titanium oxide compounds have strong affinity toward carboxylate-bearing molecules. You may want to look for a suitable compound (e.g. a silane) with -COOH as end-group. Titanium oxide materials are often hydroxilated on the surface, that is the trick.

Try to do the reaction with octadecyltrimetoxysilane ( C18H37Si(OCH3)3 ). If the surface of TiO2 is hydroxylated, it can attached like to the surface of SiO2 (there is a lot of literature on SiO2 functionalization).

Other choice: try phosphonic acids with long alkyl chains.

titanium oxide compounds have strong affinity toward carboxylate-bearing molecules. You may want to look for a suitable compound (e.g. a silane) with -COOH as end-group. Titanium oxide materials are often hydroxilated on the surface, that is the trick.

You can also try oxygen plasma treatment of your TiO2 samples to create some favorable functional group on it.

You may also try simply stearic acid coating from aqueous solution.

Use lactic acid

Hi Adam,

I suggest you to surface modify your TiO2 nanoparticles with octylphosponic acid. This surfactant is probably the best choice when you deal with PMMA. You can find the details in this paper just published on J Mater Chem C

A. Colombo et J. Mater. Chem. C, 2013,1, 2927-2934

A possible alternative is to grow directly the polymer on the nanoparticle, we used RAFT polymerization, take a look at

M. Crippa et al J. Mater. Chem. C, 2013,1, 484-492.

Thank you all so much for these valuable comments. If anyone else has any papers they'd recommend, As Roberto did, then I'd be grateful...

All metal oxide particles have reactive surface toward alky-alkoxysilane molecules (or coupling agents). Many papers in litterature deal with this subject. In genaral you have just to disperse your particles in a mixture EtOH/water (80/20 vol.) at a pH around 5 and then add small amounts of coupling agent (depending on the metal oxide size. If you adde too much molecules you can have aggregation between particle) at room temperature for 2h. You recover the nanoparticle by centrifugation. The silane is strongly adsorbed at the surface of the nanoparticles. You redisperse the nanoparticle again in a mixutre ETOH/ water and increase temperature to get reflux during 30 min in order to favorise chemical coupling between the silane and particles.

You recover you particles by centrifugation. They should then become dispersible in organic solvent.

We have functionalyzed TiO2 with 3-aminopropyltrimethoxysilane using similar procedure as described in:

a) Souza, Adriano L. ; Marques, Lygia A. ; Eberlin, Marcos N. ; Nascente, Pedro A.P. ; Herrmann, Paulo S.P. ; Leite, Fabio L. ; Rodrigues-Filho, Ubirajara P. . Self-assembled hybrid films of phosphotungstic acid and aminoalkoxysilanes on SiO2/Si surfaces. Thin Solid Films, v. 520, p. 3574-3580, 2011.

b) REIS, Rafael Machado ; GONZALEZ, Eduardo Perez ; SANTOS, Leonardo S ; EBERLIN, Marcos N ; NASCENTE, Pedro Augusto de Paula ; TANIMOTO, S. T. ; MACHADO, S. A. S. ; RODRIGUES FILHO, U. P. . Adsorption of silanes bearing nitrogenated Lewis Bases on SiO2/Si (100) model surfaces. Journal of Colloid and Interface Science, v. 286, p. 303-309, 2005.

However, the results strongly depend on the functionality you want on the semiconductor-organic layer interface as well as the organic layer-air interface.

The question is which TiO2 particle size you want to disperse into PMMA. There are basically 2 grades: truely nanoscopic TiO2 which is transparent and used as UV absorber in sunscreen, or roughly 1 - 2 µm small particle size which is the white pigment.

The former one is not easy to disperse, but I would not use any functionalisation: I would use acetone, ultrasound and disperse the nano-TiO2 therein, after having done so, add PMMA (possibly need to warm it up under reflux). Don't use too high PMMA concentration, maybe max 1% in Acetone, so maybe only 0.01% of the nano-TiO2 to be dispersed in acetone first, finally you remove the acetone and have a nice dispersion of 1% TiO2 in PMMA.

If you are looking for dispersing the real white pigment TiO2, you can easily do by melt or solution dispersion, no need for any dispersion aid, but also it wouldn't harm.