Nonwetting process for achieving surface functionalization of chemically stable poly(tetrafluoroethylene)

Direct adhesion between Cu foil and polytetrafluoroethylene without increasing surface roughness for high-frequency printed wiring boards

Polytetrafluoroethylene (PTFE) serves as a suitable dielectric substrate for high-frequency printed wiring boards (PWBs) owing to its excellent properties at high frequency. However, to the best of our knowledge, no study has investigated the strong adhesion between PTFE and Cu foil with low surface roughness. Therefore, in this study, pure-PTFE comprising a weak boundary layer (WBL) on the surface and glass-cloth-containing PTFE (GC-PTFE), which did not contain a WBL, were subjected to heat-assisted plasma (HAP) treatment. Thereafter, we investigated the surface chemical bonding state, surface morphology, and adhesion properties of the as-prepared PTFE toward Cu foil with low surface roughness. As observed, oxygen-containing functional groups were generated on the HAP-treated PTFE, and the WBL in the as-received pure-PTFE was eliminated via HAP treatment. Moreover, the surface roughness of the HAP-treated PTFE did not increase compared to that of as-received PTFE. After performing thermal compression under atmospheric conditions, the adhesion strength of both HAP-treated pure-PTFE and GC-PTFE was ∼0.9 N mm-1. In addition, the adhesion strength of Cu/pure-PTFE and Cu/GC-PTFE increased after thermal compression under a reduced pressure, and the adhesion strength of 1 N mm-1 was obtained. Although the Cu foil was not roughened, Cu/PTFE realized strong adhesive strength. The developed method is advantageous because maintaining a low interface roughness is crucial for applying PTFE to manufacture high-frequency PWBs.

Fracture Mechanism Change at a Heterogeneous Polymer-Polymer Interface Reinforced with in Situ Graft Copolymers

Dynamic secondary-ion mass spectroscopy (DSIMS) was used to investigate the change in the failure mechanism at a heterogeneous polymer-polymer interface (polystyrene (PS)/polyamide (nylon 6, Ny6)) reinforced with in situ graft copolymers produced by the reaction between Ny6 molecules and poly(styrene- co-maleic anhydride) at the interface. The variation in fracture toughness with bonding time and temperature has been explained by two different failure mechanisms: adhesive failure at the interface for short bonding times and when the bonding temperature is low and cohesive failure between chains at the interface and bulk PS for longer bonding times and when the bonding temperature is high. DSIMS results provide the direct experimental evidence that the nonreactive molecules (PS) diffuse away from the high-potential interface, which induces the cohesive failure in the bulk of the nonreactive molecules (PS) after long annealing times. The change in the adhesion strength with temperature could also cause a change in the failure mechanism. Common features of the fracture mechanisms at heterogeneous interfaces reinforced by the in situ graft copolymers are outlined, which are independent of the polymer crystallinity.

Metal mesh scaffold for tissue engineering of membranes

Engineering of the membrane-like tissue structures to be utilized in highly dynamic loading environments such as the cardiovascular system has been a challenge in the past decade. Scaffolds are critical components of the engineered tissue membranes and allow them being formed in vitro and remain secure in vivo when implanted in the body. Several approaches have been taken to develop scaffolds for tissue membranes. However, all methods entail limitations due to structural vulnerability, short-term functionality, and mechanical properties of the resulted membrane constructs. To overcome these issues, we have developed a novel hybrid scaffold made of an extra thin layer of metal mesh tightly enclosed by biological matrix components. This approach retains all the advantages of using biological scaffolds while developing a strong extracellular matrix that can stand various types of loads after implantation inside the body.

Enhanced interfacial adhesion between an amorphous polymer (polystyrene) and a semicrystalline polymer [a polyamide (nylon 6)]

We studied enhanced interfacial adhesion between an amorphous polymer (polystyrene, PS) and a semicrystalline polymer (a polyamide, Ny6). The fracture mechanism for this system was investigated to elicit a universal description on the fracture mechanism. The surface modification of PS to provide functional groups that can react with the functional groups of Ny6 was carried out with ion-beam and/or plasma treatment. These surface modifications were found to alter the interfacial adhesion strength between PS and Ny6. A remarkable enhancement was found with the surface functionalization of PS. Though the fracture toughness was varied depending on the process, its overall behavior was quite similar to that of others; the fracture toughness increased with increasing bonding temperature and bonding time, passed through a peak, and then decreased with a further increase of the bonding time or temperature. The variation of the fracture toughness with the bonding time and temperature can be plausibly explained in terms of two different failure mechanisms of adhesive failure and cohesive failure. This change appears more evidently for the interface between an amorphous polymer and a semicrystalline polymer than the interface between semicrystalline polymer pairs. Surface functionalization could exclude the effect of diffusion, thus clarifying the failure mechanisms occurring at the interface.

Surface functionalization of a poly(vinylidene fluoride): effect on the adhesive and piezoelectric properties

We studied the effect of the surface functionalization and crystalline phase change of poly(vinylidene fluoride) (PVDF) films on their adhesion and piezoelectric properties. The surface modification of PVDF was carried out with ion beam and/or plasma treatment. These surface modifications were found to alter the interfacial strength between PVDF and metal electrodes and the crystal structure of the piezoelectric PVDF film. A remarkable improvement was found in the interfacial adhesion of the films with thermally deposited metal electrodes, but some piezoelectricity of PVDF film was lost due to the changes in the crystal phase. The proper treatment condition for enhancing the adhesion and retaining piezoelectric structure was suggested.

Experimental evaluation of a new antithrombogenic stent using ion beam surface modification

A new antithrombogenic stent using ion beam surface modification nanotechnology was evaluated. The ion stent is being developed to inhibit acute and chronic stent-related thrombosis. Thirty self-expanding mesh stents were fabricated from Ti-Ni metal wires with a dimension of 4 mm (diameter) x 25 mm (length) x 0.15 mm (thickness). Twenty stents were coated with type I collagen and irradiated with a He(+) ion beam at an energy of 150 keV with fluences of 1 x 10(14) ions/cm(2) (ion stent group). Ten stents had no treatment (non-ion stent group). The self-expanding stents were implanted into the right and left peripheral femoral arteries of 15 beagle dogs (vessel diameter approximately 3 mm) via a 6Fr catheter under fluoroscopic guidance. Heparin (100 units/kg) was administered intravenously before implantation. Following stent implantation, no antiplatelet or anticoagulant drugs were administered. The 1-month patency rate for the non-ion stent group was 10% (1/10), and for the ion stent group it was 80% (16/20) with no anticoagulant or antiplatelet drugs given after stent implantation (P = 0.0004 by Fisher's exact test). Ten stents remain patent after 2 years in vivo with no anticoagulant or antiplatelet drugs. These results indicate that He(+) ion-implanted collagen-coated Ti-Ni self-expanding stents have excellent antithrombogenicity and biocompatibility. This ion stent is promising for coronary and cerebral stent applications.