Design of a Microfluidic System to Investigate the Mechanical Properties of Layer‐by‐Layer Fabricated Capsules

A microfluidic system was designed, fabricated and implemented to study the behavior of polyelectrolyte capsules flowing in microscale channels. The device contains microchannels that lead into constrictions intended to capture polyelectrolyte microcapsules which were fabricated with the well‐known layer‐by‐layer (LbL) assembly technique. The behavior of hollow capsules at the constrictions was visualized and the properties of the capsules were investigated before and after introduction into the device.

Time series of video frames showing capsules being compressed into a constriction.     

Photoinduced Polymerization in the Wall of Hollow Capsules

Summary: Novel light‐sensitive hollow capsules were fabricated from the small molecule 3‐sulfopropylacrylate potassium (SPA) and poly(allylamine hydrochloride) (PAH). With UV irradiation, SPA could be photopolymerized in the wall of hollow capsules. After photopolymerization the capsule size and surfaces showed pronounced differences. The capsules became much more rigid as indicated by an increase in the modulus of more than a factor of 5.

CLSM image of SPA/PAH hollow capsule emission at 554 nm, from rhodamine B after photopolymerization.     

A Novel Impact Modifier for Nylon 6

A new carboxylated styrene‐butadiene rubber (CSBR) in ultrafine powder form was used to modify the properties of nylon 6. The nylon 6/CSBR blends possessed higher toughness than nylon 6/maleic anhydride‐grafted polyethylene‐octene elastomer (POE‐g‐MAH) system. TEM micrographs revealed the fine dispersion of CSBR particles with a diameter of 150 nm. The effective toughening of nylon 6 with CSBR was attributed to the good interface, fine dispersion, and shear yielding.

TEM photograph of undeformed Nylon 6/CSBR (80/20) blend (×40 000).     

In‐Line Monitoring and Control of Conversion and Weight‐Average Molecular Weight of Polyurethanes in Solution Step‐Growth Polymerization Based on Near Infrared Spectroscopy and Torquemetry

Summary: It is well known that the weight‐average molecular weight ( ) is strictly dependent on conversion in step‐growth polymerizations performed in batch and that the is very sensitive to impurities and molar imbalance. This makes the work of controlling a non trivial job. In this paper a new methodology is introduced for in‐line monitoring and control of conversion and of polyurethanes produced in solution step‐growth polymerizations, based on near‐infrared spectroscopy (NIRS) and torquemetry. A calibration model based on the PLS method is obtained and validated for monomer conversion, while the weight‐average molecular weight is monitored indirectly with the relative shear signal provided by the agitator. Control procedures are then proposed and implemented experimentally to avoid gelation and allow for maximization of . The proposed monitoring and control procedures can also be applied to other step growth polymerizations.

Proposed control scheme.     

Epoxy Resin Nanofibers Prepared Using Electrospun Core/Sheath Nanofibers as Templates

A strategy is described to prepare epoxy resin nanofibers by combining coaxial electrospinning and traditional hot‐curing processes. Core/sheath nanofibers with diameters of 480 ± 80 nm are prepared at flow rates of 0.1 and 2 mL h^?1 for the core (20% w/v EP and 6% w/v curing agent in ethanol/acetone) and sheath (10% PVP in ethanol) fluids. After the curing of the nanofibers and selective removal of the sheath PVP, EP nanofibers with an average diameter of 210 ± 60 nm are obtained. ATR‐FTIR analysis shows that the EP nanofibers display no obvious difference compared with an EP film cast from the core solution. The method presented allows to develop functional EP nanoproducts and to prepare heat‐cured resin nanofibers.

     

Synthesis of Block Copolymers containing Chain‐Controlled Aramid and Fluoroethylene Segments

Summary: Novel block copolymers containing aromatic polyamide (aramid) and fluoroethylene segments were synthesized by a two‐step solution polycondensation. This synthetic method could control the chain‐length of aramid segments and these copolymers could have high structural regularity. The number‐average molecular weight ( ) of one of these polymers is over 2.0 × 10⁴. Incorporating fluoroethylene segments improves the solubility of the resulting polymer compared with conventional aramids.

