Microgels as Smart Polymer Colloids for Sensing and Environmental Remediation

Abstract

Stimuli-responsive microgels are gaining a lot of attention as a result of their excellent chemical and structural integrity with easy deformability and possibilities for being incorporated into various functionalities. The characteristic chemical and physical properties of microgels result in their widespread application. Among their many applications in the current review, we will give an overview on the design principles and synthetic approaches of microgels for sensing applications and their uses for the removal of different environmental pollutants. It is important to understanding the mechanism of sensing and adsorption, which is important for exploring further advancement. In this review, we brief these aspects.

Exploring microgel adsorption: synthesis, classification, and pollutant removal dynamics

“…The most commonly employed comonomers for polymerizing microgel adsorbents to induce multi-sensitivity and chelating properties are acrylic acid, 36 ethyleneimine, acrylamide, 35 2-acrylamido-2-methylpropane sulfonic acid, 30 and vinyl imidazole. 37 Acrylic acid (AAc) has a p K a value of 4.25, which means that when the pH exceeds its p K a , poly( N -isopropylacrylamide-AAc) P(NIPr-AAc) copolymer microgels swell due to the deprotonation of the carboxylic acid groups of AAc, as reported by Picard et al 38 The substantial negative charge present within microgels renders them highly effective as adsorbents for extracting heavy metal ions 39–42 as well as various dyes 43–49 from aqueous solutions. Additionally, positively charged microgels can be employed as efficient adsorbents for capturing negatively charged pollutants.…”

Stimuli-directed selective detection of Cu2+ and Cr2O72− ions using a pH-responsive chitosan-poly(aminoamide) fluorescent microgel in aqueous media

“…[8][9][10][11] Without the help of highly expensive instruments like atomic absorption spectroscopy (AAS), and inductively coupled plasma-mass spectrometry (ICP-MS), the fluorescence-sensor based metal ion detection technique is a straightforward and low-cost process and therefore, the development of such sensors has attracted much attention. 12,13 In this context, several advanced functional materials such as carbon dots, 14,15 quantum dots, 16,17 metal ion based fluorophores, [18][19][20] polymers, [21][22][23][24][25] small molecular organic probes, [26][27][28] micelles 29 and microgels 30,31 are reported. In most of the cases, such fluorophores can selectively detect a single ion.…”

Nonionic Microgels Adapt to Ionic Guest Molecules: Superchaotropic Nanoions

“…Many applications of microgels such as drug delivery, sensing, and catalysis involve the incorporation of solutes into microgels. − ,− , Small molecules, proteins, or nanoparticles may bind to network segments through hydrophobic or electrostatic interaction provided that they are small enough to penetrate into the polymer network depending on the mesh size, which is around 10 nm for microgels with 5% cross-linker. , When a charged solute binds to an oppositely charged chain segment, counterions are released from the network and the microgel deswells due to a decrease in osmotic pressure. , In contrast, anionic surfactants bind to uncharged network segments driven by the hydrophobic effect and thus convey their charge to the microgel, which leads to swelling and an increase in the VPTT due to intersegment electrostatic repulsion and due to dissociated counterions that are retained in the microgel and thus raise the osmotic pressure. , …”

“…Internal forces arise upon binding of solutes, , while external forces arise for example in crowded environments, upon mechanical compression with a probe, or due to osmotic pressure of large solutes that are excluded from the network . The chemical composition of the polymer network can be formulated to render the microgels addressable through external stimuli such as temperature, pH, or light or to impart in the microgel the ability to recognize and incorporate bioactive or catalytic agents. − In addition, the size (from tens of nanometers to several micrometers) and shape (spherical, anisotropic, and hollow) of microgels can be controlled through synthetic design. − Their seemingly unlimited tunability makes microgels important soft matter archetypes with wide interest as a model system in fundamental science as well as an applied system in drug delivery, − catalysis, and sensing. − …”

“…26−28 Many applications of microgels such as drug delivery, sensing, and catalysis involve the incorporation of solutes into microgels. [15][16][17][19][20][21][22]29 Small molecules, proteins, or nanoparticles may bind to network segments through hydrophobic or electrostatic interaction provided that they are small enough to penetrate into the polymer network depending on the mesh size, which is around 10 nm for microgels with 5% crosslinker. 3,30 When a charged solute binds to an oppositely charged chain segment, counterions are released from the network and the microgel deswells due to a decrease in osmotic pressure.…”