Hydrophobicity

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Glass Transition of Hard Sphere Systems: Molecular Dynamics and Density Functional Theory

The glass transition of a hard sphere system is investigated within the framework of the density functional theory (DFT). Molecular dynamics (MD) simulations are performed to study dynamical behavior of the system on the one hand and to provide the data to produce the density field for the DFT on the other hand. Energy landscape analysis based on the DFT shows that there appears a metastable (local) free energy minimum representing an amorphous state as the density is increased. This state turns out to become stable, compared with the uniform liquid, at some density, around which we also observe sharp slowing down of the $alpha$ relaxation in MD simulations.Comment: 5 pages, 5 figure

ORIENTATIONAL ENVIRONMENTS AND HIGH ORDER CORRELATION FUNCTIONS IN LIQUIDS

Recent experimental and theoretical studies of amorphous solids and supercooled liquids have generated renewed interest in triplet and higher-order correlation functions in noncrystalline materials. Here we discuss the connection between orientationally ordered condensed phases and high-order correlation functions

HETEROGENEOUS NUCLEATION OF CLATHRATES FROM SUPERCOOLED THF/WATER MIXTURES AND THE EFFECT OF AN ADDED CATALYST

The statistics of liquid-to-crystal nucleation are measured for clathrate-forming mixtures of tetrahydrofuran and water using an automatic lag time apparatus (ALTA). We measure the nucleation temperature where a single sample is repeatedly cooled, nucleated and thawed. This is done for a series of tetrahydrofuran concentrations and in several different sample tubes since the nucleation is heterogeneous and occurring on the tube wall. The measurements are also done at the same concentrations and tubes but with an added catalyst, a single crystal of silver iodide. We discuss the need for this type of measurement if the true nucleation temperature of the clathrate is to be found. Comparisons are also made with our high pressure data on real-world clathrate formers.Non UBCUnreviewe

NUCLEATION OF CLATHRATES FROM SUPERCOOLED THF/WATER MIXTURES SHOWS THAT NO MEMORY EFFECT EXISTS

The liquid-to-crystal nucleation temperature is measured for clathrate-forming mixtures of tetrahydrofuran and water using both an automatic lag time apparatus (ALTA) and a ball screening apparatus. Our results are conclusive evidence that no so-called “memory effect” exists. Either the solid form melts fully or it does not. If it does not, then no supercooling is possible on the next cooling down of that sample, and if it does then the second cooling run and freezing on a sample is just as likely to have a colder nucleation temperature as a hotter one.Non UBCUnreviewe

A NEW METHOD FOR THE STATISTICAL EVALUATION OF NATURAL GAS HYDRATE NUCLEATION AT ELEVATED PRESSURE

Nucleation is a stochastic process, most accurately represented by a probability distribution. Obtaining sufficient data to define this probability distribution is a laborious process. Here, we describe a novel instrument capable of the automated determination of hydrate nucleation probability under non-equilibrium conditions for a range of natural gas mixtures at pressures up to 10MPa. The instrument is based on the automated lag time apparatus (ALTA) which was developed to study the stochastic nature of nucleation in ambient pressure systems [1].We demonstrate that the probability distribution represents a robust and reproducible tool for the quantitative evaluation of hydrate formation risk under pseudo-realistic pressure conditions.Non UBCUnreviewe