Wetting and dewetting dynamics in aqueous solutions containing amphiphilic compounds involve intricate interactions that influence contact angles and surface tension, with broad implications in materials science and biology. This study explores the dynamics of wetting and dewetting on glass surfaces in aqueous media containing the amphiphilic compound C18OE84, focusing on capillary rise behavior. The dynamics were often characterized by an initial overshoot of the liquid meniscus, followed by relaxation toward equilibrium height. For concentrations either far below or well above the cmc, the observed overshoot in meniscus height is small, whereas near the cmc, it becomes markedly pronounced. The relaxation kinetics toward equilibrium vary with concentration, accelerating for concentrations exceeding the cmc. These observations are attributed to a nonequilibrium surface excess situation of surfactant at the liquid/vapor interface, strongly influenced by transport parameters such as concentration and diffusion constants. Given the low cmc of C18OE84, surfactant depletion due to adsorption on capillary walls may further reduce the effective concentration in the capillary, complicating the dynamics.To quantify adsorption effects, the solid/liquid interface adsorption isotherm was determined using ellipsometry. At high concentrations, the capillary rise height evolves smoothly over time. In contrast, for low to moderate concentrations, particularly below or near the cmc, the system exhibits a more complex dynamic behavior: the rise abruptly halts at a height corresponding to a specific surface tension value. This behavior is analyzed through the interplay between time-dependent contact angles and interfacial tension variations, driven by surfactant adsorption kinetics near the three-phase contact line at the solid/vapor and solid/liquid interfaces. The study also highlights how capillary preparation and pretreatment significantly impact wetting kinetics, underscoring the sensitivity of these systems to interfacial conditions. These findings provide insights into the role of surfactant transport and adsorption in controlling wetting dynamics, with potential applications in designing surfaces and formulations for targeted wetting behaviors.

The phase behavior in the oleic acid/sodium oleate/normal saline (0.15M NaCl aqueous solution) system has been determined. For this purpose visual inspection of samples between crossed polarizers, and Small Angle X-ray diffraction was used to identify the various phases and their unit cell dimensions. A rich phase behavior was observed for the ternary system, featuring reverse micellar, micellar cubic, hexagonal, and cubic phases, and large regions with lamellar phases. As expected the ratio the 'oleic acid/sodium oleate' determines the pH and as a consequence the phase behavior. The results could be modeled by an extended Henderson-Hasselbalch (HH) equation, which takes into account the electrostatic potential at the aqueous lipid interface. The knowledge obtained is important for understanding the lipolysis of triglycerides, as the phase behavior of the end-product of the reaction regulates how well the insoluble product can be dispersed and consequently the kinetics of the process.

The natural moisturizing factor (NMF) is a group of hygroscopic molecules that is naturally present in skin and protects from severe drying. Glycerol and urea are two examples of NMF components that are also used in skin care applications. In the present study, we investigate the influence of glycerol and urea on the permeability of a model drug (metronidazole, Mz) across excised pig skin membranes at different hydrating conditions. The degree of skin hydration is regulated by the gradient in water activity across the membrane, which in turn depends on the water activity of the formulation in contact with the skin membrane. Here, we determine the water activity of all formulations employed using an isothermal calorimetric method. Thus, the gradient in water activity is controlled by a novel experimental set-up with well-defined boundary conditions on both sides of the skin membrane. The results demonstrate that glycerol and urea can retain high steady state flux of Mz across skin membranes at dehydrating conditions, which otherwise would decrease the permeability due to dehydration. X-ray diffraction measurements are performed to give insight into the effects of glycerol and urea on SC molecular organization. The novel steady state flux results can be related to the observation that water, glycerol, and urea all affect the structural features of the SC molecular components in a similar manner.

