Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane
Temperature programmed desorption mass spectrometry, thermogravimetry and differential thermal analysis were used to investigate the thermal destruction of adsorbed polydimethylsiloxane (PDMS) in air and vacuum conditions. Fumed silicas, whose surface contained grafted oxygen compounds of metals or...
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Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine
2002
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Surface| _version_ | 1869291167142641664 |
|---|---|
| author | Borysenko, M. V. Bogatyrov, V. M. Dyachenko, A. G. Pokrovskiy, V. A. |
| author_facet | Borysenko, M. V. Bogatyrov, V. M. Dyachenko, A. G. Pokrovskiy, V. A. |
| author_institution_txt_mv | [
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"author": "M. V. Borysenko",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "V. M. Bogatyrov",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "A. G. Dyachenko",
"institution": "Інститут хімії поверхні НАН України"
},
{
"author": "V. A. Pokrovskiy",
"institution": "Інститут хімії поверхні НАН України"
}
] |
| author_sort | Borysenko, M. V. |
| baseUrl_str | |
| collection | OJS |
| datestamp_date | 2018-11-27T09:42:19Z |
| description | Temperature programmed desorption mass spectrometry, thermogravimetry and differential thermal analysis were used to investigate the thermal destruction of adsorbed polydimethylsiloxane (PDMS) in air and vacuum conditions. Fumed silicas, whose surface contained grafted oxygen compounds of metals or phosphorus, were used as adsorbents. VOCl3, CrO2Cl2, TiCl4, SnCl4, AlCl3, PCl3 and Zn(Acac)2 vapors were applied as modifiers. It was found that in air the presence of metal oxides and phosphorus on silica surface lead to partial depolymerization of adsorbed PDMS. Degree of depolymerization ranges up to about 80% for V/SiO2, P/SiO2 and Al/SiO2 samples containing 40% PDMS. The presence of metal oxides on silica surface decrease of starting temperatures of Si-C bond destruction in vacuum and result in elimination of methane at 140-550 and 550-850°С. |
| first_indexed | 2025-07-22T19:30:05Z |
| format | Article |
| fulltext |
11
EFFECT OF CHEMICAL MODIFICATION OF SILICA
SURFACE WITH METAL OXIDES ON THE THERMAL
PROPERTIES OF ADSORBED POLYDIMETHYLSILOXANE
M.V. Borysenko, V.M. Bogatyrov, A.G. Dyachenko, and
V.A. Pokrovskiy
Institute of Surface Chemistry, National Academy of Sciences
Gen. Naumov Str. 17, 03680 Kyiv-164, UKRAINE
Abstract
Temperature programmed desorption mass spectrometry, thermogravimetry and
differential thermal analysis were used to investigate the thermal destruction of adsorbed
polydimethylsiloxane (PDMS) in air and vacuum conditions. Fumed silicas, whose surface
contained grafted oxygen compounds of metals or phosphorus, were used as adsorbents.
VOCl3, CrO2Cl2, TiCl4, SnCl4, AlCl3, PCl3 and Zn(Acac)2 vapors were applied as modifiers. It
was found that in air the presence of metal oxides and phosphorus on silica surface lead to
partial depolymerization of adsorbed PDMS. Degree of depolymerization ranges up to about
80% for V/SiO2, P/SiO2 and Al/SiO2 samples containing 40% PDMS. The presence of metal
oxides on silica surface decrease of starting temperatures of Si-C bond destruction in vacuum
and result in elimination of methane at 140-550 and 550-850°С.
Introduction
Polymeric composites based on organosilicon compounds and inorganic fillers have a
wide application in the production of silicone rubbers, sealants, lubricants etc. [1].
Thermooxidative stability of these materials is one of the major exploitation characteristics.
