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Dynamic covalent gels have been synthesized from an aromatic trialdehyde and α,ω-dinitroalkanes via the nitroaldol reaction in organic solvents. The gelation process could be finetuned by changing the starting nitroalkanes, solvents, feed concentration, catalyst loading, or reaction temperature. The resulting organogels demonstrated good structural integrity and excellent self-healing ability. Intact xerogels were produced upon drying, without damaging the network, and the solvent-free network could recover its gel form in the presence of an organic solvent. Furthermore, the crosslinked dynameric gel depolymerized to small molecules in response to excess nitromethane.

Low-density polyethylene (LDPE) is ubiquitous in the packaging industry owing to its flexibility, toughness, and low cost. However, it is typically contaminated with other materials, seriously limiting options for mechanical recycling. Interest in chemical recycling techniques such as pyrolysis and hydrothermal liquefaction is growing, but most of these processes face technoeconomic challenges that have limited commercial deployment. This study concerns a hybrid chemomechanical approach using reactive twin-screw extrusion (TSE) for tailoring the molecular weight and chain structure of reclaimed LDPE. Two types of zeolite catalysts at several loading levels are evaluated over a range of processing conditions. Structural, thermal, and rheological properties of the extruded samples are investigated and compared to virgin LDPE and LDPE extruded without the catalyst. NMR spectroscopy is used to investigate changes in the structure of the polymer. LDPE extruded with microporous Y zeolite shows lower degradation temperature and increased short chain branching. Mesoporous MCM-41 also induces increased branching but has no effect on the degradation temperature. The theoretical mechanical energy input for the chemical modification is calculated by using process modeling. The demonstrated hybrid reactive extrusion process provides a potential low-cost, simple approach for repurposing LDPE-based flexible packaging as coatings and adhesives.

Mammalian cells are widely used in biotechnology and regenerative medicine applications, including recombinant protein production, cell therapy, 3D bioprinting, and ex vivo engineering of tissues and organs. Unlike unicellular organisms, fungi, or plants, animal cells lack a protective cell wall, and therefore are more sensitive to processing conditions, particularly mechanical forces. Hydrodynamic forces during capillary flow can damage the plasma membrane and impact cell viability and functions, limiting the yields of protein production or the success of injection-based cell delivery and 3D bioprinting of artificial tissues and organs. Here, we present nanocoating individual murine fibroblasts as a model organism with silk-based artificial cell walls to protect against mechanical stress. Cells were coated with three bilayers of silk polyelectrolytes through layer-by-layer electrostatic deposition and subjected to mechanical stress by extrusion through needles with small inner diameters or shearing using a rheometer. The silk nanocoatings preserved membrane integrity, cell survival, and proliferation after exposure to stress in viscous polyethylene glycol solution, providing a useful strategy for cytoprotection during cell delivery and 3D bioprinting applications. Use of mammalian cells is a necessity in the industrial production of biopharmaceuticals because of proper protein folding through chaperone systems and post-translational modifications such as glycosylation being essential for functional products. Moreover, transplantation of human cells holds great promise in regeneration of serious injuries in the bone, brain, or spinal cord as well as debilitating diseases such as stroke, diabetes, arterial dysfunctions, and cancers. Cell delivery by direct injection or within 3D-printed scaffolds with well-defined, patient-specific geometry and composition has potential in filling the gap of insufficient organ transplantation. Both the delivery of mammalian cells into a bioreactor through transfer pipes or cell extrusion through fine needles or nozzles for injection-based delivery or bioprinting, however, may expose the cells to extremes of mechanical stress that impair cell viability and reduce the yield of production or overall success of the transplantation therapy. The silk nanocoatings on individual cells demonstrated in this study acted as artificial cell walls for mammalian cells and provided protection against mechanical stress during capillary flow or exposure to a constant shear force and significantly limited the loss of membrane integrity and necrotic or apoptotic cell death. The safety and simplicity of the approach involving protein-based, biocompatible silk fibroin processed through organic solvent-free, nature-friendly modification pathways allows for rapid translation in biotechnology and regenerative medicine to improve cell delivery applications.

