Polarized Microscopy Techniques Research Articles

Trisodium phosphate-loaded magnesium‑aluminum layered double hydroxides/oxidized-multiwalled carbon nanotubes self-assembled 2D-nanohybrid for designing a multifunctional smart epoxy nanocomposite

In this study, a hybrid nanomaterial based on layered double hydroxides (LDH) and multi-walled carbon nanotubes (MWCN) was fabricated using a co-precipitation method. Trisodium phosphate (TP) was loaded into the designed nanocarrier to enhance the corrosion resistance of mild steel in 3.5 wt% NaCl media. Fourier transform infrared (FT-IR) spectroscopy, Raman, and X-ray diffraction (XRD) analyses were carried out to investigate the magnesium‑aluminum layered double hydroxides/oxidized-multiwalled carbon nanotubes (Mg-AL-LDH/O-MWCN) structure and morphology before and after loading of trisodium phosphate. Furthermore, the nanocarrier inhibition capability was evaluated through electrochemical impedance spectroscopy (EIS), polarization, and field emission-scanning electron microscopy (FE-SEM) techniques. Electrochemical impedance spectroscopy (EIS) was also employed to estimate the anticorrosion properties of the epoxy coating loaded with TP-LDH/O-MWCN. The EIS evaluation of the intact coating revealed the impedance at the lowest frequency (|Z|0.01 Hz) of about 109 Ω.cm2 after 42 days of immersion for the trisodium phosphate-layered double hydroxides/oxidized-multi-walled carbon nanotubes@epoxy (TP-LDH/O-MWCN@EP) sample and the lowest value of breakpoint frequency was obtained for this sample (fb = 0.063 Hz). These findings prove the trisodium phosphate-layered double hydroxides/oxidized-multi-walled carbon nanotubes (TP-LDH/O-MWCN) particles' effectiveness in the epoxy coating water/ion barrier function enhancement. EIS results indicated the enhancement of the charge transfer resistance (Rct) of the scratched coatings, from 65.97 kΩ.cm2 for the pure epoxy (EP) sample to 94.87 kΩ.cm2 for the trisodium phosphate-layered double hydroxides/oxidized-multi-walled carbon nanotubes@epoxy (TP-LDH/O-MWCN@EP) sample, revealing the self-repairing behavior of the designed coating. In addition, the adhesion properties of the samples coated with LDH/O-MWCN@EP and TP-LDH/O-MWCN@EP were studied by pull-off and cathodic disbonding tests, leading to a 33% reduction in adhesion loss and a 52.23% reduction in the diameter of cathodic delamination. The tensile test conducted on the samples indicated an increase in the ultimate tensile strength (σUTS), elongation break (Ɛb), and toughness values by 188%, 223%, and 800%, respectively, in comparison with the pure epoxy (EP) sample.

Experimental Investigation of Cationic Gemini Surfactants: Self‐Assembly, Corrosion Inhibition, Foaming and Dye Solubilization Properties

AbstractIn this study, two cationic gemini surfactants 12‐3‐12 and 12‐3(OH)‐12 were synthesized in our labrotory. The critical micelle concentration (CMC) values of synthesized surfactants were determined by conductivity measurements. The aggregation number (Nagg) of micelles was calculated using the pyrene probe fluorescence method. It was been investigated the corrosion effect of cationic gemini surfactants were denoted as 12‐3‐12 and 12‐3(OH)‐12 for carbon steel in 1 M HCl. The inhibition effect was investigated using weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) and scanning electron microscopy (SEM) techniques. It has been determined that both surfactants showed the best inhibitory effect at low concentrations. The foaming capacity (FC) and the foam stability (FS) of gemini surfactants were studied by measuring the foam volume for 0.5 % (w/v) surfactant solutions and it was observed that the foaming properties of 12‐3(OH)‐12 gemini surfactant were better. The solubility capability of both surfactants was tested with the water‐insoluble dye Sudan Red B and it was observed that the solubility increased significantly over the CMC value of the cationic gemini surfactants. Finally, the corrosion effect, foam capacity and foam stability and effects on paint solubility of the synthesized surfactants were obtained at very low concentrations.

