Surface Energy Of Substrate Research Articles

Modifying Surface Fluctuations of Polymer Melt Films with Substrate Modification.

Deposition of a plasma polymerized film on a silicon substrate substantially changes the fluctuations on the surface of a sufficiently thin melt polystyrene (PS) film atop the substrate. Surface fluctuation relaxation times measured with X-ray photon correlation spectroscopy (XPCS) for ca. 4Rg thick melt films of 131 kg/mol linear PS on hydrogen-passivated silicon (H-Si) and on a plasma polymer modified silicon wafer can both be described using a hydrodynamic continuum theory (HCT) that assumes the film is characterized throughout its depth by the bulk viscosity. However, when the film thickness is reduced to ∼3Rg, confinement effects are evident. The surface fluctuations are slower than predicted using the HCT, and the confinement effect for the PS on H-Si is larger than that for the PS on the plasma polymerized film. This deviation is due to a difference in the thicknesses of the strongly adsorbed layers at the substrate which are impacted by the substrate surface energy.

Nanorod growth of copper phthalocyanine on fluorinated phosphonic acid SAM-modified indium tin oxide substrate for organic photovoltaic devices

ABSTRACTCuPc nanorod growth was investigated on ITO substrates with and without 1H,1H,2H,2H-perfluoro-noctylphosphonic acid (FOPA) SAM modification, using vapor phase deposition, through the control of the temperature and surface energy of ITO substrates. At a substrate temperature of 200°C, copper phthalocyanine (CuPc) thin films that composed nanorods were prepared on both substrates. On FOPA-ITO, it was suggested that CuPc molecules were stacked with an edge-on orientation because of the dominant intermolecular π–π interaction through the decrease of surface energy of ITO with FOPA modification. Organic photovoltaic cells containing CuPc nanorods as a p-type semiconductor were fabricated and photovoltaic characteristics were observed.

Increasing light coupling in a photovoltaic film by tuning nanoparticle shape with substrate surface energy

Tuning metal nanoparticle (MNP) contact angle on the surface it is formed can help maximise the useful optical coupling in photovoltaic films by localized surface plasmon (LSP) resonance—opening up the possibility of building improved photovoltaic cells. In this work experimental demonstration of optical absorption increase in copper phthalocyanine (CuPc) films by tuning silver MNP shape by changing its contact angles with substrate has been reported. Thin films of poly3,4 ethylenedioxythiophene: sodium dodecycl sulphate (PEDOT:SDS) with different surface energies were formed on indium tin oxide (ITO) coated glass by electro-deposition. Silver MNPs thermally evaporated directly on ozonised ITO as well as on the PEDOT:SDS films showed contact angles ranging from 60° to 125°. The CuPc layer was deposited on top of the MNPs. For the samples studied, best optical absorption in the CuPc layer was for a contact angle of 110°.

Insights Into Interface Treatments in p-Channel Organic Thin-Film Transistors Based on a Novel Molecular Semiconductor

Organic thin-film transistors (OTFTs) were fabricated using a novel small molecule, C6-NTTN, as the semiconductor layer in several different architectures. The C6-NTTN layer was deposited via both vacuum evaporation at different substrate temperatures and via solution-processing, which yield maximum hole mobilities of 0.16 and 0.05 cm2/ ${\mathrm{ V}}\cdot {\mathrm{ s}}$ , respectively. Surface treatments of the substrate, insulator, and metal contacts used for OTFT fabrication employing polymer films and different self-assembled monolayers were investigated. In particular, in bottom-gate devices, the insulator surface hydrophobicity was optimized by the deposition of poly(methyl methacrylate) or hexamethyldisilazane, while in the top-gate geometry, pentafluorobenzenethiol was efficiently used to modify the substrate surface energy and to change the contact work function. Atomic force microscopy analysis was exploited to understand the relationship between the semiconductor thin-film morphology and the device electrical performance. The results shown here indicate an inverse proportionality between the mobility and the interface trap density, with parameters depending especially on semiconductor–insulator interfacial properties, and a correlation between the threshold voltage and the characteristics of the semiconductor–metal interface.

