Measuring Alkyl Chain Cross-Sectional Area for Gibbs Adsorption

In summary: The reference for the theoretical value of the alkyl chain is (estimated 20-25 A˚2). In summary, there are three potential methods for measuring the cross-sectional area of the alkyl chain of a surfactant molecule: vertically (refer to GREEN DOUBLE ARROWS of Figure 1), horizontally (refer to RED DOUBLE ARROWS of Figure 1), or taking the theoretical value from literature. However, the latter is not always accurate, as evidenced by a paper by Shibata et. al. that states a contradiction with the Gibbs adsorption when the molecular surface area is smaller than the cross-sectional area of the alkyl chain.
  • #1
bobey
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1. Surfactant molecule is made from water-loving head and grease-loving tail (Figure 1). My question: How do we measure the cross-sectional area of the alkyl chain of surfactant? Do we measure it vertically (refer to GREEN DOUBLE ARROWS of Figure 1) or horizontally (refer to RED DOUBLE ARROWS of Figure 1)? Or do we just take the “theoretical value" of the alkyl chain from the literature (estimated 20-25 A˚2)[http://www.physics.uoguelph.ca/~dutcher/download/handbook%20of%20biological%20physics/7.pdf]?

2. I have read a paper entitled, "New Adsorption Model - Theory, Phenomena and New Concept - " by Shibata et. al. [2]. One of the sentences in para 3 page 2 stated that, i quoted, “The important finding is that molecular surface area is less than the cross-sectional area of the alkyl chain for C16E8 and C18E8. Such small molecular surface areas strongly suggest that Gibbs adsorption just at air/water interface in an adequate. This is one of contradictions for the Gibbs adsorption."

Why does when the molecular surface area is less than the cross-sectional area of the alkyl chain, it is said to be contradicted with the Gibbs adsorption?

Reference:

[1] http://www.physics.uoguelph.ca/~dutcher/download/handbook%20of%20biological%20physics/7.pdf

[2] http://www.jstage.jst.go.jp/article/jos/64/1/64_ess14213/_pdf
 
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  • #2
bobey said:
How do we measure the cross-sectional area of the alkyl chain of surfactant?
Definition of the term "cross-section" gives you a "hint."
 

What is the purpose of measuring alkyl chain cross-sectional area for Gibbs adsorption?

The purpose of measuring alkyl chain cross-sectional area for Gibbs adsorption is to understand the behavior of surfactant molecules at the air-water interface. This measurement helps to determine the packing density of the alkyl chains, which affects their ability to reduce surface tension and form stable monolayers.

What methods are commonly used to measure alkyl chain cross-sectional area?

The most commonly used methods to measure alkyl chain cross-sectional area include Langmuir isotherm analysis, surface pressure-area isotherms, and Brewster angle microscopy. These methods involve creating a monolayer of surfactant molecules at the air-water interface and measuring the change in surface pressure or area as the concentration of the surfactant is varied.

What factors can affect the accuracy of measuring alkyl chain cross-sectional area?

The accuracy of measuring alkyl chain cross-sectional area can be affected by various factors, such as the purity of the surfactant used, temperature, pH, and the presence of other molecules or contaminants at the interface. It is important to carefully control these factors to obtain accurate measurements.

What is the significance of alkyl chain cross-sectional area in surfactant applications?

The alkyl chain cross-sectional area is a crucial parameter in surfactant applications as it determines the effectiveness of the surfactant in reducing surface tension and forming stable interfaces. It also affects the behavior of surfactant molecules in various processes, such as emulsification, foaming, and detergency.

How can measuring alkyl chain cross-sectional area aid in understanding surfactant structure-activity relationships?

Measuring alkyl chain cross-sectional area can provide valuable insights into the structure-activity relationships of surfactants. By comparing the cross-sectional area with other physical properties of the surfactant, such as the critical micelle concentration and hydrophile-lipophile balance, researchers can better understand how the molecular structure of the surfactant influences its behavior at interfaces.

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