Search

Metal injection moulding of miniaturized devices demands unique feedstock materials and mould designs with high dimensional accuracy. In this work, the influences of the powder size and powder content of 17–4 PH stainless steel feedstock and the influence of mould design on the successful production of micro-scaled structures were investigated. Ni mould inserts with high dimensional accuracy and texture sizes of 50–200 μm using a new microtexturing technique were manufactured. 17–4 PH stainless steel feedstocks with powder sizes (D90) of 10 and 22 μm and powder contents of 60 and 65 vol.-% were compounded. The rheological properties of the obtained feedstocks were characterized with a capillary rheometer to assess their flowability. The results showed that 10 μm sized particles caused a slight but not significant increase in the viscosity. The highest viscosity increase occurred when the powder content increased from 60 to 65 vol.-%. Feedstocks with the 10 μm powder particles ensured complete filling within microtextures for all mould variations. However, when using feedstocks with 22 μm particles, the filling capabilities of the 50 and 100 μm microtextures decreased with increasing powder content. The shape retention was better for those micropillars produced with mould inserts with 200 μm cavities than for the micropillars replicated with the inserts having cavities of 50 and 100 μm. The results indicated that the proposed mould insert preparation technique opens new possibilities for mass production using the μMIM process to create micro-scaled components using feedstocks without nanoparticles.

The main target in this study was to increase adhesion of unsaturated polyester (UP) adhesive to aluminum by structuring the aluminum surface on the microscale and nanoscale as well as by f...

The ice friction behavior of various microtextured polymer surfaces was studied with respect to ice temperature and applied load using a customized linear tribometer. Similar micropillar patterns were replicated on polypropylene and two rubber compounds, and when hierarchical micro–micro textures were present, all the materials exhibited superhydrophobicity. Taller protective micropillars were shown to be crucial for protecting the smaller microtextures from abrasive wear. The mechanical properties of the polymers affected the sliding friction of the microtextured surfaces on ice. High loading of hierarchical textures on rigid polypropylene or operation near the ice melting point tended to increase its adhesion tendency or resisting behavior. The sliding performance of the hard and soft rubber compounds was temperature-dependent, and the texture on the soft rubber influenced the sliding friction differently depending on the ice temperature. Consequently, textural modifications of the sliding surface enabled a certain degree of control over the sliding friction behavior on ice.

Surface texturing with lubricant mixtures was studied by dynamic coefficient of friction (COF) values on micropit and micropillar WC-Co hard metal specimens that were fabricated using a micro-working robot technique combined with metal injection molding (MIM). Lubricating grease mixed with MoS2 was investigated, and 40 wt% additive level of MoS2 reduced COF values by 45% down to 0.06 level on flat WC-Co specimens. The corresponding COF values for the micropit specimens were higher up to 0.10 that may result from the small contact area of the used pin. On the contrary, a reduction of COF values was observed for micropillar specimens compared to the flat WC-Co specimens induced by a load carrying structure of the micropillar specimen. A highly stable antiwear behavior was observed for specimens with micropits.

The main target in the study of aluminum-epoxy resin joints was to enhance adhesion by increasing the surface area of aluminum substrates and by chemical functionalizing the aluminum surface to provide coupling points for epoxy resin. The surface area of the aluminum substrates was increased by fabricating microscale structures and hierarchical micro-microstructures by utilizing a micro-mesh printing technique and sandblasting. The effects of silanization with 3-glycidoxypropyltrimethoxysilane (GPTMS) and of oxygen plasma treatment were also investigated. Compared to a smooth surface, the micro-mesh structures improved shear strength by 33% and the hierarchical micro-microstructures by 116%. The utilization of the oxygen plasma treatment and especially the silane modification of the aluminum substrates were found to be effective in promoting adhesion. The specimens modified by combining the chemical or energetic modification method with surface texturing tended to fracture more cohesively than the specimens having a single modification. The hierarchically patterned and plasma and silane modified specimens had so high adhesion that the aluminum substrates started to deflect during the shear strength measurements, thus preventing the evaluation of their maximum strength.

The purpose of this work is to study dry sliding frictional properties of a polymer pair consisting of two commonly used engineering polymers: polybutylene terephthalate (PBT) blended with PTFE and polyoxymethylene (POM). A reciprocating pin-on-flat tribometer was employed to measure the maximum initial and dynamic friction coefficients (COF). All the specimens were used as obtained from injection molding, without any abrasive pretreatment. A sufficient repeatability of the results was achieved by using a PBT pin with a spherical tip. The influence of the applied load (1, 5, 10 and 20 N) and the sliding speed (10, 30 and 50 mm/s) on the frictional performance of PBT+PTFE pin sliding against POM was examined. Frictional heating was measured with an infrared camera and the obtained temperature rises were compared with the values predicted by three analytical frictional heating models. The results showed that both the maximum initial and dynamic friction coefficients were strongly affected by the applied load. Up to 50% reduction in the values of COFs was observed by increasing load from 1 to 20 N. The electron microscopy results of the worn surfaces indicated that the decrease in friction at higher loads could be due to softening of the PBT pin by frictional heating.