At normal conditions there is a substantial water gradient over the skin as it separates the water-rich inside of the body from the dry outside. This leads to a variation in the degree of hydration from the inside to the outside of skin and changes in this gradient may affect its structure and function. In this study we raise the question: How do changes in the water gradient across skin affect its permeability? We approach this problem in novel diffusion experiments that permit strict control of the gradient in the chemical potential of water and hence well-defined boundary conditions. The results demonstrate that a water gradient can be used to regulate transport of drugs with different lipophilic characteristics across the skin barrier. It is shown that the transport of metronidazole (log Po/w=0.0) and methyl salicylate (log Po/w=2.5) across skin increases abruptly at low water gradients, corresponding to high degrees of skin hydration, and that this effect is reversible. This phenomenon is highly relevant to drug delivery applications due to its potential of temporarily open the skin barrier for transdermal drug delivery and subsequently close the barrier after treatment. Further, the results contribute to the understanding of the occlusion effect and indicate the boundary conditions of the water gradient needed to make use of this effect

At normal conditions there is a substantial water gradient over the skin as it separates the water-rich inside of the body from the dry outside. This leads to a variation in the degree of hydration along the skin and changes in this gradient may affect the structure and function of skin. In this study we raise the question: How do changes in the water gradient across skin affect its permeability? We approach this problem in experiments that permit strict control of the gradient in the chemical potential of water. The results demonstrate that an external water gradient can be used to regulate transport of drugs across the skin. It is shown that the permeability of the skin barrier increases abruptly at low water gradients, corresponding to high degrees of skin hydration, and that this effect is reversible. This phenomenon is highly relevant to drug delivery applications due to its potential of temporarily opening the skin barrier for transdermal delivery of drugs and subsequently closing the barrier after treatment. The results are explained on basis that the skin is a responding membrane, for which small changes in the environment can lead to major changes in membrane structure, which in turn affect its transport properties. We have in parallel theoretical modeling and experimental studies in model systems shown how a water gradient across multilayer lipid membrane can be used as a regulating mechanism to control the barrier properties. These principles are here applied to the barrier of stratum corneum, the upper layer of the human skin, where it can provide an explanation for the experimental findings that a water gradient can be used to regulate drug transport across the skin.

Lipid-based particles (Cubosome® particles) were surface-modified by chitosan and the ratio between particles and chitosan was optimized to minimize the free chitosan concentration in the dispersion. The modified particles were characterized by electrophoretic measurements and the pH dependence of the zeta potential could be directly related to the protonation of chitosan. Interaction between the modified particles and mucin-coated silica surfaces were subsequently investigated in situ by ellipsometry to assess the mucoadhesive properties at physiologically relevant conditions. The result showed that a substantial amount of modified particles was adsorbed to mucin-coated silica surfaces at both pH 4 and pH 6, probably due to electrostatic interactions between amino groups in chitosan and negatively charged groups in mucin. Furthermore, the amount of bound particles decreased by less than 15% upon rinsing indicating relatively strong interactions. This investigation demonstrates that ellipsometry is a useful tool to study mucoadhesive properties of particles in the submicrometer range. Moreover, the novel chitosan-modified particles may be of interest for mucosal drug delivery applications.

Cubosome particles were produced by fragmenting a cubic crystalline phase of glycerol monooleate and water in the presence of a stabilizing poly(ethylene oxide)-based polymer. The aim of our investigation was to study the interaction between these particles and mucin to gain information on how they would perform as a vehicle for mucosal drug delivery. Particle electrophoresis was used to investigate the interactions between particles and mucin in solution, and ellipsometry was utilized to study the interactions between particles and mucin-coated silica surfaces. The interaction studies were performed at relevant physiological conditions, and the pH and ionic strength were varied to gain more information about the driving forces for the interaction. The results from electrophoretic measurements showed that mucin in solution adsorbed to the particles at pH 4, whereas at pH 6 no clear interaction was detected. From ellipsometric measurements it was evident that the particles adsorb reversibly to a mucin-coated silica surface at pH 4, while no adsorption of particles could be detected at pH 6. The overall conclusion is that the interaction between these particles and mucin is weak and pH-dependent. These findings are in agreement with other investigations of the interactions between mucin and poly(ethylene oxide) chains.