Distinct thermoresponsive behaviour of oligo- and poly-ethylene glycol protected gold nanoparticles in concentrated salt solutions
Author
Chávez, Miriam
Fernández-Merino, Ángela
Sánchez-Obrero, Guadalupe
Madueño, Rafael
Sevilla, José Manuel
Blázquez, Manuel
Pineda, Teresa
Publisher
Royal Society of ChemistryDate
2021Subject
Gold nanoparticlesNanochemistry
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In this work, the methoxy terminated oligo- and polyethylene glycol of different chain lengths (EGn, n ¼ 7,
18, 45 and 136) is grafted on AuNP surfaces under conditions where they attain maximum grafting densities.
These EGn–AuNPs gain stability relative to the pristine c-AuNPs in aqueous solutions and in a wide
temperature interval and they form stable suspensions in solutions of high NaCl concentrations. To show
the thermoresponsive properties of these EGn–AuNPs, temperature titration experiments are carried out
in the presence of increasing amounts of salts. The concentrations of NaCl are chosen by checking the
stability of EGn–AuNPs at room temperature and choosing the highest concentrations that allow them
to form stable suspensions. The analysis of the temperature titration experiments monitored by UVvisible
spectroscopy and dynamic light scattering allows us to establish the existence of transitions from
individual to assembled nanoparticles, the reversibility of the temperature transitions and hysteretic
behaviour in these systems. While EG7–AuNPs only show reversible temperature transitions in the
presence of 5 mM NaCl, EG18–AuNPs do up to 1 M NaCl, becoming only partially reversible in 2 M NaCl.
The titrations of EG45–AuNPs in 3 and 5 M NaCl show irreversible temperature transitions. Finally,
EG136–AuNPs present a complex and interesting behaviour with two temperature transitions, the first
one showing hysteresis and the second being reversible.