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.

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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).

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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.

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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.

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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.

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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.

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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.

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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.

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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