Recently, the modified silica and polydimethylsiloxane (PDMS) have been used for the
synthesis of metal oxide-containing hybrid materials [2, 3]. Two main pathways of the thermal
decomposition of PDMS exist, depending on the experimental conditions. In air, thermal
destruction proceeds via oxidation of methylsilyl groups according to the following reaction
scheme [4, 5]:
-OSi(CH3)2- + 4O2 Þ SiO2 + 2CO2 + 3H2O (1)
In an inert atmosphere or in vacuum, depolymerization of siloxane chains is accompanied by
formation of the volatile cyclic compounds, mainly hexamethylcyclotrisiloxane and
octamethylcyclotetrasiloxane:
[-OSi(CH3)2-]n Þ [-OSi(CH3)2-]n-3 + (2)
O
Si
O
Si
O
Si
CH3
CH3
CH3
H3C
H3C CH3
12
Thermal decomposition of PDMS on fumed silica surface was a subject of our earlier
detailed investigation [6]. It was found that a thermolysis is accompanied by chemisorption of
the PDMS decomposition products by silica surface. The preliminary modification of fumed
silica by phosphorus oxides essentially affects on the mechanism of PDMS thermal destruction
and results in depolymerization of adsorbed macromolecules at the lower temperature [7]. In
the present paper, an effect of chemical modification of silica surface by metal oxides on
thermal destruction of adsorbed PDMS is considered.
Experimental
Following reagents were applied in our experiments: liquid polydimethylsiloxane
PMS-1000, kinematic viscosity 1036 mm2/s at 20 °С (Kremniypolimer, Zaporizhzhya,
Ukraine), aerosil A-175, A-300 (Khlorvinil, Kalush, Ukraine). Modified silica was synthesized
by interaction of fumed silica with a vapor of chlorides and oxochlorides of various metals
(Table) with consequent treatment by water vapor [8-10]. Zinc acetylacetonate was used to
obtain silica modified by zinc oxide. PDMS was adsorbed onto silica surface from hexane
solution to prepare samples contained 5, 8, 10, 20 and 40 wt. % of the polymer. Thus, the
thickness of adsorptive coating of PDMS changed proportionally to amount of polymer in a
sample.
Differential thermal analysis (DTA) and thermogravimetry (TG) were performed using
a Q-1500 D (MOM, Hungary) derivatograph. The average sample mass was 272±4 mg. The
heating rate was 5 оС min-1. The mass-spectrometric investigations were carried out using mass
spectrometer МХ 7304А (Ukraine). The sample mass was 2.0±0.3 mg.
Results and discussion
In air, the thermal decomposition of PDMS, adsorbed on the surface of fumed silica,
modified by metal oxide, is accompanied by exothermal effects (Fig. 1). An exo-effect at Tmax
450-650oC corresponds to oxidation of chemisorbed dimethylsilyl groups, which were
produced during the thermooxidizing destruction of PDMS [6,7]. It should be noted that
intensity and shape of exothermic effects on DTA curves depend strongly on a composition of
metal-oxide coating and thickness of PDMS adsorptive layer. When PDMS concentration
increases from 5 up to 40%, the broadening of the exo-effect peaks was observed for SiO2,
Cr/SiO2, Zn/SiO2 and Sn/SiO2 samples. Essential broadening of corresponding peaks was
observed for Al/SiO2 and Ti/SiO2 samples only for surface concentration of 20 to 40% PDMS.
The shape and intensity of the exothermic effect is approximately identical for different
amounts of polymer adsorbed by the V/SiO2 sample. The exo-effect, which we assign to
decomposition dimethylsilyl groups, is weak in the case of the P/SiO2 sample. The intense
exothermic effect for the phosphorus-containing sample at temperatures higher than 600°С
may correspond to formation of surface silica-phosphate structures.
Table. Preparation conditions and characteristics of modified silica samples.
Sample Modifier Reaction
temperature, оС
Element content,
wt. %
BET surface
area, m2/g
V/SiO2 VOCl3 300 V-2.7 163
Cr/SiO2 CrO2Cl2 200 Cr(VI)-2.0 161
Ti/SiO2 TiCl4 200 Ti-1.6 174
Zn/SiO2 Zn(Acac)2 200 Zn-1.9 181
Sn/SiO2 SnCl4 300 Sn – 3.5 182
13
Al/SiO2 AlCl3 200 Al – 0.8 159
P/SiO2 PCl3 180 P(III)-1.9 160
Fig. 1. DTA curves of MxOy/SiO2 samples with different amounts of adsorbed PMDS.