Here, we report a previously unreported low-temperature curable barium strontium titanate (BaXSr1−XTiO3) or BST dielectric nanoparticle ink which shows a high dielectric tunability for printed electronics/additive manufacturing applications. The newly formulated BST ink is optimized to print in aerosol jet printers and can be cured at 150°C, which will allow the fabrication of tunable radio-frequency (RF) and microwave (MW) devices on a wide range of flexible substrates. Characterization of high-frequency dielectric properties showed a high dielectric tunability (~ 15% at 10 GHz with 10 V/µm) and a high dielectric constant (~ 16 at 10 GHz). The linear-reversible tunability, which is very important for tunable devices, was confirmed by the tunability testing at 10 GHz. Characterization of temperature-dependent dielectric properties found < 10% variations of the dielectric constant at 10 GHz from −50°C to 125°C for this BST ink. Detailed information on BST nanoparticle characterization, ink formulation and characterization of dielectric properties is discussed.

Polyamides (PAs) are repeatedly exposed to environments of varying humidity throughout their service life. Due to their hygroscopic nature, moisture diffusion can alter the polymer properties, some...

Polyethylene terephthalate (PET) is one of the most commonly used polyester plastics worldwide but is extremely difficult to be hydrolyzed in a natural environment. PET plastic is an inexpensive, lightweight, and durable material, which can readily be molded into an assortment of products that are used in a broad range of applications. Most PET is used for single-use packaging materials, such as disposable consumer items and packaging. Although PET plastics are a valuable resource in many aspects, the proliferation of plastic products in the last several decades have resulted in a negative environmental footprint. The long-term risk of released PET waste in the environment poses a serious threat to ecosystems, food safety, and even human health in modern society. Recycling is one of the most important actions currently available to reduce these impacts. Current clean-up strategies have attempted to alleviate the adverse impacts of PET pollution but are unable to compete with the increasing quantities of PET waste exposed to the environment. In this review paper, current PET recycling methods to improve life cycle and waste management are discussed, which can be further implemented to reduce plastics pollution and its impacts on health and environment. Compared with conventional mechanical and chemical recycling processes, the biotechnological recycling of PET involves enzymatic degradation of the waste PET and the followed bioconversion of degraded PET monomers into value-added chemicals. This approach creates a circular PET economy by recycling waste PET or upcycling it into more valuable products with minimal environmental footprint.

This work studies, for the first time, the influence of specific mechanical energy (SME) on the reaction efficiency and blend’s performance during reactive extrusion of biopolymer compounds. Poly(lactic acid) (PLA) and poly(butylene succinate) (PBS) were compounded separately with poly(propylene carbonate) (PPC) and a premade maleic anhydride (MAH) compatibilizer to achieve functionalization. Different screw speeds (reaching 1000 rpm) and flow rates were tested. Results indicated that the grafting efficiency was directly proportional to the SME imparted in the system. The PBS blends compounded at shorter times and faster speeds experienced less degradation and better mechanical properties than blends compounded at longer times. The effect was similar but less pronounced for the PLA formulations. It is possible to optimize the reactive compatibilization of biopolymer blends by means of SME calculations and that better blend performance is achieved when conducting high-speed extrusion at short residence times.

The free radical functionalization of immiscible blends of polybutylene succinate (PBS) and polypropylene carbonate (PPC) was successfully achieved on a novel quad screw extruder. A premade compatibilizer, PPC-grafted-maleic anhydride (gPPC), was added in various amounts to trigger the chemical compatibilization and tailor the properties of the final blend. Titration of acid groups on the functionalized blends showed that the grafting efficiency increases with the addition of gPPC. Proton NMR corroborated the formation of new graft copolymers in the reactive blends. A change in the rheological behavior of the formulations evidenced the grafting reactions occurring at the interphase of the components. Also, gPPC suppressed droplet coalescence as seen in the SEM images. Finally, the addition of compatibilizer increased the tensile strain at break by more than 100%, improved up to 50% the impact resistance, and produced a small increase on flexural and elastic modulus.

