Search Results (48)

Chitosan is widely used in drug delivery applications, due to its biocompatibility, bio-degradability, and low toxicity. Nevertheless, its properties can be enhanced through the physical or chemical modification of its amino and hydroxyl groups. This work explores the electrostatic complexation of two chitosan samples of differing lengths with two poly(N-isopropylacrylamide) (PNIPAM) homopolymers of different molecular weight carrying a chargeable carboxyl end group. This interaction enables the electrostatic binding of PNIPAM side chains onto the chitosan backbone through the amino groups, and could be considered as an alternative grafting method. Dynamic and electrophoretic light scattering techniques were employed in order to study the solution/dispersion properties of the formed complexes as a function of the PNIPAM concentration, or, equivalently, the molar/charge ratio of the two components. The obtained results revealed that their mass, size, and charge mostly depend on the length of the two individual constituents, as well as their mixing ratio. Furthermore, their response to changes in their environment, namely temperature and ionic strength, was also examined, demonstrating the effect of either the thermoresponsiveness of PNIPAM or the electrostatic charge screening, respectively. Fluorescence spectroscopy, utilizing pyrene as a probe, provided information regarding the hydrophobicity of the formed complexes, while images from scanning transmission electron and atomic force microscopies further elucidated their morphology, which was found to be closely related to that of the corresponding chitosan molecule. Finally, their potential as drug delivery vehicles was also investigated, utilizing curcumin as a model drug at various loading concentrations. Full article

Cross-linked polyethylene (XLPE) insulation is used in most advanced power cable technology. However, in traditional cross-linking, the conductivity of the cross-linking system sharply increases due to the presence of additives (antioxidants and cross-linked agents). Therefore, reducing the number of antioxidants to further reduce conductivity is a very promising method. The structural design of a new dual-functional antioxidant 5-allyloxy-2-hydroxyl-3-tert-butylbenzophenone (5ATB) has been established. The antioxidant behavior and grafting reaction of 5ATB after photocatalysis under ultraviolet (UV) conditions were further studied using density functional theory (DFT). The reaction potential energy information of the six reaction channels at the B3LYP/6-311+G(d,p) level were obtained. The calculation results indicated that the reaction Gibbs energy barrier of 5ATB with O₂ is approximately 0.48 eV lower than that of the polyethylene chain with O₂ to achieve an anti-oxidative effect. Furthermore, the reaction-active site of 5ATB accepting H is located on the C of CH₂ in a C=C double bond, as demonstrated by an analysis of NBO charge populations. The proposed mechanism has the potential to further expand the design concept of insulation materials for advanced future power cables. Full article

Using the self-consistent field approach, we studied the salt-controlled vertical segregation of mixed polymer brushes immersed into a selective solvent. We considered brushes containing two types of chains: polyelectrolyte (charged) chains and neutral chains. The hydrophobicity of both types of chains is characterized by the Flory–Huggins parameters ${\chi }_C$ and ${\chi }_N$, respectively. It was assumed that the hydrophobicity is varied only for the polyelectrolyte chains (${\chi }_C$), while other polymer chains in the brush remain hydrophilic (${\chi }_N=0$) and neutral. Thus, in our model, the solvent selectivity ($\chi ={\chi }_C-{\chi }_N$) was varied, which can be controlled in a real experiment, for example, by changing the temperature. At low salt concentrations, the polyelectrolyte chains swell and occupy the surface of the mixed brush. At high salt concentrations, the hydrophobic polyelectrolyte chains collapse and give place to neutral chains on the surface. By changing the selectivity of the solvent and the ionic strength of the solution, the surface properties of such mixed brushes can be controlled. Based on the numerical simulations results, it is shown how the critical selectivity corresponding to the segregation transition in polyelectrolyte/neutral brushes depends on the ionic strength of the solution. It is shown that at the same ionic strength, the critical selectivity increases with an increasing degree of dissociation of charged groups, as well as with an increasing fraction of polyelectrolyte chains in the mixed brush. It has also been shown that at low ionic strengths, the critical selectivity of the solvent decreases with increasing grafting density, while at high ionic strengths, on the contrary, it increases. Within the framework of the mean field theory, a two-parameter model has been constructed that quantitatively describes these dependencies. Full article

