Coloured organic-inorganic coatings on glass

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Coloured organic–inorganic coatings on glass

Krzysztof Wojtach a, Katarzyna Cholewa-Kowalska a, Maria Łączka a,*, Z. Olejniczak b

a AGH-University of Science and Technology, Faculty of Materials Science and Ceramics,

Department of Technology of Glass and Amorphous Coatings, 30-059 Krakó w, Poland b Institute of Nuclear Physics, 31-342 Krakó w, Poland

Available online 10 March 2005

Abstract

Organic–inorganic hybrids were obtained by the alcoholate sol–gel method. The characteristic feature of these materials is that

CnHm

groups are connected to silicon atoms by C–Si bonds. Such structures are compatible matrices for organic dyes. The gels pre-

pared from pure tetraethoxysilane (TEOS) modified with methyltrimethoxysilane (MTMS) or phenyltriethoxysilane (PhTES) were

subjected to heat treatment in the temperature range 40–500 C. Then, they were examined by FTIR spectroscopy. All gels after

heating at 100 C were analysed by 29SiMASNMR. It has been observed that polycondensation proceeds faster in presence of

an organic modifier compared to pure TEOS. Moreover, it has been found that copolymers form between the units of TEOS

(Q) and organic modifiers (D). Thermal stability of copolymers depends on the modifier type but the temperature of 350 C should

not be exceeded. The hybrid materials were coloured by introducing organic absorption dyes to the gel matrix. Hybrid films were

deposited on glass plates by a dip-coating technique. Optical properties of those films were examined by measuring light transmis-

sion in the range of visual wavelengths (UV–vis spectroscopy).

2005 Elsevier B.V. All rights reserved.

Keywords: Coloured films; Hybrid materials; Sol–gel method; FTIR spectroscopy; UV–vis spectroscopy

1. Introduction

Organic–inorganic hybrids are relatively new materi-

als of the Ormosils group (organic modified silicates).

They combine the advantageous properties of both or-

ganic and inorganic materials. By proper selection of

an organic modifier it is possible to obtain hybrids with

the refractive index changing in a wide range and with a

controlled light transmission in the UV/vis and near IRrange. Such materials in the form of thin films on appro-

priate substrates can find application in optical wave-

guides for planar integrated circuits [1]. Hybrid gels

with proper organic modifiers and hydrophobic proper-

ties can be used also in the manufacturing of transparent

or translucent window thermal and acoustic insulations

[2,3]. Basic requirements for such applications are: high

transparency of the matrix, abrasion and scratch resis-

tance close to that of glass, very good adhesion to glass

surfaces, stable basic properties, and high stability of

colours (no fading) [4,5]. Low viscosity of the coloured

hybrid sols allows using great variety of coating tech-niques, the choice being dependent on chemical compo-

sition of the sol: dipping, spinning, spraying, brush

painting, roller coating, felt-pen painting, or screen

printing [6,7]. Organic–inorganic hybrids are also com-

patible matrices for intensive organic dyes, laser dyes

and other organic compounds.

The aim of this study was to determine structural

characteristics of the hybrid gels modified with two or-

ganic modifiers, differing in functional groups: MTMS,

0925-3467/$ - see front matter 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.optmat.2005.01.016

* Corresponding author.

E-mail addresses: [email protected] (K. Cholewa-Kowals-

ka), [email protected] (M. Łączka).

www.elsevier.com/locate/optmat

Optical Materials 27 (2005) 1495–1500

mailto:[email protected]:[email protected]:[email protected]:[email protected]


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PhTES, and stability of the hybrid structures at elevated

temperatures. The hybrid gels were used as matrices for

the commercial ORASOL-type organic dyes.

2. Experimental

Bulk samples were prepared from tetraethoxysilane(TEOS) and organic modifiers—either methyltrimethox-

ysilane (MTMS) (CH3)Si(CH3O)3, or phenyltriethoxysi-

TEOS

Organic

dye

Gels Coatings

on glass

Final

solution

H2O

Organic

modifier

Fig. 1. Scheme of gels and coatings preparation.

Table 1

Characteristic bands appearing in FTIR spectra of the obtained gels and their interpretation [8,9]

TEOS TEOS + MTMS TEOS + PhTES Origin Structural units

460 436–458 438–491 O–Si–O bend O Si O

567–572

624–626 Oop ring bend

637–698

738–740 In phase,

oop 5 adjacent HSi

H H

H

HH

800 778–802 786–795 m Si–O–Si Si–O–Si

O–Si–CH3 Si–O–Si–O–CH3950 936–954 956 Si–OH „ Si–OH

1050 1059–1085 1135 1068–1070 m Si–O–Si Si O Si1136–1137 m Si–O–Si

1276–1280 C–H „ Si–CH31407–1412 r (CH2) „ Si–CH@CH2

1430–1432 C–H, Si–C Si

1490 Ring

1595–1606 Ring

1630 1630 H–O–H H2O

2978, 3050, 3072 C–H C C–H3450 3441 3438 OH, H

Oop—out of plane; m —stretch; r —deformation.

