Surface characterization and electrochemical behavior of colloidal particles
C. PEPIN , S.H FOULGER.
E’ox (V) Eox (V) HOMO (eV) Egap (eV) LUMO (eV)
PA particles with carbazole moieties
1.15 5.55 -5.55 3.5 -2.05
PA particles with oxadiazole moieties
1.34 5.74 -5.74 3.33 -2.44
Stability and surface charge density
Zeta potential PA particles
pH
0 2 4 6 8 10 12
Zet
a P
oten
tial (
mV
)
-75
-70
-65
-60
-55
-50
-45
-40
-35
Zeta potential of PS partices vs pH
pH
0 2 4 6 8 10
Zet
a P
oten
tial (
mV
)
-60
-50
-40
-30
-20
-10
Zeta potential: -electrokinetic potential in colloidal system related to the stability of the colloidal dispersion -calculated at the surface of the shear- calculated from the electrophoretic mobility of the particles
Surface charge density:-determine the number of charge at the surface of the particles-use of conductometric titration-calculation of the surface charge density in µC/cm²
Titration of PA paticles
V(NaOH) added (µL)
0 10 20 30 40 50 60
Con
duct
ivity
(µ /
cm)
0,5
0,6
0,7
0,8
0,9
1,0
1,1
Titration of PS particles
V(NaOH) added (µL)
0 5 10 15 20 25 30 35
Co
nd
uct
ivity
(µ /
cm)
0,26
0,28
0,30
0,32
0,34
0,36
0,38
0,40
0,42
0,44
0,46
• PS particles : Charge density : 0.0225 µC/cm²
• PA particles : Charge density : 0.0218 µC/cm²
Cyclic voltammogram of PA particles
Potential (V)
-0,50,00,51,01,52,0
Cur
rent
(A
)
-2,5e-5
-2,0e-5
-1,5e-5
-1,0e-5
-5,0e-6
0,0
5,0e-6
Cyclic voltamogramm for PA/AC particles
Potential (V)
-0,50,00,51,01,52,0
Cur
rent
(A
)
-1e-4
-8e-5
-6e-5
-4e-5
-2e-5
0
2e-5
4e-5
Cyclic voltammogram of PA/AO particles
Potential (V)
-0,50,00,51,01,5
Cu
rre
nt (
A)
-2,5e-5
-2,0e-5
-1,5e-5
-1,0e-5
-5,0e-6
0,0
5,0e-6
1,0e-5
Electrochemical behavior
Cyclic Voltammetry: -important technique that can be used to determine the energy profile of an organic material HOMO-cycling a potential across a sample and measuring the resulting current
onset value of oxidation (E’ox)
Eox = E’ox +4.4 IP = -e.Eox =HOMO
Absortion carbazole molecules as a function of energy
Energy (eV)
23456
Abs
orp
tion
-0,5
0,0
0,5
1,0
1,5
2,0
2,5
Absorption of PA/AC paritcles as a function of energy
Energy (eV)
23456
Ab
sorp
tion
0,0
0,2
0,4
0,6
0,8
1,0
1,2
Absorption of oxadiazole molecules as a function of energy
Energy (eV)
23456
Ab
sorp
tion
0,0
0,2
0,4
0,6
0,8
1,0
Absorption of PA/AO particles as a function of energy
Energy (eV)
123456
Abs
orpt
ion
0,0
0,2
0,4
0,6
0,8
1,0
1,2
UV-VIS Spectroscopy:-use to determine optically the energy band gap-onset of absorption correspond to the energy needed to promote an electron from the HOMO to the LUMO
Onset of absorption= Egap
The energy profile of the material :
Ionization potentialElectron affinityBand gap energy
oxidation charge removal from the HOMO Ionization potential
reduction charge removal from the LUMO Electron affinity
Study of the redox reactions
Conclusion-study of the zeta potential of PA particles; the results show their stability over a range of pH from 9 to 2- Determination of HOMO, LUMO and energy band gap for PA/AC and PA/AO particles
Acknowledgements: Prof. S.H. Foulger, Foulger’s group (Michael, Ali , Ryan and Parul), Prof. K.Richardson and Prof. E. Fargin for the MILMI Master.
Introduction
“Particle-device” made of Poly(propargyl acrylate) with a hole transporter, an electron transporter and an emissive material
colloidcore
h+
e-
h+e-
h+
e-
h+
e-
hole transporter Oxadiazole molecule (AO)
electron transporter Carbazole molecule (AC)Poly(propargyl acrylate) (PA)
-understand the behavior of poly(propargyl acrylate) (PA) particles with surface-attached hole- and electron-transporting moieties
-characterize their colloidal stability: Zeta potential and surface charge density
-characterize their electrochemical behavior with the determination of the HOMO energy level, LUMO energy level and the energy band gap: Cyclic voltammetry and UV-VIS spectroscopy
Objective
-Ongoing interest in research focused on developing polymeric organic-light-emitting-devices (OLED)
-OLEDs could present better properties such as the ease of device fabrication, low material cost, low
environmental impact, facile synthesis routes and high rates of improvement in luminous efficiency
-A hole transporting group and an electron transporting group were “clicked” on the surface of a polymer particle to make an individual “particle device”.