In vitro, cellular processing on polymeric surfaces is fundamental to the development of biosensors, scaffolds for tissue engineering and transplantation.

We report a simple, inexpensive, rapid, and one-step method for the fabrication of a stable and biocompatible superhydrophobic and superhemophobic surface. The proposed surface comprises candle soot particles embedded in a mixture of PDMS+n-hexane serving as the base material. The mechanism responsible for the superhydrophobic behavior of the surface is explained, and the surface is characterized based on its morphology and elemental composition, wetting properties, mechanical and chemical stability, and biocompatibility. The effect of %n-hexane in PDMS, the thickness of the PDMS+n-hexane layer (in terms of spin coating speed) and sooting time on the wetting property of the surface is studied. The proposed surface exhibits nanoscale surface asperities (average roughness of 187 nm), chemical compositions of soot particles, very high water and blood repellency along with excellent mechanical and chemical stability and excellent biocompatibility against blood sample and biological cells. The water contact angle and roll-off angle is measured as 160° ± 1° and 2°, respectively, and the blood contact angle is found to be 154° ± 1°, which indicates that the surface is superhydrophobic and superhemophobic. The proposed superhydrophobic and superhemophobic surface offers significantly improved (>40%) cell viability as compared to glass and PDMS surfaces.

To our knowledge, for the first time, we explain the morphological patterns of bi-dispersed droplets on hydrophobic and hydrophilic surfaces.

We report a simple, inexpensive and rapid method for fabrication of a stable and transparent superhydrophobic (TSHB) surface and its reversible transition to a transparent superhydrophilic (TSHL) surface. We provide a mechanistic understanding of the superhydrophobicity and superhydrophilicity and the reversible transition. The proposed TSHB surface was created by candle sooting a partially cured n-hexane + PDMS surface followed by washing with DI water. The nano/microscopic grooved structures created on the surface conforms Cassie – Baxter state and thus gives rise to superhydrophobicity (water contact angle (WCA) = 161° ± 1°). The TSHB surface when subjected to oxygen plasma develops -OH bonds on the surface thus gets transformed into a TSHL surface (WCA < 1°). Both surface chemistry and surface morphology play important roles for the superhydrophobic to superhydrophilic transition. In the Cassie – Baxter relation for a composite surface, due to the capillary spreading of liquid in the nano/micro grooves, both θ1, θ2 = 0, thus giving rise to complete wetting. Rapid recovery of superhydrophobicity from superhydrophilicity was achieved by heating the TSHL surface at 150 °C for 30 min, due to a much faster adsorption of the -OH bonds into the PDMS. Thus it is possible to achieve reversible transition from TSHB to TSHL and vice versa by exposing to oxygen plasma and heat, respectively.

Transport of droplets on surfaces is important for a variety of applications such as micro liquid handling and biochemical assays. Here, we report evaporation-induced attraction, chasing, and repulsion between a target pure aqueous (water) droplet and a driver aqueous mixture droplet comprising water and a lower surface tension and lower vapor pressure liquid on a high energy surface. It is observed that for a fixed concentration of the mixture droplet, attraction/chasing or repulsion can be achieved by varying the relative time instants at which the drops are dispensed. Our study reveals that if the water droplet is dispensed within a critical time after dispensing the mixture droplet, the latter will get attracted to and chase the water droplet. On the other hand, if the water droplet is dispensed after this critical time, then it would get repelled from the mixture droplet. We explain the underlying mechanisms that govern the phenomena and demonstrate continuous transport of liquid/cell sample droplets/plugs.

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We show that adjacent liquid droplets exhibit long-range attraction and repulsion on an immiscible liquid impregnating a surface when either the drop or the impregnating liquid is volatile. Remarkably, we find that at small times the interaction is attractive, analogous to the “Cheerios effect”, but at large times the interaction becomes repulsive depicting the “reverse-Cheerios effect”. Our study reveals that the interaction is underpinned by wetting and capillarity, buoyancy, and evaporation phenomena. We experimentally observe the interaction between a pair of droplets and provide a theoretical framework to quantitatively predict their transport behavior.

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