Reactive Encapsulation Research Articles

Broadband electrical conductivity of metal/carbon nanotubes polyamide 6 composites fabricated by reactive encapsulation

This is the first broadband dielectric spectroscopy study on the temperature- and frequency-dependent electrical conductivity of polyamide 6 (PA6) composites containing both metal microparticles (Al, Fe, or Cu) and carbon nanotubes (CNT). The dually reinforced PA6 hybrids are prepared through compression molding of metal- and CNT-loaded microparticles (MP). These MP are synthesized by activated anionic ring-opening polymerization (AAROP) of ε-caprolactam in suspension, carried out in the presence of the micron-sized metal powders and the nanosized CNT fillers, with a combined load of up to 10 wt%. The good dispersion of the two loads by the AAROP strategy results in a notable increase in the electrical conductivity by up to 11 orders of magnitude. Moreover, the frequency-dependent behavior of the measured conductivity obeys the so-called universal dynamic response. This response involves a direct current (d.c.) electrical conductivity (σdc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\sigma }_{{\ ext{dc}}}$$\\end{document}) observed beyond a critical frequency, Fc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${F}_{{\ ext{c}}}$$\\end{document}, followed by a power-law response characterized by an exponent s, which fluctuates between 0.11 and 0.43. The σdc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\sigma }_{{\ ext{dc}}}$$\\end{document} of the binary composites spans from 1.42 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 10−5 to 1.63 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes$$\\end{document} 10−2 S/cm, this increase being attributed to the synergetic effect between CNT and the metal particles that contribute to the carrier mobility within the conductive network.Graphical

Patterned Electroconductive Networks in Ag‐Polyamide 6 Composites by Laser Ablation

AbstractA simple, fast, and cost‐effective method to fabricate conductive paths on insulating Ag‐containing polyamide 6 (PA6) composites by laser beam treatment is presented in this study. First, Ag‐hybrid microparticles (Ag‐MP) with a total metal load of up to 19 wt% are synthesized based on a reactive encapsulation strategy utilizing activated anionic polymerization of ε‐caprolactam in solution, in the presence of Ag nanoparticles. Then, the Ag‐MP are compression molded into plates (Ag‐PL) on which a scanning laser treatment is applied to create conductive paths in their selected parts. A comparison between structural, morphological, and thermal properties of the Ag‐MP and the molded Ag‐PL composites is performed. The electric conductive properties of the Ag‐loaded hybrid materials are investigated before and after laser ablation, and it is concluded that the laser treatment results in selected paths with widths in the range of 500 µm with conductivity values in the range of 1.12 to 8.90 S m−1 while the untreated Ag‐PA6 surface remains isolating with conductivity values of 1.27 × 10−08 S m−1. These results prove that applying laser ablation with controlled parameters on initially insulating Ag‐PL composites can efficiently produce conductive line patterns in composite plates.

A Facile and Scalable Route to the Preparation of Catalytic Membranes with in Situ Synthesized Supramolecular Dendrimer Particle Hosts for Pt(0) Nanoparticles Using a Low-Generation PAMAM Dendrimer (G1-NH2) as Precursor.

Since the first reports of Cu dendrimer-encapsulated nanoparticles (DENs) published in 1998, the dendrimer-templating method has become the best and most versatile method for preparing ultrafine metallic and bimetallic nanoparticles (1-3 nm) with well-defined compositions, high catalytic activity, and tunable selectivity. However, DENs have remained for the most part model systems with limited prospects for scale up and integration into high-performance and reusable catalytic modules and systems for industrial-scale applications. Here, we describe a facile and scalable route to the preparation of catalytic polyvinylidene fluoride (PVDF) membranes with in situ synthesized supramolecular dendrimer particles (SDPs) that can serve as hosts and containers for Pt(0) nanoparticles (2-3 nm). These new catalytic membranes were prepared using a reactive encapsulation process similar to that utilized to prepare Pt DENs by addition of a reducing agent (sodium borohydride) to aqueous complexes of Pt(II) + G4-OH/G6-OH polyamidoamine (PAMAM) dendrimers. However, the SDPs (2.4 μm average diameter) of our new mixed matrix PVDF-PAMAM membranes were synthesized in the dope dispersion without purification prior to film casting using (i) a low-generation PAMAM dendrimer (G1-NH2) as particle precursor and (ii) epichlorohydrin, an inexpensive functional reagent, as cross-linker. In addition, the membrane PAMAM particles contain secondary amine groups (∼1.9 mequiv per gram of dry membrane), which are more basic and thus have higher Pt binding affinity than the tertiary amine groups of the G4-OH and G6-OH PAMAM dendrimers. Proof-of-concept experiments show that our new PVDF-PAMAM-G1-Pt/membranes can serve as highly active and reusable catalysts for the hydrogenation of alkenes and alkynes to the corresponding alkanes using (i) H2 at room temperature and a pressure of 1 bar and (ii) low catalyst loadings of ∼1.4-1.6 mg of Pt. Using cyclohexene as model substrate, we observed near quantitative conversion to cyclohexane (∼98%). The regeneration studies showed that our new Pt/membrane catalysts are stable and can be reused for five consecutive reaction cycles for a total duration of 120 h including 60 h of heating at 100 °C under vacuum for substrate, product, and solvent removal with no detectable loss of cyclohexene hydrogenation activity. The overall results of our study point to a promising, versatile, and scalable path for the integration of catalytic membranes with in situ synthesized SDP hosts for Pt(0) nanoparticles into high-throughput modules and systems for heterogeneous catalytic hydrogenations, an important class of reactions that are widely utilized in industry to produce pharmaceuticals, agrochemicals, and specialty chemicals.

