What is the effect of water on 3-aminopropyltriethoxysilane (APTES)?

(3-Aminopropyl)triethoxysilane (APTES), an aminosilane initially developed as an adsorbent for affinity chromatography, has evolved into a versatile tool for improving surface chemistry in cell studies and microfluidic device fabrication. Following plasma cleaning, a treated material’s surface has high free energy, is free of contaminants, and is decorated with hydrophilic functional groups. Over a long period, this high-energy state abates as molecules rearrange, move back into the bulk, and ultimately take on a lower-energy configuration. Subsequent treatment with APTES swaps surface functional groups for the hydrophilic, amine-carrying molecule. This allows for long-term studies in which the surface hydrophilicity of a treated material is maintained.

The effect of water on the reaction of 3-aminopropyltriethoxysilane (APTES) with mesoporous silica is investigated by Gartmann et al. on two model systems. An MCM-41- type material with a well-defined pore size is used to investigate changes in the pore size distribution upon reaction with APTES in toluene containing various amounts of water. It is found that, with increasing amounts of water, clustering of APTES occurs, leading to a non-uniform distribution of the grafted amino groups and a scarcely functionalized pore body. A second model system with defined particle morphology and one-dimensional channels is employed to visualize the distribution of the grafted amino groups by fluorescent labeling and confocal laser scanning microscopy. The combination of nitrogen sorption and confocal laser scanning microscopy provides valuable insights concerning the role of trace water in the functionalization of mesoporous silica with alkoxysilanes.

References

[1] Nando Gartmann. “The Effect of Water on the Functionalization of Mesoporous Silica with 3-Aminopropyltriethoxysilane.” The Journal of Physical Chemistry Letters 1 1 (2010): 379–382.