Role of surface energy and nano-roughness in the removal efficiency of bacterial contamination by nonwoven wipes from frequently touched surfaces

Healthcare associated infections (HCAIs) are responsible for substantial patient morbidity, mortality and economic cost. Infection control strategies for reducing rates of transmission include the use of nonwoven wipes to remove pathogenic bacteria from frequently touched surfaces. Wiping is a dynamic process that involves physicochemical mechanisms to detach and transfer bacteria to fibre surfaces within the wipe. The purpose of this study was to determine the extent to which systematic changes in fibre surface energy and nano-roughness influence removal of bacteria from an abiotic polymer surface in dry wiping conditions, without liquid detergents or disinfectants. Nonwoven wipe substrates composed of two commonly used fibre types, lyocell (cellulosic) and polypropylene, with different surface energies and nano-roughnesses, were manufactured using pilot-scale nonwoven facilities to produce samples of comparable structure and dimensional properties. The surface energy and nano-roughness of some lyocell substrates were further adjusted by either oxygen (O2) or hexafluoroethane (C2F6) gas plasma treatment. Static adpression wiping of an inoculated surface under dry conditions produced removal efficiencies of between 9.4% and 15.7%, with no significant difference (p < 0.05) in the relative removal efficiencies of Escherichia coli, Staphylococcus aureus or Enterococcus faecalis. However, dynamic wiping markedly increased peak wiping efficiencies to over 50%, with a minimum increase in removal efficiency of 12.5% and a maximum increase in removal efficiency of 37.9% (all significant at p < 0.05) compared with static wiping, depending on fibre type and bacterium. In dry, dynamic wiping conditions, nonwoven wipe substrates with a surface energy closest to that of the contaminated surface produced the highest E. coli removal efficiency, while the associated increase in fibre nano-roughness abrogated this trend with S. aureus and E. faecalis.

Optimizing ultrathin Ag films for high performance oxide-metal-oxide flexible transparent electrodes through surface energy modulation and template-stripping procedures

Among new flexible transparent conductive electrode (TCE) candidates, ultrathin Ag film (UTAF) is attractive for its extremely low resistance and relatively high transparency. However, the performances of UTAF based TCEs critically depend on the threshold thickness for growth of continuous Ag films and the film morphologies. Here, we demonstrate that these two parameters could be strongly altered through the modulation of substrate surface energy. By minimizing the surface energy difference between the Ag film and substrate, a 9 nm UTAF with a sheet resistance down to 6.9 Ω sq−1 can be obtained using an electron-beam evaporation process. The resultant UTAF is completely continuous and exhibits smoother morphologies and smaller optical absorbances in comparison to the counterpart of granular-type Ag film at the same thickness without surface modulation. Template-stripping procedure is further developed to transfer the UTAFs to flexible polymer matrixes and construct Al2O3/Ag/MoOx (AAM) electrodes with excellent surface morphology as well as optical and electronic characteristics, including a root-mean-square roughness below 0.21 nm, a transparency up to 93.85% at 550 nm and a sheet resistance as low as 7.39 Ω sq−1. These AAM based electrodes also show superiority in mechanical robustness, thermal oxidation stability and shape memory property.

In-situ orientation and crystal growth kinetics of P3HT in drop cast P3HT:PCBM films

Effect of casting solvents on drop cast thin films of conductive conjugated polymers is largely studied by characterizing post processed films. However, the results have often been inconclusive due to the complexity of the in-situ evolution of structures. In this research we implement in-situ grazing incidence wide angle x-ray scattering (GIWAXS) approach to extracting morphological evolution information during film formation in model Poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend films that have otherwise been widely studied. Casting solvents include chloroform, benzene and tetrahydrothiophene (THT), carefully selected for their relative solubilities of P3HT and PCBM. Individual casting solvent studies show that the casting solvents' solubility for P3HT and pure solvent boiling point, along with residual solvent content in the films have significant implications on final thin film morphology and crystallization of its constituent components. For example, the orientations of P3HT in P3HT:PCBM films, cast from different solvents, are largely affected by the individual solubilities of P3HT and PCBM, and substrate surface energy. On the other hand PCBM crystal growth from different PCBM solutions predominantly depends on the solubilities of PCBM in the solvents and boiling points of solvents. In this study we correlate and distinguish the drying behavior of the blend films with respect to the drying behavior of its constituent components. These results have important ramifications for controlling desired morphology for polymer electronics, such as organic photovoltaics (OPV), organic field effect transistor (OFET) and photo-detectors.