Macro-scale surface patterns are often used with tool and working surfaces to improve gripping, sliding or other working abilities. Polyacetal (POM) samples possessing micron-scale surface structures were examined to determine effects of micro-scale patterning on the sliding friction and wear rate of POM surfaces. The micro-patterned samples were manufactured via injection molding and their friction/wear behaviors were compared to those of identically micro-patterned polypropylene (PP) surfaces. Polymer surfaces were slid against polished steel using a reciprocating pin-on-disk type measuring system. The wear and friction properties of the patterned polymers were studied as functions of surface pressure, induced by loads and pattern densities applied. For both materials, the wear rate was found to diminish with increasing surface pressure and the wear mechanism to resemble extrusion, producing flake-like particles. Dynamic friction levels were found to correlate with surface pressure, the micro-pattern having a distinct effect on friction with low loads. Both POM and PP were found to possess a friction minimum in the surface pressure range of 0.5–1.0 MPa, which is attainable by adjusting either the used load or the density of micro-patterns.

In this paper, the results of exploiting self-organized sub-micron polystyrene (PS) wrinkle patterns possessing random orientation, in preparation of a nickel stamp for hot embossing purposes, are presented. Self-organized patterns were prepared employing a method in which a stiff cross-linked capping layer on the topmost part of the soft polystyrene layer was created by using reactive ion etching (RIE) device with mild conditions and argon as a process gas, and the wrin- kle formation was initiated thermally. Different surface patternings were obtained using silicon and stainless steel (SST) wafers as substrates. Prepared Ni-stamps were employed in hot embossing of polycarbonate (PC) and cyclo-olefin polymer (COP) films, using a nano-imprinting process. The replication quality of the self-organized wrinkle structures in PC and COP films was monitored by comparing the shape and dimensions of the original and final surface structures. The hot embossed sub-micron scale features, originally formed on stainless steel substrate, were found to have influence on the optical properties of the PC and COP films by lowering their reflectances.

While the conventional photomask technique gives only two-dimensional anisotropies, in this study we fabricated microstructured polymer surfaces with a selective three-dimensional anisotropy. With the applied removable mesh, we were able to confine the contacting area between the surface and photoinitiator and provide three-dimensional wettability anisotropies. Different types of meshes were used depending on the desired micropatterns shape, size and substrate material. The results revealed the three-dimensional anisotropic micropits pattern with depth profiles, which would be applicable for the confinement and patterning of cells and biomolecules. In addition, the proposed method is applicable for creating selectively activated polymer surface as a substrate for further atomic layer deposition. Moreover, we demonstrate a low cost and fast mass productive method for patterning a viscous polymer liquid in a micro-sized scale.

Polypropylene/viscose fiber (PP/VF) composite with a surface pattern consisting of periodic, micro-scale cylindrical pillars were manufactured and the effect of fiber loading and micro-patterning on the friction and wear properties of the composites was studied. The micro-patterned viscose fiber composite surfaces were prepared via melt compounding and injection molding. SEM studies showed that the fiber dispersion within the micro-bumps was influenced by the fiber loading and high aspect ratio (300–1200) of viscose fibers. With higher fiber loadings the fiber content of the micro-bumps was prominently higher than with lower fiber loadings of the composites. The wear and friction behavior of the patterned composite series were evaluated by sliding the fabricated surfaces against rough and smooth steel surfaces with a pin-on-disc type tribometer. It was noted especially in the case of a smooth counter surface that while both high fiber content and sparse micro-bump coverage individually decreased the sliding friction, their synergetic effect produced a dramatic drop in friction coefficient.

Bioelectrode–skin contact impedances need to be minimized to enable high quality recordings of biopotentials. Low contact impedances can be achieved with large, effective bioelectrode–skin contact areas. In this study, novel dry microstructured electrodes based on electrically conductive liquid silicone rubber (LSR) were developed and characterized with electrical impedance spectroscopy (EIS) measurements. Two different micropillar structures with inter-pillar distances of 20 μm and 100 μm, respectively, were compared with smooth LSR electrodes, as such or coated with silver (Ag). A gelatin gel based skin model was used in EIS measurements to overcome the problems associated with real skin measurements. Both microstructurings were found to significantly decrease the contact impedance modulus. In addition, the Ag coating caused highly significant ( p

This study focuses on design and fabrication of new UV-curable polyurethane acrylate submicron-structured coatings that have anti-reflective and anti-wettable surface properties. The coatings were replicated on PMMA substrates with use of a pair of nickel molds containing complementary surface patterns of submicron-sized pillars or pits in a cubic grid. The period of the square-shaped mold features was 270nm and the height/depth of the grating features was 110nm. The influence of the chemical composition and the replication accuracy on optical properties was examined by UV-Vis spectroscopy and variable angle spectroscopic ellipsometry. The UV-cured coatings showed a 1.5% reflectance between 400 and 700nm of the visible spectral region. Transmittance was increased from 91% to 94% when the submicron-structure was copied onto the surface. Furthermore, the investigation of static and dynamic wetting of the coatings with water or oleic acid demonstrated that the sub-micron structure and chemical modification with fluoroalkylsilane significantly improved the water and oil resistance of the prepared coatings. Especially for pit-covered coatings, the static water contact angle increased to 146^o and the highest advancing/receding contact angles for water were 150^o/119^o.

