Key Engineering Materials Vols. 334-335

Abstract: Sheets of poly(ε-caprolactone) (PCL)/carbon nanotube composites were prepared through the solvent cast method. Multiwalled carbon nanotubes (MWCNT) functionalized with hydroxyl groups were used as an initiator for the ring opening polymerization of ε-caprolactone to introduce PCL chains to the surface of MWCNT in order to ameliorate the dispersion of MWCNT in PCL matrix. Grafting of PCL chains to MWCNT was followed by FTIR and TEM observations. Effect of the incorporation of MWCNT on the mechanical properties of PCL was explored before and after the modification of the MWCNT by the PCL grafting.

Abstract: A new method was attempted to improve the interaction between nylon 6 with a commercially available organoclay, Cloisite®25A (C25A) through modification of C25A with 3-aminopropyltriethoxy silane, 3-(trimethoxysilyl)propyl methacrylate, 3-(glycidoxypropyl) trimethoxysilane and 3-isocyanate propyltriethoxy silane. C25A and C25A modified with the silane compounds(TFC) were melt mixed with nylon 6. X-Ray diffraction and transmission electron microscopy images revealed that all the TFC layers were fully exfoliated in nylon 6 matrix irrespectively of the type of the silane compounds used for the modification. Tensile properties of nylon 6 were most significantly improved when 3-(glycidoxypropyl)trimethoxysilane modified C25A was incorporated. The chemical reaction between the epoxy groups and the end groups of nylon 6 raised the interfacial interaction and thus was responsible for the enhanced tensile properties.

Abstract: Nano-structured TiN/TiBN multilayer thin films were deposited onto unheated Si(100) substrates by reactive unbalanced dc-magnetron sputtering in an Ar-N2 gas mixture at a pulsed-bias voltage of –60 V. The effects of the bilayer thickness (Λ = 1.8-7.7 nm) on microstructures and mechanical properties have been analyzed using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and microindentation measurements. Microstructure studies revealed that the TiN layers were fcc B1-NaCl structure comprising of (111)- and (200)-oriented grains depending on Λ, while the TiBN layers were amorphous. Significant relationships were found between hardness (H) and Λ. A maximum hardness of ~30 GPa was observed in a multilayer film with
 = 1.8 nm. The possible hardness enhancement mechanism was also discussed.

Abstract: CrN/CNx nano-scale multilayered films were deposited on Si (100) substrate by closed-field unbalanced magnetron sputtering. Designed experimental parameters enabled an evaluation of the effects of negative substrate bias voltage (Vb), and bi-layer thickness λ (by changing substrate rotation rate) during deposition on the structural and mechanical properties of multilayer films. These multilayers were characterized and analyzed by transmission electron microscope (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and nanoindentation measurements. In all cases, the CNx layers were amorphous and independent of Vb, while the microstructures of the CrN layers were dependent primarily on Vb. The CrN layers showed a mixed structure phase consisting of CrN, Cr2N, and Cr at Vb = -(40-120) V. At higher Vb values (-140 V or above), the Cr2N phase was dominant along with low CrN phase content. AFM measurements revealed that the root-mean-square (rms) surface roughness of the CrN/CNx film was 2 nm at Vb= -200 V whereas the rms values were about 9.5-3.3 nm for lower Vb values of -(40-180 V). By nanoindentation measurements, a maximum hardness of about 36 GPa was observed at Vb= -140 V. The improved mechanical properties of the films are correlated to the phase formation during deposition.

Abstract: Superhydrophobic polytetrafluoroethylene (Teflon®, DuPont) sub-micro and nanostructures were fabricated by the dipping method, based on anodization process in oxalic acid. The polymer sticking phenomenon during the replication creates the sub-microstructures on the negative polytetrafluoroethylene nanostructure replica. This process gives a hierarchical structure with nanostructures on sub-microstructures, which looks like the same structures as lotus leaf and enables commercialization. The diameter and the height of the replicated nano pillars were 40 nm and 40 um respectively. The aspect ratio is approximately 1000. The fabricated surface has a semi-permanent superhydrophobicity, the apparent contact angle of the polytetrafluoroethylene sub-micro and nanostructures is about 160 °, and the sliding angle is less than 1°.

Abstract: Most structural materials existing in nature take the form of composite. After centuries’ evolution and modification, these natural materials gain highly optimized structures and prominent performances. The SEM observation on the cuticle of Hydrophilidae shows that the cuticle is a biocomposite reinforced with chitin fibers. The chitin fibers are embedded in a protein matrix of the cuticle in the form of layers. A kind of revolving fiber layup was found. Observation also shows that there is a kind of special branched fiber consisting of a long fiber and many short fibers. The maximum pullout force of the branched fiber is analyzed. The results show that the maximum pullout force of the branched fiber is distinctly larger than that of ordinary straight fiber.

Abstract: Molluscan shell is strong, stiff, tough and shows an erose fracture surface when it is broken. In this research, the SEM observation on a Rufescens’s shell shows that the shell consists of aragonite layers and collagen matrix. Each aragonite layer is parallel to the surface of the shell and consists of many thin aragonite sheets. These aragonite sheets are perpendicular to the layer where they are located. The observation also shows that the direction of the sheets in different layer is various and a kind of herringbone distribution is found. The maximum pullout force of the herringbone distribution is analyzed based on its representative model, and it shows that the herringbone distribution can markedly increase the pullout force of the distribution and improve the fracture toughness of the shell.

Abstract: This paper shows preliminary results for polymer nanocomposites consisting of “hairy” silica particles with grafted polystyrene in polystyrene matrices of controlled molecular weight and polydispersity. The goal of the work is to tailor the degree of wetting / interaction between the particles and polymer by controlling the graft density and molecular weight of the grafted polymer. This is providing an opportunity to study the properties of the interface region and to control the bulk composite properties. We have found that the predictions for flat brushes are qualitatively, but not quantitatively, applicable and that the highly curved surfaces of nanoparticles present several challenges for the design of nanoparticle interfaces. The talk will present more complete results in this system and provide an overview of other work in our group using tailored interfaces to control nanocomposite properties.