Measurement of free surface energy of laser treated aluminum substrate

The change in the surface energy of the aluminum substrate after laser treatment has been determined experimentally. Surface energy is determined using the Advance KRUSS software. The laser treatment of the surface is found to increase its free surface energy. It changes the ratio of the polar and the dispersion components. Analysis of the crystalline planes of aluminum surface after laser treatment was provided by XRD X-ray diffractometry using a Shimadzu XRD 7000S diffractometer.

VQS (vapor-quasiliquid-solid, vapor-quasisolid-solid) mechanism lays down general platform for the syntheses of graphene by chemical vapor deposition

Graphene is a relatively new material. The current state-of-the-art of the graphene synthesis has been reviewed. Existing mechanism for the graphene synthesis has been examined. The flaws of this mechanism have been described. Attempts have been made to present a new mechanism called the vapor-quasiliquid (quasisolid)-solid mechanism. For this, various physicochemical processes contributing to graphene synthesis have been considered. These processes include the substrate surface morphology, substrate surface energy, carbon solubility in the substrate surface, temperature, and pressure. Surface disturbance and surface amorphicity of the substrate, together with Knudsen diffusion of the carbon species through this surface, are the key elements of the proposed mechanism. This mechanism appears to have a common platform and a number of ground rules. It describes, for the first time, essentially all possible graphene syntheses, including the synthesis of single-layer, bilayer, few-layer, and multilayer graphene films on all possible substrates, such as metal foils, evaporated metal films, semiconductors, ceramics, and dielectrics. It addresses important features of graphene synthesis as well, namely, the role of permeability, substrate surface orientation, edge effects, etc. The results based on the proposed mechanism are in good agreements with the available experiments.

Piezo-resistive behaviour at high strain levels of PEDOT:PSS printed on a flexible polymeric substrate by a novel surface treatment

In this work a conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) thin film was deposited on a treated surface of a flexible substrate using ink-jet printed technique. The novel surface treatment method increased significantly the substrate surface energy (by 45 %) and consequently the thermoplastic polyurethane wettability. SEM and AFM evaluated the thickness uniformity and roughness of the printed ink, respectively. The printed film on the substrate was characterized for the evaluation of its mechanical and electrical properties. The printed substrate presented high flexibility and was able to follow and deform along with the substrate, without breaking or losing adhesion and its conductivity properties at 300) were achieved (higher than the typical value for available flexible metallic strain gauges) showing the potential of the material to be used in high strain sensing applications.

Increased monolayer domain size and patterned growth of tungsten disulfide through controlling surface energy of substrates

We report a surface energy-controlled low-pressure chemical vapor deposition growth of WS2 monolayers on SiO2 using pre-growth oxygen plasma treatment of substrates, facilitating increased monolayer surface coverage and patterned growth without lithography. Oxygen plasma treatment of the substrate caused an increase in the average domain size of WS2 monolayers by 78% ± 2% while having a slight reduction in nucleation density, which translates to increased monolayer surface coverage. This substrate effect on growth was exploited to grow patterned WS2 monolayers by patterned plasma treatment on patterned substrates and by patterned source material with resolutions less than 10 µm. Contact angle-based surface energy measurements revealed a dramatic increase in polar surface energy. A growth model was proposed with lowered activation energies for growth and increased surface diffusion length consistent with the range of results observed. WS2 samples grown with and without oxygen plasma were similar high quality monolayers verified through transmission electron microscopy, selected area electron diffraction, atomic force microscopy, Raman, and photoluminescence measurements. This technique enables the production of large-grain size, patterned WS2 without a post-growth lithography process, thereby providing clean surfaces for device applications.

Influence of diamond surface chemical states on the adhesion strength between Y2O3 film and diamond substrate

The Y2O3 film deposited on chemical oxidation diamond substrate exhibited high adhesion strength and survived thermal shock at 800°C. Oxygenated functionalization of the diamond surface had been successfully achieved via wet chemical oxidation with the increase in O/C atomic ratio from 0.04 to 0.13. The surface energy of the diamond substrate was significantly improved from 35.7mJ/m2 to 61.4mJ/m2. After depositing Y2O3 film on the diamond substrate, the COY bonds were observed at the interface. In addition, the quantity of COY bonds significantly increased with the chemisorbed oxygen concentration increasing. The critical scratch load of Y2O3 film deposited on chemical oxidation diamond substrate increased from 22.5N to 34.1N. Furthermore, the Y2O3 film deposited on chemical oxidation diamond substrate can withstand harsh thermal change and protect the diamond substrate from elevated temperature oxidation in atmospheric air without showing degradation of infrared optical performance.

