Fundamentals and application of the collapse transition of poly(acrylic acid) for synthesis of various polymer-templated nanoparticles
The collapse of a long chain polymer from extended to globular conformation can be the basis for a synthesis of nanoparticles. For example, a negatively charged polyelectrolyte can be collapsed by positively charged counterions, forming a nano-sized polymer-counterion particle. Upon stabilization of the nanoparticle via UV crosslinking, further chemical reaction of the counterions can be performed. In principle, the method can be carried out with different polyelectrolyte-counterions pair, and hence has enormous potential for generating different kinds of nanoparticles. For each combination, a study of various parameters affecting the collapse process is required. Parameters including the valence state of counterions, counterion concentration, pH, polymer molecular weight, polymer concentration, and UV dose were found to affect the process. The vast parameter space governing the collapse of poly(acrylic acid) (PAA) by various ions and identified optimal synthesis condition for the polymer-counterion nanoparticles was investigated. First, a counterion concentration range at which PAA was collapsed yet have not formed aggregates was determined via viscosity and turbidity measurements. Second, optimization of the UV dose was explored for crosslinking of the nanoparticles while minimizing UV-induced chain scission. The optimization method was applied to the synthesis of various nanoparticles. Lanthanide oxide nanoparticles in similar chemical environments were synthesized, and their optical and magnetic properties were studied and compared to bulk materials. While their magnetic properties were similar to those of lanthanide ions, there was a notable enhancement of the UV absorption of CexOy-PAA and the luminescence properties of TbxOy-PAA and EuxOy-PAA. TixOy-PAA and BixWyOz-PAA were also synthesized and their photocatalytic properties were demonstrated using an organic dye model system. Lastly, photocatalytic properties of a hydrothermally-synthesized WO3 system were evaluated and Pt deposition on the WO3 system improved amaranth decolourization efficiency. The versatility of the approach in creating a wide range of nanoparticles was demonstrated and a universal method for creating various polymer-counterion nanoparticles was outlined.
lanthanides, nanoparticles, photocatalysis, poly(acrylic acid), polymer collapse, UV crosslinking
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