Experimental methods in chemical engineering: Contact angles

Development and Characterization of New Miconazole-Based Microemulsions for Buccal Delivery by Implementing a Full Factorial Design Modeling

This research aimed to develop miconazole-based microemulsions using oleic acid as a natural lipophilic phase and a stabilizer mixture comprising Tween 20 and PEG 400 to solubilize miconazole as an antifungal agent known for its activity in oral candidiasis and to improve its bioavailability. The formulation and preparation process was combined with a mathematical approach using a 23-full factorial plan. Fluid and gel-like microemulsions were obtained and analyzed considering pH, conductivity, and refractive index, followed by extensive analyses focused on droplet size, zeta potential, rheological behavior, and goniometry. In vitro release tests were performed to assess their biopharmaceutical characteristics. Independent variables coded X1-Oleic acid (%, w/w), X2-Tween 20 (%, w/w), and X3-PEG 400 (%, w/w) were analyzed in relationship with three main outputs like mean droplet size, work of adhesion, and diffusion coefficient by combining statistical tools with response surface methodology. The microemulsion containing miconazole base-2%, oleic acid-5%, Tween 20-40%, PEG 400-20%, and water-33% exhibited a mean droplet size of 119.6 nm, a work of adhesion of 71.98 mN/m, a diffusion coefficient of 2.11·10-5 cm2/s, and together with remarked attributes of two gel-like systems formulated with higher oil concentrations, modeled the final optimization step of microemulsions as potential systems for buccal delivery.

Enhanced Sodium Ion Batteries' Performance: Optimal Strategies on Electrolytes for Different Carbon-based Anodes

Carbon-based materials have emerged as promising anodes for sodium-ion batteries (SIBs) due to the merits of cost-effectiveness and renewability. However, the unsatisfactory performance has hindered the commercialization of SIBs. During the past decades, tremendous attention has been put into enhancing the electrochemical performance of carbon-based anodes from the perspective of improving the compatibility of electrolytes and electrodes. Hence, a systematic summary of strategies for optimizing electrolytes between hard carbon, graphite, and other structural carbon anodes of SIBs is provided. The formulations and properties of electrolytes with solvents, salts, and additives added are comprehensively presented, which are closely related to the formation of solid electrolyte interface (SEI) and crucial to the sodium ion storage performance. Cost analysis of commonly used electrolytes has been provided as well. This review is anticipated to provide guidance in future rational tailoring of electrolytes with carbon-based anodes for sodium-ion batteries.

AKD Emulsions Stabilized by Guar Gel: A Highly Efficient Agent to Improve the Hydrophobicity of Cellulose Paper

The aim of the present study was to investigate highly efficient alkyl ketene dimer (AKD) emulsions to improve the hydrophobicity of cellulose paper. AKD emulsions stabilized by guar gel were obtained; the guar gel was prepared by hydrogen bond cross-linking sodium tetraborate and guar gum. The cross-linking was confirmed by combining FTIR and SEM. The effect of guar gel on the performance of the AKD emulsions was also studied by testing AKD emulsions stabilized by different guar gel concentrations. The results showed that with increasing guar gel concentration, the stability of the AKD emulsions improved, the droplet diameter decreased, and the hydrophobicity and water resistance of the sized packaging paper were gradually enhanced. Through SEM, the guar gel film covering the AKD emulsion droplet surface and the three-dimensional structure in the aqueous dispersion phase were assessed. This study constructed a scientific and efficient preparation method for AKD emulsions and provided a new method for the application of carbohydrate polymer gels which may avoid the adverse effect of surfactant on paper sizing and environmental problems caused by surfactant bioaccumulation.

Surface Properties of Graffiti Coatings on Sensitive Surfaces Concerning Their Removal with Formulations Based on the Amino-Acid-Type Surfactants

Water-in-oil (w/o) nanoemulsions stabilized with amino acid surfactants (AAS) are one example of nanotechnology detergents of the "brush on, wipe off"-type for removing graffiti coatings from different sensitive surfaces. The high-pressure homogenization (HPH) process was used to obtain the nanostructured fluids (NSFs), including the non-toxic and eco-friendly components such as AAS, esterified vegetable oils, and ethyl lactate. The most effective NSF detergent was determined by response surface methodology (RSM) optimization. Afterwards, several surface properties, i.e., topography, wettability, surface free energy, and the work of water adhesion to surfaces before and after their coverage with the black graffiti paint, as well as after the removal of the paint layers by the eco-remover, were determined. It was found that the removal of graffiti with the use of the NSF detergent is more dependent on the energetic properties and microporous structure of the paint coatings than on the properties of the substrates on which the layers were deposited. The use of NSFs and knowledge of the surface properties could enable the development of versatile detergents that would remove unwanted contamination from various surfaces easily and in a controlled way.

