Small angle neutron scattering near Lifshitz lines: Transition from weakly structured mixtures to microemulsions

Abstract

A structural description of liquid particle dispersions: Ultracentrifugation and small angle neutron scattering studies of microemulsionsWe have studied the phase behavior, wetting transitions, and small angle neutron scattering (SANS) of water, n-alkane, and n-alkyl polyglycol ether (C;E) systems in order to locate the transition between weakly structured mixtures and microemulsions, and to provide a measure for the transition. We first determined the wetting transition by macroscopic measurements and then measured the location of the Lifshitz lines by SANS. Starting with wel1-structured mixtures (exhibiting nonwetting middle phases and wel1-expressed scattering peaks, features that qualify them as microemulsions) the wetting transition was induced by increasing the chain length of the alkane or by changing the oil/water volume ratio, and then the Lifshitz line was crossed. Further, starting with systems past the disorder line (weakly structured mixtures that display wetting middle phases and no scattering peaks), local structure was induced by either increasing the surfactant concentration or decreasing the oil/water volume ratio or the temperature. In each case a Lifshitz line was crossed. Analyzing the scattering experiments quantitatively, allows determination of the amphiphilicity factor, which is a measure of the strength of the surfactant. The results suggest there is a sequence of roughly parallel surfaces within the three-dimensional composition-temperature space. As the amphiphilicity factor increases, first a disorder surface is encountered, then a Lifshitz surface, and finally a wetting transition surface. How and to what extent these surfaces move in the one-phase region toward smal1er surfactant concentrations, and intersect there with the body of heterogeneous phases, depends on a number of factors that are discussed in some detail. phase microemulsions become able to wet the water/oil interface for thermodynamic reasons. 24 Widom has suggested

Ternary Polymer Blends as Model Surfactant Systems

“…An amphiphilicity factor, f a ) c 1 /(4a 2 c 2 ) 1/2 , may be defined which is a measure of the structure of the microemulsion. 21 At 110°C…”

“…This surfactant-rich phase is a microemulsion; near the middle of the temperature range over which the third phase is stable, a bicontinuous structure evolves to accommodate equal volumes of the two components. 21 This bicontinuous microemulsion is a correlated, isotropic fluid with a spongelike structure. Recently, the bicontinuous microemulsion has been observed in polymer blends 15,22 where it has been shown to be stable over a substantially wider temperature range.…”

Ionic Liquids in Microemulsions—A Concept To Extend the Conventional Thermal Stability Range of Microemulsions

“…167,181 In the case of polydisperse interacting particles, the scattering intensity can be expressed as…”

Внутренняя Структура Магнитных Пористых Стекол И Сегнетоэлектрических Нанокомпозитов На Их Основе

“…Хорошо видно принципиальное раз-личие между этими двумя зависимостями I(Q): 1 -для образца Fe20MIP наблюдается хорошо выделенный пик при Q ≈ 0.15 nm −1 , а для второго образца он становится более размытым; 2 -поведение кривых при больших Q также различно, причем для Fe20MАP явно присутствует протяженная область линейной за-висимости log(S(Q)) от log(Q) при больших Q. Сна-чала рассмотрим поведение наклона I(Q) в области 0. 35 [30,31], предло-женной для двухфазных объектов и использованной, в частности, для описания данных SANS на микроэмуль-сиях. В этой модели интенсивность рассеяния от Q описывается следующим выражением:…”