Polymer Deposition Process Research Articles

Real-time Vision Sensor for Volumetric Flowrate Estimation in Robotic Fused Filament Fabrication

Fused Filament Fabrication (FFF) is one of the most widely used additive manufacturing processes where a part is built layer by layer of deposited polymer material extruded from a heated nozzle. The real-time sensing and control of the FFF process could improve the robustness of the process and the quality of the fabricated part. One of the critical process variables in FFF is the output polymer flow rate, which can be estimated by measuring the thermoplastic material extruded in real-time. Using computer vision, a live video feed of the polymer deposition process can be used as an input for in-situ extrusion width measurements. This paper explores various image processing workflows to improve the measurement latencies of a previously developed vision-based extrusion width measurement approach. The new image processing workflow helps improve the measurement rate by 6x compared to the original workflow, thereby offering prospects of realizing real-time feedback control for FFF.

Simulation of large-scale additive manufacturing process with a single-phase level set method: a process parameters study

In this work, a numerical method is presented in order to simulate the deposition of molten polymer bead onto a substrate and its cooling down in the large-scale extrusion-based additive manufacturing process. The polymer flow is treated as a single-phase flow with a free surface. This method reduces the computation time without loss of accuracy as polymer behavior significantly dominates air behavior. The governing equations of the fluid motion are solved with the finite element method on moving mesh, whereas the free surface is captured based on the level set method on another fixed mesh. Since the free surface is captured “implicitly” by the zero level of the level set function, coalescence between filaments is well defined and naturally performed. Numerical algorithm and implementation method are described in detail. This model provides detailed information on the cooling process and the bonding formation during the molten polymer deposition process. The effects of control parameters (nozzle velocity, flow rate and extrusion temperature, etc.) on the final deformed shapes of the printed parts are investigated. And finally, the numerical result from 2D simulations is compared to optical micro-graphs of the longitudinal cross-section of the printed sample, which shows good agreement between numerical and experimental results.

Additive manufacturing of PA12 carbon nanotube composites with a novel laser polymer deposition process

AbstractThe facile manufacture of PA12 MWCNT/silica (50/50 by weight) nanocomposite powders through a high energy mixing process is presented, which are useful to generate 3D objects by a novel Laser Polymer Deposition (LPD) process. The mixing as well as the LPD process led to no discernible changes in the material properties (DSC, SEM, LD) of the core‐shell nanocomposites, enabling the recycling of unconverted powder. The built parts yield ultimate tensile stresses and Young's modulus at 10%–20% of the bulk material. Partially unmolten particles and voids were identified as the main mechanical failure mechanism in the built parts. The mechanical properties are better with low additive content (Young's modulus: 89.8 ± 5.4 MPa; UTS: 12.9 ± 5.3 MPa with 0.25 wt% additives). Electronic conductivity up to the region of moderate conductivity could be achieved by multiwalled carbon nanotube (MWCNT) network formation (8 × 10−4 S cm−1 at 1.25 wt% of additives). A variant of the processing strategy revealed that a higher mechanical strength can be achieved by a laser induced remelting of the traces following their initial construction.

Encapsulation of Low-Molecular-Weight Drugs into Polymer Multilayer Capsules Templated on Vaterite CaCO3 Crystals.

Polyelectrolyte multilayer capsules (PEMCs) templated onto biocompatible and easily degradable vaterite CaCO3 crystals via the layer-by-layer (LbL) polymer deposition process have served as multifunctional and tailor-made vehicles for advanced drug delivery. Since the last two decades, the PEMCs were utilized for effective encapsulation and controlled release of bioactive macromolecules (proteins, nucleic acids, etc.). However, their capacity to host low-molecular-weight (LMW) drugs (<1–2 kDa) has been demonstrated rather recently due to a limited retention ability of multilayers to small molecules. The safe and controlled delivery of LMW drugs plays a vital role for the treatment of cancers and other diseases, and, due to their tunable and inherent properties, PEMCs have shown to be good candidates for smart drug delivery. Herein, we summarize recent progress on the encapsulation of LMW drugs into PEMCs templated onto vaterite CaCO3 crystals. The drug loading and release mechanisms, advantages and limitations of the PEMCs as LMW drug carriers, as well as bio-applications of drug-laden capsules are discussed based upon the recent literature findings.