Silica/polyacrylamide nanocomposite for inhibition of asphaltene precipitation from unstable crude oils

Among various flow assurance problems, asphaltene precipitation is a major issue. This study aims to evaluate the potential application of silica-polyacrylamide nanocomposite to inhibit asphaltene precipitation for the first time. The nanocomposites were synthesized and characterized by Fourier transform infrared and field emission scanning electron microscopy techniques. The inhibitory effect of nanocomposites in water-based nanofluid on two unstable crude oils was evaluated using viscometry, asphaltene dispersion test, dynamic light scattering, and polarized microscopy techniques. The viscosity measurements indicate that nanocomposites postpone asphaltene onset of precipitation from 34 to 44 and 23 to 36 vol% nC7 for crude oil A and B, respectively. The maximum dispersion efficiency of nanocomposite was 69% and 79% at the 1% and 2.5% nanofluid volume dosages for crude oil A and B, respectively. Dynamic Light Scattering and microscopy results indicated the asphaltene size change to lower values in the presence of nanocomposites. Polyacrylamide attached to the silica surface promotes a surface with efficient functional groups that increase the asphaltene adsorption. Asphaltene adsorption leads to decreased aggregate size and controlling the asphaltene precipitation. The prepared nanocomposite was evaluated as an efficient dispersant and inhibitor that reveals the potential application of Silica-polyacrylamide for handling the asphaltene precipitation in reservoirs.

Optimization of anti-corrosion performance of novel magnetic polyaniline-Chitosan nanocomposite decorated with silver nanoparticles on Al in simulated acidizing environment using RSM

The suitability of newly synthesized magnetic polyaniline-Chitosan nanocomposite decorated with silver nanoparticles (Ag@PANI-CS-Fe3O4) as a robust corrosion inhibitor for Aluminum (Al) in a 5 M HCl environment has been investigated via Weight Loss (WL), Alternating Current (AC)-Impedance Spectroscopy (IS), Potentiontiodynamic polarization (Tafel plots), and Scanning Electron Microscopy (SEM) techniques. The protection efficiency (PE) was mathematically modeled using the Response Surface Methodology (RSM) to fit an empirical relation in terms of temperature, nanocomposite concentration, and time using the face-centered central composite design. The model was accurate with a coefficient of determination (R2 = 99.27%). The negative Gibb's free energy of adsorption (ΔGads) values confirmed the spontaneity of Freundlich adsorption isotherm process on Al in 5 M HCl solution. The optimization simulation yielded maximum protection efficiency (of 97.88%) at 5 mg/L nanocomposite concentration, 1 h time, and an intermediate temperature of 304.8 K. Furthermore, the sensitivity of PE was evaluated to find that the low temperature 303 K is favorable for PE, whereas higher temperature will act adversely on PE. The results obtained by the RSM model are in agreement with the experimental observations.

Double-twisted nematic director configurations in cylindrical capillaries with a photocontrollable angle of twist.

The orientational configurations of thermotropic nematic liquid crystal in cylindrical capillaries with nondegenerated planar surface anchoring are investigated. The boundary conditions were determined by a photoaligning coating on the inner wall of the capillary treated with a linearly polarized UV light while rotating the capillary around its long axis, thus providing the easy alignment axis perpendicular to the polarization direction of illuminating light. By changing the angle between the incident light polarization and the capillary axis, this procedure allows us to realize axially symmetric twisted structure with any angle of twist, ranging from a trivial axial alignment with zero twist (when the UV polarization is perpendicular to the capillary axis) to the 180^{∘}-twisted configuration (when the UV polarization is along the capillary). These two extreme configurations together with an intermediate configuration induced by UV light polarized at an angle of 45^{∘} to the capillary axis were produced and their director profiles were studied using polarizing microscopy techniques. UV light intensity and polarization distribution over inner capillary surface covered with photoaligning layer were analyzed using optical ray tracing calculations. An analytical model of the observed configurations of the liquid crystal director field is proposed, which takes into account the finite anchoring on the capillary surface. By comparing the theoretically calculated and experimentally estimated director profiles, the liquid crystal anchoring energy on the photoaligned capillary surface was estimated.

Single-Shot Quantitative Polarization Imaging of Complex Birefringent Structure Dynamics.