Fig. 2. FTIR spectra of gel after heat treatment at varioustemperatures.

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lane (PhTES) C6H5 –Si(CH3CH2O)3 (Merck, Darmstadt,

Germany). Molar ratios of TEOS to the organic

modifiers were 1:1 and 4:1. Phthalocyanine Cu (ORA-

SOL BLUE GN) and chrome complexes (ORASOL

ORANGE RG, ORASOL RED BL) (CIBA Speciality

Chemicals Inc.) were added as dyes to obtain coloured

gels. Gel and coating preparation scheme is given inFig. 1. The gels were dried at 40 C and next heated to

the following temperatures: 100, 200, 300, 400 and

500 C.

Microscopic glass plates with proper surface finish

were covered with a suitable solution. The films were

deposited by means of a dip-coating technique in an appa-

ratus designed for this purpose. The rate of glass-plate

dipping in the solution was determined experimentally.

The coated specimens were dried at ambient temperature

and then at 40 C. The subsequent heat treatment was

carried out at 100 C and at 200 C.

All the bulk samples were examined by FTIR (DIG-

ILAB spectrophotometer) to determine the structure of

gels (Table 1 and Figs. 2 and 3). Bulk gels after heating

at 100 C were also analysed by the 29Si MAS NMR

spectroscopy (magnetic field of 7.05 T) (Fig. 4).

The films obtained on glass plates were observed

under a scanning electron microscope (SEM) (Fig. 5),

that allowed rough estimation of their thickness. Surface

roughness was determined according to ISO (DIS H287/

1) using Hammel Tester T500 profilometer (Mom-

melwerke GmbH, Berlin) (Table 2). Optical characteris-

tics of films in the UV/vis range were measured using a

UV–vis spectrophotometer HP 8453 (Fig. 6). Coloured

films were additionally tested for chemical resistance inrepeated cycles of washing in tap water, followed by

transmission measurements in the UV/vis range.

3. Results

It was noticed during the gel preparation procedure

that the gelation time depended on the type of organicFig. 3. FTIR spectra of gels after heat treatment at various

temperatures.

50 0 -50 -100 -150

TEOS

50 0 -50 -100 -150

29Si NMR

4 kHz MAS

29Si NMR

4 kHz MAS

TEOS + MTMS

TEOS + PhTES

ppm TMSppm TMS

Fig. 4. 29Si MAS NMR spectra of gels after heat treatment at 100 C.

K. Wojtach et al. / Optical Materials 27 (2005) 1495–1500 1497


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modifier added to the solution. A solution with an addi-

tion of MTMS gelled the fastest (2 days) and with an

addition of PhTES gelled the slowest (7 days). More-

over, the viscosity of the TEOS-PhTES sols was higher

compared to the sols obtained with an addition of

MTMS. The gels received at ambient conditions were

fully transparent and had the form of discs, 20 mm in

diameter (almost free of cracks for the molar ratios

4:1). The TEOS + MTMS gel (the molar ratio 1:1)showed some cracks, whereas the TEOS + PhTES gel

(the molar ratio 1:1) showed numerous cracks. Heating

at 100 C did not change the appearance of the gels,

however, heating at higher temperatures caused some

opacity or even complete loss of transparency. All sam-

ples were examined by FTIR spectroscopy (Figs. 2 and

3). Table 1 shows characteristic IR bands and their

interpretation [8,9].

Fig. 4 presents MAS NMR spectra of gels obtained

from TEOS, TEOS + MTMS and TEOS + PhTES after

heating at 100 C. Solutions with an addition of col-

oured dyes were used for the deposition of thin layers

on glass plates. The quality of layers was examined by

SEM. Fig. 5 presents the SEM photograph of the Orasol

Blue GN dyed film obtained from PhTES-modified

TEOS after treatment at 100 C. The results were similar

for other samples. All the films were characterized by

distinct colouring; the most intensive being that of the

TEOS + PhTES hybrid gels. The differences in the inten-

sity of colouring for the various hybrid matrices were

Fig. 5. SEM image of the Orasol Blue GN dyed film obtained from the

PhTES-modified TEOS after heat treatment at 100 C.

Table 2

The parameters of surface roughness

Sample TEOS + MTMS (1:1) TEOS + MTMS (4:1)

Ra [lm] 0.02 0.02

Rt [lm] 0.90 0.52

Ra —arithmetic mean of level roughness. Rt —maximum height

between highest peak and lowest valley.

0

20

40

60

80

100

TM_OrBlue_40oC

TM_OrBlue_100oC

TM_OrBlue_200oC

TM_base_100oC

T r a n s m i t a n c e [ % ]




Wavelength [nm]

200 400 600 800 1000

200 400 600 800 1000200 400 600 800 1000

200 400 600 800 10000

20

40

60

80

100

TPh_OrBlue_40oC

TPh_OrBlue_100oC

TPh_OrBlue_200oC

TPh_base_100oC

Wavelength [nm]

0

20

40

60

80

100

TPh_OrOrange_40oC

TPh_OrOrange_100oC

Wavelength [nm]

0

20

40

60

80

100

TPh_OrRed_40oC

TPh_OrRed_100oC

Wavelength [nm]

Fig. 6. UV–vis spectra of the base film and the Orasol Blue GN, Orasol Orange RG and Orasol Red BL dyed films obtained from the MTMS- and

PhTES-modified TEOS after heat treatment at various temperatures (40 C, 100 C, 200 C).