Melt extrusion pretreatment of poly(ethylene terephthalate) (PET) prior to enzymatic depolymerization with an unpurified leaf branch compost cutinase enzyme cocktail is explored to ascertain the efficiency gained by different processing methods on the enzymatic depolymerization of PET. Specific surface area (SSA) is investigated as a key factor in reducing depolymerization time. Higher SSA substrates (5.6 mm

Poly (butylene succinate) (PBS) is an important bio-based and biodegradable polymer and attracts lots of attention stemming from its good mechanical properties that are complementary to other biobased polyesters. PBS has relatively slow biodegradation due to its high degree of crystallinity, which limits its utility in targeted applications. It is known that enzymatic degradation depends on polymer chemistry, solid-state morphology (i.e. crystallinity), molecular weight and other structural factors. In this paper, PBS-based copolyesters were synthesized through a melt polycondensation process and enzymatic degradation was carried out using lipase from Candida rugosa. Rate of enzymatic degradation and thermal properties were found to vary depending on the ratio of butanediol to hexanediol in the copolymer. The combined analysis of the enzymatic degradation rate and change in the morphology and molecular weight of a series of PBS-based copolyesters demonstrated the relative contributions of polymer chemistry, thermal properties and crystallinity. PBS-based copolyesters with tunable enzymatic degradation show promise as a more sustainable substitute for non-biodegradable plastics in agriculture and packaging industries.

In this work, biodegradable polymers were melt compounded with urea phosphate to fabricate &ldquo, smart fertilizers&rdquo, for sustainable agriculture. Urea phosphate (UP) is typically applied as a water-soluble fertilizer to treat phosphorus deficiency in high pH soils. Due to the low diffusion rate of phosphate through slow-release fertilizer coatings, phosphate supply has been considered the &ldquo, bottleneck&rdquo, for nitrogen&ndash, phosphorous&ndash, potassium (NPK) nutrients supply. We study the influence of polymer matrix structure on release kinetics in deionized water using novel polyesters including poly (hexamethylene succinate) (PHS), poly (30% butylene succinate-co-70% hexamethylene succinate) (PBHS 30/70), and PBHS 70/30. Melt processed composites of UP and polyester were analyzed to determine UP loading efficiency and dispersion and distribution of the salt in the polymer matrix. A combined empirical model involving diffusion and erosion mechanisms was found have a good agreement with the experimental release curve. This work provides a solution for environmentally friendly controlled release phosphate fertilizer with good release performance using bio-based and biodegradable polymers.

The immiscible bio-plastic blend of poly(lactic acid) (PLA) and polyamide11 (PA11 or Nylon11) was compatibilized, using a catalyzed the ester-amide interchange chemical reaction during reactive extrusion. The effects of screw configuration on mixing and reaction optimization were explored. It was found that effective mixing and minimized degradation were achieved when kneading elements were installed only near the die end of the extruder rather than near the beginning of the melt section. However, significant degradation of PLA could not be avoided during processing, which led to a decrease in mechanical strength of blend. To prevent the molecular weight reduction, tris(nonylphenyl) phosphite (TNPP) stabilizer was introduced to improve the thermal stability of PLA matrix. Improvement to both tensile strength and elongation were achieved in the resulting PLA/PA11/TsOH/TNPP blend.