Polarization light microscopes are powerful tools for probing molecular order and orientation in birefringent materials. While a number of polarization microscopy techniques are available to access steady-state properties of birefringent samples, quantitative measurements of the molecular orientation dynamics on the millisecond time scale have remained a challenge. We propose polarized shearing interference microscopy (PSIM), a single-shot quantitative polarization imaging method, for extracting the retardance and orientation angle of the laser beam transmitting through optically anisotropic specimens with complex structures. The measurement accuracy and imaging performance of PSIM are validated by imaging a birefringent resolution target and a bovine tendon specimen. We demonstrate that PSIM can quantify the dynamics of a flowing lyotropic chromonic liquid crystal in a microfluidic channel at an imaging speed of 506 frames per second (only limited by the camera frame rate), with a field-of-view of up to 350 × 350 μm2 and a diffraction-limit spatial resolution of ~2 μm. We envision that PSIM will find a broad range of applications in quantitative material characterization under dynamical conditions.

Combined PIXE and optical microscopy characterization of calcium compounds in dental calculus

A combined PIXE and optical microscopy approach was applied to examine the dental calculus of patients with periodontal disease. PIXE was performed with the Bucharest 3 MV Tandetron with 3 MeV protons and a HPGe detector, using hydroxyapatite (HA) and other standards. Sections 30 µm thick were prepared and observed using polarization microscopy and histochemical techniques. Both methods revealed the heterogeneous nature of dental calculus. Two main types (I and II) were postulated based on Ca/P ratios (p < 0.00001). Type I consisted mainly of whitlockite and octacalcium phosphate, whereas type II was mainly HA with some calcium carbonate. They correlated with rodlet masses and amorphous areas with a powdery appearance, observed using microscopy and histochemistry. PIXE also detected two rare forms of calculus (I' and II'). The traces of Zn and S were highly variable. The different types of calculus were probably formed by different biomineralization pathways.

Corrosion Inhibition Effect of a Non-toxic Waste Compound on Stainless Steel in 0.5 Molar Concentration of Sulfuric Acid

The corrosion of metallic material is a global scientific setback affecting all areas of engineering and technology. Therefore, research on corrosion and its inhibition is of great interest in a wide range of disciplines. The toxic nature and the low inhibition effectiveness of the majority of the conventional organic molecule in inhibiting metals against corrosion in the acid-containing solution have enforced scientists to develop non-toxic compounds. The inhibitive tendency of coconut shell powder (CSP) on stainless steel UNS N08904 (SS) corrosion in 0.5 molar H2SO4 medium at 30 °C was examined in the present study via gravimetric, potentiodynamic polarization, and scanning electron microscopy techniques. The obtained result shows that CSP is an excellent inhibitor for SS against corrosion, CSP adsorption on the surface of SS obeys Langmuir and Freundlich adsorption isotherms. The inhibition efficiency of 98% was obtained using 10 g CSP after 140 h exposure. The potentiodynamic polarization result describes CSP as a mixed-type inhibitor owing to changes in the lateral repulsion effect between the inhibitor molecules. The icorr values for the uninhibited and inhibited (10 g CSP) samples were 0.000172 A/cm2 and 3.09E-05 A/cm2, respectively. The inhibitive action of CSP is also evidence by scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDX) analyses. Also, the anodic dissolution mechanism of SS was affected while the hydrogen evolution process did not change the mechanism of stainless steel with CSP due to the presence of heteroatom in the major components of CSP. The CSP can, therefore, serve as a good green inhibitor for SS corrosion in a 0.5 M H2SO4 environment.

Corrosion Inhibitive Action and Adsorption Behaviour of Justicia Secunda Leaves Extract as an Eco‐Friendly Inhibitor for Aluminium in Acidic Media

The extract of Justicia secunda (JS) leaves was investigated as an eco‐friendly corrosion inhibitor of aluminum in 0.5 M HCl using weight loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and scanning electron microscopy (SEM) techniques. The inhibitor concentrations used ranged from 50 to 250 ppm at 30, 40, and 50oC. Results show that Justicia secunda acts as a good inhibitor for aluminum. Its efficiency increased with increasing inhibitor concentration but decreased with increasing temperature. Maximum inhibition efficiency as high as 94.3% was found at 30°C for 250 ppm of the inhibitor with the weight loss technique. Tafel polarization results show that the extract acts as a mixed-type inhibitor. The Nyquist plots indicated decreasing double-layer capacitance and increasing charge transfer resistance on increasing JS concentration. The inhibition action occurred through the physical adsorption of the extract on the aluminum surface. The adsorption process was found to follow Langmuir adsorption isotherm. The formation of a protective film on the metal surface was confirmed by scanning electron microscopy.

