Influence Of Solution Viscosity Research Articles

Polyamide-imides as novel high performance primary protective coatings of silica optical fibers: Influence of the structure and molecular weight

Polyimides are commonly used as primary protective optical fiber coatings for high-temperature applications. However, a number of significant drawbacks such as thermal and hydrolytic instability of polyamiс acid, its incomplete transformation into polyimide, several deposition cycles of the required thickness and insufficient adhesion of polyimide coatings to the surface complicate the manufacture of special optical fibers and their widespread use. In this study we showed the principal possibility of utilizing polyamide-imides (PAIs) as primary protective coatings of high operational reliability. Two series of high-molecular-weight (Mw = 84–365 kDa) and thermostable (T10% = 490–520 °C) PAIs were synthesized by low temperature polycondensation of terephthaloyl chloride and various tetracarboxylic acid dianhydrides with 9,9-bis(4-aminophenyl)fluorene or 2,2′-bis(trifluoromethyl)benzidine in NMP. Coatings of a thickness of 10–15 μm with good adhesion to the optical fiber were formed from the PAIs solutions in NMP with no any additives and in a single application cycle. Apart from the influence of solution viscosity and drawing parameters on the coating quality, a particular attention was paid to the dependency of the strength and mechanical reliability of the fibers with resulting coatings on the structure and molecular weight of the polymer. It was established that the fibers coated with PAIs prepared from 2,2′-bis(trifluoromethyl)benzidine (Mw = 190–200 kDa) can withstand 3 and 72 h annealing at 350 and 300°С, respectively, retaining >80% of the original strength. Thus, PAIs are considered as a promising candidate for further studies, i.e., for the creation of optical fiber sensors for large-scale applications.

Investigating the effects of solution viscosity on the stability and success rate of SECCM imaging

Due to the capability of simultaneously detecting the morphology and electrochemical information of samples and limiting the electrochemical reaction to a range approximately the size of the inner diameter of the pipette tip opening, scanning electrochemical cell microscopy (SECCM) enables higher precision local electrochemical measurement and surface material delivery and has been demonstrating unique advantages and broad application prospects. However, the meniscus droplet at the pipette tip of SECCM is equivalent to the opening radius of the pipette tip, which is usually tens of nanometers to hundreds of nanometers. The tiny meniscus droplet makes it susceptible to evaporation and crystallization, which increases the likelihood of the pipette colliding with the sample during the scanning process, resulting in the failure of scanning. In this paper, the influence of solution viscosity on the shape variation of the droplet at the tip during the movement of the pipette of SECCM was studied by finite element analysis. It is proved that the increase of solution viscosity is helpful in reducing the shape variation of the droplet at the tip during the movement of the pipette. Then scanning experiments were carried out using a flat Au substrate and Au substrates with rounded triangle and rounded rectangular convex structures as the samples. According to the experimental results, increasing solution viscosity improves scanning success rates and scanning quality and effectively lowers the MSE of the scanning results. The experimental results also show that SECCM can image at a higher speed when the solution's viscosity increases since the deformation of the droplet at the tip is less than with a typical solution.

The Effects of Viscosity and Capillarity on Nonequilibrium Distribution of Gas Bubbles in Swelling Liquid–Gas Solution

A detailed statistical description of the evolution of supersaturated-by-gas solution at degassing has been presented on the basis of finding the time-dependent distribution in radii of overcritical gas bubbles. The influence of solution viscosity and capillarity via internal pressure in the bubbles on this distribution has been considered until the moment when the gas supersaturation drops due to depletion and stops nucleation of new overcritical gas bubbles. This study is based on our previous results for the nonstationary growth rates of overcritical bubbles depending on gas supersaturation, diffusivity and solubility in solution, solution viscosity, and surface tension on bubble surface. Other important factors are linked with the initial rate of homogeneous gas bubble nucleation and coupling between diffusivity and viscosity in the solution. Here, we numerically studied how all these factors affect the time-dependent distribution function of overcritical bubbles in their radii, maximal and mean bubble radii, and the time-dependent swelling ratio of a supersaturated-by-gas solution in a wide range of solution viscosities.