Formation of Robust and Adaptive Biopolymers via Non-Covalent Supramolecular Interactions

Biomass-originated materials are the future's next-tier polymers. This work suggests improving mechanical and barrier properties of nature-sourced polymers using non-covalent supramolecular interactions. Polysaccharide chitosan is modified with amino acids via an esterification pathway using a systematic variation of hydrogen bond and aromatic domains (Degrees of substitution 12-49%). These controlled modifications improve stability due to non-covalent interactions, resulting in biopolymers with tailored thermal (decomposition temperature 232-275 °C), mechanical (Young's modulus 540-2667 MPa), and surface properties (roughness 4-40 nm). Chitosan and natural amino acids that are already manufactured at scale are purposely selected. The facile synthesis, controlled properties, stimuli-responsive potential, and inexhaustible origin of the raw materials provide the presented findings with the potential to become the method for the formation of high-performance biodegradable alternatives to petroleum-based polymers that can be used in packaging, food, agriculture, and medicine.

Physicochemical Limitations of Capillary Models Applied to High-Concentration Polymer Solutions

Advances in binder jet printing (BJP) require the development of new binder-powder systems, for example, to increase compatibility with better performance metal alloys or to increase the strength of parts using stronger binders. The dynamics of binder absorption are principally understood through capillary models. However, validation of these models in BJP has focused on variation of powder properties. Using a design-of-experiments approach and an optical observation method to track absorption of droplets, this study tests the influence of fluid properties on absorption time against the predictions of capillary models. Properties specific to polymeric binders, such as molecular weight and entanglement state, are also considered. Capillary models are found to be generally accurate in predicting absorption time in dilute systems; however, these predictions are not accurate for highly concentrated binder solutions. The effect of polymer entanglement becomes prevalent as the solution concentration increases, which can also potentially occur as a result of increased evaporation due to powder bed heating. Specifically, concentrated solutions close to the onset of entanglement will absorb much more slowly than predicted. Future models of BJP systems must account for the possibility of polymer entanglement throughout the absorption process. Improved models will provide a more accurate understanding of the flow and solidification of the binder in the powder, allowing faster development of new binders for improved performance in printing.

Orienting Cellulose Nanocrystal Functionalities Tunes the Wettability of Water-Cast Films

Cellulose nanocrystal (CNC)-based materials display apparently erratic wetting behaviors with contact angle (CA) variations as large as 30° from sample to sample. This work hypothesizes that it is the orientation of CNC amphiphilic functionalities at the interface with air that causes the variability in CA. By exploiting relationships with the Hansen solubility parameter theory, a set of surface tension parameters is proposed for both the polar and the non-polar surfaces of cellulose I_β nanocrystals. These coefficients elucidate the wettability of CNC materials by establishing a correlation between the wetting properties of the air/sample interface and its chemical composition in terms of non-polar moieties. Advancing/receding CA experiments suggest that, while spin-coating CNC suspensions yield purely polar films, oven-casting them produces amphiphilic surfaces. We proposed a mechanism where the state of dispersion (individual or agglomerated) in which CNCs reach the air/water interface during casting is the determining factor: while individual nanocrystals find it more stable to orient their non-polar surfaces toward the interface, the aspect ratio of CNC agglomerates favors an orientation of their polar surfaces. This represents the first compelling evidence of CNC orientation at an interface and can be applied to Pickering emulsions and nanocomposites and to the production of CNC materials with tuned wettability.

Chemical affinity and dispersibility of boron nitride nanotubes

Boron nitride nanotubes (BNNTs) are electrically insulating nanoparticles that display highly competitive elastic modulus and thermal conductivity. Long presented as potential fillers for nanocomposite applications, their poor dispersibility in most commodity polymers has, however, limited their spread. In this work, the chemical affinity of purified BNNTs, measured in terms of Hansen solubility parameters (HSP), were obtained through sedimentation tests in a wide set of organic solvents, taking into account relative sedimentation time. The parameters obtained were {δ _d; δ _p; δ _h} = {16.8; 10.7; 14.7} ± {0.3; 0.9; 0.3} MPa^1/2, with a Hildebrand parameter, δ _t = 24.7 MPa^1/2 and a sphere radius of 5.4 MPa^1/2. The solubility parameters were determined considering complete dispersion of the purified nanomaterial, as well as the viscosity and density of the host solvent. These factors, combined with the high purity of the BNNTs, are crucial to minimize the uncertainty of the HSP characterization. Such refined values provide necessary insights both to optimize the solvent casting of unmodified BNNTs, and to orient the surface modification efforts that would be needed to integrate these nanomaterials into a wider range of host matrices.