Visual perception and measurements of texture and gloss of injection‐molded plastics

The effect of an imposed texture on the gloss of injection‐molded polymeric surfaces was evaluated as well as the way in which these properties are visually perceived. Specimens having small differences in surface topography were produced using two mold cavities with slight differences in texture and three different polymers. The texture and gloss were characterized using laser profilometry, gloss measurements, and by means of psychometric evaluations. The measured surface topography parameters and gloss were determined mainly by the texture of the mold surface and the gloss also by the processing conditions. Variations in surface topography due to differences in the rheological properties of the polymer melts were, in most cases, too small to be reflected in the measurements. The visual assessments of the texture and the gloss of specimens from the same cavity were in fair agreement with the measurements, although the observers could discern differences between some specimens not revealed by the measurements. When the specimens molded in the two cavities differing significantly both in gloss and texture were compared, the agreement between the measured topography parameters and the perceived roughness was poorer. It is suggested that higher gloss of a textured surface enhances the perception of a higher roughness. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

Adhesion Promoting Polymer Interlayers for Ag Layers Deposited in OLED Processing

One of the main drivers for organic electronic research are the backplanes for flexible active-matrix displays using organic light-emitting diodes (AM-OLEDs). In our work, we processed organic thin-film transistors (OTFTs) at low temperatures (<160°C) on poly(ethylene naphthalate) (PEN) foils. There are several challenges in the integration of OLEDs on top of OTFT backplanes on a foil. One of them is the interlayer between the OTFT backplane and the OLEDs. For this layer, low-temperature crosslinkable, chemically resistant polymers are required, which, on the one hand, provide proper electrical insulation to OTFT and OLED devices and, on the other hand, can be processed reliably and provide good adhesion to the OLED anode. From the point of reflectivity and, therefore, light emission efficiency, Ag would be a preferred option. The challenge from the processing point of view is the poor adhesion of evaporated or e-beam deposited Ag on most surfaces. Commonly used microelectronic approaches such as sputtered metal or Ar pre-sputtering cannot be applied because of resulting surface leakage paths on the organic dielectric caused by dangling bonds. To address this issue, we tested a variety of low-temperature crosslinkable polymers (e.g., SU-8, parylene) regarding adhesion, roughness and processability and we measured the adhesion of the Ag deposited at different thicknesses using the Scotch tape test (ASTM D 3359). The best adhesion properties were obtained with parylene N allowing Ag layers with thicknesses up to 200 nm and surface roughness around 7–8 nm.     

Fractal analysis of surfaces roughened by grit blasting

Surfaces roughened by grit blasting influence the adhesion strength of plasma-sprayed ceramic coatings. The average surface roughness has been used to evaluate the surface topography of such surfaces. It is well known that the adhesion strength of ceramic coatings reaches a maximum value at a certain substrate surface roughness. However, this result cannot be understood based on only surface roughness. The blasted surface has fractal characteristics. There are two types of fractal surfaces, which are characterized by self-similarity and self-affinity. Using fractal analysis to evaluate the surface topography of substrates, the fractal dimension was measured for the roughened surfaces. The maximum fractal dimension was attained at a blasting angle of 75°, where the adhesion strength also reached approximately its maximum value. It is concluded that the fractal dimension is a more appropriate measure than the average surface roughness for evaluation of the adhesion strength of ceramic coatings.     

The effect of polymer surface modification via interfacial polymerization on polymer–protein interaction

Membrane separation is an important processing technology used for separating food ingredients and fractionating value‐added components from food processing byproducts. Long‐term performance of polymeric membranes in food protein processing is impeded by the formation of fouled layers on the membrane surface as a result of protein adsorption onto the membrane surface. Surface modification of synthetic membranes, i.e., changing surface characteristics to reduce protein adsorption permanently, is one of the innovative ways of reducing the fouling of membrane surfaces. In this study, surface modification of flat‐sheet ultrafiltration membrane, polyethersulfone (PES), was investigated in improving the hydrophilicity of PES surfaces, thereby reducing adsorption of the protein caused by hydrophobic–hydrophobic interaction between the protein and the membrane. Hydrophilic polymer grafting through thin‐film composite using interfacial polymerization was employed to improve the hydrophilicity of the commercial PES membranes. Poly(vinyl alcohol), poly(ethylene glycol), and chitosan were chosen as hydrophilic polymers to graft on PES membrane because of their excellent hydrophilic property. Modified PES membranes were characterized by contact angle, FTIR, XPS, and AFM. Contact angles of modified PES membranes were reduced by 25 to 40% of that of the virgin PES membrane. XPS spectrum supported that the PES membranes were successfully modified by interfacial polymerization. Tapping‐mode AFM was used to examine the changes in surface topography of modified PES membranes. The PES membranes modified by interfacial polymerization showed lower roughness (from 1.2 to 2.0 nm) than that of virgin PES membrane (2.1 nm). The results of these instrumental analyses indicated that the PES membranes were successfully enhanced hydrophilically through interfacial polymerization. The protein adsorption on the modified membranes was reduced by 30 to 35% as a result of surface modification of the PES membranes using interfacial polymerization technique. Published 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Superhydrophobic durable coating based on UV‐photoreactive silica nanoparticles