Fiber-Directed Conjugated-Polymer Torsional Actuator: Nonlinear Elasticity Modeling and Experimental Validation

Existing conjugated-polymer actuators typically take the form of benders or linear extenders. In this paper, a conjugated-polymer-based torsional actuator is proposed by embedding helically wound fibers into a conjugated polymer tube during the polymer-deposition process. Upon actuation, the electrolyte-soaked tube swells, and consequently, produces torsion and other associated deformations because of fiber-induced mechanical anisotropy of the composite material. A nonlinear elasticity-based model is presented to capture the torsion, elongation, and dilation of the tube. Experiments on tubular actuators with different thicknesses, fiber-winding angles, and diameters confirm the aforementioned deformation modes and validate the effectiveness of the proposed model.

Polymeric coating of surface modified nitinol stent with POSS-nanocomposite polymer

Stent angioplasty is a successful treatment for arterial occlusion, particularly in coronary artery disease. The clinical communities were enthusiastic about the use of drug-eluting stents; however, these stents have a tendency to be a contributory factor towards late stage thrombosis, leading to mortality in a significant number of patients per year. This work presents an innovative approach in self-expanding coronary stents preparation. We developed a new nanocomposite polymer based on polyhedral oligomeric silsesquioxanes (POSS) and poly(carbonate-urea)urethane (PCU), which is an antithrombogenic and a non-biodegradable polymer with in situ endothelialization properties. The aim of this work is to coat a NiTi stent alloy with POSS-PCU. In prolonged applications in the human body, the corrosion of the NiTi alloy can result in the release of deleterious ions which leads to unwanted biological reactions. Coating the nitinol (NiTi) surface with POSS-PCU can enhance surface resistance and improve biocompatibility. Electrohydrodynamic spraying was used as the polymer deposition process and thus a few experiments were carried out to compare this process with casting. Prior to deposition the NiTi has been surface modified. The peel strength of the deposit was studied before and after degradation of the coating. It is shown that the surface modification enhances the peel strength by 300%. It is also indicated how the adhesion strength of the POSS-PCU coating changes post-exposure to physiological solutions comprised of hydrolytic, oxidative, peroxidative and biological media. This part of the study shows that the modified NiTi presents far greater resistance to decay in peel strength compared to the non-modified NiTi.

Solid‐State Dye‐Sensitized Solar Cells with Conjugated Polymers as Hole‐Transporting Materials

AbstractDSCs are a promising alternative to conventional silicon‐based solar cells owing to their low cost and relatively high efficiency. However, the utilization of a liquid electrolyte containing the iodine/iodide redox couple in traditional DSCs brings practical problems for their long‐term application, which leads to rapid development of SDSCs based on inorganic p‐type semiconductors or organic HTMs. In this review, we summarize the current research on SDSCs using conjugated polymer as HTM. Special attention is paid to understand the effects of polymer HTM structure and deposition process on SDSC performance. The limiting factors for SDSC energy conversion efficiency are discussed and strategies to improve device performance are proposed. magnified image

Plasma Pretreatment for Polymer Deposition—Improving Antifelting Properties of Wool

Wool substrates of fibers and fabrics were treated with nitrogen plasma under atmospheric pressure or subject to chlorination followed by a polymer deposition process for improving the antifelting property. The antifelting property of wool fibers was assessed by a felting ball test, which revealed that plasma treatment alone could achieve the best antifelting effect, but the hand feel was adversely affected. With the deposition of the polymer on the fiber surface, the antifelting properties were retained with an acceptable hand feel. There was a great improvement in the wettability of the chlorinated and plasma-treated wool fabrics after being qualitatively assessed by wetting time when compared with an untreated fabric sample. The wettability was further quantitatively evaluated through the contact angle measurement with different solvents. The test results showed that the contact angles were reduced implying that the wool surface became more hydrophilic. The SEM pictures showed that a relatively rougher surface was observed for the plasma-treated wool fiber when compared with the chlorinated wool fiber. In addition, X-ray photoelectron spectroscopy (XPS) analysis revealed that there was an increase in oxygen and nitrogen contents of both the chlorinated and plasma-treated wool fibers, which might improve the hydrophilicity of the wool fibers. When the two different surface treatments were compared, the plasma treatment could alter significantly both the physical and chemical surface properties as confirmed by SEM and XPS analyses. However, the chlorination could only alter the surface chemical composition. In conclusion, the improved hydrophilicity of the wool fiber surface by nitrogen plasma could enhance and achieve a better polymer deposition on the wool fiber surface for improving the antifelting properties of wool when compared with the chlorination process.

