Physical Surface Changes Research Articles

Design of an UV-C shielded biopolymer based on a poly(lactic acid)/quercetin/magnesium composite

The use of biopolymers like poly(lactic acid) (PLA) doped with natural and harmless active agents in industrial, medical and food packaging applications is of great interest due to the multitude of property enhancements included. External factors, such as UV exposure, can accelerate the degradation process of these biomaterials and cause changes in structural and mechanical properties of medical or industrial devices. In this research, PLA-based composites with different degrees of crystallinity are fabricated using magnesium (Mg) particles and quercetin (Qr) as doping agents, providing new biomaterials with different responses against an UV-C radiation source. Physical surface changes are studied by atomic force microscopy (AFM), goniometry and scanning electron microscopy (SEM). Chemical modifications are evaluated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Thermal response is studied by differential scanning calorimetry (DSC). PLA crystallinity is crucial in the polymer response to UV radiation. Under irradiation Mg particles cause a catalytic effect that enhances the degradation by hydrolysis of PLA chains. However, when Qr is present this effect is inhibited, making the Qr/Mg combination an ideal enrichment to protect the polymer from chemical photooxidation, while improving the surface mechanical properties of the new biocomposite.

A Comparison of Materials for Dry Surface Cleaning Soot-Coated Papers of Varying Roughness: Assessing Efficacy, Physical Surface Changes, and Residue

ABSTRACT To provide detailed information to aid conservators faced with soot removal, a survey comparing the removal of lamp black pigment, serving as a model soot, from three sample papers of differing roughness is presented. The efficacy of ten different dry surface cleaning materials—including sponges, firm and kneaded erasers, eraser crumbs, a cleaning putty, a solvent-free polydimethylsiloxane elastomer, and a dry swab—have been assessed using a handheld color spectrophotometer and image analysis of photomicrographs. Inspection of the cleaned substrates with a portable optical microscope revealed detailed information into how physical properties of cleaning materials influence the location of residual soot on the surface. 3D digital light microscopy and Fourier-transform infrared spectroscopy were used to assess physical changes to the paper surface and to identify potential residues from the materials after cleaning, respectively. The results of this model study were compared with spot cleaning tests performed on a fire-damaged paper book cover. Limited access to laboratory spaces during Covid-19 lockdown motivated this research to focus on affordable ways to perform hands-on technical research outside of the laboratory, details of which are noted throughout this paper.

Modification of physico-chemical surface properties and growth of Staphylococcus aureus under hyperglycemia and ketoacidosis conditions

Diabetes is a widely spread disease affecting the quality of life of millions of people around the world and is associated to a higher risk of developing infections in different parts of the body. The reasons why diabetes enhances infection episodes are not entirely clear; in this study our aim was to explore the changes that one of the most frequently pathogenic bacteria undergoes when exposed to hyperglycemia and ketoacidosis conditions. Physical surface properties such as hydrophobicity and surface electrical charge are related to bacterial growth behavior and the ability of Staphylococcus aureus to form biofilms. The addition of glucose made bacteria more negatively charged and with moderate-intermediate hydrophobicity. Ketone bodies increased hydrophobicity to approximately 75% and pathological concentrations hindered some of the bacterial surface charge by decreasing the negative zeta potential of cells. When both components were present, the bacterial physical surface changes were more similar to those observed in ketone bodies, suggesting a preferential adsorption of ketone bodies over glucose because of the more favorable solubility of glucose in water.Glucose diabetic concentrations gave the highest number of bacteria in the stationary phase of growth and provoked an increase in the biofilm slime index of around 400% in relation to the control state. Also, this situation is related with an increase of bacterial coverage. The combination of a high concentration of glucose and ketone bodies, which corresponds to a poorly controlled diabetic situation, appears associated with an early infection phase; increased hydrophobic attractive force and reduced electrostatic repulsion between cells results in better packing of cells within the biofilm and more efficient retention to the host surface.Knowledge of bacterial response in high amount of glucose and ketoacidosis environments can serve as a basis for designing strategies to prevent bacterial adhesion, biofilm formation and, consequently, the development of infections.

Effect of plasma treatment on the surface properties of polylactic acid films

Plasma treatment is one of the methods currently used to obtain polymeric materials with surface properties appropriate to the functionality for which they were designed. However, the effects achieved after surface modification are not always long lasting and involve chemical and physical changes in the outermost layer. In this context, the effects of both argon and oxygen plasma on polylactic acid (PLA) films deposited on titanium were studied to determine which physical and chemical processes occur at the surface, and their duration. Regarding physical surface changes, there were scarcely any differences between both plasmas: roughness was very similar after treatments, root mean square height (Sq) being 10 times higher than the control, without plasma. Water contact angle (WCA) showed that the surface became more hydrophilic after application of the plasma, although hydrophilization was longer lasting in the case of argon treatment.With regard to chemical changes, it was observed that the argon plasma treatment caused greater fragmentation of the polymer chains, and increased crosslinking between them. ToF-SIMS analysis made it possible to propose mechanisms to explain the formation of the fragments observed.

