Stages Of Film Formation Research Articles

Protein adsorption mechanisms on solid surfaces: lysozyme-on-mica

A methodology for discovering the mechanisms and dynamics of protein clustering on solid surfaces is reviewed and complemented by atomistic molecular dynamics (MD) simulations. In situ atomic force microscopy images of the early stages of protein film formation are quantitatively compared with Monte Carlo simulations, using cluster statistics to differentiate various growth models. We have studied lysozyme adsorption on mica as a model system, finding that all surface-supported clusters are mobile with diffusion constant inversely related to cluster size. Furthermore, our results suggest that protein monomers diffusing to the surface from solution only adhere to the bare surface with a finite probability. Fully atomistic MD simulations reveal that the lysozyme does indeed have a preferred orientation for binding to the surface, so that proteins with incorrect orientations move away from the surface rather than towards it. Agreement with experimental studies in the literature for the residues involved in the surface adsorption is found.

Nanoporous oxide formation by anodic oxidation of Nb in sulphate–fluoride electrolytes

The influence of hydrofluoric acid (HF) concentration and applied potential on the processes of anodic oxidation of Nb in sulphuric acid solution was studied by chronoamperometry, electrochemical impedance spectroscopy and scanning electron microscopy. During the first stage of the process, a compact barrier film is formed. On top of this film, a porous overlayer starts to form, then the nanopores grow into an ordered nanostructure. Subsequently, secondary 3D flower-shaped structures begin to form. These structures gradually spread all over the surface as an irregular multilayer film. The rates of the process of porous overlayer formation and subsequent growth of nanopore arrays increase with applied potential as well as with the HF concentration. The films have been characterised ex situ by electrochemical impedance spectroscopy at open circuit potential and capacitance vs. potential measurements to follow the different stages of nanoporous film formation with electrochemical methods. The impedance spectra and capacitance vs. potential curves have been interpreted using previously proposed models for the amorphous semiconductor/electrolyte interface. An attempt to rationalise the mechanism of nanoporous layer growth is presented by using the conceptual views of the mixed-conduction model and recent ideas for porous film formation on valve metals.

Initial stages of deposition and film formation during spray pyrolysis — Nickel oxide, cerium gadolinium oxide and mixtures thereof

The formation of nickel oxide (NiO), cerium gadolinium oxide (CGO) and NiO–CGO thin films by air blast spray pyrolysis was studied at two scales. First, single droplets of precursor were deposited on sapphire substrates and the morphology of the formed residue was studied as a function of the substrate surface temperature, type of metal salt, salt saturation, and organic solvent in the precursor. Second, the synthesis of continuous films from repetitively deposited droplets and crack formation in the films were studied as a function of substrate temperature and salt decomposition kinetics. Nitrates, acetates, perchlorates and chlorides of nickel, cerium and gadolinium were the metal salts used, and mixtures of ethanol or water with di-, tri- and tetraethylene glycol were used as solvents. Regular ring- or disc-shaped deposits were formed from single droplets that evaporated without boiling and were mainly observed with metal acetate- and chloride-based spray solutions or at low substrate temperatures. Disc-shaped residues were obtained for saturated salt solutions and changed to rings with diminishing rim thickness with decreasing salt saturation. The formation of bubbles in the droplet from boiling or salt decomposition during evaporation resulted in the distortion of the circular shape and was predominantly observed for metal nitrate-based precursors and at high substrate surface temperatures. Continuous, dense and crack-free films of CGO and NiO–CGO with thicknesses up to 500 and 800 nm, respectively, were prepared from metal nitrate/chloride mixtures in a tetraethylene glycol-based solvent. The maximum crack-free thickness decreased with decreasing deposition temperature and was correlated to the metal salt decomposition kinetics.