200 400 600 800 1000
0,2
0,4
0,6
en
do
ex
o
I, arb.u
Sn
Temper at ure,oC
PDMS
40%
20%
10%
8%
5%
200 400 600 800 1000
0,0
0,2
0,4
0,6
en
do
e
xo
I , arb. u
Z n
Temperat ure,oC
200 400 600 800 1000
0,2
0,4
0,6
0,8
Cr
200 400 600 800 1000
0,0
0,2
0,4
0,6
0,8
V
200 400 600 800 1 000
- 0,4
- 0,2
0,0
0,2
Ti
200 400 600 800 1000
0,0
0,2
0,4
0,6
0,8
P
200 400 600 800 1000
0,0
0,2
0,4
0,6
0,8
SiO 2
200 400 600 800 1000
-0,2
0,0
0,2
0,4
Al
14
Fig. 2. DTG curves of MxOy/SiO2 samples with different amounts of adsorbed PMDS.
200 400 600 800 1000
-0,4
-0,2
0,0
Z n
d m/ dt ,
a rb .u .
Temperatu re,oC
200 400 600 800 1000
-0,6
-0,4
-0,2
0,0
0,2
dm /dt ,
ar b. u.
Sn
Temper at ure,oC
PDMS
5 %
8%
10
20%
40%
200 400 600 800 1000
- 0,4
- 0,2
0,0
0,2
T i
200 400 600 800 1000
-0,4
-0,2
0,0
0,2
Cr
200 400 600 800 1000
-0,8
-0,6
-0,4
-0,2
0,0
0,2
0,4
V
200 400 600 800 1 000
- 0,2
0,0
0,2
P
200 400 600 800 1 000
- 0,6
- 0,4
- 0,2
0,0
0,2
A l
200 400 600 800 1 000
- 0,2
0,0
S iO2
15
With increasing of thickness of adsorptive layer, the change of displacement of Tmax position
for the exo-effect did not exceed 50oС for the most of samples. The exception was the sample
CrVI/SiO2, in which the hexavalent chromium was reduced into trivalent in the process of
thermal destruction. Thus, Tmax of exo-effect was shifted from 350 up to 600°С.
The influence of different metal oxides on thermal oxidizing destruction of PDMS
should be compared for the same thickness of adsorption layers. It was found that the maxima
of DTA peaks for samples containing 8% of PDMS varied depending on the composition of
metal-oxide coating of fumed silica, in the following row:
PIII(455оС) < CrVI(480) = V(480) < pure SiO2(500) < Zn(520) < Al(545) < Sn(590) < Ti(600).
TG and DTG curves (Fig. 2) exhibited well-defined region of mass loss at 100-550°С,
which was attributed to the oxidation of methyl groups and removal of volatile cyclic siloxanes
according to reactions (1) and (2). In the samples contained 40% of adsorbed PDMS the
greatest mass loss occurred within the interval of 100–300°С for V/SiO2, P/SiO2 and of 370-
550°С for SiO2, Al/SiO2, Ti/SiO2, Cr/SiO2, Zn/SiO2, Sn/SiO2. It was found that maxima of
these peaks shifted in the sequential series:
V(190°С) = PIII(190) < pure SiO2(350) < Zn(380) < Al(390) < CrVI(400) < Ti(415) < Sn(435).
The mass loss in samples under investigation was calculated in accordance with
reaction schemes (1) and (2). As for oxidation of dimethylsilyl groups, the calculated value of
mass loss was equal 7.6, 3.8 and 1.9% for samples contained 40, 20 and 10% adsorbed PDMS,
respectively. In the case of schema (2) PDMS was removed from the sample completely and
mass loss was equal to contents of polymer in the sample.
