Effect of structure of cationic comb copolymers on their adsorption and stabilization of titania nanoparticles

Electrosteric Control of the Aggregation and Yielding Behavior of Concentrated Portlandite Suspensions

Portlandite (calcium hydroxide: CH: Ca(OH)2) suspensions aggregate spontaneously and form percolated fractal aggregate networks when dispersed in water. Consequently, the viscosity and yield stress of portlandite suspensions diverge at low particle loadings, adversely affecting their processability. Even though polycarboxylate ether (PCE)-based comb polyelectrolytes are routinely used to alter the particle dispersion state, water demand, and rheology of similar suspensions (e.g., ordinary portland cement suspensions) that feature a high pH and high ionic strength, their use to control portlandite suspension rheology has not been elucidated. This study combines adsorption isotherms and rheological measurements to elucidate the role of PCE composition (i.e., charge density, side chain length, and grafting density) in controlling the extent of PCE adsorption, particle flocculation, suspension yield stress, and thermal response of portlandite suspensions. We show that longer side-chain PCEs are more effective in affecting suspension viscosity and yield stress, in spite of their lower adsorption saturation limit and fractional adsorption. The superior steric hindrance induced by the longer side chain PCEs results in better efficacy in mitigating particle aggregation even at low dosages. However, when dosed at optimal dosages (i.e., a dosage that induces a dynamically equilibrated dispersion state of particle aggregates), different PCE-dosed portlandite suspensions exhibit identical fractal structuring and rheological behavior regardless of the side chain length. Furthermore, it is shown that the unusual evolution of the rheological response of portlandite suspensions with temperature can be tailored by adjusting the PCE dosage. The ability of PCEs to modulate the rheology of aggregating charged particle suspensions can be generally extended to any colloidal suspension with a strong screening of repulsive electrostatic interactions.

Polymer brush coated upconverting nanoparticles with improved colloidal stability and cellular labeling

Upconverting nanoparticles (UCNPs) possess great potential for biomedical application. UCNPs absorb and convert near-infrared (NIR) radiation in the biological imaging window to visible (Vis) and even ultraviolet (UV) radiation. NIR excitation offers reduced scattering and diminished autofluorescence in biological samples, whereas the emitted UV-Vis and NIR photons can be used for cancer treatment and imaging, respectively. However, UCNPs are usually synthesized in organic solvents and are not readily suitable for biomedical application due to the hydrophobic nature of their surface. Herein, we have removed the hydrophobic ligands from the synthesized UCNPs and coated the bare UCNPs with two custom-made hydrophilic polyelectrolytes (synthesized via the reversible addition-fragmentation chain transfer (RAFT) polymerization method). Polymers containing different amounts of PEGylated and carboxylic groups were studied. Coating with both polymers increased the upconversion (UC) emission intensity and photoluminescence lifetime values of the UCNPs, which directly translates to more efficient cancer cell labeling nanoprobes. The polymer composition plays a crucial role in the modification of UCNPs, not only with respect to their colloidal stability, but also with respect to the cellular uptake. Colloidally unstable bare UCNPs aggregate in cell culture media and precipitate, rendering themselves unsuitable for any biomedical use. However, stabilization with polymers prevents UCNPs from aggregation, increases their uptake in cells, and improves the quality of cellular labeling. This investigation sheds light on the appropriate coating for UCNPs and provides relevant insights for the rational development of imaging and therapeutic tools.

