Reversible Association of Thermoresponsive Gold Nanoparticles:  Polyelectrolyte Effect on the Lower Critical Solution Temperature of Poly(vinyl methyl ether)

Abstract

Thermoresponsive gold nanoparticles (GNPs) have been prepared by the borohydride reduction of gold salt in the presence of water-soluble polymer, poly(vinyl methyl ether) (PVME). The PVME-coated GNPs (PVME-GNPs) have been assembled into large aggregates in the presence of polyelectrolytes, viz., poly(sodium-4 styrene sulfonate) and sodium salt of carboxymethylcellulose at low pH by raising the solution temperature from 20 to 40 degrees C. Increase of temperature triggers the interparticle association due to hydrophobic interaction of pendent methyl group of the surface adsorbed PVME. This assembly process is reversible with respect to temperature and pH of the medium and was studied by monitoring the change in surface plasmon resonance band of PVME-GNPs. Three-dimensional assemblies of various architectures, depending on the concentration of polyelectrolytes, were observed through transmission electron microscopy. A mechanistic model has been suggested for the reversible assembly formation that suits well with the experimental observations. The changes in optical properties of the PVME-GNPs due to their aggregation/disaggregation enabled us to use it as an effective tool to monitor the change in lower critical solution temperature (LCST) of PVME in the presence of polyelectrolytes due to interpolymer complexation at low pH. This result agrees well with the variation of LCST of pure aqueous PVME solution in the presence of polyelectrolytes measured by conventional turbidimetric technique.

Tryptophan‐Based Peptides to Synthesize Gold and Silver Nanoparticles: A Mechanistic and Kinetic Study

“…[6] These colloidal MNPs are generally prepared by borohydride/citrate reduction of metal salts followed by ligand exchange with a suitable organic molecule/biomolecule containing a SH or NH 2 group as a stabilizer, and in some cases NPs have also been prepared by reducing the metal ions in the presence of a stabilizer. [4,10] One of the disadvantages of this method is that there is always a chance of particle aggregation during the process of ligand exchange and centrifugation for the removal of the undesired product. [11] Thus, it is very important to adopt the in situ reduction technique, which can minimize the above-mentioned problems.…”

Non-ionic Thermoresponsive Polymers in Water

“…[386] T g = 60 • C [371]; T m = 149 • C for M n = 14,920 g/mol, PDI = 1.2 [365] [103,407] Polymer-protected gold nanoparticles [413] Time-limited colloidal stability; stable droplets [188]; mesoglobules above 50 • C; liquid-liquid macrophase separation within a month [55] (continued) further increase in M n hardly affects T cp [405] No hysteresis [405] Gradient, random and block copolymers with PEOVEth [424] …”

Polymer-functionalized Gold Nanoparticles as Versatile Sensing Materials

“…31 The evolution of gold cores in aggregates composed of conventional polymers without sulfur atoms results in gold nanocomposites in which the polymers interact with gold cores through multi-point physical adsorption. 32 Not only artificial polymers, such as poly(N-vinylpyrrolidine), 33 poly(vinylpyridine), 34 poly(ethyleneglycol), 35 poly(vinyl alcohol), 36 poly(vinyl methylether), 37 poly(ethyleneimine), 38 poly(dialyl dimethylammonium), 39 but also biopolymers, were examined for the "grafting to" fabrication. The drawback of using the polymer terminated with a sulfur-free group is instability of the resulting gold nanocomposites.…”