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The tailoring of the surface properties of cellulose nanocrystals (CNCs) to meet various requirements in environmental, food, and material areas has always been of great interest. In this study, the surface chemistry of CNCs was noncovalently modified by cetyltrimethylammonium bromide (CTAB), followed by characterizations and an investigation into its application as a coating material for interfacial interaction over various substrates. Due to the CTAB modification, the surface charge of the CNCs was neutralized, resulting in an increased size of each nanocrystal at the aqueous status and the aggregated microfibers when dried up. The CTAB modification not only decreased the crystallinity of the samples from 48.57% to 9.12%, but also reasonably hydrophobized the CNCs and decreased their total surface energy. Finally, the adsorption behavior of the CNCs and CTAB-CNCs over nonionic, anionic, and cationic polymers was investigated by ellipsometry. Based on the thickness of the CNC and CTAB-CNC layers over 2-Hydroxyethyl cellulose (HEC), carboxymethyl cellulose (CMC), and polyethyleneimine (PEI), we proposed that the adsorption behavior was overall influenced by electrostatic interaction, hydrogen bonding, and van der Waals forces, and the thickness of the adsorbed layers could be impacted by both the surface charge and the size of the crystals. [ABSTRACT FROM AUTHOR]

We present the evidence of universality in conical tip formation during the freezing of arbitraryshaped sessile droplets. The focus is to demonstrate the relationship between this universality and the liquid drop shape. We observe that, in the case of asymmetric drops, this universal shape is achieved when the tip reconfigures by changing its location, which subsequently alters the frozen drop shape. The proposed "two-triangle" model quantifies the change in the tip configuration as a function of the asymmetry of the drop that shows a good agreement with the experimental evidence. Finally, based on the experimental and theoretical exercise, we propose the scaling dependence between the variations in the tip configuration and the asymmetry of the drop. [ABSTRACT FROM AUTHOR]

Efficient and optimized heat exchanger design is necessary because of the continuous increase of power consumption rate of electronic equipment and the simultaneous interest in reducing the mass and dimensions of the cooling equipment. This paper presents a numerical study of laminar forced convective heat transfer from an array of solid and different types of perforated fins attached to a rectangular-horizontal base plate. Fluid-flow and heat-transfer characteristics are presented for Reynolds numbers from 100 to 350 based on the fin thickness; Pr and tl number is taken as Pr=0.71. Finite element approach with an unstructured nonuniform grid system is employed for solving the fluid-flow and heat-transfer equations. The predicted results obtained from the computational fluid dynamics simulations are verified by the previously published data, and the obtained results are in reasonable agreement. This numerical study determines the effects of various types of perforations on the pressure drop and heat-transfer performance of heat exchangers. For each type of perforation, fin effectiveness and performances are determined and compared with those of a solid fin. Results show that perforated fins have better thermal performance than solid fins. [ABSTRACT FROM AUTHOR]

