Control Of Surface Morphology Research Articles

Spontaneous formation of photochromic coatings made of reversible microfibrils and nanofibrils on an elastomer substrate.

We report the spontaneous formation of photochromic microcrystalline and nanocrystalline fibrils forming dense coatings of cactuslike supramolecular structures on the surface of a soft poly(dimethylsiloxane) (PDMS) elastomer. The initial deposition of the photochromic molecules of diarylethenes on the elastomer is done by dip adsorption, a process that permits the homogeneous distribution of the molecules not only on the surface but also in the inner part of the polymer. Detailed thermal and microscopy studies reveal that the growth process of the fibrils is initiated by the formation of crystal seeds of the diarylethene in the proximity of the elastomer's surface empty voids and progresses toward the elastomer-air interface as a result of the high mobility of the molecules at room temperature. Fibril formation is possible only when the molecules are in the open form because the UV irradiation responsible for their transformation to the close isomeric form immediately after deposition totally prohibits the crystals' formation. Furthermore, the UV irradiation of the grown supramolecular assemblies provokes their destruction, but when the irradiated samples are left to recover under ambient conditions, they form new assemblies of fibrils in a faster and more efficient way. The resulting systems exhibit superhydrophobic to slightly hydrophobic properties with differences of almost 80° in water contact angles upon dark storage-UV irradiation cycles. The proposed systems can be an alternative to the facile formation of reversible photochromic fibrils on soft polymer surfaces for utilization on diverse soft devices, where controlled surface morphology and wettability are desired.

Controlled surface morphology and hydrophilicity of polycaprolactone toward selective differentiation of mesenchymal stem cells to neural like cells.

Differentiation of mesenchymal stem cells (MSCs) into neuron cells has great potential in therapy of damaged nerve tissue. It has been shown that three-dimensional biomaterials have great ability to up regulate the expression of neuronal proteins. In this study, O2 plasma technology was used to enhance hydrophilicity of poly (ε-caprolactone) (PCL) toward selective differentiation of MSCs into neural cells. Random and aligned PCL nanofibers scaffolds were fabricated by electrospinning method and their physicochemical and mechanical properties were carried out by scanning electron microscope (SEM), contact angle, and tensile measurements. Contact angle studies of PCL and plasma treated PCL (p-PCL) nanofibers revealed significant change on the surface properties PCL nanofibers from the view point of hydrophilicity. Physiochemical studies revealed that p-PCL nanofibers were extremely hydrophilic compared with untreated PCL nanofibers which were highly hydrophobic and nonabsorbent to water. Differentiation of MSCs were carried out by inducing growth factors including basic fibroblast growth factor, nerve growth factor, and brain derived growth factor, NT3, 3-isobutyl-1-methylxanthine (IBMX) in Dulbecco's modified Eagle's medium/F12 media. Differentiated MSCs on nanofibrous scaffold were examined by immunofluorescence assay and was found to express the neuronal proteins; β-tubulin III and Map2, on day 15 after cell culture. The real-time polymerase chain reaction (RT-PCR) analysis showed that p-PCL nanofibrous scaffold could upregulate expression of Map-2 and downregulate expression of Nestin genes in nerve cells differentiated from MSCs. This study indicates that mesenchymal stem cell cultured on nanofibrous scaffold have potential differentiation to neuronal cells on and could apply in nerve tissue repair.

Directed assembly of bifunctional silica-iron oxide nanocomposite with open shell structure.

The synthesis of nanocomposite with controlled surface morphology plays a key role for pollutant removal from aqueous environments. The influence of the molecular size of the polyelectrolyte in synthesizing silica-iron oxide core-shell nanocomposite with open shell structure was investigated by using dynamic light scattering, atomic force microscopy, and quartz crystal microbalance with dissipation (QCM-D). Here, poly(diallydimethylammonium chloride) (PDDA) was used to promote the attachment of iron oxide nanoparticles (IONPs) onto the silica surface to assemble a nanocomposite with magnetic and catalytic bifunctionality. High molecular weight PDDA tended to adsorb on silica colloid, forming a more extended conformation layer than low molecular weight PDDA. Subsequent attachment of IONPs onto this extended PDDA layer was more randomly distributed, forming isolated islands with open space between them. By taking amoxicillin, an antibiotic commonly found in pharmaceutical waste, as the model system, better removal was observed for silica-iron oxide nanocomposite with a more extended open shell structure.