Cellulose nanocrystals (CNCs) are bio-based materials able to be functionalized following different approaches, which expands their range of applications. One such approach is surface-initiated polymerization, which involves the attachment of an initiator to the CNC’s surface to initiate the growth of the polymer. This work reports the modification of CNCs using the described approach. First, a CNC-based film was prepared, on which an initiator (RAFT agent) was grafted, and then (trimethylaminoethyl methacrylate, a positively charged monomer, was polymerized using reversible addition–fragmentation chain-transfer (RAFT) polymerization. The CNC film was successfully modified and fully characterized. Different degrees of polymerization were targeted to emphasize the effect of the positively charged polymer and their chain length on the adsorption efficiency. The results showed that by increasing the chain length of the grafted polymer, up to 80% of both pollutants could be removed, with a faster adsorption of PFOS as compared to PFOA. Full article

Owing to their special structure and excellent physical and chemical properties, conducting polymers have attracted increasing attention in materials science. In recent years, tremendous efforts have been devoted to improving the comprehensive performance of conducting polymers by using the technique of “doping.” Spherical polyelectrolyte brushes (SPBs) bearing polyelectrolyte chains grafted densely to the surface of core particles have the potential to be novel dopant of conducting polymers not only because of their spherical structure, high grafting density and high charge density, but also due to the possibility of their being applied in printed electronics. This review first presents a summary of the general dopants of conducting polymers. Meanwhile, conducting polymers doped with spherical polyelectrolyte brushes (SPBs) is highlighted, including the preparation, characterization, performance and doping mechanism. It is demonstrated that comprehensive performance of conducting polymers has improved with the addition of SPBs, which act as template and dopant in the synthesis of composites. Furthermore, the applications and future developments of conductive composites are also briefly reviewed and proposed, which would draw more attention to this field. Full article

In this study, we aimed to design and research proton-conducting membranes based on Aquivion^®-type material that had been modified with detonation nanodiamonds (particle size 4–5 nm, 0.25–5.0 wt. %). These nanodiamonds carried different functional groups (H, OH, COOH, F) that provided the hydrophilicity of the diamond surface with positive or negative potential, or that strengthened the hydrophobicity of the diamonds. These variations in diamond properties allowed us to find ways to improve the composite structure so as to achieve better ion conductivity. For this purpose, we prepared three series of membrane films by first casting solutions of perfluorinated Aquivion^®-type copolymers with short side chains mixed with diamonds dispersed on solid substrates. Then, we removed the solvent and the membranes were structurally stabilized during thermal treatment and transformed into their final form with –SO₃H ionic groups. We found that the diamonds with a hydrogen-saturated surface, with a positive charge in aqueous media, contributed to the increase in proton conductivity of membranes to a greater rate. Meanwhile, a more developed conducting diamond-copolymer interface was formed due to electrostatic attraction to the sulfonic acid groups of the copolymer than in the case of diamonds grafted with negatively charged carboxyls, similar to sulfonic groups of the copolymer. The modification of membranes with fluorinated diamonds led to a 5-fold decrease in the conductivity of the composite, even when only a fraction of diamonds of 1 wt. % were used, which was explained by the disruption in the connectivity of ion channels during the interaction of such diamonds mainly with fluorocarbon chains of the copolymer. We discussed the specifics of the mechanism of conductivity in composites with various diamonds in connection with structural data obtained in neutron scattering experiments on dry membranes, as well as ideas about the formation of cylindrical micelles with central ion channels and shells composed of hydrophobic copolymer chains. Finally, the characteristics of the network of ion channels in the composites were found depending on the type and amount of introduced diamonds, and correlations between the structure and conductivity of the membranes were established. Full article

