Free Energy Of Thin Films Research Articles

Properties of the Surface Layer of Thin Films of Polyaniline Doped With Phosphoric Acid

This study deals with estimation of the surface free energy of thin films of polyaniline doped with phosphoric acid, by measuring contact angles. Synthesis of polyaniline (PANI) with phosphoric acid (PA) was performed at room temperature of 20°C, and at 0°C. Thin films were obtained by means of a spin coater, applying the synthetized mixture on a glass substrate. By measuring the contact angle, first between ethylene glycol and a film and then between distilled water and a film, we thus calculated the polar, dispersion and total surface free energy. It was proved and demonstrated that the surface free energy depends on the temperature at which the solution (from which the thin films are obtained later) was synthesized.

Photocatalytic antibacterial activity of TiO2–SiO2 thin films: The effect of composition on cell adhesion and antibacterial activity

• The effect of composition of TiO 2 –SiO 2 thin films on cell adhesion was studied. • The effect of surface composition on surface free energy was studied. • SiO 2 addition favors for cell adhesion. • Strong relation was found between the bacterial adhesion and antibacterial activity. Colloidal solutions of SiO 2 –TiO 2 mixed oxides having different SiO 2 contents were synthesized by sol–gel technique and thin films were deposited over glass slides by using dip coating technique. The samples were characterized by XRD, SEM, AFM and methylene blue adsorption methods. The surface free energy of thin films was measured by sessile drop method by using diiodomethane, glycerol and water as probe liquids. The photocatalytic antibacterial activity of the samples was determined for Escherichia coli XL1-blue by using artificial solar irradiation. The surface characterization studies revealed the presence of small crystallites of anatase phase, enhanced dispersion of TiO 2 particles and increasing surface free energy at elevated SiO 2 content. Highest photocatalytic antibacterial activity was obtained over 92 wt% SiO 2 containing sample and strong correlation was found between the bacterial adhesion and antibacterial activity. Surface-adhered E. coli cells having direct contact with TiO 2 particles were inactivated at a higher rate than suspended cells.

Classical limit of the Casimir interaction for thin films with applications to graphene

The Casimir interaction between two thin material films, between a film and a thick plate and between two films deposited on substrates is considered at large separations (high temperatures) which correspond to the classical limit. It is shown that the free energy of the classical Casimir interaction between two insulating films with no free charge carriers and between an insulating film and a material plate depends on film thicknesses and decreases with separation more rapidly than the classical limit for two thick plates. The free energy of thin films characterized by the metallic-type dielectric permittivity decreases as the second power of separation, i.e., demonstrates the standard classical limit. The obtained results shed light on the possibility to describe dispersion interaction between two graphene sheets and between a graphene sheet and a material plate by modeling graphene as a thin film possessing some dielectric permittivity. It is argued that the most reliable results are obtained by describing the reflection properties on graphene by means of the polarization tensor in (2+1)-dimensional space-time.

Finite size effects on the thermodynamics of CuNi alloys: {100} and {110} thin films

A series of atomistic simulations of Cu x Ni 1 − x {100} and {110} thin films were performed as a function of Cu-concentration, temperature, and thickness in order to determine the effects of film thickness on the surface concentration and the surface free energy. The surface free energies of these films were found to differ significantly from those of the corresponding flat surfaces of bulk samples. Very thin films exhibit surface entropies ΔS which have an opposite sign to those for the bulk (positive surface entropy). These films undergo a transition from negative to positive surface entropy with increasing film thickness, composition and/or temperature. The unusual behavior of the surface free energy of thin films may be accounted for by the surface energy dependence on the surface concentration and the limited solute availability in these systems. The surface segregation in these thin films may be accurately described by the theory presented in Ref. [3]. Using the prediction of the surface composition and a simulation of a bulk flat surface it is possible to accurately predict the (surface) free energy of thin films as a function of film thickness using only properties of a bulk sample.