Transmission Spectrophotometry Research Articles

The Film Formation of Polymer Particles in Drying Thin Films of Aqueous Acrylic Latices: II. Coalescence, Studied with Transmission Spectrophotometry

The aim of this study is to determine the factors that contribute to the process of film formation of binder particles in drying aqueous dispersion coatings, based on acrylic polymers. It is known that concentrated latices of uniform size show iridescent, colored light patterns. These colors are caused by interparticle interference, and they are only present when the latex particles are ordered in a regular structure. The interparticle interference can be characterized by measuring the transmission as a function of wavelength of the incident light. It appeared that the changes of the interparticle interference of a drying latex film can be related to changes in the interparticle distance and displacement. It was also found that the interparticle distance becomes “negative” upon coalescence of the latex particles. This means that from this point on, the change in interparticle interference is directly related to the indentation or deformation of the latex particles. It became clear that the coalescence process differs from deformation mechanisms accepted in the literature. It seems that the deformation of the particles follows a biaxial mechanism. This means that the particles deform only in one direction, perpendicular to the film surface.

Orthogonal polarization spectral imaging: a new method for study of the microcirculation.

Different disease states, including diabetes, hypertension and coronary heart disease, produce distinctive microvascular pathologies. So far, imaging of the human microcirculation has been limited to vascular beds in which the vessels are visible and close to the surface (for example, nailfold, conjunctiva). We report here on orthogonal polarization spectral (OPS) imaging, a new method for imaging the microcirculation using reflected light that allows imaging of the microcirculation noninvasively through mucus membranes and on the surface of solid organs. In OPS imaging, the tissue is illuminated with linearly polarized light and imaged through a polarizer oriented orthogonal to the plane of the illuminating light. Only depolarized photons scattered in the tissue contribute to the image. The optical response of OPS imaging is linear and can be used for reflection spectrophotometry over the wide range of optical density typically achieved by transmission spectrophotometry. A comparison of fluorescence intravital microscopy with OPS imaging in the hamster demonstrated equivalence in measured physiological parameters under control conditions and after ischemic injury. OPS imaging produced high-contrast microvascular images in people from sublingual sites and the brain surface that appear as in transillumination. The technology can be implemented in a small optical probe, providing a convenient method for intravital microscopy on otherwise inaccessible sites and organs in the awake subject or during surgery for research and for clinical diagnostic applications. At present, the use of microvascular imaging in diagnosis and treatment of human disease is limited. Use has been made of nailfold capillaroscopy in the diagnosis and treatment of peripheral vascular diseases, diabetes and hematological disorders 1‐3 . Problems with movement have restricted the use of the bulbar conjunctiva for clinical applications in opthalmology 4‐6 . Other lo

Anisotropic optical properties of doped poly(3,4-ethylenedioxythiophene)

Anisotropic optical properties of doped poly(3,4-ethylenedioxythiophene) (PEDOT) thin films have been determined by using variable-angle spectroscopic ellipsometry together with intensity reflectance and transmission spectrophotometry. The optical anisotropy of the PEDOT films are of uniaxial character with the optic axis normal to the film surface. The (ordinary) index of refraction in the plane shows a metallic state behavior while the out of plane (extraordinary) index of refraction shows a near dielectric character. The metallic state behavior in the surface plane agrees well with the high electrical conductivity measured for this material. The anisotropic optical properties of doped PEDOT thin films in terms of the complex indices of refraction together with results from grazing incidence X-ray diffraction studies allow us to deduce a preferential orientation of the polymer chains.

