To reduce the probability of electric breakdown in Polyimides - as one of the most widely used is an addition of silica or alumina nanoparticles.
There are many publication where the introduction of colloidal silica is proposed to be done on the stage of polyamic acid synthesis via in situ sol-gel method - by using TEOS. As a whole - the idea of addition of inorganic nanoparticles to the final product - polyimide (P) by the above described process does work. However the size and the size distribution of nanoparticles is difficult to control. As a result often the size distribution of, for example, silica nano can range from, say 20-50nm up to >1mcm.
The sonication of the reaction mixture on the stage of polyamic acid (PAA) synthesis - usually - reduces the Mw of PAA - this negatively affects the properties of PI.
In brief, the question is: How to fill the PAA with inorganic rather small 30-100nm nanoparticles via simultaneous synthesis of inorganic fller and PAA ?
You might find some information fromt he following papers:
“An optimized sol-gel synthesis of stable primary equivalent silica particles,” Colloids and Surfaces A, vol. 294, no. 1–3, pp. 102–110, 2007.
This study reported to produce a homogeneous and stable silica nanoparticles with mean particles size of 7.1±1.9 nm (in ethanol).
Journal of Nanomaterials
Volume 2012 (2012), Article ID 132424, 15 pages
http://dx.doi.org/10.1155/2012/132424
Synthesis of Silica Nanoparticles by Sol-Gel: Size-Dependent Properties, Surface Modification, and Applications in Silica-Polymer Nanocomposites—A Review
Sir,
The question is related to simultaneous synthesis of stable silica nanoparticles of very small size during the synthesis of PAA. I am sure there are lots of references or reports of silica nanoparticle synthesis and polyamic acid synthesis but separately.
Combining inorganic (silica nanoparticles) and organic (polymer) synthesis together will be tricky as pointed out by your self; the optimum conditions chosen for one synthesis may not be the optimum for the other. One option can be first to synthesize silica particles of desired size and then carry out surface polymerization (or polymerization on surface) of the desired polymer. Other option is to synthesize properly stabilized silica nanoparticles and disperse them into the polymer solution (Nanocomposite preparation). Stabilizers or surface modifiers can be chosen in such as way that it can guarantee improved dispersability in the desired polymer matrix. But if you use bare silica nanoparticles they will aggregate during their addition in the polymer solution again as point out by you.
Hi,
Introducing pre-synthesized silica nanoparticles of define size and surface properties (using suitable silane coupling agent for surface modification) into the polymer solution can be a good option for the mentioned problem.
Following articles might be useful for you.
http://www.mdpi.com/1996-1944/3/7/4066
http://onlinelibrary.wiley.com/doi/10.1002/pc.20436/abstract
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