How does the MoCA system change colour from red to blue?

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The MoCA System Changes Colour by Altering its Morphology from Flat to Concave

The Morphable Concavity Array (MoCA) system undergoes a colour transformation from red to blue by manipulating its physical structure at the pixel level. This change is initiated when ethanol interacts with the pNIPAM hydrogel layer, causing it to swell. This swelling creates tension that pulls the overlying GPDMS elastomer layer downwards into a pre-defined hole in the array. This deformation results in a dish-like concave shape, termed a morphable concavity (MoC), which functions as an individual pixel. Once this concavity is formed, the pixel effectively blocks red light, leading to a visible shift in its colour from red to blue.
Swelling of the pNIPAM Layer Induces Structural Tension

The colour-changing mechanism of MoCA is directly linked to the swelling behaviour of its pNIPAM hydrogel component. When ethanol is introduced to this layer, it absorbs the liquid and expands in volume. This physical expansion is not isolated; instead, it generates significant tension within the structure. This tension is crucial as it exerts a pulling force on the GPDMS elastomer layer situated above it, initiating the morphological change.
Formation of Morphable Concavities Creates Colour-Shifting Pixels

The tension generated by the swollen pNIPAM layer actively pulls the GPDMS elastomer into the holes present in the underlying array structure. This action forms distinct, dish-like concave shapes, known as morphable concavities (MoCs). Each MoC serves as an independent pixel within the MoCA system. The transition between a 'flat' state and this 'concave' state is the fundamental method by which MoCA alters its local morphology and, consequently, its colour.
Light Manipulation Through Concavity Leads to Colour Change

The key to the colour shift lies in how these morphable concavities interact with light. When the MoC is formed, its specific geometry causes it to block certain wavelengths of light, specifically red light in this instance. The blocking of red light, combined with the inherent optical properties of the material and its structure, results in the observed colour change. The visible colour of the pixel is perceived as blue after the red light has been obstructed by the concave structure.

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How does the MoCA system change colour from red to blue?

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