Superhydrophobic surfaces can be obtained by tailoring both the chemistry and roughness topography, mimicking the Lotus leaf characteristics. Most of the synthetic superhydrophobic surfaces reported have been composed of micro and nanoparticles (NPs) embedded in polymer‐based coatings. The particles which tailor the topography are bonded to the base polymers by weak secondary forces. Consequently, the topography integrity is highly affected by handling and surface drag making them unsuitable for long term applications. This work is focused on promoting covalent bonding between the NPs and the base polymer to obtain durable superhydrophobic surfaces. The rough topography was achieved by ultraviolet (UV) curing of SiO₂ NPs containing a photoreactive benzophenone moiety in addition to methylated fumed silica NPs which can bind covalently to the polymer base coating, on UV radiation. The hydrophobic chemistry was obtained by fluoroalkylsilane top coating. Coating durability was evaluated using surface air drag and accelerated weathering conditions (UV radiation, humidity and temperature). Results indicated that the proposed approach resulted in superhydrophobic surfaces having high contact angle (>150°) and low sliding angle (<10°) with improved long term durability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41122.     

Correlation of morphology and barrier properties of thin microwave plasma polymer films on metal substrate

The barrier properties of thin model organosilicon plasma polymers layers on iron are characterised by means of electrochemical impedance spectroscopy (EIS). Tailored thin plasma polymers of controlled morphology and chemical composition were deposited from a microwave discharge. By the analysis of the obtained impedance diagrams, the evolution of the water uptake ?, coating resistance and polymer capacitance with immersion time were monitored and the diffusion coefficients of the water through the films were calculated. The impedance data correlated well with the chemical structure and morphology of the plasma polymer films with a thickness of less than 100 nm. The composition of the films were determined by means of infrared reflection absorption spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The morphology of the plasma polymer surface and the interface between the plasma polymer and the metal were characterised using atomic force microscopy (AFM). It could be shown that, at higher pressure, the film roughness increases which is probably due to the adsorption of plasma polymer nanoparticles formed in the plasma bulk and the faster film growth. This leads to voids with a size of a few tens of nanometers at the polymer/metal interface. The film roughness increases from the interface to the outer surface of the film. By lowering the pressure and thereby slowing the deposition rate, the plasma polymers perfectly imitate the substrate topography and lead to an excellent blocking of the metal surface. Moreover, the ratio of siloxane bonds to methyl-silyl groups increases which implies that the crosslink density is higher at lower deposition rate. The EIS data consistently showed higher coating resistance as well as lower interfacial capacitance values and a better stability over time for the film deposited at slower pressure. The diffusion coefficient of water in thin and ultra-thin plasma polymer films could be quantified for the smooth films. The measurements show that the quantitative evaluation of the electrochemical impedance data requires a detailed understanding of the film morphology and chemical composition. In addition, the measured diffusion coefficient of about 1.5×10⁻¹⁴ cm² s⁻¹ shows that plasma polymers can act as corrosion resistant barrier layers at polymer/metal interfaces.     

