A hybrid camphor–camphene wax material for studies on self-propelled motion

Löffler, Richard J. G.; Hanczyc, Martin M.; Górecki, Jerzy

doi:10.1039/c9cp04722k

Cited by 20 publications

(42 citation statements)

References 19 publications

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“…Again, these scaling properties directly explain the results (22), Nu ∼Ū 1/3 , for the Nusselt number in the limitŪ 1. The total Marangoni force should scalē F M,tot /Pe ∼ Δρ 2c (ρ = 1) ∼Ū −2/3 from the boundary layer contribution (see Eq.…”

Section: Scaling Argumentssupporting

confidence: 74%

“…Propulsion is not caused by surfactants that are anisotropically distributed along the swimmer-liquid interface but by the anisotropic distribution of surfactant at the liquid-air interface along which the soap boat propels [14]. The surfactant molecules at the liquid-air interface are emitted or dissolved from the swimmer; this can be achieved by depositing them on the floating swimmer initially [15], by soaking the swimmer in surfactant [16][17][18][19][20][21], or by using a swimmer body made from dissolving surfactant [22]. There are many examples based on DMF (dimethylformamide) [23], alcohol [15,21], soap [21], camphor [16][17][18][19][20]24] or camphene [22] that have also been investigated quantitatively.…”

Section: (): V-volmentioning

confidence: 99%

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From diffusive mass transfer in Stokes flow to low Reynolds number Marangoni boats

Ender

Kierfeld

2021

Eur. Phys. J. E

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We present a theory for the self-propulsion of symmetric, half-spherical Marangoni boats (soap or camphor boats) at low Reynolds numbers. Propulsion is generated by release (diffusive emission or dissolution) of water-soluble surfactant molecules, which modulate the air–water interfacial tension. Propulsion either requires asymmetric release or spontaneous symmetry breaking by coupling to advection for a perfectly symmetrical swimmer. We study the diffusion–advection problem for a sphere in Stokes flow analytically and numerically both for constant concentration and constant flux boundary conditions. We derive novel results for concentration profiles under constant flux boundary conditions and for the Nusselt number (the dimensionless ratio of total emitted flux and diffusive flux). Based on these results, we analyze the Marangoni boat for small Marangoni propulsion (low Peclet number) and show that two swimming regimes exist, a diffusive regime at low velocities and an advection-dominated regime at high swimmer velocities. We describe both the limit of large Marangoni propulsion (high Peclet number) and the effects from evaporation by approximative analytical theories. The swimming velocity is determined by force balance, and we obtain a general expression for the Marangoni forces, which comprises both direct Marangoni forces from the surface tension gradient along the air–water–swimmer contact line and Marangoni flow forces. We unravel whether the Marangoni flow contribution is exerting a forward or backward force during propulsion. Our main result is the relation between Peclet number and swimming velocity. Spontaneous symmetry breaking and, thus, swimming occur for a perfectly symmetrical swimmer above a critical Peclet number, which becomes small for large system sizes. We find a supercritical swimming bifurcation for a symmetric swimmer and an avoided bifurcation in the presence of an asymmetry.

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Section: Scaling Argumentssupporting

confidence: 74%

Section: (): V-volmentioning

confidence: 99%

From diffusive mass transfer in Stokes flow to low Reynolds number Marangoni boats

Ender

Kierfeld

2021

Eur. Phys. J. E

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“…(31)) determines the results for the Marangoni forces in this advective limit [see Eqs. (27), (28), (29), (30), (40) and (43)].…”

Section: High Reynolds Numbersmentioning

confidence: 99%

“…As "fuel" serve surface active molecules, which are deposited on the floating swimmer [23] or in which the swimmer is soaked [24][25][26][27][28][29], or the swimmer body itself is made from dissolving surfactant [30]. There are many examples based on DMF (dimethylformamide) [31], alcohol [23,29], soap [29], camphor [24][25][26][27][28]32] or camphene [30] that have also been characterized quantitatively. The surfactant molecules are emitted or dissolved from the swimmer and a radial concentration gradient is established at the air-water interface by diffusion, eventually aided by evaporation for volatile surfactants.…”