3D printing of fiber-reinforced soft composites: Process study and material characterization

Fiber-reinforced soft composites (FrSCs) are composites that are made up of polymeric fibers with specific material properties and hierarchical length-scales, embedded within another soft-polymer matrix. This paper is aimed at systematically studying the effect of key processing parameters viz., fiber mat alignment, area coverage, and surface energy of the fiber carrier substrate, on the tensile properties and failure mechanisms seen in 3D printed FrSCs. A novel electrospinning-based “direct-write” system is used for creating the aligned and random nylon fiber mats. The fiber mats are then characterized for their diameter distributions, effective area coverage, number density, and tensile properties. The surface energy of the fiber carrier substrate is found to be critical to the fiber transfer efficiency of the stamping operation used in the 3D printing process, with polytetrafluoroethylene-coated aluminum films being more effective due to their low surface energy. Tensile testing results show that depending on the extent of alignment and the fiber content present in the 3D printed composite, it can have a 40–260% improvement in the elastic modulus over that of the base UV-curable polymer. The composites also show evidence of characteristic failure mechanisms seen in the domain of nanocomposite materials, viz., fiber-induced local plastic deformation (crazing), crack arrest and deflection, fiber strengthening, and fiber pull-out. The evidence of fiber pull-out also points to the formation of an interfacial polymer sheath around the fibers. The elastic modulus of this sheath is estimated to be an order of magnitude higher than the base polymer.

Crystallization of Tyrian purple (6,6′-dibromoindigo) thin films: The impact of substrate surface modifications

The pigment 6,6′-dibromoindigo (Tyrian purple) shows strong intermolecular hydrogen bonds and the film formation is, therefore, expected to be influenced by the polar character of the substrate surface. Thin films of Tyrian purple were prepared by physical vapor deposition on a variety of substrates with different surface energies: from highly polar silicon dioxide surfaces to hydrophobic polymer surfaces. The crystallographic properties were investigated by X-ray diffraction techniques such as X-ray reflectivity and grazing incidence X-ray diffraction. In all cases, crystallites with “standing” molecules relative to the substrate surface were observed independently of the substrate surface energy. In the case of polymer surfaces, additional crystallites are formed containing “lying” molecules with their aromatic planes parallel to the substrate surface. Small differences in the crystallographic lattice constants were observed as a function of substrate surface energy, the corresponding small changes in the molecular packing are explained by a variation of the hydrogen bond geometries. This work reveals that despite the limited influence of the surface energy on the molecular orientation, the crystalline packing of Tyrian purple within thin films is altered and slightly different structures form.

Influences of Substrate Adhesion and Particle Size on the Shape Memory Effect of Polystyrene Particles.

Formulations and applications of micro- and nanoscale polymer particles have proliferated rapidly in recent years, yet knowledge of their mechanical behavior has not grown accordingly. In this study, we examine the ways that compressive strain, substrate surface energy, and particle size influence the shape memory cycle of polystyrene particles. Using nanoimprint lithography, differently sized particles are programmed into highly deformed, temporary shapes in contact with substrates of differing surface energies. Atomic force microscopy is used to obtain in situ measurements of particle shape recovery kinetics, and scanning electron microscopy is employed to assess differences in the profiles of particles at the conclusion of the shape memory cycle. Finally, finite element models are used to investigate the growing impact of surface energies at smaller length scales. Results reveal that the influence of substrate adhesion on particle recovery is size-dependent and can become dominating at submicron length scales.

