Changes In Surface Free Energy Research Articles

Composition-dependent morphologies of CeO2 nanoparticles in the presence of Co-adsorbed H2O and CO2: a density functional theory study.

Catalytic activity is affected by surface morphology, and specific surfaces display greater activity than others. A key challenge is to define synthetic strategies to enhance the expression of more active surfaces and to maintain their stability during the lifespan of the catalyst. In this work, we outline an ab initio approach, based on density functional theory, to predict surface composition and particle morphology as a function of environmental conditions, and we apply this to CeO2 nanoparticles in the presence of co-adsorbed H2O and CO2 as an industrially relevant test case. We find that dissociative adsorption of both molecules is generally the most favourable, and that the presence of H2O can stabilise co-adsorbed CO2. We show that changes in adsorption strength with temperature and adsorbate partial pressure lead to significant changes in surface stability, and in particular that co-adsorption of H2O and CO2 stabilizes the {100} and {110} surfaces over the {111} surface. Based on the changes in surface free energy induced by the adsorbed species, we predict that cuboidal nanoparticles are favoured in the presence of co-adsorbed H2O and CO2, suggesting that cuboidal particles should experience a lower thermodynamic driving force to reconstruct and thus be more stable as catalysts for processes involving these species.

Anisotropic Magnetic Polymeric Particles with a Controllable Structure via Seeded Emulsion Polymerization.

Magnetic polymer composites have been widely utilized in potential applications in material science, such as reduction of dyes, immunodiagnostics, biomedicals, and magnetically controllable photonic crystals owing to large surface areas, fast separation, and recyclable performance. In this work, anisotropic magnetic particles were prepared by seeded emulsion polymerization, with morphologies of "Fe3O4-shell", "hemisphere-like", "raspberry-like", "multiple lobes-like", and "sandwich-like". Poly(styrene/divinylbenzene/mono-2-(methacryloxy)ethyl succinate)@ Fe3O4 (P(St/DVB/MMES)@Fe3O4) were the seed microspheres, and P(St/DVB/MMES)@Fe3O4@polymer particles are achieved by seeded emulsion polymerizations. The morphology of the particles depends on polymerization conditions (monomer ratios and surfactant), particle properties, and so on. Then, the minimum surface free energy change principles were used to predict the equilibrium morphologies of the magnetic polymer composites. Through theory, the model gives the correct tendency and good agreement with the equilibrium morphology which was in tandem with TEM results. Lastly, after in situ surface deposition of Ag nanoparticles, magnetic composite particles with sandwich-like morphology were applied for the catalytic degradation of 4-nitrophenol (4-NP) reacting with NaBH4. The apparent rate coefficient is 0.0069 s-1, and it can keep mainly about 80% efficiency in catalysis after five cycles.

The Hydrophilicity of Samama Wood Surface Quality after Boron, Methyl Methacrylate Impregnation, and Heat Treatment

Indicators of surface roughness and surface-free energy can represent the improvement in wood surface quality. In this study, those two indicators were used to determine the change in the samama (Anthocephalus macrophyllus) wood surface following two modification steps, namely impregnation and heat treatment. The first step was boron impregnation in two forms applied separately, i.e., boric acid and borax. The second step was impregnation of methyl methacrylate followed by heat treatment at 90°C and 180°C. Surface roughness was determined following the ISO 4287:1997 standard, and surface free energy was analyzed using the Rabel Method. The results showed that the radial surface of samama wood naturally had a lower roughness than the tangential surface. Impregnation with boric acid, borax, and methyl methacrylate increased the wood surface roughness. However, heat treatment at 180°C tended to smooth the rough surface. Total surface free energy was altered after borax and methyl methacrylate impregnation. However, heat treatment seemingly withdrew the alteration. The polar components and dispersion contributed to total surface free energy with different compositions. In this study, the change in surface roughness was not congruent with the change in total surface free energy. Keywords: boron, heat treatment, impregnation, samama, surface free energy

In situ adsorption study of carboxymethylcellulose and sodium oleate on quartz using a quartz crystal microbalance with dissipation (QCM-D)

