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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]

Thin-film composite (TFC) membranes are the most widely used membranes for low-cost and energy-efficient water desalination processes. Proper control over the three influential surface parameters, namely wettability, roughness, and surface charge, is vital in optimizing the TFC membrane surface and permeation properties. More specifically, the surface properties of TFC membranes are often tailored by incorporating novel special wettability materials to increase hydrophilicity and tune surface physicochemical heterogeneity. These essential parameters affect the membrane permeability and antifouling properties. The membrane surface characterization protocols employed to date are rather controversial, and there is no general agreement about the metrics used to evaluate the surface hydrophilicity and physicochemical heterogeneity. In this review, we surveyed and critically evaluated the process that emerged for understanding the membrane surface properties using the simple and economical contact angle analysis technique. Contact angle analysis allows the estimation of surface wettability, surface free energy, surface charge, oleophobicity, contact angle hysteresis, and free energy of interaction; all coordinatively influence the membrane permeation and fouling properties. This review will provide insights into simplifying the evaluation of membrane properties by contact angle analysis that will ultimately expedite the membrane development process by reducing the time and expenses required for the characterization to confirm the success and the impact of any modification. [Display omitted] • Recent advancements in surface characterization of water treatment membranes are critically reviewed. • New insights into evaluation of membrane properties by contact angle analysis are provided. • The use of contact angle analysis to evaluate the membrane performance parameters are presented. • Estimation of surface free energy, surface charge, oleophobicity, and contact angle hysteresis are provided. • The challenges and opportunities in implicating specially wettable interfacial materials to develop next-generation membranes are discussed. [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]