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Synthesis and Characterization of Supramolecular Colloids
Published on: April 22, 2016
Anomalous silica colloid stability and gel layer mediated interactions.
Julie L Bitter1, Gregg A Duncan, Daniel J Beltran-Villegas
1Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States.
Langmuir : the ACS Journal of Surfaces and Colloids
|June 20, 2013
Summary
Total internal reflection microscopy reveals how silica (SiO2) colloid stability depends on pH and salt. Results show SiO2 gel layers influence particle interactions, explaining stability at high ionic strength and pH.
Area of Science:
- Colloid and Surface Science
- Materials Science
- Physical Chemistry
Background:
- Silica (SiO2) colloids are widely used in various applications.
- Understanding their stability under different conditions is crucial for controlling their behavior.
- Previous studies have not fully elucidated the role of surface gel layers in SiO2 colloid stability.
Purpose of the Study:
- To investigate the interactions and stability of SiO2 colloid ensembles.
- To determine the influence of pH and NaCl concentration on SiO2 colloid behavior.
- To quantify the properties of SiO2 gel layers and their impact on interparticle potentials.
Main Methods:
- Utilizing Total Internal Reflection Microscopy (TIRM) to measure SiO2 colloid ensembles on glass slides.
- Analyzing Brownian motion of colloids to obtain potential energy (U(h)) and diffusivity (D(h)) profiles.
- Fitting experimental data with models incorporating van der Waals, electrostatic, and steric potentials, including a gel layer.
Main Results:
- Potential energy and diffusivity profiles were obtained as a function of surface separation.
- SiO2 gel layers were estimated to be ~10 nm thick and exhibited ionic strength-induced collapse.
- The diffusivity profiles confirmed consistent surface separation scales for potential energy and hydrodynamic interactions.
Conclusions:
- SiO2 gel layers significantly influence van der Waals, electrostatic, and steric potentials.
- The presence and properties of gel layers explain the observed anomalous stability of SiO2 colloids at high ionic strength and pH.
- This study provides a comprehensive model for understanding SiO2 colloid interactions and stability.
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