Adsorption kinetics and conformation of sodium oleate and carboxymethylcellulose (CMC) on the quartz surface in real time remain a challenge in the flotation system of CMC /sodium oleate/quartz. In this work, in situ adsorption characteristics of CMC and sodium oleate on quartz surface was investigated by using quartz surface crystal microbalance with dissipation (QCM-D). QCM-D data showed that the conformations and kinetics were critically dependent on pH and degree of substitution (DS) of CMC. As the degree of substitution of CMC increases, the adsorption layer on the quartz surface becomes looser. There was only one adsorption stage at pH 8 and 12, and the adsorption layer was rigid at pH 12. At pH= 10, the conformation of the adsorbed layer changes from loose to rigid and then to loose again. CMC adsorbs less in the early adsorption stage, and the adsorbed layer is loose. As the adsorption proceeds, the adsorption increases, and the adsorbed layer becomes more rigid. At stage III, the adsorbed layer becomes loose, which is considered to be the formation of a hydrated layer. Under different pH conditions, the adsorption of sodium oleate on the quartz surface had only one stage, and when CMC and sodium oleate were adsorbed one after the other on the surface of the quartz surface, two distinguishable adsorption stages appeared, and the conformation of the adsorbed layer gradually changed from rigid to loose. The change of surface free energy of quartz surface before and after CMC adsorption was also calculated by Washburn kinetic equation and the van Oss - Chaudhuri-Good theory. The results showed that the surface free energy reduced and the hydrophobicity increased after the adsorption of CMC on the quartz surface.

Investigation of the hydrophilic nature and surface energy changes of HfO2 thin films prepared by atomic layer deposition

The wettability of metal oxides, which is directly related to the surface free energy (SFE), is used in a wide range of robust functional coatings, from hydrophilic to hydrophobic. Because wettability is significantly affected by solid surface properties, several studies on the determinant factors and their correlations have been conducted through the thin-film coating of metal oxides. Herein, we found that HfO2 thin films deposited via atomic layer deposition (ALD) are intrinsically hydrophilic. Simultaneously, a thickness-dependent wettability change is observed. These observations were investigated by measuring water contact angles (WCAs), film surface compositions, roughness, morphologies, and microcrystalline structures of the ALD-grown HfO2 thin films. It was deduced that the surface oxygen species significantly affected the intrinsic hydrophilicity of HfO2 thin films. In addition, the crystalline orientations evolved with film thickness, and thermal annealing was used to determine the thickness-dependent WCA trend. In particular, the transformation of the preferred m(-111) crystal orientation with a low SFE had a dominant impact on the SFE change in the HfO2 thin films. Considering the lack of fundamental studies on the SFE of ALD-grown HfO2 thin films, we believe that this study will help understand the wettability of HfO2 and its overall surface science.

Chitosan-Based High-Intensity Modification of the Biodegradable Substitutes for Cancellous Bone.

An innovative approach to treating bone defects is using synthetic bone substitutes made of biomaterials. The proposed method to obtain polylactide scaffolds using the phase inversion technique with a freeze extraction variant enables the production of substitutes with morphology similar to cancellous bone (pore size 100-400 µm, open porosity 94%). The high absorbability of the implants will enable their use as platelet-rich plasma (PRP) carriers in future medical devices. Surface modification by dipping enabled the deposition of the hydrophilic chitosan (CS) layer, maintaining good bone tissue properties and high absorbability (850% dry weight). Introducing CS increases surface roughness and causes local changes in surface free energy, promoting bone cell adhesion. Through this research, we have developed a new and original method of low-temperature modification of PLA substitutes with chitosan. This method uses non-toxic reagents that do not cause changes in the structure of the PLA matrix. The obtained bone substitutes are characterised by exceptionally high hydrophilicity and morphology similar to spongy bone. In vitro studies were performed to analyse the effect of morphology and chitosan on cellular viability. Substitutes with properties similar to those of cancellous bone and which promote bone cell growth were obtained.