Role of van der Waals force in latex film formation

Capillary pressure force and direct surface tension force are known to be sufficient though probably not necessary to drive the compaction stage of latex film formation. There is abundant evidence that van der Waals force can draw particles together progressively more around the perimeters of interparticle contacts, but their role in compaction remains unanswered. With the powerful technique of high-resolution cryogenic scanning electron microscopy (cryo-SEM), together with fast-freezing and freeze-drying followed by controlled annealing at temperatures below and around the nominal glass transition temperature, we have documented the role of van der Waals force in film formation in the water-free condition, i.e., with capillary pressure and surface tension forces absent. Results of imaging the freeze-dried and annealed coatings are fully consistent with the hypothesis that van der Waals force alone can compact a latex coating. The rate at which particles flatten and thus the coating compacts by annealing increases, as expected, with temperature and time. The results of rewetting tests of coatings annealed at various temperatures demonstrate that compacted coating is not necessarily coalesced, and that even full compaction of solid particles can be elastic, hence reversible, rather than viscoelastic or viscoplastic. Some of the results suggest that soluble ionic surfactant and oligomeric and grafted polymeric stabilizers at particle surfaces, collapse to undetectable dimensions during freeze-drying, yet reswell to detectable size during rewetting, if they have not dissolved into polymer particles during annealing.

Poly (styrene) latex/modified Na-activated bentonite nanocomposite films: A fluorescence study

We studied film formation of composites of surfactant-free polystyrene (PS) nanoparticles and modified Na-activated bentonite (MLB), by steady state fluorescence (SSF) technique. The films were prepared from a mixture of pyrene (P)-labeled PS particles and MLB at various compositions at room temperature. These films were annealed at elevated temperatures above the glass transition ( T g) temperature of polystyrene for 10 min. Scattered light ( I s) and fluorescence intensities ( I P) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of the composite films was monitored by using photon transmission intensity, I tr. Atomic force microscopy (AFM) was used to detect the variation in physical structure of annealed composite films. The nanocomposite films exhibited a percolation threshold at 20 wt.% MLB content. Below this fraction two distinct film formation stages were observed which are known as void closure and interdiffusion and above this fraction no film formation was detected. At 0–20 wt.% MLB, minimum film formation, T 0, void closure, T v and healing, T h temperatures were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. Void closure activation energies decreased as the percent of MLB increased, no variation was observed in backbone activation energies.

Boundary film formation from overbased calcium sulfonate additives during running-in process of steel–DLC contact

The initial stage of boundary film formation from overbased calcium sulfonate at steel–DLC (diamond like carbon) contact was studied. A running-in process was clearly observed by the combination of fresh DLC with fresh steel or fresh DLC with rubbed steel. On the other hand, rubbed DLC does not possess the running-in process. Surface analysis by TOF-SIMS was applied to investigate the formation process and structure of films. It was found that the transfer of iron from the steel ball on to the DLC surface plays a significant role in the formation of boundary film. The depth profile of the film was also obtained by means of an etching technique. The boundary film on steel ball and DLC are mainly composed of iron and calcium oxide. However the depth profiles indicate that distribution of calcium oxide on steel ball is different from that on DLC coated disk.

Stable aqueous film coating dispersion of zein

The effects of plasticizers, pH, and electrolytes on film formation and physical stability of aqueous film coating dispersions (pseudolatexes) of zein were evaluated. The influence of plasticizer on film formation mechanism and minimum film-formation temperature (MFT) were monitored by means of hot stage microscopy (HSM). Furthermore, the effects of pH and electrolytes on the short-term physical stability of pseudolatexes were investigated by measuring relative absorbance, zeta potential, and particle size of the dispersions. With aqueous coating dispersions of zein, stages of film formation were identified. The dispersions plasticized with 20% (w/w) PEG 400 or glycerol formed mechanically strong and flexible films with the lowest glass transition temperature ( T g ). Physical stability of the aqueous zein dispersions was dependent on both pH and electrolyte content. At a pH ranging from 3 to 4, the aqueous dispersions of zein were stable for at least 2 months exhibiting the highest values for zeta potential, the smallest particle size, and a low volume of aggregates. The stable dispersion could be obtained containing a lower concentration of electrolytes (e.g., 10 −5 M). The physical stability of aqueous zein dispersions can be determined by the combined measurements of relative absorbance, zeta potential, and particle size.