Experimental and CFD study on influence of viscosity on layer melt crystallization

• Layer melt crystallization of aqueous sucrose solutions with different viscosities. • Viscosity influence on freezing based on ice crystal yield and purity results. • CFD study on heat transfer inside melt crystallizer prior to ice crystallization. • Temperature distributions and thermal boundary layers of undercooled solutions. In the present work, the influence of solution viscosity on growth kinetics and purification efficiency in layer melt crystallization was investigated. Melt crystallization experiments were conducted for three different types of aqueous sucrose solution as they are ideal solutions and a relatively wide viscosity range can be investigated with a moderate change of freezing points. The aqueous 10 wt%, 23 wt%, and 30 wt% sucrose solutions have a dynamic viscosity value of 2.01 mPas, 4.74 mPas, and 7.21 mPas at their respective freezing points of −0.63 °C, −1.78 °C, and −2.64 °C. The solution temperature distribution was predicted by computational fluid dynamics (CFD) simulations run in COMSOL Multiphysics 5.6 software. Experimental results showed that a higher solution viscosity caused a higher crystal layer impurity and lower crystal yields in static layer melt crystallization. The cooling process of different solutions predicted by a CFD heat transfer study showed that the supersaturation region is wider for less concentrated solutions as cooling proceeds more rapidly. Hence, the temperature gradients obtained follow the boundary layer theory, i.e., the thinner the boundary layer, the faster the heat transfer.

Influence of viscosity on chondrogenic differentiation of mesenchymal stem cells during 3D culture in viscous gelatin solution-embedded hydrogels

Differentiation of human bone marrow-derived mesenchymal stem cells (hMSCs) is regulated by a variety of cues of their surrounding microenvironments. In particular, mechanical properties of cell culture matrices have been recently disclosed to play a pivotal role in stem cell differentiation. However, it remains elusive how viscosity affects the chondrogenic differentiation of hMSCs during three-dimensional (3D) culture. In this study, a 3D culture system that was established by embedding viscous gelatin solution in chemically cross-linked gelatin hydrogels was used for 3D culture of hMSCs in gelatin solutions with different viscosities. The influence of solution viscosity on chondrogenic differentiation of hMSCs was investigated. Viscous gelatin solutions promoted cell proliferation in the order of low, middle and high viscosity while elastic hydrogels restricted cell proliferation. High viscosity gelatin solution led to increased production of the cartilaginous matrix. Under the synergistic stimulation of chondrogenic induction factors, high viscosity was beneficial for the chondrogenic differentiation of hMSCs. The results suggested the role of viscosity should be considered as one of the dominant mechanical cues affecting stem cell differentiation.

Flow analysis on microcasting with degassed polydimethylsiloxane micro-channels for cell patterning with cross-linked albumin.

Patterned cell culturing is one of the most useful techniques for understanding the interaction between geometric conditions surrounding cells and their behaviors. The authors previously proposed a simple method for cell patterning with an agarose gel microstructure fabricated by microcasting with a degassed polydimethylsiloxane (PDMS) mold. Although the vacuum pressure produced from the degassed PDMS can drive a highly viscous agarose solution, the influence of solution viscosity on the casting process is unknown. This study investigated the influences of micro-channel dimensions or solution viscosity on the flow of the solution in a micro-channel of a PDMS mold by both experiments and numerical simulation. It was found experimentally that the degassed PDMS mold was able to drive a solution with a viscosity under 575 mPa·s. A simulation model was developed which can well estimate the flow rate in various dimensions of micro-channels. Cross-linked albumin has low viscosity (1 mPa·s) in aqueous solution and can undergo a one-way dehydration process from solution to solid that produces cellular repellency after dehydration. A microstructure of cross-linked albumin was fabricated on a cell culture dish by the microcasting method. After cells were seeded and cultivated on the cell culture dish with the microstructure for 7 days, the cellular pattern of mouse skeletal myoblast cell line C2C12 was observed. The microcasting with cross-linked albumin solution enables preparation of patterned cell culture systems more quickly in comparison with the previous agarose gel casting, which requires a gelation process before the dehydration process.

