Thermoresponsive nanoparticle agglomeration reversibility in salt: Dependence on graft density

by Vasicek, Thad; Vaz, Leticia; Stenken, Julie Ann

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Gold nanoparticles with different graft densities of poly(N-iso-Pr acrylamide) were synthesized, and their salt induced agglomeration was studied by monitoring their localized surface plasmon resonance, hydrodynamic diam., and direct visualization. Below the lower crit. soln. temp. of the polymer, the hydrodynamic diam. and localized surface plasmon resonance displayed no difference between the high and low graft d. coated particles. All particles were stable in water both above and below the lower crit. soln. temp. of the polymer. However above the polymer's lower crit. soln. in a salt soln., nanoparticle agglomeration occurred. The degree of agglomeration was dependent upon the graft d., with higher degrees of agglomeration occurring for lower graft densities. The agglomeration was irreversible for low graft densities.