Fabrication of Cationic Poly(vinyl alcohol) Films Cross-Linked Using Copolymers Containing Quaternary Ammonium Cations, Benzoxaborole, and Carboxy Groups

Water-insoluble cationic poly(vinyl alcohol) (PVA) films were fabricated using a mixed aqueous solution of PVA and poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC)-co-methacrylic acid (MAAc)-co-5-methacrylamido-1,2-benzoxaborole (MAAmBO)) copolymer (3D). The surface of the PVA film is typically negatively charged, and simple fabrication methods for water-insoluble PVA films with cationic surface charges are required to expand their application fields. METAC, which has a permanent positive charge owing to the presence of a quaternary ammonium cation, was selected as the cationic unit. The MAAc and MAAmBO units were used as two types of cross-linking structures for the thermal cross-linking of the hydroxy and carboxy groups of the MAAc unit (covalent bonding) as well as the diol and benzoxaborole groups of the MAAmBO unit (dynamic covalent bonding). The films were thermally cross-linked at 135 °C for 4 h without the addition of materials. After immersion in surplus water at 80 °C for 3 h, the cross-linked PVA/3D films retained almost 100% of their weights. The ζ-potential of the water-insoluble PVA/3D film was 9.4 ± 0.8 mV. The PVA/3D film was strongly dyed using anionic acid red 1 (AR1) because of its positively charged surface. Interestingly, it could also be slightly dyed using cationic methylene blue (MB) and became transparent (original state) after immersion in water for 2 days. These results suggested that positive and negative charges coexisted in the PVA/3D film, and the surface properties were positively inclined. Moreover, the degree of hemolysis of the PVA/3D films was similar to that of the negative control, which showed high blood compatibility. To our knowledge, this is the first report on the fabrication of water-insoluble cationic PVA films using two types of cross-linking structures containing carboxy and benzoxaborole groups. The cross-linked PVA films were analyzed using Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), and contact angle (CA) and ζ-potential measurement, as well as by determining the mechanical properties, adsorption of charged molecules, and biocompatibility. These readily fabricated water-insoluble PVA films with positive charges can show potential applications in sensors, adsorption systems, and antimicrobial materials.

Effect of Cationic Brush-Type Copolymers on the Colloidal Stability of GdPO4 Particles with Different Morphologies in Biological Aqueous Media

In this study, we present the synthesis of cationic brush-type polyelectrolytes and their use in the stabilization of GdPO4 particles in aqueous media. Polymers of various compositions were synthesized via the RAFT polymerization route. SEC equipped with triple detection (RI, DP, RALS, and LALS) was used to determine the molecular parameters (Mn, Mw, Mw/Mn). The exact composition of synthesized polymers was determined using NMR spectroscopy. Cationic brush-type polymers were used to improve the stability of aqueous GdPO4 particle dispersions. First, the IEPs of GdPO4 particles with different morphologies (nanorods, hexagonal nanoprisms, and submicrospheres) were determined by measuring the zeta potential of bare particle dispersions at various pH values. Afterward, cationic brush-type polyelectrolytes with different compositions were used for the surface modification of GdPO4 particles (negatively charged in alkaline media under a pH value of ∼10.6). The concentration and composition effects of used polymers on the change in particle surface potential and stability (DLS measurements) in dispersions were investigated and presented in this work. The most remarkable result of this study is redispersible GdPO4 nanoparticle colloids with increased biocompatibility and stability as well as new insights into possible cationic brush-type polyelectrolyte applicability in both scientific and commercial fields.

Bioinspired Adhesion Polymers: Wear Resistance of Adsorption Layers

Mussel adhesive polymers owe their ability to strongly bind to a large variety of surfaces under water to their high content of 3,4-dihydroxy-l-phenylalanine (DOPA) groups and high positive charge. In this work, we use a set of statistical copolymers that contain medium-length poly(ethylene oxide) side chains that are anchored to the surface in three different ways: by means of (i) electrostatic forces, (ii) catechol groups (as in DOPA), and (iii) the combination of electrostatic forces and catechol groups. A nanotribological scanning probe method was utilized to evaluate the wear resistance of the formed layers as a function of normal load. It was found that the combined measurement of surface topography and stiffness provided an accurate assessment of the wear resistance of such thin layers. In particular, surface stiffness maps allowed us to identify the initiation of wear before a clear topographical wear scar was developed. Our data demonstrate that the molecular and abrasive wear resistance on silica surfaces depends on the anchoring mode and follows the order catechol groups combined with electrostatic forces > catechol groups alone > electrostatic forces alone. The devised methodology should be generally applicable for evaluating wear resistance or "robustness" of thin adsorbed layers on a variety of surfaces.