Fig. 3. Conversion degree of PDMS into SiO2 and volatile cyclic
methylsiloxanes according to TG data.
The experimental values of the mass loss for samples of MxOy/SiO2/PDMS in the
interval 100-1000°С were determined. The calculated and experimental data were used to
obtain the conversion degree of PDMS into SiO2 or cyclic organosiloxane (Fig. 3). The
experimental data showed that for samples of SiO2/PDMS the practically complete oxidation
of dimethylsilyl groups occurred, according to the reaction (1). Presence of metal oxides on
silica surface lead to partial depolymerization of adsorbed PDMS according to the reaction (2).
10 20 30 40
0
20
40
60
80
100
SiO
2
Al
P
Ti
V
Cr
Zn
PDMS, %
O
xi
da
tio
n,
%
100
80
60
40
20
0
Sn
D
epolym
erization, %
16
Fig. 4. Mass-spectrometric thermograms for PDMS adsorbed by pure fumed silica:
a - methane (16+m/z) and hexamethylcyclotrisiloxane (207+m/z) evolution from the sample
with 10% of adsorbed PDMS; b - hexamethylcyclotrisiloxane (207+m/z) evolution from the
samples with different contents of adsorbed PDMS: 1 – 5.3; 2 – 8.8; 3 – 10.2; 4 – 21.2 wt. %
Fig. 5. Mass-spectrometric thermograms of methane (16+m/z) resulting
from the destruction of MexOy/SiO2/PDMS (10%) samples.
Fig. 6. Mass-spectrometric thermograms for MexOy/SiO2/PDMS (10%) samples:
a - methane (16+m/z), b - hexamethylcyclotrisiloxane (207+m/z).
17
Oxides of vanadium, aluminum and phosphorus on silica surface promoted depolymerization of
PDMS to greater extent in comparison with other metal oxides. Degree of depolymerization
ranges up to about 80% for V/SiO2, P/SiO2 and Al/SiO2 samples contained 40% PDMS.
Thermal decomposition of PDMS in vacuum was analyzed by temperature-
programmed desorption mass spectrometry (TPD MS). The thermal destruction of
SiO2/PDMS samples resulted in formation of methane and volatile cyclic methylsiloxanes
(Fig. 4). Methane appeared simultaneously with the formation of cyclic products. Mainly, the
formation of hexamethylcyclotrisiloxane took place (207+ m/z). Contribution of
octamethylcyclotetrasiloxane (281+ m/z) was less than 10 mol. % in relation to
hexamethylcyclotrisiloxane. Formation of cyclic products in TPD MS experiment with polymer
adsorbed onto pure fumed silica took place in temperature range 250-700°C (Fig. 4, b).
However, in the mass-spectrum of the sample, contained 5.3% PDMS, the appropriate to
cyclic products signal was not observed. This fact may be explained by adsorption of PDMS
molecules in unfolded state. In this case the multidotted adsorption took place, which
essentially reduced molecular mobility of polymeric chain and prevented occurrence of loops
and rings, necessary for formation of volatile cyclic products.
Modification of silica surface by metal oxides expanded temperature interval of Si-C
bond destruction, accompanied by evolving of methane. Figs. 5 and 6, а demonstrate that
formation of methane in the vicinity of Тmax at 700-730°С was observed for all samples with
the modified surface, except silica modified by vanadium oxide.
Decomposition of Si-C bonds and formation of methane in the region of temperature
200-550°С was specific for each metal oxide. Chemical modification of silica surface with
products of polymer chain decomposition occurred during the thermal treatment of the
samples. Resulting chemisorbed dimethylsiloxane groups were responsible for the methane
formation at temperature higher than 550°С. Appearance of hexamethylcyclotrisiloxane at
vacuum decomposition of modified silica samples (Fig. 6, b) was observed in wider interval of
temperatures than it was observed for unmodified silica. This process began at 140-300°С and
was completed at 600-700°С, depending on modified silica composition (for samples with
10 % PDMS).