Preparation and characterization of superhydrophobic FEP-Teflon surfaces

Abstraet-Supcrhydrophohic FEP-Teflon was prepared by argon ion etching followed by oxygen glow discharge treatment of commercially available FEP-Teflon sheet material. This combined treatment yielded an increase in water contact angle from 109° to > 140°. Ion etching alone caused a small increase in surface roughness and a loss of fluorine from the surface, but the water contact angles increased only to 120°. Scanning electron micrographs of ion-etched surfaces showed stalky protrusions with a diameter of approximatcly 40 nm. Glow discharge treatment of ion-etched surfaces reduced the length of these protrusions and therewith the microscopic surface roughness. However, in all cases the macroscopic surface roughness was less than 1 um (R_A value). X-Ray photoelectron spectroscopy indicated major changes in elemental surface composition as a result of the treatments. These modifications did not influence the infrared absorption spectra (attenuated total reflection) of the modified surfaces, indicating that the chemical changes brought about are really superficial. It is concluded that the superhydrophobicity created is mainly due to changes in the specific, microscopic surface topography resulting from ion etching, but also partly due to the role of the glow discharge treatment, restoring a high surface concentration of fluorine after ion etching.     

Atomic force microscopy observations of a single crystal diamond surface lifted-off via ion implantation

The microscopic surface morphology of “lifted-off” surfaces, produced via ion implantation was observed by atomic force microscopy. A polished single-crystal diamond substrate with an average surface roughness of less than 0.1 nm was used for precise observations. After the lift-off process, the lifted-off surface became rough with pits appearing. Hydrogen plasma treatment close to the chemical vapor deposition conditions for diamond (1150 °C, 160 Torr) completely removed these pits and the surface was subsequently covered by a strip-like structure consisting of atomic steps. The surface roughness, however, was not further influenced by the plasma treatment. The observed morphological evolution reflects the graphite/diamond interface formed by the lift-off.     

Carbon fibers and composites with epoxy resins: Topography, fractography and interphases

Interphases exist in hybrid materials and significantly influence their mechanical performance. To find a bridge between the microscopic and macroscopic mechanical properties, this work investigates the nanoscopic nature of surface/interphases in terms of topography, fractography, adhesion and stiffness. Here, we show that variations in both adhesive and attractive forces on oxidized high modulus (HM) and intermediate modulus (IM) carbon fiber surfaces appear to result from the coating layer. The coating layer is critical for adhesive interaction with two different epoxy resins. The HM fiber has the apparently higher roughness but lower surface area than the IM fiber on the scanning scale of 200 nm. The surface roughness on a few tens of nanometer scale has no significant contribution to interphase adhesion from ‘mechanical interlocking’. In contrast, the true contact area on the nanometer scale plays a dominant role in interfacial adhesion. Using force volume nanoindentation, the stiffness of the resin region near the finished fiber surface was found to not depend on the distance from the fiber surface. Our observations suggest an energy-geometry link between critical interphase energy release rate by micromechanical testing and detailed fracture surface features.     

Atomic force microscopy (AFM) studies of liquid crystalline polymer (LCP) surfaces

An atomic force microscope (AFM) operating in tapping or contact mode was used to study the surface topography and the molecular organization of Vectra‐A and Vectra‐B films. Large‐scale (15 × 15 μm) AFM images revealed that ribbonlike fibrils with a width/height ≫ 1.0 are the dominant surface features of these liquid crystalline polymers (LCPs). The region of local disorder, surface debris, and interfibrillar debris as well as possible amorphous regions were observed in both LCP samples. Large fibrils, 5.0–10.0 μm in width, can be thought of as formed by smaller microfibrils capable of forming ordered structures. Microfibrils can bend upward, forming raised surface features; bend inward, originating cracks 1–2 μm wide on the film surface; or divide and subdivide into smaller units. Longitudinal and lateral stresses are believed responsible for the variation in fibril size, shape, and orientation. AFM images containing molecular‐scale details showed that microfibrils consists of chains of molecules coiled around a central axis and that they can be only about 2.0 nm wide. These submicron surfaces consist of white spots (representing molecules) that can form ordered structures or that can cluster to form agglomerates distributed in a random manner. Submicron fibrils are believed to represent the LCP basic structural unit. AFM results indicate that the surface topography of Vecta‐B is more ordered and uniform than is the one observed for Vectra‐A. Seemingly, amorphous particles form debris on Vectra‐A surfaces. Short rods oriented crosswise on the fibril surface are instead what increases the Vectra‐B roughness. These LCPs can have a surface topography similar to the one observed in AFM images of a spiderweb. However, the spiderweb fibrils are formed by more uniform microfibrils that are oriented parallel to each other. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2243–2254, 1999     

Study of nisin adsorption on plasma-treated polymer surfaces for setting up materials with antibacterial properties

