1

Large area defrosting windows based on

electrothermal heating of highly conducting and

transmitting Ag wire mesh

S. Kiruthika, Ritu Gupta# and Giridhar U. Kulkarni

*

Chemistry & Physics of Materials Unit and Thematic Unit of Excellence in Nanochemistry,

Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O.,

Bangalore 560 064, India

#Author’s Present Address:

Birck Nanotechnology Centre, Purdue University, West Lafayette, Indiana-47907, USA

Electronic Supplementary Material (ESI) for RSC Advances.This journal is © The Royal Society of Chemistry 2014

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S1-Characterization of crackle precursor

500 nm

(a) (b)

4000 3000 2000 1000

0.0

0.2

0.4

0.6

0.8

1.0

Tra

nsm

itta

nce

Wavenumber (cm-1)

We

igh

t (%

)

Temperature ( C)

0 100 200 300 400 500 600

20

40

60

80

100(c) N-H or

O-H

Phenyl

group

Ester

group

C-X 0 1 2 3

Si K

O K

keV

C K

Fig. S1 (a) High magnification image of crackle paint and its EDS spectrum overlaid. (b) Infrared

spectrum of crackle precursor. (c) TGA curve of crackling precursor shows that the decomposition

starts around 300 °C and left behind SiO2.

The crackle presursor is basically a colloidal dispersion of SiO2 nanoparticles which is

confirmed from EDS spectrum. IR spectrum shows the presence of ester based solvent in

crackle precursor. Thermogravimetric analysis shows that crackle precursor start

decomposing ~ 300 °C leaving behind SiO2 (20%).

S2-Optimizing precursor concentration for interconnected crackle network

(d) (c)

(b) (a) Mean Width = 21 6.5 µm Mean Width = 35 11 µm

Mean Width = 57 14 µm Mean Width = 70 16 µm

Fig. S2 The optical microscope images of crackle network formed by paint diluted with thinner for

different concentrations. (a) 0.4 g/mL (b) 0.65 g/mL (c) 1.0 g/mL and (d) 1.1 g/mL. Scale bar 200 µm.

The precursor solution of 1.0 mL was used for coating 18 cm2 area, in each case.

The concentration of the crackle precursor is optimized to result in an interconnected crackle

network (Fig. S2a-d). For lower concentration dispersion (0.4 g/mL), networks were less

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interconnected (Fig. S2a) and for the higher concentrations (1.1 g/mL), wider crackles were

obtained (Fig. S2d). The concentration of 0.6 to 1.0 g/ml was found to give highly

interconnected crackles with narrow crackle width (Fig. S2b & c) on drop coating, which is

further used in all experiments.

S3- Uniform wet layer coating

After

coating

Fig. S3 Photograph taken immediately after drop coating of crackle precursor over glass substrate (37

× 25 cm2). The film coating was smooth reflecting the image of a nearby tree.

S4- Optical microscope and SEM image of crackle network

2 mm 50 µm

Crackle

paint

(a) (b)

Fig. S4 (a) Optical microscopic image of the crackle network. (b) SEM image of crackles formed by

the crackle paint over glass substrate.

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S5 & S6 Crackle fill factor analysis

2 1

4

3

6

Fig. S5 Fill factor of crackle region from different position of large area crackle networks. Scale bar is

1 mm.

FF =21.6%

FF =20.4% FF =19.7% FF =22%

FF =19.9% FF =18.8% 4

3 2 1

5 6

Fig. S6 The fill factor calculation on crackles formed at similar conditions over six different substrate.

Scale bar is 1 mm.

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S7- Template over large area by drop coating technique

(a) (b)

Fig. S7 (a) Developing crackle template by drop coating crackle precursor over 155 × 102 cm2 PET

substrate. The wet layer is left 2-3 h for self-drying. (b) The dried layer crackle itself and optical

microscope image of crackled film is shown in the inset.

S8-EDS mapping of Ag mesh

Ag L (b) O K (c) (a)

Fig. S8 (a) SEM image and EDS mapping of (b) Ag L and (c) O K signal from the patterned

substrate. Scale bar is 50 µm.

The spontaneously formed crackles were used as template for deposition of Ag followed by

removal of template layer leaving behind Ag only in the crackle grooves. The resulting Ag

network was characterized by SEM along with EDS mapping from the same region (see Fig.

S8a-c). EDS map clearly shows continuous Ag signal in the form of an interconnected

junctionless wire (Fig. S8b). The O K signal in Fig. S8c is only present in the substrate

(glass) area outside of Ag wires indicating that the Ag surface is clean and pristine.

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S9-Average of transmittance spectrum (of Ag mesh) measured from 10 positions

400 500 600 700 8000

20

40

60

80

100

Tra

nsm

itta

nce (

%)

Wavelength (nm)

Fig. S9 Average of transmittance spectrum of Ag mesh measured from 10 positions.

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S10-Transparent heater using Ag mesh

(a) (b)

Temperature ( C)

Counts

6 V (c) C

125

100

75

50

25

150 9V

Ag e

poxy

Ag e

poxy

80 100 120 140 1600

100

200

Counts

Fig. S10 (a) Photograph of the as-prepared Ag mesh fabricated as heater. Thermal image collected

from backside of the TCE at 6 V (b). Scale bar is 1 cm. (c) Histogram showing the temperature

distribution from marked region in inset of Fig. 4a.

A photograph of the Ag mesh fabricated as heater is shown in Fig. S10a. The water pond in

the background illustrates the transparency of the heater. The Ag mesh electrode was tested

for heater application by applying a DC voltage across the two Ag epoxy contact pads as seen

in Fig. S10a. The temperature of electrode surface increases with increase in applied voltage.

The temperature of the electrode raised to ~ 90 °C with 6 V (Fig. S10b). The distribution of

temperature over the marked region in inset of Fig. 4a (9 V) is shown as histogram in Fig.

S10c.

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S11- Electrode stability for defrost cycling test

(a) (b)

(d) (c)

(e) (f)

(g) (h)

(i) (j)

Cycle

1

Cycle

2

Cycle

3

Cycle

4

Cycle

5

25

50

75

100

125 C

Fig. S11 Photographs on the left were taken while performing defrosting experiment and those on the

right were captured after complete defrosting. The corresponding IR images are in the insets.

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20 40 60 80 100

2θ

(200)

(111)

(220) (311)

(222)

Fig. S12 X-ray diffraction pattern of Ag mesh after 6 h of exposure to LN2 vapors and

defrosting conditions. The peaks are matching well with Ag peak positions.