supporting information for 0.004 0.006 absorbance wavenumber (cm-1) ph2 ph3 ph4 ph5 ph5.5 ph6 ph6.5...
TRANSCRIPT
Supporting Information for
Tunable pH and Temperature Response of Weak Polyelectrolyte Brushes: Role
of Hydrogen Bonding and Monomer Hydrophobicity
Yiming Lu, Aliaksandr Zhuk,Li Xu, Xing Liang, Eugenia Kharlampievaand Svetlana
Sukhishvili
Fig. S1. A calibration curve obtained with mixtures of A) PEAA and PNIPAM or B)
PMAA and PNIPAM of various compositions used for conversion of FTIR
absorbances to molar compositions of P(aAA-co-NIPAM) copolymers.
Electronic Supplementary Material (ESI) for Soft MatterThis journal is © The Royal Society of Chemistry 2013
0 2 4 6 80
10
20
30
40
50
0 2 4 6 80
10
20
30
40
50 B
PAA PMAA PEAA
A
Th
ickn
ess
(n
m)
Time (hr)
Th
ick
ne
ss
(n
m)
Time (hr)
P(AA-co-NIPAM) P(MAA-co-NIPAM) P(EAA-co-NIPAM)
0
3
6
9C
PEAAPMAACoCo HomoHomo
PAACoHomo
Gro
wth
Rat
e (n
m/h
r)
Fig. S2. Kinetics of brush growth for 7:3 P(aAA-co-NIPAM) copolymer and PaAA
homopolymer brushes (A and B, respectively) as measured by ellipsometry. Each data
point is an averaged over three points. C) Comparison of growth rates for PaAA
homopolymers (solid bars) and P(aAA-co-NIPAM) copolymer brushes (patterned
bars).
Electronic Supplementary Material (ESI) for Soft MatterThis journal is © The Royal Society of Chemistry 2013
0 5 10 15 20 250
10
20
30
40
50
Th
ickn
ess
(nm
)
Time (hr)
Fig. S3. Kinetics of brush growth for PNIPAM homopolymer brush.
Fig. S4. Representative 1H NMR spectrum of P(EAA-co-NIPAM) from solution
polymerization. Solvent (methanol-d4) peaks with chemical shifts at 4.9 ppm and 3.29
ppm are shown by arrows.
Electronic Supplementary Material (ESI) for Soft MatterThis journal is © The Royal Society of Chemistry 2013
Fig. S5. FTIR transmission measurements of P(AA-co-NIPAM) (A),
P(MAA-co-NIPAM) (B) and P(EAA-co-NIPAM) (C) brushes synthesized on undoped
silicon wafers. Comparison of copolymer compositions included within brush or
synthesized in solution using the same RAFT procedure and the same 7:3
acid:NIPAM molar feed ratio is illustrated in Table 2. Fractions of 2-alkylacrylic acid
were determined using calibration curves shown in Fig. S1. In the cases of
P(AA-co-NIPAM) and P(MAA-co-NIPAM) brushes (thicknesses 34.8nm and 35.5nm,
respectively), measurements were performed with single silicon wafers. In the case of
thinner P(EAA-co-NIPAM) brushes (thickness ~10nm), spectra were collected with a
stack of three brush-modified wafers.
Electronic Supplementary Material (ESI) for Soft MatterThis journal is © The Royal Society of Chemistry 2013
DC
B
PMAA pH 7PMAA Dry
PAA pH 7
10m10m
10m10m
10m10m
80nm20nm
0nm0nm
80nm
0nm10m10m
20nm
0nm
PAA Dry A
Fig. S6. AFM measurement of dry (A,C) and wet (B,D) PAA and PMAA
homopolymer brushes, showing brush swelling ratios 3.5~4 times. Dry thickness of
PAA and PMAA brushes was ~12 nm and ~ 15 nm, respectively.