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due to different thickness of the deposited layers. The

TEOS + PhTES films were the thickest (about 3–4 lm)

while the TEOS + MTMS ones were thinner (about 2–

3 lm). The larger thickness was related to higher viscos-

ity of the sols modified with PhTES. The parameters of

surface roughness are similar for all the samples exam-

ined (Table 2). The optical UV/vis characteristics of the layers after heating at 40, 100 and 200 C are given

in Fig. 5. For the coatings dyed with Orasol Blue GN

maximum heat-treatment temperature was 200 C, while

for the coatings with Orasol Red BL and Orasol Orange

RG it was 100 C.

4. Discussion

4.1. Structure of the hybrids

The structure of the organic–inorganic gels was deter-mined basically from FTIR and MAS NMR spectro-

scopic examinations. In the spectra of the hybrid gels

there appear bands related to the vibrations of both, inor-

ganic and organic, structural units. The most intensive

band, at about 1100 cm1, is connected to the asymmetric

stretching vibrations of the Si–O–Si bridges. In the case of

hybrid structures this band becomes clearly split into two

separate bands at about 1060 cm1 and 1130 cm1.

Vibrations of the silicon–oxygen bridges are also

responsible for the bands at about 800 cm1 (the sym-

metric stretching vibrations) and at about 450 cm1

(the bending vibrations). The band related to vibrationsof the Si–OH groups is observed at about 950 cm1.

Bands connected to vibrations of the organic groups

are usually very sharp and are situated in the ranges of

wavenumbers 1400–3070 cm1 and 540–740 cm1. These

are the bands related to vibrations of C–H, Si–C,

CH@CH2 as well as to the ring structures. So, the FTIR

spectra indicate that both organic and inorganic struc-

tural units are present in the obtained gels. The analysis

of the band intensities related to the organic components

as a function of the heating temperature of the gels (100–

500 C) indicates that complete decomposition of the or-

ganic components takes place at temperatures exceeding

500 C. The organic–inorganic hybrid structure is re-tained up to 400 C. The type of bonds between the inor-

ganic and organic components of the hybrid structure is

an important issue. Chemical properties of the organic

modifiers (compounds of the R4nOSiRn type) suggest

that these compounds should take part in polycondensa-

tion with the precursor of the inorganic component, i.e.

Si(OR)4 (TEOS). This reaction should yield copolymers

with the following bonds:

Si O Si CnHm

According to Gunzler and Gremlich [8] interpretation

the band situated in the range 800–770 cm1 originates

from vibrations of the O–Si–CH3 group. At 800 cm1

there appears in the spectrum also a band induced by

bending vibrations of O–Si–O. In IR spectra of all ob-

tained hybrids distinct, sharp bands at about 770 cm1

occurs, which become shifted towards higher wave num-bers with increasing temperature of heating of the sam-

ples (Table 1, Figs. 2, 3). This is and indication that

organic and inorganic components of the hybrids are

connected by chemical bonds.

The presence of copolymers in the obtained organic–

inorganic materials is also indicated by the spectra 29Si

MAS NMR (Fig. 4). In these spectra there appear the

peaks originating from the structural TEOS units

(100–110 ppm). However, there appear also additional

peaks at 50–70 ppm (TEOS + MTMS) and 70–90 ppm

(TEOS + PhTES). In agreement with the earlier inter-

pretation given by Brus and Dybal [10] these additional

peaks can be ascribed to copolymers formed from the

organic and inorganic structural units of the hybrid.

4.2. Evaluation of quality of the thin films and their

optical characteristics

All the hybrid films were essentially crack-free and

showed very good adhesion to the substrates. Intensive

absorption bands, characteristic of the particular dyes,

were observed in the optical spectra of the films (Fig.

6). In the case of the TEOS + PhTES hybrid matrix

the absorption band intensities were the highest becausethe obtained films were the thickest. Heating of glass

plates with the deposited films dyed with Orasol Blue

GN to 200 C did not change the optical characteristics

of the layers. In the case of the coloured films obtained

with Orasol Red BL and Orasol Orange RG, heat treat-

ment at 200 C induced bleaching of the films. It was

probably caused by decomposition of the dyes at higher

temperatures. Repeated washing under running water

did not cause any decolourisation of the films or changes

in the absorption spectra.

The results of this work indicate that the dyes were

firmly incorporated in the hybrid matrix probably being

trapped in some structural voids. The high intensity of colouring and stability of the hybrid films demonstrate

the usefulness of the developed method of preparation

and deposition in the manufacturing of coloured glass

and ceramics.

Acknowledgment

This investigation was financially supported by the

Polish State Committee for Scientific Research, under

Project No.: 11.11.160.113.

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Coloured organic-inorganic coatings on glass