RESUMO
The structures, sizes, and refractive indices (RI) of protein aggregates formed in a fibrinogen-thrombin system are examined using laser phase microscopy (LPM) accompanied by dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements. Fibrin aggregates found in pure fibrinogen and fibrinogen with thrombin solutions by the DLS method, after drying the sample, form complex structures of different shapes and sizes on a glass surface. The LPM reveals submicron-sized dimeric structures in the pure fibrinogen solution, elongated micron-length structures, and rectangular structures in the fibrinogen-thrombin sample. AFM measurements show that the elongated structures form branched fibers, which in turn assembly into rectangular structures. All sizes obtained by LPM and AFM are consistent with DLS measurements. The refractive indices of all the structures, estimated by optical thickness, vary from 1.53 to 1.62, which indicates that they are fibrinogen derivatives. Effective visualization of the structure and determination of the optical properties for fibrin gel indicate that laser phase microscopy is capable of tissue imaging and characterization.
RESUMO
The swelling of a polymer ion-exchange membrane Nafion in water with various heavy isotope contents (D2O) was studied by photoluminescent UV spectroscopy. The photoluminescence arises because of the presence of sulfonic groups attached to the ends of the perfluorovinyl ether groups that form the tetrafluoroethylene (Teflon) backbone of Nafion. The width of the colloidal region, which is formed near the membrane surface as a result of the outgrowth of Nafion microfibers toward the bulk liquid, varies non-monotonically with D2O content, displaying a narrow maximum in the low concentration region. A significant insight into the unexpected isotopic effects revealed in swelling Nafion in deuterated water is provided. Mainly, the polymer swelling is very sensitive to small changes (on the order of several tens of parts per million) in the content of deuterium, which, for instance, can help in understanding the isotopic effects in living tissues.
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A droplet formation in aqueous solutions of tetrahydrofuran (THF) has been experimentally detected at the submicrometer scale using two independent laser diagnostic techniques (dynamic light scattering and laser phase microscopy) and described in terms of THF-water intermolecular hydrogen bonding. It is shown that the nanodroplets have a mean size of 300 nm, their refractive index is higher than that of the ambient liquid, and they are highly enriched with THF molecules. The maximum of light scattering intensity falls within the THF concentration range 2-8 mol. %, which corresponds to the volume number density of the nanodroplets â¼1010-1011 cm-3. A theoretical explanation of forming the nanodroplets with a high content of THF, which is based on a model of dichotomous noise being applied to the so-termed "twinkling" hydrogen bonds and involves spinodal decomposition in the unstable region enclosed within the dichotomous binodal, is proposed. The parameters of hydrogen bonds in the molecular system "water-THF" were found, and the phase diagram of the solution with allowance for cross-linking hydrogen bonds was constructed.
RESUMO
Results of experiments with dynamic light scattering, phase microscopy, and polarimetric scatterometry allow us to claim that long-living gas nanobubbles and the clusters composed of such nanobubbles are generated spontaneously in an aqueous solution of salt, saturated with dissolved gas (say, atmospheric air). The characteristic sizes of both nanobubbles and their clusters are found by solving the inverse problem of optical wave scattering in ionic solutions. These experimental results develop our earlier study reported by Bunkin et al. [J. Chem. Phys. 130, 134308 (2009)] and can be treated as evidence for the special role of ions in the generation and stabilization of gas nanobubbles.
RESUMO
A quantitative model of ion-stabilized gas bubbles is suggested. Charging the bubbles by the ions, which are capable of adsorption, and the screening by a cloud of counter-ions, which are less absorptable, is modeled. It is shown that, subject to the charge of bubble, two regimes of such screening can be realized. For low-charged bubbles, the screening is described in the framework of the known linearized Debye-Huckel approach, when the sign of the counter-ion cloud is preserved everywhere in the liquid, whereas at large charge this sign is changed at some distance from the bubble surface. This effect provides the mechanism for the emergence of two types of compound particles having the opposite polarity, which leads to the aggregation of such compound particles into fractal clusters. Based on experimental data, arguments in favor of the existence of the clusters composed of the ion-stabilized bubbles in aqueous electrolyte solutions are advanced. This paper provides theoretical grounds for the experimental results presented in the previous paper (part I) published in this journal.
RESUMO
Within the present experimental working it has been shown that in the vicinity of naphione (ion-exchange membrane) the water refraction coefficient grows approximately by a factor of 1.1 in comparison with its value in a liquid. The refractive coefficient changes at the wavelength of about 50 microns. The effect of the refractive coefficient is measured by the pH value and the temperature of the liquid. In the experimental study of the "glycerin/water" mixture at different concentrations it has been found that the refractive coefficient may increase because naphione surface attracts the dipole of water clusters. This effect occurs due to the swelling of naphione in water and its surface takes a charge.
Assuntos
Polímeros/química , Soluções/química , Água/química , Sulfato de Magnésio/química , Microscopia , Modelos Teóricos , Cloreto de Sódio/químicaRESUMO
Results of experiments with laser modulation interference microscopy and the Mueller-matrix scatterometry show that macroscopic scatterers of light waves are present in doubly distilled water free of external solid impurities. The experimental data can be interpreted using a computational model of micron-scale clusters composed of polydisperse air bubbles having effective radii of 70-90 nm. The fractal dimension of such clusters was evaluated as 2.4-2.8 and their concentration appeared to be approximately 10(6) cm(-3).