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What kind of bonds silica bead forms with polystyrene? Silica is now as ~100 $\mu$m spherical particles in bulk polystyrene that is made by melting.

How can I bond the silica particles

  1. more tightly

  2. more loosely

to the polystyrene?

Can this be generalized to any nano/micro particle and plastics? I am thinking now metal oxides and other thermoplastics.

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    $\begingroup$ The main chemical groups on the surface of silica beads are silanol groups –SiOH. The main control one over their surface chemistry is thus the functionalization of these silanol groups. $\endgroup$ – F'x May 12 '12 at 21:58
  • $\begingroup$ First, You should define what You mean with "silica beads"! Some kinds of (the dozens of materials called silica) have maybe silanol groups, but most important Polystyrene will not form bonds to them. Why do You think there are bonds? $\endgroup$ – Georg May 15 '12 at 21:15
  • $\begingroup$ Polymers do hydrogen bonding (van der Waals, etc.) with each other, right? Then silanol groups should bond with these? Lets assume that these particles are basic hardware stuff that is used for sand blasting (vwr part number 201-0481 [EN]GLASS BEADS SILIBEADS S D0,04-0,07MM). I would assume that they are very inert. And the question is, how can I activate or deactivate (functionalize/defunctionalize) these bonds to react with polystyrene? $\endgroup$ – Juha May 18 '12 at 8:02
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You can functionalize silica to add polymer "brushes" to the surface. You can also buy pre-made functionalized silica, although the downside to that is it isn't always easy to get the manufacturer to tell you exactly what is on the surface.

This isn't really going to increase the attractive interactions between the silica and the polystyrene, however. Polystyrene has a bulky aromatic ring hanging off of each monomer, and no sites that can participate in hydrogen bonding. When you add hydrophobic brushes to the surface of the silica, what you are doing is limiting the ability of the silica to aggregate due to hydrophilic interactions with itself. As a result, given enough kinetic energy (temperature for melt casting, or sonication for solvent casting) you can get the particles to disperse. Then, if you solidify the polymer quickly enough, they will be kinetically trapped in a dispersed state.

Depending on what your goal is, this could be enough for your application. However, if you want to get the particles to strongly attract to the polystyrene, you aren't going to be able to get much farther than van der Waals interactions. That's a limitation of the polystyrene, not the silica.

Other particles (gold, or carbon nanotubes, for example) will be more hydrophobic and easier to disperse without functionalizing, but you still are not going to get very strong attractive forces between the particles and the polymer.

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