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The Colloidal State

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 precipitates

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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...

Colloids and Suspensions

Colloids and Suspensions

Children at play often make suspensions such as mixtures of mud and water, flour and water, or a suspension of solid pigments in water known as tempera paint. These suspensions are heterogeneous mixtures composed of relatively large particles visible to the naked eye or seen with a magnifying glass. They are cloudy, and the suspended particles settle out after mixing. The suspended particles in a suspension settle out after some time of mixing. The separation of particles from a suspension is...

Colloids

Colloids

Children at play often make suspensions such as mixtures of mud and water, flour and water, or a suspension of solid pigments in water known as tempera paint. These suspensions are heterogeneous mixtures composed of relatively large particles that are visible to the naked eye or can be seen with a magnifying glass. They are cloudy, and the suspended particles settle out after mixing. On the other hand, a solution is a homogeneous mixture in which no settling occurs and in which the dissolved...

Factors Affecting Dissolution: Particle Size and Effective Surface Area

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Dissolution kinetics, an essential aspect of oral drug delivery, is significantly influenced by the drug's particle size. According to the Noyes-Whitney dissolution model, the dissolution rate correlates directly with the drug's surface area. The larger the surface area, the higher the drug's solubility in water, leading to a faster drug dissolution rate. Reducing particle size increases the effective surface area, enhancing the dissolution process. Micronization and nanosizing are employed to...

Theories of Dissolution: Diffusion Layer Model

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Dissolution, the process by which drug particles dissolve in a solvent, is explained by the diffusion layer model, a theoretical framework that simulates the absorption of oral drugs and allows us to analyze experimental data.
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Related Experiment Video

Updated: May 25, 2026

Measuring and Modeling Contractile Drying in Human Stratum Corneum

Measuring and Modeling Contractile Drying in Human Stratum Corneum

Published on: March 1, 2017

Autostratification in drying colloidal dispersions: experimental investigations.

R E Trueman¹, E Lago Domingues, S N Emmett

¹Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, United Kingdom.

Langmuir : the ACS Journal of Surfaces and Colloids

|January 20, 2012

Summary

This study investigates particle stratification in colloidal films, finding that diffusion drives layering but other flows are also important. Optimal stratification occurs with stable dispersions and specific Peclet numbers.

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Synthesis and Characterization of Supramolecular Colloids

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Published on: April 22, 2016

Area of Science:

Materials Science
Colloid Science
Surface Science

Background:

Understanding particle distribution in thin films is crucial for material properties.
Previous models predict diffusional stratification in colloidal dispersions.
Experimental validation of these models is needed.

Purpose of the Study:

To experimentally investigate particle distribution normal to the substrate in films cast from two-particle-size colloidal dispersions.
To compare experimental findings with a diffusional model.
To identify conditions favoring particle stratification.

Main Methods:

Casting thin films from colloidal dispersions with two distinct particle sizes.
Utilizing atomic force microscopy (AFM) for surface topography and particle analysis.
Employing Nuclear Magnetic Resonance (NMR) profiling for in-depth concentration analysis.

Main Results:

Observed evidence of diffusion-driven particle stratification within the films.
Highlighted the significant influence of other flow dynamics beyond diffusion.
Identified key conditions enhancing stratification: stable dispersions, low initial volume fractions, low stratifying particle concentration, and Peclet numbers straddling unity.

Conclusions:

Diffusional effects contribute to particle stratification in colloidal films.
Non-diffusional flows play a critical role in the stratification process.
Specific colloidal and flow conditions optimize particle layering for material applications.