Section: Introductionmentioning

confidence: 99%

Surfactant-loaded capsules as Marangoni microswimmers at the air–water interface: Symmetry breaking and spontaneous propulsion by surfactant diffusion and advection

et al. 2021

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We present a realization of a fast interfacial Marangoni microswimmer by a half-spherical alginate capsule at the air–water interface, which diffusively releases water-soluble spreading molecules (weak surfactants such as polyethylene glycol (PEG)), which act as “fuel” by modulating the air–water interfacial tension. For a number of different fuels, we can observe symmetry breaking and spontaneous propulsion although the alginate particle and emission are isotropic. The propulsion mechanism is similar to soap or camphor boats, which are, however, typically asymmetric in shape or emission to select a swimming direction. We develop a theory of Marangoni boat propulsion starting from low Reynolds numbers by analyzing the coupled problems of surfactant diffusion and advection and fluid flow, which includes surfactant-induced fluid Marangoni flow, and surfactant adsorption at the air–water interface; we also include a possible evaporation of surfactant. The swimming velocity is determined by the balance of drag and Marangoni forces. We show that spontaneous symmetry breaking resulting in propulsion is possible above a critical dimensionless surfactant emission rate (Peclet number). We derive the relation between Peclet number and swimming speed and generalize to higher Reynolds numbers utilizing the concept of the Nusselt number. The theory explains the observed swimming speeds for PEG–alginate capsules, and we unravel the differences to other Marangoni boat systems based on camphor, which are mainly caused by surfactant evaporation from the liquid–air interface. The capsule Marangoni microswimmers also exhibit surfactant-mediated repulsive interactions with walls, which can be qualitatively explained by surfactant accumulation at the wall. Graphic Abstract

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“…This information allowed us to investigate the object's trajectory and velocity. A similar analysis for pills made of camphene-camphor wax was reported in [24]. This method allowed for the comparison of the properties of the new camphene-camphor-polypropylene plastic with the properties of the camphenecamphor wax previously described.…”

Section: Methodsmentioning

confidence: 85%

A Perfect Plastic Material for Studies on Self-Propelled Motion on the Water Surface

2021

Self Cite

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We describe a novel plastic material composed of camphene, camphor, and polypropylene that seems perfectly suited for studies on self-propelled objects on the water surface. Self-motion is one of the attributes of life, and chemically propelled objects show numerous similarities with animated motion. One of important questions is the relationship between the object shape and its motility. In our previous paper, {R. Löffler et al. PCCP, 2019, 21, 24852–24856}, we presented a novel hybrid material, obtained from the solution of camphor in camphene, that allowed making objects of various shapes. This hybrid material has wax-like mechanical properties, but it has a very high tackiness. Here, we report that a small amount of polypropylene removed this undesirable feature. We investigated the properties of camphor–camphene–polypropylene plastic by performing the statistical analysis of a pill trajectory inside a Petri dish and compared them with those of camphor-camphene wax. The plastic showed the stable character of motion for over an hour-long experiment. The surface activity of objects made of plastic did not significantly depend on the weight ratios of the compounds. Such a significant increase in usefulness came from the polypropylene, which controlled the dissipation of camphor and camphene molecules.

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A hybrid camphor–camphene wax material for studies on self-propelled motion

Abstract: A new material that combines self-propelled motion with wax-like mechanical properties and can be formed into non-trivial shapes is presented.

Cited by 20 publications

References 19 publications

From diffusive mass transfer in Stokes flow to low Reynolds number Marangoni boats

From diffusive mass transfer in Stokes flow to low Reynolds number Marangoni boats

Surfactant-loaded capsules as Marangoni microswimmers at the air–water interface: Symmetry breaking and spontaneous propulsion by surfactant diffusion and advection

A Perfect Plastic Material for Studies on Self-Propelled Motion on the Water Surface

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