本文選題：聚合物刷 + 納米流體　； 參考：《吉林大學(xué)》2015年碩士論文

【摘要】：科技文明的迅速發(fā)展讓越來(lái)越多的未知事物走入了人們的視野中，現(xiàn)代機(jī)械設(shè)計(jì)技術(shù)和制造工藝的日臻完善也不斷改變著人們的生活。納米流體作為新興科技研究的代表成果，以其性能良好、制備便捷、用途廣泛而越來(lái)越多地應(yīng)用到各行各業(yè)中。先前的研究理論充分利用了納米流體的傳熱特性，在多種熱交換設(shè)備中顯示出主導(dǎo)地位，隨著對(duì)微觀領(lǐng)域的不斷開拓，更多鮮為人知的流體特性被開發(fā)出來(lái)，納米流體是一種修正流道的有利工具，觀察發(fā)現(xiàn)納米顆粒會(huì)在流動(dòng)中進(jìn)行無(wú)規(guī)則運(yùn)動(dòng)，抵御顆粒沉降、凝聚和阻塞，其光滑的表面效應(yīng)和空間小尺寸效應(yīng)也極大地改善了機(jī)器設(shè)備的磨損，納米流體可以保持長(zhǎng)時(shí)間的平穩(wěn)流動(dòng)，不僅改善流動(dòng)工況，同時(shí)還增加液體黏度，達(dá)到高效傳送的目的。 與此同時(shí)，高分子聚合物刷通過其獨(dú)特的空間結(jié)構(gòu)和材料性能也成為現(xiàn)代機(jī)械、化學(xué)、醫(yī)療等領(lǐng)域的研究重點(diǎn)。聚合物刷具有多種豐富的空間形態(tài)構(gòu)象和運(yùn)動(dòng)規(guī)律，可以隨著流體系統(tǒng)宏觀性質(zhì)的改變而做出反應(yīng)，如光照強(qiáng)度、酸堿性和溫度等，同時(shí)組成聚合物刷的單體大分子間長(zhǎng)程作用力和短程分子勢(shì)能的交互也為聚合物刷添加了更加多樣的變化，在防止蛋白質(zhì)凝結(jié)、潤(rùn)滑和“智能表面”等領(lǐng)域都有突出的應(yīng)用場(chǎng)合。將納米流體引入到接枝有聚合物刷的微流道中，納米流體的流動(dòng)特性就不再是原先單一的運(yùn)動(dòng)規(guī)律，聚合物刷擾動(dòng)下的納米流體會(huì)呈現(xiàn)出新穎的流動(dòng)特性。二者的結(jié)合為是現(xiàn)代技術(shù)探索機(jī)械特性提供了新路徑，兩種介質(zhì)的綜合反應(yīng)也為研究更多新產(chǎn)品提供了思路。通過分子動(dòng)力學(xué)計(jì)算機(jī)模擬，可以跨越多種實(shí)驗(yàn)中難以企及的苛刻條件，簡(jiǎn)化工作量，并實(shí)時(shí)觀測(cè)和讀取研究數(shù)據(jù)信息，為研究納米流體的流動(dòng)特性提供了有利條件。 本文首先采用分子動(dòng)力學(xué)模擬方法研究壓力驅(qū)動(dòng)的納米流體流動(dòng)特性，同時(shí)微流道表面接枝中性聚合物刷。研究在多種接枝密度和納米顆粒體積分?jǐn)?shù)的條件下，流體速度變化以及粒子密度分布。隨著接枝密度增大，整體速度呈現(xiàn)下降趨勢(shì)，然而在流道中心速度卻快速回升，說(shuō)明聚合物刷的作用范圍局限在靠近墻壁附近。納米顆粒在流道中心起到了更具決定性的作用，溶液中添加的納米顆粒越多，流體速度越慢，摩擦阻尼和粘滯效應(yīng)表現(xiàn)得越強(qiáng)烈。不接枝聚合物刷的納米流體和不添加納米顆粒的純流體作為參考。接枝聚合物刷可以有效地控制納米流體的速度范圍。驅(qū)動(dòng)力的變化同樣是一個(gè)重要因素，通過向每個(gè)粒子施加由大到小的驅(qū)動(dòng)力來(lái)研究流動(dòng)變化，雖然更大的驅(qū)動(dòng)力可以提高流體速度，但是添加納米顆粒的效果更能有效改變整個(gè)溶液的流動(dòng)特性，其作用程度超過了驅(qū)動(dòng)力的改變。 在中性聚合物刷的基礎(chǔ)上，進(jìn)一步研究流道中接枝聚電解質(zhì)刷后納米流體的流動(dòng)性質(zhì)。接枝密度與納米顆粒體積分?jǐn)?shù)的變化同樣會(huì)對(duì)流動(dòng)速度產(chǎn)生巨大的影響力，從邊界區(qū)域到流道中心穩(wěn)步升高，并在流道中心趨于重合。水分子與反離子的分布區(qū)域依然相對(duì)穩(wěn)定，隨接枝密度的變化，聚電解質(zhì)刷逐步伸展。納米顆粒的含量越多就會(huì)越限制流速并降低。