Supramolecular mechanisms responsible for the high activity of aerosol stimulants of atmospheric moisture nucleation

Water vapor nucleation preceding crystal nucleation was studied by computer simulation; the role of crystal defects on the surface with a structure complementary to the structure of ice was investigated. The Gibbs energy and microdrop formation energy were calculated at the molecular level. The structure and thermodynamic stability of nuclei in the fields of crystal defects of different types were analyzed. It was found that crystal point defects could not stimulate the formation of large nuclei. Extended defects such as wedge-shaped fractures were shown to be the most effective stimulants. The stage of monomolecular film formation in fractures was preceded by the formation of three-dimensional microdrops. The conclusion was drawn that microcrystallization was favored by a relatively large surface of contact with microfracture walls, the three-dimensional structure of nuclei, and their high thermodynamic stability in the transverse microfracture field; these factors drastically accelerated the growth of nuclei and their coalescence on the surface of aerosol particles.

EIS investigation of passive film formation on mild steel in oxalic acid solution

The properties of oxide films on mild steel formed anodically in aqueous solution containing oxalic acid were investigated by means of electrochemical impedance spectroscopy (EIS). The morphology of the passive layers at different stages of film formation was investigated using scanning electron microscopy (SEM). Passivation of mild steel in oxalic acid solution is a multi-stage process that occurs before passive layer breakdown. The influence of potential on the electrochemical behavior of the passive layer was also investigated. Depending on the passive layer potential, the EIS spectra obtained exhibited a one- or two-time constant system. This suggests the formation of either a one layer or two layer oxide film on the mild steel surface, depending on the passivation potential.

Combined Scanning Tunneling Microscopy and Synchrotron X-Ray Photoemission Spectroscopy Results on the Oxidative CuI Film Formation on Cu(111)

The initial stage of oxidative CuI film formation on Cu(111) has been studied in an electrochemical environment by means of cyclic voltammetry (CV), in situ scanning tunneling microscopy (STM) and ex situ synchrotron X-ray photoemission spectroscopy (SXPS). Cyclic voltammetric studies indicate a significant acceleration of copper oxidation in the presence of iodide. The reason for that is the iodide-mediated stabilization of cuprous species resulting in a downward shift of the onset potential for copper oxidation. Reactive sites for the copper oxidation followed by iodide complexation are exclusively defects such as substrate step edges. It is the surface-confined supersaturation of mobile CuI species that leads to the two-dimensional (2D) CuI film formation via nucleation and growth of a Cu/I bilayer on top of the preadsorbed iodide phase. In an advanced stage of copper oxidation, however, terraces are directly transformed into the 2D CuI film at the reactive boundary between metallic copper and the growing 2D CuI film. Structurally, this 2D CuI film is closely related to the (111) plane of crystalline CuIbulk (zinc blende type). There is no significant passivation of the copper surface against the oxidative dissolution reaction in the presence of the 2D CuI film. Copper dissolution in the presence of the 2D CuI film proceeds also via an inverse step flow mechanism involving the concerted receding of four atomic layers. A model of this process will be discussed on the basis of STM results. The transition from 2D to a three-dimensional (3D) CuI growth mode is observed for an advanced stage of copper oxidation.

Motion of agglomerates on the surface in the formation of methane hydrate crystals

A study of the formation of a crystal hydrate film CH4 · 6H2O on the surface of an immobile solution of methane in water have shown that, at early stages of film formation, hydrate crystals and their agglomerates are in motion at a velocity of 2–5 mm/s caused by crystal growth. Collisions of agglomerates are accompanied by their rotations at a Ω ∼ 0.2–2 rad/s rate. The motion of crystals and agglomerates is explained using the hydrodynamic model that takes into account the surface tension and the difference in the pressure exerted by the medium on the growing and nongrowing faces of crystals, which sets them in chemoreactive motion.

