Environmental Scanning Electron Microscopy Techniques Research Articles

The influence of structure and morphology on ion permeation in commercial silicone hydrogel contact lenses.

The importance of the microstzructure of silicone hydrogels is widely appreciated but is poorly understood and minimally investigated. To ensure comfort and eye health, these materials must simultaneously exhibit both high oxygen and high water permeability. In contrast with most conventional hydrogels, the water content and water structuring within silicone hydrogels cannot be solely used to predict permeability. The materials achieve these opposing requirements based on a composite of nanoscale domains of oxygen-permeable (silicone) and water-permeable hydrophilic components. This study correlated characteristic ion permeation coefficients of a selection of commercially available silicone hydrogel contact lenses with their morphological structure and chemical composition. Differential scanning calorimetry measured the water structuring properties through subdivision of the freezing water component into polymer-associated water (loosely bound to the polymer matrix) and ice-like water (unimpeded with a melting point close to that of pure water). Small-angle x-ray scattering, and environmental scanning electron microscopy techniques were used to investigate the structural morphology of the materials over a range of length scales. Significant, and previously unrecognized, differences in morphology between individual materials at nanometer length scales were determined; this will aid the design and performance of the next generation of ocular biomaterials, capable of maintaining ocular homeostasis.

The Influence of Structure and Morphology on Ion Permeation Behaviour in Commercial Silicone Hydrogel Contact Lenses

The importance of the microstructure on the permeability of silicone hydrogels is widely appreciated but is poorly understood and minimally investigated. In contrast with most conventional hydrogels, the water content and water structuring within silicone hydrogels cannot be solely used to predict their permeability. To ensure comfort and eye health, these materials must simultaneously exhibit both high oxygen permeability and high water permeability. The materials achieve these opposing requirements based on a composite of nanoscale domains of oxygen-permeable (silicone) and water-permeable hydrophilic components. This study correlated the ion permeation coefficients of a selection of commercially available silicone hydrogel contact lenses with their morphological structure and chemical composition. Donor/receiver conductivity measurements were recorded using a dual-chamber diffusion system, which allowed permeability profiles and coefficients to be calculated. Differential scanning calorimetry was used to measure water structuring properties through subdivision of the freezing water component into polymer-associated water (loosely bound to the polymer matrix) and ice-like water (unimpeded with a melting point close to that of pure water). Small-angle x-ray scattering, and environmental scanning electron microscopy techniques were used to investigate the structural morphology of the material over a range of length scales. Significant, and previously unrecognised, differences in morphology between individual materials at nanometre length scales were determined. These exploratory techniques facilitate the understanding of the effects of the bulk morphology on the permeability behaviour of each silicone material; this will aid the design and performance of the next generation of ocular biomaterials, capable of maintaining enhanced ocular homeostasis.

Enhanced Environmental Scanning Electron Microscopy Using Phase Reconstruction and Its Application in Condensation.

Environmental scanning electron microscopy (ESEM) is a broadly utilized nanoscale inspection technique capable of imaging wet or insulating samples. It extends the application of conventional scanning electron microscopy (SEM) and has been extensively used to study the behavior of liquid, polymer, and biomaterials by allowing for a gaseous environment. However, the presence of gas in the chamber can severely degrade the image resolution and contrast. This typically limits the ESEM operating pressure below 1000 Pa. The dynamic interactions, which require even-higher sensitivity and resolution, are particularly challenging to resolve at high-pressure conditions. Here, we present an enhanced ESEM technique using phase reconstruction to extend the limits of the ESEM operating pressure while improving the image quality, which is useful for sensing weak scattering from transparent or nanoscale samples. We applied this method to investigate the dynamics of condensing droplets, as an example case, which is of fundamental importance and has many industrial applications. We visualized dynamic processes such as single-droplet growth and droplet coalescence where the operating pressure range was extended from 1000 to 2500 Pa. Moreover, we detected the distribution of nucleation sites on the nanostructured surfaces. Such nanoscale sensing has been challenging previously due to the limitation of resolution and sensitivity. Our work provides a simple approach for high-performance ESEM imaging at high-pressure conditions without changes to the hardware and can be widely applied to investigate a broad range of static and dynamic processes.

