I am no expert in XRD, so please excuse me if make silly suggestions~

I think it all depends on what kind of information you would like to gain from those experiments~ if your samples are difficult to dry, maybe SAXS (can be used for both solution and solid samples) will do the trick? 

All the best with your research~

x ray diffraction or small angle xray scattering can certainly be done using synchrotron radiation to measure colloids.

As synchrotron sources develop and are able to provide higher coherence, other techniques also become possible such as ptychography for imaging and XPCS for studying colloid dynamics.

The following papers (amongst many others) might be helpful/interesting:

https://www.researchgate.net/publication/257525423_X-ray_and_neutron_imaging_with_colloids

https://www.researchgate.net/publication/257525055_XPCS_Nanoscale_motion_and_rheology

Article X-ray and neutron imaging with colloids

Article XPCS: Nanoscale motion and rheology

you can also use an environmental SEM (or TEM) to determine the size distribution of such nano particles in suspension (or after partial drying). 

Well, I don't like to dry them! Actually, I have SAXS measurements of these samples and I know that using WAXS is possible to obtain Bragg reflections but, as I have understood, these measurements are not suitable for Rietveld refinement. I would like to obtain something similar to X-ray powder diffraction but, for liquid samples.

Yes, we have done some measurements on colloidal crystals at PETRA III, Hamburg, Germany.

Article In situ X-ray crystallographic study of the structural evolu...

Article Structural Evolution of Colloidal Crystal Films in the Proce...

Article Revealing three-dimensional structure of individual colloida...