Agarose-based Hydrogel as an electrografting cell
Brigitte Mouanda*, Veronique Eyeffa, Serge Palacin
CEA-Saclay, DSM-DRECAM-SPCSI, F-91191 Gif-sur-Yvette Cedex, France
Supplementary Material
SM1: XPS spectra of the survey and the core levels C1s and O1s of the electrografted PNP
thin film on gold surface
20000
Au4f
Au4d
Au4p O1s
N1s
Counts/s
15000
10000
O1s
C1s
5000
0
1200
1000
800
600
400
200
0
Binding Energy/eV
Fig. Sup. Mat. a1: XPS global spectrum of electrografted PNP on gold slides.
The presence of the Au4f peak centred at 84 eV indicates that the thickness of the PNP
grafted film is less than 5 nm.
C1s
-C=C- (Phenyl)
Counts/s
2400
-C-N
1800
288
287
286
285
284
283
282
Binding energy/eV
Fig. Sup. Mat. a2: XPS spectrum of the C1s binding energy region of electrografted PNP on
gold slides.
The peak centred at 284 eV is attributed to the carbon double bond of the aromatic
nucleus. The deconvolution of this peak shows the carbon directly bonded to the nitrogen
atom.
1
O1s
Counts/s
3000
2500
538
536
534
532
530
528
Binding energy/eV
Fig. Sup. Mat. a3: XPS spectrum of the O1s binding energy region of electrografted PNP on
gold slides.
The peak centred at 533 eV is characteristic of the NO2 group.
SM2: Influence of the final potential
The influence of the final potential was studied with the couple NBDT/Acrylic acid. The
final potential applied to the gel varied from -0.8 V to -1.8 V. The electrochemical solution
was prepared by mixing 3.5 ml (3.7 M) of AA with 54 mg (2.3 10-2 M) of NBDT in 10 ml of
de-ionized water. The electrografting conditions were 10 voltammetric cycles from the
equilibrium to the final potential at 10 mV s-1 scan rate. The IRRAS spectra of the grafted
films represented in Fig. Sup. Mat. b show the influence of the final potential on the
percentage of transmittance of the major acid band at 1727 cm-1. Thicker grafted films are
obtained with more cathodic final potential
-0.8V
Transmittance / %
1.00
-1V
-1.4V
-1.2V
0.99
0.98
-C=O
acid
-1.6V
-1.8V
0.97
1900
1850
1800
1750
1700
1650
1600
Wavenumber/cm-1
Fig. Sup. Mat. b: IRRAS spectra of electrografted PAA on gold slides. Influence of the final
potential on the percentage of transmittance of the major acid band at 1727 cm-1.
.
2
SM3: Influence of the acrylic acid concentration
The influence of the concentration of acrylic acid was studied. The electrochemical
solution was prepared as described above, only the acrylic acid concentration was changed
between 3.7 M to 7.4 M. The electrografting conditions were 10 voltammetric cycles from the
equilibrium to the final potential at -1.8 V with 10 mV s-1 scan rate. The IRRAS spectra of the
grafted films represented in Fig. Sup. Mat. c show the influence of acrylic acid concentration
on the percentage of transmittance of the major acid band at 1727 cm-1. Thicker grafted films
are obtained when the concentration of the monomer increases in the electrochemical
solution.
3.7M
Transmittance/%
1.00
0.98
5.2M
0.96
0.94
-C=O
acid
0.92
7.4M
0.90
1800
1750
1700
1650
1600
Wavenumber/cm-1
Fig. Sup. Mat. c: IRRAS spectra of electrografted PAA on gold slides. Influence of the monomer
concentration on the percentage of transmittance of the major acid band at 1727 cm-1.
3
SM4: Influence of the gel thickness
All the conditions are identical to those applied in experiment SM2, only the gel thickness
was modified in the range 0.8 to 2.2 cm. In Fig. Sup. Mat. d, the thickness of the gel seems to
have a minor influence, as observed on the IRRAS spectra on similar samples. In fact, the
synthesis of grafted film requires very small quantities of compounds (≤ 10-6 mole). As
mentioned in the text the planarity and the pressure applied are the most important parameters
and explain the weak variations observed in IRRAS spectra.
3.5
-1
% CO (acid) at 1727 cm (FTIR)
4.0
3.0
2.5
2.0
1.5
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
-1
Gel thickness/cm
Fig. Sup. Mat. d: Influence of the gel thickness on the percentage of transmittance of the major
acid band at 1727 cm-1.