A new approach of synthesis and morphological control of poly(ethylene terephthalate)-g-polyacrylonitrile composite film with a porous surface

Poly(ethylene terephthalate)-g-polyacrylonitrile (PET-g-PAN) composite film with a porous surface was fabricated via gamma-ray-radiation-induced graft polymerization on PET film in an aqueous solution system. The original PET film was first irradiated by gamma ray in the aqueous solution of acrylic acid. Next, the graft polymerization of acrylonitrile (AN) was induced by gamma ray on the surface of the above modified PET film in an aqueous solution of AN. The prepared PET-g-PAN composite film has a smaller static water contact angle than the original PET film. The SEM and AFM images show that the grafted PAN layer on the surface of PET-g-PAN composite film is composed of closely-arranged spherical PAN microspheres with an average diameter of 30nm. The gaps between the PAN microspheres form fine pores (less than 30nm) on the surface. The gas barrier property of the PET-g-PAN composite film is much better than that of the original PET film. This work provides a facile and green method to prepare PET-g-PAN composite film with a controllable porous surface morphology by taking advantage of the radiation-induced graft polymerization technique in an aqueous solution system.

Bio-Inspired Multistructured Conical Copper Wires for Highly Efficient Liquid Manipulation

Animal hairs are typical structured conical fibers ubiquitous in natural system that enable the manipulation of low viscosity liquid in a well-controlled manner, which serves as the fundamental structure in Chinese brush for ink delivery in a controllable manner. Here, drawing inspiration from these structure, we developed a dynamic electrochemical method that enables fabricating the anisotropic multiscale structured conical copper wire (SCCW) with controllable conicity and surface morphology. The as-prepared SCCW exhibits a unique ability for manipulating liquid with significantly high efficiency, and over 428 times greater than its own volume of liquid could be therefore operated. We propose that the boundary condition of the dynamic liquid balance behavior on conical fibers, namely, steady holding of liquid droplet at the tip region of the SCCW, makes it an excellent fibrous medium to manipulate liquid. Moreover, we demonstrate that the titling angle of the SCCW can also affect its efficiency of liquid manipulation by virtue of its mechanical rigidity, which is hardly realized by flexible natural hairs. We envision that the bio-inspired SCCW could give inspiration in designing materials and devices to manipulate liquid in a more controllable way and with high efficiency.

Controlling surface segregation of reactively sputtered Ag/TiOx nanocomposites

Reactive sputtering of silver/titania nanocomposites is potentially attractive for antibacterial, photocatalytic, and optical coatings. However, previous studies on such coatings showed strong segregation of silver towards the surface, which could lead to undesirable properties. Here we present results of our investigations of the mechanism of silver surface segregation and influence of sputter parameters on the morphology of reactively sputtered Ag/TiOx nanocomposites. It was observed that silver surface segregation depends on the silver filling factor of the composite and that it is largely independent of the oxygen partial pressure used in the sputtering process. At high total pressure even sputtering of pure TiOx barriers is—unlike non-reactive sputtering of TiOx—not sufficient to prevent the strong surface segregation effect. Surface segregation is only thoroughly suppressed by reduction of the total pressure during reactive sputtering, allowing the formation of a dense composite film. Based on this principle silver surface segregation can be further reduced by deposition of TiOx barriers with very high sputtering rates. Furthermore, the relation between the morphology of the nanocomposites and their optical properties is presented. Nanocomposites produced under these conditions show a controllable surface morphology for functional applications.

Controlled surface morphology of polyamide membranes via the addition of co-solvent for improved permeate flux

Polyamide membranes with a controlled surface morphology were prepared by the interfacial polymerization of 1,3-phenylenediamine (MPD) with 1,3,5-benzenetricarbonyl trichloride (TMC) on polysulfone ultrafiltration supports. In a novel polymerization method, co-solvents, which included acetone, ethyl acetate, diethyl ether, toluene, isopropyl alcohol (IPA) and N,N′-dimethyl formamide (DMF), were added into the organic phase which made it possible to control the surface morphology and polyamide network structures. As-prepared, the membranes showed multi-layered ridge-and-valley structures, and the types of co-solvent successfully controlled permeate flux and rejection. Polyamide membranes prepared by the addition of 2wt% ethyl acetate, showed the best performance with NaCl rejection of 99% and permeate flux of more than 1m3/(m2d) at 1.5MPa, which was about twice that of a membrane prepared without a co-solvent.

