Joanna Karasiewicz

Effect of the type of fluorofunctional organosilicon compounds and the method of their application onto the surface on its hydrophobic properties

Fluorofunctional silanes, polysiloxanes and silsesquioxanes were used for the modification of glass surfaces and their influence on hydrophobic properties were determined. To increase hydrophobicity of the surface, the modification was performed in two stages: (i) by a pretreatment using a silica sol (a rise in the surface roughness), and (ii) modification with the above silicon compounds. The hydrophobicity was determined by measuring the contact angle by drop profile tensiometry. The fluorocarbofunctional organosilicon derivatives examined were found to be good precursors for the synthesis of highly hydrophobic materials and coatings. In some cases the contact angles measured after surface modification exceeded 150°, i.e. they fell in the range characteristic of superhydrophobic surfaces.

Hydrophobic Materials Based on Fluorocarbofunctional Spherosilicates

Consecutive hydrosilylation-based syntheses were performed of silsesquioxanes containing mixed groups 1H,1H,2H,2H-perfluorooctyl (PFD) or octafluoropentyloxypropyl (OFP) and trimethoxysilylethyl (TMS) in different stoichiometric ratios. The presence of TMS makes it possible to form covalent bonds with substrates due to the reactivity of this group. All obtained derivatives were applied to hydrophobization of glass plates and by comparison of water contact angles (WCA) on modified surfaces the effect of silsesquioxane structure as well as TMS and fluoroalkyl group contents on hydrophobic properties was determined. Moreover, an additional glass plates surface modification was performed in order to obtain superhydrophobic surfaces. Two silica types of different specific surface (300 and 130 m2/g) and particle size (7 and 16 nm) parameters were used in this case for initial surface modification in order to increase its roughness. Irrespectively of particle size of applied silica, a dependence was found between the increase in water contact angle and the number of fluoroalkyl substituents in a molecule.

Fluoroalkylsilane versus alkylsilane as hydrophobic agents for silica and silicates

Hydrophobic powders were obtained via surface modification of silica or magnesium silicate with selected silanes. A modified precipitation method, carried out in an emulsion system, was used for monodisperse silica synthesis, while magnesium silicate was precipitated in a traditional water system. Functionalization of the obtained inorganic supports was performed with selected alkylsilanes: one newly synthesized, 3-(2,2,3,3,4,4,5,5-octafluoropentyloxy)propyltriethoxysilane (OPF), and two commercial, octadecylsilane (ODS) and octyltriethoxysilane C14H32O3Si (OCS), in amounts of 3, 5, or 10 weight parts by mass of SiO2. It was determined how the chemical modification of the silica or magnesium silicate surface affected its physicochemical properties. The dispersive characteristics of both unmodified and functionalized silica-based systems were evaluated. The morphology and microstructure of the samples obtained were analyzed using scanning electron microscopy. The parameters of porous structure of the prepared systems were evaluated on the basis of BET equation as well as nitrogen adsorption/desorption isotherms. Wettability tests as well as elemental analysis of the obtained inorganic oxide hybrids were also performed. In order to verify the effectiveness of silica and magnesium silicate surface functionalization with selected silanes, FTIR spectra were investigated. The resulting experimental data allowed calculation of the degree of coverage of the silica-based systems with modifying agents.

Interfacial behaviour of cubic silsesquioxane and silica nanoparticles in Langmuir and Langmuir–Blodgett films

In recent years fluorinated polyhedral oligomeric silsesquioxanes (POSS) have been established as useful for the fabrication of superhydrophobic surfaces, however little attention has been paid to their use for making ultrathin coatings by the Langmuir–Blodgett method. On the other hand, recently POSS compounds have been recognized as a new group of film-forming materials. In this study the interfacial behavior of fluorinated polyhedral oligomeric silsesquioxanes (POSS) mixed with silica nanoparticles was studied at the air/water interface. Surface pressure-area isotherms and Brewster angle microscopy revealed the formation of a mixed film. Incorporation of nanoparticles in a POSS monolayer caused formation or more condensed and rigid film as shown by analysis of compressibility and dilatational viscoelasticity. On the other hand POSS molecules act as an excellent dispersant which prevents silica nanoparticles from aggregation. Deposition of the Langmuir–Blodgett film composed of POSS and silica nanoparticles allowed a hydrophobic surface showing water contact angles reaching 135° to be obtained, which suggests possible application of our approach in the fabrication of ultrathin, water-repellent coatings.

Corrosion Protection of Stainless Steel by Triethoxyoctylsilane and Tetraethoxysilane

Different methods of silane coating deposition on the surface of 304 stainless steel were studied. Deposition was performed in different solutions with a variety of pH values. Three types of solutions were prepared i.e. neutral, containing only methanol with triethoxyoctylsilane and two acidic consisting of methanol, triethoxyoctylsilane, tetraethoxysilane and hydrochloric acid which was used to establish pH values equal to 1 and 3.5. Surface electrochemical analysis carried out using a 3.5 wt% NaCl solution and several common techniques including corrosion potential monitoring at open circuit conditions, linear polarization and electrochemical impedance spectroscopy tests showed that the way in which silane solution is prepared and silane coating is deposited is heavily influencing on the type of corrosion inhibition. Additionally, spectroscopic methods were employed. Due to oxide passive film on the steel surface, metal-O-Si bonds are formed, thus creating an intermediate layer between the oxide layer and the outermost siloxane layer (Si-O-Si). Furthermore, a long aliphatic chain of triethoxyoctylsilane compound increases steel surface hydrophobicity.