Thermoreversible Gelation of Polybenzimidazole in Phosphoric Acid

Summary: We report a study of thermoreversible gelation of polybenzimidazole (PBI) in phosphoric acid (PA). The PBI gel in PA exhibits fibrillar network morphology and reversible first order phase transition. The gelation rate is measured by the tube tilting method and found to depend both upon gelation concentration and gelation temperature. The UV‐vis study demonstrates that the gelation process is a two‐step process: conformational transformation and aggregation which produces crystallites for gel formation. The WAXS study supports the presence of crystallites in the gel. The PA doping level of the membrane increases significantly because of gelation.

Thermoreversible gelation of polybenzimidazole in phosphoric acid and the membrane produced from the gel.     

Synthesis and Alignment of Iron Oxide Nanoparticles in a Regenerated Cellulose Film

Summary: A polymer‐iron oxide nanocomposite film has been successfully synthesized by using a microporous regenerated cellulose film as template and aqueous ferrous chloride as precursor. The nanocomposite film was investigated with XRD, XPS, SEM, TEM, and VSM. The nanoparticles synthesized in situ were disk‐shaped with a mean diameter of ≈24 and thicknesses of 2.5–3.5 nm. For the first time, the nanodisks were well aligned in the cellulose matrix to form an ordered multibilayer structure by the shrinkage of the hybrid film while drying. The nanocomposite film displayed anisotropic magnetic properties as a result of the alignment of magnetic nanodisks. This work provides a novel and facile method for template synthesis of nanoparticles and aligned nanocomposites.

TEM image of the air‐dried nanocomposite film; slice perpendicular to the film plane.     

Submicron Polymer Gratings: Optical Diffraction and Spontaneous Brillouin Scattering

Summary: Brillouin light scattering (BLS) from submicron‐size patterned polyurethane (PU) films was found to display rich spectral features. Their identification allows the determination of the mechanical properties of the PU and the characterization of the periodicity and the coherence of the structure. A temperature‐dependent study demonstrates that BLS is a sensitive tool to monitor changes of the mechanical properties and/or of the morphology.

(a) Scheme of the sample structure and the scattering geometry, (b) SEM top view of the PU features.     

Co‐Continuous Polymeric Nanostructures via Simple Melt Mixing of PS/PMMA

Blends of polystyrene/poly(methyl methacrylate) (PS/PMMA) (30/70) prepared by simple melt mixing form a droplet (PS) in‐matrix (PMMA) morphology. It is found that addition of a carefully designed copolymer PS‐b‐P(S‐ran‐MMA) (SSM) compatibilizer could convert the morphology into a co‐continuous system. Indeed, the continuity of the dispersed PS phase increased with an increase in PS‐b‐P(S‐ran‐MMA) content, and a fully co‐continuous morphology (continuity = 100%) was obtained at 20% SSM fraction with a characteristic size of 100 nm.

     

Fluorescence Investigations of Oxygen‐Doped Simple Amine Compared with Fluorescent PAMAM Dendrimer

Blue emission of oxygen‐doped tertiary amine (triethylamine), a key unit of fluorescent poly(amido amine) dendrimer, was demonstrated. It was found that the fluorescence intensity could be further enhanced if the tertiary amines locate densely in the dendrimer interior as the branching sites. Moreover, a solvatochromic phenol blue, instead of oxygen, is able to induce the blue fluorescence of the tertiary amino‐branching sites based on a guaranteed host‐guest complexation of phenol blue molecules and dendrimer interior.

     

A New Strategy for the Synthesis of Polyaniline Nanostructures: From Nanofibers to Nanowires

A new approach for the synthesis of polyaniline (PANI) nanostructures under UV light illumination has been developed, which is the first report of a templateless chemical process for preparing pure PANI nanowires. The acceleration effect of photo‐assistance on the polymerization can promote the homogeneous nucleation and elongation of the nanofibers and nanowires, leading to easy preparation of tunable diameters of the nanowires and nanofibers of PANI.

     

Bioactive Amphiphilic Peptide Derivatives with pH Triggered Morphology and Structure

A series of bioactive amphiphilic peptide derivatives that contain the RGD (Arg‐Gly‐Asp) sequence have been designed and prepared by the standard solid‐phase peptide synthesis (SPPS) technique. The influence of the molecular structure and pH change on the morphology of the amphiphilic peptide derivatives in aqueous solution is investigated. The results reveal that the amphiphilic peptide derivatives with different molecular structures exhibit different self‐assembly behavior in response to environmental changes. Furthermore, by adjusting the pH, the molecular interactions of amphiphilic peptide derivatives are tuned, which results in a morphology change.

