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501 KiB

Open AccessArticle

Experimentally Justified Model-Like Description of Consolidation of Precipitated Silica

by Hussein Sahabi and Matthias Kind

Polymers 2011, 3(4), 2156-2171; https://doi.org/10.3390/polym3042156 - 20 Dec 2011

Cited by 2 | Viewed by 6311

Colloidal gels are intermediates in the production of highly porous particle systems. In the production process, the gels are fragmented after their creation. These gel fragments consolidate to particles whose application-technological properties are determined by their size and porosity. A model of the [...] Read more.

Colloidal gels are intermediates in the production of highly porous particle systems. In the production process, the gels are fragmented after their creation. These gel fragments consolidate to particles whose application-technological properties are determined by their size and porosity. A model of the consolidation process is proposed: The consolidation process of a gel fragment is simulated with the Molecular Dynamics (MD) method with the assumption of van der Waals forces in interplay with the thermal motion as driving forces for the consolidation. The simulation results are compared with experimental data and with a Monte Carlo (MC) simulation. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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1294 KiB

Open AccessArticle

Polymer and Water Dynamics in Poly(vinyl alcohol)/Poly(methacrylate) Networks. A Molecular Dynamics Simulation and Incoherent Neutron Scattering Investigation

by Gaio Paradossi, Ivana Finelli, Francesca Natali, Mark T. F. Telling and Ester Chiessi

Polymers 2011, 3(4), 1805-1832; https://doi.org/10.3390/polym3041805 - 17 Oct 2011

Cited by 20 | Viewed by 10701

Abstract

Chemically cross-linked polymer networks of poly(vinyl alcohol)/poly(methacrylate) form monolitic hydrogels and microgels suitable for biomedical applications, such as in situ tissue replacement and drug delivery. In this work, molecular dynamics (MD) simulation and incoherent neutron scattering methods are used to study the local [...] Read more.

Chemically cross-linked polymer networks of poly(vinyl alcohol)/poly(methacrylate) form monolitic hydrogels and microgels suitable for biomedical applications, such as in situ tissue replacement and drug delivery. In this work, molecular dynamics (MD) simulation and incoherent neutron scattering methods are used to study the local polymer dynamics and the polymer induced modification of water properties in poly(vinyl alcohol)/poly(methacrylate) hydrogels. This information is particularly relevant when the diffusion of metabolites and drugs is a requirement for the polymer microgel functionality. MD simulations of an atomic detailed model of the junction domain at the experimental hydration degree were carried out at 283, 293 and 313 K. The polymer-water interaction, the polymer connectivity and the water dynamics were investigated as a function of temperature. Simulation results are compared with findings of elastic and quasi-elastic incoherent neutron scattering measurements, experimental approaches which sample the same space-time window of MD simulations. This combined analysis shows a supercooled water component and an increase of hydrophilicity and mobility with temperature of these amphiphilic polymer networks. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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230 KiB

Open AccessArticle

Preparation and Characterization of Organic-Inorganic Hybrid Hydrogel Electrolyte Using Alkaline Solution

by Masanobu Chiku, Shoji Tomita, Eiji Higuchi and Hiroshi Inoue

Polymers 2011, 3(4), 1600-1606; https://doi.org/10.3390/polym3041600 - 26 Sep 2011

Cited by 6 | Viewed by 7251

Abstract

Organic-inorganic hybrid hydrogel electrolytes were prepared by mixing hydrotalcite, cross-linked potassium poly(acrylate) and 6 M KOH solution. The organic-inorganic hybrid hydrogel electrolytes had high ionic conductivity (0.456–0.540 S cm⁻¹) at 30 °C. Moreover, the mechanical strength of the hydrogel electrolytes was [...] Read more.

