Second harmonic generation and confined acoustic phonons in highly excited semiconductor nanocrystals

The photo-induced enhancement of second harmonic generation and the effect of nanocrystal shape and pump intensity on confined acoustic phonons in semiconductor nanocrystals have been investigated with time-resolved scattering and absorption measurements. The second harmonic signal showed a sublinear increase of the second-order susceptibility with respect to the pump pulse energy, indicating a reduction of the effective one-electron second-order nonlinearity with increasing electron-hole density in the nanocrystals. The coherent acoustic phonons in spherical and rod-shaped semiconductor nanocrystals were detected in a time-resolved absorption measurement. Both nanocrystal morphologies exhibited oscillatory modulation of the absorption cross section, the frequency of which corresponded to their coherent radial breathing modes. The amplitude of the oscillation also increased with the level of photoexcitation, suggesting an increase in the amplitude of the lattice displacement as well.     

Lysozyme as diffusion tracer for measuring aqueous solution viscosity

Measuring tracer diffusion provides a convenient approach for monitoring local changes in solution viscosity or for determining viscosity changes in response to multiple solution parameters including pH, temperature, salt concentrations or salt types. One common limitation of tracer diffusion in biologically relevant saline solutions is the loss of colloidal stability and aggregation of the tracer particles with increasing ionic strength. Using dynamic light scattering to measure tracer diffusion, we compared the performance of two different types of tracer particles, polystyrene nanobeads vs. the small protein lysozyme, for viscosity measurements of saline solutions. Polystyrene beads provide reliable values for water viscosity, but begin flocculating at ionic strengths exceeding about 100 mM. Using lysozyme, in contrast, we could map out viscosity changes of saline solutions for a variety of different salts, for salt concentrations up to 1 M, over a wide range of pH values, and over the temperature range most relevant for biological systems (5–40 °C). Due to its inherently high structural and colloidal stability, lysozyme provides a convenient and reliable tracer particle for all these measurements, and its use can be readily extended to other optical approaches towards localized measurements of tracer diffusion such as fluorescence correlation spectroscopy.     

Application of PET deprotection for orthogonal photocontrol of aqueous solution viscosity

Photorelease and photoisomerization of trans-cinnamic acid in aqueous CTAB solutions induces a bulk solution viscosity increase and decrease, respectively, triggered by orthogonal irradiation wavelengths.     

Back propagation modeling of shear stress and viscosity of aqueous Ionic-MXene nanofluids

Journal of Thermal Analysis and Calorimetry - Back-propagation modeling of viscosity and shear stress of Ionic-MXene nanofluid is carried out in this work. The data for Ionic-MXene nanofluid of...     

Generation of nanostructures of mica supported lysozyme molecules in aqueous solution by atomic force microscopy

Nanostructures of lysozyme molecules adsorbed to mica were generated by the tip of an atomic force microscope in contact, tapping, and force-distance mode in aqueous solution. In contact mode at high ionic strength and adjusted lysozyme concentration a monolayer of defined pattern and orientation could be formed by the scan process of the tip. A lysozyme monolayer with minimal pattern size of about 60 nm was achieved by line scan. At larger loading forces besides a monolayer also 3D-aggregates of lysozyme molecules could be generated. In force-distance mode the volume of 3D-aggregates grows with increasing generation time, lysozyme concentration in the bulk phase, loading force, and frequency of up- and down-movement of the substrate toward the fixed cantilever. In tapping mode 3D-aggregates could be generated as well. It is postulated that reduction of electrostatic interaction between the oppositely charged lysozyme molecules and mica surface by sufficient high ionic strength is essential for monolayer formation. It is discussed that for the underlying mechanism of monolayer generation in contact mode lysozyme molecules of the bulk phase adsorb to the tip, become pulled off and attach to the mica surface by the scan process of the tip.     

Ranges of frequency dispersion for the shear viscosity coefficients of aqueous solutions of electrolytes

The range of frequency dispersion for dynamic coefficient of shear viscosity η _S (ω) of electrolyte solutions obtained through kinetic equations under the condition of recovering the steady-state structure of a liquid exponentially or according to the diffusion law is considered. Numerical calculations of η _S (ω) are performed for an aqueous solution of NaCl depending on density ρ, temperature T, concentration C, and frequencies ω to select the potential of intermolecular interaction Φ _ab (|r|) and equilibrium radial distribution function g _ab (|r|). It is noted that the calculated theoretical results of η _S (ω) are in quantitative accordance with the experimental data. It is shown that the range of frequency dispersion η _S (ω) based on the diffusion mechanism is broad (～10⁵ Hz) and is narrow in the case of exponential attenuation of the viscous stress tensor (～10² Hz); this corresponds to both acoustic measurements and results from phenomenological theory.     

