The dynamics of capillary-driven flow was studied for water and water–glycerol mixtures in open hydrophilic microchannels (embedded in a hydrophobic matrix). The position of the advancing meniscus was recorded as a function of time using high speed microscopy and compared with the Washburn equation. The square of the position of the liquid front increased linearly with time, as predicted by Washburn. For a channel of the same depth, irrespective of the shape of the channel cross-section (rectangular or curved), the liquid flow was faster with decreasing channel width. A modified Washburn equation, accounting for the different flow profile in the open, noncylindrical channels, was developed. The theoretical prediction was in good agreement with the experimental data for a no-slip boundary condition at the liquid–air interface.

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The growing number of patient morbidity related to nosocomial infections has placed an importance on the development of new antibacterial coatings for medical devices. Here, we utilize the versatile adhesion property of polydopamine (pDA) to design an antibacterial coating that possesses low-fouling and nitric oxide (NO)-releasing capabilities. To demonstrate this, glass substrates were functionalized with pDA via immersion in alkaline aqueous solution containing dopamine, followed by grafting of low-fouling polymer (poly­(ethylene glycol) (PEG)) via Michael addition and subsequent formation of N-diazeniumdiolate functionalities (NO precursors) by purging with NO gas. X-ray photoelectron spectroscopy confirmed the successful grafting of PEG and formation of N-diazeniumdiolate on polydopamine-coated substrates. NO release from the coating was observed over 2 days, and NO loading is tunable by the pDA film thickness. The antibacterial efficiency of the coatings was assessed using Gram-negative Pseudomonas aeruginosa (i.e., wild-type PAO1 and multidrug-resistant PA37) and Gram-positive Staphylococcus aureus (ATCC 29213). The NO-releasing PEGylated pDA film inhibited biofilm attachment by 96 and 70% after exposure to bacterial culture solution for 24 and 36 h, respectively. In contrast, films that do not contain NO failed to prevent biofilm formation on the surfaces at these time points. Furthermore, this coating also showed 99.9, 97, and 99% killing efficiencies against surface-attached PAO1, PA37, and S. aureus bacteria. Overall, the combination of low-fouling PEG and antibacterial activity of NO in pDA films makes this coating a potential therapeutic option to inhibit biofilm formation on medical devices.

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the canadian Journal of chemical engineering 669Collisions and bouncing of the bubbles with water/gas and water/solid interfaces occurring within a time scale of milliseconds were studied. It was shown that the bubble kinetic energy at the moment of collision has a profound influence on the bubble bouncing prior to the bubble rupture at the liquid/gas interface and attachment to the hydrophobic or remaining arrested beneath hydrophilic solid plates. The mechanism of the bubble bouncing was analyzed and degrees of exchange of the kinetic energy into the bubble surface energy were determined. It was found that in the case of solids the degree of the energy conversion was lower for the hydrophobic solid-most probably due to the presence of air.On a étudié les collisions et les rebonds des bulles avec les interfaces eau/gaz et eau/solide qui surviennent dans des échelles de temps de la milliseconde. On montre que l'énergie cinétique des bulles au moment de la collision a une profonde influence sur le rebondissement des bulles avant la rupture des bulles à l'interface liquide/gaz, sur l'attachement à la plaque solide hydrophobe ou en dessous de la plaque solide hydrophile. On a analysé le mécanisme de rebond des bulles et déterminé les niveaux d'échange de l'énergie cinétique dans l'énergie de surface des bulles. On a trouvé que dans le cas des solides, le degré de conversion d'énergie était inférieur pour le solide hydrophobe, très probablement à cause de la présence d'air.

The presence of dissolved gas at the solid/liquid interface can play a crucial role in heterogeneous cavitation. Here we focus our attention on the relationship between gas conditions and cavitation nucleation at planar solid surfaces with alternating hydrophobic/hydrophilic properties. Tapping mode atomic force microscopy and optical microscopy were used to monitor the gas adsorption on the patterns before sonication. Scanning electron microscopy revealed the effects of collapsing cavitation bubbles on the irradiated surfaces. High intensity ultrasonic irradiation (20 kHz) induces the formation of an interfacial gas layer at the solid surface immersed in different liquid media (water saturated with different gases, such as argon, nitrogen or carbon dioxide) by accelerating the adsorption of dissolved gas. Subsequently, the gas rearranges in diverse nano-or microstructures which take further part in the cavitation process. A solvent-exchange method was also applied to induce the formation of artificial gaseous domains accumulated at the solid surface in order to facilitate the cavitation process. By varying the gas adsorption time it is possible to accelerate or to slow down heterogeneous cavitation.The experimental findings on heterogeneous cavitation are discussed in terms of interfacial bubble nucleation and bubble attraction and growth on patterned solid surfaces in liquid media.

Tapping mode atomic force microscopy has been used to investigate the spreading of molecularly thin (up to a few nanometers) precursor films emerging from drops of ionic liquids that partially wet smooth mica surfaces. The lateral extent of the film increases with time and reaches values as large as few millimeters within 12 h. From the observations of the precursor film at several positions and times, its extent l(t) was estimated and used to determine bounds for the coefficient D 1 (defined by l(t) = √D 1 t) that characterizes the rate of spreading. The spreading rate and the film morphology (at micrometer scale) for three different ionic liquids of varying cation molecular structures are compared.