Organic-inorganic hybrid hydrogel electrolytes were prepared by mixing hydrotalcite, cross-linked potassium poly(acrylate) and 6 M KOH solution. The organic-inorganic hybrid hydrogel electrolytes had high ionic conductivity (0.456–0.540 S cm⁻¹) at 30 °C. Moreover, the mechanical strength of the hydrogel electrolytes was high enough to form a 2–3 mm thick freestanding membrane because of the reinforcement with hydrotalcite. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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1321 KiB

Open AccessArticle

The Effect of Co-Monomer Content on the Swelling/Shrinking and Mechanical Behaviour of Individually Adsorbed PNIPAM Microgel Particles

by Anna Burmistrova, Marcel Richter, Michael Eisele, Cagri Üzüm and Regine Von Klitzing

Polymers 2011, 3(4), 1575-1590; https://doi.org/10.3390/polym3041575 - 26 Sep 2011

Cited by 113 | Viewed by 13559

Abstract

The swelling/deswelling behaviour of microgel particles in the bulk and at the surface was studied and correlated to their mechanical properties. We focused on two kinds of particles: pure PNIPAM and PNIPAM-co-AAc particles. It was shown that the two step volume [...] Read more.

The swelling/deswelling behaviour of microgel particles in the bulk and at the surface was studied and correlated to their mechanical properties. We focused on two kinds of particles: pure PNIPAM and PNIPAM-co-AAc particles. It was shown that the two step volume phase transition found for PNIPAM-co-AAc particles in the bulk disappears after the adsorption at the surface and only a one step transition was identified. The transition temperature increased strongly with increasing the co-monomer content. The dependence of the Young’s modulus of the adsorbed microgel particles on the temperature and the co-monomer content was discussed. The investigations were performed via DLS and SFM. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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612 KiB

Open AccessArticle

Consolidation of Inorganic Precipitated Silica Gel

by Hussein Sahabi and Matthias Kind

Polymers 2011, 3(3), 1423-1432; https://doi.org/10.3390/polym3031423 - 29 Aug 2011

Cited by 8 | Viewed by 8605

Abstract

Colloidal gels are possible intermediates in the generation of highly porous particle systems. In the production process the gels are fragmented after their formation. These gel fragments compact to particles whose application-technological properties are determined by their size and porosity. In the case [...] Read more.

Colloidal gels are possible intermediates in the generation of highly porous particle systems. In the production process the gels are fragmented after their formation. These gel fragments compact to particles whose application-technological properties are determined by their size and porosity. In the case of precipitated silica gels, this consolidation process depends on temperature and pH, among other parameters. It is shown that these dependencies can be characterized by oedometer measurements. Originally, the oedometer test (one-dimensional compression test) stemmed from soil mechanics. It has proven to be an interesting novel examination method for gels. Quantitative data of the time-dependent shrinkage of gel samples can be obtained. The consolidation of the gels shows a characteristic dependence on the above parameters. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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634 KiB

Open AccessArticle

Influence of the Hydrophobicity of Polyelectrolytes on Polyelectrolyte Complex Formation and Complex Particle Structure and Shape

by Mandy Mende, Simona Schwarz, Stefan Zschoche, Gudrun Petzold and Andreas Janke

Polymers 2011, 3(3), 1363-1376; https://doi.org/10.3390/polym3031363 - 25 Aug 2011

Cited by 13 | Viewed by 7701

Abstract

Polyelectrolyte complexes (PECs) were prepared by structural uniform and strongly charged cationic and anionic modified alternating maleic anhydride copolymers. The hydrophobicity of the polyelectrolytes was changed by the comonomers (ethylene, isobutylene and styrene). Additionally, the n₋/n₊ ratio of the molar [...] Read more.

Polyelectrolyte complexes (PECs) were prepared by structural uniform and strongly charged cationic and anionic modified alternating maleic anhydride copolymers. The hydrophobicity of the polyelectrolytes was changed by the comonomers (ethylene, isobutylene and styrene). Additionally, the n₋/n₊ ratio of the molar charges of the polyelectrolytes and the procedure of formation were varied. The colloidal stability of the systems and the size, shape, and structure of the PEC particles were investigated by turbidimetry, dynamic light scattering (DLS) and atomic force microscopy (AFM). Dynamic light scattering indicates that beside large PEC particle aggregates distinct smaller particles were formed by the copolymers which have the highest hydrophobicity (styrene). These findings could be proved by AFM. Fractal dimension (D), root mean square (RMS) roughness and the surface profiles of the PEC particles adsorbed on mica allow the following conclusions: the higher the hydrophobicity of the polyelectrolytes, the broader is the particle size distribution and the minor is the swelling of the PEC particles. Hence, the most compact particles are formed with the very hydrophobic copolymer. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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555 KiB