Ion beam sputtering and dual ion beam sputtering of titanium oxide films

Ion beam sputtering and dual ion beam sputtered films of titanium oxide were prepared and investigated at room temperature and compared with similar films prepared by e-beam (EB) gun deposition. Optical properties, i.e. Refractive index n and extinction coefficient k of films were determined by transmission spectrophotometry ( lambda =350-1100 nm) and at lambda =632.8 nm by ellipsometry. These were all found to be very dependent on deposition parameters (rate, substrate temperature and partial pressure of oxygen (PO2) in the case of EB deposition of TiO2). For ion beam sputtering (IBS) deposition the main controlling deposition parameter on the optical properties was PO2. The maximum refractive index achieved at 300 degrees C for EB deposited TiO2 films was n=2.35. Films deposited by IBS and dual ion beam sputtering (DIBS) at room temperature showed higher values of n(TiO2)=2.41-2.47 for lambda =550 nm. Values of extinction coefficient were similar and of the order of 10-4. X-ray diffraction (XRD) measurements revealed that all films deposited by IBS, DIBS and EB deposition were amorphous except for those films deposited by EB deposition at T>or=320 degrees C which were polycrystalline. DIBS of TiO2 with low-energy Ar and O2 ions (Ea=200-300 eV) and low currents (Ja=0-35 mu A cm-2) was not beneficial. Films bombarded with Ar+ were absorbing while films bombarded with O2+ showed no change in n or k. Different bonding states in IBS deposited TiO2 films were determined by x-ray spectroscopy (XPS) while the composition of films and contaminants were determined by Rutherford backscattering spectroscopy (RBS). TiO2 films formed by IBS contained approximately=0.4% Ar which originated from the reflected argon neutrals from the sputtering target while assisted deposition slightly increased argon content. Stress in the films deposited by IBS was measured and was compressive with a typical value of sigma =3.75-108 Pa.

Ion-beam and dual-ion-beam sputter deposition of tantalum oxide films

Ion-beam sputter deposition (IBS) and dual-ion-beam sputter deposition (DIBS) of tantalum oxide films was investigated at room temperature and compared with similar films prepared by e-gun deposition. The optical properties, i.e., refractive index and extinction coefficient, of IBS films were determined in the 250- to 1100-nm range by transmission spectrophotometry and at λ=632.8 nm by ellipsometry. They were found to be mainly sensitive to the partial pressure of oxygen used as a reactive gas in the deposition process. The maximum value of the refractive index of IBS deposited tantalum oxide films was n=2.15 at λ=550 nm and the extinction coefficient of order k=2×10 -4 . Films deposited by e-gun deposition had refractive index n=2.06 at λ=550 nm. Films deposited using DIBS, i.e., deposition assisted by low energy Ar and O 2 ions (E a =0 to 300 eV) and low current density (J i =0 to 40 μA/cm 2 ), showed no improvement in the optical properties of the films. Preferential sputtering occurred at E a (Ar)=300 eV and J i =20 μA/cm 2 and slightly oxygen deficient films were formed. Different bonding states in the tantalum-oxide films were determined by x-ray spectroscopy, whereas composition of the film and contaminants were determined by Rutherford backscattering spectroscopy (RBS). Tantalum oxide films formed by IBS contained relatively high Ar content (2.5%) originating from the reflected argon neutrals from the sputtering target whereas assisted deposition slightly increased the Ar content. Stress in the IBS-deposited films was measured by the bending technique. IBS-deposited films showed compressive stress with a typical value of s=3.2×10 9 dyn/cm 2 . Films deposited by concurrent ion bombardment showed an increase in the stress as a function of applied current density. The maximum was s5.6×10 9 dyn/cm 2 for E a =300 eV and J i =35 μA/cm 2 . All deposited films were amorphous as measured by the x-ray diffraction (XRD) method

Optical Transmittance of Thin Films of SrFeO2.5+x at Elevated Temperatures and Applications to Gas Sensing

AbstractNon-stoichiometric perovskites with the general formula SrFeO2.5+x have potential in oxygen sensing applications. Thin films of these compositions have been grown onto various substrates by pulsed laser deposition techniques. At elevated temperatures, (T > 550K), the films react rapidly and reversibly with oxygen and the bulk oxygen content, x, of the films changes. Accompanying the change in oxygen stoichiometry are significant changes in the optical transmittance and reflectance of the films. Transmission spectrophotometry in the uv-vis region has been used to determine the relationship of transmittance with oxygen composition in the gas phase. Spectrophotometric data have been obtained by a batch method and also in-situ in a flow cell at T = 690K. The data show a large variation in transmittance, exceeding 103 for the batch measurements, with SrFeO3 showing the highest opacity. The design of the flow cell is also described.