Twin screw extrusion at speeds exceeding several thousand rotations per minute (RPM) has the potential to provide extreme shear typically required to break up aggregates and provide good dispersion in polymer nanocomposites. In this work, a novel twin screw extruder with ultra-high screw speed capability has been used to compound the polystyrene (PS) with organically modified nanoclay without using any compatibilizer. The rheological properties and the morphology of the nanocomposites were investigated and compared with simulation after compounding. Screw profiles imparting more and less aggressive mixing were compared over a range of screw speeds from 400 to 4000 RPM. Morphological characterization revealed the necessity of intense shear stress for achieving intercalation and exfoliation when chemical interactions between filler and matrix are unfavorable. The nanocomposites exhibited greater elasticity indicating reinforcement up to a critical screw speed for each screw profile, but further increasing the screw speed resulted in significant polymer degradation, and thus lower viscosity and storage modulus. Moreover, based on calculations of the theoretical adhesion force between the organoclay layers and the shear stress imparted through mixing, the optimized screw speed for a specific screw profile was determined that would overcome lamellar adhesion to form exfoliated nanocomposites, while minimizing the effect of degradation. The resulting model could be extended to any well-defined extruder system as well as other agglomerated nanofillers.

Herein, aqueous suspensions of poly(3-hexylthiophene)/poly(styrene) (P3HT/PS) blended colloids with varied ratios were prepared using a miniemulsion process. The effects of composition and marginal solvent amount on the aggregates, optical and hole-transport properties of P3HT/PS blended colloids were investigated. Both PS and THF promoted P3HT chain aggregation and electronic coupling, resulting in a red-shift and increased absorbance intensity at the 0-0 and 0-1 vibronic peaks in aqueous suspensions. But, PS prevented further chain packing and aggregation during thermal annealing in solid-state of P3HT/PS blended colloid films, compared to pure P3HT colloids. The crystal lattice spacing in alkyl packing direction of P3HT was not affected by either PS or THF. Additionally, the hole mobility of FETs using pure P3HT colloids was 9.08 × 10−5 cm2/Vs, which decreased when P3HT/PS blended colloids were used. However, incorporation of THF enhanced the hole mobility of FETs using P3HT/PS(2/8) blended colloids, from 0.76 × 10−5 cm2/Vs for FETs using blended colloids made from solvent without THF to 1.24 × 10−5 cm2/Vs for FETs using blended colloids made from solvent mixture with 10 vol% THF. These performance improvements will enable greener, more industrially-relevant water-processing of polymers for emerging organic electronics.

The key approach to achieve high performance field effect transistor fabricated from semiconducting/insulating polymer blends with majority insulating polymer phase is the formation of connected fibrous structures of semiconducting polymer and good interfacial interaction of semiconducting polymer with the dielectric layer. Herein, tetrahydrofuran (THF) as a marginal solvent was used as an additive in marginal/good solvent mixtures to control the crystallite structure, phase segregation, and hole transport properties of poly(3-hexylthiophene)/poly(styrene) (P3HT/PS; weight ratio: 1/4) blends, with the advantage that marginal/good solvent mixture gives P3HT sufficient time for phase segregation and relatively better solvent quality to aggregate to more stable structures compared to other reported strategies as bad/good solvent mixtures or directly marginal solvents. Incorporation of THF reduces the P3HT solubility, forming connected fibrous structures as observed in both neat P3HT and blend films; it appea...

Addition of keto groups to polyethylene helps it degrade while maintaining its properties

Immiscible PLA/PA11 of 80/20 and 50/50 wt% were compatibilized through addition of p-toluenesulfonic acid (TsOH) catalyst in reactive ultra-high speed twin-screw extrusion. Two mixing screw designs were compared for their ability to disperse the PA11 droplets in the PLA matrix as a function of screw speed up to 2000 rpm. The size and polydispersity of droplets of dispersed PA11 decreased when a high shear (HS) screw was used, whereas broad droplet size distribution was produced in the low shear (LS) screw. Two models predicting the droplet size dependence on shear rate, viscosity ratio and interfacial tension were fit to the experimental data. The Serpe model including volume fraction effects produced a better fit compared to the Wu model, which does not include volume fraction effects. Mechanical testing indicated that the compatibility of PLA/PA11 blends was improved through addition of TsOH catalyst for 50/50 wt% blends due to ester – amide exchange reactions at the interfaces in the immiscible PLA and PA11 phases. The enhancement of ductility was greater after processing with the LS screw configuration than the HS screw configuration. The inferior properties after high shear mixing were likely due to molecular weight degradation during processing. While the aggressive shear in the HS screw design resulted in fine dispersion, care should be taken to minimize degradation, especially for shear sensitive polymers.