The synthesis of the fluoroethylene‐aramid block copolymers.     

Thermal and Thermomechanical Behaviour of Polycaprolactone and Starch/Polycaprolactone Blends for Biomedical Applications

Summary: Polycaprolactone (PCL) and starch/PCL blends (SPCL) are shown to have the potential to be used in a range of biomedical applications and can be processed with conventional melting‐based procedures. In this paper, the thermal and thermomechanical analyses of PCL and SPCL were performed, using DSC, optical microscopy and DMA. Starch effectively increased the non‐isothermal crystallisation rate of PCL. Non‐isothermal crystallisation kinetics was analyzed using Ozawa model, and a method, which combines the theories of Avrami and Ozawa. Starch effectively reinforced PCL and enhanced its damping properties, which indicated that SPCL could be more suitable than PCL in some biomedical applications, as it might help in the dissipation of the mechanical energy generated by the patient movements.

Dynamic mechanical behaviour of PCL and SPCL at 1 Hz.     

Thermo‐Physical and Impact Properties of Epoxy Containing Epoxidized Linseed Oil, 1

Summary: Biobased neat epoxy materials containing epoxidized linseed oil (ELO) were processed with an anhydride curing agent. A defined amount of the diglycidyl ether of bisphenol F (DGEBF) was replaced by ELO. The selection of the DGEBF, ELO, and an anhydride curing agent resulted in an excellent combination, to provide a new biobased epoxy material showing high elastic modulus, high glass transition temperature, and high heat distortion temperature (HDT) with larger amounts of ELO. The Izod impact strength was almost constant while changing the amount of ELO. This is a promising result for future industrial applications in different engineering industries.

The effect of changing ELO concentration of the anhydride‐cured neat epoxy on the storage modulus.     

Coaxial Electrospinning with Triton X‐100 Solutions as Sheath Fluids for Preparing PAN Nanofibers

Coaxial electrospinning using surfactants as sheath fluid for preparing high‐quality polymer nanofibers is studied. PAN nanofibers are fabricated using this process with Triton X‐100 solutions in DMF. FESEM demonstrates that the Triton X‐100 solution has a significant influence on the quality of the nanofibers. The nanofiber diameters can be controlled by adjusting the concentration of Triton X‐100 in the sheath fluids with a scaling law D = 640 C^?0.32. The mechanism of the influence of Triton X‐100 solutions on the formation of PAN fibers is discussed and it is demonstrated that coaxial electrospinning with surfactant solution is a facile method for achieving high‐quality polymer nanofibers.

     

Morphology Dependent Double Yielding in Injection Molded Polycarbonate/Polyethylene Blend

Summary: Polycarbonate (PC)/polyethylene (PE) blend was injection molded at different molding temperatures. The morphological observation by scanning electronic microscope (SEM) indicated that the sample molded at 190 °C contained only uniformly dispersed spherical PC particles. The samples molded at 230 and 275 °C had a typical skin‐core structure, and there were many injection‐induced PC fibers in the subskin. While the sample molded at 190 °C had the usual stress‐strain behavior, the samples obtained at 230 and 275 °C showed apparently double yielding behavior. It was suggested that the double yielding points were morphology‐dependent. The first one was the result of the yielding of PE at low strain, and the second one was caused by the yielding of the PC fibers. Moreover, it is the frictional force in the interfaces between PC and PE that transferred the stress to the PC fibers, hence giving rise to the reinforcement of PE by PC.

Stress‐strain curves of PC/PE blends injection molded at various temperatures showing first (I) and second (II) yielding points.     

Influence of Screw Speed on Electrical and Rheological Percolation of Melt‐Mixed High‐Impact Polystyrene/MWCNT Nanocomposites

The influence of screw speed on the electrical and rheological percolation of HIPS/MWCNT composites prepared via melt mixing was investigated. Microscopic examination of these composites using POM, FESEM and HRTEM revealed optimum MWCNT dispersion was achieved at intermediate screw speeds. On addition of MWCNTs to HIPS, the electrical conductivity of HIPS increased by up to 12 orders of magnitude. At screw speeds up to 100 rpm an electrical percolation of 1–3 wt.‐% was achieved. This increased to 3–5 wt.‐% when the screw speed was increased to 150 rpm. The onset of a rheological percolation was detected for an MWCNT loading of 5 wt.‐%, irrespective of screw speed employed. An up‐shift in the Raman G‐band of 24 cm^?1 was observed, implying strong interfacial interaction between HIPS and MWCNTs.

