TRANSMISSION ELECTRON MICROSCOPY OF AQUEOUS POLYMER GEL NETWORK MORPHOLOGY

Freeze-fracture TEM images of polymer network structure in aqueous hydroxypropyl guar (HPG) gels permit direct correlations between observed gel morphology and macroscopic chemical and mechanical properties. HPG in aqueous solution associates via hydrogen bonding, even without titanate crosslinker, to form an extended network, the structure of which depends on the electrolyte concentration. The titanate crosslinker acts only to weld together polymer molecules already associated by hydrogen bonding. Mechanical shear degrades the gel by breaking up the network inhomogeneously to form "fractured gel particles," small domains of well-crosslinked gel separated by fluid domains.