Described herein are fluid complex coacervates that produce solid adhesives in situ. Oppositely charged polyelectrolytes were designed to form fluid adhesive complex coacervates at ionic strengths higher than the ionic strength of the application site, but an insoluble adhesive solid or gel at the application site. When the fluid, high ionic strength adhesive complex coacervates are introduced into the lower ionic strength application site, the fluid complex coacervate is converted to a an adhesive solid or gel as the salt concentration in the complex coacervate equilibrates to the application site salt concentration. In one embodiment, the fluid complex coacervates are designed to solidify in situ at physiological ionic strength and have numerous medical applications. In other aspects, the fluid complex coacervates can be used in aqueous environment for non-medical applications.