     

A Reactive Flame Retardant as a Poly(propylene)‐Sized Glass Adhesion Promoter

Summary: Contact‐mode AFM adhesion strength measurements were employed in order to investigate the capability of PBBMA FR as an adhesion promoter in PP composites. The reactive FR exhibited superior coupling properties in comparison to conventional coupling agents such as PP‐g‐ma introduced in reinforced PP composites.

AFM image showing the recess carved out by the AFM tip in a PBBMA layer deposited on glass treated with APS.     

Novel Poly(N‐isopropylacrylamide)‐graft‐poly(vinylidene fluoride) Copolymers for Temperature‐Sensitive Microfiltration Membranes

In the present work, we report on the synthesis and characterization of poly(vinylidene fluoride) (PVDF) with N‐isopropylacrylamide (NIPAAM) polymer side chains from molecular graft copolymerization in solution. The copolymer can be readily cast into temperature‐sensitive microfiltration (MF) membranes by the phase inversion technique. The copolymer approach to membrane fabrication allows a much better control of the physicochemical nature of the membrane pores through the variation in graft concentration, membrane casting temperature and concentration of the membrane casting solution.

     

Elaboration of Poly(ε‐caprolactone)‐g‐TiNbO5 Nanocomposites via in situ Metal Complex Initiated Intercalative Polymerization

Summary: The preparation of poly(ε‐caprolactone)‐g‐TiNbO₅ nanocomposites via in situ intercalative polymerization of ε‐caprolactone initiated by an aluminium complex is described. These nanocomposites were obtained in the presence of HTiNbO₅ mineral pre‐treated by AlMe₃, but non‐modified by tetraalkylammonium cations. These hybrid materials obtained have been characterized by Fourier transform infrared absorption spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and dynamic mechanical analysis. Layered structure delamination and homogeneous distribution of mineral lamellae in the poly(ε‐caprolactone) (PCL) is figured out and strong improvement of the mechanical properties achieved. The storage modulus of the nanocomposites is enhanced as compared to pure PCL and increases monotonously with the amount of the filler in the range 3 to 10 wt.‐%.

SEM image of the fractured surface of a PCL‐TiNbO₅ nanocomposite film.     

Analysis of Crosslinked Styrene‐Butadiene Rubbers by Liquid Chromatography and FT‐IR Spectroscopy, 1

Crosslinked styrene‐butadiene and butadiene rubbers can efficiently be analyzed by liquid chromatography and FT‐IR spectroscopy. In a first step the vulcanizate is pyrolyzed under mild conditions. The resulting high molar mass fragments are extracted from the bulk material and analyzed by size exclusion chromatography. The molar masses of the extractables are in the range of 3 000 to 25 000 g/mol. The chemical composition as a function of molar mass is visualized by coupled SEC‐FT‐IR spectroscopy. By quantitative analysis of the FT‐IR spectra the concentrations of the different structural units, including styrene, 1,4‐trans‐butadiene, 1,2‐vinylbutadiene, and 1,4‐cis‐butadiene, are determined. It is shown that the chemical composition of the original non‐crosslinked rubbers and the chemical composition of the extractables are rather identical. Therefore, this technique can be used to obtain structural information on rubber formulations even in the case when the material is already vulcanized.

SEC chromatograms of SBR 1712 and the extractables after pyrolysis, stationary phase: SDV linear, mobile phase: THF, detector: ELSD.     