Setting up antibacterial materials by nisin adsorption on surfaces depends mainly on the surface properties and the surface treatments allowing the modification of such properties. In order to investigate the factors affecting such adsorption, the native low density polyethylene (LDPE) was modified using Argon/Oxygen (Ar/O₂) plasma, nitrogen (N₂) plasma and plasma-induced grafting of acrylic acid (AA). The films were studied by various characterization techniques. The chemical surface modification was confirmed by X-ray photoelectron spectroscopy (XPS), the wettability of the surfaces was evaluated by contact angle measurements, the surface charge was determined by the zeta potential measurements, and the changes in surface topography and roughness were revealed by atomic force microscopy (AFM). Nisin was adsorbed on the native and the modified surfaces. The antibacterial activity, the nisin adsorbed amount, and the peptide distribution were compared for the four nisin-functionalized films. The highest antibacterial activity was recorded on the Ar/O₂ followed by AA then by N₂ treated films and the lowest activity was on the native film. The observed antibacterial activity was correlated to the type of the surface, hydrophobic and hydrophilic interactions, surface charge, surface topography, nisin adsorbed amount, and nisin distribution on the surfaces.     

Effect of surface pre-treatment on surface characteristics and adhesive bond strength of aluminium alloy

In this work aluminium alloy surfaces have been subjected to three different methods of surface pre-treatments such as solvent degreasing, FPL (Forest Products Laboratory) etching and priming using an epoxy based primer. The treated surfaces were evaluated for surface energy, contact angle, surface topography, surface roughness and adhesive strength characteristics. The influence of surface pre-treatments on the variation of polar, dispersive and total surface energy of the surfaces is addressed. A wettability test was performed on the surfaces using an epoxy adhesive in order to assess the influence of the pre-treatment techniques on substrate/adhesive interaction. Theoretical work of adhesion values for the various pre-treated surfaces were calculated using the contact angle data and further tested experimentally by adhesive bond strength evaluation by tensile testing of a single lap aluminium-epoxy-aluminium assembly. The method of surface pre-treatment showed a profound effect on the surface topography and roughness by AFM. This study reveals that a combination of high surface energy and high surface roughness of the substrate along with good wettability of the adhesive contributed to the highest joint strength for the aluminium alloy through the FPL etching pre-treatment.     

Application of polymer nanoparticle coating for tuning the hydrophobicity of cellulosic substrates

Nanoparticles of partially imidized poly(styrene–maleic anhydride) were applied from an aqueous dispersion as a one- or two-layer coating onto paper substrates, for controlling the paper surface hydrophobicity and improving the water barrier resistance. The effect of deposition conditions and thermal treatments on the topography and properties of the coating was studied by scanning electron microscopy, atomic force microscopy (AFM), contact angle measurements, and friction measurements. The wettability of paper surfaces with adsorbed nanoparticles can be controlled by tuning the chemical and topographical surface parameters: the water contact angles were found to increase at higher imide content as determined by Raman spectroscopy (depending on synthesis and thermal treatment), and higher average surface roughness determined by AFM (depending on the deposition method). The present technique may serve as a unique replacement for chemical treatments hydrophobizing fibrous substrates.     

Surface Modification of Polyamide 6 Immobilized with Collagen: Characterization and Cytocompatibility

Polyamide 6 (PA6) membranes were exposed to Ar plasma to produce peroxides on their surfaces, followed by grafting polymerization of methacrylic acid (MAA) introducing -COOH on surfaces. PA6 membranes immobilized with collagen I were obtained by coupling collagen to the MAA graft chains. The physicochemical properties were characterized by contact angle measurement, ATR-FTIR, XPS, and AFM. The results showed that the hydrophilicity of the surface improved after surface modification. The surface topography of the original and the modified PA 6 membranes showed an increase in roughness. Moreover, collagen immobilized onto PA 6 membranes showed enhanced growth in ROB culture tests.     