To enhance the direct current (DC) dielectric properties of cross-linked polyethylene (XLPE) for high-voltage (HV) cable insulation, the polyethylene molecular chain is modified by grafting bismaleimide ethane (BMIE), which creates carrier deep traps within the polymer material. Compared to the traditional modified molecule maleic anhydride (MAH), BMIE has a significantly higher boiling point than the production temperature of XLPE. Additionally, it does not release bubbles during the production process and, thus, preserves the dielectric properties. It was proved by infrared spectroscopy and a gel content test that BMIE was successfully grafted onto the polyethylene molecular chain and had no effect on the crosslinking degree of the polymer while reducing the amount of crosslinker, thereby reducing the influence of the by-products of the decomposition of dicumene peroxide (DCP) on the electrical resistance of polymers. The analysis of DC breakdown field strength, current density, and space charge distribution at various temperatures demonstrates that grafting BMIE can greatly enhance the dielectric properties of insulation. Polar groups in the BMIE molecule create deep trap energy levels in XLPE-g-BMIE, and these trap energy levels contribute to the formation of a charged layer near the electrode, which is shielded by Coulomb potential. As a result, the charge injection barrier increases. Additionally, the presence of these polar groups reduces the mobility of charge carriers through trap-carrier scattering, effectively suppressing the accumulation of space charge within the material. First-principle calculations also confirm that bound states can be introduced as carrier traps by grafting BMIE onto polyethylene molecules. The agreement between experimental results and simulation calculations indicates that grafting BMIE to enhance the dielectric properties of polyethylene is a new and feasible research direction in the exploitation of materials for HVDC cables. Full article

Biological fouling is one of the main reasons that limits the application of traditional polypropylene (PP) fishing nets in aquaculture. Here, a new environmentally friendly and broad–spectrum antibacterial agent called cationic poly(hexamethylene guanidine) (PHMG) was grafted onto PP molecular chains via permanent chemical bonding to inhibit the biological fouling. The antibacterial monofilaments were obtained by blending different contents of PP–g–PHMG with PP by melt spinning. FTIR results found PHMG to be stably present in the mixed monofilaments after high–temperature melt spinning molding. The crystallinity, relaxation behavior, mechanical properties, water absorptivity, and antibacterial and antifouling efficiencies of the PP–g–PHMG/PP blends were strongly dependent on PP–g–PHMG. The crystallinity increased with increasing PP–g–PHMG content. Adding PP–g–PHMG improved the breaking strength, knotting strength, and elongation at the break for all ratios of PP–g–PHMG/PP blends. However, the water absorption caused by PHMG is low, ranging between 2.48% and 3.45% for the PP–g–PHMG/PP monofilaments. The monofilaments showed excellent nonleaching antimicrobial activities against Staphylococcus aureus and Escherichia coli. The electrostatic adsorption of the negatively charged bacteria and the destruction of their cell membrane allowed the growth inhibition to reach 99.69% with a PP–g–PHMG content of 40%. The marine fish farming experiment also showed a long–term antifouling effect. Full article

A pH-responsive membrane is expected to be used for applications such as drug delivery, controlling chemical release, bioprocessing, and water treatment. Polyacrylic acid (PAA) is a pH-responsive polymer that swells at high pH. A tubular α-alumina porous support was coated with PAA by grafting to introduce appropriate functional groups, followed by polymerization with acrylic acid. The permeances of acetic acid, lactic acid, phenol, and caffeine were evaluated by circulating water inside the membrane, measuring the concentration of species that permeated into the water, and analyzing the results with the permeation model. The permeance of all species decreased with increasing pH, and that of phenol was the largest among these species. At high pH, the PAA carboxy group in the membrane dissociated into carboxy ions and protons, causing the swelling of PAA due to electrical repulsion between the negative charges of the PAA chain, which decreased the pore size of the membrane and suppressed permeation. Furthermore, the electrical repulsion between negatively charged species and the PAA membrane also suppressed the permeation. The results of this study demonstrated that the PAA-coated α-alumina porous support functioned as a pH-responsive membrane. Full article