Attachment of an aminoglycoside, amikacin, to implantable collagen for local delivery in wounds

Cultured skin substitutes consisting of implantable collagen (COL) and cultured human skin cells often fail clinically from destruction by microbial contamination. Hypothetically, addition of selected antimicrobial drugs to the implant may control microbial contamination and increase healing of skin wounds with these materials. As a model for drug delivery, bovine skin COL (1 mg/ml) and amikacin (AM; 46 micrograms/ml) were modified by covalent addition of biotin (B-COL and B-AM, respectively) from B-N-hydroxysuccinimide and bound together noncovalently with avidin (A). B-COL was incubated with A and then with B-peroxidase (B-P) or by serial incubation with B-AM and B-P, before P-dependent chromogen formation. Colorimetric data (n = 12 per condition) from spot tests on nitrocellulose paper were collected by transmission spectrophotometry. Specificity of drug binding in spot tests was determined by (i) serial dilution of B-COL; (ii) reactions with COL, AM, or P that had no B; (iii) removal of A; or (iv) preincubation of B-COL-A with B before incubation with B-P. Binding of B-AM was (i) dependent on the concentration of B-COL; (ii) specific to B-COL, A, and B-P (P < 0.05); and (iii) not eluted by incubation in 0.15 or 1.0 M NaCl. B-AM was found to block binding of B-P to the B-COL-A complex and to retain bacteriocidal activity against 10 clinical isolates of wound bacteria in the wet disc assay. Antimicrobial activity of B-AM was removed from solution by treatment with magnetic A and a permanent magnet. These results suggest that selected antimicrobial drugs can be biotinylated for attachments to COL-cultured cell implants without loss of pharmacologic activity. Because this chemistry utilizes a common ligand, any molar ratio of agents may be administered simultaneously and localized to the site of implantation.

Pulse oximetry: Theoretical and experimental models

In the paper a pulse oximetry model is developed using an approach which combines both theoretical and empirical modelling. The optical properties of whole blood are measured as a function of cuvette depth by transmission spectrophotometry using red (660 nm) and infra-red (950 nm) light-emitting diodes as light sources. Twersky's theoretical model gives the best fit to the experimental data. A simple theoretical model which takes into account the nonlinear relationship between optical density and cuvette depth is then used to obtain an expression for the R:IR ratio, which relates the measurement of transmission at the two wavelengths. The R:IR ratio is found to be more or less independent of cuvette depth (SD = 0.14 at 100 per cent SaO2). To validate the predictions of the theoretical model, the results of a previous experiment in which the relationship between SaO2 and the R:IR ratio was recorded using a flexible cuvette are used. The experimental values are found to lie within one standard deviation from the theoretical curve relating SaO2 and the R:IR ratio. It is argued that a reasonably accurate model for pulse oximetry which is based on whole blood and not haemoglobin solutions has been developed.

Turbidity study of the process of film formation of polymer particles in drying thin films of acrylic latices: I. Intrastructure of acrylic latices studied with transmission spectrophotometry

The aim of this study is to determine the factors that define the process of film formation of binder particles in drying aqueous dispersion coatings, based on acrylic polymers. The film formation process is investigated with transmission spectrophotometry. In this paper static measurements are used to relate the turbidity behavior of thin latex films with the physical properties of the latex. This paper focuses on the intrastructure in films of concentrated acrylic dispersions. In concentrated latices the binder particles are arranged in closely packed structures, which cause colored light patterns, due to Bragg diffraction. Light waves traveling in the latex film are scattered at the internal structures of the spheres and the water voids. The pattern of the light transmission as a function of wavelength reveals the internal structure of the latex film. The influence of weight fraction, particle size, film thickness, and particle size distribution on the transmission pattern has been investigated. The results are verified with other particle size measurements and imaging techniques.

