1. INFLUENCE OF ADSORBED PDMS-400 ON THE TEXTURAL FEATURES
CCTA th CONFERENCE ON CALORIMETRY AND THERMAL ANALYSIS
of the POLISH SOCIETY OF CALORIMETRY AND THERMAL ANALYSIS (PTKAT)
and
5th JOINT CZECH - HUNGARIAN - POLISH - SLOVAKIAN
THERMOANALYTICAL CONFERENCE
INFLUENCE OF ADSORBED PDMS-400
ON THE TEXTURAL FEATURES
OF THE TERNARY CeO2–ZrO2/SiO2 NANOOXIDES
I. Sulym1*, D. Sternik2, M. Borysenko1, A. Deryło-Marczewska2 1Chuiko Institute of Surface Chemistry, National Academy of Sciences of Ukraine, 17 General Naumov Str., Kyiv 03164, Ukraine, 2Faculty of Chemistry, Maria Curie-Skłodowska University, pl. Maria Curie-Skłodowska 3, Lublin, Poland
INTRODUCTION
Polymer nanocomposites based on poly(dimethylsiloxane) (PDMS) matrices reinforced with metal nanooxides (silica, zirconia and ceria) have attracted attention due to easy chemical processing, good mechanical, thermochemical, and non-toxic properties allowing the use in various applications.
The current work presents the studies of textural and morphological properties of CeO2–ZrO2/SiO2/PDMS composites by using low temperature nitrogen adsorption/desorption, FTIR spectroscopy, TG/DTG analysis and scanning electron microscopy (SEM).
EXPERIMENTAL
Ceria–zirconia coated silica nanocomposites were prepared by liquid-phase method with the use of Zr(acac)4 and Ce(acac)3 solutions in CCl4, and fumed SiO2 and then subjected to thermal treatment at 550 °С. The content of grafted CeO2 varied from 3 to 10 wt. %, while ZrO2 content was held constant at 10 wt. % (CeZrSi1 and CeZrSi2, respectively). Liquid PDMS-400 fluid (molecular weight Mw ≈ 5700, polymerization degree dp = 75) was adsorbed onto oxide surfaces in the amounts of 5 and 40 wt. %.
RESULTS AND DISCUSSION
Nitrogen adsorption-desorption isotherms for neat oxides (SiO2, CeZrSi1, CeZrSi2) (Fig. 1, Table 1) and after adsorption of PDMS at 5 – 40 wt. % (SiO2P5, SiO2P40, ZrCeSi1P5, ZrCeSi1P40, ZrCeSi2P5, ZrCeSi2P40) demonstrate sigmoidal-shaped behavior with narrow hysteresis loops of the H3 type in the p/p0 range between 0.8 and 1.0 (Fig. 1a,b). This indicates the formation of aggregates of initially non-porous particles that are characterized by textural porosity. The incremental pore (the voids between particles in aggregates) size distribution functions (Fig. 1c) show that the textural characteristics of SiO2 change after the modification. The values of the specific surface area SBET (Table 1) do not demonstrate significant changes after grafting of ceria/zironia. Furthermore, analysis of the results suggests the existence of mainly meso-porosity for aggregates of initial SiO2 and mainly macro-porosity for aggregates of modified SiO2 (Fig. 1c).
Table 1. Textural characteristics of initial oxides and oxide/PDMS-400 composites
In general, the average pore radii (RV in Table 1) are by almost 2 times greater in ZrCeSi1 and ZrCeSi1, as compared to the unmodified SiO2. The textural characteristics of the oxides were modified due to adsorption of PDMS (Table 1 and Fig. 1d). Specific surface area, SBET, of all composites was reduced with increase of polymer content. The value of SBET decreases by 74%, 75% and 78% (in comparison to the initial oxides) for SiO2P40, ZrCeSi1P40 and ZrCeSi2P40, respectively, after the adsorption of 40 wt. % of PDMS (Table 1). The polymer adsorption leads to suppression of the pore volume (Vp) as well as Vmeso and Vmacro. After addition of PDMS, the average pore radii (Table 1, RV) decrease. In general, the addition of polymer can change the porosity characteristics because each long macromolecule can be able to bind several oxide nanoparticles and their aggregates in more compacted structures. This leads to the decrease in the volume of voids between particles.
Sample
SБET
(m2/g)
Smicro
Smeso
Smacro
Vmicro
(cm3/g)
Vmeso
Vmacro Vp
cm3/g RV nm
SiO2
283.4
21.0
224.9
37.5
0.008
0.348
0.569
0.925 29
SiO2P5
224.8
27.1
131.9
65.8
0.002
0.054
2.168
2.224
SiO2P40
73.9
2.2
49.6
22.1
0.000
0.027
0.952 36
ZrCeSi1
250.8
23.2
146.7
80.9
0.007
0.067
1.257
1.331 54
ZrCeSi1P5
204.8
32.0
139.8
33.0
0.018
0.678
0.703
1.399 26
ZrCeSi1P40
63.0
4.1
26.4
32.5
0.080
0.668
0.75 40
ZrCeSi2
258.9
14.2
158.3
86.4
0.004
0.073
1.353
1.430 55
ZrCeSi2P5
201.3
30.2
144.6
26.5
0.017
0.729
0.549
1.295 23
ZrCeSi2P40
57.9
6.8
35.9
15.2
0.001
0.048
0.333
0.382 28
Note. Specific surface area in total, SBET, of micropores, Smicro, mesopores, Smeso, macropores, Smacro, and respective specific pore volumes, Vp, Vmicro, Vmeso, Vmacro. RV represents the average pore radii determined from the differential PSD with respect to the pore volume.
Figure 2 illustrates the SEM images changes in the outer surfaces of samples due to the adsorption of PDMS. One can clearly observe in Fig. 2a-b the structures (aggregated) varying between 50 and 250 nm in size.
Fig. 2. SEM micrographs of SiO2/PDMS (a) and CeZrSi1/PDMS (b) composites at CPDMS = 40 wt. %.
Fig. 1. Nitrogen adsorption–desorption isotherms (a, b) and incremental pore size distributions (c, d) of oxides before (a, c) and after adsorption of PDMS-400 (b, d).
Acknowledgement. This work was supported by the People Programme
(Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/ / under REA grant agreement n° PIRSES-GA
Zakopane, Poland, 6  - 10 September 2015