Considerable attention is currently being devoted less to the question of whether it is possible to produce superhydrophobic polymer surfaces than to just how robust they can be made. The present study demonstrates a new route for improving the mechanical durability of water-repellent structured surfaces. The key idea is the protection of fragile fine-scale surface topographies against wear by larger scale sacrificial micropillars. A variety of surface patterns was manufactured on polypropylene using a microstructuring technique and injection molding. The surfaces subjected to mechanical pressure and abrasive wear were characterized by water contact and sliding angle measurements as well as by scanning electron microscopy and roughness analysis based on optical profilometry. The superhydrophobic polypropylene surfaces with protective structures were found to maintain their wetting properties in mechanical compression up to 20 MPa and in abrasive wear tests up to 120 kPa. For durable properties, the optimal surface density of the protective pillars was found to be about 15%. The present approach to the production of water-repellent polymer surfaces provides the advantages of mass production and mechanical robustness with practical applications of structurally functionalized surfaces.

We report results of preparation of wrinkled polystyrene (PS) surfaces on silicon substrate employing two different methods, solvent-assisted wrinkling (SAW) and thermal wrinkling (TW). In both methods an argon (Ar) plasma treatment of PS/silicon bi-layer by reactive ion etching (RIE) was used for creation of cross-linked PS layer acting as a capping layer. In SAW method the layered system was exposed after the plasma treatment to solvent vapor and in TW method the layered system was heated above the glass-transition temperature of PS employed. Wave-like patterns were achieved with the both initiation methods and using the two polystyrenes having different molar masses. The plasma treatment time was found to have influence on the wrinkle formation by affecting the thickness of the cross-linked part of PS layer, and influencing slightly the dimensions of the wrinkles. The molar mass of PS was found to have effect on overall size-scale of the forming patterns. Moreover, employing TW as a wrinkling method yielded somewhat higher wrinkles.

A comparative study was made to find out how two cellulose based micron-sized fillers affect the morphological, thermal, and mechanical properties of high density polyethylene (HDPE). The fillers used in this study were commercial microcrystalline cellulose (MCC) and viscose fibers (filler content of 5, 10, 20 and 40 wt.%). The composites were prepared by melt mixing using maleic anhydride grafted polyethylene (PEgMA) as a polymeric compatibilizer in order to improve the chemical compatibility of the fillers and the matrix. SEM images of the composites revealed that the PEgMA improved adhesion between the cellulose fillers and the HDPE matrix. Cellulose was found to have a clear effect on the thermal dimensional stability of the HDPE. The viscose fibers and the MCC decreased the coefficients of the linear thermal expansion (CLTE) of the HDPE matrix in the flow direction, CLTEs (at 25 °C) as low as 37 ppm/°C (40 wt.% of viscose fiber) and 79 ppm/°C (40 wt.% of MCC) were achieved for the composites compared to 209 ppm/°C for the HDPE. The Young’s modulus and the tensile strength of the HDPE significantly increased and elongation at break decreased with a filler content. Enhanced adhesion in the presence of the PEgMA increased the mechanical properties of the composites, especially tensile strength. The highest values for Young’s modulus and tensile strength, and the lowest values for CLTE in the flow direction were achieved with the viscose fibers. The measured Young’s moduli for the viscose fiber composites were compared to those calculated by composite theories. The Halpin–Tsai composite theory successfully predicted the elastic moduli for the viscose fiber composites.

The morphological, mechanical, thermal, and tribological properties of high-density polyethylene (HDPE) composites reinforced with organo-modified nanoclay (3 and 6 wt%) were studied. A commercial maleic anhydride-based polymeric compatibilizer (PEgMA) was used to improve the adhesion between the polyethylene and clay. Transmission electron microscopy (TEM) characterization of composites revealed that nanoclay exists mainly in a multilayered structure in the HDPE matrix. Mechanical testing of composites showed that Young's modulus and tensile strength increased with nanoclay content. Coefficients of the linear thermal expansion (CLTE) of HDPE–PEgMA–clay composites were slightly lower in the flow direction than those of HDPE–PEgMA. The tribological properties were measured in dry conditions against a steel counterface. The friction coefficient of the matrix was decreased by the addition of clay. Electron microscopic results suggested that the wear mechanism for HDPE and HDPE composites was mainly adhesive. Clay agglomerates were observed on the worn surfaces of the composites, which may partly explain decreased friction. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

The influence of well-defined periodic micro-scale pillars on the friction and wear behavior of polypropylene (PP) surfaces was examined in dry sliding against roughened steel surfaces. The steel surfaces were linearly ground, allowing monitoring of the difference in friction when samples passed over the grooves and ridges of the steel surface in perpendicular and parallel directions. Micro-scale patterns with different surface coverage (SC) on the PP surface were produced by preparation of micro-depressions on aluminum foil and subsequent use of the foils as mold inserts in injection molding. The effects of the patterning on friction and wear of the PP surface were evaluated as a function of surface coverage of the micro-pillar features. The friction behavior in sliding of the patterned PP against steel surfaces was affected by the micro patterns. The coefficient of friction (COF) was slightly lower for the less densely patterned surfaces than the unpatterned PP. The COF increased with further SC. Patterning reduced the noise of the COF curves of the micro-patterned surfaces. Wear of the PP surface was strongly affected by the percentage of surface covered by the micro bumps. Scanning electron microscopy studies of the contact surfaces revealed that the transfer layer between PP and the steel surface evolved at different rates for perpendicular and parallel passing direction.

