The innovation engine for new materials

Diego Bracho Garcia

Diego Bracho Garcia


University of Chile


Chemical Engineering


Jason Spruell

Faculty Sponsor(s): 

Craig Hawker

Faculty Sponsor's Department: 

Chemistry and Biochemistry

Project Title: 

Rheological properties of hydrogels driven by ionic coacervation

Project Description: 

We have developed a modular design for hydrogel formation based around the rich chemistry of poly(allyl glycidyl ether-block-ethylene glycol-block-allyl glycidyl ether) (P(AGE-b-EG-b-AGE)) copolymers. P(AGE) endblocks were functionalizated with oppositely charged sulfonate (S-) or guanidinium (G+) groups through tiol-ene chemistry. Mixing diluted solutions of the S- and G+ functionalized triblocks leads to physical association of the oppositely charged, ionic endblocks into polymer dense coacervate domains, while the hydrophilic PEG midblock bridges adjacent coacervates resulting in hydrogelation. The main goal of this research is to test the rheological properties of these hydrogels and correlate this with their chemical structure. Strong solid like gels were formed from polymers bearing high molecular weight ionic endblocks, as well as low molecular weight PEG midblocks. Interestingly, some of these strong gels macrophase separate into aqueous and gel phases at low concentrations (<10 wt%). It was determined that polymer pairs with low molecular weight endblocks form only viscous liquids. At low frequency the storage moduli (G’) fitted a power law ~3/2, which could mean the gel is somehow in-between an ordered lamellar and disordered structure. Long chain mid-blocks can lead to a disordered structure, nevertheless when a strong gel is formed it was determined that an increase of the midblock molecular weight from 10 to 20 KDa leads to a more solid gel, with a relaxation time 30 times higher. A raise of the polymer concentration increases both the moduli and relaxation time as expected.