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Silk layering as studied with neutron reflectivity.
- Source :
-
Langmuir : the ACS journal of surfaces and colloids [Langmuir] 2012 Aug 07; Vol. 28 (31), pp. 11481-9. Date of Electronic Publication: 2012 Jul 26. - Publication Year :
- 2012
-
Abstract
- Neutron reflectivity (NR) measurements of ultrathin surface films (below 30 nm) composed of Bombyx mori silk fibroin protein in combination with atomic force microscopy and ellipsometry were used to reveal the internal structural organization in both dry and swollen states. Reconstituted aqueous silk solution deposited on a silicon substrate using the spin-assisted layer-by-layer (SA-LbL) technique resulted in a monolayer silk film composed of random nanofibrils with constant scattering length density (SLD). However, a vertically segregated ordering with two different regions has been observed in dry, thicker, seven-layer SA-LbL silk films. The vertical segregation of silk multilayer films indicates the presence of a different secondary structure of silk in direct contact with the silicon oxide surface (first 6 nm). The layered structure can be attributed to interfacial β-sheet crystallization and the formation of well-developed nanofibrillar nanoporous morphology for the initially deposited silk surface layers with the preservation of less dense, random coil secondary structure for the layers that follow. This segregated structure of solid silk films defines their complex nonuniform behavior in the D(2)O environment with thicker silk films undergoing delamination during swelling. For a silk monolayer with an initial thickness of 6 nm, we observed the increase in the effective thickness by 60% combined with surprising decrease in density. Considering the nanoporous morphology of the hydrophobic silk layer, we suggested that the apparent increase in its thickness in liquid environment is caused by the air nanobubble trapping phenomenon at the liquid-solid interface.
- Subjects :
- Animals
Bombyx physiology
Crystallization
Electrochemical Techniques
Fibroins biosynthesis
Fibroins isolation & purification
Fibroins ultrastructure
Hydrophobic and Hydrophilic Interactions
Larva physiology
Microscopy, Atomic Force
Nanofibers ultrastructure
Neutron Diffraction
Protein Structure, Secondary
Scattering, Small Angle
Silicon chemistry
Surface Properties
Water chemistry
Fibroins chemistry
Nanofibers chemistry
Subjects
Details
- Language :
- English
- ISSN :
- 1520-5827
- Volume :
- 28
- Issue :
- 31
- Database :
- MEDLINE
- Journal :
- Langmuir : the ACS journal of surfaces and colloids
- Publication Type :
- Academic Journal
- Accession number :
- 22697306
- Full Text :
- https://doi.org/10.1021/la300916e