Behnam Akhavan

Hydrophobic plasma polymer coated silica particles for petroleum hydrocarbon removal.

In recent years, functionalized hydrophobic materials have attracted considerable interest as oil removal agents. This investigation has applied plasma polymerization as a novel method to develop hydrophobic and oleophilic particles for water purification. 1,7-Octadiene was plasma polymerized onto silica particles using a radio frequency inductively coupled reactor fitted with a rotating chamber. Plasma polymerized 1,7-octadiene (ppOD) films were deposited using plasma power of 40 W and monomer flow rate of 2 sccm, while polymerization time was varied from 5 to 60 min. The surface chemistry of ppOD coated particles was investigated via X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy, while Washburn capillary rise measurements were applied to evaluate the hydrophobicity and oleophilicity of the particles. The effectiveness of ppOD coated particles for the removal of hydrophobic matter from water was demonstrated by adsorption of motor oil, kerosene, and crude oil. Petroleum hydrocarbon removal was examined by varying removal time and particle mass. The morphology of oil-loaded ppOD coated particles was examined via environmental scanning electron microscopy observations. Increasing the polymerization time increased the concentration of hydrocarbon functionalities on the surface, thus also increasing the hydrophobicity and oil removal efficiency (ORE). The ppOD coated particles have shown to have excellent ORE. These particles were capable of removing 99.0-99.5% of high viscosity motor oil in 10 min, while more than 99.5% of low viscosity crude oil and kerosene was adsorbed in less than 30 s. Plasma polymerization has shown to be a promising approach to produce a new class of materials for a fast, facile, and efficient oil removal.

Plasma Polymer-Functionalized Silica Particles for Heavy Metals Removal

Highly negatively charged particles were fabricated via an innovative plasma-assisted approach for the removal of heavy metal ions. Thiophene plasma polymerization was used to deposit sulfur-rich films onto silica particles followed by the introduction of oxidized sulfur functionalities, such as sulfonate and sulfonic acid, via water-plasma treatments. Surface chemistry analyses were conducted by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. Electrokinetic measurements quantified the zeta potentials and isoelectric points (IEPs) of modified particles and indicated significant decreases of zeta potentials and IEPs upon plasma modification of particles. Plasma polymerized thiophene-coated particles treated with water plasma for 10 min exhibited an IEP of less than 3.5. The effectiveness of developed surfaces in the adsorption of heavy metal ions was demonstrated through copper (Cu) and zinc (Zn) removal experiments. The removal of metal ions was examined through changing initial pH of solution, removal time, and mass of particles. Increasing the water plasma treatment time to 20 min significantly increased the metal removal efficiency (MRE) of modified particles, whereas further increasing the plasma treatment time reduced the MRE due to the influence of an ablation mechanism. The developed particulate surfaces were capable of removing more than 96.7% of both Cu and Zn ions in 1 h. The combination of plasma polymerization and oxidative plasma treatment is an effective method for the fabrication of new adsorbents for the removal of heavy metals.

Development of oxidized sulfur polymer films through a combination of plasma polymerization and oxidative plasma treatment.

A novel two-step process consisting of plasma polymerization and oxidative plasma treatment is introduced in this article for the first time for the fabrication of -SO(x)(H)-functionalized surfaces. Plasma-polymerized thiophene (PPT) was initially deposited onto silicon wafers and subsequently SO(x)(H)-functionalized using air or oxygen plasma. The effectiveness of both air and oxygen plasma treatments in introducing sulfur-oxygen groups into the PPT film was investigated as the plasma input specific energy and treatment time were varied. The surface chemistries of untreated and treated PPT coatings were analyzed by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS), whereas spectroscopic ellipsometry was used to evaluate the film thickness and ablation rate. Surface chemistry analyses revealed that high concentrations of -SO(x)(H) functionalities were generated on the surface upon either air or oxygen plasma treatment. It was found that, at low plasma input energies, the oxidation process was dominant whereas, at higher energies, ablation of the film became more pronounced. The combination of thiophene plasma polymerization and air/oxygen plasma treatment was found to be a successful approach to the fabrication of -SO(x)(H)-functionalized surfaces.