In this article, a kinetic model is introduced in conjunction with experimental extrusion results to predict the evolution of depolymerization reaction at various operating conditions during ultra-high speed twin screw extrusion (TSE). A commercially available flow simulation software (LUDOVIC®) was used to calculate thermomechanical flow parameters for various screw profiles. The simulated local material temperature and mechanical shear rate were used as inputs to develop a kinetic model that separately describes the effects of temperature and shear on the extent of degradation reaction due to extruding at very high speeds. The model is validated through comparison with experimental gel permeation chromatography (GPC) results on extruded samples. A good agreement was found between theoretical and experimental results. This validation makes the model practically useful for processing optimization, which is a considerable challenge for realizing compounding benefits in ultra-high speed TSE.

Polymeric materials hold several advantages over metal components in heat exchangers such as cost savings, lighter weight and corrosion resistance. However, it is challenging to engineer plastics with good heat transfer characteristics, processability and required strength. Neat polymer resins have inferior mechanical and thermal properties relative to metals, requiring careful consideration of the entire heat exchanger system from materials to system design, to achieve sufficient performance. This review summarizes the physical parameters governing polymer and composite thermal conductivity, as well as the latest research on augmenting thermal conductivity. Highly filled composites containing carbon or metal have achieved thermal conductivity an order of magnitude higher than that of neat polymers. The effects of critical additive characteristics, such as interfacial compatibility, filler shape factor, loading level and processing technique, are reviewed. In addition to lower material costs, high volume processing technologies such as injection molding and extrusion are responsible for the cost savings of polymers over metals. Thus, the manufacturing considerations for the most promising high thermal conductivity polymer composites are also reviewed.

Biobased aliphatic polyesters are of interest for their biodegradability and potential to offset the use of unsustainable fossil resources. In addition, many of the bio-sourced monomers are inherently less toxic than those used in conventional polymers. In this work, biobased poly(butylene succinate-co-hexamethylene succinate) (P(BS-co-HS)) copolyesters with butylene succinate (BS)/hexamethylene succinate (HS) molar ratios over the entire compositional range were synthesized from succinic acid, butanediol and 1,6-hexanediol using direct melt polycondensation. The chemical and crystalline structure, thermal properties, solubility and mechanical properties of P(BS-co-HS) copolyesters were investigated. The results confirmed successful synthesis of all copolymers, and the melting temperature, glass transition temperature and crystallization temperature of P(BS-co-HS) copolyesters were tunable depending on BS/HS composition. The crystallinity of P(BS-co-HS) copolyesters decreased to a minimum of 6.0% when the BS/HS ratio was close to 1. Moreover, the incorporation of HS altered the tensile failure mechanism from brittle failure for neat PBS to ductile for P(BS-co-HS) copolyesters with HS content higher than 30 mol%. The solubility of these biobased copolymers and their thermal, mechanical and crystallization behavior over the full compositional range are disclosed for the first time. The polyesters show promise as greener coatings for biodegradable paper packaging.