Hyaluronic Acid-Shelled Disulfide-Cross-Linked Nanopolymersomes for Ultrahigh-Efficiency Reactive Encapsulation and CD44-Targeted Delivery of Mertansine Toxin.

It was and remains a big challenge for cancer nanomedicines to achieve high and stable drug loading with fast drug release in the target cells. Here, we report on novel hyaluronic acid-shelled disulfide-cross-linked biodegradable polymersomes (HA-XPS) self-assembled from hyaluronic acid-b-poly(trimethylene carbonate-co-dithiolane trimethylene carbonate) diblock copolymer for ultrahigh-efficiency reactive encapsulation and CD44-targeted delivery of mertansine (DM1) toxin, a highly potent warhead for clinically used antibody-drug conjugates. Remarkably, HA-XPS showed quantitative encapsulation of DM1 even with a high drug loading content of 16.7 wt %. DM1-loaded HA-XPS (HA-XPS-DM1) presented a small size of ∼80 nm, low drug leakage under physiological conditions, and fast glutathione-triggered drug release. MTT assays revealed that HA-XPS was noncytotoxic while HA-XPS-DM1 was highly potent to MDA-MB-231 cells with an IC50 comparable to that of free DM1. The in vitro and in vivo inhibition experiments indicated that HA-XPS could actively target MDA-MB-231 cells. Notably, HA-XPS-DM1 while causing little adverse effect could effectively inhibit tumor growth and significantly prolong survival time in MDA-MB-231 human breast tumor-bearing mice. HA-XPS-DM1 provides a novel and unique treatment for CD44-positive cancers.

Crosslink network rearrangement via reactive encapsulation of solvent in epoxy curing: A combined molecular simulation and experimental study

Encapsulation of solvent during cure is proposed as one way to alter the network topology of crosslinked polymers. We performed all-atom molecular dynamics simulations to study systems comprised of Epon828 epoxy resin and Jeffamine-D400 diamine crosslinkers cured with varying amounts of the inert solvent dichloromethane (0–50 wt%) and then dried and annealed. Densities, glass transition temperatures, and Young's moduli are observed to be insensitive to the initial amount of dichloromethane. These findings were verified by experiment. Simulations also showed that radial distribution functions and dihedral angle distributions were insensitive to the amount of dichloromethane present. However, using Dijkstra's algorithm, we observed that the distribution of minimum path lengths between crosslinks shifts appreciably to larger values as the amount of dichloromethane increases. This suggests that solvent-encapsulated curing can allow for control over network topology without changing crosslink density or intermolecular packing, and the properties derived from it, in highly crosslinked polymers.