Synergistic Effect of Orange Oil Adjuvant on Acetamiprid in the Control of Edentatipsylla shanghaiensis

We explore the effects of orange oil adjuvant (a kind of spray adjuvant) on the physicochemical properties of acetamiprid (pesticide) when foliage-applied to the surface of pittosporum tobira leaves. The leaf surface was characterized by the OCG (Van Oss–Chaudhury–Good) method, and the relationship between the wetting behavior of various pesticide droplets, including the change in surface free energy (SFE), adhesion force, and adhesion work, is explored to offer insight into the control of the pittosporum tobira psyllid, Edentatipsylla shanghaiensis Li et Chen. Results showed that SFE values for the adaxial and adaxial leaf surfaces were 40.13 mJ/m2 and 37.06 mJ/m2, respectively, while acetamiprid liquids had SFE values of 67.43 mJ/m2 and 63.26 mJ/m2. SFE values of the acetamiprid liquids are greater than that of the leaf surface, and the droplets on the leaves with a smaller adhesion force and lager adhesion work exhibited moderate-to-poor wettability estimated by contact angles. When the concentration of the orange oil adjuvant was between 0.10% and 1.00% above CMC (critical micellar concentration, 0.09%), the SFE values of the acetamiprid liquids were less than that of the leaf surface. The adhesion tension was greatly increased, and the adhesion work decreased by 14.46–28.13%. Meanwhile, droplets on the leaves exhibited good wettability. Field experiments showed that the synergistic effect of acetamiprid against E. shanghaiensis was significantly improved after spraying with orange oil adjuvant at the concentrations 0.10% and 1.0% above CMC. This study demonstrated the use of an orange oil adjuvant with a concentration above CMC to improve the synergistic effect of the insecticide directly through improved leaf wetting, which can provide reference for reducing pesticide dosage and increasing efficiency during the chemical control of pests.

Adhesion properties of polypropylene fabric treated with atmospheric pressure plasma and coated with polyurethane: Studies on ageing process

Polypropylene (PP) tape by tape fabric was modified with atmospheric pressure non-thermal plasma (APNTP) for improved hydrophilicity and adhesion to polyurethane (PU) coating. The major drawback of plasma surface modification is “ageing” of the modified surface with respect to time. In this study polypropylene fabric was subjected to atmospheric plasma treatment and its effect on adhesion properties of plasma treated and polyurethane (PU) coated fabric was studied with respect to ageing behaviour up to 4 weeks. Helium plasma treated and coated PP fabrics showed significant improvement in the adhesion strength as compared to untreated samples. Power and time of the plasma were found to be the most effective parameters for adhesion improvement of the coated fabric. Surface morphological changes were analysed using scanning electron microscope (SEM). Change in surface chemistry was also analysed by Attenuated Total Reflection- Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray Photoelectron Spectroscopy (XPS). Contact angle measurements were carried out to analyse changes in surface wettability and surface free energy was determined. Changes in adhesion strength with respect to ageing time was analysed by statistical significance ANOVA test and found to be stable up to three weeks when PP samples were treated with optimised plasma processing parameters.

Tailoring TiO2-lignin hybrid materials as a bio-filler for the synthesis of composites based on epoxy resin

In this publication, the functional TiO2-lignin hybrid materials were designed and characterized. Based on elemental analysis and Fourier transform infrared spectroscopy, the efficiency of the mechanical method used to obtain systems was confirmed. Hybrid materials were also characterized by good electrokinetic stability, in particular in the inert and alkaline environments. The addition of TiO2 improves thermal stability in the entire analyzed range of temperatures. Similarly, as the content of inorganic component increases, the homogeneity of the system and the occurrence of smaller nanometric particles increase. In addition, a novel synthesis method of cross-linked polymer composites based on a commercial epoxy resin and an amine cross-linker was described as a part of the article, where additionally newly designed hybrids were also used. Subsequently, the obtained composites were subjected to simulated tests of accelerated UV-aging, and then their properties were studied, including changes in wettability (using water, ethylene glycol, and diiodomethane as measurement liquids) and surface free energy by the Owens-Wendt-Eabel-Kealble method. Changes in the chemical structure of the composites were monitored by FTIR spectroscopy due to aging. Microscopic studies of surfaces were also carried out as well as measurements in the field of changes in color parameters in the CIE-Lab system.