Nanostructured anti-bacterial poly-lactic-co-glycolic acid films for skin tissue engineering applications

Major issues faced with the use of today's skin grafts are infection, scar tissue formation, insufficient keratinocyte (or skin producing cells) proliferation and high production costs. To overcome these limitations, we propose here for the first time, a nanofeatured poly(lactide-co-glycolide) (PLGA) membrane as a next generation antibacterial skin graft material. An alkaline surface treatment method was used to create random nanofeatures on PLGA membranes where sodium hydroxide (NaOH) concentration and exposure times were altered to control surface morphology. Most significantly, and without the use of antibiotics, results showed a decrease in Staphylococcus aureus (a dangerous pathogen infecting skin grafts) growth for up to ∼40% after 2 days of culture on nanofeatured PLGA membranes compared to untreated controls. Results also showed that while bacteria growth was stunted, mammalian cell growth was not. Specifically, cell culture results showed an increase in human epidermal keratinocyte density, while the density of scar tissue forming human dermal fibroblasts, did not change on nanofeatured PLGA surfaces compared to the untreated controls after 3 days of culture. These findings indicate that the alkaline treatment of PLGA membranes is a promising quick and effective manner to limit scar tissue formation and bacterial invasion while increasing skin cell proliferation for improving numerous wound-healing applications.

Controllable surface morphology and properties via mist polymerization on a plasma-treated polymethyl methacrylate surface.

Surface modification by grafting polymers on solid materials is an important strategy used to improve surface properties. This article reports that under appropriate conditions, very thin layers with desired morphologies may be constructed on a plasma-treated substrate by feeding a small quantity of a monomer with a mist stream carrying droplets produced from monomer solutions. We investigate the effects of process parameters that affect layer morphology, including exposure time to the mist stream, concentration of the monomer solution, and solvent selectivity. For a methyl methacrylate solution in ethanol, nanoparticles are uniformly grown with increasing monomer concentration or exposure time and finally form a porous layer at 3.65 mol L(-1) for 30 min. Decreasing solvent polarity not only affects surface morphology, but also increases hydrophobicity of the resulting surface. With 2,2,3,4,4,4-hexafluorobutyl methacrylate as the monomer, SEM and AFM micrographs indicated that mist polymerization results in numerous microspheres on the activated surface. These experimental results were interpreted by a mechanism in terms of an in situ polymerization accompanied by a phase transformation of the resulting polymer. Specifically, plasma treatment provides highly active cations and radicals to initiate very rapid polymerization, and the resulting polymers are consequently deposited from the liquid onto the surface under phase transition mechanisms.

Optimizing the preparation of multi-layered polyamide membrane via the addition of a co-solvent

Polyamide membranes with controlled surface morphology were prepared by the interfacial polymerization of 1,3-phenylenediamine (MPD) with 1,3,5-benzenetricarbonyl trichloride (TMC) on polysulfone ultrafiltration supports. The addition of co-solvents (acetone, ethyl acetate, and diethyl ether) into the organic phase was used to control both the surface morphology and the polyamide network structures. The as-prepared membranes had multi-layered polyamide structures, which consisted of large (1μm) and ordinal (100–300nm) ridge-and-valley formations. Permeate flux and rejection reactions were successfully controlled by the types and amounts of co-solvents that were added. The optimal membrane conditions included the addition of 3wt% ethyl acetate, with a NaCl rejection of more than 99% and a permeate flux of more than 1.8m3/(m2d) at 1.5MPa, which was more than three times higher than the membranes prepared without a co-solvent.

Capillary evaporator development and qualification for loop heat pipes

In the present paper, design consideration, fabrication techniques and post-assembly qualification tests to guarantee reliable structure of the capillary evaporator for loop heat pipe (LHP) with high heat flux transport capability has been presented. Cylindrical evaporator with nickel as high performance capillary pump, copper as high conductivity containment material and water as superior heat transfer working fluid was designed to transport 500 W heat load up to distance of 250 mm. Nickel powder with average particle diameter of 12 μm was sintered to obtain wick with high porosity (>65%) and fine pore radius <7.2 μm. High volumetric shrinkage (4–50% @750–1000 °C respectively) of the sintered wick results in poor control over the sample dimensions which makes wick integration inside evaporator difficult. Special procedures were conducted to develop machined nickel wick with good dimensional control (±0.15 mm) and high-roughness surface morphology, which provide high evaporation area and high surface porosity. These machined wick were successfully installed inside the evaporator using different integration methods. Qualification tests to validate evaporator structural integrity has been discussed in detail. For the designed loop heat pipe prototype, the minimum value of 0.15 °C/W for total thermal resistance was observed at maximum heat load of 500 W. In summary, capillary evaporator fabrication techniques (including wick development) and structural integrity qualification tests developed in this investigation can be used to fabricate miniature to large-scale loop heat pipes with high heat flux management capabilities.