Control System of the Experimental Research of Deposition Process in Vacuum

The control system for near-atomic thin films deposition is disclosed. The system is consisting of three parts: vapor pressure control, film conductivity control and stepwise coverage control. All three subsystems are explored experimentally and found to have the sufficient potential to give improved repeatability of deposition of near-atomic thin films. The results and conclusions from stepwise coverage experiments, followed by AFM and XPS analysis is presented as an evidence of direct relationship between the in-situ recorded voltage pattern and the film formation stages. Ill. 6, bibl. 10 (in English; abstracts in English, Russian and Lithuanian).

The STM view of the initial stages of polycrystalline Ag film formation

The growth of Ag thin films deposited at 300 K on amorphised Si surfaces under ultra high vacuum conditions is investigated by in situ scanning tunnelling microscopy. The analysis of film morphology as a function of film thickness together with additional annealing experiments allow a quite complete picture of the film formation processes to be obtained.

In situ STM of pulsed laser nanostructured deposits: First stages of film formation

In the synthesis of nanostructured thin films the characterization of the growth processes plays a fundamental role for the control of the film and surface properties. Moreover when the deposition technique is based on the production and the assembling of nanoparticles/clusters the characterization of the precursor size distribution is of fundamental importance. We have designed a pulsed laser deposition (PLD) apparatus for the production of nanostructured thin films and surfaces, connected to a UHV variable temperature scanning tunneling microscope (STM). The whole system is devoted to the synthesis and in situ study of nanostructured and nanoporous functional metal and metal oxide films and surfaces. We have deposited W nanoparticles produced by a few hundreds laser pulses in order to investigate the initial mechanisms of the film growth. Different deposition conditions have been explored by controlling the laser generated plasma expansion through a background gas in the PLD chamber. STM measurements have been performed on W thin films deposited on different substrates to study both the size distribution and the aggregation of the precursors on the surface. Although substrate effects must be taken into account, the control of the background gas pressure and of the target-to-substrate distance allows to produce surfaces with different morphologies. This opens the possibility to tailor the material properties through the control of the size and deposition energy of the building nano-units.

Film formation from TiO2-polystyrene latex composite: a fluorescence study

This work reports the use of the steady state fluorescence (SSF) technique for studying film formation from TiO2 covered polystyrene (PS) latex particles. The composite films were prepared from pyrene (P)-labeled PS particles by covering them with TiO2 at room temperature and then annealed at elevated temperatures in 10 min time interval above glass transition (T g) temperature of polystyrene. Five different composite films were studied in various TiO2 layer contents. Fluorescence intensities I P from P were measured after each annealing step to monitor the stages of film formation. Films showed considerable increase in I P above the certain onset temperature called minimum film forming temperature, T 0. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 23.12 and 92.80 kJ mol−1, respectively.

Fluorescence Study of Fılm Formatıon From Hard/ Soft Latex Blends

AbstractThe effects of blend composition on film formation is studied using the SSF and UV-visible (UVV) techniques. Latex blend films were prepared from mixtures of two types of particles in dispersion, one composed of a high-Tg (hard) pyrene (P) labeled polystyrene (PS) latex; the other a low-Tg (soft) poly(n-butyl acrylate) (BuA1). Twelve different blend films were prepared in various hard/soft latex compositions at room temperature and annealed at elevated temperatures above glass transition temperature (Tg) of polystyerene for 10 min. Fluorescence intensity (IP) from P was measured after each annealing step to monitor the stages of film formation. The evolution of transparency of latex films was monitored using photon transmission intensity, Itr. Film morphologies were examined by atomic force microscopy (AFM). The results showed that as the amount of hard component in the blend is decreased, a significant change occured in both IP and Itr curves at a certain critical weight fraction (50%wt) of PS hard latex. Above this fraction two distinct film formation stages, which are named as void closure and interdiffusion were seen in fluorescence data. However, below 50%wt PS no film formation stages were observed. Below this fraction, Itr data showed that phase separation process occurs between PS and BuA1 polymers. These results were also confirmed by AFM pictures. Film formation stages for 50-100%wt range of PS were modeled and related activation energies were calculated. There was no observable change in activation energies confirming that film formation behavior is not affected by varying the blend composition.

