3][4][5][6][7][8][9][10][11]. Applications of these materials include solid dye lasers and nonlinear optics.…”

“…This effect to avoid aggregation has been called the ''matching effect.'' The second approach is to incorporate a third component into the interlayer spacing of clay as a ''spacer,'' together with dye molecules [4][5][6][7][8][9]. The aggregation of dye molecules or ions can be suppressed in pyrene=cationic surfactant=silica or rhodamine 6G=cationic surfactant=clay hybrid by choosing the appropriate surfactant=dye ratio; light emission from dye monomers was observed in film and powder samples or in aqueous solution.…”