Investigation of Chemical and Physical Surface Changes of Thermally Conditioned Glass Fibres

A number of analytical techniques were applied to investigate changes to the surface of unsized boron-free E-glass fibres after thermal conditioning at temperatures up to 700 °C. Novel systematic studies were carried out to investigate the fundamental strength loss from thermal conditioning. Surface chemical changes studied using X-ray photoelectron spectroscopy (XPS) showed a consistent increase in the surface concentration of calcium with increasing conditioning temperature, although this did not correlate well with a loss of fibre strength. Scanning electron microscopy fractography confirmed the difficulty of analysing failure-inducing flaws on individual fibre fracture surfaces. Analysis by atomic force microscopy (AFM) did not reveal any likely surface cracks or flaws of significant dimensions to cause failure: the observation of cracks before fibre fracture may not be possible when using this technique. Fibre surface roughness increased over the whole range of the conditioning temperatures investigated. Although surface roughness did not correlate precisely with fibre strength, there was a clear inverse relationship at temperatures exceeding 400 °C. The interpretation of the surface topography that formed between 400–700 °C produced evidence that the initial stage of phase separation by spinodal decomposition may have occurred at the fibre surface.

Effects of different sterilization methods on the physico-chemical and bioresponsive properties of plasma-treated polycaprolactone films

For most tissue engineering applications, surface modification and sterilization of polymers are critical aspects determining the implant success. The first part of this study is thus dedicated to modifying polycaprolactone (PCL) surfaces via plasma treatment using a medium pressure dielectric barrier discharge, while the second part focuses on the sterilization of plasma-modified PCL. Chemical and physical surface changes are examined making use of water contact angle goniometry (WCA), x-ray photoelectron spectroscopy and atomic force microscopy. Bioresponsive properties are evaluated by performing cell culture tests. The results show that air and argon plasmas decrease the WCA significantly due to the incorporation of oxygen-containing functionalities onto the PCL surface, without modifying its morphology. Extended treatment times lead to PCL degradation, especially in the case of air plasma. In addition to surface modification, the plasma potential to sterilize PCL is studied with appropriate treatment times, but sterility has not been achieved so far. Therefore, plasma-modified films are subjected to UV, H2O2 plasma (HP) and ethylene oxide (EtO) sterilizations. UV exposure of 3 h does not alter the PCL physico-chemical properties. A decreased wettability is observed after EtO sterilization, attributable to the modification of PCL chain ends reacting with EtO molecules. HP sterilization increases the WCA of the plasma-treated samples, presumably due to the scission of the hydrophilic bonds generated during the prior plasma treatments. Moreover, HP modifies the PCL surface morphology. For all the sterilizations, an improved cell adhesion and proliferation is observed on plasma-treated films compared to untreated ones. EtO shows the lowest proliferation rate compared to HP and UV. Overall, of the three sterilizations, UV is the most effective, since the physical alterations provoked by HP might interfere with the structural integrity when it comes to 3D scaffolds, and the chemical modifications caused by EtO, in addition to its toxicity, interfere with PCL bioactivity.

On the Hydrophilicity and Water Resistance Effect of Styrene‐Acrylonitrile Copolymer Treated by CF4 and O2 Plasmas

A commercial formulation of styrene‐acrylonitrile copolymer (SAN) sheets were surface‐modified by using non‐thermal radiofrequency and microwave plasma treatments. In order to evaluate the possible improvement of SAN surface properties, the modification was performed using oxygen and tetraflouromethane (CF4) discharges under different treatment durations and output powers. The untreated and treated samples were chemically and morphologically characterised by X‐ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM), and surface charge was evaluated by zeta potential (ζ) measurements. In addition, water contact angle measurements were employed for evaluating the extent of hydrophilicity and hydrophobicity on the treated specimens. The overall outcome indicated drastic chemical and physical surface changes, which vary according to the carrier gas. Surface became noticeably hydrophilic after few seconds of oxygen plasma treatments, whilst the surface became hydrophobic after the CF4 treatments. The present approach might serve as a feasible and promising method to alter the surface properties of styrene‐acrylonitrile copolymers.

