What is a gradient structure?
Gradient refers to the increase or decrease in the size or extent of a particular property (ie, temperature, pressure, concentration).
To a material scientists or engineer, a gradient structure will demonstrate gradually changing mechanical properties along a defined direction for example stiff to elastic or solid to porous.
Gradient structures in biology
Gradient structures in textiles
In textiles, the French term òmbre which means shadow is used to describe fabrics with a dyed, printed, or woven design in which the colour hue is blended gradually into another, usually moving tints and shades from light to dark.
So far, gradient systems exist in textiles primarily for aesthetic effects and focus on transition of colour hue. However, there are numerous processes and techniques that enable the designer to gradually alter other aspects of a textile such as the density of interlacing/looping, transition of one yarn to another.
Gradient structures aid
Consider a grain of wild wheat…
Grains are specials structures composed of the seed and seed coat whose job is to make sure that the seed finds the perfect location to germinate and grow. One of the most extraordinary grains in nature are those of wild wheat who have evolved the ability to plant themselves into the soil.
The drilling or planting action is carried out by the specially designed seed coat which features two long bristles called awns. In the dry daytime, the awns are bent outwards. During the night, as the air dampens, the awns become straight. Over the course of several days, the movement of bending and straightening, submerges the grain into the earth.
The mechanism behind this behaviour is located within the structure of the awns. The bristles are made primarily of cellulose. On a molecular level, strings of cellulose molecules form fibrils or microscopic fibres. On one side of the awn, the cellulose fibrils are tightly packed together forming a stiff region, on the other side, the fibrils are less tightly packed as such are more bendy but also allow moisture to stick to them which causes this area to swell.
In the damp of the night, this causes the awn to appear straight, as the environment becomes drier, the moisture evaporates causing this area of cellulose to shrink. This makes the awn appear bent inwards in the dry of day.
This is classified as a gradient structure because the density of the cellulose fibrils gradually reduces across the width of the awn.