Rheological Behavior Of Photoinduced HEUR And Its Performance Improvement

Associative thickeners are widely used as rheology modifiers in aqueous coatings and other aqueous systems.Unlike conventional polymeric thickeners,increasing the viscosity of the aqueous phase by dissolving,associative thickeners play its role with intermolecular and intramolecular hydrophobic interactions,through which the thickeners can attach on the interfaces among emulsion polymer and inorganic colloidal particle surfaces.What we want is to obtain high-performance associative polymeric thickeners,so that we designed and prepared a complex of worm-like micelles with azobenzene-modified polyurethane and an anthracene-modified polymer.The main contents and results of this work are as follows:1.Basedonpreviousresearchesaboutphoto-inducedHEUR,azobenzene-modified polyurethane thickeners were prepared and mixed with cetyltrimethylammonium bromide and sodium salicylate worm-like micelle systems.Changing each concentration and ratio of both in the mixed system,we compared their steady-state shear and dynamic shear properties,by which we found that the mixed system has a significant synergistic effect.The relaxation time greatly increases,the plateau modulus remains basically unchanged,the zero shear viscosity increases significantly,and the gel presents good viscoelasticity.Increasing the concentration of polyurethane can continuously improve the performance of the system,while the effect of worm-like micelles is limited,among them,the ratio of0.9-2.1 has the optimal performance.By using the transmission electron microscopy to observe the microstructure of the mixed system,compared with each of single system,it was found that in the aqueous solution,the average size of worm-like micelles can match the ones of the spherical micelles.UV-vis spectral analysis on the mixed system proved that the azobenzene group can still be free to convert between the trans-cis structure.Due to the limitation of worm-like micelles,the performances o mixed system under UV-vis irradiation are more stable than the azobenzene-modified polyurethane itself.Finally,we obtained a binary photo-induced thickener with a high synergetic effect.2.Based on the photo-induced dimerization properties of anthracene,we prepared an anthracene-modified polyurethane capping agent and synthesized an anthracene-cappd associative polyurethane thickener.Through steady-state shear and dynamics shear properties test,we found that the anthracene-modified polyurethane thickener with a concentration of more than 1 wt%show weak thickening effect.After UV irradiation,the thickening effect is significantly improved.A 1wt%aqueous solution can be converted from a liquid to a viscoelastic liquid,and a solution of4wt%sample can even reach a shear viscosity of 10~5 order.With the irradiation time increasing,the modulus and viscosity remain steady growth.At last,we got a photo-induced thickener with excellent thickening effect,which can be adjusted by irradiation strength and time,suitable for various applications where viscosity adjustment is required.