Characteristics of Hybrid Bioglass-Chitosan Coatings on the Plasma Activated PEEK Polymer

Polyetheretherketone (PEEK) is a biocompatible, chemically and physically stable radiolucent polymer that exhibits a similar elastic modulus to the normal human bone, making it an attractive orthopedic implant material. However, PEEK is biologically inert, preventing strong enough bonding with the surrounding bone tissue when implanted in vivo. Surface modification and composite preparation are the two main strategies for the improvement of the bioactivity of PEEK. In this study, the plasma activated PEEK surfaces with the embedded bioglass, chitosan, and bioglass-chitosan mixed layers applying from the solution dip-coating technique were investigated. The most prominent factors affecting the coating biocompatibility are strictly connected with the composition of its outer surface (its charge and functional groups), hydrophilic-hydrophobic character, wettability and surface free energy, and topography (size of pores/substructures, roughness, stiffness), as well as the personal characteristics of the patient. The obtained surfaces were examined in terms of wettability and surface-free energy changes. Additionally, FTIR (Fourier Transformation Infrared Spectrometry) and SIMS (Secondary Ion Mass Spectrometry) were applied to establish and control the coating composition. Simultaneously the structure of coatings was visualized with the aid of SEM (Scanning Electron Microscopy). Finally, the obtained systems were incubated in SBF (Simulated Body Fluid) to verify the modifications' influence on the bioactivity/biocompatibility of the PEEK surface. Different structures with variable compositions, as well as changes of the wettability, were observed depending on the applied modification. In addition, the incubation in SBF suggested that the bioglass-chitosan ratio influenced the formation of apatite-like structures on the modified PEEK surfaces.

Fabrication of a Hydrophobic Hierarchical Surface on Shale Using Modified Nano-SiO2 for Strengthening the Wellbore Wall in Drilling Engineering

Wellbore stability is essential for safe and efficient drilling during oil and gas exploration and development. This paper introduces a hydrophobic nano-silica (HNS) for use in strengthening the wellbore wall when using a water-based drilling fluid (WBF). The wellbore-strengthening performance was studied using the linear swelling test, hot-rolling recovery test, and compressive strength test. The mechanism of strengthening the wellbore wall was studied by means of experiments on the zeta potential, particle size, contact angle, and surface tension, and with the use of a scanning electron microscope (SEM). The surface free energy changes of the shale before and after HNS treatment were also calculated using the contact angle method. The experimental results showed that HNS exhibited a good performance in inhibiting shale swelling and dispersion. Compared with the use of water, the use of HNS resulted in a 20% smaller linear swelling height of the bentonite pellets and an 11.53 times higher recovery of water-sensitive shale—a performance that exceeds those of the commonly used shale inhibitors KCl and polyamines. More importantly, the addition of HNS was effective in preventing a decrease in shale strength. According to the mechanism study, the good wellbore-strengthening performance of HNS can be attributed to three aspects. First, the positively charged HNS balances parts of the negative charges of clay by means of electrostatic adsorption, thus inhibiting osmotic hydration. Second, HNS fabricates a lotus-leaf-like surface with a micro-nano hierarchical structure on shale after adsorption, which significantly increases the water contact angle of the shale surface and considerably reduces the surface free energy, thereby inhibiting surface hydration. Third, the decrease in capillary action and the effective plugging of the shale pores reduce the invasion of water and promote wellbore stability. The approach described herein may provide an avenue for inhibiting both the surface hydration and the osmotic hydration of shale.

