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Surface modification of cured cement pastes by silane coupling agents.
Andrew Stewart1, Brett Schlosser, Elliot P Douglas
1Department of Material Science and Engineering, University of Florida, Box 116400, Gainesville, Florida 32611, USA.
ACS Applied Materials & Interfaces
|January 15, 2013
Summary
Silane coupling agents modify cement paste surfaces, altering surface energy and forming covalent bonds. X-ray photoelectron spectroscopy and contact angle measurements confirmed successful silane-cement interactions, influenced by silane type and water-to-cement ratio.
Area of Science:
- Materials Science
- Surface Chemistry
- Nanotechnology
Background:
- Silane coupling agents are crucial for enhancing interfacial adhesion in composite materials.
- Understanding silane interactions with cementitious materials is key to improving durability and performance.
- Cement paste surfaces possess hydroxyl groups that can react with silanes.
Purpose of the Study:
- To investigate the surface interactions between different silane coupling agents and cured cement paste.
- To evaluate the impact of silane end groups and water-to-cement ratio on surface properties.
- To confirm the formation of covalent bonds between silanes and cement paste.
Main Methods:
- X-ray photoelectron spectroscopy (XPS) was employed to analyze surface elemental composition and chemical states.
- Static contact angle measurements were used to assess changes in surface energy and hydrophobicity/hydrophilicity.
- Deconvolution of O 1s and Si 2p XPS peaks provided insights into bridging and nonbridging atom contributions.
Main Results:
- Aminopropyltriethoxy silane (APTES) decreased contact angle, while methoxy-terminated polydimethylsiloxane (PDMS) increased it; 3-glycidyloxypropyltrimethoxy silane (GPTMS) showed no significant change.
- Higher water-to-cement ratios (0.5 vs. 0.4) resulted in a greater change in contact angle, indicating more surface hydroxyl groups.
- XPS analysis revealed an increase in bridging silicon and oxygen atoms, signifying successful silane condensation and covalent bond formation.
Conclusions:
- Silane coupling agents effectively interact with cement paste surfaces, with varying effects based on their chemical structure.
- Surface hydroxyl group availability, influenced by the water-to-cement ratio, plays a significant role in silane reactivity.
- The study confirms the formation of covalent bonds between silanes and cement paste, crucial for material enhancement.
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