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Related Concept Videos

Common Ion Effect03:24

Common Ion Effect

Compared with pure water, the solubility of an ionic compound is less in aqueous solutions containing a common ion (one also produced by dissolution of the ionic compound). This is an example of a phenomenon known as the common ion effect, which is a consequence of the law of mass action that may be explained using Le Châtelier’s principle. Consider the dissolution of silver iodide:
Factors Affecting Activity Coefficient01:17

Factors Affecting Activity Coefficient

The extended Debye-Hückel equation indicates that the activity coefficient of an ion in an aqueous solution at 25°C depends on three partially interdependent properties: the ionic strength of the solution, the charge of the ion, and the ion size. 
The activity coefficient value for an ion is close to one when the solution has almost zero ionic strength, i.e., when the solution shows close to ideal behavior. As the ionic strength of the solution increases from 0 to 0.1 mol/L, a decrease in the...
The Colloidal State01:29

The Colloidal State

The formation of a colloidal system is exemplified by an aqueous solution containing Cl− ions is introduced to another containing Ag+ ions, resulting in the precipitation of solid AgCl as extremely tiny crystals. Instead of settling out as a filterable precipitate, these crystals remain suspended in the liquid, showcasing a colloidal system.A colloidal system involves colloidal particles within the approximate range of 1 to 1000 nm in at least one dimension, dispersed in a medium called the...
Colloidal precipitates01:09

Colloidal precipitates

The high insolubility of some precipitates can result in an unfavorable relative supersaturation. This can lead to colloidal particles with a large surface-to-mass ratio, where adsorption is promoted. For instance, in the precipitation of silver chloride, silver ions are adsorbed on the surface of the colloidal particles, forming a primary layer. This layer attracts ions of opposite charge (such as nitrate ions), forming a diffuse secondary layer of adsorbed ions. This electric double layer...
Ion Exchange01:17

Ion Exchange

Ion exchange chromatography separates charged molecules from a solution by reversibly exchanging them with mobile, or 'active', ions associated with the oppositely charged stationary phase. This method can be used to separate ions, soften and deionize water, and purify solutions. The polymers comprising the ion-exchange column are high-molecular-weight and chemically stable polymers, crosslinked to be porous and essentially insoluble. They are also functionalized with either acidic or basic...

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Related Experiment Video

Updated: Jul 17, 2026

Isothermal Titration Calorimetry for Measuring Macromolecule-Ligand Affinity
08:45

Isothermal Titration Calorimetry for Measuring Macromolecule-Ligand Affinity

Published on: September 7, 2011

Equivalent temperature and specific ion effects in macromolecule-coated colloid interactions.

Gregory E Fernandes1, Michael A Bevan

  • 1Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122, USA.

Langmuir : the ACS Journal of Surfaces and Colloids
|January 24, 2007
PubMed
Summary

Temperature and ion concentration reversibly control interactions between macromolecule-coated particles and surfaces. This discovery enables tunable stability and self-assembly of colloidal systems using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers.

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Area of Science:

  • Colloid and Surface Science
  • Polymer Science
  • Materials Science

Background:

  • Macromolecule-coated colloids are crucial in various applications, but controlling their interactions remains challenging.
  • Understanding the influence of environmental factors like temperature and ions on polymer layer behavior is key for targeted applications.
  • Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers are widely used for surface modification.

Purpose of the Study:

  • To quantify reversible interaction potentials between PEO-PPO-PEO block copolymer-coated colloids and surfaces.
  • To investigate the effects of temperature and magnesium sulfate (MgSO4) concentration on these interactions.
  • To establish a basis for controlling colloidal behavior through environmental stimuli.

Main Methods:

  • Ensemble total internal reflection microscopy was employed to measure interaction potentials.
  • Experiments were conducted across a temperature range of 20–47°C and MgSO4 concentrations of 0.2–0.5 M.
  • Analysis involved comparing measured potentials with van der Waals attraction, considering copolymer adsorption and surface roughness.

Main Results:

  • Measured potentials showed good agreement with theoretical predictions, accounting for copolymer layer collapse.
  • A universal curve was obtained by transforming the temperature scale, demonstrating the equivalence of temperature and MgSO4 concentration effects.
  • The study successfully mapped nanometer- and kT-scale interactions under varying conditions.

Conclusions:

  • Reversible control over colloid-surface interactions is achievable by tuning temperature and MgSO4 concentration.
  • The findings provide a framework for designing and manipulating colloidal systems for specific applications.
  • This research enables precise control over the stability, phase behavior, and self-assembly of PEO-PPO-PEO coated colloids.