Simultaneous use of polarization microscopy and dark field techniques in the study of microorganisms.

Simultaneous application of polarization microscopy and dark field techniques has been used to study the internal structure of microbial cells. The dark field technique displays subtle cell structures like glowing objects on a dark background. In the polarizing microscope, cross polarizing filters along with the first-order quartz compensator and a rotary table show the maximum birefringence of the individual structures. The material containing microorganisms was collected in the villages of Sýkořice and Zbečno (Křivoklátsko Protected Landscape Area). The objects were studied in a laboratory microscope Carl Zeiss Jena type NfpK equipped with In Ph 160 basic body with variable dark field, special condenser with interchangeable diaphragm apertures, a rotary table, Meopta Praha polarizer, analyzer, first-order quartz compensator from LOMO Sankt Petersburg, and a digital Nikon D 70 DSLR camera. Three orders of microorganisms were studied: Siphonocladales, Chlorococcales, and Peritricha. Anisotropic structures in different amounts and sizes (e.g., granules and microfibrils) or in different configurations (e.g., cell walls or pellicle) have been found in all Protista organisms under study. Filamentous algae of the genus Cladophora (Cladophoraceae, Siphonocladales, Ulvophyceae) featured a strongly birefringent cell wall (shape birefringence) surrounded by less birefringent periphyton (microbial biofilm), at the edges of which cyanobacterial fibers could be recognized-a very important finding. The coccal algae of the genus Scenedesmus (Scenedesmataceae, Chlorococcales, Chlorophyceae) exhibited not only strongly birefringent granules, but also strongly birefringent microfibrils in the cytoplasm outside the strongly birefringent cell walls-very important finding. Of all the studied microorganisms, the weakest birefringence was shown in the surface membrane (pellicle) of the Vorticella (Vorticellidae, Peritricha, Ciliata). On the other hand, the ring of cilia on the top of the body had a somewhat stronger birefringence-an important finding. In conclusion, the dark field technique provides a high contrast image in the microscope and, if supplemented simultaneously by polarization microscopy, will allow us to partially infer the composition of the examined structures.

A New Rock Brittleness Index Based on the Characteristics of Complete Stress–Strain Behaviors

Rock brittleness is an essential mechanical property, which plays a significant role in rock classifications and rockburst risk evaluations. To overcome the problems associated with the traditional brittleness indexes not comprehensively charaterizing the rock strength and deformation behaviors, this study systematically summarized the existing rock brittleness indexes. Then, a novel brittleness index (BICSS) based on the complete stress–strain curves of rock under different confining pressures was proposed. Its advantages included innovatively considering the characteristic stresses and strains at the stage of crack initiation, the peak points, and residual points. The index also described the stress growth rates from the pre-peak crack-initiation stress to the peak stress points, as well as the stress drop rates from the peak stress to the residual stress points. This study conducted uniaxial and triaxial compression tests of metamorphic sandstone, granite, and gneiss obtained from a deeply buried long-line tunnel group. The aforementioned tests were combined with wave velocity tests and thin-section identification tests using polarizing microscopy techniques. The reliability and applicability of the index were then successfully verified. The results showed that the BICSS could not only quantify and classify the brittleness characteristics of different rock types and characterize the confining pressure inhibition behaviors of rock brittleness, but could also comprehensively express the influences of homogeneity, mineral compositions, and particle sizes on the rock brittleness. Finally, through the parameter sensitivity analysis of the BICSS, the influences of subjective errors in the results of the cracking initiation stress and strain values caused by the different selections during the linear elastic phase could be successfully excluded, resulting in the further verification of the stability of the BICSS.

