pH-Sensitive Self-Motion of a Solid Scraping on an Aqueous Phase

Abstract

The self-motion of a solid scraping at an air/water interface was investigated. The self-motion of a camphoric acid scraping changed characteristically depending on the pH of the aqueous phase. With an acidic aqueous phase, the camphoric acid scraping maintains a fairly constant velocity. At neutral pH, intermittent motion was observed. These characteristic motions are discussed in relation to the surface free energy which results when the camphoric acid layer diffuses from the scraping. The nature of the diffusion of the camphoric acid layer at the water surface could be observed by adding CaSO4 powder. These results imply the realization of chemomechanical energy transduction under isothermal conditions.

Evolution of Self‐Propelled Objects: From the Viewpoint of Nonlinear Science

“…2À concentration. [70,[85][86][87][88][89] When camphanic acid (R'-COOH, R' = C 9 H 13 O 2 )i su sed in the place of camphoric acid, no oscillatory motion is generated under our experimental conditions up to pH 12.5. [89,90] In the case of an aspirin disk (R''-COOH, R'' = C 8 H 7 O 2 ), oscillatory motion was observed in NaOH aqueous solution with high pH ( % 11).…”

“…Ac amphoric acid disk or boat is placed on ab asic aqueous solution (e.g.,c ontaining the phosphate ion HPO 4 2À ), in which self-propelled motion is coupled with acid-base reactioni nt he aqueous phase (Figure 8b). [70,[85][86][87][88][89] Here, the hydrophobic R-(COOH) 2 decreases the surfacet ension,w hereas the hydrophilicR -(COO À ) 2 does not affect it. Thus, R-(COOH) 2 provides the driving force of selfmotion rather than R-(COO À ) 2 .A saresult, ac amphoric acid disk/boat exhibits continuous motion at low HPO 4 2À concentration, and oscillatory motion at high HPO 4…”

“…Camphoric acid (R‐(COOH) 2 , R=C 8 H 14 ) can be used as the source of the driving force. A camphoric acid disk or boat is placed on a basic aqueous solution (e.g., containing the phosphate ion HPO 4 2− ), in which self‐propelled motion is coupled with acid‐base reaction in the aqueous phase (Figure b) . Here, the hydrophobic R‐(COOH) 2 decreases the surface tension, whereas the hydrophilic R‐(COO − ) 2 does not affect it.…”

A theoretical and experimental study on the unidirectional motion of a camphor disk

“…The self-sustaining motion of liquid droplets [1][2][3][4][5][6][7][8][9][10][11][12], solid grains [13][14][15][16][17][18][19][20][21], and gels [22,23] has been investigated by simple experiments in attempts to both understand non-equilibrium systems and to invent novel chemomechanical transducers for isothermal conditions [24][25][26]. The spontaneous motion of a droplet or solid grain at an immiscible interface is generated by Marangoni flow [27][28][29], which is induced by non-uniformity of the concentration or a thermal gradient acting on the droplet or grain .…”

Theoretical study on the translation and rotation of an elliptic camphor particle

“…What attracts us are the various manners of these motions and relevant phenomena, such as spatiotemporal patterning. Examples include locomotion of motor proteins in living organisms [1], swimming motions of motile bacteria [2], the chemical locomotion of metallic nanorods in aqueous solutions [3], the spontaneous motion of surfactant particles atop liquid surfaces [4][5][6], spontaneous droplet motions [7][8][9][10] and propagating solitary waves in a vertically vibrating suspension [11].…”