Grafting parameters and surface free energy components of photosensitive poly(methacrylated spiropyran) brushes

Poly(methacrylated spiropyran) (P(MMASP)) brushes on silicon wafers were synthesized using the interface-mediated RAFT polymerization of methacrylated spiropyran (MMASP) monomers to determine their grafting density and surface free energy changes during photoinitiation. The grafting parameters of P(MMASP) layers such as the grafting density (σ), the radius of gyration (Rg ) and average distance between polymer chains (D) were calculated. It is found that 1.25 P(MMASP) chains covered per nm2 area of wafers, and the distance between chains was 1.0 nm which is smaller than doubled Rg , 1.1 nm. Thus, P(MMASP) chains overlapped each other and forced themselves to stretch away from the interface. We evaluated the surface free energy components of P(MMASP) brushes during photo initiation. Van Oss-Good method was used to calculate the surface free energy components of brushes. It is found that spiropyran (SP)-merocyanine (MC) system significantly influenced the surface energy components of P(MMASP) brushes. The electron acceptor and electron donor surface free energies of SP and MC form of P(MMASP) brushes were found as and respectively. It is concluded that MC form of P(MMASP) brushes possess high base character; whereas, SP forms have low base character.

The influence of pressure on the acoustic cavitation in saturated CO2-expanded N, N-dimethylformamide

CO2-expanded organic solvent is a kind of important fluid medium and has broad applications in chemical industry, environmental protection and other fields. Ultrasonic cavitation in gas expanded liquids (GXLs) is conducive to enhancing mass transfer and producing many exciting phenomena. In this paper, the ultrasonic cavitations and streaming in the saturated CO2-expanded liquid N, N-dimethylformamide (DMF) at 4.2 MPa and 5.2 MPa are observed by a high-speed camera. The cavitation intensity and time trace of pressure pulses are recorded using a PZT hydrophone. The influences of gas–liquid equilibrium pressure and ultrasonic power on the cluster dynamics of transient and stable cavitation are examined. The excess molar enthalpies required for CO2 dissociation from DMF are calculated by Peng-Robinson equations of state and the change of surface free energy of CO2-expanded DMF is predicted. The results show that the excess enthalpy of the mixture is one of the key factors to control ultrasonic cavitation at high pressurized conditions, while the surface tension is the key factor for low pressure. As the increase of applied ultrasonic power, the formation and collapsing frequency of bubble clusters increases, and the amplitude and cyclic frequency of pressure pulse are enhanced. The transient cavitation intensity increases as it reaches a maximum value at a certain ultrasonic power and then decreases. The change trends of stable cavitation intensity under different pressures are basically same. It can be concluded from the evidence that ultrasonic cavitation in CO2-expanded DMF is affected by the combined effect of compression and substitution: compression depresses the nucleation and growth of bubbles, while the high solubility of CO2 in DMF is conducive to the generation of bubbles in cavitation.

Methane Adsorption Behavior and Energy Variations of Brittle Tectonically Deformed Coal under High Temperature and High Pressure.

This paper aims to reveal the methane adsorption characteristics of brittle tectonically deformed coal (TDC) under high temperature and high equilibrium pressure and the surface free energy changes during methane adsorption. Taking the anthracite of the Yangquan mining area of China as the research object, methane adsorption tests of high temperature and high pressure were conducted to discuss the influences of coal deformation, temperature, and pressure on the gas adsorption behaviors of coal under the in situ conditions of deep coal seams. Results indicated that coal deformation and pressure had positive effects on the methane adsorption capacity of coal, whereas temperature showed negative effects. Meanwhile, the negative influences of temperature rise on gas adsorption gradually increased with the equilibrium pressure and the enhancement of coal deformation. In a given adsorption system, the adsorption potential decreased with increasing pressure while increased with temperature. In contrast, the adsorption space increased with increasing pressure and decreased with temperature rise. Meanwhile, adsorption potential decreased with the increase in adsorption space. In the process of methane adsorption, with increasing adsorption pressure, the cumulative reduction of surface free energy gradually increased, whereas the surface free energy reduction at each pressure point decreased. The cumulative and incremental reduction of surface free energy at each pressure point gradually decreased with the increase in temperature. The reduction of adsorption space and cumulative surface free energy and the changes in surface free energy at each pressure point of brittle TDCs were higher than those of primary structure coal, and the changes in the strongly deformed coal (granulitic and mortar coal) were more significant than those of the weakly deformed coal (cataclastic coal). Based on the adsorption potential theory, we drew the adsorption characteristic curves and established adsorption capacity prediction models of primary structure coal and brittle TDCs.