Polar group-modified crosslinked polyethylene (XLPE) materials are developed with a peroxide thermochemical method of individually grafting chloroacetic acid allyl ester (CAAE) and maleic anhydride (MAH) to polyethylene molecular-chains, which are dedicated to ameliorating dielectric characteristics through charge-trapping mechanism. By free radical addition reactions, the CAAE and MAH molecules are successfully grafted to polyethylene molecular chains of XLPE in crosslinking process, as verified by infrared spectroscopy molecular characterizations. Dielectric spectra, electric conductance, and dielectric breakdown strength are tested to evaluate the improved dielectric performances. Charge trap characteristics are investigated by analyzing thermal stimulation depolarization currents in combination with first-principles electronic-structure calculations to reveal the polar-group introduced mechanisms of contributing dipole dielectric polarization, impeding electric conduction, and promoting electrical breakdown field. The grafted polar-group molecules, especially for MAH, can introduce deep-level charge traps in XLPE materials to effectively restrict charge injections and hinder charge carrier transports, which accounts for the significant improvements in electric resistance and dielectric breakdown strength. Full article

With the recognition of the multiple advantages of sulfonated hydrocarbon-based polymers that possess high chemical and mechanical stability with significant low cost, we employed molecular dynamics simulation to explore the morphological effects of side chain length in sulfonated polystyrene grafted poly(arylene ether sulfone)s (SPAES) proton exchange membranes. The calculated diffusion coefficients of hydronium ions (H₃O⁺) are in range of 0.61–1.15 × 10⁻⁷ cm²/s, smaller than that of water molecules, due to the electrical attraction between the oppositely charged sulfonate group and H₃O⁺. The investigation into the radial distribution functions suggests that phase segregation in the SPAES membrane is more probable with longer side chains. As the hydration level of the membranes in this study is relatively low (λ = 3), longer side chains correspond to more water molecules in the amorphous cell, which provides better solvent effects for the distribution of sulfonated side chains. The coordination number of water molecules and hydronium ions around the sulfonate group increases from 1.67 to 2.40 and from 2.45 to 5.66, respectively, with the increase in the side chain length. A significant proportion of the hydronium ions appear to be in bridging configurations coordinated by multiple sulfonate groups. The microscopic conformation of the SPAES membrane is basically unaffected by temperature during the evaluated temperature range. Thus, it can be revealed that the side chain length plays a key role in the configuration of the polymer chain and would contribute to the formation of the microphase separation morphology, which profits proton transport in the hydrophilic domains. Full article

In order to improve electrical matching between ethylene-propylene-diene misch-polymere (EPDM) reinforce insulation and crosslinked polyethylene (XLPE) main insulation in direct current (DC) cable accessories, the glyceryl monooleate (GMO) organic compound composed of several polar-groups and one long carbon chain is employed for chemical graft modification on EPDM to ameliorate DC electrical performances. Charge trap characteristics are analyzed by testing thermal stimulation current (TSC) and verified by calculating first-principles electronic properties to elucidate the GMO-graft-modified charge trapping mechanism accounting for DC electric conductance and dielectric breakdown. The grafted GMO molecules introduce substantial shallow charge traps that lead to nonlinear profiles of electric conduction versus electric field and cause hopping transports of percolation conductance. Electric conductance of EPDM is significantly improved by GMO graft for electrical matching with XLPE, while a high level of dielectric breakdown strength is retained sufficiently for reinforce insulation in cable accessories. Shallow charge traps introduced by GMO graft are capable of capturing charge carriers to form homocharge layers near electrodes which can scatter the transporting charge carriers and exclude further charge injections, thus to mitigate the dielectric breakdown strength reduction caused by electric conductivity improvement. Electric field finite-element simulations demonstrate that the electric field in DC cable terminals can be evidently homogenized by using GMO-grafted EPDM as reinforce insulation. Full article