Biobased and biodegradable polymers are a promising solution for agricultural plastics problems, especially for pollution and toxic residue from disposed non-degradable plastic mulch films. Application of biobased and biodegradable mulch films has been hindered by poor mechanical properties and higher cost than conventional plastic mulch film (polyethylene and poly (vinyl chloride)). This work explores the performance of multi-layer fertilizer-infused mulch papers fabricated via blade coating and melt compression molding with biodegradable poly (butylene succinate) (PBS), poly (hexamethylene succinate) (PHS), and their copolyesters. The water absorption, tear propagation properties, enzymatic degradation, and fertilizer release behavior of these multi-layer constructions are characterized. The influence of processing methodology on the coating performance is also discussed. It was found that a polymer concentration of 90 mg/ml in the blade coating process increased the coating thickness to about 30 μm, which slowed water absorption; however, the composition ratio of PBHS polymer coatings had little effect on water absorption. The coatings improved the tear propagation resistance up to 3 N (comparable with that of PE mulch film, 1.6 N) and biodegradation resistance of MP in soil. In this work, PHS coated MP provide an optimal strategy for the dual functions of mulching and fertilizer controlled release, as demonstrated by the barrier properties, degradation rate and mechanical properties. Plant growth trials demonstrated improved fertilizer utilization from slow-release coated papers, as shown by acceleration of the blossom and root growth.

Poly(ether ether ketone) (PEEK) is increasingly used in selective laser sintering (SLS) due to its superior mechanical and thermal properties and biocompatibility. It is well known that the properties of selective laser sintering (SLS) powder govern the processability and quality of the parts. The SLS printing process exposes the PEEK bed/feedstock to variable elevated temperatures (above 300 °C) for a prolonged time. The effect of this thermal history on the part quality is unknown. This work evaluates the changes that occur in thermally treated PEEK powder through spectroscopic, morphological, and rheological characterizations. It was found that crystallinity increased marginally within the first two hours, but particle size and shape remained virtually unchanged. The thermal treatment also resulted in a significant increase in the melt viscosity of the PEEK powder, and its flowability slightly improved. Understanding these changes could help to reduce waste through recycling of some portion of PEEK powders used in SLS printing.

Here, we report a previously un-reported printed electronics/additive manufacturing (AM) approach to fabricate conductive/resistive features on novel insulating silver–barium strontium titanate (Ag–BST) printed composite films. Ag–BST composite functional ink was formulated by blending a conductive Ag nanoparticle ink and an insulating BST nanoparticle ink. The blending ratio of Ag and BST inks was optimized to obtain the insulating phase after the initial curing and the conductive/resistive phase following selective laser sintering under ambient conditions. Selective laser sintered Ag–BST resistors showed an ohmic behavior and the resistivity could be adjusted by varying the laser sintering parameters, such as the wavelength, power and the rastering speed/pitch of the laser. This insulator to conductor/resistor transitioning Ag–BST ink paves a new path for direct write printed electronics/AM applications. Proofs of concept for potential applications utilizing this functional ink are demonstrated. Also, this Ag–BST ink can be used as a conventional resistive ink for dispensing printers. Thermally sintered Ag–BST resistors showed less than 8% variation in resistance between −50 °C and 150 °C.

This article characterizes a novel twin screw extrusion (TSE) process with the capability of rotating at speeds up to 4500 rpm. The resulting extreme high shear rate is expected to result in molecular weight changes due to thermomechanical degradation of the polymeric materials being extruded, polystyrene (PS) in this case. In order to differentiate between mechanical and thermal factors affecting degradation of PS running at ultrahigh speeds and also to evaluate the relative importance of the two mechanisms, PS has been extruded at different screw speeds and different barrel temperatures with corresponding melt temperatures. Viscosity measurements and size exclusion chromatography measurements show the extent of degradation due to mechanical stress as a result of high screw rotational speeds. Furthermore, through analyzing the kinetics of PS depolymerization, the reaction rate and hypothetical apparent temperatures at each screw speed have been calculated. All results support the idea that the mechanical shear stress can be considered as the controlling factor of polymer degradation in ultrahigh speed TSE. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

In this work, aqueous suspensions of poly(3-hexylthiophene) (P3HT) colloids were fabricated using three different surfactants with varied degrees of conjugation. The morphology, crystalline structure and optical properties of these colloids were characterized by scanning electron microscopy, wide angle X-ray diffractometry and UV–vis spectrometry, respectively. Results indicated that the morphology and crystalline were similar for all the colloids, while the optical properties and aggregation could be tuned by surfactant conjugation. Increasing conjugation in surfactant corresponded to increased chain order, conjugation length, and red-shifted absorbance spectrum in P3HT colloids. Field effect transistors (FETs) made from these colloids showed a hole mobility on the order of 10 −3 cm 2 /Vs, also tunable by surfactant conjugation and comparable to FETs made from P3HT solution.