Topography characterization and initial cellular interaction of plasma‐based Ar+ beam‐treated PDMS surfaces

Assuming that the existence of an ion‐flow in the plasma volume could strength the surface modifying effect, including its durability, a parallel plate reactor in reactive ion etching mode was employed to obtain surface modified PDMS with improved cellular interaction. The discharge power was varied at 100, 1200, and 2500 W to ensure varied ion‐flow density. The changes in the surface topography were observed by SEM and AFM, and the surface roughness was characterized by both: mean roughness, R_a, and root‐mean‐square, R_q. Time dependent water contact angle measurements were performed to control the durability of the hydrophilizing effect. Anisotropic etching, accompanied with decrease of the PDMS surface roughness, was observed up to discharge power of 1200 W that turns in intense isotropic one, accompanied with a sharp increase of the surface roughness over 1200 W, most probably because of arise of reverse sputtered neutrals diffracting the main plasma Ar⁺ flow. Human fibroblasts were applied as an in vitro model to learn more about the initial cellular interaction of the modified surfaces and to identify the optimal treatment conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Enhanced adhesion of epoxy-bonded steel surfaces using O2/Ar microwave plasma treatment

Steel surfaces have been modified using low pressure microwave plasma to enhance its adhesion with an epoxy adhesive. Optimization of the wettability of the surface was done using contact angle measurements for varying plasma parameters. Maximum wettability (19.9°) was obtained at 1000 W microwave power with 20 min of treatment time, −50 V sample bias and 1.67% O₂/Ar gas flow rate ratio. Enhanced wettability of the steel surface was attributed to increased surface roughness and oxide deposition. Using atomic force microscopy, surface roughness was observed to increase from 64.4 nm for the untreated surface to 76.7 nm for the O₂/Ar plasma treated surface. Deposition of oxides on the steel surface was also confirmed by the energy dispersive x-ray spectroscopy. Moreover, the increase in the total surface energy to 53.2 mN/m for the O₂ plasma treated steel surface supported the enhancement of its wettability, and hence, the adhesion with epoxy. Based on tensile test results, the adhesion strength of epoxy-bonded O₂/Ar plasma treated surfaces at optimum settings was increased to 3816.0 N, which is significantly higher compared to 3038.3 N for the epoxy-bonded untreated surfaces.     

Fabrication and characterisation of polymer thin-films derived from cineole using radio frequency plasma polymerisation

The development of organic polymer thin-films is critical for the progress of many fields including organic electronics and biomedical coatings. This paper describes the fabrication of an organic polymer thin film produced from 1,8-cineole via radio frequency plasma polymerisation. A deposition rate of 55 nm/min was obtained under the polymerisation conditions employed. Infrared spectroscopic analysis demonstrated that some functional groups observed in the monomer were retained after the polymerisation process, while new functional groups were introduced. The refractive index and extinction coefficient were estimated to be 1.543 (at 500 nm) and 0.001 (at 500 nm) respectively. The polymers were shown to be optically transparent. AFM images of the polymer established a very smooth and uniform surface with average roughness of 0.39 nm. Water contact angle data demonstrated that the surface was stable while in contact with water.     

Centimeter-scale low-damage micromachining on single-crystal 4H–SiC substrates using a femtosecond laser with square-shaped Flat-Top focus spots

Femtosecond (fs) lasers have been proved to be reliable tools for high-precision and high-quality micromachining of ceramic materials. Nevertheless, fs laser processing using a single-mode beam with a Gaussian intensity distribution is difficult to obtain large-area flat and uniform processed surfaces. In this study, we utilize a customized diffractive optical element (DOE) to redistribute the laser pulse energy from Gaussian to square-shaped Flat-Top profile to realize centimeter-scale low-damage micromachining on single-crystal 4H–SiC substrates. We systematically investigated the effects of processing parameters on the changes in surface morphology and composition, and an optimal processing strategy was provided. Mechanisms of the formation of surface nanoparticles and the removal of surface micro-burrs were discussed. We also examined the distribution of subsurface defects caused by fs laser processing by removing a thin surface layer with a certain depth through chemical mechanical polishing (CMP). Our results show that laser-induced periodic surface structures (LIPSSs) covered by fine SiO₂ nanoparticles form on the fs laser-processed areas. Under optimal parameters, the redeposition of SiO₂ nanoparticles can be minimized, and the surface roughness Sa of processed areas reaches 120 ± 8 nm after the removal of a 10 μm thick surface layer. After the laser processing, micro-burrs on original surfaces are effectively removed, and thus the average profile roughness Rz of 2 mm long surface profiles decreases from 920 ± 120 nm to 286 ± 90 nm. No visible micro-pits can be found after removing ~1 μm thick surface layer from the laser-processed substrates.