For achieving successful chemotherapy against cancer, designing biocompatible drug delivery systems (DDSs) with long circulation times, high cellular endocytosis efficiency, and targeted drug release is of upmost importance. Herein, a well-defined PEG-b-P(MASSChol-co-MANBoc) block copolymer bearing redox-sensitive cholesteryl-side group was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization (with non-redox PEG-b-P(MACCChol-co-MAN-DCA) as the reference), and 1,2-dicarboxylic-cyclohexene acid (DCA) was then grafted onto the hydrophobic block to endow it with charge-convertible characteristics under a tumor microenvironment. The amphiphilic copolymer could be assembled into polymeric spherical micelles (SSMCs) with polyethylene glycol (PEG) as the corona/shell, and anti-cancer drug doxorubicin (DOX) was successfully encapsulated into the micellar core via strong hydrophobic and electrostatic interactions. This nanocarrier showed high stability in the physiological environment and demonstrated “smart” surface charge conversion from negative to positive in the slightly acidic environment of tumor tissues (pH 6.5~6.8), as determined by dynamic light scattering (DLS). Moreover, the cleavage of a disulfide bond linking the cholesterol grafts under an intracellular redox environment (10 mM GSH) resulted in micellar dissociation and accelerated drug release, with the non-redox-responsive micelles (CCMCs) as the control. Additionally, a cellular endocytosis and tumor proliferation inhibition study against MCF-7 tumor cells demonstrated the enhanced endocytosis and tumor cell inhibitory efficiency of dual-responsive SSMCs/DOX nanomedicines, revealing potentials as multifunctional nanoplatforms for effective oncology treatment. Full article

A kind of terpyridine derivative (NH₂-Tpy) in which the amino was incorporated by a short alkyl chain was synthesized. Through grafting of terpyridine units into the hydrophilic copolymers of maleic anhydride and acrylic acid PAAMa via the reaction of the amino groups in NH₂-Tpy and the maleic anhydride units, a series of gelator polymers—P1, P2, and P3—containing different contents of terpyridine units was synthesized. Under coordination of Ni²⁺ and terpyridine ligands in linear polymers, the supramolecular hydrogels H1, H2, and H3 with different cross-linking degrees were prepared. The linear polymers P1–P3 had a strong absorption peak at about 290 nm in the UV-vis spectra which was attributed to π–π* transition, and there was a new peak at about 335 nm led by the metal-to-ligands charge transfer (MLCT) when coordinated with Ni²⁺ ions. According to the rheological behaviors, the storage modulus (G′) was larger than the loss modulus (G′′). These hydrogels showed typical gel-like characteristics when the terpyridine content of the hydrogels exceeded 10%, and the hydrogels showed liquid-like characteristics when the terpyridine content of the hydrogels was less than 7%. The results of the micromorphological investigation of the xerogels from SEM illustrated the metal–terpyridine coordination cross-linking could have an important influence on the microstructures of the resulting hydrogels. Furthermore, these hydrogels based on supramolecular cross-links exhibited reversible solution–gel transition at different environmental temperatures. At the same time, the equilibrium swelling of the supramolecular hydrogels was 8.0–12.3 g/g, which increased with the decrease in the content of the terpyridine units in the resulting hydrogels. Full article

The goal of the current article was to obtain data regarding the application of a series of grafted pullulan derivatives, as flocculating agents, for removal of some pesticide formulations from model wastewater. The pullulan derivatives are cationic polyelectrolytes, with various content and length of grafted poly[(3-acrylamidopropyl)-trimethylammonium chloride] chains onto the pullulan (P-g-pAPTAC)]. The commercial pesticides are either fungicide (Bordeaux Mixture) (BM) or insecticides (Decis (Dc)—active ingredient Deltamethrin, Confidor Oil (CO)—active ingredient Imidacloprid, Confidor Energy (CE)—active ingredients Deltamethrin and Imidacloprid and Novadim Progress (NP)—active ingredient Dimethoate). The removal efficiency has been assessed by UV-Vis spectroscopy measurements as a function of some parameters, namely polymer dose, grafted chains content and length, pesticides concentration. The P-g-pAPTAC samples showed good removal efficacy at dose_op, more than 94% for BM, between 84 and 90% for DC, CO and CE and around 93% for NP. The maximum percentage removal decreased with the pesticides (DC, CO, CE, NP) concentration declining; no effect of BM concentration in suspension on its removal efficiency process has been noted. Differences indicated by zeta potential and particle size distribution measurements regarding the pesticides removal mechanisms by pullulan derivatives (charge neutralization, bridging, etc.) are discussed. Full article