Applications of SEM and ESEM in Microstructural Investigation of Shale-Weathered Expansive Soils along Swelling-Shrinkage Cycles

Understanding the microstructure of expansive soils is of vital importance in physical interpretation and mechanical modeling of expansive soil behavior at the macro scale. To approach this objective, two natural expansive soils were compacted and imaged to disclose their microstructure using both conventional scanning electron microscopy (SEM) and environmental scanning electron microscopy (ESEM). The micrographs of the samples at their initial compacted state showed comparable results when using SEM and ESEM techniques. The structural changes in response to two wetting-drying cycles were monitored through the ESEM experiments in order to simulate the volumetric evolution at the macro scale. Despite the significant macroscopic volume changes, it was difficult to detect structural changes at the micro scale. The ESEM test results only qualitatively described structural shrinkage upon the first drying cycle but showed little structural modification thereafter, due to the limited duration of vapor exchange between the chamber atmosphere and the sample under the microscope. In addition, the combined effects of plasticity and original microstructure determined how the microstructure evolved as a function of sample consolidation. Based on the analysis of results, limitations of both SEM and ESEM approaches in microstructural investigations of expansive soils are discussed and summarized.

Development of Savlon Containing Polyvinyl Alcohol Based Cryogels as Potential Biomaterials for Burn Healing Applications

Novel membranes of hydrogels were prepared by freeze-thaw method and characterized by Fourier transform infrared (FTIR) and environmental scanning electron microscopy techniques. The FTIR spectra clearly reveal that savlon loaded poly (vinyl alcohol) cryogels are held together through hydrogen bonding. The scanning electron microscope analysis suggests that cryogels show a well-defined porous morphology. The cryogels were also studied for swelling and deswelling behaviors. The results show that the swelling and deswelling greatly depend on the factors such as chemical composition of the cryogels, number of freeze-thaw cycles, and pH and temperature of the swelling bath. The savlon loaded cryogels were also investigated for their in vitro blood compatibility and antibacterial activity.

Edge profile of commercially available square-edged intraocular lenses

To analyze the sharpness of the posterior optic edge profile and edge thickness of intraocular lenses (IOLs) marketed with a square-edged profile. Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom. Seventeen square-edged 20.0 diopter IOLs of different manufacture, design, and material were selected. After the environmental scanning electron microscopy technique was standardized, repeatability of the technique was tested. Posterior optic edges of all IOLs were scanned at a magnification of x 500. Local radii of curvature of the posterior optic edges were measured by purpose-designed software. Optic edge thickness was also measured from the electron micrographs. The repeatability of the scanning technique was excellent (+/-0.10 microm). The radius of curvature of posterior optic edges ranged from 7.6 to 23.1 microm. Hydrophilic acrylic IOLs (except the HumanOptics MC Microlens 611 MI-B and 1CU) had radii of curvatures more than 10.0 microm of the posterior optic edge compared with hydrophobic acrylic and silicone IOLs (<10.0 microm) except the Hoya AF-1 (19.9 microm). Alcon AcrySof single-piece (SN60WF), HumanOptics 1CU, and AMO Clariflex CLRFLXC IOLs had the thinnest optic edges in the hydrophobic, hydrophilic, and silicone groups, respectively. Commercially marketed square-edged IOLs differed in the sharpness of the posterior optic edge. Hydrophobic acrylic and silicone IOLs have sharper posterior optic square edge than most hydrophilic acrylic IOLs. This probably reflects difference in manufacturing techniques. Differences in posterior optic edge profile may explain variation in posterior capsule opacification performance with different IOLs and materials.

