Micellization in pH-sensitive amphiphilic block copolymers in aqueous media and the formation of metal nanoparticles

Abstract

Dynamic light scattering, potentiometric titration, transmission electron microscopy and atomic force microscopy have been used to investigate the micellar behaviour and metal-nanoparticle formation in poly(ethylene oxide)-block-poly(2-vinylpyridine), PEO-b-P2VP, poly(hexa(ethylene glycol) methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate), PHEGMA-b-PDEAEMA, and PEO-b-PDEAEMA amphiphilic diblock copolymers in water. The hydrophobic block of these copolymers (P2VP or PDEAEMA) is pH-sensitive: at low pH it can be protonated and becomes partially or completely hydrophilic leading to molecular solubility whereas at higher pH micelles are formed. These micelles consist of a P2VP or PDEAEMA core and a PEO or PHEGMA corona, respectively, where the core forming amine units can incorporate metal compounds due to coordination. The metal compounds (e.g., H2PtCl6, K2PtCl6) can either be introduced in a micellar solution, where they are incorporated within the micelle core via coordination with functional groups, or can be added to a unimer solution at low pH, where they lead to a metal-induced micellization. In these micellar nanoreactors, metal nanoparticles nucleate and grow upon reduction with sizes in the range of a few nanometers as observed by TEM. The effect of the metal incorporation method on the characteristics of the micelles and of the synthesized nanoparticles is investigated.

Biomimetic micro/nanostructured functional surfaces for microfluidic and tissue engineering applications

“…A prominent example of smart macromolecules involves the so-called pH responsive polymers, in which protonation/deprotonation events occurring due to pH variations around their effective pK ␣ values alter the degree of ionization of the monomer repeat units ͑weak acid or weak base behavior͒, thus modifying the polymer-solvent interactions leading to changes of the polymer chain conformations and to the formation of smart polymer nanostructures. 101,102 Controlled reorganization of interfacial layers based on environment-sensitive polymers has been widely utilized for the design and fabrication of smart/responsive material surfaces. Polymer brushes created by end-grafting stimuli-sensitive polymers 103,104 onto surfaces with hierarchical micro/nanoroughness have been frequently utilized for the development of such smart surfaces that can respond to changes in pH temperature and solvent quality.…”

Temperature‐Dependent Gelation Behaviour of Double Responsive P2VP‐b‐PEO‐b‐P(GME‐co‐EGE) Triblock Terpolymers: A SANS Study

“…40 8C [35] ), similar to the behaviour of PEO but at significantly lower temperatures. [45][46][47][48][49] The observed shrinkage of the CSC micelles with P2VP cores is important later on in the discussion on the mechanism of the temperatureinduced gel-sol-gel transition at pH ¼ 7. Figure 4B shows the SANS profile and the corresponding fit for the same solution at pH ¼ 3 and T ¼ 60 8C.…”

“…This goes along with a significantly increased scattering contrast of the ''shell'', and thus can be explained by the commonly observed shrinkage of the PEO block at elevated temperatures. [45][46][47][48][49] It is finally noted, that the intensity profile obtained at pH ¼ 3 and T ¼ 60 8C exhibits a shoulder in the high q-range, which was fitted assuming the presence of unimolecular micelles, that is, single triblock terpolymer chains with a collapsed P(GME-co-EGE) block shielded by the hydrophilic P2VP (protonated at pH ¼ 3) and PEO blocks, along with inverse CSC micelles. Applying this procedure, a radius of gyration for the unimolecular micelles of 6 nm was obtained.…”

Amphiphilic linear–hyperbranched polymer poly(ethylene glycol)–branched polyethylenimine–poly(ϵ‐caprolactone): synthesis, self‐assembly and application as stabilizer of platinum nanoparticles

“…8 The shell of the micelles prevents the agglomeration of metal nanoparticles via steric hindrance repulsive forces because metal nanoparticles are surrounded in the core and/or in the shell of the micelles. 9 Compared to other stabilizers such as inorganic ions, organic ions, organic solvents and surfactants, amphiphilic polymer-stabilized metal nanoparticles usually have superior stability because the self-assembly of amphiphilic polymers is a spontaneous process and the resulting micelles are thermodynamically and dynamically stable in solution. Also, hyperbranched polymers embed/surround metal nanoparticles (usually, the resulting metal nanoparticles have 692 www.soci.org Y Dai, X Zhang, R Zhuo very good dispersity) and prevent their agglomeration via electrostatic repulsion and/or steric hindrance repulsive forces.…”