磁性奈米流體中粒徑分佈與磁黏效應的關係

磁性奈米流體為液體中穩定懸浮有磁性奈米粒子的懸浮液，其黏度可因外加磁場而改變、而此一現象被稱為磁黏效應。本文旨在研究懸浮粒子粒徑與磁黏效應的關係，共完成如下三項工作。(i)透過對製程溫度的控制，以化學共沉澱法產生兩種不同粒徑的四氧化三鐵(Fe3O4)粒子：B粒子(溫度25°C，單體粒子平均粒徑Dmo = 6.49 nm，包覆油酸懸浮在煤油中粒子的z平均粒徑Dza ≈ 29 nm)、和C粒子(75°C下，Dmo = 9.44 nm及Dza ≈ 39 nm)。再利用此兩種粒子(均先包覆油酸)按不同比例分散在變壓器油內，以合成五種體積百分率均為2%的磁性奈米流體，粒子比例分別為：100% B粒子、95% B粒子和5% C粒子、90% B粒子和10% C粒子、80% B粒子和20% C粒子、及100% C粒子。(ii)以磁化儀量測上述五種流體的磁化率、並採用磁性粒徑分析法計算上述五種磁性奈米流體之磁性粒徑分佈。(iii)以改裝式布氏(Brookfield)黏度計，對上述五種流體在20°C及不同強度(60、100及140 Gauss)的週期性磁場下進行磁黏實驗，得到以下結論：(1)磁性奈米流體在磁場作用下之黏度增益值隨添加之大顆粒數量增加而提升。(2)磁性奈米流體之黏度於磁場開啟時快速增加、在磁場關閉時亦可迅速回復原值。(3)添加不同數量之大顆粒子於以小顆粒子為主體之奈米流體中，從黏度實驗及粒徑分佈結果可判斷其黏度增益值主由較大顆粒之粒子所造成；文獻中(Odenbach, 2002)有提出一項猜測，指因大顆粒子的存在，使粒子間較易形成磁誘導鏈狀結構、而導致黏度增加，本研究對此一猜測提供了實驗佐證。

關鍵字

磁性奈米流體；磁黏效應；四氧化三鐵粒子；磁性粒徑分析；粒徑分佈

並列摘要

Magnetic nanofluid is a liquid suspended stability with magnetic nano particles. Its viscosity can be altered by the application of a magnetic field, and the associated phenomenon is called magnetoviscosity. The goal of this thesis is to study the effect of particle size distribution on magnetoviscosity. The works completed are as follows. (i) Through the temperature control in the chemical processes, two Fe3O4 particles with different sizes can be generated using the chemical co-precipitation method: the B particles (reaction temperature 25°C, the average monomer diameter Dmo = 6.49 nm, and the z-average particle diameter, Dza ≈ 29 nm, for particles coated with oleic acid in kerosene), and the C particles (reaction temperature 75°C, Dmo = 9.44 nm and Dza ≈ 39 nm). Five nanofluids with different compositions of B and C particles (coated with oleic acid) were synthesized by dispersing them into transformer oil at volume fraction 2%, they are: 100% B particles, 95% B and 5% C particles, 90% B and 10% C particles, 80% B and 20% C particles, and 100% C particles. (ii) Measure the magnetization of the above five fluids, and apply the results to calculate the magnetic particle size distribution using magnetogranulometric analysis. (iii) Measure the viscosity of those five nanofluids using a modified Brookfield viscosity at 20°C in an applied cyclic magnetic field with different strengths (60、100, and 140 Gauss). We found: (1) The viscosity enhancement is proportional to the amount of larger (C) particles in the fluid. (2) The fluid responds sharply as the magnetic field is switched on and off, and can recover the original value without magnetic effect when the field is off. (3) By comparing the viscosity enhancement with the magnetic particle size distribution, it was found that the viscosity enhancement is mainly associated with the larger particles in the fluid. This supports experimentally the reasoning proposed by Odenbach(2002), that particle chains can be initiated and formed easily in nanofluids through the dipole-dipole interaction associated with larger particles, in comparing with that associated with smaller particles.

並列關鍵字

Magnetic nanofluids ； Magnetoviscous effect ； Fe3O4 particles ； Magnetogranulometric analysis ； Particle size distribution

參考文獻

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磁性奈米流體中粒徑分佈與磁黏效應的關係

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