Preparation and Characterization of Low Dispersity Anionic Multiresponsive Core–Shell Polymer Nanoparticles

Abstract

We prepared anionic multistimuli responsive core-shell polymer nanoparticles with very low size dispersity. By using either acrylic acid (AA) or methacrylic acid (MA) as a comonomer in the poly(N-isopropyl acrylamide) (PNIPAM) shell, we are able to change the distribution of negative charges in the nanoparticle shell. The particle size, volume phase transition temperature, and aggregation state can be modulated using temperature, pH, or ionic strength, providing a very versatile platform for applications in sensors, medical diagnostics, environmental remediation, etc. The nanoparticles have a glassy poly(methyl methacrylate) (PMMA) core of ca. 40 nm radius and a cross-linked PNIPAM anionic shell with either AA or MA comonomers. The particles, p(N-AA) and p(MA-N), respectively, have the same total charge but different charge distributions. While the p(MA-N) particles have the negative charges preferentially distributed toward the inner shell, in the case of the p(N-AA) particles the charge extends more to the particle outer shell. The volume phase transition temperature (T(VPT)) of the particles is affected by the charge distribution and can be fine-tuned by controlling the electrostatic repulsion on the particle shell (using pH and ionic strength). By suppressing the particle charge we can also induce temperature-driven particle aggregation.

Fabrication and characterization of bifunctional spherical polyelectrolyte brushes

“…The reactivity of comonomers determined the sequence of blocks. According to literatures, [35,36] the sequence of reactivity of comonomers was the following: NIPAM > AA > DEA. In other words, NIPAM had priority to be grafted from the surface of PS cores as competing with AA monomer and then polymerized with AA at the last stage of polymerization.…”

“…In all, the outer shell charges distribution of P(NIPAM-AA) could inhibit the shrinkage of polymer layers and afford wider temperature for accommodation at different pH values. [35] nanoparticles if the shell SR was above 30%. The SR of P(NIPAM-AA) and P(AA-DEA) at different pH values was illustrated in Figure 10.…”

“…It was ascribed to the outer shell AA distribution of P(NIPAM-AA) which had more mobility to prevent polymer layers from shrinkage than inner shell distribution of P(AA-DEA). [35] Cationic dye adsorption of SPBs Cationic Basic Violet 14 dye was introduced to be adsorbed in the shell of P(NIPAM-AA)-0.5% and P(AA-DEA)-0.5% with temperature increment in Figure 11. There are three factors determined the dye adsorption, including electrostatic interaction, volume of layers, and hydrophobicity.…”

“…The other was that the outer shell AA distribution of P(NIPAM-AA) exhibited higher mobility to prevent the shrinkage of polymer chains and enhance the LCST. [35] …”

Multi-Stimuli-Responsive Polymer Materials: Particles, Films, and Bulk Gels

“…The negatively charged nanoparticles were comprised of a glassy PMMA as the core and two different types of temperature‐responsive shell. The size, volume phase transition temperature, and aggregation state of these particles could be finely tuned by temperature, pH, or ionic strength 206…”