Photoinduced Electron Transfer and Changes in Surface Free Energy in Polythiophene-Polyviologen Bilayered Thin Films.

Bipyridiniums, also known as viologens, are well-documented electron acceptors that are generally easy to synthesize on a large scale and reversibly cycle between three oxidation states (V2+, V•+, and V0). Accordingly, they have been explored in a number of applications that capitalize on their dynamic redox chemistry, such as redox-flow batteries and electrochromic devices. Viologens are also particularly useful in photoinduced electron transfer (PET) processes and therefore are of interest in photovoltaic applications that typically rely on electron-rich donors like polythiophene (PTh). However, the PET mechanism and relaxation dynamics between interfacing PTh and viologen-based thin films has not been well studied as a function of thickness of the acceptor layer. Here, a novel, bilayered thin film composite was fabricated by first spin-coating PTh onto glass slides, followed by spin-coating and curing polyviologen (PV)-based micron-sized films of variable thicknesses (0.5-11.3 μm) on top of the PTh layer. The electron-transfer mechanism and relaxation dynamics from the PTh sublayer into the upper PV film were investigated using femtosecond transient absorption (fTA) spectroscopy and electrochemistry to better understand how the charge-transfer/relaxation lifetimes could be extended using thicker PV acceptor films. The fTA experiments were performed under inert N2 conditions as well as in ambient O2. The latter shortened the lifetimes of the electrons in the PV layer, presumably due to O2 triplet-based trap sites. Contact angle measurements using H2O and MeI were also performed on top of the bilayered films to measure changes in surface free energy that would aid the assessment related to efficiency of the combined processes involving light penetration, photoexcitation, electron mobility, and relaxation from within the bilayered thin films. Insights gained from this work will support the development of future devices that employ viologen-based materials as an alternative electron-acceptor that is both easily processable and scalable.

Physicochemical characteristics of chitosan-TiO2 biomaterial. 2. Wettability and biocompatibility

The study aimed to determine the chemical nature, energy state, and topography of chitosan and/or TiO 2 thin layers, which were transferred from different aqueous solutions or dispersions onto a solid support (mica) by a dip-coating method using the Langmuir-Blodgett trough. The surface topography was analysed using an optical profilometer. The performed wettability measurements were used to estimate changes in the total surface free energy based on the theoretical mathematical Lifshitz-van der Waals-Acid-Base model. In addition, the Langmuir technique was employed to determine the effect of Ch-TiO 2 and/or hyaluronic acid (HA) on the model membrane properties in aspect of biocompatibility. The prepared materials can be classified as high-energy, hydrophilic, with roughness in the nanometric scale. Physicochemical parameters have a significant impact on the processes that take place in the surface layer of the biomaterial being in contact with the biological environment. • Biocompatible chitosan-TiO 2 coating with nano-scale irregularities was obtained on mica. • Surface properties of novel material (Ch-HA-TiO 2 ) were characterized. • Relationship between wettability and surface microstructure was shown. • Hybrid biomaterial exhibited the high surface free energy. • Presence of the hyaluronic acid increased the biocompatibility of Ch-TiO 2 combination.

Recycling of electrode materials from spent lithium-ion battery by pyrolysis-assisted flotation

In this study, the flotation technology is used for the separation and purification of cathode and anode material after removing organics by pyrolysis. Effects of surface microscopic properties on the flotation efficiency of spent electrode materials are investigated, and on this basis, surface analysis combined with flotation foundation tests are conducted to reveal pyrolysis-assisted surface modification mechanism. Residual electrolyte and organic binders decrease the difference in wettability of cathode and anode material, and hinder the interaction between electrode particles and collecting agent. Organics and their pyrolysis products can be adequately removed at the optimum pyrolysis temperature of 550 °C. After pyrolysis, the change of Zeta potential and surface free energy demonstrates that hydrophilic components of cathode material increase while the hydrophobic components of the anode material increase. The induction time of cathode material rises from 190 ms to 650 ms while the induction time of the anode material decrease from 145 ms to 37 ms. Collector adsorption capacity of anode material is obviously improved and anode material is easy to incorporate with bubbles and will be collected in the froth product. After one stage flotation, the recovery rate of cathode material is 83.75% with a high grade of 94.72%.