Conclusion
The thermooxidizing stability of dimethylsilyl groups, chemisorbed on fumed silica
surface, depends on composition of modifying metal oxide. The presence of metal oxides in
silica surface layer promoted depolymerization of adsorbed polydimethylsiloxane. The presence
of metals oxide on fumed silica surface resulted in decrease of starting temperatures of Si-C
bond destruction in vacuum and evolution of methane at 140-550 and 550-850°С.
References
1. Sobolevskii M.V., Skorokhodov I.I., and Grinevich K.P. Oligoorganic Siloxanes,
Khimiya, Moscow, 1985 (in Russian).
2. Alonso B. and Sanchez C. Structural investigation of polydimethylsiloxane-vanadate
hybrid materials // J. Mater. Chem. – 2000.- V.10. – P.377-386.
3. Wen J. and Mark J.E. Precipitation of silica-titania mixed oxide fillers into
poly(dimethylsiloxane) networks // Rubber Chemistry and Technology - 1994. - V.67, N5.
– P.806-818.
4. Kharitonov N.P. and Ostrovsky V.V. Thermal and Thermooxidizing Destruction of
Organopolysiloxanes. Nauka, Leningrad, 1982 (in Russian).
5. Bryk M.T. Destruction of Filled Polymers. Khimiya, Moscow, 1989 (in Russian).
18
6. Bogatyrev V.M. and Borisenko N.V. Thermal degradation of polydimethylsiloxane on the
surface of pyrogenic silica // Russ. J. Appl. Chem. - 1999. - V.72, N2. - P.305-311.
7. Bogatyrov V.M. and Borysenko M.V. Thermal destruction of polydimethylsiloxane on a
phosphorus-containing silica surface // J. Therm. Anal. Cal. - 2000. - V.62. - P.335-344.
8. Vansant E.F., Van Der Voort P., and Vrancken K.C. Characterization and Chemical
Modification of the Silica Surface // Studies in Surface Science and Catalysis. - V.93. -
Elsevier. Amsterdam – Tokyo, 1995.
9. Borysenko M.V., Gomenyuk A.A., Mutovkin P.O., Mykolaichuk V.V., Isarov O.V., and
Chuiko O.O. Study of reactions of chemical vapour deposition of chlorides and
oxochlorides of V and VI groups elements on a disperse silica surface // Chemistry of
Silica Surface. – Kyiv, 2001. - V.2. - P.327-368.
10. Bogatyrov V.M. and Chuiko O.O. Chemical and thermal transformations of surface
structures of a phosphorus-containing disperse silica surface // Ibid. - P.447-486.
M.V. Borysenko, V.M. Bogatyrov, A.G. Dyachenko, and
V.A. Pokrovskiy
V.A. Pokrovskiy
V.A. Pokrovskiy
V.A. Pokrovskiy
V.A. Pokrovskiy
V.A. Pokrovskiy
V.A. Pokrovskiy
Gen. Naumov Str. 17, 03680 Kyiv-164, UKRAINE
Sample
Modifier
Modifier
Zn-1.9
Zn-1.9
Zn-1.9
Conclusion
|
| id | oai:ojs.pkp.sfu.ca:article-78 |
| institution | Surface |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2025-07-22T19:30:05Z |
| publishDate | 2002 |
| publisher | Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | surfacezbircomua/12/9abe1a2d65b13bb594e106582944cc12.pdf |
| spelling | oai:ojs.pkp.sfu.ca:article-782018-11-27T09:42:19Z Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane Borysenko, M. V. Bogatyrov, V. M. Dyachenko, A. G. Pokrovskiy, V. A. Temperature programmed desorption mass spectrometry, thermogravimetry and differential thermal analysis were used to investigate the thermal destruction of adsorbed polydimethylsiloxane (PDMS) in air and vacuum conditions. Fumed silicas, whose surface contained grafted oxygen compounds of metals or phosphorus, were used as adsorbents. VOCl3, CrO2Cl2, TiCl4, SnCl4, AlCl3, PCl3 and Zn(Acac)2 vapors were applied as modifiers. It was found that in air the presence of metal oxides and phosphorus on silica surface lead to partial depolymerization of adsorbed PDMS. Degree of depolymerization ranges up to about 80% for V/SiO2, P/SiO2 and Al/SiO2 samples containing 40% PDMS. The presence of metal oxides on silica surface decrease of starting temperatures of Si-C bond destruction