Harnessing the Melting Peculiarities of Ultra‐High Molecular Weight Polyethylene Fibers for the Processing of Compacted Fiber Composites

Summary: Compacted fiber composites offer unique properties due to their lack of an extraneous matrix. The conditions of processing ultra‐high molecular weight polyethylene (UHMWPE) fibers were simulated in a heated pressure cell. In situ X‐ray diffraction measurements were used to follow the relevant transitions and the changes in the degree of crystallinity during melting and crystallization. The results strongly support the suggestion that the hexagonal crystal phase, in which the chain conformation is extremely mobile on the segmental level, constitutes the physical basis of compaction technologies for processing UHMWPE fibers into a single‐polymer composite. This report suggests that using a pseudo‐phase diagram outlining the occurrence of different phases during slow heating and the degree of crystallinity can provide valuable insight into the technological parameters relevant for optimal processing conditions.

Degree of crystallinity as a function of pressure and temperature in a region relevant to compaction processes.     

Modeling of Ethylene‐Norbornene Copolymer Microstructure in Solution Polymerization with Homogeneous Metallocene Catalysts

Summary: The microstructure of ethylene‐norbornene copolymer produced in solution polymerization is analyzed through kinetic modeling and experiments using homogeneous rac‐Et(1‐indenyl)₂ZrCl₂/methylaluminoxane catalyst in toluene at 70 °C. The sequence distribution function and average chain length equations are derived for terminal model and penultimate model. The model simulations show that both models provide similar predictions of average copolymer composition, especially at low norbornene concentration in the copolymer. However, at higher norbornene concentrations the penultimate model yields much better predictions of norbornene sequence length distribution than the terminal model. The terminal model has been inadequate in describing the copolymerization rate, whereas the penultimate model yields excellent predictions of rate behavior. The model calculations also indicate that at norbornene concentration in the copolymer larger than about 10 mol‐%, the maximum ethylene block length is smaller than 70, prohibiting the formation of crystalline copolymer.

Ethylene sequence distribution curves at different mol‐% of norbornene in copolymer.     

PTFE Micropowder Functionalized with Carboxylic Acid Groups

PTFE powder irradiated in air at room temperature was studied by infrared spectroscopy, potentiometric titration with sodium hydroxide, and polyelectrolyte titration with poly(diallyl dimethylammonium chloride). Through the radiation‐induced degradation ? COF groups are formed in the material, which can be hydrolyzed to ? COOH groups. About 10–20% of the ? COOH groups are located at the surface of the PTFE particle. The ? COOH groups start to decompose under oxidizing conditions at temperatures above 200 °C. The decarboxylation results in the formation of ? CF?CF₂ groups, which are oxidized to ? COF groups in the presence of air.

     

Some Mechanical Properties of Poly[(acrylic acid)‐co‐(itaconic acid)] Hydrogels

Two series of hydrogels of poly[(acrylic acid)‐co‐(itaconic acid)] have been prepared by copolymerization in solution using tetrafunctional N,N′‐methylenebisacrylamide (NMBA) as cross‐linker. The resulting polymer was swollen in water at 298 K to yield homogenous transparent hydrogels. These hydrogels were characterized in terms of swelling and compression‐strain measurements. The influence of the comonomer composition and concentration of cross‐linking agent on volumetric swelling and the mechanical properties of these hydrogels were investigated. Inefficient cross‐linking is indicated by the small values of ν_e relative to the theoretical cross‐linking densities.

Dependence of measured affective cross‐linking density (ν_e) on the theoretical cross‐linking density (ν_t) for acrylic acid/itaconic acid hydrogels prepared at a fixed composition of AA80/AI20 wt.‐%, but at different concentrations of NMBA.     

An NMR‐MOUSE® for Analysis of Thin Objects

A special unilateral NMR sensor has been designed for investigations of thin samples with a thickness of less than 1 mm and of surface effects of polymers. For use with the bar‐magnet NMR‐MOUSE®, the so‐called “crazy coil” is introduced with a low penetration depth. It is a flat meander coil etched on a printed circuit board with wiggles in the conductors. The design of the new coil and FEM simulations of the B ₁ field are presented. Different applications are discussed by means of illustrative examples. They are the detection of surface damage in rubber samples, the swelling and drying of a latex membrane exposed to cyclohexane vapor mimicking a chemical sensor, and the drying of a thin sprayed adhesive layer.

Bar‐magnet NMR‐MOUSE® with crazy coil.