characteristics of colored inorganic–organic hybrid materials

5
Characteristics of colored inorganic–organic hybrid materials K. Wojtach a, * , M. Laczka a , K. Cholewa-Kowalska a , Z. Olejniczak b , J. Sokolowska c a AGH-University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Glass Technology and Amorphous Coatings, Avenue Mickiewicza 30, 30-059 Krakow, Poland b Institute of Nuclear Physics, ul. Radzikowskiego 152, 31-342 Krakow, Poland c Technical University of Lodz, Faculty of Chemistry, ul. _ Zeromskiego 116, 90-924 Ło ´ dz ´, Poland Available online 24 April 2007 Abstract Inorganic–organic hybrid glasses are relatively new nanometric materials of Ormosil’s group (organic modified silicates). There co- existence, on a molecular scale, exists between inorganic structures in the form of silica-oxide network and organic structures based on carbon links. Properties of these materials are intermediate between those of inorganic glasses (hardness, chemical and thermal resis- tance) and organic polymers (low temperature of obtaining, elasticity of structure). The hybrid materials are compatible matrices for organic compounds such as organic dyes, laser dyes, photo-chromic compounds, etc. Inorganic–organic hybrid glasses are usually pro- duced in the form of thin coatings on various bases using a low-temperature sol-gel process. These coatings, depending on the kind and amount of units, building their structure, show various properties: refractive index changing in a wide range, anti-static properties, anti- reflection, corrosion protection, intensive color, luminescence and others. That is why these materials found application as protective and colored covering of glass articles as well as in new technical areas. The aim of this paper is obtaining and characterizing colored inor- ganic–organic coatings on glass, considering both protective and colored properties. These materials have been produced from phenyltr- iethoxysilane (PhTES), 3-glycidoxypropyltrimethoxysilane (GPTMS), aluminium tri-sec-butylate (TBA); (PGT matrix). The structure of PGT matrix was determined using the FTIR, 29 Si MAS NMR and 27 Al MAS NMR examinations. It has been found that chemical bonds occur between structural units. The two groups of organic dyes were used for coloring the coatings. The first group consisted of ORA- SOL dyes, chiefly based on various metal complexes. These dyes have a wide range of commercial utilization. The second group included the organic, intensive dyes obtained in the laboratory and are inaccessible for sale. The coloring coatings were coated on flat glass using the dip-coating method. The samples were submitted for thermal treatment at temperatures of 100 and 200 °C. Investigation of chemical resistance (boiling in water for 1 h) was made for coated materials after thermal treatment at 100 °C. UV–VIS transmission of colored coatings was examined after each stage of thermal treatment and also after hydrolytic resistance examination. The quality of the coatings and their thickness were estimated by SEM observations. The obtained, inorganic–organic coatings were characterized by good chemical resistance and stability of color. Ó 2007 Elsevier B.V. All rights reserved. PACS: 81.07.Pr; 81.20.Fw Keywords: FTIR measurements; NMR, MAS-NMR and NQR; Organic–inorganic hybrids; Short-range order 1. Introduction Recently, a new class of multifunctional materials has emerged, i.e. inorganic–organic hybrids, being a unique combination of inorganic structure in the form of a silicon oxide network and the organic structures based on car- bon–carbon chemical bonding. The properties of these materials are intermediate between traditional ceramics (hardness, chemical and thermal resistance) and organic polymers (low preparation temperature, elastic structure). It has been found that the hybrid materials are a compatible matrix for numerous organic compounds, such as organic dyes, laser dyes, and compounds that exhibit photo-chromic behavior and many more [1–3]. Usually, inorganic–organic 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.02.032 * Corresponding author. Tel.: +48 12 6172455; fax: +48 12 6172509. E-mail address: [email protected] (K. Wojtach). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 2099–2103

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Page 1: Characteristics of colored inorganic–organic hybrid materials

www.elsevier.com/locate/jnoncrysol

Journal of Non-Crystalline Solids 353 (2007) 2099–2103

Characteristics of colored inorganic–organic hybrid materials

K. Wojtach a,*, M. Laczka a, K. Cholewa-Kowalska a, Z. Olejniczak b, J. Sokolowska c

a AGH-University of Science and Technology, Faculty of Materials Science and Ceramics, Department of Glass Technology and Amorphous Coatings,

