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Related Concept Videos

Polymer Classification: Crystallinity01:21

Polymer Classification: Crystallinity

Unlike ionic or small covalent molecules, polymers do not form crystalline solids due to the diffusion limitations of their long-chain structures. However, polymers contain microscopic crystalline domains separated by amorphous domains.
Crystalline domains are the regions where polymer chains are aligned in an orderly manner and held together in proximity by intermolecular forces. For example, chains in the crystalline domains of polyethylene and nylon are bound together by van der Waals...
Chemistry of Carbohydrates03:25

Chemistry of Carbohydrates

Carbohydrates are an essential part of the diet in humans and animals. Grains, fruits, and vegetables are natural sources of carbohydrates that provide energy to the body, particularly through glucose, a simple sugar that is a component of starch and an ingredient in many staple foods. The stoichiometric formula (CH2O)n, where n is the number of carbons in the molecule represents carbohydrates. In other words, the ratio of carbon to hydrogen to oxygen is 1:2:1 in carbohydrate molecules. This...
Chemistry of Carbohydrates03:25

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Carbohydrates are an essential part of the diet in humans and animals. Grains, fruits, and vegetables are natural sources of carbohydrates that provide energy to the body, particularly through glucose, a simple sugar that is a component of starch and an ingredient in many staple foods. The stoichiometric formula (CH2O)n, where n is the number of carbons in the molecule represents carbohydrates. In other words, the ratio of carbon to hydrogen to oxygen is 1:2:1 in carbohydrate molecules. This...
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Structures of Solids02:22

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Solids in which the atoms, ions, or molecules are arranged in a definite repeating pattern are known as crystalline solids. Metals and ionic compounds typically form ordered, crystalline solids. A crystalline solid has a precise melting temperature because each atom or molecule of the same type is held in place with the same forces or energy. Amorphous solids or non-crystalline solids (or, sometimes, glasses) which lack an ordered internal structure and are randomly arranged. Substances that...
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Molecules have characteristic shapes that are crucial for their function. The arrangement of various electron groups around the central atom dictates their molecular geometry. Electron pairs in the valence shell of a central atom will adopt an arrangement that minimizes repulsions between the electron pairs by maximizing the distance between them. The valence electrons form either bonding pairs, located primarily between bonded atoms, or lone pairs.Two regions of electron density in a diatomic...

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Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
14:55

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Published on: September 17, 2017

Molecular packing in amorphous carbohydrate matrixes.

Sam Townrow1, Duncan Kilburn, Ashraf Alam

  • 1H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK.

The Journal of Physical Chemistry. B
|October 20, 2007
PubMed
Summary

Investigating amorphous carbohydrate blends with Positron Annihilation Lifetime Spectroscopy (PALS) reveals water

Area of Science:

  • Food science and technology
  • Materials science
  • Polymer chemistry

Background:

  • Amorphous carbohydrates, like maltopolymers and maltose, are crucial in food and pharmaceutical applications.
  • Understanding their molecular packing and free volume is key to controlling material properties.
  • The influence of water and molecular weight distribution on these properties remains an area of active research.

Purpose of the Study:

  • To investigate the molecular packing and free volume hole characteristics of amorphous carbohydrate blends.
  • To determine the effects of varying maltose content and water activity on these properties.
  • To elucidate the complex role of water as both a plasticizer and matrix component.

Main Methods:

  • Positron Annihilation Lifetime Spectroscopy (PALS) was employed to analyze free volume hole sizes.

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  • Specific volume measurements were conducted to complement PALS data.
  • Carbohydrate blends were equilibrated at various water activities (0-0.75) at 25°C.

    • Main Results:

    • In the rubbery state, hole size showed weak dependence on carbohydrate molecular weight at constant water content.
    • In the glassy state, significant differences in hole size were observed with varying blends.
    • Increasing maltose content decreased specific volume and hole volume up to 40 wt%.
    • Water acted as a hole-filler at low water content, potentially causing anti-plasticization.
    • At higher water content, water increased average hole volume by disrupting hydrogen bonds and expanding packing.

    Conclusions:

    • Molecular packing in amorphous carbohydrate blends is sensitive to composition and water content, particularly in the glassy state.
    • Water's role is dual: filling holes at low concentrations and expanding the matrix at higher concentrations by affecting hydrogen bonding.
    • These findings provide critical insights into the physical behavior of carbohydrate-based materials.