「様式３」Project No. 2064

Self-propelled aero-GaN liquid marbles rotating in pulses［ １ ］ Organization: Technical University ofMoldova
Project Leader：Ion Tiginyanu（National Center for Materials Studyand Testing, Technical University of Moldova）
Representative at RIE：Hidenori Mimura
Research Institute of Electronics,
Shizuoka University）
Participants：Tudor Braniste（National Center for Materials Studyand Testing, Technical University of Moldova）［３］Results(３－１) Research results
We studied two types of liquid marbles, namely
marbles with spherical shape and marbles withelongated ellipsoidal shape. We established thatmarbles with spherical shape exhibit rectilinear
motion, while marbles with elongated ellipsoidal
shape show rotational or combined translationaland rotational motion. The marbles characterized
by rotational motion are divided into two types:
exhibiting uniform rotation and pulsed rotation.

［２］Research Progress
We have developed gallium nitride hollow
microtetrapods with the thickness of the walls of
about a few tens of nanometers. The inner surfaceof the microtetrapods is covered by an ultrathin
film of ZnO which leads to the occurrence offascinating dual hydrophilic/hydrophobic properties,
the hydrophilicity being caused by the inner ZnO
coverage, while hydrophobicity being inherent toouter GaN surface. Microtetrapods prepared indifferent technological conditions have been used tofabricate self-propelled liquid marbles which
represent droplets consisting of aqueous solutions of
alcohol covered by a layer of microtetrapods. The
phenomenon of self-propulsion proves to be causedby the Marangoni solutocapillary flow emerging
when a gradient of surface tension of the fluid
support is generated in the surrounding vicinity of
the liquid marble [I. Tiginyanu, T. Braniste et al,Nano Energy, Vol. 56, 759-769 (2019)]. We foundthat the liquid marbles exhibit rectilinear orrotational motion as well as combined translationaland rotational motion, and studied the features ofthe motion as a function of various parameters,
including weight of marbles, technologicalconditions for the preparation of GaN
microtetrapods, shape of liquid marbles etc. As aresult, the shape of the marbles was identified to be
the key parameter determining the type of motionof liquid marbles under consideration.

(３－２) Ripple effects and further developments
In case of uniform rotation, we found that thebigger the weight, the smaller the speed ofrotation of marbles. Pulsed rotation was detected
for relatively light liquid marbles. The mostintriguing phenomenon is the existence of athreshold speed for liquid marbles rotating inpulses. In other words, a liquid marble
characterized by self-propelled spinning starts torotate with acceleration, and after reaching athreshold speed exhibits sharp braking. The
acceleration and braking processes are repeatedon their own, the attained threshold speed being
practically the same within half an hour. For
example, a self-propelled liquid marble with theweight of 6.5 mg shows periodic acceleration andbraking, and the maximum rotational speed
attained is as high as 4 rotations per second. At
present an analytical model is under development
for the purpose of throwing light upon theobserved phenomena. The experimental andanalytical data will be used to write and promotea joint research paper.
［４］Achievements (List of Publications)
We have no joint publications on this subject yet.
No travel has been realized up to now under thisjoint project.