New approaches to the fabrication of microstructures of special shape were developed for polymers. Unusual superhydrophobic surface structures were achieved with the use of flexible polymers and hierarchical molds. Flexible polyurethane−acrylate coatings were patterned with microstructures with use of microstructured aluminum mold in a controlled UV-curing process. Electron microscope images of the UV-cured coatings on polymethylmethacrylate (PMMA) substrates revealed micropillars that were significantly higher than the corresponding depressions of the mold (even 47 vs. 35 μm). The elongation was achieved by detaching the mold from the flexible, partially cured acrylate surface and then further curing the separated microstructure. The modified acrylate surface is superhydrophobic with a water contact angle of 156° and sliding angle of Acrylic thermoplastic elastomers (TPE) were patterned with micro−nanostructured aluminum oxide molds through injection molding. The hierarchical surface of the elastomer showed elongated micropillars (57 μm) with nail-head tops covered with nanograss. Comparison with a reference microstructure of the same material (35 μm) indicated that the nanopores of the micro−nanomold assisted the formation of the nail-shaped micropillars. The elasticity of the TPE materials evidently plays a role in the elongation because similar elongation has not been found in hierarchically structured thermoplastic surfaces. The hierarchical micronail structure supports a high water contact angle (164°), representing an increase of 88° relative to the smooth TPE surface. The sliding angle was close to zero degrees, indicating the Cassie–Baxter state.

A multilayer photocatalytic TiO 2 coating on a high-density polyethylene (HDPE) disk was found to degrade aqueous methylene blue in a batch reactor study. The TiO 2 coating was fabricated by a low-temperature method using polyurethane resin (PU) as a barrier layer for HDPE and as a binding agent for two TiO 2 layers. Adequate adhesion between the HDPE substrate and PU barrier in aqueous environment was ensured with an oxygen plasma treatment. The photocatalytic effect of immersed TiO 2 coating on the degradation of methylene blue in aqueous solution was monitored by UV–vis spectrometry as a function of UV-illumination time. Samples were allowed to adsorb methylene blue in the dark for 1 h before the UV-degradation experiments were started. The percentages of methylene blue degraded during 6 h UV illumination ( λ = 365 nm) varied from 80% to 92%. The degradation followed pseudo-first order reaction kinetics, and the observed rate constants ( k obs ) were between 0.27 and 0.43 h −1 .

Study was made of the effect of multiwall carbon nanotubes (MWCNTs) and polymeric compatibilizer on thermal, mechanical, and tribological properties of high density polyethylene (HDPE). The composites were prepared by melt mixing in two steps. Carbon nanotubes (CNTs) were melt mixed with maleic anhydride grafted polyethylene (PEgMA) as polymeric compatibilizer to produce a PEgMA–CNT masterbatch containing 20 wt% of CNTs. The masterbatch was then added to HDPE to prepare HDPE nanocomposites with CNT content of 2 or 6 wt%. The unmodified and modified (hydroxyl or amine groups) CNTs had similar effects on the properties of HDPE–PEgMA indicating that only non-covalent interactions were achieved between CNTs and matrix. According to SEM studies, single nanotubes and CNT agglomerates (size up to 1 μm) were present in all nanocomposites regardless of content or modification of CNTs. Addition of CNTs to HDPE–PEgMA increased decomposition temperature, but only slight changes were observed in crystallization temperature, crystallinity, melting temperature, and coefficient of linear thermal expansion (CLTE). Young’s modulus and tensile strength of matrix clearly increased, while elongation at break decreased. Measured values of Young’s moduli of HDPE–PEgMA–CNT composites were between the values of Young’s moduli for longitudinal (E11) and transverse (E22) direction predicted by Mori-Tanaka and Halpin–Tsai composite theories. Addition of CNTs to HDPE–PEgMA did not change the tribological properties of the matrix. Because of its higher crystallinity, PEgMA possessed significantly different properties from HDPE matrix: better mechanical properties, lower friction and wear, and lower CLTE in normal direction. Interestingly, the mechanical and tribological properties and CLTEs of HDPE–PEgMA–CNT composites lie between those of PEgMA and HDPE.

