Synthesis and Properties of Ligand-Coaatedted Meetal tal ...

Synthesis and Properties of
Ligand-Coated Metal Nanoparticles

Chemistry of Nanomaterial Systems
Chem 8813

November 17, 19, and 21, 2003

Joseph W. Perry

School of Chemistry and Biochemistry
Georgia Institute of Technology

Outline

o Synthesis of ligand-coated metal nanoparticles
o Processing and thin film properties of metal

nanoparticles
o Attachment of conjugated chromophores to metal

nanoparticles and their optical properties.

Metal nanoparticles

molecule 1nm<d<100nm bulk material

d
Increasing size

nanoparticle

Surface plasmon resonance - Stabilization
collective excitation of the ‘free’
electrons within the conduction Æ Electrostatic
band -+ -+
+- - + -
+ +
- + - +
+ -+ + -+
- -

Æ Steric

Duomo, Milan Metal Ligands

Brust method for synthesis of Ag
nanoparticles

Thiolated ligands capping metallic cores
with “one phase” method*

AgNO3 + RSH EtOH (RSAg)n + H+ Layered
compound

Ag+ NaBH4 Ag0

(RSAg)n +mAg0 (RS)n Agm+n Nanoparticle

• Particle size controlled via ligand to salt molar ratio SSSSSASSgSSSSSSS
• Monolayer coverage 60 to 90%

• Multiple ligand types can be attached in one step with ligand mixtures

• Ligand composition can be modified via subsequent exchange reactions

*Brust et. al. Chem Commun., 1655, 1995.

Control of particle size

Ligands Particle Size histograms

increasing SH 10
ligand HS 9

3:1 ocanethiol/dodecanethiol 8 Average size=10.06nm

concentration 7
6
SH 5 50nm
HS 4
3
3:1 ocanethiol/dodecanethiol 2
1
0

diameter (nm)

35

30

25 Average size=4.91nm

20

15

10

5

0
diameter (nm)

Order-disorder behavior of
nanoparticle films

Solid interdigitated state liquid state

Solid de-interdigitated state

DHde-int DHsol

DSC- 4

Differential CAB1-cycle 1
Scanning 2 CAB1-cycle 2
Calorimetry
0

< ENDO -2 liquid decomposition

-4

DH
-6 deinterdigitation

-8

0 50 100 150 200 250 300

temperature C Pradeep et al, Phys. Rev. B, 2(62), R739,2000.

Badia et. al. Chem. Europ. J., 2(3), 359,1996.

Ligand Length Effect

Sample ligand DH(kJ/mol organic)* Temp(K)

d = 5 nm octadecanethiol 42.3 402
35.5
d = 5 nm dodecanethiol 402 increasing
length

d = 5 nm octanethiol 20.7 401

Result-
Extent of interdigitation lower for shorter ligands

* DH is for the ordered to disordered transition

Nanoparticle Size Effect

Sample ligand relative ligand
amount DH(kJ/mol org) Temp(K)

d = 5 nm octanethiol 1 20.7 401

larger d = 7 nm 1/3 13.5 401

d = 5 nm 3:1 oct/dod 1 20.7 382
larger d = 8 nm 1/2 5.7 377

Result- larger nanoparticles less curvature less interdigitation

Less ligand

Mixed Ligand Effect

Sample ligand DH(kJ/mol org) Temp(K)
d = 7 nm 3:1 oct/dod 5.7 377

N SH

d = 5 nm 6.0 384

1:3 carbazolethiol/oct

d = 5 nm 1:1:1 oct/hep/dod 9.5 380

d = 5 nm 1:1 octadecane/dodecane 20.6 420

d = 5 nm 3:1 hep/dod 14.1 384

Result
Ligands of differing lengths/types do not interdigitate well

IR evidence of chain disordering

Silver nanoparticles DSC peak @128ºC

CAB3 pellet IR CAB3 initial *Gold nanoparticle
heat@124C 10min
8 105 heat@143C 20min
heat@143 1 day
0
absorption(arb. units) -8 105
-1.6 106
-2.4 106 2950 2900 2850 2800
-3.2 106
-4 106 wavenumbers cm-1
-4.8 106

3000

*Badia A, et. al. Chemistry-A European Journal, 2:(3) 359-363 March 1996

Free energy of solvation

DGsolv = DGmelt + DGmisc

DGsolvation

Solid Solution

DGmelt DGmiscibility

liquid

DGsolv = DHmelt + DHmisc-TDSmelt -TDSmisc

Impact on polymer nanocomposite
film quality

Increasing nanoparticle solubility improves film quality

Original Film Decrease ligand length Improved Film

Ligand mixtures

200mm Ligand terminal groups

~5 x 1011 W/cm2 Increase core size 200mm

DHde-int = 42.3 kJ/mol org ~1.5 x 109 W/cm2

DHde-int= 5.7 kJ/mol org

Quasi-ordered Ligand Coated Ag
Nanoparticle films

@1220C @200C

De-interdigitated 10nm Interdigitated

Evidence for Thermal Annealing of
Quasi-Ordered Nanoparticle Films

SEM Reflectance of TEM
Annealed Thick film

As formed film with a 50 nm
thickness of ~ 20nm
Submonolayer Film

After 1 thermal cycle 10 nm 10 nm

After 4 thermal cycles After 5 thermal cycles