Comparative Evaluation of Physical Surface Changes and Incidence of Separation in Rotary Nickel-Titanium Instruments: An in Vitro SEM Study.

The aim of the present study was to comparatively evaluate the physical surface changes and incidence of separation in rotary nickel-titanium (NiTi) instruments using scanning electron microscope (SEM). A total number of 210 freshly extracted human maxillary and mandibular first molars were selected and distributed between three groups. Three different systems of rotary NiTi instruments, namely ProFile (PF), RaCe (RC) and Twisted File (TF), were used to prepare the canals using crown-down technique. All instruments were evaluated by means of SEM with 500× and 1500× magnifications, at four different stages; before use, after preparation of 7 and 14 canals and after instrument separation. Photomicrographs were also taken. The data was analyzed using the Kruskal-Wallis test and the level of significance was set at 0.001. It was found that H (HAT matrix) was 15.316 with 2 degrees of freedom. Moreover the various groups were compared using the Student-Newman-Keuls test with P<0.05 and it was found that all groups were significantly different. RC showed the maximum wear of the surface followed by TF (P<0.05). PF showed the minimum wear except for its tip. There was no correlation between electropolishing and file fracture. Insignificant difference was observed in the mean number of canals shaped by PF and TF before their separation. Clinically, TF performance was superior, followed by PF then RC. RC fracture rate was the greatest after preparing the least number of canals.

Wetting ability modifications in biocompatible polymers induced by pulsed lasers

Wetting ability was measured in the surface of different biocompatible polymers, such as mylar, polyethylene, poly-methyl-methacrylate and teflon. Nanosecond pulse lasers at intensities of the order of 108 W/cm2 were employed at different doses to irradiate the polymeric surfaces and to induce wetting ability modifications due to the chemical and physical surface changes vs. irradiation time and laser wavelength. In particular, the contact angle as a function of the surface roughness was investigated, as will be presented and discussed.

Chemical and physical changes in surface of Argon plasma treated cotton fabrics

Hydrophilic cotton fabrics were exposed by low-pressure DC glow discharge plasma in argon atmosphere. The influence of different operating parameters such as treatment time, discharge potential, and operating pressure on the chemical and physical properties of the cotton fabrics is studied. Surface analysis and characterization of the plasma-treated cotton fabrics is performed using vertical wicking experiments, X-ray photoelectron spectroscopy, scanning electron microscopy, and weight loss measurements. The cotton fabrics show a significant increase in wicking behavior, an effect that increases with increasing treatment time. Results also show that low-pressure DC glow treatment leads to surface attrition of the cellulose fibers, accompanied by an incorporation of oxygen-containing groups (C–O, C=O, O–C–O, and O–C=O) on the cotton fibers.

Effects of Thermobifida fusca cutinase-carbohydrate-binding module fusion proteins on cotton bioscouring

Previously, we presented a novel approach for increasing Thermobifida fusca cutinase adsorption on cotton fibers by fusing cutinase with a carbohydrate-binding module (CBM). A preliminary study showed that two fusion proteins, namely cutinase-CBMCel6A and cutinase-CBMCenA, with similar stabilities and catalytic properties, had potential applications in bioscouring. In the present study, an indepth analysis of both cutinase-CBMs in bioscouring was explored. Effects of cutinase-CBMs on cotton bioscouring were investigated by characterizing the chemical and physical surface changes in enzyme-treated cotton fabrics. Gas chromatography/mass spectrometry was used to analyze the degradation of the cotton fabric cuticle; Fourier transform infrared microspectroscopy was used to study changes in the chemical composition of the cotton fabric epidermal layer; and scanning electron microscopy was used to monitor minor changes in the morphology of the fiber surface. Our results indicated that cutinase-CBMs in combination with pectinase had a greater effect on cotton fabric than did cutinase. Following scouring with cutinase-CBMs and pectinase, the performance of cotton fabric in terms of its wettability and dyeability was similar to that following alkali scouring. Our study provides a foundation for the further application of cutinase-CBM to bioscouring.