Degradation of a heat cured polyurethane (PU) dispersion was studied on BK7 glass substrates coated with titanium dioxide. Two titanium dioxide layers on the substrate were bound with waterborne polyurethane dispersion that was diluted with water and then cured. Four dilutions (PU dispersion/H 2 O mass ratios of 1:12, 1:8, 1:4, and 1:2) were tested. The study showed that TiO 2 photocatalysis causes polyurethane to degrade as a function of UV-illumination time. Degradation of polyurethane was analyzed by FTIR-ATR, surface electron microscopy imaging and gravimetric analysis. Both the FTIR method and gravimetric analysis showed the degradation of polyurethane to follow pseudo-first-order reaction kinetics. The reaction rate constants determined for degradation of polyurethane at dilution 1:4 were k obs = 0.021 h −1 by FTIR-ATR and k obs = 0.0023 h −1 by gravimetric analysis. Gravimetric analysis indicated that the rate of degradation is slower when the amount of polyurethane is increased (dilution 1:2 k obs = 0.0013 h −1 ). This is because the titanium dioxide becomes covered by polyurethane, as verified by SEM imaging. When both the photocatalytic efficiency of TiO 2 in self-cleaning coatings and the binding of titanium dioxide to the substrate are important, all three analytical methods suggest that the optimal dilution of PU binder is 1:4.

Anisotropic surfaces with micropillar- or micropillar/nanobump structures and anisotropic wetting behavior were fabricated. Structures were arranged as three parallel zones where the structure of the middle zone differed from that of the edge zones. The widths of the middle zones were increased systematically, and the effects of the middle zone structures and widths on the contact and sliding angles of water were investigated. Structures were fabricated on PP by injection molding. Microstructured mold inserts for injection molding were obtained by structuring aluminum foils with a microworking robot, and hierarchically structured mold inserts by anodizing the microstructured foils. It was possible to create surfaces where the microstructure in the middle zone was lower or higher than on the edges, or where the middle zone had only nanostructure or was unstructured. The behavior of water on the surfaces was characterized by measuring the dynamic contact angles and sliding angles parallel and perpendicular to the zones. Hydrophobic surfaces were achieved. With appropriate middle zone widths, clearly differing parallel and perpendicular contact angles were measured and elongation of droplets along the middle zones was detected.

Micropit surfaces and hierarchically structured micropit/nanodepression surfaces were fabricated in polypropylene by injection moulding. The first step in the process was the microstructuring of aluminium foils with a micro-working robot to obtain a pattern of micropits. Dimensions of the micropits could be controlled by adjusting the working parameters of the robot. The microstructured faces of some of the foils were anodized to aluminium oxide giving a surface in which both micropits and the smooth areas between were covered with nanopores. Mould inserts for the injection moulding were obtained by cold mounting of an epoxy resin mixture on the foils. After the epoxy resin had hardened, the foils were etched away. Dimensions of the micropillars and micropillars/nanobumps on the epoxy related to the dimensions of the structures on the foils. Finally, structures were replicated in polypropylene as micropits and hierarchical micropits/nanodepressions by injection moulding. The dimensions of these hollow structures corresponded well with those of the epoxy pillars and the original micropits. Static and dynamic contact angles on the micropit-structured polypropylene surfaces were elevated from the slightly hydrophobic values of smooth polypropylene. With hierarchical micropit/nanodepression structures, the contact angles approached the superhydrophobic limit of 150°. The work demonstrates an inexpensive and reproducible technique to fabricate hollow structures of various dimensions and scales on polypropylene and modify the surface properties of the polymer.

Anisotropically microstructured and hierarchically micro/nanostructured surfaces were fabricated on polypropylene by injection moulding. Microstructured mould inserts were obtained by structuring electropolished aluminium foils with a micro-working robot, and hierarchically structured mould inserts by anodizing the microstructured aluminium foils. On both types of inserts, the microstructures were anisotropic, consisting of alternating smooth and microstructured zones. Anisotropy, and other properties of microstructures, can be controlled by adjusting the parameters of the micro-working robot. The mould inserts were used to prepare micro- and hierarchically structured polypropylene discs by injection moulding. Replication accuracy at both structure levels can be controlled through the moulding conditions. The behaviour of water on the structures was characterized by measuring the contact and sliding angles parallel and perpendicular to the microstructured zones. Surfaces with microstructures alone were highly hydrophobic, where water droplets adopted the Wenzel state and had clearly different parallel and perpendicular contact angles. Surfaces with dual structures had contact angles near 170° and sliding angles near 0°, and again the angles in parallel and perpendicular directions differed. Superhydrophobic, anisotropic Cassie–Baxter state was achieved.

A photocatalytic self-cleaning titanium dioxide (TiO2) coating was prepared as a multilayer coating structure by the spin-coating method. Three substrate materials (two thermoplastics and one ceramic) were used: (1) high-density polyethylene (HDPE), (2) poly(vinyl chloride), and (3) borosilicate glass (BK7). The multilayer structure consisted of a polyurethane protective layer on the substrate, two layers of photocatalytic TiO2 on the protective layer, and finally immobilized TiO2 particles bound in a diluted polyurethane dispersion. Photocatalytically active surfaces were achieved by reactive oxygen-plasma surface etching of the fabricated coatings. The structure and properties of the coating surfaces were characterized with scanning electron microscopy and contact-angle measurements. The coatings on HDPE and BK7 were rendered superhydrophilic by an oxygen-plasma treatment. The photocatalytic activity and self-cleaning properties of the prepared surfaces were studied with palmitic acid (model soil), the degradation of which was confirmed by contact-angle measurements and gas chromatography analysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Nanostructured coatings increase the transmittance and decrease the reflection of polycarbonate (PC). In this work, nanoporous anodized aluminum oxide (AAO) coating was formed electrochemically on a PC surface. The reflection properties of the AAO-coated PC were modified by varying the thickness of the AAO layer, the anodization parameters, and the pore size of AAO. Transmittance and reflection were measured by ellipsometry. The optical transmittance of the AAO film on PC was 86–94% in the wavelength range 420–780 nm, which was about four percentage units higher than the transmittance of uncoated PC. The minimum reflection of 0.2% was observed for PC with an AAO coating of 177 nm. The reflection was about five percentage units less than the corresponding value for uncoated polycarbonate. Nanoporous surfaces and profiles of AAO were characterized by Scanning Electron Microscope.