Development of the flow behavior model for 3D scaffold fabrication in the polymer deposition process by a heating method

The flow behavior model for 3D scaffold fabrication in the polymer deposition process by the heating method was developed for enhanced efficiency of the deposition process. The analysis of the polymer flow property is very important in the fabrication process of precise micro-structures such as scaffolds. In this study, a deposition model considering fluid mechanics and heat transfer phenomena was built up and introduced for the estimation of the fluid behavior of molten polymer. The effectiveness of the simulation model was verified through comparison with the experimental result in the case of PCL biomaterial. In addition, the effects of various parameters, such as pressure, temperature and nozzle size, were predicted through simulation before experimental approaches. Through the fabrication of 3D scaffold, it is concluded that this model is useful in predicting the flow behavior characteristics in the micro-structure fabrication process, which is based on the heating method.

Liquid Polymer Deposition on Free-Standing Microfabricated Parts for Self-Assembly

In this paper, we present a method for the self-assembly of micrometer-scale silicon parts, using a cross-linkable liquid polymer as the intermediate for binding into three-dimensional (3-D) structures. A method to deposit the liquid polymer on free-standing micrometer-scale parts was developed and thoroughly characterized. The polymer deposition was achieved by the following: a) tailoring surface energies of target areas on micrometer-scale parts by formation of self-assembled molecular monolayers; b) suspending the parts in a polymer-solvent solution; and c) gradually forcing the polymer to leave the solution and deposit on areas with lower surface energy by introducing a third liquid miscible with the polymer solvent but not with the polymer itself. The polymer-deposition method presents a unique capability for targeted placement of liquid polymer on micrometer-scale parts after their release from substrates. The polymer-deposition process was modeled considering a precipitation step as a breakup of a polymer thin film into droplets, and considering forces acting on the droplets. The polymer-deposition process on microfabricated and surface energy-tailored templates was studied using normal and high-speed video microscopy. The effect of parameters such as surface energy of template regions, polymer concentration, and size of template regions on the polymer-deposition process was quantified. The observed experimental trends of deposited polymer thickness as a function of polymer concentration were in good agreement with modeling results. We microfabricated 20-100-mum-sized silicon parts, functionalized their surfaces with self-assembled monolayers, employed the polymer-deposition technique to place volumes of a cross-linkable polymer on predefined part areas, and showed their self-assembly into 3-D structures

Progress toward fabrication of graded doped beryllium and CH capsules for the National Ignition Facility

Current ignition designs require graded doped beryllium or CH capsules. This paper reports on the progress toward fabricating both beryllium and CH capsules that meet the current design criteria for achieving ignition on the National Ignition Facility (NIF) [S. Hann et al., Phys. Plasmas 12, 056316 (2005)]. NIF scale graded copper doped beryllium capsules have been made by sputter coating, while graded germanium doped CH capsules have been made by plasma polymer deposition. The sputtering process used for fabricating graded beryllium shells was produced with a void fraction of ∼5%. Varying the deposition parameters can lead to several different beryllium microstructures, which have been tuned to reduce the void size and fraction to within specifications. In addition, polishing of beryllium-coated shells reduces the outer surface roughness of shells to ignition specifications. Transmission electron microscopy has been used to characterize void fraction and grain structure of beryllium coatings. The plasma polymer deposition process has produced dense, void-free graded doped CH shells that nearly meet the ignition surface finish requirements. Layer thickness and dopant concentrations have been measured by quantitative contact radiography.