本文繼續(xù)研究流體系統(tǒng)中的其他粒子作用效果，在添加單一價(jià)態(tài)的反離子和混合價(jià)態(tài)反離子后觀察流體系統(tǒng)的流速變化，價(jià)態(tài)越高，則速度會(huì)有一定程度的提高，同時(shí)低價(jià)態(tài)的反離子分布范圍更加寬泛，吸引了聚電解質(zhì)刷的伸展，而混合添加不同比例的單價(jià)和三價(jià)反離子后速度沒有明顯變化，兩種反離子的分布區(qū)域則受到靜電吸引力的強(qiáng)弱規(guī)律而呈現(xiàn)稀疏到密集的分布。 研究聚電解質(zhì)刷的電荷序列對(duì)流動(dòng)速度產(chǎn)生的影響，設(shè)定不同序列的電荷狀態(tài)，并與中性刷對(duì)比，流速會(huì)隨著電量的下降而被抑制減弱，而且單體伸展也有所不同，通過計(jì)算刷層高度反映出單體的空間塌縮形態(tài)。 研究納米流體的固液界面特性，通過計(jì)算得到流體的邊界滑移長(zhǎng)度和黏度特性以及分析相應(yīng)的影響因素，接枝了聚合物刷的納米流體系統(tǒng)會(huì)改善原有的流動(dòng)性質(zhì)。最后進(jìn)行一個(gè)驗(yàn)證性流動(dòng)實(shí)驗(yàn)，通過制作微流道和聚合物涂層，定性分析系統(tǒng)流量，并以此驗(yàn)證先前的模擬結(jié)果，保證研究結(jié)論真實(shí)可靠。 本文使用分子動(dòng)力學(xué)計(jì)算方法，采用模擬與實(shí)驗(yàn)相結(jié)合的研究體系，對(duì)接枝聚合物刷的流道中，納米流體的流動(dòng)特性進(jìn)行全面細(xì)致的研究，分析了流動(dòng)速度的變化趨勢(shì)以及溶劑粒子、反離子和單體等密度變化范圍，得到微觀視野下納米流體與聚合物刷結(jié)合后的流動(dòng)效果，為今后二者的結(jié)合應(yīng)用到實(shí)際機(jī)械設(shè)備中奠定了基礎(chǔ)，并對(duì)微觀探究更多流體性能提供了理論依據(jù)和技術(shù)支持，，具有廣泛良好的應(yīng)用前景。
[Abstract]:The rapid development of scientific and technological civilization has made more and more unknown things into the field of vision. Modern mechanical design technology and manufacturing technology are constantly changing people's life. As the representative achievement of new technology research, nanofluids have been applied to each other more and more with its good performance, convenient preparation, wide use and more and more applications. In all walks of life, the previous research theory made full use of the heat transfer characteristics of nanofluids, showing a dominant position in a variety of heat exchange equipment. With the continuous development of the micro field, more well known fluid characteristics were developed. Nanofluids are a favorable tool for correcting the flow channel. Irregular motion is carried out to resist particle sedimentation, condensation and blocking. The smooth surface effect and small space size effect also greatly improve the wear of the machine equipment. The nanofluid can maintain a long steady flow, not only improve the flow condition, but also increase the viscosity of the liquid body, and achieve the purpose of high efficiency transmission.
