Gold nanoparticle distribution in polyelectrolyte brushes loaded at different pH conditions

Abstract

Composites made of polymer brushes with inclusions of gold nanoparticles (AuNPs) combine the responsive nature of polymer brushes with the optical properties of the AuNPs, which offers the possibility to be used as colorimetric sensors. To this end, it is crucial to know how AuNPs are distributed inside the brush. Here, this distribution was elucidated by neutron reflectometry with contrast variation and a self-consistent reflectivity analysis based on the analytical parameterization of the volume fraction profiles of all chemical components. In contrast to former studies, this analysis allows the determination of the spatial distribution of components separately from each other: polyelectrolyte, AuNP, and water. Cationic poly-[2-(Methacryloyloxy) ethyl] trimethylammonium chloride (PMETAC) brushes were loaded with 5 nm AuNPs, which were coated with a pH-sensitive capping. The pH was varied during the incubation of the brush in the AuNP suspension. At a lower pH, AuNPs form aggregates in suspension and are attached to the brush periphery. They adsorb into the brush but do not fully penetrate it due to their bulkiness. At a higher pH, AuNP suspensions are electrostatically stabilized and the AuNPs penetrate the brush entirely. However, the AuNP distribution over the brush is not homogeneous but decreases gradually toward the substrate. Penetration of the AuNPs leads to a more extended conformation of the brush. According to the results of the detailed analysis of all components, an increase in water content could be excluded as a reason for brush swelling but replacement of water by the AuNP was observed.

Homogeneous Embedding of Magnetic Nanoparticles into Polymer Brushes during Simultaneous Surface-Initiated Polymerization

“…Moreover, the Fe + profile indicates homogeneous distribution of SPIONs along the brush thickness and even somehow higher content of SPIONs in the proximity of the silicon substrate. This observation is opposite to those of the systems prepared by incubation of polymer brushes in the suspension of nanoparticles for which the distribution is typically not homogeneous and even decreases gradually toward the substrate [28,36].…”

“…For better control on the size and composition of NPs it is often desired to form them ex situ and the polymer matrix volume should be limited for the formation of functional nanocomposites. There have been numerous attempts at incorporation of NPs into polymeric matrices but obtaining a thin layer with a thickness comparable to the diameter of the nanoparticles while maintaining their homogenous distribution in the layer is still a challenge [26,27,28] and typically much thicker polymer matrices have been used for that purpose [29,30].…”

New insights into the solid–liquid interface exploiting neutron reflectivity

“…for sensors). [72,73] These show the strength of H/D contrast variation to extract the locations of the different components, alongside combining x-ray and neutron scattering. Figure 4 shows an example of how the different distributions of polymer and nanoparticles can be determined using NR, with a clear pH dependence on the structure.…”

“…Figure 4 shows an example of how the different distributions of polymer and nanoparticles can be determined using NR, with a clear pH dependence on the structure. [72] Polymers can also be combined with dendrimers and surfactants,(e.g. [74]) enabling some very complex architectures.…”

Coupling pH-Regulated Multilayers with Inorganic Surfaces for Bionic Devices and Infochemistry

“…51 A kinetic study of polyelectrolyte molecules and counterion diffusion was preformed. 52 A better understanding of the influence of charged groups of polymers on the ionic conductivity was provided by the study of diffusion in polyelectrolyte hydrogels. It was indicated that zwitterionic PEs are more favorable to ion transportation.…”