An Investigation On Locomotion And Velocity Prediction Of Bubble-propelled Tubular Micromotors

Micro/Nano motors are small devices that can drive themselves by converting environmental energies into kinetic energy when immersed in a special solution.These energies include chemical energy,electrical energy,light energy and heat energy.Due to their small geometric size,high powers to transport cargo and low power consumption,micromotors are extensively applied in cell separation,targeted drug delivery,nanosurgery,and environmental sustainability.Bubble-propelled catalytic micromotors belong to catalytic-driven motors.The tubular bubble-propelled ones have been widely used in many fields,which are ascribed to their own advantages: the manufacturing process is simple;the composition and ‘fuel' solution are easy to acquire;external force is not required and the speed is fast.These advantages help them be a hot research topic.At present,the research focuses on manufacture and application.The propelled mechanism and motion control is the key to its application.The driving mechanism of bubble-propelled catalytic micromotors is not fully understood.In particular,the source of driving force is unclear.Accurate and widely applied theoretical models are not obtained as well.Both restrict their controllability and application.The main work and results can be divided into the following four sections:(1)Based on the experimental parameter bubble generation rate and drag force,we first established the velocity-prediction model.And then we investigated relationships between the velocity of tubular micromotor and four influence factors.The influence factors include: concentration of the fuel solution,the semi-cone angle,the length-radius ratio and the viscosity of the fuel solution.The results predicted by the model are consistent with experiments.All the mentioned factors(semi-cone angle,length-radius ratio,fluid concentration,and fluid viscosity)have big influence on the velocity of the micromotors.(2)Based on the theory of life cycle of bubble,a quantitative driving force model for tubular micromotors is established.The traditional driving force model is mainly based on the qualitative description.The model in this work defined the life cycle into four stages: nucleation,growth,sliding and injection.Driving force from bubbles in the life cycle was quantitatively given.(3)By the dimensional analysis method,drag force of micromotors is determined to be related to Reynolds number,semi-cone angle and length-radius ratio of micromotors.And then,we calculated the drag force and the coefficient of it with different parameters.The results show,the drag force from the inner wall is obvious.However,the traditional model neglected this influence.The expression of the dimensionless coefficient of fluid resistance was obtained by fitting data.Based on this,the theoretical model for drag force of tubular micromotors was proposed.In this model,the drag force from the whole wall of micromotors is considered.(4)The locomotion model of tubular micromotors was proposed by combing driving force model(see section 2.)and drag force model(see section 3.).The velocity of motors was predicted using the proposed model.The predicted theoretical results are consistent with experiments,which justify the accuracy and applicability of the model.We can quantitatively explain the source of driving force acting on bubble-propelled tubular motomotors by the proposed model.