Surface wetting on micromilled and laser-etched aluminum with ion-beam postprocessing

In this work, micromilling and laser-etching microfabrication techniques are trialed for mimicking the super water repellence of the lotus leaf and the directional water droplet control of the Namib desert beetle. To further alter the surface wetting properties, subsequent ion-beam surface modification techniques are used. Ion-beam postprocessing is used to create an additional nanoroughness on a microstructure as well as a controllable Gibbs surface free energy change of the substrate material. The in-plane spreading for control (smooth) surfaces are compared to the micropatterned surfaces and combined micropatterned and ion-beam processed surfaces. Combined microscale surface engineering via milling or laser etching and ion-beam surface modification allows engineering both hydrophobic and mass-transport properties directly from a bulk material rather than involving a coating. Such surfaces have potential applications in advanced heat-exchanger technology (increasing the condensation heat transfer coefficient), wind turbine technologies (delaying or eliminating ice/frost formation under extreme weather conditions), as well as for atmospheric water harvesting and condensation control on industrial heat exchangers.

Plasma pre-treatment of polypropylene surface for industrial purposes

ABSTRACT The paper describes an experimental investigation of the possibility of industrial modification of surface wettability and adhesion of polymers by the action of a plasma of a gliding discharge generated in air at atmospheric pressure in a simulated production process. The test material was polypropylene plates (PP). The modification was performed by a device with a multi-electrode (four pairs) system, which is not common. The quality of pre-processing and usability was evaluated primarily in terms of the industrial requirements, which means a change in wettability and adhesion expressed by the contact angle/surface free energy value in dependence to sample exposure time expressed by the conveyor belt speed. The surface free energy assessment of a treated polymeric surface by contact angle measurement was carried out by analyzing static sessile drops and evaluated by Owens–Wendt–Rabel–Kaelble (OWRK) model. The results determined a set of operating parameters at which the modification process meets the industrial requirements. By evaluating the change in surface free energy in relation to the storage time, the degree of hydrophobic recovery of the treated samples, i.e. the time stability of the plasma-treated surface, was also determined. It has been found that plasma-treated PP surface fully meets industrial demands and can be stored for at least 50 days.

Changes in Surface Free Energy and Surface Conductivity of Carbon Nanotube/Polyimide Nanocomposite Films Induced by UV Irradiation.

Changes in surface energy and electrical conductivity of polyimide (PI)-based nanocomposite films filled with carbon nanotubes (CNTs) induced by UV exposure are gaining considerable interest in microelectronic, aeronautical, and aerospace applications. However, the underlying mechanism of PI photochemistry and oxidation reactions induced by UV irradiation upon the surface in the presence of CNTs is still not clear. Here, we probed the interplay between CNTs and PIs under UV exposure in the surface properties of CNT/PI nanocomposite films. Changes in contact angles and surface electrical conductivity at the surface of CNT/PI nanocomposite films after UV exposure were measured. The unpaired electron intensity of free radicals generated by UV exposure was monitored by electron paramagnetic resonance. Our study indicates that the covalent interactions between CNTs and radicals generated by UV irradiation on the PI surfaces tailor the surface energy and surface conductivity through anchoring radicals on CNTs. Surprisingly, adding CNTs into PI films exposed to UV leads to antagonistic contributions of dispersion and polar components to the surface energy. The surface electrical conductivity of the CNT/PI nanocomposite films has been improved due to an enhanced hopping behavior with dense π-conjugated CNT sites. To explain the observed changes in surface energy and surface conductivity of CNT/PI nanocomposite films induced by UV exposure, a qualitative model was put forward describing the covalent interactions between UV-induced PI free radicals and CNTs, which govern the chemical nature of surface components. This study is helpful for characterizing and optimizing nanocomposite surface properties by tuning the covalent interactions between components at the nanoscale.