Techniques for Studying In Situ Corrosion and Related Surface and Interfacial Phenomena

An in situ optical microscopy and electrochemical analysis method is presented for studying corrosion processes of metals and alloys (316L SS, Al 6061, Mg) in aerated and deaerated solutions (0.5 M and 6M NaCl, 1M H2SO4). Real time optical images were recorded for various in situ physical surface changes (etching, pitting, surface discoloration, gas bubbles), microstructure (inclusions, grain boundaries, dislocation slip traces, twins) and correlated to the electrochemical (potentiostatic, potentiodynamic, polarization) data measured simultaneously. This technique is reviewed along with other in situ surface analytical probes including recent advances in optical microscopy methods involving higher resolution imaging and the results are discussed in terms of theories and current applications in the field of study. This super-resolution patent review highlights developments in optical microscopy [14], phototransformable optical labels [14, 17, 19], and double confocal microscopy [17], and corrosion results from near-field scanning optical microscopy, and in situ confocal laser scanning microscopy compared to our in situ optical microscopy plus electrochemical analysis. Keywords: In situ, optical, potentiostatic, potentiodynamic, SEM-EDS, etching, pitting, grain boundaries, twins, 316L, Al6061, Mg 0.5M, 6M NaCl, 1M H2SO4, Situ Corrosion, chloride ions, oxide film, aluminum oxide, tunneling microscopy

Characterization and Adhesion of Interacting Surfaces in Capacitive RF MEMS Switches Undergoing Cycling

The performance and reliability of capacitive-type Radio Frequency Microelectromechanical Systems (RF MEMS) switches are affected by interfacial interactions such as strong attractive adhesion forces that could cause the switch to get temporarily or permanently stuck, thus rendering the device nonfunctional. Such adhesion forces could be induced and progressively increase during cycling by mechanical surface changes, such as increased real contact area or electrical effects such as increased electrostatic forces by dielectric charging. Both effects can occur simultaneously, which makes the characterization of capacitive switch behavior more complex than metal-to-metal switches. In this work, capacitive RF MEMS switches with Ti-on-silicon nitride contact surfaces were fabricated and tested for different numbers of cycles. After cycling, the Ti beam and Si3N4 dielectric contact surfaces were exposed and examined topographically (using Atomic Force Microscopy), chemically (using Time-Of-Flight Secondary Ion Mass Spectrometry) and nanomechanically (using nanoindentation) to measure surface changes induced by cycling. Such surface changes could explain adhesion behavior and failure of capacitive RF MEMS switches. Topographical roughness analysis showed that physical surface changes occurred early (during the first few hundred cycles). Chemical and nanomechanical analyses also showed surface property changes with cycling, in agreement with the roughness analysis. Therefore, RF MEMS switch surface changes occur with cycling and such changes are readily detectable and could adversely affect (increase) interactive adhesion forces and thus render the switch inoperable.

Cuticular damage to African–American hair during relaxer treatments – A microfluorometric and SEM Study

Citation: IFSCC Magazine, 11 (2008) (2) 131–137Abstract: In earlier publications [1,2,3 we discussed several in‐depth studies of characterization and quantification of damage done to European dark brown hair fibres by photochemical and cosmetic‐chemical oxidation (bleaching) and reduction (perming) processes. These earlier studies established considerable changes in surface chemistry such as an increase in acidity and hydrophilicity. We discussed in detail the breakdown of the lipid domains (delipidation) of the outer ®‐layer of the exposed scale faces and generation of anionic (sulphonic acid) groups (acidification) on the hair surface caused by these oxidative and reduction processes. The goal of this current study is to characterize and quantify the level of chemical and physical changes in the surface of African–American hair caused by various »lye‐based« and »no‐lye« relaxer treatments [4]. This study attempts to establish which product delivers the best »hair straightening« performance while resulting in the least chemical and physical changes in the hair surface. We again use a microfluorometric technique with the help of the cationic fluorochrome Rhodamine B to detect, map and quantify relaxer‐induced changes in the surface chemistry of human hair fibre. In addition, we also use SEM at various magnifications to highlight relaxer‐induced changes in the physical nature of the hair surface. We attempt to associate the level of increase in fluorescence intensity, which represents an increased level of delipidation/acidification of the hair surface, with the damage level to the hair topography, and thus, determine the least damaging cosmetic chemical process. Damage to the physical nature of the hair topography as observed by SEM shows a clear difference between treatments involving lab‐made relaxer solutions and commercial relaxer systems.Keywords: African‐American hair, commercial relaxer systems, microfluorometry, relaxer‐induced surface changes/damage, physical nature, surface chemistry, relaxer solutions, SEM, +lye‐based1/2 and +no‐lye1/2 relaxers,

Strength degradation of polymer concrete in acidic environments

This paper presents an assessment of the chemical resistance of eight different compositions of polymeric mortars using four different concentrations of filler, fly ash, and two types of unsaturated polyester resins, namely isophtalic polyester and orthophtalic polyester. The samples were exposed to seven different acid environments that represent those that often account for corrosive processes in industrial environments. None of the compositions in the study showed evidence of physical surface changes nor weight loss. There was a decrease in the flexural strength of the samples exposed to corrosive agents and this effect was more pronounced in the compositions with lower filler concentrations. However, even in those samples, the remaining flexural strength values remained far higher than those found in mortars prepared with Portland cement, an inorganic binder. Statistical analysis showed that the type of resin, the concentration of filler and the type of corrosive solution used have a significant effect on the chemical resistance of the polymeric mortars investigated in this study. SEM analyses also showed that the chemical attack occurred in the polymer matrix–aggregate interface.

