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磁流體實驗. Role of magnetic fluids. In the early 20 th century. Solid state physics. . 1960 ~. Condensed matter physics. Nanoscale science & technology. . Including Soft Materials : Fluids Liquid crystals Polymers Emusions Colloids. Nanoparticles
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Role of magnetic fluids In the early 20th century Solid state physics 1960 ~ Condensed matter physics Nanoscale science & technology Including Soft Materials : Fluids Liquid crystals Polymers Emusions Colloids Nanoparticles Nanostructured materials Nanodevices Magnetic fluids
Outline • What Is Magnetic Fluids (Ferrofluids)? • Properties of Magnetic Fluids • Properties of Magnetic Fluid Thin Films under Magnetic Fields (perpendicular/parallel) • Ordered Structures of Magnetic Fluid Films • Optical Properties of Magnetic Fluid Films • Outlook
What Is Magnetic Fluids (Ferrofluids) ? Liquid Carrier 100Å Magnetic particle Surfactant (界面活性劑)
Properties of Magnetic Fluids Fundamental Properties - Magnetic Characterizations - I 0 I = 0 H I/r
- Thermal Conductivity - Magnetic fluid has good thermal conductivity. (Air: 26.2 mW/m/k @ T = 300 K)
Applications - Loudspeaker (high thermal conductivity of MF) -
Magnets Oil Liquid Research Ltd. Magnetic fluid - Sealing of magnetic fluids - S High-pressure region Low-pressure region MF N
- Other Applications • Inkjet printing : coding (magnetic particles) • Surface polishing (nanoparticles) Most applications are focused on mechanical purposes. Applications in bio-medical and optical-electronics are new interesting topics
mixing coating Water FeCl2 & FeCl3 H2O NH4OH co-precipitate, Fe3O4 dextran Fe3O4 centrifugal removing salt residue & large particles Dextran removing unbound dextran gel filtration chromatography homogeneous water-basedFe3O4 magnetic fluid • Preparation of Magnetic Fluids
FeCl2 + FeCl3+8NaOH → Fe(OH)2 + Fe(OH)3 + 8NaCl • Fe(OH)2 + 2Fe(OH)3→ Fe3O4 + 4 H2O
Properties of Magnetic Fluid Thin Films under Magnetic Fields (perpendicular/parallel) Ordered Structures of Magnetic Fluid Films Under Perpendicular Magnetic Fields Under Parallel Magnetic Fields Optical Properties of Magnetic Fluid Films Magnetochromatics (perpendicular) Birefringence (parallel) Transmittance (perpendicular/parallel) Refractive Index (perpendicular)
H - Formation of Ordered Structure in a Magnetic Fluid Film - Top View glass Magnetic fluid Si wafer/ glass H.E. Horng et al., JAP, 81, 4275(1997) APL, 75, 2196(1999) APL, 79, 2360(2001)
Ordered Structures of Magnetic Fluid Films Magnetic fluid film Under Perpendicular Magnetic Fields - Observation of Ordered Structure in a Magnetic Fluid Film - Magnetic fluid Au
5 m H = 53 Oe, d = 5.14 m H = 0 Oe H = 34 Oe H = 77 Oe, d = 3.36 m H H =630Oe, d = 2.37 m H = 560 Oe, d = 2.37 m H = 210 Oe, d = 3.27 m H =200 Oe, d = 3.36 m ~1 m, h~6 m 107 ~ 108 particles Ms = 5.6 emu/g, T = 18.0 C, dH/dt = 5 Oe/s, L = 6 m
Fast Fourier Transformation r 10 m The ordered structure is characterized by d (distance between two neighboring columns, d varies from submicron to several m): d = 2/k 磁點排列成 六角形分佈 H H.E. Horng et al.,JAP, 81, 4275(1997) APL, 75, 2196(1999) APL, 79, 2360(2001)
- Control Parameters for the Magnetically Tunable Ordered Structure - Sweep rate Film thickness Concentration Temperature Material . . . Important Result: Well-controlledandtunableordered structure
Magnetochromatic Effects in Magnetic Fluid Thin Films H.E. Horng, Chin-Yih Hong, Wai Bong Yeung, and H.C. Yang Cover page of Applied Optics, Vol. 37, 1 May(1998)
Optical Properties of Magnetic Fluid Films A B D I J I G F E G H Magnetochromatics (perpendicular) A: PC B : Camera C: Solenoid D : Magnetic fluid film E : Mirror F : Telescope G : White source H :Current source I : Lens J : Aperture C H.E. Horng et al., Appl. Opt., 37, 2674(1998) JAP, 83, 6771(1998) JAP, 88, 5904(2000)
- Controllable Magnetochromatics - H = 50 Oe (d = 2.34 m) H = 100 Oe (d = 2.26 m) H = 200 Oe (d = 1.64 m)
Under Parallel Magnetic Fields H = 200 Oe dH/dt = 100 Oe/s W = 10 μm L = 1.5 μm Ms = 17.6 emu/g td = 3 min Δx = 1.45 μm H x 10 m - Periodic one dimensional grating -
Magnetochromatics of the Magnetic Fluid Film under a Dynamic Magnetic Field Herng-Er Horng, S.Y. Yang, S.L. Lee, Chin-Yih Hong, and H.C. Yang Appl. Phys. Lett., 79, 350 (2001) H (Oe) 60 200 = 15.2o
We have well controlled and understood the ordered structures and the optical properties of the magnetic fluid thin films. Future Works Applications of Magnetic Fluids
m m 10 10 m m Magnetic Field Dependent nMF(H) The nMF is increased under a higher field. The increase in nMF is suggested to be due to the column formation.
Working Principle (a) H = 0, ncore > nMF, total reflection occurs IH=0 Magnetic fluid core cladding (b) H 0, ncore< nMF, total reflection vanishes IH0 IH0 < IH=0
Modulation of Transmitted Light Intensity L = 796 m Ms = 0.61 emu/g H (Oe) Transmission loss (%) Transmission loss = (IT-IT,H=0)/IT,H=0
- Experimental Setup H Transmission axis Transmission axis He-Ne laser ( = 632.8 nm) w/0.01o resolution Polarizer Ein Eout Sample Analyzer
Summary The refractive index of magnetic fluid films can well manipulated. The feasibility of the magnetic-fluid-based optical modulator and switch is demonstrated.
What else? • Conclusions Magnetically labeled immunoassay Photonic Crystal Switch CWDM Modulator Magnetic fluids