Avenue Mickiewicza 30, 30-059 Krakow, Polandb Institute of Nuclear Physics, ul. Radzikowskiego 152, 31-342 Krakow, Poland

c Technical University of Lodz, Faculty of Chemistry, ul. _Zeromskiego 116, 90-924 Łodz, Poland

Available online 24 April 2007

Abstract

Inorganic–organic hybrid glasses are relatively new nanometric materials of Ormosil’s group (organic modified silicates). There co-existence, on a molecular scale, exists between inorganic structures in the form of silica-oxide network and organic structures based oncarbon links. Properties of these materials are intermediate between those of inorganic glasses (hardness, chemical and thermal resis-tance) and organic polymers (low temperature of obtaining, elasticity of structure). The hybrid materials are compatible matrices fororganic compounds such as organic dyes, laser dyes, photo-chromic compounds, etc. Inorganic–organic hybrid glasses are usually pro-duced in the form of thin coatings on various bases using a low-temperature sol-gel process. These coatings, depending on the kind andamount of units, building their structure, show various properties: refractive index changing in a wide range, anti-static properties, anti-reflection, corrosion protection, intensive color, luminescence and others. That is why these materials found application as protective andcolored covering of glass articles as well as in new technical areas. The aim of this paper is obtaining and characterizing colored inor-ganic–organic coatings on glass, considering both protective and colored properties. These materials have been produced from phenyltr-iethoxysilane (PhTES), 3-glycidoxypropyltrimethoxysilane (GPTMS), aluminium tri-sec-butylate (TBA); (PGT matrix). The structure ofPGT matrix was determined using the FTIR, 29Si MAS NMR and 27Al MAS NMR examinations. It has been found that chemical bondsoccur between structural units. The two groups of organic dyes were used for coloring the coatings. The first group consisted of ORA-SOL dyes, chiefly based on various metal complexes. These dyes have a wide range of commercial utilization. The second group includedthe organic, intensive dyes obtained in the laboratory and are inaccessible for sale. The coloring coatings were coated on flat glass usingthe dip-coating method. The samples were submitted for thermal treatment at temperatures of 100 and 200 �C. Investigation of chemicalresistance (boiling in water for 1 h) was made for coated materials after thermal treatment at 100 �C. UV–VIS transmission of coloredcoatings was examined after each stage of thermal treatment and also after hydrolytic resistance examination. The quality of the coatingsand their thickness were estimated by SEM observations. The obtained, inorganic–organic coatings were characterized by good chemicalresistance and stability of color.� 2007 Elsevier B.V. All rights reserved.

PACS: 81.07.Pr; 81.20.Fw

Keywords: FTIR measurements; NMR, MAS-NMR and NQR; Organic–inorganic hybrids; Short-range order

1. Introduction

Recently, a new class of multifunctional materials hasemerged, i.e. inorganic–organic hybrids, being a uniquecombination of inorganic structure in the form of a silicon

0022-3093/$ - see front matter � 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.jnoncrysol.2007.02.032

* Corresponding author. Tel.: +48 12 6172455; fax: +48 12 6172509.E-mail address: [email protected] (K. Wojtach).

oxide network and the organic structures based on car-bon–carbon chemical bonding. The properties of thesematerials are intermediate between traditional ceramics(hardness, chemical and thermal resistance) and organicpolymers (low preparation temperature, elastic structure).It has been found that the hybrid materials are a compatiblematrix for numerous organic compounds, such as organicdyes, laser dyes, and compounds that exhibit photo-chromicbehavior and many more [1–3]. Usually, inorganic–organic

Page 2: Characteristics of colored inorganic–organic hybrid materials

Stiring at ambient

temperature

PhTES

Ethyl alcohol

GPTMS

TBA

H2O+HCl Organic

dye

Final solution

Fig. 1. Scheme of hybrids preparation.

2100 K. Wojtach et al. / Journal of Non-Crystalline Solids 353 (2007) 2099–2103

hybrid glasses are obtained in the form of thin coatings ondifferent substrates by means of a low-temperature sol-gelprocess. Since the properties of the hybrids depend on thekind and amount of the units building their structure, thecoatings are characterized by various properties, e.g. arefractive index changing within a wide range, anti-staticand anti-reflectivity, corrosion protection, intensive color,and luminescence [4,5]. For this reason the hybrid materialshave found application as protective and decorative, coloredcoatings for glass items, as well as in new technical branches.

