Adhesion between fillers and a polymeric matrix is an essential characteristic for mixed-matrix membranes for molecular separation to avoid defects and cavities that would decrease selectivity. We demonstrate here how solution rheology can be an excellent tool to identity polymer–filler pairs with strong interaction. The investigated system was polytriazole with and without hydroxyl functionalization (PTA-OH and PTA) and ZIF-8. ZIF-8/PTA-OH forms stable gels even with a small filler content, which was investigated under increasing shear rates and different temperatures, while analogous systems without OH functionalization do not gel. The investigations were supported by spectroscopic methods, electron microscopy, and dynamic mechanical analysis of the final solid film. While small ZIF contents lead to sensitive changes in the solution viscosity, only minor changes in the Fourier transform infrared and NMR spectra were detected for the same system. The good adhesion between PTA-OH and ZIF-8 could be seen by electron microscopy, while the analogous PTA/ZIF-8 composites provided films with poor matrix–filler adhesion and undesired cavities. The methods described in this work can be extended as useful tools in the development of composites such as mixed-matrix membranes applied to a large variety of currently available metal–organic frameworks and polymers.