Open AccessArticle

Microspheres Containing Cibacron Blue F3G-A and Incorporated Iron Oxide Nanoparticles as Biomarker Harvesting Platforms

by Alexis Patanarut, Elissa H. Williams, Emanuel Petricoin, Lance A. Liotta and Barney Bishop

Polymers 2011, 3(3), 1181-1198; https://doi.org/10.3390/polym3031181 - 28 Jul 2011

Cited by 4 | Viewed by 9035

Abstract

In this work, magnetic functionality was introduced to cross-linked acrylamide-based particles via the in situ coprecipitation of iron oxide nanoparticles within the hydrogel particle interior. Cibacron Blue F3G-A was then incorporated onto the magnetic hydrogel scaffold to facilitate the harvest of targeted protein [...] Read more.

In this work, magnetic functionality was introduced to cross-linked acrylamide-based particles via the in situ coprecipitation of iron oxide nanoparticles within the hydrogel particle interior. Cibacron Blue F3G-A was then incorporated onto the magnetic hydrogel scaffold to facilitate the harvest of targeted protein species. The dye-loaded magnetic particles were physically characterized, and their protein sequestration performance was investigated. The results of these studies indicated that dye-loaded magnetic particles sequestered a greater amount of lower molecular weight proteins from the test solution than was achieved using reference particles, dye-loaded cross-linked N-isopropylacrylamide-based core-shell particles. This difference in protein harvesting ability may reflect the higher degree of dye-loading in the magnetic particles relative to the dye-loaded core-shell particles. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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387 KiB

Open AccessArticle

In Vitro and In Vivo Evaluation of a Folate-Targeted Copolymeric Submicrohydrogel Based on N-Isopropylacrylamide as 5-Fluorouracil Delivery System

by M. Dolores Blanco, Sandra Guerrero, Marta Benito, Ana Fernández, César Teijón, Rosa Olmo, Issa Katime and José M. Teijón

Polymers 2011, 3(3), 1107-1125; https://doi.org/10.3390/polym3031107 - 18 Jul 2011

Cited by 28 | Viewed by 10062

Abstract

Folate-targeted poly[(p-nitrophenyl acrylate)-co-(N-isopropylacrylamide)] nanohydrogel (F-SubMG) was loaded with 5-fluorouracil (5-FU) to obtain low (16.3 ± 1.9 μg 5-FU/mg F-SubMG) and high (46.8 ± 3.8 μg 5-FU/mg F-SubMG) load 5-FU-loaded F-SubMGs. The complete in vitro drug release took place in [...] Read more.

Folate-targeted poly[(p-nitrophenyl acrylate)-co-(N-isopropylacrylamide)] nanohydrogel (F-SubMG) was loaded with 5-fluorouracil (5-FU) to obtain low (16.3 ± 1.9 μg 5-FU/mg F-SubMG) and high (46.8 ± 3.8 μg 5-FU/mg F-SubMG) load 5-FU-loaded F-SubMGs. The complete in vitro drug release took place in 8 h. The cytotoxicity of unloaded F-SubMGs in MCF7 and HeLa cells was low; although it increased for high F-SubMG concentration. The administration of 10 μM 5-FU by 5-FU-loaded F-SubMGs was effective on both cellular types. Cell uptake of F-SubMGs took place in both cell types, but it was higher in HeLa cells because they are folate receptor positive. After subcutaneous administration (28 mg 5-FU/kg b.w.) in Wistar rats, F-SubMGs were detected at the site of injection under the skin. Histological studies indicated that the F-SubMGs were surrounded by connective tissue, without any signs of rejections, even 60 days after injection. Pharmacokinetic study showed an increase in MRT (mean residence time) of 5-FU when the drug was administered by drug-loaded F-SubMGs. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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252 KiB

Open AccessArticle

Thermal Cloud Point Fractionation of Poly(vinyl alcohol-co-vinyl acetate): Partition of Nanogels in the Fractions

by Leonard I. Atanase and Gérard Riess

Polymers 2011, 3(3), 1065-1075; https://doi.org/10.3390/polym3031065 - 04 Jul 2011

Cited by 12 | Viewed by 8409

Abstract

Poly(vinyl acetate-co-vinyl alcohol) (PVA), well-known as emulsion stabilizers, are obtained by partial hydrolysis of poly(vinyl acetate) (PVAc). Their thermal cloud point fractionation was performed in aqueous medium between 40 and 75 °C. This fractionation was carried out in order to get [...] Read more.

