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Boiling Point Elevation

The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform

Masahiro Yoshizawa – 1st expert on this subject based on the ideXlab platform

  • ionic liquids by proton transfer vapor pressure conductivity and the relevance of δpka from aqueous solutions
    Journal of the American Chemical Society, 2003
    Co-Authors: Masahiro Yoshizawa, Wu Xu, Charles Angell

    Abstract:

    We describe the behavior of the conductivity, viscosity, and vapor pressure of various binary liquid systems in which proton transfer occurs between neat Bronsted acids and bases to form salts with melting Points below ambient. Such liquids form an important subgroup of the ionic liquid (IL) class of reaction media and electrolytes on which so much attention is currently being focused. Such “protic ionic liquids” exhibit a wide range of thermal stabilities. We find a simple relation between the limit set by Boiling, when the total vapor pressure reaches one atm, and the difference in pKa value for the acid and base determined in dilute aqueous solutions. For ΔpKa values above 10, the Boiling Point Elevation becomes so high (>300 °C) that preemptive decomposition prevents its measurement. The completeness of proton transfer in such cases is suggested by the molten salt-like values of the Walden product, which is used to distinguish good from poor ionic liquids. For the good ionic liquids, the hydrogen bond…

Richard W. Hartel – 2nd expert on this subject based on the ideXlab platform

  • Non-equilibrium States in Confectionery
    Non-Equilibrium States and Glass Transitions in Foods, 2016
    Co-Authors: Richard W. Hartel, Christine M Nowakowski

    Abstract:

    Many confections are governed by non-equilibrium states and glass transitions, both during manufacture and throughout shelf life. In general, sugar confections contain sucrose and glucose syrup as the main sweeteners, along with a variety of additives that distinguish each class of confections. The sugar syrup is boiled to remove excess water, and the final cook temperature determines the final water content through the Boiling Point Elevation curve. During cooling, other ingredients may be added (e.g., colors, flavors, and acids) and/or other operations performed (e.g., aeration), again to distinguish the class of confections. Upon cooling to ambient temperatures, these confections generally are categorized as supersaturated solutions, in either the amorphous or glassy state. As such, they are unstable and prone to changes during storage, which may include moisture uptake or loss, crystallization, and flavor loss. This chapter will provide an overview of manufacture and formation of these products before delving into stability during storage and the mechanisms of collapse.

  • Moisture and Shelf Life in Sugar Confections
    Critical Reviews in Food Science and Nutrition, 2010
    Co-Authors: Roja Ergun, R. Lietha, Richard W. Hartel

    Abstract:

    From hardening of marshmallow to graining of hard candies, moisture plays a critical role in determining the quality and shelf life of sugar-based confections. Water is important during the manufacturing of confections, is an important factor in governing texture, and is often the limiting parameter during storage that controls shelf life. Thus, an understanding of water relations in confections is critical to controlling quality. Water content, which is controlled during candy manufacturing through an understanding of Boiling Point Elevation, is one of the most important parameters that governs the texture of candies. For example, the texture of caramel progresses from soft and runny to hard and brittle as the moisture content decreases. However, knowledge of water content by itself is insufficient to controlling stability and shelf life. Understanding water activity, or the ratio of vapor pressures, is necessary to control shelf life. A difference in water activity, either between candy and air or betwe…

  • Moisture and shelf life in sugar confections
    Critical Reviews in Food Science and Nutrition, 2010
    Co-Authors: Recai Ergun, R. Lietha, Richard W. Hartel

    Abstract:

    From hardening of marshmallow to graining of hard candies, moisture plays a critical role in determining the quality and shelf life of sugar-based confections. Water is important during the manufacturing of confections, is an important factor in governing texture, and is often the limiting parameter during storage that controls shelf life. Thus, an understanding of water relations in confections is critical to controlling quality. Water content, which is controlled during candy manufacturing through an understanding of Boiling Point Elevation, is one of the most important parameters that governs the texture of candies. For example, the texture of caramel progresses from soft and runny to hard and brittle as the moisture content decreases. However, knowledge of water content by itself is insufficient to controlling stability and shelf life. Understanding water activity, or the ratio of vapor pressures, is necessary to control shelf life. A difference in water activity, either between candy and air or between two domains within the candy, is the driving force for moisture migration in confections. When the difference in water activity is large, moisture migration is rapid, although the rate of moisture migration depends on the nature of resistances to water diffusion. Barrier packaging films protect the candy from air whereas edible films inhibit moisture migration between different moisture domains within a confection. More recently, the concept of glass transition, or the polymer science approach, has supplemented water activity as a critical parameter related to candy stability. Confections with low moisture content, such as hard candy, cotton candy, and some caramels and toffees, may contain sugars in the amorphous or glassy state. As long as these products remain below their glass transition temperature, they remain stable for very long times. However, certain glassy sugars tend to be hygroscopic, rapidly picking up moisture from the air, which causes significant changes that lead to the end of shelf life. These products need to be protected from moisture uptake during storage. This review summarizes the concepts of water content, water activity, and glass transition and documents their importance to quality and shelf life of confections.

Charles Angell – 3rd expert on this subject based on the ideXlab platform

  • ionic liquids by proton transfer vapor pressure conductivity and the relevance of δpka from aqueous solutions
    Journal of the American Chemical Society, 2003
    Co-Authors: Masahiro Yoshizawa, Wu Xu, Charles Angell

    Abstract:

    We describe the behavior of the conductivity, viscosity, and vapor pressure of various binary liquid systems in which proton transfer occurs between neat Bronsted acids and bases to form salts with melting Points below ambient. Such liquids form an important subgroup of the ionic liquid (IL) class of reaction media and electrolytes on which so much attention is currently being focused. Such “protic ionic liquids” exhibit a wide range of thermal stabilities. We find a simple relation between the limit set by Boiling, when the total vapor pressure reaches one atm, and the difference in pKa value for the acid and base determined in dilute aqueous solutions. For ΔpKa values above 10, the Boiling Point Elevation becomes so high (>300 °C) that preemptive decomposition prevents its measurement. The completeness of proton transfer in such cases is suggested by the molten salt-like values of the Walden product, which is used to distinguish good from poor ionic liquids. For the good ionic liquids, the hydrogen bond…