A series of poly[4-(4-cyanoazobenzene-4′-oxy)alkyl methacrylate]s, side-chain liquid crystalline polymers (azoLCPs) were synthesized with methylene groups as spacers varying from 5 to 12. The thermal properties and phase transition temperatures of the polymers were characterized with differential scanning calorimetry and polarized optical microscopy and a relationship between spacer lengths, glass transition (Tg) and clearing temperatures (Tc) of the polymers was established. The Tg decreased with increasing spacer length, while the Tc exibited an odd–even effect with varying spacer length. X-ray diffraction was used to determine the degree crystallinity above and below Tc. The azoLCPs exhibited smectic ↔ nematic ↔ isotropic phases. Increasing crystallinity correlated linearly with decreasing gas permeability as measured using an oxygen permeation analyzer, which was used to measure the films’ permeability to oxygen (O2) gas. Switching of the azoLCPs from a liquid crystalline to an isotropic state was accomplished by heating the films above their Tc, which resulted in at least a 10-fold increase in the O2 permeability coefficient (PO2). Increasing the methylene spacer length of the azoLCP had little or no effect on gas permeability however it did decrease the Tc, allowing fine control of the temperature at which the switch in PO2 takes place by tuning the mesophase between nematic and isotropic states.

Herein, aqueous suspensions of poly (3-hexylthiophene) (P3HT) colloids with tunable particle size were fabricated using a miniemulsion process followed by solvent evaporation. The effects of solvent evaporation temperature, sonication time and surfactant amount on colloid properties and field effect transistor performance were investigated. The particle size distribution and morphology of the colloids were characterized by dynamic light scattering and atomic force microscopy. It was found that increasing solvent evaporation temperature leads to larger particle size; longer sonication leads to smaller particle size and careful selection of these variables along with controlled surfactant amount can be used to tune colloid sizes. Organic field-effect transistors (FETs) prepared using P3HT colloids displayed increasing hole mobility and decreasing threshold voltage as the colloidal particle size decreased. The trend in performance can be explained by considering the geometric factors governing carrier density and carrier transport.

The ability of the time-dependent diffusion–double-reptation (TDD-DR) theory to predict the molecular structure and dynamics of polymer nanocomposites is investigated for poly(butylene succinate) blended with fumed silica particles with contrasting surface treatments (unmodified and modified with silanes). Structural and dynamic parameters such as confined polymer fraction (ϕ s) and relaxation time are extracted from fitting the experimental curves for relaxation modulus G(t) by the TDD-DR model with fluctuation effects included. A good fit of experimental data over seven time decades is obtained after modification of the TDD-DR model to account for Rouse relaxation on the short time scale. The fraction of confined polymer extracted from model fitting is in quantitative agreement with the value obtained from the specific reversing heat capacity for poly(butylene succinate) (PBS)/fumed silica nanocomposites. Based on parameters deduced from rheological data, we study the influence of surface functionality on the microstructure of polymer matrix. We conclude that increasing the polymer–particle compatibility through introduction of a hydrophobic functionality on the surface of the particles results in increased amount of confined PBS chains and strong immobilization of the PBS molecules. These interface effects are discussed for the first time in terms of TDD-DR model that takes into account the dynamics of bound polymer chains, allowing prediction of the universal nature of the confinement effect and its role in polymer nanocomposite processing and bulk physical properties.