Colored hybrid coatings are relatively low cost methodfor modifying the glass materials with a sophisticated shapeand high surface area. A matrix based on aluminium tri-sec-butylate (TBA), phenyltrimethoxysilane (PhTMS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) seems to beparticularly suitable for these applications. Kron et al. dem-onstrated that the coatings based on this matrix possess thebest mechanical parameters when TBA:PhTMS:GPTMSratio was 20%:10%:70%. Such coatings were characterizedby an increased hydrophobicity of the glass surfaces, as wellas a very good adhesion and abrasion resistance, whenapplied onto a soda-lime glass [6]. Also, it was found byChu et al. that introducing GPTMS during the synthesisled to increased density and layer thickness, as well as theenhanced adhesion on the polymer substrate [7]. The influ-ence of the GPTM presence during the synthesis on the cor-rosion resistance of the obtained coatings was investigatedby Metroke et al., who showed that the coatings can be usedfor protection of the aluminium-based alloys against corro-sion [8]. The structure of the materials in GPTMS/PhTMS/TEOS group was studied by Peeters et al. by means of 29SiMAS NMR. They reported that in the presence of GPTMS,an increase in condensation of the tetrafunctional siliconatoms (Q) is related to the presence of the trifunctional sil-icon atoms (T), while the number of bondings within thethree dimensional lattice of T atoms decreases with anincreasing size of the organic tail [9]. According to Peetersand Kentgens, when aluminium originating from TBA isintroduced in the composition of the PhTES/GPTMS/TEOS system, the Al atoms occur in tetrahedral and octa-hedral surrounding. While the amount of the atoms in agiven position depends on the hybrid synthesis route, alow water content during synthesis favors the tetrahedralAl position [10].

The aim of this paper was to obtain the colored inor-ganic–organic coatings on glass substrates, based on PGTmatrix (phenyltriethoxysilane (PhTES), 3-glycidoxypropyl-trimethoxysilane (GPTMS), and aluminium tri-sec-buty-late (TBA)), and characterize their structure, opticaltransmission, as well as the chemical resistance and thermalstability of color.

2. Experimental

The materials have been produced from phenyltrieth-oxysilane (C6H5)Si(CH3CH2O)3 (PhTES), 3-glycidoxypro-pyltrimethoxysilane (OCH3)3Si(CH2)3OCH2CHOCH2

(GPTMS), and aluminium tri-sec-butylate Al(OCH(CH3)-C2H5)3 (TBA). The solutions were prepared at roomtemperature according to the scheme given in Fig. 1. Themolar ratio of particular substrates was 0.5:0.3:0.2. Themixing times were selected empirically. The organic dyesused in the experiment fall into two classes. The first groupconsisted of ORASOL dyes, chiefly based on various metalcomplexes: Red BL (chrome complex), Orange G (cobaltcomplex), Orange RG (chrome complex), Blue GN (Cu-phthalocyanine), Yellow 4GN (metal-free monoazo), BlackRLI (chrome complex). These dyes have a wide range ofcommercial applications. The second group includedorganic dyes of high color intensity, obtained from theUniversity of Lodz laboratory. They also represented var-ious metal complexes, but their composition is patentedand they are not commercially available. The color andthe symbols of these dyes are as follows: R9 (brown–red),R12 (yellow–orange), R16 (violet), PAS (pink), B1(orange), B2 (black–violet), CzE6B (brown), and ZGGW(yellow). The dyes in the form of powder were added tothe solutions. The amount of the dye was kept constant,at 1–2% of the wet gel weight. The synthesis time did notexceed 2 h. Finally, the coatings were applied from the pre-viously prepared solutions on the microscopic glass platesby means of dip-coating technique. The immersion-with-drawal rate was identical for all the samples and was equalto about 4 cm/min. The coatings were then dried at roomtemperature and subsequently in the dryer at 40 �C for10–21 days. Next, the samples were treated thermally.Some of the samples heated at 100 �C were boiled in waterat 98 �C for 1 h.