Substrate-Regulated Growth of Plasma-Polymerized Films on Carbide-Forming Metals

Although plasma polymerization is traditionally considered as a substrate-independent process, we present evidence that the propensity of a substrate to form carbide bonds regulates the growth mechanisms of plasma polymer (PP) films. The manner by which the first layers of PP films grow determines the adhesion and robustness of the film. Zirconium, titanium, and silicon substrates were used to study the early stages of PP film formation from a mixture of acetylene, nitrogen, and argon precursor gases. The correlation of initial growth mechanisms with the robustness of the films was evaluated through incubation of coated substrates in simulated body fluid (SBF) at 37° for 2 months. It was demonstrated that the excellent zirconium/titanium-PP film adhesion is linked to the formation of metallic carbide and oxycarbide bonds during the initial stages of film formation, where a 2D-like, layer-by-layer (Frank-van der Merwe) manner of growth was observed. On the contrary, the lower propensity of the silicon surface to form carbides leads to a 3D, island-like (Volmer-Weber) growth mode that creates a sponge-like interphase near the substrate, resulting in inferior adhesion and poor film stability in SBF. Our findings shed light on the growth mechanisms of the first layers of PP films and challenge the property of substrate independence typically attributed to plasma polymerized coatings.

Development of negatively charged particulate surfaces through a dry plasma-assisted approach

A dry two-step plasma process is introduced for the fabrication of particulate surfaces showing negative charges over a wide range of pH. Plasma polymerized thiophene (PPT) was initially deposited onto silica particles using an inductively coupled plasma polymerization reactor fitted with a rotating barrel. Sulfur-functionalized particles were further chemically modified through an oxidative air or water plasma treatment. Wide ranges of plasma specific energies (0.06–2.4 kJ cm−3) and treatment times (5–60 minutes) were employed to manipulate the surface chemistry, hydrophobicity and surface charge of the silica particles. Surface chemistry of the modified silica particles was studied using X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS). Changes in hydrophobicity and surface charge of the modified particles were quantified via Washburn capillary rise measurements and electrokinetic analysis, respectively. Plasma treatment of PPT coated particles resulted in homogenous formation of –SOx(H) functionalities such as sulfonate (SO3−), sulfonic acid (SO3H), and sulfate (SO42−) on surfaces. Such changes in surface chemistry significantly decreased the zeta potential and isoelectric point of the particles as well as their degree of hydrophobicity. In comparison to air plasma, water plasma was found to be a better candidate for the treatment of PPT coated particles as it produced surfaces with lower zeta potentials and isoelectric points. Our introduced solvent-free approach is applicable for the modification of almost any other particles regardless of their shape and surface chemistry. Such surface engineered particles could be utilized as protein detectors/adsorbents, solid-state catalysts, and heavy metal removal agents.

Electric fields control the orientation of peptides irreversibly immobilized on radical-functionalized surfaces

Surface functionalization of an implantable device with bioactive molecules can overcome adverse biological responses by promoting specific local tissue integration. Bioactive peptides have advantages over larger protein molecules due to their robustness and sterilizability. Their relatively small size presents opportunities to control the peptide orientation on approach to a surface to achieve favourable presentation of bioactive motifs. Here we demonstrate control of the orientation of surface-bound peptides by tuning electric fields at the surface during immobilization. Guided by computational simulations, a peptide with a linear conformation in solution is designed. Electric fields are used to control the peptide approach towards a radical-functionalized surface. Spontaneous, irreversible immobilization is achieved when the peptide makes contact with the surface. Our findings show that control of both peptide orientation and surface concentration is achieved simply by varying the solution pH or by applying an electric field as delivered by a small battery.Implanted materials can be rejected by the body, and coating the surfaces with peptides is seen as an option to overcome this problem. Here, the authors investigated how pH and electric fields can be used to prepare defined peptide coatings.