A solid-like particle network structure induced by steady shear flow is observed in polymer nanocomposites for the first time. This unique structural evolution is evidenced by the stress overshoot during start-up of steady shear. After the steady shear ordering event, the enhanced rubbery response is measured using small amplitude oscillatory shear. The particle surface chemistry dominates the formation of the percolation structure: the shear-induced reinforcement effect is observed at lower particle loadings for hydrophobic filler than for hydrophilic filler. These results indicate that reinforcement in nanocomposites can be controlled by filler surface functionality and shearing effects, enabling improved mechanical properties with low filler loadings.

A durable superhydrophobic coating formulation with epoxy binder thermoset was used to coat on surfaces, which provide high quality for corrosion protection, reduced biofouling and improved hydrodynamic behavior. The single and double layers coating of these nanostructured epoxy were fabricated and coated on a novel quartz crystal microbalance (QCM) technique to investigate their hydrophobic properties. Different static and dynamic wettability were obtained and characterized by evaluating the electrical impedance of QCM coated with nanostructured epoxy in air and DI water. It was found that QCM is able to quantitatively characterize the hydrophobicity of these nanostructured polymer surfaces. For double layer coating, the frequency shift in DI water was smaller in comparison to the single layer one. The reduction in mechanical impedance of QCM clearly demonstrates the effect of enhanced hydrophobicity for both single and double layers. The experimental results show that the hydrophobic surface resulted in smaller mechanical impedance loading, while the hydrophilic surface exerted much larger mechanical impedance. The outcome of this research will build a solid foundation for the further improvement of vehicles coated with superhydrophobic surfaces operating in water and increased equipment life.Copyright © 2017 by ASME

The linear melt viscoelasticity of poly(butylene succinate) (PBS) nanocomposites containing different types of fumed silica nanoparticles (unmodified and modified fumed silica) was studied. Depending on the primary particle size and surface chemistry of fillers, distinct modes of polymer/filler interactions could be identified in the nanocomposites. The PBS nanocomposites containing silica nanoparticles with larger surface area appear to have higher density of temporary physical network structures leading to significantly increased modulus. Increasing the polymer–particle compatibility through introduction of a hydrophobic functionality on the surface of the particles resulted in strong immobilization of the PBS molecules. The presence of such improved polymer/filler interactions was confirmed by the secondary relaxation mode and rubber-like behavior, indicative of stronger adhesion between the modified SiO2 and the PBS matrix. The entangled polymer dynamic theory was used to discuss the influence of polymer/filler interactions on the relaxation behavior of PBS molecules. The relaxation hierarchy can be identified from the linear viscoelastic responses of PBS/modified fumed silica nanocomposites. Dynamic mechanical measurements showed that glass transition range was widened and the peak temperature was also shifted to higher temperature in the composites with enhanced PBS/silicainteractions.

Polymer blends are of significant interest for reinforcing bioplastics via addition of a second polymer and a blend compatibilizer or in situ reaction. However, increased costs associated with additional materials and extra processing steps can limit the viability of this solution. Here, a simple, continuous reactive extrusion processing method was examined for producing tougher bioplastic blends. p-Toluenesulfonic acid (TsOH) catalyst was added to two immiscible biobased polymers, poly(lactic acid) (PLA) and polyamide11 (PA11), to induce ester-amide exchange reaction. The mechanical properties of PLA were improved through mixing with PA11 by introducing copolymers at the interface thereby reducing interfacial tension. The morphology, chemical structure analysis, and tensile testing supported that copolymerization reaction occurred resulting in improved bonding between PLA and PA11 with 0.5 wt % TsOH catalyst in the batch mixing, but depolymerization dominated at higher shear stress (2000 rpm) and catalyst loading (over 2 wt %). The PLA/PA11 blend with 0.5 wt % TsOH catalyst displayed around 50% improvement in elongation at break in twin-screw extruder blending (around 5 min mixing time) at 250 rpm screw speed, which was similar to the improvement using batch mixing (20 min mixing time). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43350.