Phenylethynyl-terminated Imide Oligomers Modified by Reactive Diluent for Resin Transfer Molding Application

To meet the processing requirements of resin transfer moulding(RTM)technology,reactive diluent containing m-phenylene moiety was synthesized to physically mixed with phenylethynyl terminated cooligoimides with well-designed molecular weights of 1500-2500 g/mol derived from 4,4’-(hexafluoroisopropylidene)diphthalic anhydride(6 FDA),3,4’-oxydianiline(3,4’-ODA)and m-phenylenediamine(m-PDA).This blend shows low minimum melting viscosity(<1 Pa·s)and enlarged processing temperature window(260–361℃).FPI-R-1 stays below 1 Pa·s for2 h at 270℃.The relationship between the molecular weight of the blend and its melting stability was first explored.Blending oligoimides with lower molecular weights exhibit better melting stability.Upon curing at 380℃for 2 h,the thermosetting polyimide resin demonstrates superior heat resistance(T_g=420-426℃).     

Enhanced thermal conductivity and mechanical properties of polymeric composites through formation of covalent bonds between boron nitride and rubber chains

Hexagonal boron nitride (BN) platelets, also known as white graphite, are often used to improve the thermal conductivities of polymeric matrices. Due to the poor interfacial compatibility between BN platelets and polymeric matrices, in this study, polyrhodanine (PRd) was used to modify BN platelets and prepared functionalized BN-PRd platelets, thereby enhancing the interfacial interaction between the thermal conductive filler and polymeric matrix. Then, BN-PRd platelets were dispersed into the nitrile butadiene rubber (NBR) matrix to yield high thermally conductive composites. The presence of N? C═S groups in PRd allowed the combination of PRd and NBR chains containing stable covalent bonds via vulcanization reaction. The thermal conductivity of the as-prepared 30 vol% BN-PRd/NBR composite reached 0.40 W/mK, representing an increment of 135% over pure NBR (0.17 W/mK). In addition, the largest tensile strength of NBR composite containing 30 vol% BN-PRd platelets was 880% times of pure NBR. The 30 vol% BN-PRd/NBR composite also displayed a relatively high dielectric constant (9.35 at 100 Hz) and a low dielectric loss tangent value (0.07 at 100 Hz), indicating their usefulness as dielectric flexible materials of microelectronics. In sum, the simplicity and good efficiency of formation of covalent bonds between boron nitride and rubber chains look very promising for large-scale industrial production of high thermally conductive composites.     

Synthesis and characterization of fluorine functionalized graphene oxide dispersed quinoline-based polyimide composites having low-k and UV shielding properties

Polyimide nanocomposites having low-k and UV shielding properties have been developed using fluorine functionalized graphene oxide and bis(quinoline amine) based polyimide. The polyimide was synthesized using bis(quinoline amine) and pyromellitic dianhydride at appropriate experimental conditions, and its molecular structure was confirmed through various spectral analysis such as FTIR and NMR. The polyimide (PI) composites were prepared using bis(quinoline amine), pyromellitic dianhydride, and separately filled with 1, 5, 10 wt% of fluorinated graphene oxide (FGO) through in situ polymerization. The polymer composites were characterized using thermo gravimetric analysis (TGA), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). In addition, the water contact angle, dielectric behavior, and UV–Vis shielding behavior of FGO/PI composites were evaluated. The value of the water contact angle of the polyimide was increased with increment of FGO in the polyimide matrix. The highest water contact angle of polyimide composites observed 108° was obtained for 15 wt% FGO reinforced polyimide composite. The value of the dielectric constant for neat, 1, 5, and 15 wt% FGO reinforced polyimide composites was obtained as 4.5, 3.7, 2.6, and 2.0, respectively. It is also observed from by UV–Vis spectroscopy analysis that the FGO reinforced polyimide composites have good UV shielding behavior.     

A new ultrasonic measurement system for the cure monitoring of thermosetting resins and composites

Measurements of the ultrasonic sound speed of thermosetting resins and composites can be used as an in-process cure monitoring technique. Ultrasonic measurements have an advantage over other in-process techniques in that ultrasonic sensors do not make contact with the part (thus leaving no imbedded sensor or witness mark) and can make true bulk measurements of the part. A new commercially available ultrasonic cure monitoring system has been developed which easily enables ultrasonic measurements to be made in compression molding, resin transfer molding, and autoclave processes. Advancements in ultrasonic sensor technology enable the sensor to maintain good coupling to the part during thermal cycling to 260C. Data is presented showing the change in ultrasonic sound speed during the compression molding of a graphite-epoxy prepreg. The data shows a good relationship to the ionic conductivity and resistivity data collected via dielectric cure monitoring.This effort was sponsored by the Manufacturing Technology Directorate, Wright Laboratory (WL/MTX), Air Force Material Command, USAF, under cooperative agreement award(s) to NCMS. The U. S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Wright Laboratory or the U.S. Government.     

