Colloidal Silica Surface Modification for Organic Solvent Stability
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Solution Overview
Problem
Existing processes for producing colloidal silica particles in organic solvent-dispersed silica sols face issues with stability, leading to viscosity increases, gelation, and decomposition of organic compounds, particularly due to poor electrostatic repulsion and catalytic action by solid acid sites, which affects their compatibility and reactivity with resins.
Innovation Solution
A process involving the addition of polyvalent metal elements like iron, aluminum, or zinc to silica sols, followed by acid treatment and exchange resin interactions, to control the surface charge and reduce solid acid action, resulting in colloidal silica particles with improved stability and dispersion in organic solvents and polymerizable compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If alkali metal ions are removed from aqueous silica sol by cation exchange to improve compatibility with organic solvents, then the silica sol can be mixed with organic solvents, but the electrostatic repulsion between colloidal silica particles decreases and gelation occurs over time
Solution Approach 1:
The patent changes the chemical parameter of the silica sol by introducing polyvalent metal ions (such as Al³⁺, Fe³⁺, Zn²⁺) to replace alkali metal ions. This parameter change maintains electrostatic repulsion between particles while improving compatibility with organic solvents, preventing both gelation and decomposition
Solution Approach 2:
The patent uses polyvalent metal ions as intermediary substances that mediate between the colloidal silica particles and the organic solvent environment. These metal ions provide both electrostatic stabilization and compatibility with organic solvents, resolving the contradiction between stability and adaptability
2Ease of manufacture
If acidic aqueous silica sol is used as raw material for organic solvent-dispersed silica sol, then the production process is simplified, but the solid acid sites cause decomposition and discoloration of organic compounds
Solution Approach 1:
The patent changes the chemical composition parameter by introducing polyvalent metal ions that modify the surface properties of silica particles. This reduces the solid acid catalytic activity while maintaining the simplified production process from acidic silica sol, preventing decomposition and discoloration of organic compounds
Solution Approach 2:
The patent converts the harmful solid acid sites into beneficial sites by introducing polyvalent metal ions that reduce excessive acidity while maintaining colloidal stability. The metal ions transform the harmful catalytic activity into controlled surface properties that prevent organic compound decomposition
3Productivity
If silica concentration is increased in acidic aqueous silica sol to improve substitution efficiency, then more silica can be dispersed, but viscosity increases and gelation occurs due to poor electrostatic repulsion
Solution Approach 1:
The patent changes the electrostatic parameter by introducing polyvalent metal ions that enhance the repulsion between particles. This allows higher silica concentration to be achieved without gelation, improving substitution efficiency while maintaining stability
Solution Approach 2:
The patent performs preliminary stabilization by introducing polyvalent metal ions before increasing silica concentration. This preliminary action ensures that electrostatic repulsion is sufficient to prevent gelation even at high concentrations, enabling efficient substitution
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process produces colloidal silica particles with enhanced stability and reduced decomposition in organic solvents and polymerizable compounds, enabling their use as effective reforming agents for resins without causing gelation or discoloration, and achieving high silica concentrations in cured epoxy products with improved heat resistance and strength.
Implementation Method 1
alkali metal ions such as Na ions contained in the aqueous silica sol are previously removed by cation exchange
Implementation Method 2
The alkaline aqueous silica sol containing the alkali metal ions has poor compatibility with many organic solvents such as alcohols and ethers and thus the mixing with such organic solvents causes the aggregation or the gelation of the colloidal silica particles
Implementation Method 3
the obtained sol is aged without treatment or in the presence of a small amount of an acid to diffuse the alkali metal ions in the colloidal silica particles into the colloid dispersion medium
Implementation Method 4
an aqueous silica sol and an organic solvent are mixed and then the mixture is dehydrated with an ultrafiltration membrane
Data Source
AI summary
There is provided colloidal silica particles comprising at least one polyvalent metal element M selected from a group consisting of iron, aluminum, zinc, zirconium, titanium, tin, and lead in an average content of 0.001 to 0.02 in terms of an M/Si molar ratio, and having an average primary particle diameter of 5 to 40 nm, wherein the content of the polyvalent metal element M present in an outermost layer of the colloidal particles is 0 to 0.003 atom per square nanometer (nm2) of a surface area of the colloidal particles; and a silica sol that the colloidal silica particles are dispersed in an organic solvent, a silica sol that the colloidal silica particles are dispersed in a polymerizable compound, and a silica sol that the colloidal silica particles are dispersed in a dicarboxylic anhydride. The colloidal silica particles do not cause decomposition, discoloration and the like of an organic compound even when they are dispersed in the organic compound, although the prior colloidal silica particles have caused them due to the action of solid acid on the surface thereof. The silica sols of the present invention do not cause decomposition, discoloration and the like of a resin even when they are mixed into the resin, and have good dispersion stability to a dispersion medium.