Special Issue "Polymer Microgels: Synthesis and Application"

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Chemistry".

Deadline for manuscript submissions: 31 December 2021.

Special Issue Editor

Dr. Roberta Angelini
E-Mail Website1 Website2
Guest Editor
Istituto dei Sistemi Complessi del Consiglio Nazionale delle Ricerche (ISC-CNR), Sede Sapienza, 00185 Roma, Italy
Interests: soft matter; colloids; polymers; structure; dynamics; glasses; gels; experiments; scattering techniques; rheology; calorimetry

Special Issue Information

Dear Colleagues,

Polymer microgels have attracted great attention in fundamental studies as good model systems for understanding the intriguing behaviors of soft colloids thanks to their elastic and deformable particles that provide a very rich phenomenology. These cross-linked particles with nanometric to micrometric dimensions are characterized by many fascinating properties such as swelling, softness, and responsivity that depend on their macromolecular architecture and can be triggered during the synthesis process. Moreover, they are highly attractive systems for several technological applications due to their high sensitivity to external stimuli. Smart microgels have indeed many applications in the pharmaceutics industries, in artificial organs, tissue engineering, agriculture, construction, and cosmetics.

This Special Issue focuses on experiments, simulation, synthesis methods, and applications of homopolymeric, interpenetrating polymer network (IPN), copolymerized, and core-shell microgels. The topics may include local structure, phase diagrams, interparticle interactions, and synthesis methods besides the manifold applications.

Both original contributions and reviews are welcome.

Dr. Roberta Angelini
Guest Editor

Manuscript Submission Information

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Keywords

  • Microgels
  • Polymers
  • Crosslinking
  • Colloids
  • Stimuli-responsive
  • Synthesis
  • Swelling
  • PNIPAM
  • Core-shell
  • Interpenetrated networks
  • Rheology
  • Scattering
  • Drug delivery
  • Tissue engineering
  • Sensors

Published Papers (4 papers)

