Influence of TiO 2 on the Pore Structure and Texture of SiO 2 -PDMS Hybrid Materials
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EE9.20.1
Influence of TiO2 on the Pore Structure and Texture of SiO2-PDMS Hybrid Materials Lucía Téllez1, Juan Rubio2, Miguel A.Valenzuela3, Fausto Rubio2, Ernesto Morales2 and José L. Oteo2 1
Dpt. Ingeniería Metalúrgica. ESIQIE-Instituto Politécnico Nacional. Zacatenco, 07738, México D.F., México. 2 Instituto de Cerámica y Vidrio. C.S.I.C. Campus de Cantoblanco, 28049. Madrid. Spain. 3 Lab. Catálisis y Materiales. ESIQIE-Instituto Politécnico Nacional. Zacatenco, 07738, México D.F., México.
ABSTRACT Porous SiO2-PDMS-TiO2 hybrid materials have been prepared by the Sol-Gel method using tetraethoxysilane (TEOS), silanol terminated-Polydimethylsiloxane (PDMS) and tetrabuthylortotitanate (TBT) as precursors. These materials were characterized by means of nitrogen adsorption, mercury porosimetry and helium picnometry. It was found that the meso and microporosity are predominant in all samples. The influence of the TBT concentration in the final pore structure and texture of SiO2-PDMS-TiO2 hybrid materials was studied. Results showed that increasing the TBT concentration decreases the pore volume of micropores, mesopores and macropores. On the other hand the specific surface areas of meso and macropores decreases with increasing TBT content, but micropore areas increase with TBT. These results are assigned to the formation of ultramicropores when TBT is added. In addition, surface roughness is found to increase with TBT concentration which is attributed to the formation of hydrous titanium oxide based nanoparticles. INTRODUCTION The development of hybrid materials is based on the incorporation of oligomerics and polymeric species into the inorganic matrix constituted by Si-O-Si linkages. Tetra-alkoxysilanes give “in-situ” the inorganic matrix from hydrolysis and polycondensation reactions into organic polymers [1,2]. PDMS can be incorporated into a siloxane network derived from TEOS [3,4]. Mackenzie et al. [4] have demonstrated that the incorporation of PDMS gives different properties such as porosity, hydrophobicity, etc. Hybrid materials from the PDMS–TEOS system possess different pore structures depending on many factors such as PDMS/TEOS, HCl/TEOS, H2O/TEOS, solvent/TEOS ratios, temperature and reaction time, molecular weight and average chain length of PDMS, etc. [4-7]. Titanium alkoxides instead of/with TEOS have also been incorporated into these hybrid materials [8,9]. Babonneau [10] has shown that the TBT can act as a crosslinking agent between organosilicon units affecting the structure. Rubio et al. [11] have studied the incorporation of TiO2 from titanium alkoxide into the TEOS-PDMS system using PDMS with 1750 molecular weight, HCl/ inorganic ratio of 0.3. They showed that the increase of TiO2 increases the volume of micropores and decreases the volume of mesopores and macropores.The aim of this work is to know the influence of the TBT concentration in the final pore structure and texture of TEOS-PDMS-TBT hybrid materials when both low molecular weight PDMS and low acid concentration are used.
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