In order to determine the hybrid structure, the FTIRexaminations for all gels were performed, using DIGILABspectrophotometer. Also, for the gels treated thermally at100, 200, 300 and 400 �C, 29Si MAS NMR and 27Al

Page 3: Characteristics of colored inorganic–organic hybrid materials

T

Q

100oC

29Si NMR4 kHz MAS

PGT

K. Wojtach et al. / Journal of Non-Crystalline Solids 353 (2007) 2099–2103 2101

MAS NMR measurements were carried out. Optical trans-mission of coatings was measured within UV and visibleranges using a UV–VIS spectrophotometer HP 8453. Thesemeasurements were performed for the samples after a com-plete thermal treatment, as well as for the ones boiled inwater.

-180-160-140-120-100-80-60-40-200

300oC

400oC

200oC

ppm from TMS

Fig. 3. 29Si MAS NMR spectra of PGT gels, after treatment at 100, 200,300 and 400 �C.

[AlO6]

27Al NMR8 kHz MAS PGT

100 oC

[AlO4]

3. Results and discussion

The PGT matrix represents hybrid material composedof inorganic and organic units. In this structure each siliconatom, besides the links with oxygen Si–O–R (R@CnHm)(trifunctional silicon atoms), forms S–C bond representinga link either with the phenyl group (PhTES precursor) orwith carbon chain ended with an epoxide group (GPTMSprecursor). The inorganic network is additionally modifiedby the tetrahedral [AlO4] (TBA precursor). Such type ofhybrid structure has been confirmed by the results of FTIRand 29Si MAS NMR examinations (Figs. 2–4). In the FTIRspectra of the PGT gels the bands derived from vibrationsof both inorganic and organic structural units occurred(Table 1) [14]. However, in the spectra of samples heatedto a temperature of 200 �C, the bands characteristic forthe symmetric stretching vibrations (about 800 cm�1) andbending vibrations (about 440 cm�1) of Si–O–Si bridgesdo not appear, while a distinct band derived from Si–O–C bonds at about 1110–1133 cm�1 (stretching vibrations)is observed. It indicates that in this structure the bridging

Fig. 2. FTIR spectra of PGT gels after heat treatment at varioustemperatures (40, 100, 200, 300 and 400 �C).

-100-50050100150200

200 oC

400 oC

300 oC

ppm from Al(NO3)3

Fig. 4. 27Al MAS NMR spectra of B class gels, after treatment at 100,200, 300 and 400 �C.

oxygen between two silicon atoms –Si–O–Si– does notoccur at all. This same conclusion results from NMRexaminations. In the 29Si MAS NMR spectra of PGT gelsheated to a temperature 200 �C (Fig. 3), the signals derivedfrom Q units are not observed, which is an indication thatthere are no tetrahedral [SiO4] in which the Si ion would becombined by an oxygen bridge. On the other hand, thereoccur two distinct group effects at about 70 and 80 ppmderived from T units, in which besides Si–O bonds thereoccurs Si–C bond [9,13]. Separation of the peaks isundoubtedly connected with the fact that through the

Page 4: Characteristics of colored inorganic–organic hybrid materials

Table 1Characteristic bands appearing in FTIR spectra of obtained hybrid gelsand their interpretations on the base of [14]

Band Origin Structural units

487 O–Si–O bendO Si O

701 oop Ring bend

742 In phase, oop 5 adjacent H Si

H H

H

HH

1110–1133 m Si–O–SiSi O Si

– Si – O – C – Si–O–C

1200–1201 C–O–C C–O–C in GPTMS

1460 Ring15952937 C–H C C–H 3429 OH, H H–O–H

200 300 400 500 600 700 800 900 1000 11000

10

20

30

40

50

60

70

80

90

100

Tran

smita

nce

[%]

PGT_OrBlue GN_40oC PGT_OrBlue GN_100oC PGT_OrBlue GN_200oC PGT_OrBlue GN_100oC_H PGT_base_100oC

Wavelength [nm]

Fig. 5. UV–VIS spectra of base film and Orasol Blue GN dyed films aftertreatment at various temperatures (40, 100 and 200 �C) and after boiling inwater (H).