To enhance their surface properties, micro-injection mold inserts made of electroplated nickel were coated with thin films of molybdenum nitride and tungsten nitride by atomic layer deposition. Alkylimido–alkylamido complexes were used as precursors together with ammonia. In addition, a perfluorinated hydrophobic coating was deposited by gas-phase method from tridecafluoro-1,1,2,2-tetrahydrooctylmethyl-bis(dimethylamido)silane. Injection molding tests were performed with two plastic materials: poly(4-methyl-1-pentene) copolymer TPX™ and polycarbonate Makrolon® DP1-1265. With both plastics, the nickel insert with thin film of molybdenum nitride was clearly more resistant to contamination than the uncoated insert. Also the perfluorosilane coating provided good resistance to contamination. After the 15,000 shot injection molding test, all of the coatings were still attached to the insert. Friction coefficients were determined between the nitride and silane coatings and the plastic materials. The coatings showing good contamination resistance in injection molding also had a low coefficient of friction.

Small plastic components with sub-micron and micron gratings for diffractive optics were prepared by micro-injection molding. The aim of the work was to improve the filling of binary diffractive gratings with high aspect ratio by varying the molding parameters. Tests were made under conventional processing conditions with four transparent thermoplastics: polycarbonate (PC), cyclo-olefin polymer (COP), styrene–acrylonitrile copolymer (SAN), and hexafluoropropylene–tetrafluoroethylene–ethylene terpolymer (HFP–TFE–Et). Melt and mold temperatures were kept as recommended by the manufacturer. Other molding parameters (injection speed, shot size, vacuum, holding pressure, and injection plunger diameter) were varied, and their effect on the profile of the gratings was measured by atomic force microscopy. The filling of the gratings (500 nm and 1000 nm) was clearly affected by injection speed, shot size, and injection piston diameter, but the most significant factor was the type of material. Replication fidelity was highest with PC and lowest with SAN.

Superhydrophobic polyolefin surfaces were prepared by simultaneous micro- and nanostructuring. Electropolished aluminum foil was microstructured with a micro working robot and then anodized in polyprotic acid. The surface microstructure can be tailored by adjusting the settings of the micro working robot and the nanostructure by adjusting the parameters of the anodization procedure. Surface structuring was done by injection molding where a microstructured anodized aluminum oxide mold insert was used to pattern the surfaces. Structuring had a marked effect on the contact angle between the injection-molded polyolefins and water. When the optimized microstructure was covered with nanostructure, the static contact angle between polypropylene and water obtained a value of about 165 degrees and the sliding angle decreased to about 2.5 degrees. The superhydrophobic state was achieved.

Cycloolefin copolymer (COC) and poly(vinyl chloride) (PVC) surfaces were patterned with nanopillars or with microbumps on which nanopillars were superimposed. The area of patterned surfaces was several square centimeters. Patterning was achieved by applying nanoporous anodized aluminum oxide (AAO) membrane as a mask in injection molding or imprinting. Nanostructures superimposed on microstructures were achieved by patterning the AAO mask with microstructures before anodization. Micro- and nanometer-sized structures could then be transferred simultaneously to polymer surfaces. Structures were characterized by SEM, AFM, and contact profilometry. The effect of different-sized structures on properties of the polymer surface was studied by contact angle measurements. Relative to the smooth surface, the increase in water contact angle on a COC surface with nanostructures superimposed on microstructures was up to 50°.

Diamond-like, tetrahedrally bonded amorphous carbon (ta-C) coating was used to enhance the wear resistance of laboratory-made microstructured poly(vinyl chloride) (PVC) surfaces. Formulation of PVC samples was kept simple; they contained only stabilizer and plasticizer added to PVC. Two sizes of microstructures were imprinted on PVC. Both smooth and microstructured PVC surfaces were coated with amorphous diamond and the surfaces were characterized by spectroscopic ellipsometry, AFM and contact profilometry. In addition, water contact angles were measured. The plasticizer, plasticizer concentration and amorphous carbon coating affected the topography of the microstructure and the water contact angles on surfaces. The ta-C-coated microstructured surfaces were worn with a soiling and wearing drum tester to study their wearing behavior. Surface topographies were measured with a profilometer after wearing studies.

A quantitative radiochemical measuring procedure was used to investigate soil adhesion on laboratory-made polyvinyl chloride (PVC) surfaces. The materials contained different plasticizers and microstructures. Both the quality and amount of plasticizers and the microstructure affected the cleanability of the PVC samples. The surface topography and structures were examined with a contact angle meter, atomic force microscopy (AFM) and a contact profilometer.