Design and Characterization of Hybrid Morphology Nanoarrays as Plasmonic Raman Probes for Antimicrobial Detection

Advances in nanofabrication have allowed the production of new and more reproducible substrates for the Raman detection of trace antimicrobials in water. The superior substrate uniformity combined with the ability to control surface morphology represents a significant step forward in the design of substrates with improved enhancement factors and trace-detection capabilities. The work presented herein successfully combines electron-beam lithography (EBL) and reactive ion-etching (RIE) protocols for the construction, testing, and validation of plasmonic hybrid morphology nanoarrays for the detection of arsenic antimicrobials in water. The fabricated substrates consist of 2500 μm(2) Ag-coated silicon dioxide (SiO2)/Si pillar nanoarrays of alternating hexagonal and elliptical features. Control of simple fabrication parameters such as inter-particle spacing (gap) and its orientation relative to the laser polarization vector (parallel or orthogonal) result in over a tenfold improvement in the apparent Raman response under optimized conditions. At a 633 nm excitation frequency, the best substrate performance was observed on parallel-oriented features with a 200 nm gap, with over one order of magnitude increase in the apparent surface-enhanced Raman scattering (SERS) signal relative to standard silver-polydimethylsiloxane (Ag-PDMS) nanocomposites. Monitoring of the characteristic As-C stretching band at 594 cm(-1) allowed the detection of arsenic antimicrobials in water well within the parts per million range. Calculated surface-enhancement factors (SEF) for this substrate, employing 532, 785, and 633 nm excitation wavelengths, was within five, six, and seven orders of magnitude, respectively. The effect of substrate morphology and nanofabrication process on the Raman enhancement factor is presented.

Swift heavy ion irradiation induced modification of structure and surface morphology of BiFeO3 thin film

BiFeO3 (BFO) thin films of thickness about 800 nm deposited on Si (100) substrates by sol–gel spin coating method were irradiated by 200 MeV Ag ions. Modification of structure and surface morphology of the films under irradiation was studied using glancing incidence X-ray diffraction (GIXRD) and atomic force microscope (AFM). Fluence dependence of GIXRD peak intensity indicated formation of 10 nm diameter cylindrical amorphous columns in crystalline BFO due to 200 MeV Ag ion irradiation. AFM analysis indicated that the pristine film consists of agglomerated grains with diffuse grain boundary. Irradiation led to reduced agglomeration of the grains with the formation of sharper grain boundaries. The rms roughness (σ rms) estimated from AFM analysis increased from 6·2 in pristine film to 12·7 nm when the film irradiated at a fluence of 1 × 1011 ions cm − 2. Further irradiation led to decrease of σ rms which finally saturated at a value of 7–8 nm at high ion fluences. The power spectral density analysis indicated that the evolution of surface morphology of the pristine film is governed by the combined effect of evaporation condensation and volume diffusion processes. Swift heavy ion irradiation seems to increase the dominance of volume diffusion in controlling surface morphology of the film at high ion fluences.

Semiconductor nanostructure properties. Molecular Dynamic Simulations

The need for research is based on the fact that development of non-planar semiconductor nanosystems and nanomaterials with controlled properties is an important scientific and industrial problem. So, final scientific and technological problem is the creation of adequate modern methods and software for growth and properties simulation and optimization of various III-V (GaAs, InAs, InP, InGaAs etc.) nanostructures (e.g. nanowires) with controlled surface morphology, crystal structure, optical, transport properties etc. Accordingly, now we are developing a specialized computer code for atomistic simulation of structural (distribution of atoms and impurities, elastic and force constants, strain distribution etc.) and thermodynamic (mixing energy, interaction energy, surface energy etc.) properties of the nanostructures. Some simulation results are shown too.

Evaluation of thin metal film thickness from light attenuation and multi-reflection effects on micro-Raman response

An optical model for Raman response of thin metal films has been developed, taking into account attenuation effects and multi-reflections occurring at film edges. Film thickness and surface morphology of nanometer thin NbN films have been inferred in the framework of this model using micro-Raman measurements. Results have been compared with those obtained by means of spectroscopic ellipsometry. The absolute value of the thickness is determined with a precision better than 20% on nanometric scale allowing us to control surface morphology with high accuracy also on large areas.

