Laser surface modification of carbon fiber reinforced composites

The removal of top resin layer is an essential task prior to adhesive bonding of carbon fiber reinforced polymer (CFRP) composites. This paper investigates the technical feasibility of using a low power continuous wave carbon dioxide laser for removing the top resin layer of CFRP without damaging the underlying fiber. The operating window and damaging threshold were experimentally determined. Irradiating the CFRP surface at a power of 14 W, scanning speed of 880 mm/sec, and a beam overlap of 25% provides an optimal thermal condition for removal of top resin layer. A finite element model was used to explain the removal mechanisms

A rapid technique for the direct metallization of PDMS substrates for flexible and stretchable electronics applications

Metallization of a polydimethylsiloxane (PDMS)-based substrate is a challenge due to the difficulties in forming crack-free polymer and metal features using standard deposition techniques. Frequently, additional adhesion layers, rigid substrates, multiple processing steps (lift-off and etching) and expensive metal sputtering techniques are required, to achieve such metal patterns. This work presents a novel and rapid technique for the direct metallization of PDMS substrates using photolithography and electroless copper plating. The method has the advantage of not requiring expensive vacuum processing or multiple metallization steps. Electroless copper layer is demonstrated to have a strong adhesion to PDMS substrate with a high conductivity of (3.6 ± 0.7) × 107 S/m, which is close to the bulk copper (5.9 × 107 S/m). The copper-plated PDMS substrate displays mechanical and electrical stability whilst undergoing stretching deformations up to 10% due to applied strain. A functional electronic circuit was fabricated as a demonstration of the mechanical integrity of the copper-plated PDMS after bending

Selective Electroless Copper Deposition by Using Photolithographic Polymer/Ag Nanocomposite

This paper presents a novel, direct, selective, vacuum-free, and low-cost method of electroless copper deposition, allowing additive patterning of nonconductive surfaces. Ag nanoparticles (NPs) synthesized inside a photosensitive polymer are acting as seeds for electroless copper deposition. The resulting copper film surface morphology was studied with scanning electron microscopy. Copper films were shown to display a rough grain like structure, covering substrate uniformly with good metal-substrate adhesion. Copper thickness was studied as a function of the plating time, temperature, and Ag NPs seed concentration. A maximal copper thickness of 0.44 ± 0.05 μm was achieved when plated at 30 °C with 0.4 M Ag(I). The minimum feature resolution of copper patterns, grown with 0.025- and 0.1-M silver salt, is attained down to 10 μm. The maximum electrical conductivity of the copper film prepared with 0.025-, 0.1-, and 0.4-M Ag(I) approaches (0.8 ± 0.1) × 10⁷ S/m, (1.1 ± 0.1) ×10⁷ S/m and (1.6 ± 0.4)×10⁷ S/m, respectively. Electroless copper interconnections and LED circuit on glass substrate were fabricated as a proof of concept demonstrators

Microstructural and mechanical characterisation of laser-welded high-carbon and stainless steel

The final publication is available at Springer via http://dx.doi.org/10.1007/s00170-015-7111-5Laser welding is becoming an important joining technique for welding of stainless steel to carbon steel and is extensively used across various sectors, including aerospace, transportation, power plants, electronics and other industries. However, welding of stainless steel to high-carbon steel is still at its early stage, predominantly due to the formation of hard brittle phases, which undermine the mechanical strength of the joint. This study reports a scientific investigation on controlling the brittle phase formation during laser dissimilar welding of high-carbon steel to stainless steel. Attempts have been made to tailor the microstructure and phase composition of the fusion zone through influencing the alloying composition and the cooling rate. Results show that the heat-affected zone (HAZ) within the high-carbon steel has significantly higher hardness than the weld area, which severely undermines the weld quality. To reduce the hardness of the HAZ, a new heat treatment strategy was proposed and evaluated using a finite element analysis-based numerical simulation model. A series of experiments has been performed to verify the developed thermo-metallurgical finite element analysis (FEA) model, and a qualitative agreement of predicted martensitic phase distribution is shown to exist

PEI/Ag as an Optical Gas Nano-Sensor for Intelligent Food Packaging

In this work we report research carried out on the manufacturing of an optical sensor based on polyetherimide (PEI) and Ag nanoparticles (NPs) for food packaging and food freshness control applications. PEI/ Ag films were fabricated and tested as optical sensors by exposing them to 0.01 M and 0.005 M of 2-mercaptoethanol (2-ME). Thiol groups of 2-ME react on the surface of the sample and reduce the silver ions to Ag NPs, which lead to the change of color. The real-time measurement of meat freshness was performed for salmon, chicken, turkey and beef. The colorimetric and UV-vis absorbance responses were measured over duration of 80 hours. The PEI/Ag sensor shows a good response to the released gases by meat. Moreover, salmon, chicken and turkey are shown to produce color changes of PEI/Ag films after 20 hours of exposure, and beef after 60 hours of exposure. Therefore, this nano-sensor has a potential to serve as an indicator of food spoilage in the packaging

Selective Metallization of 3D Printable Thermoplastic Polyurethanes

This paper presents a selective metallization method for the newly developed 3D printable thermoplastic polyurethane elastomers (TPU): FilaFlex (R), SemiFlex (TM), PolyFlex (TM), and NinjaFlex (R). Silver nanoparticles were fabricated in-situ by photo-reduction on the surface of TPUs and acted as catalysts for copper ion adsorption. This method demonstrates the successful fabrication of copper patterns on flexible TPU filaments. Furthermore, Polyflex (TM) and acrylonitrile butadiene styrene (ABS) filaments printed in the same part have been used to enable selective electroless plating directly on Polyflex (TM) material. Electroless copper deposited onto Polyflex (TM) has a sheet resistance of (139.4 ± 7.2) m Ω/ and a copper conductivity of (1.1 ± 0.1) × 10⁷ S/m that is comparable with bulk copper. Copper-plated Polyflex (TM) interconnects were fabricated as a proof of concept demonstrators