The Motion Behavior of Chemically Powered Colloidal Motors Modulated by the Grafted Temperature and Salt-responsive Polymre Brush

Author:Ji Yu Xing

Supervisor:he qiang


Degree Year:2019





Micro-/nanomotor as a tiny machine has attracted considerable attentions due to its ability to convert diverse types of energies into mechanical motions by themselves.With the benefits of the simplicity in fabrication,controllable size and velocity during propulsion,colloidal motors provide potential diverse applications including environmental remediation,targeted delivery,and biomedicine.The motion modulation of the colloidal motors is mainly accomplished through the concentration of fuel,and the movement directionality can be controlled by utilizing external magnetic field,acoustic field,and light.However,these colloidal motors are still largely insufficient to fulfill the modulation of their movement with sensing the surrounding environment like the natural bacteria.The polymer brushes possessing sensitive under environmental stimuli,simple synthesis process,and controllable in length of resulting polymer brush,are expected to be novel intelligent material.In this thesis we demonstrate the construction of salt-responsive polymer brush-grafted bubble-propelled Janus capsule motors,thermo-responsive polymer brusher-grafted Janus Au-Pt motors and glucose-powered nanomotors with self-electrophoresis,and we will also investigate the dependence of temperature and salt concentration on the velocity,directionality,and mechanism during the propulsion of motors,to provide and theoretical and technical investigation for various applications such as drug delivery.The stimuli-responsive polymer brush as an intelligent and responsive material materials has the advantage on living/controlling synthesis and the stablie reversibility.The stimuli-responsive polymer brushes are able to response under various stimuli such as salt,pH and temperature.The purpose of this paper is building the bubble driven colloid motor for salt-responsive,self-electrophoresis driven bimetallic Janus Au-Pt motor for thermo-responsive and an enzyme-catalyzed nanomotor.To explore the effects of changes of temperature and salt solution on the velocity,direction and environmental monitorization.With the combination of layer-by-layer assembly technique and surface-initiated atom transfer radical polymerization(SI-ATRP),the poly[(2‐(methacryloyloxy)ethyl)trimethylammonium chloride](PMETAC)cationic polymer brush was grafted onto the asymmetric motor to construct salt-responsive polymer brush-functionalized bubble-propelled capsule motors.Scanning election microscope(SEM)characterization illustrated the hollow asymmetric geometry,the thickness of the polymer brush is90 nm.When the types or concentration of anion changed,the change of conformation of the polymer brushes occurred accordingly,resulting in the wettability of the capsule motors.Such change on surface of motors achieved the continuous modulation of velocity of capsule motors.Upon the concentration of hydrogen peroxide of 15%and Cl-,ClO4-and PP as anions,the velocity of the motors is 12.3μm/s,15.4μm/s,and 8.7μm/s,respectively.Alternate addition of ClO4-and PP endowed the switch between low velocity and high velocity,providing new platform of the salt-responsive intelligent colloidal motors.The thermo-responsive polymer brush,poly(N-isopropylacrylamide)(PNIPAM),was grafted onto the Janus Au-Pt motors to construct thermo-responsive Janus Au-Pt motors(PNIPAM@Au-Pt).SEM results verified that the PNIPAM brushes with thickness of100 nm is successfully modified onto the motors.Such PNIPAM@Au-Pt motors displayed different movement behavior in velocity and directionality above and below the phase transition temperature(32 oC).At 25 oC,the PNIPAM@Au-Pt motors performed propulsion with orientation of Au-Pt at a velocity of 7.1μm/s involving self-electrophoresis mechanism similar as Au-Pt motors.In contrast,the propulsion of the PNIPAM@Au-Pt motors showed a lower velocity of 2.3μm/s with orientation of Pt-Au,which is diffusiophoresis similar as the SiO2-Pt motors.Additionally,the investigation of dependence of PNIPAM graft density on the velocity and directionality indicated that the velocity of PNIPAM@Au-Pt motors was minimal and the direction changed once the density of polymer brush is 3/4.Such change of propulsion behavior is attributed to the temperature-triggered conformation of PNIPAM molecular chain,leading to the shift of propulsion mechanism from self-electrophoresis to self-diffusiophoresis.The strategy to modulate the velocity and direction of motors due to the phase transition of polymer chain conformation upon the temperature,provides considerable promises to construct environment-sensitive intelligent micro-/nanomotors.The construction of polymer brush-grafted glucose oxidase(GOx)-powered(PNIPAM@JAu@GOx)nanomotors was carried out based on SI-ATRP and partial modification of GOx onto Janus Au nanoparticles(JAu).The microscopy observation in dark field and dynamic light scanning were employed to characterize the movement behavior of the PNIPAM@JAu@GOx nanomotors.Upon 100 mM of glucose as fuel,the translational diffusion coefficient of PNIPAM-grafted nanomotors increased from10.64μm2/s to 12.87μm2/s,and the velocity increased about 2 times,indicating the PNIPAM enhance the translational diffusion of the nanomotors.Particularly,the nanomotors exhibited the bacteria-mimicking positive chemotactic motion along the glucose gradient.Such chemotaxis of nanomotors can be utilized to seek the targeted positions,which make these bacteria-mimicking nanomotors attractive to meeting the biomedical application in the future.Here,we realized the fabrication of environmental responsive Janus motor.The modified polymer brush can construct a thermo-responsive or salt-responsive intelligent motor,it can realize the control on motion speed,motion direction and motion mechanism of chemical driven motion,and combined with the bionic idea was prepared with simulating the behavior of bacterial chemotaxis nanomotor.Therefore,this paper provides a theoretical basis for the design and preparation of intelligent motors.