The influence of “small molecules” on properties of TiO2 films prepared by sol–gel method

• Addition of “small molecules” influences surface properties of prepared TiO2 films.
• Addition of “small molecules” decreases of adhesion force, stiffness and roughness.
• “Small molecules” increase dispersion component and decreases polar component of SFE.
• Influence of acetylacetone and acetic acid is result of their complex effect.
• During film formation, hydrolysis, particle growth, thermal treatment are influenced.

The sol–gel method was used for preparation of TiO2 sols without and with the addition of “small molecules” — acetylacetone and acetic acid. The TiO2 films were made by dip-coating method in different time intervals after preparation of sols. Properties of film surface, such as morphology, rms-roughness and adhesion force were studied using atomic force microscopy (AFM). The contact angle of water and diiodomethane was measured for identification of polar and dispersion component of the surface free energy (SFE). From the obtained results, it can be seen that “small molecules” influence the morphology of films. During the first days after the sol preparation, there is the increase of roughness of films prepared from sols with “small molecules” but with the increasing time, the roughness decreases. There is no crystallization of films with acetylacetone. For films prepared from sols with acetylacetone, the polar component of SFE is lower than in the case of films prepared from sols without “small molecules” and with acetic acid. The “small molecules” decrease the stiffness and adhesion force mainly for films prepared several days after sol preparation. This influence is the result of complex effect of “small molecules” on processes occurring during preparation of films, from hydrolysis reaction over process of particle growth to thermal treatment.