Rubber composites were prepared by mixing bromobutyl rubber (BIIR) with silica particles in the presence of 1-butylimidazole. In addition to pristine (precipitated) silica, silanized particles with aliphatic or imidazolium functional groups, respectively, were used as filler. The silanization was carried out either separately or in situ during compounding. The silanized particles were characterized by TGA, 1H-29Si cross polarization (CP)/MAS NMR, and Zeta potential measurements. During compounding, the bromine groups of BIIR were converted with 1-butylimidazole to ionic imidazolium groups which formed a dynamic network by ionic association. Based on DMA temperature and strain sweep measurements as well as cyclic tensile tests and stress-strain measurements it could be concluded that interactions between the ionic groups and interactions with the functional groups of the silica particles strongly influence the mechanical and viscoelastic behavior of the composites. A particularly pronounced reinforcing effect was observed for the composite with pristine silica, which was attributed to acid-base interactions between the silanol and imidazolium groups. In composites with alkyl or imidazolium functionalized silica particles, the interactions between the filler and the rubber matrix form dynamic networks with pronounced self-healing behavior and excellent tensile strength values of up to 19 MPa. This new approach in utilizing filler-matrix interactions in the formation of dynamic networks opens up new avenues in designing new kinds of particle-reinforced self-healing elastomeric materials with high technological relevance.
This work shows a successful example of coupling of theory and experiment to study the tribology of bubble rubbing on solid surface. Such kind of investigation is reported for the first time in the literature. A theory about wetting film intercalated between bubble and moving solid surface was developed, thus deriving the non-linear evolution differential equation which accounted for the friction slip coefficient at the solid surface. The stationary 3D film thickness profile, which appears to be a solution of the differential equation, for each particular speed of motion of the solid surface was derived by means of special procedure and unique interferometric experimental setup. This allowed us to determine the 3D map of the lift pressure within the wetting film, the friction force per unit area and the friction coefficient of rubbing at different speeds of motion of the solid surface. Thus, we observed interesting tribological details about the rubbing of the bubble on the solid surface like for example: 1. A regime of mixed friction between dry and lubricated friction exists in the range of 6-170 µm/s, beyond which the rubbing between the bubble and solid becomes completely lubricated and passes through the maximum; 2. The friction coefficient of rubbing has high values at very small speeds of solid's motion and reduces substantially with the increase of the speed of the solid motion until reaching small values, which change insignificantly with the further increase of the speed of the solid. Despite the numerous studies on the motion of bubble/droplet in close proximity to solid wall in the literature, the present investigation appears to be a step ahead in this area as far as we were able to derive 3D maps of the bubble close to the solid surface, which makes the investigation more profound.
This is the first interferometric study in the literature on wetting film entrapped between bubble and moving solid substrate. Unique experimental setup was specially designed for monitoring the thickness profiles of wetting film, intercalated between the bubble and moving solid surface. For this reason, special procedure developed for this study was applied for determination of 3D film thickness profiles. This allowed us to determine 3D profiles of the disjoining, the lift pressures as well as the viscous stress tensor as a function of the velocity of the solid surface. Thus, one can see that a strong linear dependence between the average film thickness and the speed of motion of the solid surface exists until a certain critical speed of motion, beyond which the dependence becomes weaker but keeps its linear trend. Similar is the propensity with the average lift pressure. Moreover, one can observe how the inhomogeinity of the film surfaces changes upon increasing the speed of motion of the solid surface. The proposed technique reveals new possibilities for investigation of bubbles and solid surfaces on deeper level when they are in relative motion towards each other. Thus, one can conduct detailed tribological studies on bubbles moving in close proximity to solid surfaces.
The behavior of thin wetting films on chemically patterned surfaces was investigated. The patterning was performed by means of imprinting of micro-grid on methylated glass surface with UV-light (λ=184.8 nm). Thus imprinted image of the grid contained hydrophilic cells and hydrophobic bars on the glass surface. For this aim three different patterns of grids were utilized with small, medium and large size of cells. The experiment showed that the drainage of the wetting aqueous films was not affected by the type of surface patterning. However, after film rupturing in the cases of small and medium cells of the patterned grid the liquid from the wetting film underwent fast self-organization in form of regularly ordered droplets covering completely the cells of the grid. The droplets reduced significantly their size upon time due to evaporation. In the cases of the largest cell grid, a wet spot on the place of the imprinted grid was formed after film rupturing. This wet spot disassembled slowly in time. In addition, formation of a periodical zigzag three-phase contact line (TPCL) was observed. This is a first study from the planned series of studies on this topic.
Wettability , Hydrophobic and Hydrophilic Interactions , Particle Size , Surface Properties