The effect of clay particles on film formation from polystyrene latex

AbstractFilm formation from surfactant‐free polystyrene (PS) latex was performed in the presence of 5% Na‐montmorillonite (NaMMT). The composite films were prepared from pyrene (P)‐labeled PS particles at room temperature and annealed at elevated temperatures above the glass‐transition (Tg) temperature of polystyrene. Scattered light (Is) and fluorescence intensity (IP) from P were measured after each annealing step to monitor the stages of composite film formation. Minimum film formation temperature, T0, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were measured. From these results, it was found that the presence of NaMMT in the PS latex film only affects the minimum film formation, but does not affect the void closure and backbone motion activities. POLYM. COMPOS., 27:299–308, 2006. © 2006 Society of Plastics Engineers

Film formation stages for poly(vinyl acetate) latex particles: a photon transmission study

Photon transmission technique was used to monitor the evolution of transparency during film formation from poly(vinyl acetate) (PVAc) latex particles. The latex films were prepared below the glass transition temperature (Tg) of PVAc. These films were annealed at elevated temperatures in various time intervals above the Tg of PVAc. It is observed that transmitted photon intensity (Itr) from these films increased as the annealing temperature is increased. It is seen from Itr curves that there are two film formation stages. These successive stages are named void closure (viscous flow) and interdiffusion. The activation energies for viscous flow (ΔH) and backbone motion (ΔEb) were obtained by using well-defined models. The averaged values of the backbone (ΔEb) and the viscous flow activation energies (ΔH) were found to be 188.6 and 5.6 kcal/mol, respectively. The minimum film formation (τM,TM) and healing points (τH,TH) were determined. Minimum film formation (ΔEM) and healing activation energies (ΔEH) were measured using these time–temperature pairs. ΔEM and ΔEH were found to be 32.5 and 28.3 kcal/mol, respectively.

Viscoelastic Analysis in the Formation of Organic Thin Films

ABSTRACT The initial stage of film formation has been analyzed using the quartz crystal microbalance (QCM) method. The resonance frequency and resistance of the QCM covered with paraffin thin film indicate that the viscoelastic properties of films can be changed even before the film formation from the melt or the solution, i.e., pre-transition phenomena can be observed. The QCM analysis also reveals that liquid crystalline molecules can be adsorbed as a solid phase in the vicinity of the interface even in the nematic liquid crystal phase.

Film formation from polystyrene–poly(butyl acrylate-co-methyl methacrylate) latex blends

We have employed steady sate fluorescence (SSF) and UV-visible (UVV) techniques to determine the film formation behavior of latex blends. Blend films were prepared from mixtures of a high-Tg pyrene (P) labeled polystyrene (PS) latex and a low-Tg copolymer of poly(butyl acrylate-co-methyl methacrylate) (BuA/MMA4). Eleven different blend films were prepared in various hard/soft latex compositions at room temperature and annealed at elevated temperatures above glass-transition (Tg) temperature of polystyerene for 10 min. Fluorescence intensity (IP) from P was measured after each annealing step to monitor the stages of film formation. The evolution of transparency of latex films was monitored using photon transmission intensity, Itr. Film morphologies were examined by atomic force microscopy (AFM). A significant change occurs in both IP and Itr intensities at a certain critical weight fraction of hard latex (Rc = 0.3). Above Rc, two distinct film formation stages, which are named as void closure and interdiffusion processes, were seen in fluorescence data. Transparency of the films was decreased with decreasing PS content, indicating that a phase separation process occurs between PS and BuA/MMA4 phases by thermal treatment, which results in turbid films. However, below Rc, no change was observed in IP and Itr upon annealing, whereas transparency increased overall with increasing BuA/MMA4 ratio. We explained this result as the phase separation process between PS and BuA/MMA4 blends. These results were also confirmed by AFM pictures. Film formation stages above Rc were modeled and related activation energies were calculated. POLYM. COMPOS., 27:431–442, 2006. © 2006 Society of Plastics Engineers