Tran

smita

nce

[%]

200 300 400 500 600 700 800 900 1000 11000

10

20

30

40

50

60

70

80

90

100

Wavelength [nm]

PGT_R12_40oC PGT_R12_100oCPGT_R12_100oC_H

Fig. 6. UV–VIS spectra of the R12 dyed films obtained from PGT matrixafter heat treatment at various temperatures (40 and 100 �C) and afterboiling in water (H).

2102 K. Wojtach et al. / Journal of Non-Crystalline Solids 353 (2007) 2099–2103

Si–C bond, various units combine with silicon [12]. Increaseof the temperature of the gels treatment up to 300–400 �Ccauses a distinct change in the 29Si MAS NMR spectra(Fig. 3), indicating the decomposition of the Si–C bondand formation of inorganic network composed only ofthe Q units. These results are also confirmed by FTIR spec-tra of gels heated at 300 and 400 �C (Fig. 2), in which thebands characteristic for vibrations of Si–O–Si groupsappeared. In the 27Al MAS NMR spectra (Fig. 4), thereoccur two peaks situated at about 5 and 50 ppm, whichmay be connected with the occurrence of Al in the hybridstructures in the tetrahedral (55 ppm) and octahedral(5 ppm) coordinations [10,11].

The coatings, obtained on the base of PGT matrix, con-taining Orasol dyes, were of a highly intensive color, char-acteristic for the applied dyes. A similar behavior wasobserved for the coatings from the second group, exceptfor those dyed with B2, CzE6B and ZGGW, where thecolor intensity was much lower. Interestingly, after addi-tion of the R9, PAS or CzE6B, the observed color of thematrix was different in comparison to the dye itself, i.e.coatings were red–pink, yellow and red, probably due tothe interaction between the dye molecules and the matrix.The UV–VIS spectra reveal the bands originating fromthe applied dyes. Taking into account the high intensityof the coloring, it is likely that the absorption bandsobserved in the spectra result from the allowed electronictransitions in the dye molecules. The UV–VIS spectra forall the coatings dried at 40 �C and heated at 100 �C arealmost identical (Figs. 5 and 6). After heating at 200 �Cthe coloring intensity of the coatings with Orasol dyes isslightly decreased, while for the coatings containing thedyes from the second group bleaching is observed, proba-bly causing decomposition of the dye. It is most likely con-nected with the lower thermal resistance of these dyes, as

compared to Orasol dyes. The coloring stability and a highintegrity of the coatings were also confirmed by boiling thesamples in a water bath, indicating the dye stability withinthe matrix. Exceptionally, for the coatings with R12 andR16 dyes there was a decrease in the coloring intensity(washing away of the dye), followed by the decreased integ-rity of the coating. However, for the coating with R9 theintegrity remained unaffected by the bleaching process.

The SEM observations confirmed a high quality of thecoatings. The layers were smooth, no inclusions or crackswere observed (Fig. 7). Also, they showed a high adhesionto the substrate. The fracture images served for estimatingthe layer thickness, which was about 15–20 lm (Fig. 8).

4. Conclusions

The PGT hybrid materials are compatible matrices fororganic dyes. Furthermore, the obtained color coatings

Page 5: Characteristics of colored inorganic–organic hybrid materials

Fig. 7. SEM image of the Orasol Orange RG dyed film obtained fromPGT after heat treatment at 100 �C.

Fig. 8. SEM image of the fracture of Orasol Blue GN dyed film obtainedfrom PGT after heat treatment at 100 �C.

K. Wojtach et al. / Journal of Non-Crystalline Solids 353 (2007) 2099–2103 2103

based on PGT matrix are characterized by high quality.However, the intensity, as well as thermal stability of colorand chemical resistance, depends on the kind of the intro-duced dyes. The application of the commercial Orasol dyesleads to obtaining intensive dyed coatings with good chem-ical resistance and thermal stability of color up to a temper-

ature of 200 �C. The behavior of no-commercial dyesobtained in the laboratory was diverse. Part of thembehave similar as Orasol dyes, however, some of themshowed low intensity as well as low chemical and thermalresistance. Therefore, the coatings with Orasol dyes canbe easily applied for decorative and protective layers andsecond group of dyes requires further examinations.

Acknowledgement

This investigation is financially supported by the PolishState Committee for Scientific Research Project No. 3T08D 41 29.

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