Polymer film deposition with fine pitch openings by stencil printing

It is confirmed that stencil printing with a novel developed printable polyimide paste can be used for polymer film deposition on LSI wafers. A thick polyimide film with openings for solder ball bumping can be deposited on all of the LSIs on a wafer by stencil printing at one time. This stencil printing process does not need an expensive lithography process, providing cost-effective wafer-level chip scale packages (WLCSPs). In this study, a novel polyimide paste was tailored to have a higher thixotropy ratio than conventional printable polyimide materials. The novel printable polyimide paste shows that the viscosity ratio of more than 3.5 at the shear rate of 1 to 10 s −1 and that the viscosity increases rapidly after the shear rate is lowered. Fine spaces of 40 μm between 250 μm openings were obtained for 10 μm thick polyimide films on Si wafers. It has been also confirmed that the new paste shows the variation range of 30 μm at the opening size of 385 μm within 100 continuously printed wafers. Even after the new paste was shear-thinned repeatedly, rheological behavior of the new paste was not changed. This robustness leads to higher efficiency of the materials for mass-producing. From the reliability viewpoint of the printed polyimide films, no peelings were observed on plasma-CVD SiN films after the pressure cooker test under the condition of 127 °C and 0.25 MPa with the humidity of 100% for 300 h. The optimal stencil printing process using the novel developed paste will lead to significant cost reduction of a patterned polymer deposition process. Finally, WLCSPs using the stencil printing of the new polyimide paste have been demonstrated for SRAM LSIs on 8-in. wafers.

Atomic force microscopy lithography as a nanodevice development technique*

Nanoscale science and technology is today mainly focused on the fabrication of nanodevices. Ourapproach makes use of lithography processes to build the desired nanostructures directly. Thefabrication process involves an electron-beam lithography technique to define metallicmicrostructuresonto which nanometre scale patterning is performed using an atomic force microscope (AFM) as amechanical modification tool. Both direct material removal and AFM-assisted mask patterning areapplied in order to achieve the smallest possible separation between electrode pairs. The samplepreparation involves a polymer deposition process that results in conformal growth and in surfaceroughness comparable to that of the substrate. The results of the application of this technique showthat the process is reproducible and exhibits a good operation control during the lithographic steps,both ensured by the imaging facilities of the AFM. The nanolithography technique has been used tofabricate nanogap electrodes to be used for molecular devices. The study reported here can beconsidered as a reliable starting point for the development of more complex nanodevices, such assingle-electron transistors.

Factors influencing polybutadiene deposition within porous chromatographic zirconia

We have studied the effect of the conditions for the deposition of polymers in the preparation of polybutadiene-coated porous zirconia particles for reversed-phase chromatography. Chromatographic performance improves when the particle surface is pre-coated with elemental carbon by a chemical vapor deposition (CVD) process. Conversely, performance is significantly degraded when the solvent is removed very slowly during the deposition process. No improvement results when the particles are coated using small sequential loads of polymer. We hypothesize that the polymer deposition process is controlled by the rate at which the solvent meniscus recedes during solvent evaporation, by the affinity of the polymer for the zirconia surface, and by polymer–solvent and polymer–polymer interactions.

A Kelvin probe force microscopic study of the local dopant distribution in conducting polybithiophene

Local dopant distribution in electrochemically deposited polybithiophene films as well as the effect of the electrochemical treatment were studied ex situ using the technique of Kelvin probe force microscopy (KFM). The doping-level distribution was found to be directly related to the polymer surface morphology. For the as-grown polymer, most of the doping anodic charge was found to be located at the grain tops. The polymer that was further electrochemically doped featured relatively higher doped grain periphery and less doped grain tops. On the contrary, undoping of the polymer resulted in no pronounced change in the dopant distribution pattern. The effect of the pretreatment of the HOPG support on the properties of the polymer films is also discussed. A model is proposed that relates the observed inhomogeneity to the lateral distribution of the primary polymer nuclei formed during the initial steps of the polymer deposition process. The results suggest that the KFM is a powerful tool for studying dopant distribution in conducting polymers.

Ethylene/ ammonia plasma polymer deposition for controlled adhesion of graphite fibers to PEEK

Quenching and annnealing of polyetheretherketone (PEEK) was performed to study the changes in its physical properties and its interfacial shear strength with AS4 graphite fibers. Physical and mechanical properties of the PEEK matrix were studied using Differential Scanning Calorimetry (DSC) and tensile tests. Plasma polymer deposition of ethylene and ammonia gas mixtures was carried out on the fiber surface to improve the graphite fiber/PEEK matrix adhesion. The adhesion of treated fibers to PEEK was studied using single fiber composite (SFC) tests. Graphite fiber strength were not affected by the plasma polymer deposition process. The SFC tests showed that the interfacial shear strength (IFSS) between graphite fibers treated with ammonia/ethylene gas mixture plasma and PEEK increased by about 84%. However, 100% ethylene plasma deposition, which was strongly hydrocarbon in nature, had no effect on the IFSS. It was found that annealing increases the maximum yield stress, but has no effect on the initial modulus of PEEK. The effect of heat treatment time on the interface strength was also studied. The interface strength increased by a factor of two after the heat treatment.