Characterization of the Residual Pink Color in Cooked Turkey Breast and Pork Loin

ABSTRACTThe residual redness was characterized in well cooked meat from turkey breast and pork loin. A simple method of scanning thin slices by transmission spectrophotometry was used to evaluate the meat pigments in situ. Absorption bands at 414, 520, and 550 nm of the spectra obtained from cooked meat led to the conclusion that residual pink color was caused by cytochrome c. The method was further modified to study the effect of air contact on meat color after cooking. Other pigments were spontaneously oxidized as soon as meat surface was exposed to air. The concentrations of hemoproteins in turkey and pork were determined and found to be related to cooked meat color.

Infrared absorption spectra ranging from 2.5 to 10 μm at various layers of human normal abdominal aorta and fibrofatty atheroma in vitro

The infrared absorption spectra ranging from 2.5 to 10 microns in wavelength at various layers of both the human normal abdominal aorta wall and the fibrofatty atheroma were measured by conventional transmission spectrophotometry. Optical specimens 7 microns in thickness were prepared using a cold microtome. Pathological examination was simultaneously performed to identify tissue type of the optical specimen. We found that the presence of characteristic absorption peaks at 5.75 and 3.4 microns was restricted to the atheromatous (fibrofatty) layer of the aorta wall. These peaks may be attributed to the accumulated cholesterol deposits. We also discovered that the normal media layer had strong absorption at 6.05 microns. The discrimination between normal media, fibrofatty atheroma, and aged intimal tissue was made possible by the normalized peak ratio which was based on the ratio of the 5.75- and 6.05-microns absorption peaks. These results may be significant for selective laser ablation of atheromatous tissue, as well as tissue diagnosis, to prevent artery perforation during laser angioplastic procedures.

Influence of water vapor on the morphology of Cu(II)O films produced by MOCVD

In the MOCVD production of oxide thin films, the use of oxygen saturated with water has been largely to reduce residual carbon and fluorine content. In this paper, the influence of water-saturated oxygen on the morphology of thin films of Cu(II)O produced by low temperature metalorganic chemical vapor deposition onto quartz, magnesium oxide and cubic zirconia substrates is described. The Cu(II)O films were characterized by scanning electron microscopy, energy dispersive X-ray microanalysis, optical transmission spectrophotometry and X-ray powder diffraction.

The ultraviolet microscopic transmission characteristics of human stratum corneum

Synopsis This study has evaluated the ultraviolet light transmission characteristics of human stratum corneum at the single cell level using a low light level video microscope to measure the mean percentage transmission of light at different wavelengths and the variation in transmission across the stratum corneum. Stratum corneum was isolated by an enzymic technique and examined on a low light level UV video microscope. Quantitative evaluation of the transmitted monochromatic light for the underside of the layer was measured directly using a Kontron UNIPS image processor or indirectly with a Quantimet 920 image processor after video recording. Transmission distribution histograms were obtained from samples of stratum corneum taken from human breast, scalp, abdomen and leg. Mean transmission values were also derived and compared with diffuse transmission values obtained using the same tissue mounted on an integrating sphere. The UV microscopic transmission characteristics of enzyme separated stratum corneum clearly demonstrated that this structure was not an ideal diffuser. Uniform light intensity on the surface of the stratum corneum led to areas of transmitted intensity in close proximity that differed by factors ofthree to six fold, e.g. between regions of high (>70%) and low (<20%) brightness. However, the average transmission was found to be compatible with published data obtained by diffuse transmission spectrophotometry, taking into account the enhanced transmission arising from stratum corneum immersion in phosphate buffered saline. This was confirmed by the elevated values obtained by diffuse transmission spectrophotometry in this study for samples of stratum corneum prepared for UV microscopy being higher than these found in published data. It is obvious from these findings that viable cells in the epidermis are not exposed to a uniform incident light intensity even when this is true for the surface of skin. Studies of skin response to ultraviolet light at the single cell level must take account of the possibility of preferential exposure of specific sites in any subsequent explanation of cell sensitivity. This is in addition to the already well established cell cycle dependent ultraviolet sensitivity.

