Adhesion and Disintegration Phenomena on Fractal Agar Gel Surfaces

Kudo, Ayano; Sato, Marika; Sawaguchi, Haruna; Hotta, Jun‐ichi; Mayama, Hiroyuki; Nonomura, Yoshiaki

doi:10.5650/jos.ess16085

Cited by 3 publications

(7 citation statements)

References 11 publications

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“…Nearly no adhesion forces between the fractal agar gel substrates in water (1) or the surfactant aqueous solution (2) were observed. This outcome was consistent with the result reported by Kudo et al 18 The adhesion force increased with the oil-phase proportion in the O/W emulsions. The largest adhesion force was determined for the O/W emulsion (5).…”

Section: ■ Results and Discussionsupporting

confidence: 93%

“…The system was composed of a digital force gauge (ZTA-20N, Imada Co., Ltd., Aichi, Japan) and a vertical motorized test stand (EMX-1000N, Imada Co., Ltd., Aichi, Japan). Detailed specifications of the employed devices are provided elsewhere . The detailed procedure of the evaluation method is demonstrated in Section S3 of the Supporting Information.…”

Section: Experimental Sectionmentioning

confidence: 99%

“…Detailed specifications of the employed devices are provided elsewhere. 18 The detailed procedure of the evaluation method is demonstrated in Section S3 of the Supporting Information.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…Furthermore, the roughness of the human tongue varies depending on the site, with the arithmetic average roughness ( R a ) determined to be in the range of 1–100 μm . The rough surface is covered with a hydrophilic mucous membrane, which plays an important role in nutrient absorption and sensory perception. , For our study, a fractal agar gel was selected as a biological model exhibiting the abovementioned features, and its surface adhesion and wettability properties were evaluated. , …”

Section: Introductionmentioning

confidence: 99%

“…15,16 For our study, a fractal agar gel was selected as a biological model exhibiting the abovementioned features, and its surface adhesion and wettability properties were evaluated. 17,18 Owing to their flexibility, shape-retention ability, and remarkably high lubricity, gels and their composite materials are widely employed in various fields. Several researchers have reported complex friction characteristics on gel surfaces.…”

Section: ■ Introductionmentioning

confidence: 99%

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

2021

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In this study, the friction properties of emulsions in an oral environment were investigated to understand the food-texture recognition mechanisms occurring on biological surfaces. Numerous publications have suggested that the friction phenomena depend on friction conditions, such as the surface characteristics, as well as the shape and movement of contact probes. Traditional friction evaluation systems are unsuitable for mimicking the oral environment. Thus, in this study, the friction forces between two fractal agar gel substrates in an emulsion were examined using a sinusoidal motion friction evaluation system that effectively mimics the oral environment. The physical properties of the fractal agar gel, including the elasticity, hydrophilicity, and surface roughness, were analogous to those of the human tongue. Furthermore, the sinusoidal motion imitated the movements of living organisms. Depending on the samples, three friction profiles were observed. For water, the surfactant aqueous solution, and olive oil, the friction profiles of the outward and homeward processes were symmetric (stable pattern). Interestingly, for an oil-in-water (O/W) emulsion, friction behaviors with not only an asymmetric friction profile (unstable pattern I) but also a lubrication phenomenon, which temporarily decreased the friction force (unstable pattern II), were noted. The probability for the appearance of unstable patterns and adhesion force between the gel substrates increased with the oil content of the O/W emulsions. These characteristic friction phenomena were attributed to the strong adhesive force in the emulsion, which was sandwiched between the agar gel substrates. The findings obtained in this study would contribute significantly to understanding the food-texture recognition mechanisms and dynamic phenomena occurring on biological surfaces.

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Section: ■ Results and Discussionsupporting

confidence: 93%

Section: Experimental Sectionmentioning

confidence: 99%

“…Detailed specifications of the employed devices are provided elsewhere. 18 The detailed procedure of the evaluation method is demonstrated in Section S3 of the Supporting Information.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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

2021

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Anomalous Friction between Agar Gels under Accelerated Motion

2018

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Understanding the friction phenomena on a gel surface under accelerated conditions is important for the designing of functional materials. However, there are few reports on friction under such conditions. In the present study, the effects of velocity, normal force, and gel hardness on the friction force were evaluated between two agar gels under sinusoidal motion. We found a friction phenomenon with an extremely low friction coefficient on the gel surfaces: the friction coefficient became less than 0.02 when sliding velocity increased. In addition, the profile of the friction coefficient was different between outward and homeward processes in the reciprocating sliding motion. In the outward direction, the low friction coefficient was maintained even if the sliding velocity decreased. On the other hand, the friction coefficient increased with sliding velocity in the homeward direction. This characteristic friction profile is caused by a long relaxation time on the gel surfaces. When the gel substrate is rubbed for a shorter time than the relaxation time, the morphology of the gel surface becomes unstable. Under such conditions, the formation and extinction of a thick liquid film can induce a super lubrication state and the asymmetric friction phenomena. These findings are useful not only for developing functional materials but also for understanding nonequilibrium phenomena in soft biological systems.

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

et al. 2020

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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.

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Adhesion and Disintegration Phenomena on Fractal Agar Gel Surfaces

Cited by 3 publications

References 11 publications

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

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

Anomalous Friction between Agar Gels under Accelerated Motion

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

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