We apply the Lifshitz theory of dispersion forces to find a contribution to the free energy of peptide films which is caused by the zero-point and thermal fluctuations of the electromagnetic field.For this purpose, using available information about the imaginary parts of dielectric permittivity of peptides, the analytic representation for permittivity of typical peptide along the imaginary frequency axis is devised. Numerical computations of the fluctuation-induced free energy are performed at room temperature for the freestanding peptide films, containing different fractions of water, and for similar films deposited on dielectric (SiO 2 ) and (Au) substrates. It is shown that the free energy of a freestanding peptide film is negative and, thus, contributes to its stability.The magnitude of the free energy increases with increasing fraction of water and decreases with increasing thickness of a film. For peptide films deposited on a dielectric substrate the free energy is nonmonotonous. It is negative for thicker than 100 nm films, reaches the maximum value at some film thickness, but vanishes and changes its sign for thinner than 100 nm films. The fluctuation-induced free energy of peptide films deposited on metallic substrate is found to be positive which makes films less stable. In all three cases, simple analytic expressions for the free energy of sufficiently thick films are found. The obtained results may be useful to attain film stability in the next generation of organic microdevices with further shrinked dimensions.
Abstract.A non-destructive optical control of dynamics of protein aqueous solution drying under different conditions is considered. The processes of organization of different structures in protein films are discussed.
The Casimir free energy and pressure of thin peptide films deposited on a dielectric substrate are investigated in the region of parameters where they change their sign. Numerical computations are performed for a modelled peptide film on a silica glass plate. The Casimir free energy is computed at room temperature as a function of the film thickness and the fraction of water contained in the film. It is shown that the values of the Casimir pressure change from negative to positive when the film thickness decreases to below some value in the region from 115 to 133 nm depending on the fraction of water in the film. Possible applications of the obtained results to the problem of stability of peptide coatings are discussed.
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