Preparation of diamond films with controllable surface morphology, orientation and quality in an overmoded microwave plasma CVD chamber

In the present work, a detailed and systematic investigation of diamond films deposited on silicon is realized in an overmoded microwave plasma CVD reactor chamber. It was observed that there is a coupled effect between carbon concentration and substrate temperature on the growth of diamond films. The substrate temperature should be increased with increasing carbon concentration in order to obtain similar surface morphology. And the relative high 〈111〉 or 〈100〉 orientation diamond films can be obtained when the two parameters are both appropriate. The investigation carried out with 1.5% carbon concentrations further ascertains the rules of the coupled effect. The results indicate that there are five statuses for the surface morphology and the diamond films with 〈100〉 and 〈111〉 orientation can be deposited at the substrate temperature from around 810°C to 870°C and around 920°C to 960°C, respectively. The quality of the diamond films increases rapidly while the substrate temperature increasing from 750°C to 870°C and keeps relative stable at higher substrate temperature. The experimental results, in some degree, indicate that the diamond films with controllable characters can be deposited in the MPCVD apparatus.

The Controllable Surface Morphology of Polyimide (PI) Electrospun Fibers

Electrospun materials have been proposed for application for gas filtration, drug carriers, and tissue engineering. The surface morphology of electrospun fibers is the key for consideration for the above applications, such as pore size on the fiber surface, surface area, and roughness. In this work, we investigated the influence of polymer/solvent properties on soluble polyimide (PI) fibers. The studied PIs included three fluorinated aromatic polyimides containing naphthalene pendant groups. By using various solvents we adjusted the size, shape, and structure of the fibers. As a result, PI electrospun fibers could be achieved with width around 10 μm. The rough and smooth surface morphologies were studied by scanning electron microscopy (SEM). Surface wettability of the electrospun fiber membranes were characterized by contact angle measurement. The contact angles on the electrospun PI fiber mats for water and glycerol were in the range of 137.6°–144.5° and 139.1°–143.6°, respectively. Moreover, the rough fiber surface could make the electrospun fiber membrane possess good adhesive force for liquids. The results suggest that we could widen the application of electrospun membranes through controlling the fiber morphology.

Front Cover Advanced Engineering Materials 6/2012

SLM is a direct AM technique that can be used to produce micro-porous structures with global morphological properties that are highly controlled through robust computer design. Despite these advantages, some AM techniques still hold several functional constraints, resulting from present technical device limits and consequently the inability to control surface morphology at a microscale level. A novel protocol for surface modification of 3D titanium alloy-based open porous structures is developed, applying a combination of chemical etching (CHE) and electrochemical polishing (ECP) using HF-based solutions. This protocol achieves a significant and controllable roughness reduction and homogenisation of 3D additive manufactured Ti6Al4V open porous structures. Further details can be found in the article by G. Pyka et.al. on page 363.

Studying femtosecond-laser hyperdoping by controlling surface morphology

We study the fundamental properties of femtosecond-laser (fs-laser) hyperdoping by developing techniques to control the surface morphology following laser irradiation. By decoupling the formation of surface roughness from the doping process, we study the structural and electronic properties of fs-laser doped silicon. These experiments are a necessary step toward developing predictive models of the doping process. We use a single fs-laser pulse to dope silicon with sulfur, enabling quantitative secondary ion mass spectrometry, transmission electron microscopy, and Hall effect measurements. These measurements indicate that at laser fluences at or above 4 kJ m−2, a single laser pulse yields a sulfur dose &amp;gt;(3 ± 1) × 1013 cm−2 and results in a 45-nm thick amorphous surface layer. Based on these results, we demonstrate a method for hyperdoping large areas of silicon without producing the surface roughness.

Electron-beam deposition of polyethylene composite coatings at various initiators and inhibitors

Polyethylene (PE) composite coatings were prepared on silicon substrate by electron-beam deposition (EBD) using mixed powders of low-density polyethylene and various dopants (i.e., initiator and inhibitor) as evaporated target. The structural and morphological behaviors of PE composite coatings were investigated in dependence of initiator and inhibitor by attenuated total reflectance-Fourier transform infrared spectroscopy and atomic force microscope. Free-radical polymerization and cationic polymerization could be observed in the formation process of PE composite coatings by EBD. The initiating system of AlCl3 and benzoyl peroxide as well as the inhibiting system of diphenylamine and hydroquinone used in EBD, in comparison with conventional synthesis methods, exhibited different effect on reaction mechanism of PE composite coatings. These results might contribute to the synthesis of polymer coatings with expectant molecule structure and controllable surface morphology. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers