Well‐defined correlations exist between the maxima in mechanical loss factor and the local maxima in temperature‐ or loading‐speed‐dependent fracture toughness. The non‐linear viscoelastic fracture processes and small‐strain deformations are characterised by the same Arrhenius‐type activation enthalpies. The local increase in toughness is linearly correlated with the relaxation strength of molecular relaxation processes. Stable crack propagation can be understood as a three‐phase process resulting in steady‐state stable crack growth. The normalised steady‐state crack‐tip‐opening displacement is independent of matrix material, temperature and loading speed.
Novel fluoroalkyl end‐capped oligomer/hydroxyapatite nanocomposites have been easily prepared by the reaction of disodium hydrogenphosphate and calcium chloride in the presence of self‐assembled molecular aggregates formed by fluoroalkyl end‐capped oligomers in aqueous media. The fluorinated hydroxyapatite nanocomposites thus obtained were found to exhibit a good dispersibility in a variety of media, and were applied to the surface modification of glass.
Unmodified (LDH) and modified (mLDH) layered double hydroxides have been added to gum and ZnO‐cured carboxylated nitrile rubber (XNBR). It was observed that both LDH and mLDH inhibit the formation of ionic cross‐links between XNBR and ZnO quite significantly, as is evident from DMA and FT‐IR studies. The suppression of ionic cross‐links formation was also reflected in the mechanical properties of the resulting composites. A tentative sketch has also been suggested for the possible mechanism involved in the inhibition of ionic cross‐links by LDHs. X‐ray diffraction and STEM studies were performed to see the dispersion of LDH's in the elastomer matrix.
Sheets of cellulosic paper were modified with PAni nanoparticles through a chromatographic process. When exposed to acidic conditions, strips of the modified paper sheets are subject to RGB color changes that can be detected by a scanner (and similar devices used for image analyses). As a consequence, cellulosic paper sheets modified with PAni can be used for analyses of acid concentrations in liquid and gaseous streams. Aqueous solutions of hydrochloric acid were used for modeling purposes and it was observed that color changes were most significant when the HCl content was between 0–500 ppm range. Materials were characterized by FT‐IR spectroscopy, optical microscopy, AFM, and SAXS techniques, in order to reveal the main characteristics of the produced materials.
A fluorinated acrylic resin was synthesized for use as a co‐monomer with a commercially available epoxy resin for UV‐cured interpenetrating polymer network preparation. Hybrid IPN networks were achieved with morphology ranging from a co‐continuous IPN to complete phase separation simply by changing monomer ratios. Highly hydrophobic coatings with good adhesion properties on glass substrates were obtained.
An effective approach is presented for designing and tailoring diffusion‐controlled systems for targeted release rate profiles. The diffusion‐controlled system consists of PBA networks with precisely controlled crosslink densities via RAFT copolymerization of BA with ethylene glycol dimethacrylate, which gives a desired diffusivity. One‐dimensional releases in the crosslinked PBA matrix (CPM) slabs are evaluated with a hydrophobic dye. Fick's second law is used to model the transient mass transfers in the CPMs with a mixed Newton‐Tikhonov regularization method for determination of their diffusion coefficients. A two‐layer CPM (CPM‐2) with controlled crosslink densities is constructed. The dye release results from the CPM‐2 agreed well with theoretical predictions.
A novel CMRF is synthesized from modified silicone oil, containing composite polyurethane microsphere additives, and surface‐coated iron particles. The CMRF is designed to act as a liquid spring with controllable damping properties in a damper system. The fluid compressibility is characterized by force/displacement measurements. The addition of composite polyurethane‐microspheres increases the strength and compressibility of the fluid. It also decreases the concentration of iron particles needed in order to achieve the same yield stress as commercially available MRF. Surface coating surface of the iron particles with poly(2,3,4,5,6‐pentafluorostyrene) via RAFT provides dispersion stability.
MMA‐EHA copolymers with different compositions and with a low amount of AA were synthesized and used as impact modifier for epoxy networks. The effect of the copolymers on the tensile and dynamic mechanical properties as well as impact resistance of the epoxy network was evaluated. The addition of 10 phr of low‐molar‐mass MMA‐EHA copolymer with defined composition resulted in a significant increase in impact resistance without any significant changes in the tensile strength, modulus, and glass transition temperature. The morphology of the modified epoxy network depends upon the copolymer composition.
Strong honeycomb like nanocomposite sponges were fabricated from starch and PVA by using repeated cycles of freezing and thawing and reinforcing with cellulose whiskers. Their structure and properties were investigated with WAXD, FT‐IR, SEM, DMTA, rheological measurements, and LSCM. The results revealed that the repeated freezing/thawing cycles induced a physically crosslinked chain packing between starch and PVA, as well as a phase separation caused by the crystalline ice and syneresis. Thus, larger pores and tougher walls emerged in the sponges, leading to a high swelling degree. The sponges reinforced with cellulose whiskers exhibited improved dimensional stability and enhanced strength. These nanocomposite sponges are promising for wound dressing and tissue engineering applications.
This is the first report on a thermoformable bionanocomposite based on a natural nanocrystal and formed by grafting long polymer chains onto the surface of microcrystalline cellulose. For the cellulose nanocrystal‐graft‐poly(ε‐caprolactone), the “graft from” strategy contributed to long and dense “plasticizing” PCL tails onto the CN surface as the key of thermoforming. The grafted PCL chains shielded the hydrophilic surface of CN and, hence, showed high water‐resistance. Moreover, a strategy for developing new bionanocomposite materials based on natural nanocrystals has been presented.