Influence of wormin mebendazole on the corrosion of mild steel in 1.0M sulphuric acid

This investigation described the inhibitive influence of Mebendazole (MBZ) on mild steel corrosion in 1M sulphuric acid. Potentiodynamic polarization and scanning electron microscopy techniques were employed. Mebendazole effectively protected mild steel in H2SO4 at 298K and 333K with maximum inhibition efficiencies of 98.02% and 99.53% respectively. The adsorption of the inhibitor on the surface of mild steel followed the mixed mode physical adsorption of Langmuir adsorption model. The corrosion rate of specimens decreased from about 47.467 ​mm/yr for the blank specimen to about 1.7968 ​mm/yr for the specimen immersed in 1M sulphuric acid containing 2.5 ​g/l of MBZ at 298K. However, at 333K the corrosion rates were respectively 1455 ​mm/yr and 6.7854 ​mm/yr. Scanning electron microscopy revealed that the addition of Mebendazole to the corroding system sustained a surface morphology relatively devoid of pits on the test specimens at 5 days of immersion in 2.5 ​g/l of inhibitor in 1M sulphuric acid.

Combined application of extended depth of field imaging, image stitching and polarized microscopy techniques in identification of Spatholobus suberectus

ObjectiveAs traditional techniques for microscopic identification of Chinese medicines currently lack objective and high-quality reference images, here we developed a systemic procedure to be used in microscopic identification of Chinese medicines, which would lead to more objective, effective and accurate identification process. MethodsSpatholobi Caulis (Jixueteng in Chinese) was used as the specimen in the development of such procedure. Jixueteng samples were microscopically examined in bright- and dark-field microscopy. Microscopic images were obtained by regular, EDF, and image stitching techniques. ResultsThe microscopic images of the characteristics in pulverized Jixueteng were captured, thanks to EDF imaging and image stitching techniques which allowed the detailed and full sighting of each characteristic to be obtained simultaneously. Different layers in anatomical transverse section, including cork, phelloderm, cortex, phloem, cambium, xylem and pith, were distinctively observed. Moreover, by comparing images of bright- and dark-field microscopy, birefringent and non- birefringent components could readily be distinguished. ConclusionWith application of the developed procedure, high-definition, panoramic and microscopic images were acquired, which could be used as the reference images for microscopic identification of Chinese medicines.

Electrically induced transformations of defects in cholesteric layer with tangential-conical boundary conditions

Electric-field-induced changes of the orientational structures of cholesteric liquid crystal layer with the tangential-conical boundary conditions have been investigated. The samples with the ratio of the cholesteric layer thickness d to the helix pitch p equalled to 0.57 have been considered. The perpendicularly applied electric field causes a decrease of the azimuthal director angle at the substrate with the conical surface anchoring. In the cells with d = 22 μm, the defect loops having the under-twisted and over-twisted areas are formed. At the defect loop the pair of point peculiarities is observed where the 180° jump of azimuthal angle of the director occurs. Under the action of electric field the loops shrink and disappear. In the cells with d = 13 μm, the over-twisted and under-twisted defect lines are formed. Applied voltage results in the shortening of lines or/and their transformation into a defect of the third type. The director field distribution near defect lines of three types has been investigated by the polarising microscopy techniques. It has been revealed that the length ratio between the over-twisted and third-type defect lines can be controlled by the electric field.

Statistical parameters-based image enhancement techniques in pure and nanodispersed 6O.O8 liquid crystalline compounds

ABSTRACTSynthesis, characterization and phase-transition studies in pure and 20 µl citrate-capped Au nanodispersed liquid crystalline (LC) N-(p-n-hexyloxybenzylidene)-p-n-octyloxy aniline, 6O.O8, compounds are carried out using a polarizing microscope attached with hot stage and camera. The polarizing microscopy technique is used to measure the phase-transition temperatures. Differential scanning calorimetry is used to determine the transition temperatures and enthalpy values. By the dispersion of citrate-capped Au nanoparticles into the LC compounds, the nematic transition temperature is decreased. Furthermore, statistical parameters-based image enhancement algorithm is proposed to identify the crystalline phases in the pure and nano-doped LC compound. Empirical result analysis clearly reveals the robustness of this method over existing image enhancement methods.

