A Novel Reactive Processing Technique: Using Telechelic Polymers To Reactively Compatibilize Polymer Blends

Difunctional reactive polymers, telechelics, were used to reactively form multiblock copolymers in situ when melt-blended with a blend of polystyrene and polyisoprene. To quantify the ability of the copolymer to compatibilize the blends, the time evolution of the domain size upon annealing was analyzed by SEM. It was found that the most effective parameter to quantify the ability of the copolymer to inhibit droplet coalescence is Kreltstable, the relative coarsening constant multiplied by the stabilization time. These results indicate that intermediate-molecular-weight telechelic pairs of both highly reactive Anhydride-PS-Anhydride/NH2-PI-NH2 and slower reacting Epoxy-PS-Epoxy/COOH-PI-COOH both effectively suppress coalescence, with the optimal molecular weight being slightly above the critical molecular weight of the homopolymer, Mc. The effects of telechelic loading were also investigated, where the optimal loading concentration for this system was 0.5 wt %, as higher concentrations exhibited a plasticizing effect due to the presence of unreacted low-molecular-weight telechelics present in the blend. A determination of the interfacial coverage of the copolymer shows that a conversion of ∼1.5−3.0% was required for 20% surface coverage at 5.0 wt % telechelic loading, indicating a large excess of telechelics in this system. At the optimal loading level of 0.5 wt %, a conversion of 15% was required for 20% surface coverage. The results of these experiments provide a clear understanding of the role of telechelic loading and molecular weight on its ability to reactively form interfacial modifiers in phase-separated polymer blends and provide guidelines for the development of similar reactive processing schemes that can use telechelic polymers to reactively compatibilize a broad range of polymer blends

Enhanced Polymer Grafting from Multiwalled Carbon Nanotubes through Living Anionic Surface-Initiated Polymerization

Anionic surface-initiated polymerization of ethylene oxide and styrene has been performed using multiwalled carbon nanotubes (MWNTs) functionalized with anionic initiators. The surface of MWNTs was modified via covalent attachment of precursor anions such as 4-hydroxyethyl benzocyclobutene (BCB-EO) and 1-benzocyclobutene-1′-phenylethylene (BCB-PE) through Diels−Alder cycloaddition at 235 °C. Surface-functionalized MWNTs-g-(BCB-EO)n and MWNTs-g-(BCB-PE)n with 23 and 54 wt % precursor initiators, respectively, were used for the polymerizations. Alkoxide anion on the surface of MWNTs-g-(BCB-EO)n was generated through reaction with potassium triphenylmethane for the polymerization of ethylene oxide in tetrahydrofuran and phenyl substituted alkyllithium was generated from the surface of MWNTs-g-(BCB-PE)n using sec-butyllithium for the polymerization of styrene in benzene. In both cases, the initiation was found to be very slow because of the heterogeneous reaction medium. However, the MWNTs gradually dispersed in the reaction medium during the polymerization. A pale green color was noticed in the case of ethylene oxide polymerization and the color of initiator as well as the propagating anions was not discernible visually in styrene polymerization. Polymer grafted nanocomposites, MWNTs-g-(BCB-PEO)n and MWNTs-g-(BCB-PS)n containing a very high percentage of hairy polymer with a small fraction of MWNTs (1H NMR, Raman spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy (TEM). Size exclusion chromatography of the polymer grafted MWNTs revealed broad molecular weight distributions (1.3 Mw/Mn < 1.8) indicating the presence of different sizes of polymer nanocomposites. The TEM images showed the presence of thick layers of polymer up to 30 nm around the MWNTs. The living nature of the growing polystyryllithium was used to produce diblock copolymer grafts using sequential polymerization of isoprene on the surface of MWNTs

Controlled Covalent Functionalization of Multiwalled Carbon Nanotubes using [4 + 2] Cycloaddition of Benzocyclobutenes

Controlled Covalent Functionalization of Multiwalled Carbon Nanotubes using [4 + 2] Cycloaddition of Benzocyclobutene

Modeling and design of high-sensitivity dual optical feedback interferometry measurement system enhanced by period-one dynamics

Laser optical feedback interferometry (OFI) is a unique one-channel interferometric measurement technology with the advantages of compact structure, low implementation cost and easy alignment. However, it has a critical challenge that the visibility of interference fringe is often low and further induces low measurement sensitivity, especially in occasions when the optical feedback strength is feeble, e.g., biomedical and fluid detection. Recently, it has been demonstrated that period-one (P1) dynamics can enhance the measurement sensitivity by introducing extra optical feedback to form a dual optical feedback interferometry (DOFI) system. However, the details of the enhancement mechanism and how to design such a system are still required to unveil. In this paper, comprehensive discussions of designing a DOFI system with high measurement sensitivity enhanced by P1 dynamics are presented. First, based on the modified Lang-Kobayashi equations, a mathematical sensing model of a DOFI system working in P1 state was established. Then, simulations were carried out to verify the validity of the proposed model. After that, factors that determine the sensitivity enhancement were analyzed, based on which, theoretical analysis of achieving optimal sensitivity enhancement was performed. Next, we discussed the operation region of a DOFI system in P1 state and investigated the influence of the system parameters on the operation region. At last, experiments were conducted to verify the theoretical analyses. The results of this work provide helpful guidance for the construction of high-sensitivity DOFI sensing and measurement systems