The formation of an integral asymmetric membrane composed of a cylinder‐forming polystyrene‐block‐poly(2‐vinylpyridine) on a nonwoven by using solvent casting followed by solvent/nonsolvent exchange (phase inversion) is reported for the first time. The influence of parameters such as solvent composition, evaporation time of the solution‐cast block copolymer film before phase inversion, and immersion bath temperature is demonstrated. The optimized membranes are characterized in terms of stimuli‐responsive water flux properties. The morphologies of the membranes as well as of the bulk of the block copolymer are imaged by scanning force microscopy, scanning electron microscopy, and transmission electron microscopy.
Hybrid organic–inorganic membranes were prepared by size‐exclusion deposition and thermal sintering of fluorescent polyphenylsilsesquioxane nanoparticles on a ceramic support. Fluorescent polyphenylsilsesquioxane particles were prepared by a two‐step co‐polymerization of phenyltriethoxysilane with 0.1 mol‐% N‐(triethoxysilylpropyl)dansylamide. Because they were larger than the pores in the support, the particles formed a layer on top of the ceramic support that was sintered at 300 °C into a homogeneous, non‐porous membrane. Fluorescence of the modified polyphenylsilsesquioxane provided a valuable tool to monitor particle deposition and assist in characterization of the membranes.
A new, nickel‐coated graphite resistance‐change‐based method for gel‐point determination for epoxy‐based thermoset resins is presented and compared with DSC and rheological methods. Gelation times determined by this new method are in very good agreement with conventional techniques; this new method is potentially simpler and less time consuming than existing ones.
Antimicrobial poly(vinyl alcohol) nanofibres are produced using AquaQure biocide as additive to the polymer solution. AquaQure is an aqueous antimicrobial agent containing mainly Cu2+ and Zn2+. Antimicrobial tests show that the fibres achieve up to a 5 log reductions in populations of E. coli, S. aureus, S. typhimurium, P. aeruginosa and K. pneumoniae bacteria. Reusability of the nanofibre membranes is investigated to establish if the nanofibres retain their morphology and antimicrobial effectiveness over six cycles of water filtration. Leaching of AquaQure constituents from the nanofibres into filtered water is assessed and found to be at acceptable levels.
The influence of molecular weight and comonomer content on the mechanical properties of several melt‐processable polytetrafluoroethylene (MP PTFE) materials is studied. Additionally, a comparison of mechanical properties including tensile properties and their dependence on environment as well as fatigue life of PTFE, MP PTFE and perfluoroalkoxy copolymer (PFA) is made. PTFE homopolymer and PTFE copolymers exhibit considerably different mechanical properties. The small strain deformation behaviour up to yielding correlates with the degree of crystallinity and comonomer content, whereas the large strain deformation was found to depend on intercrystalline connections, such as tie molecules and chain entanglements. The special role of these elements in determining the fatigue life and sensitivity to environmental stress cracking is also demonstrated.
A systematic study of the effects of , flow rate, voltage, and composition on the morphology of electrospun PLGA nanofibers is reported. It is shown that changes of voltage and flow rate do not appreciably affect the morphology. However, the of PLGA predominantly determines the formation of bead structures. Uniform electrospun PLGA nanofibers with controllable diameters can be formed through optimization. Further, multi‐walled carbon nanotubes can be incorporated into the PLGA nanofibers, significantly enhancing their tensile strength and elasticity without compromising the uniform morphology. The variable size, porosity, and composition of the nanofibers are essential for their applications in regenerative medicine.
A recently developed electrohydrodynamic printing method is described that can be used to create ordered structures and complex patterns using coarse processing needles and two polymeric materials. The results highlight the method's potential for direct 3D writing of biomedical polymers and composites for a variety of biomedical applications.
Hybrid organic/inorganic acrylic nanostructured films were prepared by a UV/thermal dual‐curing process. The role of a fluorinated hydroxyl acrylate monomer (AF) as coupling agent was investigated. Increased Tg values and modulus of the dual‐cured films were achieved by increasing the TEOS inorganic precursor. The coupling agent deeply modified the surface properties of the cured films: the formation of hybrid films characterized by high hydrophobicity together with an increase on surface hardness was achieved. TEM analysis clearly evidenced the reducing of the nanosize dimensions of the inorganic silica domains by increasing the coupling agent content in the photocurable formulation.
This review presents the state of the art regarding the improvement of scratch resistance of polymeric coatings. In particular, our attention is focused on the effect of inorganic nanometric fillers on the scratch resistance of organic coatings. Two main strategies are described for the achievement of such nanostructured hybrid organic/inorganic coatings: either a top‐down or a bottom‐up approach.
This paper demonstrates how the electric‐field‐assisted thermal annealing of octadecylamine‐functionalized SWNT/PMMA films induces an increase in the composite transversal conductivity of several orders of magnitude and a decrease in the lateral conductivity. This difference has been rationalized in terms of the nanotube alignment into the polymer matrix along the electric field direction. This result provides an initial understanding of how electric fields can be used to control the bulk physical properties of such nanocomposites.