     

The Use of a Low‐Molar‐Mass Self‐Assembled Template to Direct the Crystallisation of Poly(ε‐caprolactone)

Summary: We show that small quantities of dibenzylidene sorbitol dispersed in poly(ε‐caprolactone) provide a self‐assembling nanoscale framework to yield high levels of crystal orientation. During modest shear flow of the melt, the additive forms highly extended nanoparticles which adopt a preferred alignment with respect to the flow field and, on cooling, polymer crystallisation is directed by these particles. We speculate that atomistic level epitaxy is unlikely to be the only directing influence.

SAXS pattern of PCL/DBS in the melt at 80 °C and subjected to a shear flow of 10 s⁻¹ for 1 000 shear units. The flow direction is vertical.     

Automated Raman Spectroscopy as a Tool for the High‐Throughput Characterization of Molecular Structure and Mechanical Properties of Polyethylenes

Raman spectroscopy, which does not require a time‐consuming sample preparation, is described as an analytical tool for the high‐throughput characterization of polyethylenes. The content of comonomer and the amount of methyl groups per 1 000 carbon atoms of polyethylenes can be predicted from Raman spectra using multivariate data analysis. In addition, macroscopic properties, such as density and elastic modulus as well as yield stress, can be derived from Raman spectra.

Raman spectra of selected metallocene‐catalyzed polyethylenes of different comonomer content.     

Reinforcement Efficiency of Carbon Nanotubes – Myth and Reality

Different micromechanical models for the prediction of mechanical properties of CNT/polymer composites, taking into consideration filler percolation throughout the matrix, are considered. It is demonstrated that the critical filler volume fraction, where a percolating network of CNTs is forming, marks a “turning point” in the reinforcement efficiency. Expectations for the reinforcing effect of CNTs at concentrations above a percolating threshold with the current technology are in general unrealistic.

     

Binding and Sulfonation of Poly(acrylic acid) on Iron Oxide Nanoparticles: a Novel,Magnetic, Strong Acid Cation Nano‐Adsorbent

Summary: A novel, magnetic, strong acid cation nano‐adsorbent has been developed by the covalent binding of poly(acrylic acid) on the surface of Fe₃O₄ nanoparticles followed by sulfonation using sulfanilic acid via carbodiimide activation. The nano‐absorbent can be easily recovered or manipulated with an external magnetic field and shows a good capacity for the rapid and efficient adsorption of multivalent metal cations from aqueous solutions.

An illustration for the binding and sulfonation of PAA on Fe₃O₄ nanoparticles to produce a magnetic, strong acid cation nano‐adsorbent.     

Direct Measurement of Cure‐Induced Stress in Thermosetting Materials by Means of a Dynamic Mechanical Analyzer

Summary: Significant stresses develop during cure in functional and structural applications of polymeric materials ranging from glass fiber composites to advanced functional polymers used in microelectronics, optoelectronics, and biomaterials applications. These stresses arise from a combination of chemical shrinkage and stiffness buildup in a confined geometry. In this paper, a new method for direct measurement of cure‐induced stresses during curing of thermosetting materials by using the iso‐strain mode of a dynamic mechanical analyzer (DMA) has been developed. A thermal tape was used to facilitate maintaining a constant strain and initiate the iso‐strain measurement. Two quartz rods with a small gap were used to contain the material. The top of the quartz rod and one side of the thermal tape were secured by the fixed clamp, while the bottom quartz rod and the other side of the thermal tape were clamped with the moveable force probe. The cure force was thereby directly measured by the probe during the curing process. The cure stress buildup was observed to occur after a certain duration that corresponds to the gel point. Experimental results clearly show that curing at lower temperature could lead to higher cure stress due to the earlier onset of vitrification. An investigation of the stress buildup as a function of degree of cure indicates that a majority of the cure stress was generated in the vitrification regime. The methodology proposed herein provides an accurate experimental approach to investigate the cure‐induced stress generated in a thermosetting material in applications ranging from microelectronics and optoelectronics packaging to biomaterials amongst others.

Evolution of cure force and heat flow measured by means of DMA and DSC, respectively, at cure temperature 100 °C.     

Computer Simulation of a Gold Nanoparticle Coated by Thiol‐Terminated Hydroquinonyl Oligoethers

Molecular dynamics simulations were carried out to investigate the structure of a gold‐nanoparticle including 169 Au atoms coated by 42 thiol terminated hydroquinonyl oligoether chains. Three nanoparticle systems were constructed and investigated for structural comparison. The simulation showed that in all three nanosystems thiol‐chains self‐assembled on the surface of the gold cluster to form a stable gold nanoparticle. The configurations of the thiol chains and stacking of the phenylene rings were analyzed. The thiol‐chains are bundled into groups. Each group contains no more than four chains, in which phenylene rings in the thiol‐chains are correlated in parallel and perpendicular forms. Simple quantum mechanical calculations are carried out to elucidate the correlation of the phenylene rings.

A snapshot of a TTOE‐Au nanoparticle.