TY - JOUR
T1 - Structural colouration in the Himalayan monal, hydrophobicity and refractive index modulated sensing
AU - Rashid, Ijaz
AU - Hassan, Muhammad Umair
AU - Nazim, Muhammad
AU - Elsherif, Mohamed
AU - Dou, Qian
AU - Hu, Debo
AU - Kamran, Muhammad
AU - Dai, Qing
AU - Butt, Haider
PY - 2020/11/7
Y1 - 2020/11/7
N2 - The Himalayan monal is a bird in the pheasant family, and it is the national bird of Nepal. The bird possesses spectacular iridescent plumage with a range of different metallic colours. Here, we have studied the internal structure of its feathers from different parts of the bird's body and showed that its beautiful colours and iridescence are due to photonic structures present in the internal structure of the feathers. Sharp changes in the reflected brilliance were observed from the feathers upon changing the illumination conditions, such as horizontal and azimuthal angles. The feathers exhibited interesting hydrophobic properties, with the dull-coloured proximal end showing lower hydrophobicity with a contact angle between 90° and 110° compared with the iridescent distal end of a feather exhibiting a contact angle between 115° and 120°, attributed to the change in the internal structure and/or density of the feathers. A quick reversible change in colours of these feathers was observed when they were soaked in water and other liquids, which reversed upon drying. The shift in colour was suggested to be due to the swelling of the keratin layer of barbules that absorbed liquids and as a result modified the refractive index and periodicity of the internal photonic structures. The colour shift response of feathers was different in the case of alcohols and other water-based solutions, suggesting different swelling behaviour of keratin against different liquids; the water-based solution had the more pronounced effect. Such photonic modulation can be utilized in colour selective filters and sensing devices.
AB - The Himalayan monal is a bird in the pheasant family, and it is the national bird of Nepal. The bird possesses spectacular iridescent plumage with a range of different metallic colours. Here, we have studied the internal structure of its feathers from different parts of the bird's body and showed that its beautiful colours and iridescence are due to photonic structures present in the internal structure of the feathers. Sharp changes in the reflected brilliance were observed from the feathers upon changing the illumination conditions, such as horizontal and azimuthal angles. The feathers exhibited interesting hydrophobic properties, with the dull-coloured proximal end showing lower hydrophobicity with a contact angle between 90° and 110° compared with the iridescent distal end of a feather exhibiting a contact angle between 115° and 120°, attributed to the change in the internal structure and/or density of the feathers. A quick reversible change in colours of these feathers was observed when they were soaked in water and other liquids, which reversed upon drying. The shift in colour was suggested to be due to the swelling of the keratin layer of barbules that absorbed liquids and as a result modified the refractive index and periodicity of the internal photonic structures. The colour shift response of feathers was different in the case of alcohols and other water-based solutions, suggesting different swelling behaviour of keratin against different liquids; the water-based solution had the more pronounced effect. Such photonic modulation can be utilized in colour selective filters and sensing devices.
UR - http://www.scopus.com/inward/record.url?scp=85094982944&partnerID=8YFLogxK
U2 - 10.1039/D0NR06382G
DO - 10.1039/D0NR06382G
M3 - Article
SN - 2040-3364
VL - 12
SP - 21409
EP - 21419
JO - Nanoscale
JF - Nanoscale
IS - 41
ER -