The purpose of this work was to study how viscose fiber behaves in polypropylene (PP) matrix when maleated polypropylene (MAPP) is used as a coupling agent. The influences of processing conditions on composite properties was of interest. Composites were characterized by FTIR and mechanical testing. The most notable result was the effect of the MAPP concentration on the tensile strength of the composites; the tensile strength increased from 40 to 69 MPa when MAPP was added in amounts up to 6 wt % of the fiber weight. The interaction between MAPP and fiber was confirmed with FTIR. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1895–1900, 2003

The reinforcement mechanics of viscose-fiber-reinforced polypropylene (PP) composites were studied. The effect of the coupling agent, maleated polypropylene (MAPP), was of special interest. The fibers, coupling agent, and PP were extruded and injection-molded. The composition, mechanical properties, fracture morphology, and dispersion of the composites were examined. Thermogravimetric analysis showed that the fiber content in the tensile specimens varied slightly with the sample location; however, the differences in the values were within 1.0%. Scanning electron microscopy images of the fracture surfaces of the composites showed that the surfaces of the composites without MAPP were covered with fibers pulled out from the matrix. A lack of adhesion further appeared as a cracked matrix–fiber interface. A new scanning thermal microscopy method, microthermal analysis, was used to study the dispersion of the fibers in the composites. Local thermal analyses gave further information about the location of the fibers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2676–2684, 2004

A dynamic test method for the measurement of the underwater sliding properties of model boats has been developed. Surface-modified model boats were examined to assess how the surface wettability properties affect sliding. Along with the surface properties, the influence of the boat shape was considered. We studied various coatings in the contact angle range of 3–162[Formula: see text] with two model boat shapes. The hydrophobicity of the surfaces influenced the sliding speed of the model boat depending on the boat shape. The method is applicable to study sliding properties of model boats with different surfaces in variable flow conditions.

In this paper, the wettability properties of coatings with hierarchical surface structures and low surface energy were studied. Hierarchically structured coatings were produced by using hydrophobic fumed silica nanoparticles and polytetrafluoroethylene (PTFE) microparticles as additives in polyester (PES) and polyvinyldifluoride (PVDF). These particles created hierarchical micro–nano structures on the paint surfaces and lowered or supported the already low surface energy of the paint. Two standard application techniques for paint application were employed and the presented coatings are suitable for mass production and use in large surface areas. By regulating the particle concentrations, it was possible to modify wettability properties gradually. Highly hydrophobic surfaces were achieved with the highest contact angle of 165[Formula: see text]. Dynamic contact angle measurements were carried out for a set of selected samples and low hysteresis was obtained. Produced coatings possessed long lasting durability in the air and in underwater conditions.

While surface patterns are effective in improving tribological properties, nevertheless they alter the surface wettability, which will in turn affect the surface–lubricant interactions. When there is a shortage of lubricant on a patterned surface, the lubricant stored inside the cavities will be extracted to compensate the surface lubricant dissipation. Additionally, the lubricant retention effect provided by the cavities is competing with the release of the lubricant. With weak surface–lubricant interaction, the retention is limited. Therefore, the lubrication will have a sudden failure, giving a dramatic transition to abrasive wear. To improve the performance of polar lubricants on hydrophobic polymer surfaces, both topographical and selective surface modifications were incorporated on injection molded polypropylene surfaces. Distinctive lubrication improvement was observed when the surface structure density for the lubricant storage was high, and the release of the lubricant was controlled by the interaction with the selectively modified surfaces.

The adhesion and contact guidance of human primary osteogenic sarcoma cells (Saos-2) were characterized on smooth, microstructured (MST) and micro- and nano-structured (MNST) polypropylene (PP) and on the same samples with a silicon-doped carbon nitride (C(3)N(4)-Si) coating. Injection molding was used to pattern the PP surfaces and the coating was obtained by using ultra-short pulsed laser deposition (USPLD). Surfaces were characterized using atomic force microscopy and surface energy components were calculated according to the Owens-Wendt model. The results showed C(3)N(4)-Si coated surfaces to be significantly more hydrophilic than uncoated ones. In addition, there were 86% more cells in the smooth C(3)N(4)-Si coated PP compared to smooth uncoated PP and 551%/476% more cells with MST/MNST C(3)N(4)-Si coated PP than could be obtained with MST/MNST uncoated PP. Thus the adhesion, spreading and contact guidance of osteoblast-like cells was effectively improved by combining surface texturing and deposition of osteocompatible C(3)N(4)-Si coating.