Influence of solution viscosity on hydrothermally grown ZnO thin films for DSSC applications

Zinc oxide (ZnO) nanowire arrays (NWAs) were grown onto zinc oxide-titanium dioxide (ZnO-TiO2) seeded fluorine doped tin oxide (FTO) conductive substrate by hydrothermal technique. X-ray diffraction (XRD) patterns depict that ZnO thin films are preferentially oriented along the (002) plane with hexagonal wurtzite structure. Viscosity measurements reveal that viscosity of the solutions linearly increases as the concentrations of the polyvinyl alcohol (PVA) increase in the growth solution. Field emission scanning electron microscope (FE-SEM) images show that the NWAs are vertically grown to seeded FTO substrate with hexagonal structure, and the growth of NWAs decreases as the concentration of the PVA increases. Stylus profilometer and atomic force microscopic (AFM) studies predict that the thickness and roughness of the films decrease with increasing the PVA concentrations. The NWAs prepared at 0.1% of PVA exhibits a lower transmittance and higher absorbance than that of the other films. The band gap of the optimized films prepared at 0.0 and 0.1% of PVA is found to be 3.270 and 3.268 eV, respectively. The photo to current conversion efficiency of the DSSC based on photoanodes prepared at 0.0 and 0.1% of PVA exhibits about 0.64 and 0.82%, respectively. Electrochemical impedance spectra reveal that the DSSC based on photoanode prepared at 0.1% of PVA has the highest charge transfer recombination resistance.

Organic fouling and reverse solute selectivity in forward osmosis: Role of working temperature and inorganic draw solutions

The water flux of several draw solutions (DSs, solutes: KCl, NaCl, CaCl2, Na2SO4) and fouling propensity of two different organic foulants (humic acid and alginate) were systematically investigated using forward osmosis (FO) and unpressurized pressure-retarded osmosis. In addition, reverse solute selectivity was evaluated to characterize the water and salt transport mechanisms at different temperatures and in the presence of four different inorganic DS compounds. The influence of solution viscosity has significant implications in FO applications, because the water molecules easily penetrated and diffused throughout the FO membrane active layer (AL) and supporting layer (SL) with increasing temperatures, which is mainly correlated with the lower water viscosities with increasing temperatures. The results indicated that the water flux on average significantly increased from 9.5 to 13.7 and 24.9 LMH when the operating temperature was increased from 5 to 20 and 45°C, which corresponded to a 44 and 262% increase in the water flux, compared to the FO mode at 5°C. However, the water flux and viscosity exhibited generally constant trends with respect to the elevating temperature. In addition, elevating temperature increased the reverse solute flux selectivity (RSFS), not only by decreasing the internal concentration polarization (the AL and SL) and the wettability within the effective porosity of the SL, but also via the improvement of water molecule diffusion kinetics rather than solute diffusion. In addition, the RSFS was inversely related to the solute permeability of the different DSs and followed the order Na2SO4>CaCl2>NaCl>KCl. These results have significant implications for the prediction of water flux behavior and the selection of DSs at different temperatures in osmotically driven FO processes.

The influence of solution viscosity on the dissolution rate of soluble salts, and the measurement of an "effective" viscosity.

Abstract The rate of solution of KCl and NaCl from compressed discs has been determined under controlled conditions, in water at 25° and in solutions of varying concentrations of polyvinylpyrrolidone (molecular weight 360 000), polyoxyethylene glycol 6000 and cetomacrogol 1000. Dissolution rate constants decrease with increasing bulk solution viscosity, as expected, but no one equation relating rate constant and bulk viscosity fits the results for the systems studied. Calculation of an effective viscosity from the diffusion coefficients of the salts in water and the diffusion coefficients of the salt in the polymer solutions enables an empirical correlation of the results to be made. The relation of the effective viscosity to the microscopic viscosity is discussed in an Appendix.

Influence of solution viscosity and injection protocol on distribution patterns of jet injectors: Application to photodynamic tumour targeting

Photodynamic therapy of deep or nodular skin tumours is currently limited by the poor tissue penetration of the porphyrin precursor 5-aminolevulinic acid (ALA) and preformed photosensitisers. In this study, we investigated the potential of jet injection to deliver both ALA and a preformed photosensitiser ( meso-tetra ( N-methyl-4-pyridyl) porphine tetra tosylate, TMP) into a defined volume of skin. Initial studies using a model hydrogel showed that as standoff distance is increased, injection depth decreases. As the ejected volume is increased, injection depth increases. It was also shown, for the first time, that, as injection solution viscosity was increased, for a given injection setting and standoff distance, both total depth of jet penetration, L t, and depth at which the maximum width of the penetration pattern occurred, L m, decreased progressively. For a standoff distance of zero, the maximum width of the penetration pattern, L w, increased progressively with increasing viscosity at each of the injection settings. Conversely, when the standoff distance was 2.5 mm, L w decreased progressively with increasing viscosity. Studies with neonate porcine skin revealed that an injection protocol comprising an 8.98 mPas solution, an arbitrary injection setting of 8 and a standoff distance of zero was capable of delivering photosensitisers to a volume of tissue ( L t of 2.91 mm, L m of 2.14 mm, L w of 5.10 mm) comparable to that occupied by a typical nodular basal cell carcinoma. Both ALA and TMP were successfully delivered using jet injection, with peak tissue concentrations (67.3 mg cm −3 and 5.6 mg cm −3, respectively) achieved at a depth of around 1.0 mm and substantial reductions in drug concentration seen at depths below 3.0 mm. Consequently, jet injection may be suitable for selective targeting of ALA or preformed photosensitisers to skin tumours.

