You seem to battle with similar issues that I have to consider in my research, but my particles are completely different than yours it seems. Nevertheless - if this helps - I once played around Coulombic interactions so that either the hydrogel pre-polymers or pre-cursors were allowed to reach an equilibrium with NPs, after which the polymerization or cross-linking was initiated. There are many parameters involved there as NPs might catalyze (or retard) reactions and even react by themselves, but at least it seemed to work fairly well with my NPs (i.e. I was able to polymerize hydrogel from its monomeric species on NP surface). Results might also be interesting since the NPs could affect to polymer tacticity (hydrogels ought to be random though?). Well, anyhow, this was just one idea to play around.

To answer that, it will be really useful to know which is the polymeric matrix of the hydrogel.

I would disperse first the nanoparticles in water (or any proper solvent) using ultrasound (15-25 min.), them I will use this solution to prepare the hydrogel (by reaction or just by swelling) after good mixing all components through a mechanical stirring.

How do you define 'uniformly'? You mean particles are evenly distributed in the matrix without touching each other? or they are well dispersed but small clusters forms? Generally, for the former, you need to increase the interaction between the nanoparticles and the matrix; for the latter, you can simply do it by increasing the miscibility of the two phase.

Please refer to my review paper: Cobalt-based magnetic nanocomposites: fabrication, fundamentals and applications

Link:

http://iopscience.iop.org/0022-3727/44/39/393001

Thanks for your answers. In fact, I am dealing with two different methods of synthesizing nanocomposite hydrogels. In the case of Fe2O3 and Ag, I use in situ approach, but for MWCNTs ex situ. @ Milsloslav>> The question is that how I can synthesize these particles with highest stability and dispersion in in situ approach and MWCNT can be better dispersed in the matrix in ex situ.

@Vera>> defferent polymeric matrix are being tested. Acrylamide-based, Carrageenan-based and Chitosan-based hydrogels.

If particle concentration you need is low, you may try to use polymer-transition metal salts (for example, Fe acrylate) and complexes (metal coordinated with chitosan) to prepare both nanoparticles and gel matrix by distribution of the salt in water and then reducing agent addition.

It is important the compatibilization of particle and hydrogel matrix. For example, PVP stabilizes Ag nanoparticles, so this kind of nanoparticles can be uniformly dispersed on PVP hydrogels. You can funcionalize the particles with a polymer compatible with your hydrogel, or synthesize your particles in the presence of a little amount of the polymer that composes the gel.

i would prefer, dispersing the nano particle in to the monomer , ultrasonicate the mixture for dispersing them properly ( 15-25 min, it may vary) and then add the initiator, cross-linker to the mixture for polymerization to occur. in my case it works well.Good luck.

Actually, an interesting approach would be to prepare coated nanoparticles, containing hydrophylic groups (like amide) and vinyl or acrylic at the same time on the surface. Initialization of polymerisation could lead to polynanoparticles, that form gel due to amide groups. Probably, vinyl or acrylic groups should be attached to nanoparticle by long spacer...

I think, the most important is the compatibility of hydrogel and nanoparticles. should have close or equal index of refraction to maintain the transparency. The size and solubility of the particle (whatever solvent ) is also important. Large size particle can result into scattering of light. If the particle is completely soluble, then high concentration of particle can be loaded.

Hi Hadi, when you say Fe2O3 you mean maghemite? We were successful in the preparation of magnetite nanoparticles in carrageenan hydrogel matrices (kapa, iota and lambda) using in situ co-precipitation method. You can find more details in the article:In situ synthesis of magnetite nanoparticles in carrageenan gels.

Ana L Daniel-da-Silva, T Trindade, Brian J Goodfellow, Benilde F O Costa, Rui N Correia, Ana M Gil , Biomacromolecules . 09/2007; 8(8):2350-7. DOI:10.1021/bm070096q

Thanks Ana, I have already studies your researches and publications, namely those on magnetic nanocomposite hydrogel, published in carbohydrate polymers and ..... Thanks any way.

Thanks to every all you for your valuable comments,

Try to study the wetability of thee matrix with the nano particle.