Sessile drop technique

About: Sessile drop technique is a research topic. Over the lifetime, 2827 publications have been published within this topic receiving 68943 citations.

Thermosensitive Copolymer Coatings with Enhanced Wettability Switching

Abstract: Expanded cross-linked copolymers of poly(N-isopropylacrylamide) (PNiPAAm) and poly(acrylic acid) (PAAc) of varying monomer ratios were grafted from a crystalline silicon surface. Surface-tethered polymerization was performed at a slightly basic pH, where electrostatic repulsion among acrylic acid monomer units forces the network into an expanded polymer conformation. The influence of this expanded conformation on switchability between a hydrophilic and a hydrophobic state was investigated. Characterization of the copolymer coating was carried out by means of X-ray photoelectron spectroscopy (XPS) ellipsometry, and diffuse reflectance IR. Lower critical solution temperatures (LCSTs) of the copolymer grafts on the silicon surfaces were determined by spectrophotometry. Temperature-induced wettability changes were studied using sessile drop contact angle measurements. The surface topography was investigated by atomic force microscopy (AFM) in Milli-Q water at 25 and 40 °C. The reversible attachment of a fluorescently labeled model protein was studied as a function of temperature using a fluorescence microscope and a fluorescence spectrometer. Maximum switching in terms of the contact angle change around the LCST was observed at a ratio of 36:1 PNiPAAm to PAAc. The enhanced control of biointerfaces achieved by these coatings may find applications in biomaterials, biochips, drug delivery, and microfluidics.

PEGylation of porous silicon using click chemistry.

Abstract: Porous silicon has received considerable interest in recent years in a range of biomedical applications, with its performance determined by surface chemistry. In this work, we investigate the PEGylation of porous silicon wafers using click chemistry. The porous silicon wafer surface chemistry was monitored at each stage of the reaction via photoacoustic Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, whereas sessile drop contact angle and model protein adsorption measurements were used to characterize the final PEGylated surface. This work highlights the simplicity of click-chemistry-based functionalization in tailoring the porous silicon surface chemistry and controlling protein−porous silicon interactions.

Effect of various key factors on the law of droplet evaporation on the heated horizontal wall

Abstract: Water evaporation in a wide range of initial droplet diameters and at different wall temperatures on structured surface was studied experimentally. With an increase in the wall temperature from 31 to 72 °С and an increase in the initial droplet diameter, exponent n in the evaporation law increases from 1 to 1.37. Under the transitional regime, exponent n = 1.6 reaches its maximum. Usually, while simulating droplet evaporation, a linear relationship of the evaporation rate of water vapor and droplet radius R is considered (dm/dt ∼ Rn, n = 1). In this paper, it is shown that exponent n increases with a growth of the wall temperature. In generalization of droplet evaporation rate, the exponent for the Rayleigh number (Ra) is 0.457 due to the predominant role of gas convection. For large water drops (for air–vapor mixture over the droplet surface) high Reynolds numbers are achieved (Ra = 2 × 105). A diffusion vapor layer on the droplet surface and boundary layer of air on the surface of the heated cylinder, whose diameter exceeds the droplet diameter, are formed. A neglect of free convection understates simulation results in comparison with experimental data more than by the factor of 10. The sequence of key factors, taking into account their influence on the rate of droplet evaporation, is as follows: 1) convection in a vapor–gas medium; 2) effect of wall roughness, wettability, and convection in a liquid; 3) thermal inertia of the metal wall. The calculation methodology for a sessile drop enables a qualitative analysis for a high-temperature gas-droplet flow.

Wetting of Rough Surfaces

Abstract: This paper focuses on effects of roughness on wettability. According to Wenzel's equation, the transition of theoretical wetting contact angles is 90°, whereas many experimental results have indicated that such a transition takes place at contact angles smaller than 90°. A new model of wetting on roughness surface is established in this paper. The model indicates that the influencing factors of wetting on roughness surface include not only equilibrium contact angle θ0 and surface roughness, but also the system of liquids and solid substrates. There is a corresponding transition angle for every surface roughness, and the transition angle is lower than 90°. Surface roughness is propitious to improve the contact angle only when θ0 is lower than the transition angle. The effect of surface roughness on the contact angle increases with the increase of rE. To engineer the surface with different roughnesses, a Ti test sample is polished with sandpaper with abrasive number 350, 500, 1000 and 2000; the contact angles of water on Ti are measured by the sessile drop method. The results of the theoretical analysis agree with experimental ones.

Estimation of the surface energy and acid-base properties of wood by means of wetting method

Abstract: The important surface energy and acid-base properties for pine wood (Pinus silvestris L.) have been estimated by using two contact angle techniques (CAT), e.g., the sessile drop method and the Wilhelmy plate method, respectively. According to the results, the pine wood may be characterized as a low surface energy polymer due to its low surface energy. The surface energy, γ s , for the pine wood was being larger in the direction parallel to the grains as compared with the perpendicular direction. The Lifshitz-van der Waals (LW) energy component, γ s LW is the major energy component for the pine wood as compared with the acid-base energy component, γ s AB . Furthermore, it seems that the LW energy component, γ s LW , of pine wood is independent of the choice of wetting methods and of the chemical composition of the surface. However, the surface acid-base (AB) energy component, γ s AB , for the pine wood seems to be dependent on the wetting methods chosen. Subdivided into its contributions, the surface of pine wood seems to be weaker in the acidic energy parameter, γ s + , and stronger in the basic energy parameter, γ s - . Rough estimation of the contact angle hysteresis (CAH) and surface roughness (SR) has also been measured separately in the parallel direction and the perpendicular directions, respectively.