Inhomogeneous Growth of Micrometer Thick Plasma Polymerized Films

Plasma polymerization is traditionally recognized as a homogeneous film-forming technique. It is nevertheless reasonable to ask whether micrometer thick plasma polymerized structures are really homogeneous across the film thickness. Studying the properties of the interfacial, near-the-substrate (NTS) region in plasma polymer films represents particular experimental challenges due to the inaccessibility of the buried layers. In this investigation, a novel non-destructive approach has been utilized to evaluate the homogeneity of plasma polymerized acrylic acid (PPAc) and 1,7-octadiene (PPOD) films in a single measurement. Studying the variations of refractive index throughout the depth of the films was facilitated by a home-built surface plasmon resonance (SPR)/optical waveguide (OWG) spectroscopy setup. It has been shown that the NTS layer of both PPAc and PPOD films exhibits a significantly lower refractive index than the bulk of the film that is believed to indicate a higher concentration of internal voids. Our results provide new insights into the growth mechanisms of plasma polymer films and challenge the traditional view that considers plasma polymers as homogeneous and continuous structures.

Evolution of target condition in reactive HiPIMS as a function of duty cycle: An opportunity for refractive index grading

Competition between target erosion and compound layer formation during pulse cycles in reactive HiPIMS opens up the possibility of tuning discharge conditions and the properties of deposited films by varying the duty cycle in situ without altering the reactive gas mixture. Three different reactive systems, hafnium in oxygen, tungsten in oxygen, and tungsten in oxygen/nitrogen, are studied in which amorphous films of hafnium oxide (HfO2), tungsten oxide (WO3), and tungsten oxynitride (WOxNy) are deposited. We show that the cyclic evolution of the target surface composition depends on the properties of the target including its affinity for the reactive gas mix and the compound layer melting point and volatility. We find that pulse length variations modulate the target compound layer and hence the discharge chemistry and properties of the films deposited. The refractive indices of HfO2 and WO3 were progressively reduced with the duty cycle, whereas that of WOxNy increased. These variations were found to be d...

Controlled deposition of plasma activated coatings on zirconium substrates

Zirconium-based alloys are promising materials for orthopedic prostheses due to their low toxicity, superb corrosion resistivity, and favorable mechanical properties. The integration of such bio-implantable devices with local host tissues can strongly be improved by the development of a plasma polymerized acetylene and nitrogen (PPAN) that immobilizes bio-active molecules. The surface chemistry of PPAN is critically important as it plays a key role in affecting the surface free energy that alters the functionality of bio-active molecules at the surface. The cross-linking degree of PPAN is another key property that directly influences the water-permeability and thus also the stability of films in aqueous media. In this study we demonstrate that by simply tuning the zirconium bias voltage, control over the surface chemistry and cross-linking degree of PANN is achieved.

Direct covalent attachment of silver nanoparticles on radical-rich plasma polymer films for antibacterial applications

Prevention and treatment of biomaterial-associated infections (BAI) are imperative requirements for the effective and long-lasting function of orthopedic implants. Surface-functionalization of these materials with antibacterial agents, such as antibiotics, nanoparticles and peptides, is a promising approach to combat BAI. The well-known silver nanoparticles (AgNPs) in particular, although benefiting from strong and broad-range antibacterial efficiency, have been frequently associated with mammalian cell toxicity when physically adsorbed on biomaterials. The majority of irreversible immobilization techniques employed to fabricate AgNP-functionalized surfaces are based on wet-chemistry methods. However, these methods are typically substrate-dependent, complex, and time-consuming. Here we present a simple and dry strategy for the development of polymeric coatings used as platforms for the direct, linker-free covalent attachment of AgNPs onto solid surfaces using ion-assisted plasma polymerization. The resulting coating not only exhibits long-term antibiofilm efficiency against adherent Staphylococcus aureus (S. aureus), but also enhances osteoblast adhesion and proliferation. High resolution X-ray photoelectron spectroscopy (XPS), before and after sodium dodecyl sulfate (SDS) washing, confirms covalent bonding. The development of such silver-functionalized surfaces through a simple, plasma-based process holds great promise for the fabrication of implantable devices with improved tissue-implant integration and reduced biomaterial associated infections.