An effective solution mixing method starting from a synthesis solution of SiO2 nanoparticles was developed for dispersing nanoparticles into high-density polyethylene (HDPE). Spherical SiO2 nanoparticles with narrow size distribution (50–100 nm) were prepared by Stober method, and solvents of the synthesis solution (EtOH/NH4OH) were gradually replaced with toluene by evaporation under reduced pressure. The SiO2 nanodispersion, in toluene and residual ethanol, was mixed and refluxed with dissolved maleic anhydride grafted polyethylene (PEgMA) at a relatively high SiO2 content (17.8 wt %). The PEgMA-SiO2 masterbatch was filtered, dried under vacuum, and mixed with HDPE by melt compounding. SiO2 contents in the final HDPE nanocomposites were 3 and 5 wt %. SEM images of the masterbatch and final composites showed the SiO2 nanoparticles to be well dispersed in HDPE. No agglomerates were observed. FTIR results suggest that the interactions between the maleic anhydride group of PEgMA and hydroxyl groups of SiO2 surface involve ester and/or hydrogen bonding. Addition of SiO2 particles and PEgMA to HDPE slightly increased Young's modulus, tensile strength, breaking strength, and elongation at break, indicating enhanced toughness of the nanocomposites. The measured Young's moduli of HDPE-PEgMA-SiO2 composites agreed well with Young's moduli predicted by Mori-Tanaka composite theory. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The wetting properties of polypropylene (PP) surfaces were modified by adjusting the dimensions of the surface nanostructure. The nanostructures were generated by injection molding with nanoporous anodized aluminum oxide (AAO) as the mold insert. Atomic layer deposition (ALD) of molybdenum nitride film was used to control the pore diameters of the AAO inserts. The original 50-nm pore diameter of AAO was adjusted by depositing films of thickness 5, 10, and 15 nm on AAO. Bis(tert-butylimido)-bis(dimethylamido)molybdenum and ammonia were used as precursors in deposition. The resulting pore diameters in the nitride-coated AAO inserts were 40, 30, and 20 nm, respectively. Injection molding of PP was conducted with the coated inserts, as well as with the non-coated insert. Besides the pore diameter, the injection mold temperature was varied with temperatures of 50, 70, and 90 degrees C tested. Water contact angles of PP casts were measured and compared with theoretical contact angles calculated from Wenzel and Cassie-Baxter theories. The highest contact angle, 140 degrees , was observed for PP molded with the AAO mold insert with 30-nm pore diameter. The Cassie-Baxter theory showed better fit than the Wenzel theory to the experimental values. With the optimal AAO mask, the nanofeatures in the molded PP pieces were 100 nm high. In explanation of this finding, it is suggested that some sticking and stretching of the nanofeatures occurs during the molding. Increase in the mold temperature increased the contact angle.

Nature's functional surfaces are typically hierarchical multiscale structures. There are several techniques for producing such artificial structures on polymers but their mass production is not straightforward. We present here a simple and versatile method for manufacturing hierarchical multiscale polymer surface patterns. The microroughening technique permits the single-step production of multilevel three-dimensional surface architectures in a mechanically durable nickel mold. The molding technique is suitable for area-controlled fabrication of structures with various geometrical shapes on smooth and curved surfaces. The mold structures were transferred to polypropylene surfaces by means of injection molding. The fabricated surface structures were characterized by using a filtered power spectral density method which facilitated a quantitative study of the roughness distributions at different length scales of structure periodicities. Analysis showed that the microroughening technique is an appropriate tool for controlled production of surface roughness at a micro-nanometer scale. Roughness distribution values can be used for predicting surface structure-related properties such as wetting, and the distributions can also be simulated without an experimental preparation process. The work presents a suitable approach for mass production of hierarchical polymer surfaces at different length scales and provides a new route for designing surface structures with tunable wetting properties.

For reliable function, bioelectrodes require a stable, low-impedance contact with the target tissue. In biosignal monitoring applications, in which low ion current densities are recorded, it is important to minimize electrode contact impedances. Recently, several flexible electrode concepts have been introduced for single-patient use. These electrodes conform well on the patient skin enabling an artifact-free, low-noise recording. In this study, polydimethylsiloxane (PDMS) elastomer was used as an electrode substrate material. One half of the substrates were surface-patterned with micropillars produced by using micro-working robot-made mold inserts and a replica molding technique. The substrates were subsequently coated with thin films of titanium (Ti), copper (Cu), silver (Ag) or silver?silver chloride (Ag/AgCl). Electrical impedance spectroscopy studies revealed that the micropillar structure caused statistically significant reductions in impedance modulus and phase for each coating candidate. The relative effect was strongest for pure Ag, for which the values of the real part (Z?) and the imaginary part (Z?) decreased to less than one tenth of the original (smooth) values. However, Ag/AgCl, as expected, proved to be a superior electrode material. Coating with chloride drastically reduced the interfacial impedance compared to pure Ag. Further significant reduction was achieved by the micropillars, since the phase angle declined from 10?13? (for smooth samples, f < 50?Hz) to a value as low as 5?. Equivalent circuit modeling was used to obtain a better understanding of phenomena occurring at various electrode?electrolyte interfaces. The knowledge obtained in this study will be exploited in the further development of flexible electrodes and miniaturized biointerfaces with improved electrochemical characteristics.

Two transparent semi-crystalline poly(4-methyl-1-pentene) copolymers (P4MP1) of different molar mass distributions were used for injection molding of high aspect ratio (height/width) diffractive gratings. High quality sub-micron and micron features with aspect ratios of 1.6:1 were obtained with low mold temperatures. According to SEM and AFM measurements, replication of the features depended on substrate thickness and polymer. The copolymer with lower Mn and Mw penetrated deeper into the feature cavities in thin substrates, but showed poorer thermal stability and replication fidelity.