Molecular sieving by electropolymerized porphyrin films only a few monolayers thick

Polymeric films can be formed on smooth Pt electrodes by oxidative polymerization of cobalt tetrakis(o-aminophenyl)porphyrin, (Co(o-NH{sub 2})TPP). Although the films are extremely thin, as few as two monomolecular layers of porphyrin sites, they exhibit permeabilities to molecular monomers that fall in a regular order of permeant molecular volume. The molecular sieving property is taken as evidence that membrane transport, rather than pinhole transport, is the predominant transport mechanism in these films. The permeability data are supported by film thickness measurements by electrochemical reactivity, surface profilometry, transmission spectrophotometry, ellipsometry, and X-ray photoelectron spectroscopy.

An evaluation of irganox 565 as a stabilizer for dammar picture varnishes

AbstractChanges during the aging of dammar resin films containing the antioxidant Irganox 565 were observed using ultraviolet-visible light transmission spectrophotometry and solubility tests. The concentration of the stabilizer was monitored with the aid of high performance liquid chromatography. Although the additive stabilizes dammar during heat aging in the dark, it breaks down rapidly during fadeometer aging and during natural aging behind a window facing south. Furthermore, colored degradation products of Irganox 565 cause increased yellowing during combined fadeometer-heat aging. In view of the fact that light plays an important role in the autoxidation of dammar, Irganox 565 is not recommended as a stabilizer for dammar varnishes.

Reflection spectrophotometry (OxySat-2®) for monitoring oxygen saturation and hematocrit during extracorporeal circulation

Continuous measurement of sO2 and hematocrit during extracorporeal circulation has become feasible using reflection spectrophotometry. We have compared simultaneous measurements with in-line reflection spectrophotometry (OxySat-2® American Bent-ley), and in-vitro transmission spectrophotometry (OSM3 Hemoximeter® Radiometer) on discrete samples.In 8 patients undergoing open heart surgery during hypothermic extracorporeal circulation with hemodilution arterial and venous sO2 and hematocrit were measured continuous in-line in the extracorporeal circuit. Simultaneous and anaerobically collected blood samples were analyzed within one minute in the OSM3. The relationship between hemoglobin concentration (cHb) measured in the OSM3 and hematocrit (Hct) measured by the OxySat-2 was estimated from a mean cell hemoglobin concentration of 20 mmol·l-1, i.e. Hct (%) = 100 cHb/20.There was a systematic difference between the OxySat-2 and the reference method for sO 2</sb and cHb, the mean difference being: −2.4 s.d.2.8 ...

Intact organ spectrophotometry and single-photon counting.

In toxicology, it is of interest not only to assess enzyme levels and capacities for potential fluxes, but it is also useful to develop methods for determining actual concentrations and fluxes in the intact cell and organ. To this end, several noninvasive techniques have been developed over the years. Our interest has been largely in photometric techniques. Transmission spectrophotometry through solid organs permits monitoring of the cytochromes of the mitochondrial respiratory chain and cytochrome P-450 as well as other pigments of biological interest. Furthermore, the steady state level of catalase Compound I in liver provides information on rates of H2O2 production. These are in the nM to microM concentration range. More recently, the monitoring of photoemission from intact organs has been useful in toxicological problems. The major photoemissive species, singlet molecular oxygen and excited carbonyls, can now be monitored with good signal/noise ratio. Redox cycling of quinones and the generation of photoemissive species were studied in menadione metabolism. Inhibition of phase II led to a significant increase in the steady state level of singlet oxygen, as did the inhibition of two-electron reduction by using the inhibitor dicoumarol for DT diaphorase. Conversely, the induction of DT diaphorase by pretreatment with BHA protected by decreasing the level of reactive oxygen species.