Poly(vinyl acetate-co-vinyl alcohol) (PVA), well-known as emulsion stabilizers, are obtained by partial hydrolysis of poly(vinyl acetate) (PVAc). Their thermal cloud point fractionation was performed in aqueous medium between 40 and 75 °C. This fractionation was carried out in order to get an insight in the partition of the initially present nanogels in the different fractions. All the fractions were characterized by size exclusion chromatography (SEC), NMR and dynamic light scattering (DLS) giving access to average degree of polymerization , DPw average degree of hydrolysis DH, average sequence lengths of vinyl acetate VAc, volume fraction and average size diameter (Dv) of nanogels and “free PVA chains”. The polydispersity of the samples in DPw, DH and VAc could be confirmed. The nanogels characterized by the highest values of volume fraction and Dv, in the range of 40–43 nm, were separated in the first coacervate fraction, whereas the most soluble fraction with low VAc content does not contain nanogels but only “free chains” of a Dv value of around 7–8 nm. The nanogels in the various fractions could further be disaggregated into “free chains” by complex formation with sodium dodecyl sulfate (SDS). Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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397 KiB

Open AccessArticle

Rotational Diffusion of Macromolecules and Nanoparticles Modeled as Non-Overlapping Bead Arrays in an Effective Medium

by Hengfu Wu, Umar Twahir, Alishia Davis, Ebenezer Duodo, Bahareh Kashani, Young Lee, Cindy Pena, Noni Whitley and Stuart A. Allison

Polymers 2011, 3(2), 846-860; https://doi.org/10.3390/polym3020846 - 13 May 2011

Viewed by 8320

Abstract

In this work, the retarding influence of a gel on the rotational motion of a macromolecule is investigated within the framework of the Effective Medium (EM) model. This is an extension of an earlier study that considered the effect of a gel on [...] Read more.

In this work, the retarding influence of a gel on the rotational motion of a macromolecule is investigated within the framework of the Effective Medium (EM) model. This is an extension of an earlier study that considered the effect of a gel on the translational motion of a macromolecule [Allison, S. et al. J. Phys. Chem. B 2008, 112, 5858-5866]. The macromolecule is modeled as an array of non-overlapping spherical beads with no restriction placed on their size or configuration. Specific applications include the rotational motion of right circular cylinders and wormlike chains modeled as strings of identical touching beads. The procedure is then used to examine the electric birefringence decay of a 622 base pair DNA fragment in an agarose gel. At low gel concentration (M ≤ 0.010 gm/mL), good agreement between theory and experiment is achieved if the persistence length of DNA is taken to be 65 nm and the gel fiber radius of agarose is taken to be 2.5 nm. At higher gel concentrations, the EM model substantially underestimates the rotational relaxation time of DNA and this can be attributed to the onset of direct interactions that become significant when the effective particle size becomes comparable to the mean gel fiber spacing. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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Review

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374 KiB

Open AccessReview

Stimulus-Responsive Heteroaggregation of Colloidal Dispersions: Reversible Systems and Composite Materials

by Melanie Bradley, Azwan Mat Lazim and Julian Eastoe

Polymers 2011, 3(3), 1036-1050; https://doi.org/10.3390/polym3031036 - 01 Jul 2011

Cited by 16 | Viewed by 9247

Abstract

Heteroaggregation is the aggregation of mixed particle systems where the colloidal particles may differ in charge, size and chemical composition. The phenomenon of heteroaggregation is of great relevance in industrial processes and the natural environment. This review will focus on binary heteroaggregation where [...] Read more.

Heteroaggregation is the aggregation of mixed particle systems where the colloidal particles may differ in charge, size and chemical composition. The phenomenon of heteroaggregation is of great relevance in industrial processes and the natural environment. This review will focus on binary heteroaggregation where at least one of the particles is a stimulus-responsive smart particle. Aggregation under various conditions of pH, temperature, light and relative concentration can be induced by the careful manipulation of any one or more of these environmental conditions during the heteroaggregation of smart particles. Stimulus response provides the potential for reversibility from an aggregated to a stable system and exceptional control over inter-particle interactions. The significant fundamental and applied studies that have made an impact in this area will be discussed. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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