Friction Dynamics of Hydrogel Substrates with a Fractal Surface: Effects of Thickness

Abstract

Interfacial phenomena on soft and wet materials, such as hydrogels, are important for modeling physical phenomena, such as friction, wetting, and adhesion on hydrophilic biosurfaces. Interfacial phenomena on soft material surfaces are not only affected by the properties of the surface but also by the geometry of the substrate. However, there are few reports on the influence of geometry and deformability on friction behavior at gel interfaces. In this study, we evaluate the effects of the thickness ( H ) of the upper agar gel layer on the friction force between gels under a sinusoidal movement. Although H does not significantly affect the friction force or pattern, the normalized delay time (δ), which is the normalized time lag in the friction force response to the contact probe’s movement, increases with H . A regression analysis between δ and H shows that δ increased linearly with H . We present a simple model incorporating a shear modulus to qualitatively explain the experimental results. The analysis and our model indicate that one must not only consider surface properties, such as adhesion, but also thickness and rigidity when studying friction behavior at the gel–surface interface. These findings will be useful for understanding friction phenomena on soft biological systems, such as the tongue, throat, esophagus, and gut surfaces.

Preparation, Characterization and Evaluation of Organogel-Based Lipstick Formulations: Application in Cosmetics

“…However, it should be noted that all pay-off lipsticks had passed the minimum requirement. The higher pay-off values between LMOG-based and “classical” lipstick formulations could be explained by a higher frictional force change attributed to gel samples [ 39 ].…”

Nonlinear Friction Dynamics of Oil-in-Water and Water-in-Oil Emulsions on Hydrogel Surfaces

“…Contrarily, in the friction evaluation of the fractal agar gel, the asymmetric friction profile was not observed because the fractal structure of the gel surface prevented the formation of a thick liquid film . Although the thickness of the upper agar gel does not significantly affect the friction force or profile, the normalized delay time (δ), which is the normalized time lag in the friction force response to the contact probe’s movement, increases linearly with the thickness of the gel . In addition, we showed the correlation between the friction data of thickener aqueous solutions and the sensory thickness and the recognition mechanism of this sensation during the process of eating, using a biomimetic friction evaluation system .…”

“…Traditional systems are not suitable for mimicking the oral environment; therefore, we designed a friction evaluation system that combined a sinusoidal motion device with fractal agar gel substrates. − The developed system effectively mimicked the oral environment during eating. To evaluate the nonlinear mechanical response on a soft material surface, we created a unique device that can be used to evaluate friction under sinusoidal motion.…”

“…We recently evaluated the friction properties of agar gel substrates displaying different surface structures and thicknesses of the substrate under sinusoidal motion. ,, Three friction profiles were observed when the friction evaluation of a flat agar gel was performed at different sliding velocities and normal force values . The first involved a friction profile with nearly identical friction behaviors in the outward and homeward directions (stable pattern).…”

Preliminary Study of the Potential Photoprotective Effect of Organogel-Based Lipstick Formulations: Texture Analysis, Rheological, Thermal and Sensory Properties

“…However, it should be noted that all pay-off lipsticks had passed the minimum requirement. The higher pay-off values between LMOG-based and "classical" lipstick formulations can be explained by an higher frictional force change attributed to gels with roughest surface [44]. Considering the overall mechanical attributes, LMOGs have a great potential to replace part of waxes in lipstick formulations and to contribute in attaining the desired textural properties for photoprotective cosmetics.…”