Differences in brain cytochrome responses to carbon monoxide and cyanide in vivo.

Cytochrome oxidation-reduction responses to two mitochondrial electron transport inhibitors, carbon monoxide (CO) and cyanide (CN), were studied in the intact brains of fluorocarbon-circulated rats. In vivo reflectance spectrophotometry indicated that cortical b-type cytochromes (564 nm) were highly resistant to reduction by CN in the presence of O2 but showed reduction responses to the administration of 1-5% CO in 90% O2. In contrast, cyanide-sensitive cytochromes aa3 (605 nm) and c + c1 (551 nm) did not increase their reduction levels during exposure to 5% CO in 90% O2. The in vivo CO-mediated b-cytochrome reduction responses did not occur after pretreatment with the cytochrome b inhibitor, antimycin A. Transmission spectrophotometry of superfused hemoglobin-free rat brain slices confirmed cortical b-type cytochromes to be CN-resistant in the presence of O2. Another cytochrome absorbing at 445 nm also was resistant to reduction by 1-mM cyanide in vitro, but it could be reduced anaerobically. The reduced 445-nm cytochrome bound CO in the presence of cyanide. We postulate that this CN-resistant CO binding component might account for in vivo cytochrome aa3-CO interactions and directly or indirectly modulate cytochrome b reduction responses to CO. In any event, the spectral data indicate different primary tissue target sites for CO and CN in living rat brain and also suggest different bioenergetic consequences of exposure to the two agents.

Role of light scattering in whole blood oximetry.

We investigated the role of light scattering in whole blood oximetry by transmission spectrophotometry. To delineate the role of scattering and absorbance in the measurement of oxyhemoglobin saturation, we applied Twersky's theory of radiation scattering and measured the apparent optical density of whole blood and hemoglobin solutions. The optical density versus hematocrit relationship predicted by Twersky's theory was found to give a good fit to the data obtained at 660, 813, 880, and 940 nm. A semi-empirical variation of Twersky's equation and photon diffusion equations were also compared to the data, and Twersky's original equation was found to give the best fit. Therefore, Twersky's equation was employed throughout the rest of the data analysis. Total scattering effects were shown to be wavelength and oxygenation dependent. Moreover, the relationship between total scattering effects and percent O2 saturation was approximately linear, and it had a greater slope (at 660 nm) than absorbance versus O2 saturation. Thus, scattering effects in the red-infrared range do not detract from the linearity of whole blood oximeters. By contrast, scattering effects increase the sensitivity of oximeters by contributing linearly to the total O. D. change that occurs with altered oxygenation.

Light‐induced, dark‐reversible colour shifts in petals of Phlox

Flowers of some Phlox (Phlox x paniculata L.) varieties undergo daily colour shifts, being blue in the early morning, turning red during the day, and returning to blue in the evening. The colour shift, which occurs only in the upper (adaxial) petal surfaces, is due to the daily changes in ambient light. In the laboratory, colour shifts could be induced by 2.5 h of ultraviolet, visible or far‐red light and recorded by reflectance spectrophotometry.There are indications that irradiations with different kinds of light cause qualitatively different colour shifts, and that thus more than one photoreceptor pigment and more than one primary light reaction may be involved. The presence of phytochrome was demonstrated in petals of white Phlox flowers by in vivo transmission spectrophotometry. It is therefore possible that colour shifts in coloured Phlox flowers are mediated by phytochrome. Possibly the movement of ions (e.g. hydrogen ions) into or out of the vacuole (where the visible pigments are located) is affected by light absorption in a pigment in the tonoplast.