4
SM5: Repetitiveness of the process
All the conditions are identical to those applied in experiment SM2. For this test, the
agarose gel was immersed only once in the electrolytic seeding solution and then used several
times for hydrogel-cell electro-induced radical grafting. The IRRAS spectra of the PAA
grafted films are collected on Fig. Sup. Mat. e. The results show that agarose gel can be used
several times without refilling and without any significant decrease in the thickness of the
resulting grafted films.
1.2
x = experiment
1
Transmittance /%
1
5,6%
1.1
2
5,1%
3
4,5%
1.0
4
2,5%
5
4,2%
0.9
6
-C=O
acid
0.8
2000
3,9%
1500
1000
Wavenumber/cm-1
Fig. Sup. Mat. e: IRRAS spectra of electrografted PAA on gold slides synthesized one after
the other with an agarose gel immersed only once in the electrolytic seeding solution.
5
SM6: Comparison HEMA/AA (same conditions)
The HEMA was compared with AA in similar conditions. So, the electrochemical solution
was prepared by mixing 3.5 ml (3.7 M) of AA or 8 ml (3.7 M) of HEMA with 70 mg (3 10 -2
M) of NBDT in 10 ml of de-ionized water. The electrografting conditions were 10
voltammetric cycles from the equilibrium to the final potential (-1.8 V) and at 10 mV s-1 scan
rate. The IRRAS spectra of the grafted films represented in Fig. Sup. Mat. f are almost the
same, which implies that film thicknesses are very close.
1.02
1.01
PAA
Transmittance /%
5.7%
1.00
-C=O
acid
0.99
NO2
0.98
0.97
4.8%
PHEMA
-C=O
ester
0.96
4000
3500
3000
2500
2000
1500
1000
Wavenumber/cm-1
Fig. Sup. Mat. f: IRRAS spectra of electrografted PAA and PHEMA on gold slides in the
same conditions.
6
SM7: Agarose gel synthesized according to the “monomer (HEMA)-inside” route
IRRAS was used to check the behaviour of HEMA added to the starting agarose gel
solution before the heating step. Following that preparation route, the monomer was present in
the gel from its formation. Only the diazonium salt was added by diffusion just before using
the hydrogel-cell.
The IRRAS spectrum (Fig. Sup. Mat. g) of the gel synthesized in presence of the HEMA
monomer shows that:
The vinylic monomer resists to the temperature applied during the gel preparation, as
shown by the presence of the vinylic groups C=C at 1636 cm-1.
- The vinylic monomer is deeply embedded within the agarose gel, as shown by the
shift of the CO stretching band from 1715 cm-1 (“H bond free C=O") to 1703 (“H
bonded C=O"). H-bonds indeed develop when HEMA is surrounded by dextran
molecules within the gel
Actually, the IRRAS spectrum of the HEMA monomer in its liquid state already shows a low
amount of H bonded C=O (see the shoulder on Fig. Sup. Mat. g, bottom part), that arises from
direct H bonding between HEMA molecules, together with a major contribution at 1715 cm-1
from the H-bond free HEMA molecules. That latter part is absent in the gel.
1.1
HEMA monomer
Transmittance / %
1.0
0.9
0.8
0.7
a/b = 0.37
a = -C=C
b = -C=O (ester)
a
0.6
b
0.5
a
0.4 Agarose gel + HEMA "inside"
a/b = 0.31
0.3
4000
b
3500
3000
2500
2000
1500
1000
Wavenumber/cm-1
Transmittance/%
1.0
HEMA "immobilized" in the gel
0.8
0.6
1715.6 cm-1
0.4
1703 cm-1
HEMA liquid state
1750
1700
1650
Wavenumber/cm-1
Fig. Sup. Mat. g: IRRAS spectra of HEMA monomer: spectrum of the agarose gel containing
HEMA monomer compared with the spectrum of the liquid HEMA monomer. The bottom
part shows a zoom of the C=O region for both spectra.
7
The IRRAS spectra in Figure (Sup. Mat. h) of the gel synthesized in presence of the HEMA
monomer and the gel immersed in HEMA/NBDT/H2SO4 aqueous solution show that the
HEMA concentration in the contact area increases by a factor 3 when the gel is prepared in
presence of the monomer.
1.15
"HEMA-inside" route
Transmittance (%)
1.10
1.05
-C=O ester
1.00
0.95
15%
0.90
"HEMA-free"route
0.85
5%
0.80
0.75
4000
3500
3000
2500
2000
1500
1000
Wavenumber/ cm-1
Fig. (Sup. Mat. h): IRRAS spectra of HEMA monomer: spectrum of the agarose gel
containing HEMA monomer compared with the spectrum of the gel immersed in HEMA
aqueous solution.
8