Immunoaffinity-based extraction of phenylurea herbicides using mixed antibodies against isoproturon and chlortoluron

Summary The analysis of several phenylurea herbicides in different waters is described using an immunoaffinity column clean-up and determination by high performance liquid chromatography. The pesticides were selectively retained on a solid phase extraction column containing antibodies to chlortoluron and to isoproturon immobilised onto silica. Selected phenylureas were eluted using a simple phosphate buffered saline/ethanol mixture at low pH. The immunoaffinity approach gave extracts free of interfering substances and allowed detection limits comparable to those required for pesticides in water in the European Community. The proposed method was successfully applied to the determination of chlortoluron, isoproturon, linuron and chlorbromuron in tap and river water. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Spatiotemporal organization of coacervate microdroplets

Liquid–liquid phase separation (LLPS) has emerged as a new paradigm in the fields of soft matter, colloid chemistry, prebiotic chemistry, and cell biology. As phase separation is a dynamic assembly process, how to spatiotemporally regulate the assembly and disassembly of these micrometre-sized droplets, which are referred as biomolecular condensates in biology is essential for their diverse applications in various disciplines. Herein, we discuss recent advances in the spatiotemporal control of phase separation using different physical tools and external environmental stimuli in bulk solutions and living cells. Specifically, the exploration of phase transition in a compartmentalized protocellular system, which can bridge the gap between synthetic and intracellular LLPS systems, is summarized, and the challenges and future research directions are discussed.     

Organo-Polyoxometalate-Based Hydrogen-Bond Catalysis

Several urea-inserted organo-polyoxometalates (POMs) derived from polyoxotungstovanadate [P₂V₃W₁₅O₆₁]⁹⁻ were prepared. The insertion of the carbonyl into the polyoxometallic framework activates the urea toward Hydrogen-bond catalysis. This was shown on the Friedel-Crafts arylation of trans-β-nitrostyrene. Modelling shows that the most stable form of the organo-POMs features a cis-trans arrangement of the two N−H bonds, but that the likely catalytically active trans-trans form is accessible at room temperature. Finally, it is possible that the oxo substituents next to the vanadium atoms may help the approach of the nucleophile via H-bonding.     

Electrokinetic actuation of an uncharged polarizable dielectric droplet in charged hydrogel medium

Electrokinetic transport of an uncharged nonconducting microsized liquid droplet in a charged hydrogel medium is studied. Dielectric polarization of the liquid drop under the action of an externally imposed electric field induces a non-homogeneous charge density at the droplet surface. The interactions of the induced surface charge of the droplet with the immobile charges of the hydrogel medium generates an electric force to the droplet, which actuates the drop through the charged hydrogel medium. A numerical study based on the first principle of electrokinetics is adopted. Dependence of the droplet velocity on its dielectric permittivity, bulk ionic concentration, and immobile charge density of the gel is analyzed. The surface conduction is significant in presence of charged gel, which creates a concentration polarization. The impact of the counterion saturation in the Debye layer due to the dielectric decrement of the medium is addressed. The modified Nernst–Planck equation for ion transport and the Poisson equation for the electric field is considered to take into account the dielectric polarization. A quadrupolar vortex around the uncharged droplet is observed when the gel medium is considered to be uncharged, which is similar to the induced charge electroosmosis around an uncharged dielectric colloid in free-solution. We find that the induced charge electrokinetic mechanism creates a strong recirculation of liquid within the droplet and the translational velocity of the droplet strongly depends on its size for the dielectric droplet embedded in a charged gel medium.     

Characterization of polyoxometalate/polymer photo-composites: A toolbox for the photodegradation of organic pollutants

Different inorganic/organic photocomposites based on polyoxometalate (POM) nanoparticles have been developed for photocatalytic applications. Currently, polyoxometalate nanoparticles have been successfully in-situ embedded into an acrylate polymer network by photopolymerization upon mild visible light irradiation at 405 nm. The proposed POM/polymer photocomposites have been characterized using complementary techniques for a better understanding of their photocatalytic activity. Interestingly, the obtained photocomposites exhibit high rigidity, excellent thermal stability, a non-negligible porosity and new functionalities such as light reactivity and redox properties. Moreover, developed composites showed efficient catalytic activity for the color removal of aqueous solutions of erythrosine and rose Bengal under Light Emitting Diodes LED@375 nm irradiation reaching 80 and 90% as a final color removal, respectively.     

Fe(II) Spin Crossover/Polymer Hybrid Materials: Investigation of the SCO Behavior via Temperature-Dependent Raman Spectroscopy,Physicochemical Characterization and Migration Release Study

Polymeric composites constitute an appealing class of materials with applications in various fields. Spin crossover (SCO) coordination complexes are switchable materials with potential use in data storage and sensors. Their incorporation into polymers can be considered an effective method for their wider practical application. In this study, Fe(II) SCO/polylactic acid hybrid polymeric composites have been prepared by film casting. The mononuclear coordination complex [Fe{N(CN)₂}₂(abpt)₂] was incorporated into polylactic acid. The morphological, structural and thermoanalytical characterization of the composite films were performed via scanning electron microscopy (SEM), attenuated total reflectance (ATR/FTIR), Raman spectroscopy and differential scanning calorimetry (DSC). In addition, the migration release study (MRS) of the SCO compound from the polymeric matrix into the food simulant 50% v/v water/ethanol solution was also examined via UV/Vis absorption. Of particular interest was the investigation of the SCO behavior of the coordination complex after its incorporation into the polymer matrix; it was accomplished by temperature-dependent micro-Raman spectroscopy. The described attempt could be considered a preparatory step toward the development of SCO-based temperature sensors integrated into food packaging materials.