The Flow Characteristics Study Of Pressure-driven Nanofluids In Polymer Brush Gratfed Microchannel

With the rapid development of science and technology civilization, people begin toknow more about the unknown, and their life is also being changed constantly by thegradual perfection of modern mechanical design and manufacturing technology. As arepresentative result of the emerging technological research, nanofluids have been appliedin every walk of life for its good performance, convenient preparation and extensive use.Nanofluids’heat-transfer properties have been taken full advantage in the previous researchtheory, showing a dominant position in all kinds of heat exchange equipments. With thecontinuous study of micro-field, more rarely known fluid properties have been developed.Nanofluids is a favorable tool in fixing the flow channel, and the observation shows thatnanoparticles move irregularly in the flow, resist particles sedimentation, coagulation andblock, and its smooth surface effect and the spatial little-size effect also greatly improve thewear of machinery and equipment. Nanofluids can sustain the steady flow over a longperiod of time, not only improve the flow condition, but also increase the viscosity,realizing high effectively transmission.At the same time, with the unique spatial structure and material performance, thepolymer brush is becoming the focus in modern machinery, chemical, medical researchfiled. Polymer brush has a variety of rich space conformation and movement rules, reactingwith the change of the fluid system macroscopic properties, such as light intensity, pH, andtemperature, etc. Meanwhile the interaction of long-range force and short-range molecularpotential energy that making up polymer macromonomer also adds more variety of changesto polymer brush, playing an outstanding applications in the fields of proteinanticoagulation, lubrication and smart surface. If the nanofluids flow in the polymer brushgrafted microchannel, it will present a new flow characteristic instead of the original singlemovement rules under the disturbance of polymer brush. Their combination provides a newpath to explore mechanical properties with modern technology, and the comprehensivereaction provides new thought to research more new products. It can provide favorable conditions for the study of nanofluids flow characteristics by molecule dynamic computersimulation, which would leave out the harsh conditions in the experiments, simplify theworkload, observe and read the data information in real time.In this paper, we study the flow characteristics of pressure-driven nanofluids bymolecule dynamics simulation method, with polymer brush grafted on the surface ofmicrochannel at the same time. This paper studied the changes in fluid velocity and particledensity distribution in the condition of a variety of grafting density and nanoparticlevolume fraction. As the grafting density increases, the overall velocity showed a trend ofdecline, however, it recovery rapidly in the center of the channel, showing that the actionrange of polymer brush is limited near the wall. Nanoparticles play a decisive role in thecenter of the channel, the more nanoparticles added in the solution, the slower flowvelocity is, the stronger the friction damping and viscous effect behave. Meantime makethe conditions that nanofluids without polymer brush and pure fluid without nanoparticlesas a reference. Polymer brush can effectively control the velocity range of nanofluids. Thechange of driving force is also an important factor, we can study the flow changes byputting the force from strong to weak to each particle. Although the larger driving force canimprove the fluid velocity, the effect of adding nanoparticles can change the flowcharacteristics of the entire solution, whose effect has been beyond driving force.On the basis of neutral polymer brush, we further research on the flow properties ofnanofluids with polyelectrolyte brush grafted on the channel. The change of graftingdensity and nanoparticles volume fraction would also have a huge influence on the velocity,the velocity rises steadily from the border area to the channel center, and trend to overlap inthe center. The distribution area of the water molecule and counterions remained relativelystable, along with the change of grafting density, the polyelectrolyte brushes extendgradually. The more the content of nanoparticles, the velocity is limited to reduce. Thispaper continues to study the effect of other particles in the fluid system, and observes thechange of velocity after adding single valence state and mixed valence state of ions. Thehigher the valence is, the velocity will have a certain degree of increase. At the same time,low state of ions distributed more board, and attracted the extension of polyelectrolyte brushes. However, the velocity doesn’t change significantly after adding differentproportions of single valence and three valence of counterions, the distribution area of twokinds of counterions present from sparse to dense by the strength law of electrostaticattraction.This paper studies the effect of the charge sequences of polyelectrolyte brushes on theflow velocity, we set the charge state of different sequences and compared with neutralbrush, the velocity will be weakened as the power declined, and monomer stretch is alsodifferent, the calculation results of brush height can reflects the monomer space collapse.This paper studies solid-liquid interface properties of nanofluids, obtaining theboundary slip length, viscosity and the corresponding influence factors by computing, thenanofluids system with polymer brushes grafted will improve the flow properties. Finallywe make a verifying experiment by making microchannel and polymer coating, analyzingthe flow of system qualitatively in order to verify the previous simulation results andguarantee the truthfulness and reliability of the research conclusion..By using molecule dynamic calculation method, simulation and experimentcombination research system, this paper makes a comprehensive and meticulous researchon the nanofluids flow characteristics in the channel grafted by polymer brushes, analyzingthe change trend of flow velocity, and the density range of solvent particles, counterionsand monomer density, and obtains the flow effect of the combination of nanofluids andpolymer brush in the micro view. It lays a solid foundation for the future combinationapplication in the actual mechanical equipment, and provides theoretical basis andtechnical support for the micro research of more fluid performance, which will have a wideand bright application prospect.