CAREER: Magnetic Field-Driven Self-Assembly of Magnetic
and Multifunctional Nanochains in Bulk Matrices
(DMR-1056653)
Joseph B. Tracy, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695
Magnetic Field-Directed Self-Assembly
uniform field:
solenoid
inhomogeneous
field:
permanent magnet
t
t
Large-Scale Synthesis of Gold Nanorods (GNRs) with Secondary Growth
Polarization-Controlled Photothermal Heating in Aligned Polymer Fibers
J.B. Tracy, T.M. Crawford MRS Bulletin 2013, 38, 915-920.
K.A. Kozek, K.M. Kozek, W.-C. Wu, S.R. Mishra, J.B. Tracy Chemistry of Materials 2013, 25, 4537.
P.J. Krommenhoek, J.B. Tracy Particle & Particle Systems Characterization 2013, 30, 759.
S. Maity, K.A. Kozek, W.-C. Wu, J.B. Tracy, J.R. Bochinski, L.I. Clarke
Particle & Particle Systems Characterization 2013, 30, 193.
• Application of a magnetic field aligns the moments of
magnetic nanoparticles
• Attractive head-to-tail interactions drive assembly into
chains, and repulsive interactions push the chains apart
cross section of side view
end viewFe3O4
nanoparticlesside view
H (Oe)-1000 -500 0 500 1000
M (
arb
itra
ry u
nits)
parallel
perpendicular
no field (control)
H (Oe)-400 -200 0 200 400
M (
arb
itra
ry u
nits)
parallel
perpendicular
no field (control)
T (K)0 50 100 150 200 250 300
M (
arb
itra
ry u
nits) parallel
perpendicular
no field (control)
5 K hysteresis
300 K hysteresis
thermal remanent magnetization
• Bulk polymerization of methacrylates containing Fe3O4
nanoparticles in an applied field (10 kOe) in a plastic cuvette (1
cm path length) preserves the chains
• The chains exhibit significant magnetic anisotropy and magnetize
more easily parallel rather than perpendicular to the chain axis
5 µm
5 µmhorizontallypolarized light
808 nm
vert
ical
lyp
ola
rize
d li
ght
80
8 n
m
5 µm
100 nm
808 nm
excitation
temperature monitoring
via temperature-sensitive
dye molecule within the
fibers
Growth solution:
CTAB, HAuCl4, AgNO3
ascorbic acid (AA)
1. Synthesize small seeds 2. Primary growthseeds
3. Secondary growth
Continuous AA addition
with stirring
Seed solution:
CTAB, HAuCl4 NaBH4 1.1 mol AA:
mol Au≥ 1.5 mol AA: mol Au
wavelength (nm)
400 500 600 700 800 900
ab
so
rba
nc
e
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
seed: 1.10 AA:Au
1.20 AA:Au, 31 min
1.30 AA:Au, 62 min
1.40 AA:Au, 93 min
1.50 AA:Au, 124 min
1.59 AA:Au, 155 min
wavelength (nm)
400 500 600 700 800 900
ab
so
rba
nc
e
0.0
0.5
1.0
1.5
2.0
seed
1.25x IR
2.5x IR
5x IR
10x IR
1.25 2.5
seed
5 10
seeds
1.10 AA:Au
57 15 nm
1.20 AA:Au
65 17 nm
1.30 AA:Au
71 19 nm
1.40 AA:Au
76 21 nm
1.50 AA:Au
83 22 nm
1.59 AA:Au
83 23 nm
61 15 nm
83 24 nm
71 27 nm
10 nm longer
11 nm thicker
22 nm longer
9 nm thicker
190 mg GNRs
per L solution
• At a fast injection rate (IR) of ~2.5 hours, the aspect ratio is preserved, while increasing the size
• The aspect ratio decreases as the injection rate is decreased from 10× IR (~3 hours) to 1.25× IR (~23 hours)
• During electrospinning, gold nanorods (GNRs) align within poly(ethylene oxide) (PEO) fibers
• Linearly polarized light on resonance with the longitudinal surface plasmon resonance of the
GNRs at ~800 nm heats and melts the fibers only when polarized parallel to the fibers and the
GNR long axes. Therefore, polarization-selective heating is possible.
• The temperature of the fibers can be measured in situ using a perylene, a fluorescent dye
