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