Time-multiplexed laser self-mixing sensor for measurement of multiple material elastic moduli

The mechanical properties of materials hold significant importance in fundamental research, material, mechanical and civil engineering. These properties are often characterized by some elastic parameters, e.g., Young's modulus, shear modulus and Poisson's ratio. Self-mixing interferometry (SMI) is a unique non-destructive sensing technology that requires minimal components. In this work, we have developed a time-multiplexed fiber-coupled laser SMI sensor in conjunction with impulse excitation technique to simultaneously measure Young modulus, shear modulus and Poisson's ratio of materials. Two specimens made of brass and aluminum 6061 were assessed to validate the feasibility of the designed sensor. The measured values of Young's modulus (101.2 GPa for brass and 69.5 GPa for aluminum 6061), shear modulus (36.3 GPa for brass and 29.5 GPa for aluminum 6061), and Poisson's ratio (0.39 for brass and 0.34 for aluminum 6061) aligned with values reported in existing literature and industry standards. The standard deviations for these three measured parameters were 0.4 GPa, 0.05 GPa, and 0.06 for brass and 0.12 GPa, 0.02 GPa, and 0.003 for aluminum 6061, respectively. The proposed sensor offers several advantages, including a simple structure, high measurement precision, and ease of operation, which contributes to a precise tool for assessing material mechanical properties, benefiting both fundamental research and practical engineering applications. It also provides a promising direction for the development of a serial multi-object measurement solution based on SMI using a single laser source

Single Nanoparticle Imaging and Characterization of Different Phospholipid-Encapsulated Quantum Dot Micelles

Phospholipid quantum dot (QD) micelles have been extensively used as fluorescent tags in single nanoparticle imaging for biomedical imaging. In this work, the microscopic structures and photophysical properties of the phospholipid QD micelles were studied at the single nanoparticle level. Two commonly used types of phospholipid QD micelles were prepared and tested both on a solid-phase surface and in liquid phase, including 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-encapsulated QD micelles (DSPE–QDMs) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-<i>N</i>-[methoxy­(polyethylene glycol)-2000]-encapsulated QD micelles (PEG–DSPE–QDMs). Their fluorescence intensities and diffusion trajectories were determined by a total internal reflection fluorescence-based single nanoparticle imaging platform and comparatively analyzed carefully. It was demonstrated that DSPE–QDMs possessed a comparably wider intensity distribution and lower diffusion coefficient than that of PEG–DSPE–QDMs. PEG–DSPE–QDMs exhibited an obvious fluorescent intermittence. The results suggested that for most of the DSPE–QDMs, more than one QD were encapsulated in a single micelle. On the other hand, only one QD was embedded in a single micelle of PEG–DSPE–QDMs for most of the cases. Such variances suggested that phospholipids play a key role in the fabrication of the QD micelles. This work provides a useful foundation for their further biomedical applications

Design strategies of performance-enhanced Se cathodes for Li-Se batteries and beyond

Lithium-selenium (Li-Se) batteries are deemed as an emerging high energy density electrochemical energy storage system owing to their high specific capacity and volume capacity. Prior to their practicality, a series of critical challenges from the Se cathode side need to be overcome including low reactivity of bulk Se, shuttle effect of intermediates, sluggish redox kinetics of polyselenides, and volume change etc. In this review, recent progress on design strategies of functional Se cathodes are comprehensively summarized and discussed. Following the significance and key challenges, various efficient functionalized strategies for Se cathodes are presented, encompassing covalent bonding, nanostructure construction, heteroatom doping, component hybridization, and solid solution formation. Specially, the universality of these functional strategies are successfully extended into Na-Se batteries, K-Se batteries, and Mg-Se batteries. At last, a brief summary is made and some perspectives are offered with the goal of guiding future research advances and further exploration of these strategies

High Responsivity Photoconductors Based on Iron Pyrite Nanowires Using Sulfurization of Anodized Iron Oxide Nanotubes

Iron pyrite (FeS₂) nanostructures are of considerable interest for photovoltaic applications due to improved material quality compared to their bulk counterpart. As an abundant and nontoxic semiconductor, FeS₂ nanomaterials offer great opportunities for low-cost and green photovoltaic technology. This paper describes the fabrication of FeS₂ nanowire arrays via sulfurization of iron oxide nanotubes at relatively low temperatures. A facile synthesis of ordered iron oxide nanotubes was achieved through anodization of iron foils. Characterization of the iron sulfide nanowires indicates that pyrite structures were formed. A prototype FeS₂ nanowire photoconductor demonstrates very high responsivity (>3.0 A/W). The presented method can be further explored to fabricate various FeS₂ nanostructures, such as nanoparticles, nanoflowers, and nanoplates