A novel comb-typed poly(oligo(ethylene glycol) methylether acrylate) as an excellent aqueous lubricant

HYPOTHESIS

Aqueous lubricants exhibit versatile advantages over oil-based lubricants. However, it still remains a challenge for the aqueous solutions to obtain excellent lubrication properties with high contact pressure on macroscale.

EXPERIMENTS

In this work, a comb-typed poly(oligo(ethylene glycol) methylether acrylate) (P(OEGMA)) was successfully synthesized via RAFT polymerization. Rheological, morphological and tribological properties of prepared P(OEGMA) aqueous solutions were characterized via a rheometer, cryo-SEM and ball-on-disk tribometer, respectively.

FINDINGS

The synthesized P(OEGMA) exhibited a uniformly smaller size than that of the commercial linear polyethylene glycol (PEG), leading to reduced viscosities in aqueous solutions. The obtained P(OEGMA) aqueous solutions achieved outstandingly ultralow friction coefficients (μ < 0.01) and a good wear-resistance under high pressure (>300 MPa, two-fold increase than reported in the previous literature). The desirable lubricating performances can be attributed to the well-established running-in period, a good interfacial adsorption property between polymer molecules and solid surfaces, the hydration effect as well as the hydrodynamic effect. The current finding reveals the excellent aqueous lubrication properties possessed by the synthesized comb-typed P(OEGMA), which can broaden the development of aqueous lubricants in practical engineering fields.

Bifunctional ultraviolet/ultrasound responsive composite TiO2/polyelectrolyte microcapsules

Designing and fabricating multifunctional microcapsules are of considerable interest in both academic and industrial research aspects. This work reports an innovative approach to fabricate composite capsules with high UV and ultrasound responsive functionalities that can be used as external triggers for controlled release, yet with enhanced mechanical strength that can make them survive in a harsh environment. Needle-like TiO2 nanoparticles (NPs) were produced in situ into layer-by-layer (LbL) polyelectrolyte (PE) shells through the hydrolysis of titanium butoxide (TIBO). These rigid TiO2 NPs yielded the formed capsules with excellent mechanical strength, showing a free standing structure. A possible mechanism is proposed for the special morphology formation of the TiO2 NPs and their reinforcing effects. Synergistically, their response to UV and ultrasound was visualized via SEM, with the results showing an irreversible shell rapture upon exposure to either UV or ultrasound irradiation. As expected, the release studies revealed that the dextran release from the TiO2/PE capsules was both UV-dependent and ultrasound-dependent. Besides, the biocompatibility of the capsules with the incorporation of amorphous TiO2 NPs was confirmed by an MTT assay experiment. All these pieces of evidence suggested a considerable potential medicinal application of TiO2/PE capsules for controlled drug delivery.

Triple-responsive inorganic–organic hybrid microcapsules as a biocompatible smart platform for the delivery of small molecules

We designed novel hybrid inorganic/organic capsules with unique physicochemical features enabling multimodal triggering.

Functionalization of surfaces with branched polymers

This review summarizes recent developments in the field of surfaces functionalized with branched polymers, including the fabrication methods, morphologies, properties and applications.

Nanoscale deposition of metal–organic framework films on polymer nanosheets

We demonstrate the first example of surface-attached metal–organic framework film deposition on polymer nanosheets fabricated using Langmuir–Blodgett technique.

Synthesis and characterization of “comb-like” poly(ionic liquid-co-styrene): expected applications in graphene dispersion and CO2 separation

A new PIL “comb-like” copolymer was synthesized by directly polymerizing ionic liquid monomer by ATRP using macroinitiator. This polymer is potentially useful in graphene dispersion and CO₂ separation.