Transcript of the dispersion animation

Scene one

Scene one shows two dry aggregates of clay particles settled on a solid surface. This scene is accompanied with the text 'Two aggregates of clay particles within a sodic soil. The negative charge on the clay surface attracts positive ions (known as cations). Sodium (Na⁺) is the dominant cation attached to the clay surface.'

Scene two

Water fills the screen, hydrating the sodic clay particles until they repel one another and begin floating around the water as individual clay particles. A magnification bubble shows the layer of Na⁺ surrounding the clay particles swelling as the soil is hydrated to create a thick layer of positive charge around each particle. The scene is accompanied with the text 'As water is added to the dry sodic soil, Na⁺ is hydrated and the layer of positive charge gets wider until the clay particles begin to repel one another and disperse.'

Scene three

The clay particles move through the water in a random motion as individual particles. This frame is accompanied with the text 'Random movement of clay particles further disperses them as the wide layer of positive charge repels other positive charged particles.'

Scene four

The clay particles continue to move through the water in a random motion as individual particles. This frame is accompanied with the text 'If the width of the layer of positive charge can be decreased, we can control dispersion. The particles can get close together and attractive forces can take hold.'

Scene five

This scene shows calcium ions (Ca²⁺) being added to the soil, replacing the Na⁺ ions with Ca²⁺ and decreasing the thickness of the layer of positive charge around each clay particle. A magnification bubble shows the thick layer of Na⁺ ions around a clay particle being replaced with Ca²⁺ ions and the thickness of the layer of positive charge decreasing. The scene is accompanied with the text 'Adding calcium (Ca²⁺) as gypsum to a sodic soil replaces Na⁺ with Ca²⁺ ions. This decreases the width of the layer of positive charge as one Ca²⁺ ion replaces two Na⁺ ions.'

Scene six

The final scene shows the clay particles, now surrounded by a thin layer of positive charge of Ca²⁺ ions, aggregating and settling to the bottom of the water. The scene is accompanied with the text 'The thinner layer of positive charge means that attractive forces dominate repulsive forces, dispersion is controlled and aggregates reform.'

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