Tunable mesoporosity and hydrophobicity of natural rubber/hexagonal mesoporous silica nanocomposites

Abstract

Polymer/silica nanocomposites with diverse mesoporosity and hydrophobic properties have actual and potential applications in the area of catalysis, adsorption and drug delivery. The present work reports a simple but efficient approach to tune the mesostructure and hydrophobicity of natural rubber (NR)/hexagonal mesoporous silica (HMS) nanocomposites synthesized via the in situ sol-gel technique in the presence of different primary amines (C n H 2 n +1 NH 2 , n = 8, 10, 12, 14 and 16) as structural templating agents. The change in the mesostructure ordering and textural properties of the NR/HMS nanocomposites with different template sizes was similar to that for the pure silica HMS series. Powder X-ray diffraction and transmission electron microscopy analyses revealed an expansion of the hexagonal unit cell and channel wall thickness of the nanocomposites due to the incorporated rubber molecules. Using amine templates with longer alkyl chains provided NR/HMS materials with a higher NR content at 13.7–15.6 wt% but decreased the rubber phase dispersion and hydrophobic properties. X-ray photoelectron spectroscopy indicated that the amount of NR exposed at the composite's surface was 7.99–9.48 wt%, while the remaining NR was incorporated into the mesostructured silicate framework and/or entrapped in the mesopores. The hydrophobic interaction between the NR molecules and the alkyl chains of primary amine template was probably a crucial factor that determined the rubber phase dispersion, and so the hydrophobic character, in the NR/HMS nanocomposites. • A series of NR/HMS nanocomposites were synthesized via in situ sol-gel method. • Their mesoporosity and hydrophobicity varied with type of primary amine template. • Using longer amine templates enhanced the rubber content but lowered dispersion. • Using shorter amine templates gave the materials with more hydrophobic surface.