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Research

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Article
The Double-Faced Electrostatic Behavior of PNIPAm Microgels
Polymers 2021, 13(7), 1153; https://doi.org/10.3390/polym13071153 - 04 Apr 2021
Cited by 1 | Viewed by 646
Abstract
PNIPAm microgels synthesized via free radical polymerization (FRP) are often considered as neutral colloids in aqueous media, although it is well known, since the pioneering works of Pelton and coworkers, that the vanishing electrophoretic mobility characterizing swollen microgels largely increases above the lower [...] Read more.
PNIPAm microgels synthesized via free radical polymerization (FRP) are often considered as neutral colloids in aqueous media, although it is well known, since the pioneering works of Pelton and coworkers, that the vanishing electrophoretic mobility characterizing swollen microgels largely increases above the lower critical solution temperature (LCST) of PNIPAm, at which microgels partially collapse. The presence of an electric charge has been attributed to the ionic initiators that are employed when FRP is performed in water and that stay anchored to microgel particles. Combining dynamic light scattering (DLS), electrophoresis, transmission electron microscopy (TEM) and atomic force microscopy (AFM) experiments, we show that collapsed ionic PNIPAm microgels undergo large mobility reversal and reentrant condensation when they are co-suspended with oppositely charged polyelectrolytes (PE) or nanoparticles (NP), while their stability remains unaffected by PE or NP addition at lower temperatures, where microgels are swollen and their charge density is low. Our results highlight a somehow double-faced electrostatic behavior of PNIPAm microgels due to their tunable charge density: they behave as quasi-neutral colloids at temperature below LCST, while they strongly interact with oppositely charged species when they are in their collapsed state. The very similar phenomenology encountered when microgels are surrounded by polylysine chains and silica nanoparticles points to the general character of this twofold behavior of PNIPAm-based colloids in water. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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Article
Microstructured Macromaterials Based on IPN Microgels
Polymers 2021, 13(7), 1078; https://doi.org/10.3390/polym13071078 - 29 Mar 2021
Cited by 2 | Viewed by 735
Abstract
This study investigates the formation of microstructured macromaterials from thermo- and pH-sensitive microgels based on interpenetrating networks of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA). Macromaterials are produced as a result of the deposition of microgel particles and subsequent crosslinking of polyacrylic acid subnetworks [...] Read more.
This study investigates the formation of microstructured macromaterials from thermo- and pH-sensitive microgels based on interpenetrating networks of poly-N-isopropylacrylamide (PNIPAM) and polyacrylic acid (PAA). Macromaterials are produced as a result of the deposition of microgel particles and subsequent crosslinking of polyacrylic acid subnetworks to each other due to the formation of the anhydride bonds during annealing. Since both PNIPAM and PAA are environment-sensitive polymers, one can expect that their conformational state during material development will affect its resulting properties. Thus, the influence of conditions of preparation for annealing (pH of the solution, the temperature of preliminary drying) on the swelling behavior, pH- and thermosensitivity, and macromaterial inner structure was investigated. In parallel, the study of the effect of the relative conformations of the IPN microgel subnetworks on the formation of macromaterials was carried out by the computer simulations method. It was shown that the properties of the prepared macromaterials strongly depend both on the temperature and pH of the PNIPAM-PAA IPN microgel dispersions. This opens up new opportunities to obtain materials with pre-chosen characteristics and environmental sensitivity. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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Article
Importance of pH in Synthesis of pH-Responsive Cationic Nano- and Microgels
Polymers 2021, 13(5), 827; https://doi.org/10.3390/polym13050827 - 08 Mar 2021
Cited by 1 | Viewed by 711
Abstract
While cationic microgels are potentially useful for the transfection or transformation of cells, their synthesis has certain drawbacks regarding size, polydispersity, yield, and incorporation of the cationic comonomers. In this work, a range of poly(N-isopropylacrylamide) (PNIPAM) microgels with different amounts of [...] Read more.
While cationic microgels are potentially useful for the transfection or transformation of cells, their synthesis has certain drawbacks regarding size, polydispersity, yield, and incorporation of the cationic comonomers. In this work, a range of poly(N-isopropylacrylamide) (PNIPAM) microgels with different amounts of the primary amine N-(3-aminopropyl)methacrylamide hydrochloride (APMH) as the cationic comonomer were synthesized. Moreover, the pH-value during reaction was varied for the synthesis of microgels with 10 mol% APMH-feed. The microgels were analyzed by means of their size, thermoresponsive swelling behavior, synthesis yield, polydispersity and APMH-incorporation. The copolymerization of APMH leads to a strong decrease in size and yield of the microgels, while less than one third of the nominal APMH monomer feed is incorporated into the microgels. With an increase of the reaction pH up to 9.5, the negative effects of APMH copolymerization were significantly reduced. Above this pH, synthesis was not feasible due to aggregation. The results show that the reaction pH has a strong influence on the synthesis of pH-responsive cationic microgels and therefore it can be used to tailor the microgel properties. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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Review

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Review
Chemical-Physical Behaviour of Microgels Made of Interpenetrating Polymer Networks of PNIPAM and Poly(acrylic Acid)
Polymers 2021, 13(9), 1353; https://doi.org/10.3390/polym13091353 - 21 Apr 2021
Cited by 1 | Viewed by 550
Abstract
Microgels composed of stimuli responsive polymers have attracted worthwhile interest as model colloids for theorethical and experimental studies and for nanotechnological applications. A deep knowledge of their behaviour is fundamental for the design of new materials. Here we report the current understanding of [...] Read more.
Microgels composed of stimuli responsive polymers have attracted worthwhile interest as model colloids for theorethical and experimental studies and for nanotechnological applications. A deep knowledge of their behaviour is fundamental for the design of new materials. Here we report the current understanding of a dual responsive microgel composed of poly(N-isopropylacrylamide) (PNIPAM), a temperature sensitive polymer, and poly(acrylic acid) (PAAc), a pH sensitive polymer, at different temperatures, PAAc contents, concentrations, solvents and pH. The combination of multiple techniques as Dynamic Light Scattering (DLS), Raman spectroscopy, Small Angle Neutron Scattering (SANS), rheology and electrophoretic measurements allow to investigate the hydrodynamic radius behaviour across the typical Volume Phase Transition (VPT), the involved molecular mechanism and the internal particle structure together with the viscoelastic properties and the role of ionic charge in the aggregation phenomena. Full article
(This article belongs to the Special Issue Polymer Microgels: Synthesis and Application)
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