HAL Id: hal-02894658
https://hal.univ-angers.fr/hal-02894658
Submitted on 9 Jul 2020
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Phase segregation on electroactive mixed SAMs: a numerical approach for describing interactions
O. Alévêque, Pierre-Yves Blanchard, Tony Breton, M. Dias, Christelle Gautier, E. Levillain
To cite this version:
O. Alévêque, Pierre-Yves Blanchard, Tony Breton, M. Dias, Christelle Gautier, et al.. Phase segrega- tion on electroactive mixed SAMs: a numerical approach for describing interactions. The 61st Annual Meeting of the International Society of Electrochemistry, Sep 2010, NICE, France. �hal-02894658�
The Laviron's interaction model, dedicated to randomly distributed electroactive adsorbed species, was extended to a non-random distribution in order to extract the current–voltage characteristics from any surface distribution of electroactive centers on self-assembled monolayer (SAM). Confronted to electrochemical behaviour of nitroxyl radical SAMs, the agreement observed between theory and experiments provides evidence of a distribution independence of the interaction parameters.
Phase segregation on electroactive mixed SAMs:
a numerical approach for describing interactions
O. Alévêque, P.-Y. Blanchard, T. Breton, M. Dias, C. Gautier, E. Levillain
olivier.aleveque@univ-angers.fr
Laboratoire MOLTECH ANJOU - Université d’Angers - CNRS UMR6200 - 2, boulevard LAVOISIER - 49045 ANGERS Cedex - FRANCE
We generalized the LAVIRON’s interaction model by introducing the ɸ parameter calculated in the first step.
Generalization of Lateral Interaction Model for any surface distribution Nitroxyl radical self-assembled monolayers on gold
Application
C15-TEMPO Electroactive
C 10 SH
Non electroactive
Can we obtain informations about the surface distribution with the shape of cyclic voltammograms ? Surface distribution is controlled by several factors
like the elaboration protocol and the binary used
0.3 0.4 0.5 0.6 0.7
-20 -15 -10 -5 0 5 10 15 20
I / A
E / V(AgAgNO
3)
N OH
N O
N O e-
e- e-, H+
e-, H+ N
OH
N O
N O e-
e- e-, H+
e-, H+
+ e
-Random distribution Phase segregation
For a fast reversible system (k s = ∞),
the i-E characteristics can be expressed as : CNT model
RND model
FIRST STEP : NUMERICAL MODEL
Generation of two surface distributions with two numerical models simulating the phase of adsorption :
• A "constraint" model (CNT) which simulates preferential adsorption of a molecule in interaction with a similar molecule.
• A "random" model (RND) which simulates the absence of interaction between molecules.
ɸ is representative of lateral interactions per electroactive site.
q is the normalized surface coverage of electroactive species
For a given q T matrix image, with random (RND) or non random (CNT) distribution, and initially composed of R species (q R = q T ), we :
• simulate an oxidation process (left)
• follow the interactions between redox species (right) (here f OO (q O ,q T ) for q T = 50%).
SECOND STEP : GENERALIZATION OF THE MODEL
In both models, numerical simulations exhibited a linear dependence of f ij (q O , q T ), leading to :
For a random distribution :
In order to test this new model, we elaborate C15-TEMPO mixed SAMs using two protocols leading to two surface distributions.
Successive adsorptions of C15-TEMPO and C 10 SH Favors random distribution
Partial desorption of a densely packed SAM of C15-TEMPO under ultrasonication Favors surface segregation
The 61st Annual Meeting of the International Society of Electrochemistry
September 26th - October 1st, 2010, Nice, France
G = 1.13 S = 1.14 G = 1.13 S = 1.19
Distribution independence of G and S parameters. The surface distribution ɸ can be deduced with the shape of cyclic voltammograms.
0 '
p T T
E ( ) E RT
n ( )
F S
q f q
2 2
max T
T T
p
n F vA i ( )
RT 2 2 G ( )
q
q f q
T T
RT 3 2
FWHM( ) 2ln 2 2 3
n G
F ( )
2
q f q
OO RR OR RO OO RR OR RO
G S
with = a + a - a - a and = a - a + a - a
T
ij O T j
T
( )
( , ) N N the maximum possible neighbors
with
i and j are species O or R f q q f q q
q
T T
ij O T j j j
T T
N
RND( ) N
( , ) f q q N
f q q q q q
q q
0
0
O O R
T T
s max
1
R R O
T T
T
OO OR
RR RO
T T
O O
max '
T
'
(t) exp 2 (t) 2 (t)
i t nFAk
(t) exp 2 (t) 2 (t)
d d
i t nFA nFA
dt dt
E - E
where exp
( ) (
nF and E
a a
RT E
)
( ) (
a a )
f q f q
f q f q
q q q
q q
q q q q q
q
O 0
R 0 '
s
b - RT ln
nF b
and n, F, A, R, k , T, E have their usual meanings.
OO RR O
O R
T O R
R RO
and , normalized surface coverage of oxidized and reduced species = + , normalized surface coverage
and are the interaction constants between molecules of O
a , a , a
, molec a
ules of
q q
q q q
i
T
R and molecules of O and R respectively.
a is positive for an attraction and negative for a repulsion.
The a values are assumed to be independent of the potential.
, "segregation factor", is
( ) rep r
f q esentative of the average
number of lateral interactions per electroactive site
T R D
T N
( ) q f
f q
T TT T
T