Characterization of bioscoured cotton fabrics using FT-IR ATR spectroscopy and microscopy techniques

The effects of bioscouring were investigated by characterizing the chemical and physical surface changes of cotton fabrics using a purified pectinase enzyme from Bacillus subtilis strain WSHB04-02. Fourier-transform infrared (FT-IR) attenuated total-reflectance (ATR) spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) techniques were employed. FT-IR ATR spectroscopy provided a fast and semi-quantitative assessment of the removal of pectins and/or waxes on the cotton surface by comparing the changes in intensity of the carbonyl peak induced by HCl vapor treatment at around 1736cm−1. The bioscoured surface could be clearly distinguished from those of untreated and alkali-treated cotton fibers using a combination of SEM and AFM. The images produced using these techniques revealed that the surface morphography and topography of the cotton fibers were shaped by the etching action mode of pectinases during bioscouring. These findings demonstrated that AFM is a useful supplement to SEM in characterizing cotton surfaces.

Interaction of Capillary Plasma with Double-Base and Composite Propellants

Experiments were conducted to characterize the electrothermal capillary plasma and its interaction with a double-base propellant, JA2, and two nitramine composite propellants, M43 and XM39, in closed-chamber and open-air conditions. Pressure-time histories were recorded during ignition and burning of the propellants in the closed chamber. Experimental results indicate significant differences in ignition and combustion of the propellants. The composite propellants exhibited a two-stage burning behavior: one stage of rapid burning driven by the plasma and a second stage of slower self-sustained burning, which occurred with a clear delay after the first stage. During the burning that is driven by the plasma, the burn rate was largely independent of propellant type. Optical microscopic images of recovered propellant samples showed clear physical changes in surface and possibly in subsurface structure, an indication of in-depth melting, vaporization, and possibly chemical reactions. Plasma-induced mass losses for the three propellants were obtained from open-air testing and compared to the values calculated based on the pressure data from closed-chamber tests.

A study of tribology of Travan heads in linear tape recording

Tape cycling experiments were performed with a Travan™ linear tape system using metal particle (MP) media. The effects of various environmental conditions, particularly water content, on the tribology of the head/tape interface were studied. Auger electron spectroscopy (AES) and atomic force microscopy (AFM) were used to characterise the chemical and physical surface changes that occurred at the head surfaces. Transfer of material from the media to the head was observed at each condition. X-ray photoelectron spectroscopy (XPS) was used to identify the chemical changes that occurred at the media surface. This showed that in all areas of the tape, the amount of detected iron had increased, while the nitrogen (binder indicator) signal had decreased. Significant differences in elemental concentrations were also detected between areas directly in contact with the cartridge drive belt compared to those not in contact. Pole tip recession (PTR) was around 50–65 nm after 5000 passes, but increased at the higher water contents. AES results showed that stain is a function of water content, not relative humidity. It was noted that a larger ceramic grain size seemed to increase PTR.

Interactions at the head–tape interface of a linear tape system

In this study, tape cycling experiments were performed using two different experimental metal particle media in combination with a Travan™ linear tape system. The aim was to investigate the effect of head/tape contact on the tribological properties and signal performance of the system. A combination of cycling at extreme environmental conditions, use of experimental media, and cycling beyond the normal limit of operation ensured a worst-case scenario for the head–tape interactions. Auger electron spectroscopy (AES) and atomic force microscopy (AFM) were used to characterize the chemical and physical surface changes that occurred on and in the head surfaces. X-ray photoelectron spectroscopy (XPS) was used to identify the chemical changes that occurred at the media surface and these changes were correlated to variation in signal dropout rate. Measurements were made as functions of number of cycles. The cycling experiments for the two different tapes were performed at conditions of 32°C, 80% RH and 5°C, 10% RH and transfer of material from the media to the head was observed at each condition for both tape types. The degree of material transfer was influenced by the environmental operating conditions, but was governed by localized heating effects, such as those originating from active magnetoresistive (MR) elements and frictional interactions between the head and media. XPS analyses of the surface of the media revealed a reduction of nitrogen with increasing number of cycles indicating binder depletion. Significant differences in elemental concentrations were also detected between areas corresponding to regions directly under the cartridge belt compared to those off belt.