Contact angle titration has recently been introduced as a feasible alternative to the streaming potential technique for the determination of the surface isoelectric point, as well as the surface zeta potential. In this context, a few theoretical models have been developed. However, each model was discretely developed for a specific surface for the evaluation of either the isoelectric point or the surface zeta potential. The surface potential measured using these models also differ considerably with that measured by widely applied streaming potential analysis method. In this study, all three different contact angle based theoretical frameworks, namely Holmes-Farley and Hurwitz unified, Gibbs-Young, and Lippmann-Young equations were examined for the first time for the evaluation of both the isoelectric point and the surface electrical potential on a variety of surfaces with different physicochemical heterogeneity (e.g., glass, polyamide membrane, and polypropylene films). The results obtained from the contact angle titration curves were compared with the streaming potentials. After critical evaluation of the limitation of the existing models, new theoretical frameworks were developed considering the necessary modifications of the former models. The comparison of the contact angle-based data with the results obtained by a streaming potential analyzer indicated that the Lippmann-Young equation exhibited the highest deviations (δ >100%) for all the samples. The modification of Holmes-Farley and Hurwitz unified model reduced the deviation from 95.4% to 66.3% for glass, and from 82.5% to 38.8% for polyamide (PA) membrane, while the modification of Gibbs-Young model reduced the deviation from 47.2% to 41.8% for glass and from 423.6% to 270% for polyamide membrane. However, no obvious pH dependence of the contact angle titration was observed for the hydrophobic polypropylene film with an exception at the surface isoelectric point where the lowest contact angle was observed. The findings of this study will help to identify the appropriate model for the determination of both the isoelectric point and surface electrical potential on a particular surface of physicochemical heterogeneity as well to understand the surface phenomena that should be considered while developing the theoretical models for a particular surface of interest. Image 1 • Three contact angle titration models were examined for the determination of the surface charge properties of surfaces. • New theoretical frameworks were developed to improve the accuracy of determining the surface charge properties. • Reliable accuracy was obtained for the hydrophilic surfaces when compared to the streaming potential analyzer. • The modified theoretical frameworks provide better accuracy for one surface over the other. • Contact angle data provides better results for hydrophobic surfaces than the streaming potential analyzer. [ABSTRACT FROM AUTHOR]

• A new under-liquid solid surface wettability characterization method is proposed. • Interfacial tension of surfaces varies more significantly under-liquid than in air. • The developed theoretical framework predicts the wettability within a 20% deviation. • Wettability transition can be achieved by just altering medium interfacial tension. The wetting of a solid surface by a liquid droplet under a liquid medium not only includes the solid-droplet molecular interactions but also involves the interfacial interaction with the surrounding medium. Such wettability adaptation evolves either due to the formation of a thin film of the surrounding medium over the solid surface, or the molecular reorganization at the solid–liquid interfacial region. Here we developed a theoretical framework and proposed a novel experimental approach to evaluate the solid-medium interfacial tension by implicitly involving the adaptation behavior of a solid surface in the presence of another liquid. We investigated the wettability of three solid surfaces, namely glass, poly(methyl methacrylate) (PMMA), and polytetrafluoroethylene (PTFE), for a wide range of polar and non-polar oil droplets underwater. From our proposed two-liquid approach, we measured the polar and non-polar solid surface tension components. Our experimental results revealed the significant impact of interfacial tension of both droplet and the surrounding medium on the overall wettability of the solid-medium-droplet system. The predicted results were within ±25% deviation from that of the experimental observation for most of the cases. In contrast, the application of the previously reported theories resulted in a larger deviation (above ± 35%) for all samples. [ABSTRACT FROM AUTHOR]

The impact of surface nanoscale physical heterogeneity on the wettability of polymeric membranes is still elusive. Conventional wettability analysis includes quantifying the membrane surface roughness using AFM followed by measuring the apparent equilibrium contact angle of DI water over the membrane surface. Here, we present a novel experimental approach, solely based on contact angle analysis, to elucidate the impact of surface heterogeneity on the wettability of dense polymeric membranes. The proposed approach involves evaluation of equilibrium and advancing contact angles of at least three non-polar liquids over the membrane surface. Using this information, the wettability parameters including the surface roughness-ratio, frictional pinning force, and the dispersive surface tension component of the polymeric membranes were successfully quantified. The comparison with the conventional approach showed that there are 10%–20% discrepancies between the AFM-based and contact angle-based wettability parameters. The results revealed that the AFM measurements strongly depend on the size of the scanned area, particularly for samples with large surface heterogeneity. Furthermore, the water flux decline due to colloidal fouling was found to be in good agreement with the results of our proposed model. This study can provide new insights into developing advanced membrane materials with desired surface wettability and antifouling property. Image 1 • Surface physical heterogeneity of dense polymeric membranes is determined. • The new method uses solely contact angle measurements. • Non-polar probe liquids are employed to minimize the polar interactions. • The new approach provides fast, reliable, and simultaneous predication of surface roughness-ratio and surface tension. [ABSTRACT FROM AUTHOR]