At the same time, the polymer brush has become the focus of modern mechanical, chemical, medical and other fields through its unique spatial structure and material properties. The polymer brush has a variety of abundant spatial conformation and motion laws, which can be reacted with the change of the macroscopic properties of the fluid system, such as light intensity, acid-base and temperature. At the same time, the interaction of the long-range force between the monomers and the short range molecular potential energy of the polymer brushes also adds a variety of changes to the polymer brushes. It has prominent applications in the fields of preventing protein condensation, lubrication and "intelligent surface". The flow characteristics of the rice fluid are no longer the original single motion law. The nanofluids under the disturbance of the polymer brush will present a novel flow characteristic. The combination of the two provides a new path for the modern technology to explore the mechanical properties. The comprehensive reaction of the two media provides a way of thinking for the study of more new products. The computer simulation can span the harsh conditions which are difficult to reach in many experiments, simplify the workload, and observe and read the data information in real time. It provides a favorable condition for the study of the flow characteristics of nanofluids.
In this paper, the flow characteristics of pressure driven nanofluids are studied by molecular dynamics simulation. At the same time, a neutral polymer brush is grafted on the surface of the micro channel. The velocity changes and the particle density distribution are studied under the conditions of the grafting density and the volume fraction of nanoparticles. With the increase of the grafting density, the overall velocity decreases. However, the velocity of the flow in the center of the flow path, however, increases rapidly, indicating that the scope of the polymer brush is limited to the vicinity of the wall. The nanoparticles play a more decisive role in the center of the flow channel. The more nano particles are added in the solution, the slower the fluid speed, the stronger the friction damping and viscosity effect. Rice fluid and pure fluid without nanoparticles are used as reference. Graft polymer brushes can effectively control the velocity range of nanofluids. The change of driving force is also an important factor, by applying a large to small driving force to each particle to study the flow change, although the greater driving force can improve the velocity of the fluid. The effect of nano particles can effectively change the flow characteristics of the whole solution, and its extent of action exceeds the change of driving force.
On the basis of neutral polymer brushes, the flow properties of nanofluids after the grafting of polyelectrolyte brushes in the flow channel are further studied. The change of the grafting density and the volume fraction of nanoparticles will also have a great influence on the flow velocity, which increases steadily from the boundary area to the channel center, and tends to coincide in the center of the flow channel. The distribution area of the sub is still relatively stable, with the change of the grafting density, the polyelectrolyte brush extends gradually. The more the content of the nanoparticles will limit the flow rate and decrease. This paper continues to study the effect of other particles in the fluid system, and observe the flow velocity change of the fluid system after the addition of the single valence state reverse ion and the mixed valence state reverse ion. The higher the valence state the higher the valence state, the velocity will be improved to a certain extent. At the same time, the distribution of the reverse ion in the low valence state is more extensive, which attracts the extension of the polyelectrolyte brush, but the velocity of the mixed adding of the different proportion of the monovalent and trivalent ions does not change obviously. The two kinds of reverse ion distribution regions are subject to the strong and weak law of the electrostatic attraction. It is sparse to dense distribution.
The effect of charge sequence on the flow velocity of polyelectrolyte brushes is studied, and the charge state of different sequences is set, and compared with the neutral brush, the flow velocity will be suppressed with the decrease of the quantity of electricity, and the extension of the monomer is also different, and the space collapse form of the monomer is reflected by the calculation of the height of the brush layer.
The characteristics of the solid-liquid interface of nanofluids are studied. The boundary slip length and viscosity characteristics of the fluid are calculated and the corresponding influencing factors are analyzed. The nanofluid system grafted with polymer brushes will improve the original flow properties. Finally, a confirmatory flow experiment is carried out, and the qualitative analysis is made by making the microfluidic and polymer coatings. System flow, and verify the previous simulation results to ensure that the conclusions are true and reliable.
In this paper, the molecular dynamics calculation method is used to study the flow characteristics of the nanofluid in the flow channel of the graft polymer brush. The change trend of the flow velocity and the variation range of the density of the solvent particles, the reverse ion and the monomer are analyzed, and the nanometers in the microscopic field of vision are obtained. The flow effect of the combination of the fluid and the polymer brush has laid a foundation for the application of the two in the future to the actual mechanical equipment, and provides a theoretical basis and technical support for the micro exploration of more fluid performance, and has a broad and good application prospect.

【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB383.1

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