Structure of Microgels with Debye–Hückel Interactions

Kobayashi, Hideki; Winkler, Roland G.

doi:10.3390/polym6051602

Cited by 62 publications

(63 citation statements)

References 47 publications

(55 reference statements)

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“…As can be seen in the upper panels, the heterogeneity due to the specific topology of the networks is reflected in monomer density profiles and becomes evident as the dissociation fraction f increases and the nanogel swells. Such heterogeneities in density profiles have been observed in simulations and were related both to solvent quality conditions 19 and to monomer-ion steric repulsion 20 . Interestingly, it has been speculated that the void created at the center of the nanogel particle might have potential to act as a drug carrier 18 , but our results suggest that the density profiles are inherent to the structure of the network considered, corroborating recent experimental evidences 44 .…”

Section: Simulation Resultsmentioning

confidence: 64%

Influence of network topology on the swelling of polyelectrolyte nanogels

Rizzi

Levin

2016

The Journal of Chemical Physics

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It is well-known that the swelling behavior of ionic nanogels depends on their cross-link density, however it is unclear how different topologies should affect the response of the polyelectrolyte network. Here we perform Monte Carlo simulations to obtain the equilibrium properties of ionic nanogels as a function of salt concentration Cs and the fraction f of ionizable groups in a polyelectrolyte network formed by cross-links of functionality z. Our results indicate that the network with cross-links of low connectivity result in nanogel particles with higher swelling ratios. We also confirm a de-swelling effect of salt on nanogel particles.

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Section: Simulation Resultsmentioning

confidence: 64%

Influence of network topology on the swelling of polyelectrolyte nanogels

Rizzi

Levin

2016

The Journal of Chemical Physics

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“…The μG was designed as follows. Fully stretched subchains of an ideal μG (all subchains have equal length) were connected through tetrafunctional cross-links 57 and repeated a unit cell of the diamond crystal lattice (zoom-in in Figure 1). Then, we constructed a cubic frame consisting of 3×3×3 unit cells of the diamond crystal lattice ( Figure 1).…”

Section: ■ Computer Simulationsmentioning

confidence: 99%

Electrostatic Interactions and Osmotic Pressure of Counterions Control the pH-Dependent Swelling and Collapse of Polyampholyte Microgels with Random Distribution of Ionizable Groups

et al. 2015

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In this work, different systems of colloidally stable, ampholytic microgels (μGs) based on poly(N-vinylcaprolactam) and poly(N-isopropylacrylamide), wherein the anionic and cationic groups are randomly distributed, were investigated. Fourier transmission infrared spectroscopy and transmission electron microscopy confirmed the quantitative incorporation and random distribution of ionizable groups in μGs, respectively. The control of hydrodynamic radii and mechanical properties of polyampholyte μGs at different pH values was studied with dynamic light scattering and in situ atomic force microscopy. We have proposed a model of pH-dependent polyampholyte μG, which correctly describes the experimental data and explains physical reasons for the swelling and collapse of the μG at different pHs. In the case of a balanced μG (equal numbers of cationic and anionic groups), the size as a function of pH has a symmetric, V-like shape. Swelling of purely cationic μG at low pH or purely anionic μG at high pH is due to electrostatic repulsion of similarly charged groups, which appears as a result of partial escape of counterions. Also, osmotically active counterions (the counterions that are trapped within the μG) contribute to the swelling of the μG. In contrast, electrostatic interactions are responsible for the collapse of the μG at intermediate pH when the numbers of anionic and cationic groups are equal (stoichiometric ratio). The multipole attraction of the charged groups is caused by thermodynamic fluctuations, similar to the those observed in Debye−Huckel plasma. We have demonstrated that the higher the fraction of cationic and anionic groups, the more pronounced the swelling and collapse of the μG at different pHs. ■ INTRODUCTIONStimuli-responsive nano-and microgels (μGs) represent unique macromolecular objects, which are potentially useful for applications including biotechnology, 1−8 drug delivery, 9−15 semiconducting materials, 16,17 sensor technology, 18,19 and many others. It is believed that the internal structure of μGs resembles elements of macroscopic polymer networks: linear chains (subchains) are covalently linked with each other into a three-dimensional frame of size ranging between tens of nanometers and a few micrometers. As a result, μGs show some properties of macroscopic gels, like high elasticity as well as the ability to swell and collapse depending on the solvent quality and external stimuli 20−22 (temperature, pH, etc.). Swollen μGs (good solvent conditions) are usually characterized by welldefined shape due to the swelling of each individual subchain, by low polymer volume fraction, and by high stability toward aggregation. In contrast, collapsed μGs have smaller size as compared to swollen μGs and high polymer density because of effective attraction between monomer units. As a result, they have poor colloidal stability and can aggregate (precipitate). However, compared to macroscopic gels, μGs reveal much faster responses to stimuli, which are primarily controlled by their size.Water-soluble polye...

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“…The microgel is designed as follows. Fully stretched subchains of an ideal microgel (all subchains have equal length) are connected through tetrafunctional cross-links 21 and repeat a unit cell of the diamond crystal lattice. Then, we construct a cubic frame consisting of 6 × 6 × 6 unit cells.…”

Section: /2lmentioning

confidence: 99%

Communication: Intraparticle segregation of structurally homogeneous polyelectrolyte microgels caused by long-range Coulomb repulsion

Rumyantsev

Rudov

2015

The Journal of Chemical Physics

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Structurally homogeneous polyelectrolyte microgels in dilute aqueous solutions are shown to exhibit inhomogeneous density profile including intraparticle “phase” coexistence of hollow core and dense “skin.” This effect is a consequence of long-range Coulomb repulsion of charged groups which appear because of entropy-driven escape of monovalent counterions into the outer solvent. Excess of the charged groups at the periphery of the microgel particle reduces electrostatic energy and overall free energy of the system despite a penalty in the elastic free energy of strongly stretched subchains in the hole. This finding can serve as additional tool controlling encapsulation, transport, and release of high- and low-molecular-weight species in processes where the microgels are used as delivery systems.

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Structure of Microgels with Debye–Hückel Interactions

Cited by 62 publications

References 47 publications

Influence of network topology on the swelling of polyelectrolyte nanogels

Influence of network topology on the swelling of polyelectrolyte nanogels

Electrostatic Interactions and Osmotic Pressure of Counterions Control the pH-Dependent Swelling and Collapse of Polyampholyte Microgels with Random Distribution of Ionizable Groups

Communication: Intraparticle segregation of structurally homogeneous polyelectrolyte microgels caused by long-range Coulomb repulsion

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