Heterocyclic pyridine-based liquid crystals: synthesis and mesomorphic properties

ABSTRACTA series of new calamitic liquid crystals, 4-{[(pyridin-4-yl)methylidene]amino}phenyl 4-alkoxybenzoates comprising a heterocyclic (pyridine) and two phenyl rings core system, terminal alkoxy chain, imine and ester linkers were synthesised and characterised. This series consists of nine members wherein the members differ by the length of alkoxy chain (CnH2n+1O–, where n = 2, 4, 6, 8, 10, 12, 14, 16, 18). Spectral analysis results were in accordance with the expected structure. Their thermotropic behaviours were studied by using differential scanning calorimetry, optical polarising microscopy and powder X-ray diffraction techniques. A single mesophase (nematic) was observed for the first three members of the series (n = 2, 4 and 6). As the alkoxy chain increased to n = 8 and n = 10, the nematic phase appeared together with an additional smectic A (SmA) phase. When moving from n = 12 until the highest members (n = 18), the nematic phase disappeared and these compounds only exhibited a single mesophase (SmA).

Continuously adjustable period optical grating based on flexoelectric effect of a bent-core nematic liquid crystal in planar cells

The structures of flexodomains, which are similar to optical gratings and can be controlled by the amplitude of applied voltage and temperature, were verified through polarizing microscopy and light diffraction techniques. The properties of the optical grating induced by a bent-core nematic liquid crystal in planar cells with varied cell gaps and pretilt angles were studied. The period of optical grating decreases with the increase in the amplitude of the applied voltage and pretilt angle. In addition, the period increases with the increase in cell gap and temperature. The period of optical grating has a linear relationship with temperature. The continuously adjustable period has the potential to become an important and extended application of optical grating.

Super-resolution fluorescence polarization microscopy

Fluorescence polarization is related to the dipole orientation of chromophores, making fluorescence polarization microscopy possible to reveal structures and functions of tagged cellular organelles and biological macromolecules. Several recent super resolution techniques have been applied to fluorescence polarization microscopy, achieving dipole measurement at nanoscale. In this review, we summarize both diffraction limited and super resolution fluorescence polarization microscopy techniques, as well as their applications in biological imaging.

Synthesis and phase transition behaviours of laterally substituted liquid crystals containing methylhydroquinone: emerging of smectic C phase for higher homologues

ABSTRACTA series of laterally substituted low-molar-mass liquid crystals with molecular geometry were constructed with three phenyl rings bridged through ester central groups as the rigid core and a lateral methyl group as the flexible part of a molecule, with a view to understanding and establishing the effect of molecular structure on liquid crystal behaviour. Low-molar-mass mesogens known as 1,4-bis[(4′-n-alkyloxybenzoyl)oxy]toluene with different number of carbon (n) at the alkyl chain have been prepared. Their molecular structures were proposed via physical measurements and spectroscopic techniques. Mesomorphic properties were studied by using differential scanning calorimetry, optical polarizing microscopy and powder X-ray diffraction techniques. The results showed that the melting points as well as the clearing temperatures decreased upon lengthening of the terminal alkyloxy chain lengths. Members with the shorter chain (n = 2–10) exhibited nematic phase. As for higher homologues, members with n = 12, 14, 16 and 18 showed polymorphism, whereby these compounds displayed both smectic and nematic properties.

Multiscale electrochemical analysis of the corrosion of titanium and nitinol for implant applications

Surface electrochemical activity of titanium and nitinol biomaterials in naturally aerated Ringer’s physiological solution was investigated using potentiodynamic polarization and scanning electrochemical microscopy (SECM) techniques. SECM was operated in feedback and redox competition modes as a function of potential applied to the substrate. The kinetics of the electron transfer rate on both materials was characterized by mathematical modelling of the Z-approach curves monitored under feedback conditions. The rate constant values greatly depended on the characteristics of the passive layers formed over the metals under potentiostatic control. A more insulating film was found on nitinol when biased at low polarizations, resulting in smaller tip current increments during tip approach to the investigated surface under positive feedback and competition operation modes. However, at higher anodic polarizations, nitinol passive layers experience breakdown, and therefore tip current values reflect the release of metal cations from the biomaterial surface.