Immobilization of poly(ethylene oxide) on poly(ethylene terephthalate) using a plasma polymerization process

AbstractPoly(ethylene oxide) (PEO) has been covalently immobilized on poly(ethylene terephthalate) (PET) films using a radio frequency glow discharge polymer deposition process, followed by chemical coupling. Amino or hydroxyl groups were introduced onto the surface of the PET by exposing the films to allylamine and allyl alcohol plasmas. These functional groups were activated with cyanuric chloride, and then they were reacted with PEO. ESCA and water contact angle studies were used to characterize the surfaces of these films during the different stages of the reaction. The films containing the higher molecular weight PEO exhibited an increase in the CO peak of the Cls ESCA spectrum and an increase in oxygen content on the film surfaces. Increasing the molecular weight of the PEO attached to the PET also resulted in an increased wettability of the films.

Hollow cathode etching and deposition

The hollow cathode has yielded high-rate low-pressure operation, with good etch selectivity and etched angle control. This paper shows that high SiO2 etch selectivity is most easily obtained at low pressure in the CF4/H2 process. The etched angle is controlled by metal film deposition which can be independent of the etch selectivity. A combined (metal+polymer) deposition and SiO2 etch process has been tested on commercial complementary metal–oxide semiconductor wafers with excellent yield and reliability results. This multiple deposition and etch process is best done in a new trielectrode hollow cathode chamber which exhibits 1 μm/min SiO2 etch rate with better than ±1% etch uniformity, an etched angle of ∼75°, and SiO2/Si selectivities of 50 (wafer edge) and 150 (wafer center). In addition, polymer deposition on surfaces near the wafer has been eliminated. The voltage and pressure dependence of Si deposition from SiH4 is described, and the hollow cathode ion bombardment is shown to give best planarization at low pressures (2 Pa) and low deposition rates (0.2 μm/min). A planarized SiO2 film is also shown.

Microfabrication Technologies for Advanced VLSI Devices

ABSTRACTRecent progress in microfabrication technologies for advanced VLSI devices, such as 16M and 64MDRAM, is presented. First, an EB delineator with a vector-scanned VSB on a moving stage has been developed for printing 0.25 μm patterns employing PMMA, high dose exposure, and 50 KeV EB. Optical lithography also has been extended toward lower submicron geometry. A Krf excimer laser reduction projection system, using a quartz/CaF2 lens, resolves successfully 0.35 μm patterns. Ga field ion beam technology has been developed with new applications in fuse-cutting of redundancy and in optimizing sense amplifier by cutting transistor gates in the SRAM device. For fine line etching technology, collimated reactive ions produced by 10−3 Torr magnetron discharge achieves deep Si trench etching and tapered Al etching by using a polymer deposition process in addition to the original thin sidewall film. Finally, a damage-free excimer laser etching process has been developed which can etch n+ poly-Si with resist mask and with pattern transfer using an optics down to 0.5 μm and 0.9 μm resolutions respectively.

Microfabrication Technologies for Advanced VLSI Devices

AbstractRecent progress in microfabrication technologies for advanced VLSI devices, such as 16M and 64MDRAM, is presented. First, an EB delineator with a vector-scanned VSB on a moving stage has been developed for printing 0.25 μm patterns employing PMMA, high dose exposure, and 50 KeV EB. Optical lithography also has been extended toward lower submicron geometry. A Krf excimer laser reduction projection system, using a quartz/CaF2 lens, resolves successfully 0.35 μm patterns. Ga field ion beam technology has been developed with new applications in fuse-cutting of redundancy and in optimizing sense amplifier by cutting transistor gates in the SRAM device. For fine line etching technology, collimated reactive ions produced by 10-3 Torr magnetron discharge achieves deep Si trench etching and tapered Al etching by using a polymer deposition process in addition to the original thin sidewall film. Finally, a damage-free excimer laser etching process has been developed which can etch n+ poly-Si with resist mask and with pattern transfer using an optics down to 0.5 μm and 0.9 μm resolutions respectively.