Poly-L-lactide nanofibers by electrospinning – Influence of solution viscosity and electrical conductivity on fiber diameter and fiber morphology

Abstract Poly-L-lactide (PLA) fibers were obtained by electrospinning of PLA / dichloromethane solutions. Formation of beaded fibers combined with decreased fiber diameters were observed for low PLA concentrations in solution. Increase of the electrical conductivity by addition of pyridinium formiate (PF) caused a significant reduction of bead formation. The electrospinning of dilute PLA / PF / dichloromethane solutions resulted in PLA nanofibers. Systematic variations clearly identified the solution viscosity and the electrical conductivity at otherwise fixed parameters (surface tension, molecular weight, electrode geometry, electrical field, etc.) as crucial parameters for the formation of beads upon electrospinning of PLA / dichloromethane solutions.

Viscosity effects on Dean vortex membrane microfiltration

AbstractThe influence of changing viscosity by adding polyethylene glycol (PEG) during microfiltration of silica suspensions in the presence and absence of Dean vortices was determined. A new microfiltration membrane module design containing helically wound hollow fibers (with Dean vortices) was compared with a standard commercial cross‐flow module (without Dean vortices) containing linear hollow fibers during filtration of poly(ethylene) glycol solutions and silica suspensions. The influence of solution viscosity on permeation flux behavior was evident through two separate effects. First, increased viscosity effected the formation and stability of vortices and, hence, wall shear rate and convective back‐flow. Second, permeation flux was reduced with increasing fluid viscosity. Flux improvements (linear vs. helical membranes) of up to 45% were observed for all value of the silica suspensions with and without PEG. The energy required to obtain these improvements, however, was considerable. Flux advantages of the helical design decreased and eventually disappeared as the viscosity of the solution increased up to 12 times that of water at 27°C. New mass‐transfer correlations for microfiltration of poly(ethylene) glycol solutions containing silica concentrations for laminar flow in a helical and a linear module were obtained with respect to the solution viscosity, for a silica particle concentration of 0.1 wt. %.

ゾル-ゲル法によるSiO<sub>2</sub>被膜の保護性に及ぼす溶液の粘度の影響

ゾル-ゲル法によるSiO<sub>2</sub>被膜の保護性に及ぼす溶液の粘度の影響

The influence of solution viscosity on nasal spray deposition and clearance

Three hydroxypropyl methylcellulose solutions, having kinematic viscosities 36, 120 and 430 mm 2·s −1, were administered as nasal sprays to 8 healthy subjects. The solutions were radiolabelled with 99mTc-labelled diethylenetriaminepentaacetic acid and the sites of deposition and the rates of clearance from the nasal cavity monitored using a gamma camera. The areas of deposition were the same for all the solutions. The clearance rates decreased with increasing solution viscosity, the half-times being 1.0, 1.7 and 2.2 h. Thus increasing the solution viscosity may provide a means of prolonging the therapeutic effect of nasal spray preparations.

Fluorescence drainage profiles of thin liquid films

Fluorescence drainage-profiles of thin liquid films formed from Rhodamine solutions containing anionic, cationic and non-ionic surfactants have been investigated. It is found that the influence of system variables such as electrolyte concentration, dye concentration, film environment and solution viscosity can be evaluated by means of the profiles. The addition of sodium chloride leads to the expansion (non-ionic surfactant), or contraction (anionic surfactant) of the profiles. In the case of the cationic surfactant, it reduces the number of fringes in the profiles. The height of selected fringes changes linearly with dye concentration, and no fringes are observed when the films are submerged in non-polar solvents. The influence of solution viscosity on film thickness and drainage rate is demonstrated by the number and frequency of fringes in the profile. The formation of first and second “black films” from solutions containing varying concentrations of sodium chloride can be shown.