in vacuum and result in elimination of methane at 140-550 and 550-850°С. Temperature programmed desorption mass spectrometry, thermogravimetry and differential thermal analysis were used to investigate the thermal destruction of adsorbed polydimethylsiloxane (PDMS) in air and vacuum conditions. Fumed silicas, whose surface contained grafted oxygen compounds of metals or phosphorus, were used as adsorbents. VOCl3, CrO2Cl2, TiCl4, SnCl4, AlCl3, PCl3 and Zn(Acac)2 vapors were applied as modifiers. It was found that in air the presence of metal oxides and phosphorus on silica surface lead to partial depolymerization of adsorbed PDMS. Degree of depolymerization ranges up to about 80% for V/SiO2, P/SiO2 and Al/SiO2 samples containing 40% PDMS. The presence of metal oxides on silica surface decrease of starting temperatures of Si-C bond destruction in vacuum and result in elimination of methane at 140-550 and 550-850°С. Temperature programmed desorption mass spectrometry, thermogravimetry and differential thermal analysis were used to investigate the thermal destruction of adsorbed polydimethylsiloxane (PDMS) in air and vacuum conditions. Fumed silicas, whose surface contained grafted oxygen compounds of metals or phosphorus, were used as adsorbents. VOCl3, CrO2Cl2, TiCl4, SnCl4, AlCl3, PCl3 and Zn(Acac)2 vapors were applied as modifiers. It was found that in air the presence of metal oxides and phosphorus on silica surface lead to partial depolymerization of adsorbed PDMS. Degree of depolymerization ranges up to about 80% for V/SiO2, P/SiO2 and Al/SiO2 samples containing 40% PDMS. The presence of metal oxides on silica surface decrease of starting temperatures of Si-C bond destruction in vacuum and result in elimination of methane at 140-550 and 550-850°С. Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine 2002-06-12 Article Article application/pdf https://surfacezbir.com.ua/index.php/surface/article/view/78 Surface; No. 7-8 (2002): Chemistry, Physics and Technology of Surface; 11-18 Поверхность; № 7-8 (2002): Химия, физика и технология поверхности; 11-18 Поверхня; № 7-8 (2002): Хімія, фізика та технологія поверхні; 11-18 3154-8091 3154-8083 en https://surfacezbir.com.ua/index.php/surface/article/view/78/76 Авторське право (c) 2001 M.V. Borysenko, V.M. Bogatyrov, A.G. Dyachenko, V.A. Pokrovskiy |
| spellingShingle | Borysenko, M. V. Bogatyrov, V. M. Dyachenko, A. G. Pokrovskiy, V. A. Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane |
| title | Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane |
| title_alt | Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane |
| title_full | Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane |
| title_fullStr | Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane |
| title_full_unstemmed | Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane |
| title_short | Effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane |
| title_sort | effect of chemical modification of silica surface with metal oxides on the thermal properties of adsorbed polydimethylsiloxane |
| url | https://surfacezbir.com.ua/index.php/surface/article/view/78 |
| work_keys_str_mv | AT borysenkomv effectofchemicalmodificationofsilicasurfacewithmetaloxidesonthethermalpropertiesofadsorbedpolydimethylsiloxane AT bogatyrovvm effectofchemicalmodificationofsilicasurfacewithmetaloxidesonthethermalpropertiesofadsorbedpolydimethylsiloxane AT dyachenkoag effectofchemicalmodificationofsilicasurfacewithmetaloxidesonthethermalpropertiesofadsorbedpolydimethylsiloxane AT pokrovskiyva effectofchemicalmodificationofsilicasurfacewithmetaloxidesonthethermalpropertiesofadsorbedpolydimethylsiloxane |