Tuning the Swelling Properties of Smart Multiresponsive Core-Shell Microgels by Copolymerization

Abstract

The present study focuses on the development of multiresponsive core-shell microgels and the manipulation of their swelling properties by copolymerization of different acrylamides—especially N-isopropylacrylamide (NIPAM), N-isopropylmethacrylamide (NIPMAM), and NNPAM—and acrylic acid. We use atomic force microscopy for the dry-state characterization of the microgel particles and photon correlation spectroscopy to investigate the swelling behavior at neutral (pH 7) and acidic (pH 4) conditions. A transition between an interpenetrating network structure for microgels with a pure poly-N,-n-propylacrylamide (PNNPAM) shell and a distinct core-shell morphology for microgels with a pure poly-N-isopropylmethacrylamide (PNIPMAM) shell is observable. The PNIPMAM molfraction of the shell also has an important influence on the particle rigidity because of the decreasing degree of interpenetration. Furthermore, the swelling behavior of the microgels is tunable by adjustment of the pH-value between a single-step volume phase transition and a linear swelling region at temperatures corresponding to the copolymer ratios of the shell. This flexibility makes the multiresponsive copolymer microgels interesting candidates for many applications, e.g., as membrane material with tunable permeability.

Intelligent Poly(N-Isopropylmethacrylamide) Hydrogels: Synthesis, Structure Characterization, Stimuli-Responsive Swelling Properties, and Their Radiation Decomposition

“…The effect of α-methyl substitution on the interpolymer complex showed that α methylation provides higher glass transition temperatures (168-228 • C) and delays of thermal degradation [22]. The structure of doubly-temperature sensitive core-shell microgels based on p(NiPMAm) and p(NiPAm) was examined [23,24]. The swelling and mechanical behavior of negatively charged p(NiPMAm) hydrogels, depending on temperature in water and in aqueous NaCl solutions at room temperature, were investigated [25].…”

Effect of Methacrylic Acid in PNNPAM Microgels on the Catalytic Activity of Embedded Palladium Nanoparticles

“…Subsequent addition of a reducing agent confined metal nanoparticles within their gel templates. This incorporation method offers the advantage that the nanoparticles can be specifically incorporated at the particular copolymer localization, [32,65,66] instead of randomly dispersing them throughout the microgel material. [67] In our study we wanted to incorporate an equal amount of palladium surface per polymer mass in the microgels so that the respective palladium surfaces are surrounded with different MAc concentrations in the microgel network.…”

Surface‐Bound Microgels for Separation, Sensing, and Biomedical Applications

“…By switching between charged and uncharged states depending on the solution pH, these monomers govern the microgel's swelling by promoting electrostatic repulsion among the chains and forming hydrogen bonds with water. [142][143][144][145] For example, Li et al sandwiched AA-containing microgels between thin films and utilized the pH-induced microgel swelling to vary the distance between the films. [33] Giraud et al explored the effects of charge and inter-particle spacing on the sliding friction between sheets of pH-responsive P(S-co-AA) microgels.…”