Experimental study of surfactant driven nematic liquid crystal (NLC) anchoring transitions at solid surfaces: role of solid surface energy and anisotropic NLC – solid interfacial energy

The fundamental understanding of nematic liquid crystal (NLC) alignment on solid surfaces is significant for the operation of liquid crystal displays and devices. We investigate the effect of structure and concentration of surfactants on the anchoring of NLC 4-cyano-4′-pentylbiphenyl (5CB) at 5CB–solid interface. 5CB molecules undergo an ordering transition from parallel to normal anchoring near the surfactant critical micelle concentration depending on the chemical structure of the surfactant tails. In contrast to the previous studies which point to the solubilization of 5CB in surfactant micelles, our experiments indicate that NLC anchoring transition occurs due to the ability of 5CB molecules to penetrate into the surface surfactant layer. The surfactant-driven 5CB anchoring is further related to the surface tension of 5CB (γ5CB), surfactant adsorbed substrate surface energy (γsa), anisotropic 5CB–surface interfacial energy (Δγsl), and spreading coefficient (S). Our experimental results agree with the Creagh–Kahn criterion of predicting surface anchoring from relative values of γsa and γ5CB. A change in the sign of Δγsl and S is also observed along with the anchoring transition. Using a semi-empirical approach, we show that dipolar interactions dominate over dispersion interactions when 5CB molecules exhibit perpendicular anchoring at the solid–5CB interface.

Preparation of Ordered Monolayers of Polymer Grafted Nanoparticles: Impact of Architecture, Concentration, and Substrate Surface Energy

Rapid fabrication of large area, ordered assemblies of polymer grafted (hairy) nanoparticles (PGNs) will enable additive manufacturing of novel membrane, electronic, and photonic elements. Herein, we discuss the relationship between select processing conditions, substrate surface energy, and canopy architecture on the hierarchical structure of sub- to monolayer PGN assemblies. Varying concentrations (10, 20, and 70 nM) of polystyrene (PS) grafted (σ ∼ 1 chain/nm2) gold nanoparticles (AuNP, r0 = 9 nm) were flow-coated onto surface-modified silicon wafers (γs ∼ 20 mN/m, hydrophobic to 80 mN/m, hydrophilic). The profile of an isolated gold–polystyrene (PS) PGN depends on substrate–canopy interface energy. At low substrate–PS interface energy (20 mN/m), the PS canopy spreads to maximize contact with the surface, whereas at high substrate–PS interface energy (80 mN/m), the chains minimize contact area resulting in a more compact, thicker PGN corona. This behavior is translated up to monolayer assemblies, where...

Self-Assembly of Spherical Colloidal Photonic Crystals inside Inkjet-Printed Droplets

The manufacturing of three-dimensional colloidal structures on solid substrates is an important topic of applied research, aiming for photonic components especially in photovoltaic and sensor applications. Whereas conventional techniques such as wet self-assembly are based on engineering of the substrate surface energy, alternative strategies envisage the independence of the interfacial conditions. We report on inkjet printing of colloidal suspensions of monodisperse silica or polystyrene nanoparticles or both and their self-assembly to spherical colloidal photonic crystals. The formation process of the colloidal nanoparticles into stable spherical colloidal assemblies (SCAs) is achieved by a self-assembly process inside tiny droplets of a stochastic mist generated intentionally instead of a jet of individual single droplets using inkjet printing. The mist-jetted, shrinking droplets serve as confined geometries for the solidification of the nanoparticles during the evaporation; thus the particles are pack...

Ordering of lamellar block copolymers on oxidized silane coatings

Thin films of lamellar poly(styrene-b-methyl methacrylate) (PS–PMMA) block copolymers are widely investigated for surface patterning. These materials can generate dense arrays of nanoscale lines when the lamellar domains are oriented perpendicular to the substrate. To stabilize this preferred domain orientation, we tuned the substrate surface energy using oxidation of hydrophobic silane coatings. This simple approach is effective for a broad range of PS–PMMA film thicknesses when the oxidation time is optimized, which demonstrates that the substrate coating is energetically neutral with respect to PS and PMMA segments. The lamellar films are characterized by high densities of defects that exhibit a strong dependence on film thickness: in-plane topological defects disrupt the lateral order in ultrathin films, while lamellar domains in thick films can bend and tilt to large misorientation angles. The types and densities of these defects are similar to those observed with other classes of neutral substrate coatings, such as random copolymer brushes, which demonstrates that oxidized silanes can be used to control PS–PMMA self assembly in thin films.

The effect of the surface energy and structure of the SiC substrate on epitaxial graphene growth

The theoretical calculations and experiments were employed to study the effect of the exposed SiC surface on epitaxial graphene growth.