TY - JOUR
T1 - Viscoelastic characterization of TEOS sols in three different solvents when DBTL is used as polycondensation catalyst
AU - Salazar-Hernández, Carmen
AU - Cervantes, Jorge
AU - Alonso, Sergio
N1 - Funding Information:
Acknowledgments The authors wish to acknowledge the financial support of the Consejo Nacional de Ciencia y Tecnología (CONA-CYT-Mexico) through grant 25397.
PY - 2010/4
Y1 - 2010/4
N2 - The gelation process of TEOS sols in three different solvents using di-n-butyltin dilaurate (DBTL) as polycondensation catalyst has been investigated. Sol compositions were similar to those employed in the field of stone consolidation for the conservation of historical buildings. Three different systems were studied: TEOS in ethanol (S-EtOH) which was tested to explain gelation in protic solvents; TEOS in a mixture of methylethylketone/ acetone (S-MA) to represent aprotic solvents; and TEOS in a blend of MEK/ethanol (S-ME) for comparison of a system with properties intermediate between protic and aprotic solvents. The gelation process was studied by measuring the viscoelastic behavior near the gelation point (GP). A scaling exponent (Δ) was determined for the elastic modulus, G(ω) and the viscous modulus, G (ω), which both follow the same power law, ωΔ, at GP. The fractal dimension, df, was calculated from the scaling exponent, Δ, for each TEOS-DBTL system. For each type of solvent studied, values of Δ from 0.34 to 0.53 with df of 1.9-2.2 were obtained. The results suggest that DBTL leads to a TEOS polycondensation mechanism similar to that observed for a base-catalyst system. However, the change in df suggests that there is a significant effect of the solvent on aggregation mechanisms of the gelation process. A diffusion limited cluster-cluster aggregation mechanism (DLCCA) was observed when ethanol was used as protic solvent, while a reaction limited cluster-cluster aggregation mechanism (RLCCA) was observed for MEK/acetone (aprotic solvent).
AB - The gelation process of TEOS sols in three different solvents using di-n-butyltin dilaurate (DBTL) as polycondensation catalyst has been investigated. Sol compositions were similar to those employed in the field of stone consolidation for the conservation of historical buildings. Three different systems were studied: TEOS in ethanol (S-EtOH) which was tested to explain gelation in protic solvents; TEOS in a mixture of methylethylketone/ acetone (S-MA) to represent aprotic solvents; and TEOS in a blend of MEK/ethanol (S-ME) for comparison of a system with properties intermediate between protic and aprotic solvents. The gelation process was studied by measuring the viscoelastic behavior near the gelation point (GP). A scaling exponent (Δ) was determined for the elastic modulus, G(ω) and the viscous modulus, G (ω), which both follow the same power law, ωΔ, at GP. The fractal dimension, df, was calculated from the scaling exponent, Δ, for each TEOS-DBTL system. For each type of solvent studied, values of Δ from 0.34 to 0.53 with df of 1.9-2.2 were obtained. The results suggest that DBTL leads to a TEOS polycondensation mechanism similar to that observed for a base-catalyst system. However, the change in df suggests that there is a significant effect of the solvent on aggregation mechanisms of the gelation process. A diffusion limited cluster-cluster aggregation mechanism (DLCCA) was observed when ethanol was used as protic solvent, while a reaction limited cluster-cluster aggregation mechanism (RLCCA) was observed for MEK/acetone (aprotic solvent).
KW - Aggregation mechanism
KW - DBTL
KW - Fractal dimension
KW - Solvent
KW - TEOS
KW - Viscoelasticity
UR - http://www.scopus.com/inward/record.url?scp=77951255910&partnerID=8YFLogxK
U2 - 10.1007/s10971-010-2160-6
DO - 10.1007/s10971-010-2160-6
M3 - Artículo
SN - 0928-0707
VL - 54
SP - 77
EP - 82
JO - Journal of Sol-Gel Science and Technology
JF - Journal of Sol-Gel Science and Technology
IS - 1
ER -