Retrieval analysis of clinical explanted vena cava filters

Vena cava filters are the most commonly used mechanical devices to prevent pulmonary embolism. A retrievable permanent filter has been available since 1999. That has allowed the direct study of thrombi captured in humans and the punctual interaction of blood and device at long and short term. Through traditional histologic methods, captured thrombi and the tissues formed around the filter were observed. An innovative environmental scanning electron microscopy technique allowed detection of micro- and nanosized foreign bodies inside thrombi and tissues, and chemical analysis could be carried out by means of energy dispersive spectroscopy. All specimens contained different quantities of foreign debris ranging from few tens of microns to 50 nanometers; their chemistry was not homogeneous when patients were compared, and also differed considerably within the same filter. The constant presence of debris deeply embedded in all thrombi observed may mean that they are the cause that triggered the formation of those thrombi as a result of the interaction between foreign bodies and blood components.

Swelling–shrinkage kinetics of MX80 bentonite

The swelling–shrinkage kinetic of an industrial Bentonite (MX80) was investigated using a new technique of environmental scanning electron microscopy (ESEM) coupled with a digital image analysis (DIA) program (Visilog). This expansive clay was characterized by several analytic tools (ICP-AES, SEM, STEM, XRD, etc.), before applying the new ESEM technique. The swelling–shrinkage was directly observed at high magnification and at different relative humidity states in an ESEM. Nine wetting/drying cycles were performed on the sample. Each cycle was performed at different relative humidities (55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, and 95%). A DIA program was used to determine swelling–shrinkage. This method consists of estimating the percent augmentation of the surface as a function of time. Finally, a swelling–shrinkage kinetic model was tested, based on a first-order linear kinetic equation. The results show that the coupled ESEM and DIA can be a powerful method of estimating the swelling/shrinkage potential of expansive clays. The exponential model fits well with the experimental data.

Studies of a novel polymerizable amphiphilic dendrimer

In the present study, we have synthesized a polymerizable amphiphilic dendrimer by attaching 10,12-pentacosadiynoic acid (PDA) to a third generation poly(amidoamine) (PAMAM) dendrimer core (PDA-PAMAM). This dendrimer was characterized by 1H NMR and MALDI-TOF mass spectroscopy. The amphiphilic property of this dendrimer has been studied. Surface pressure and surface dipole moment–area isotherm measurements have shown that PDA-PAMAM forms a stable monolayer at the air–water interface with a limiting molecular area of 460 Å 2 per molecule. The compressed monolayer can be readily polymerized upon UV irradiation, as like other PDA derivatives. The topography of the monolayer was observed by Brewster angle microscopy (BAM) as well as by the environmental scanning electron microscopy (ESEM). We found a good correlation between the size and shape of monolayer domains observed with the BAM and ESEM techniques. To our knowledge, this is the first time wet mode ESEM has been used to characterize L–B film. The wet mode ensures that L–B films remain intact without being damaged by the high vacuum system of traditional SEM. As a preliminary study, we have found that this new dendrimer forms colloidal particles in chloroform solution and can be readily polymerized by UV irradiation.

Observation of ferroelectric domains in LiTaO3

Periodic and partially reversed 180° domain patterns in LiTaO3 single crystals, engineered through pulse poling, can be directly observed by using environmental scanning electron microscopy (ESEM) in secondary electron emission mode. The ESEM technique does not require surface treatment and can be used to observe ferroelectric domains on a natural cracked surface in a bulk material. This is very important since the domain patterns obtained by this technique can truly represent the domain configurations in a bulk. The domain structures are confirmed by chemical etching and scanning electron microscopy. The ESEM gives stable and high resolution images.

Environmental Scanning Electron Microscopic Investigation of Failure Mechanisms in Electronic Packages

Environmental Scanning Electron Microscopy (E-SEM) is a technique which provides the capability to investigate surface morphologies over a variety of controllable environmental conditions. This paper discusses the principal of the E-SEM and presents three experimental investigations of failure mechanisms in electronic packages using E-SEM techniques. The first is a study of thermally induced failures of MMIC devices. The second investigation focuses on mechano-sorptive properties of multilayer thin-film polyimides. The third investigation concentrates on relative humidity and thermal cycling effects on interfacial bonding characteristics of resin/fiber interfaces in printed wiring boards, and microcracks surrounding plated-through-holes.