Electronic Supplementary Material (ESI) for Soft MatterThis journal is © The Royal Society of Chemistry 2013
Fig. S7 FTIR spectra of P(EAA-co-NIPAM) copolymer brush exposed to pH 2 or pH
8 prior to measurements in a dry state (brush thickness ~ 10 nm). The absence of 1705
cm-1 band with wafers pre-exposed to pH 8 indicates complete ionization of
carboxylic groups. FTIR spectra were collected with stacks of three identical
brush-modified undoped wafers.
Electronic Supplementary Material (ESI) for Soft MatterThis journal is © The Royal Society of Chemistry 2013
1500 1600 1700 1800
0.000
0.004
0.008
0.012
0.016
Ab
sorb
ance
Wavenumber (cm-1)
pH2 pH3 pH4 pH5 pH5.5 pH6 pH6.5 pH7 pH7.5 pH8 pH9
PMAA BrushA
2 3 4 5 6 7 8 9
0.00
0.25
0.50
0.75
1.00PMAA Brush
Ion
izat
ion
Deg
ree
pH
B
2.0
2.4
2.8
3.2
3.6
4.0
Sw
elling
Ra
tio
1500 1600 1700 1800
0.000
0.002
0.004
0.006
Ab
sorb
ance
Wavenumber (cm-1)
pH2 pH3 pH4 pH5 pH5.5 pH6 pH6.5 pH7 pH7.5 pH8 pH9
P(MAA-co-NIPAM) BrushC
1 2 3 4 5 6 7 8 9 10
0.00
0.25
0.50
0.75
1.00 P(MAA-co-NIPAM) Brush
Ion
izat
ion
De
gre
e
pH
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Sw
ellin
g R
atio
D
Fig. S8 FTIR spectra (A, C), calculated ionization degrees (α), and ellipsometric
swelling ratios (B, D) for PMAA and P(MAA-co-NIPAM) brushes at 25oC. Blue
dashed lines indicate pH values (pH 4.8 for PMAA and pH 5.8 for
P(MAA-co-NIPAM) of half-swollen brushes, which correspond to α=0.125 for
PMAA, and to α=0.25 for P(MAA-co-NIPAM) brush.
Electronic Supplementary Material (ESI) for Soft MatterThis journal is © The Royal Society of Chemistry 2013
2 3 4 5 6 7 8
20
30
40
50
60
70
80
2 3 4 5 6 7 8 2 3 4 5 6 7 8
2 3 4 5 6 7 8
20
30
40
50
60
70
80
2 3 4 5 6 7 8 2 3 4 5 6 7 8
Co
nta
ct A
ng
le (
o)
pH
No Salt 0.2M NaCl
A PAA
P(aAA) Brush
B PMAA
pH
C PEAA
pH
D P(AA-co-NIPAM)
Co
nta
ct A
ng
le (
o)
pH
No Salt 0.2M NaClP(aAA-co-NIPAM) Brush
E P(MAA-co-NIPAM)
pH
F P(EAA-co-NIPAM)
pH
Fig. S9 Contact angles of P(aAA) homopolymer and P(aAA-co-NIPAM) copolymer
brushes as a function of pH measured with 0.01 buffer solutions with and without
0.2M NaCl.
Electronic Supplementary Material (ESI) for Soft MatterThis journal is © The Royal Society of Chemistry 2013
Table S1.Grafting densities for homo- and copolymers calculated based on GPC data
of polymer solutions and ellipsometric thicknesses of corresponding brushes.
Polymer Homopolymer
PAA PMAA PEAA
Mn (g/mol) 91,900 78,100 84,500
PDI 1.12 1.16 1.56 Thickness
(nm) 35 28 6.5
Grafting Density ~ 0.27 ~ 0.26 ~ 0.09
(σ, chain/nm2)
Polymer Copolymer (aAA:NIPAM = 7:3)
P(AA-co-NIPAM) P(MAA- co-NIPAM) P(EAA- co-NIPAM)
Mn (g/mol) 76,800 85,600 79,400
PDI 1.17 1.18 1.24
Thickness (nm) 32 25 10.3
Grafting Density ~ 0.24 ~ 0.21 ~ 0.1
(σ, chain/nm2)
Electronic Supplementary Material (ESI) for Soft MatterThis journal is © The Royal Society of Chemistry 2013