Enhanced optical breakdown in KB cells labeled with folate-targeted silver-dendrimer composite nanodevices

Enhanced optical breakdown of KB tumor cells folate-targeted with silver-dendrimer composite nanodevices (CNDs) is described. CNDs [(Ag 0) 25-PAMAM_E5.(NH 2) 42(NGly) 74(NFA) 2.7] were fabricated by reactive encapsulation, using a biocompatible template of dendrimer–folic acid (FA) conjugates. Preferential uptake of the folate-targeted CNDs (of various treatment concentrations and surface functionality) by KB cells was visualized with confocal microscopy and transmission electron microscopy. Intracellular laser-induced optical breakdown threshold and dynamics were detected and characterized by high-frequency ultrasonic monitoring of resulting transient bubble events. When irradiated with a near-infrared, femtosecond laser, the CND-targeted KB cells acted as well-confined activators of laser energy, enhancing nonlinear energy absorption, exhibiting a significant reduction in breakdown threshold and thus selectively promoting intracellular laser-induced optical breakdown. From the Clinical Editor This study presents a novel method to selectively destroy cancer cells by combining biochemical targeting with topical laser irradiation. A human epidermoid cancer cell line was targeted with folated silver-dendrimer composite nanodevices and the labeled cancer cells were subsequently destroyed by the microbubbles generated due the enhanced energy uptake of the silver nanoparticles from the laser irradiation, as compared to unlabeled cells.

Nanoporous Thermosetting Polymers

Potential applications of nanoporous thermosetting polymers include polyelectrolytes in fuel cells, separation membranes, adsorption media, and sensors. Design of nanoporous polymers for such applications entails controlling permeability by tailoring pore size, structure, and interface chemistry. Nanoporous thermosetting polymers are often synthesized via free radical mechanisms using solvents that phase separate during polymerization. In this work, a novel technique for the synthesis of nanoporous thermosets is presented that is based on the reactive encapsulation of an inert solvent using step-growth cross-linking polymerization without micro/macroscopic phase separation. The criteria for selecting such a monomer-polymer-solvent system are discussed based on FTIR analysis, observed micro/macroscopic phase separation, and thermodynamics of swelling. Investigation of resulting network pore structures by scanning electron microscopy (SEM) and small-angle X-ray scattering following extraction and supercritical drying using carbon dioxide showed that nanoporous polymeric materials with pore sizes ranging from 1 to 50 nm can be synthesized by varying the solvent content. The differences in the porous morphology of these materials compared to more common free radically polymerized analogues that exhibit phase separation were evident from SEM imaging. Furthermore, it was demonstrated that the chemical activity of the nanoporous materials obtained by our method could be tailored by grafting appropriate functional groups at the pore interface.

Design and characterization of nanoporous polymeric materials via reactive encapsulation of a chemically inert solvent

Nanoporous polymeric materials are used as polyelectrolytes in fuel cells, separation membranes, sensors and actuators, templates for nanoparticle synthesis, and electroactive material in biomedical applications. Design of nanoporous polymeric materials for such applications entails controlling permeability by tailoring the pore size and pore chemistry. A novel method of synthesizing nanoporous polymeric materials is employed in this work. This technique involves the synthesis of nanoporous polymeric materials by reactive encapsulation of an inert solvent using a step-growth cross-linking polymerization reaction carried out until completion without micro/macroscopic phase separation. Key structural features of the porous materials synthesized in this way were investigated by scanning electron microscopy (SEM) after extraction and supercritical drying using carbon dioxide. Micrographs of the materials synthesized using the reactive encapsulation technique showed that materials with pore sizes less than 100 nm are obtained. Micrographs also showed that the reactive encapsulation technique can be employed to synthesize nanoporous polymeric materials of desired porosity and pore size by changing the solvent content.

Nanoporous thermosets via Reactive Encapsulation of a Chemically Inert Solvent versus Free Radically Polymerized and Phase Separating Systems

ABSTRACTNanoporous thermosets are used as polyelectrolytes in fuel cells, separation membranes, and sensors and actuators, etc. Design of nanoporous thermosets for such applications entails controlling permeability by tailoring the pore size and pore chemistry. Usually free radically polymerizing and simultaneously phase separating systems are used to synthesize porous thermosets. A novel method of synthesizing nanoporous polymeric materials is employed in this work. This technique involves the synthesis of nanoporous thermosets by reactive encapsulation of an inert solvent using step-growth crosslinking polymerization reaction carried out until completion without phase separation into macroscopic phases. Key structural features of the porous materials synthesized by the reactive encapsulation technique were investigated by Scanning Electron Microscopy (SEM) after extraction and supercritical drying using carbon dioxide. Micrographs of the materials synthesized using the reactive encapsulation technique showed that the porous materials of pore size less than 100nm are obtained. Micrographs also showed that the reactive encapsulation technique can be employed to synthesize nanoporous polymeric materials of desired porosity and pore size by changing the solvent content. In addition, porous thermosets were also synthesized using free radical chemistry and phase separating system. The differences in the porous morphology of both these systems were enunciated using SEM micrographs.