玉米支链淀粉在单糖、寡糖水溶液中的粘度行为

通过乌氏粘度计和数字流变仪研究了玉米支链淀粉在单糖和寡糖溶液中的特性粘度和表观粘度.发现在稀溶液中,玉米支链淀粉的特性粘度随糖浓度的增加而降低;浓溶液中,玉米支链淀粉的糖溶液的表观粘度随糖浓度的增加而升高.小分子糖对支链淀粉在糖溶液中的特性粘度和表观粘度的影响由强到弱依次为蔗糖>麦芽糖>葡萄糖>半乳糖>果糖.     

Intrinsic viscosity of rigid macromolecules in dilute solution in steady shear flow

A rigid linear array of beads in a Newtonian fluid is used to model a rod-like macromolecule in a dilute solution. Following the work of Kotaka, an expression is obtained relating the intrinsic viscosity to the velocity gradient. Computed results are compared with the experimental results of Strömberg.     

Calculating the electrostatic field in the bulk of an aqueous solution

The problem of an external electric field penetrating into the bulk of an electrolyte solution is investigated. An exact solution to the problem of calculating the static electric field in a finite electrolyte volume between two galvanically isolated flat electrodes is found. Corresponding examples of applying the obtained relations are considered.     

Construction of nanostructures in aqueous solution from amphiphilic glucose‐derived polycarbonates

Carbohydrates are the fundamental building blocks of many natural polymers, their wide bioavailability, high chemical functionality, and stereochemical diversity make them attractive starting materials for the development of new synthetic polymers. In this work, one such carbohydrate, d ‐glucopyranoside, was utilized to produce a hydrophobic five‐membered cyclic carbonate monomer to afford sugar‐based amphiphilic copolymers and block copolymers via organocatalyzed ring‐opening polymerizations with 4‐methylbenzyl alcohol and methoxy poly(ethylene glycol) as initiator and macroinitiator, respectively. To modulate the amphiphilicities of these polymers acidic benzylidene cleavage reactions were performed to deprotect the sugar repeat units and present hydrophilic hydroxyl side chain groups. Assembly of the polymers under aqueous conditions revealed interesting morphological differences, based on the polymer molar mass and repeat unit composition. The initial polymers, prior to the removal of the benzylidenes, underwent a morphological change from micelles to vesicles as the sugar block length was increased, causing a decrease in the hydrophilic–hydrophobic ratio. Deprotection of the sugar block increased the hydrophilicity and gave micellar morphologies. This tunable polymeric platform holds promise for the production of advanced materials for implementation in a diverse range of applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 432–440     

A thin liquid film thickness shear mode bulk acoustic wave sensor for determination of Proteus mirabilis

A thickness shear mode bulk acoustic wave sensor coated with a thin liquid culture medium film was developed and applied to determine the concentration of Proteus mirabilis (P. mirabilis). Experiments demonstrated that there was a good linear relationship between the turning point time and the logarithm of the P. mirabilis concentration in the range 2.0 x 10(2)-2.0 x 10(6) cells ml(-1). The detection was fast and accurate because of the sharp turning point of the response due to the thin culture film on the sensor surface. Other problems concerning the experiments are discussed in detail.     

Extraction and recovery of lignosulfonate from its aqueous solution using bulk liquid membrane

The paper presents an experimental study on the coupled transport of lignosulfonate (LS) through bulk liquid membrane (BLM) and thereby to identify the best set of solvent, operating conditions and mode of transport that would yield optimum performance of the BLM. Trioctylamine (TOA) is used as carrier. Among various solvents, tested for the above purpose, dichloroethane is found to be the best. The effects of operating condition, viz. pH, temperature, and carrier concentration, on the equilibrium distribution of LS are investigated. The effects of temperature, stirring of aqueous and organic phases, stirring speed, carrier concentration, initial feed and strip phase concentration on the separation of LS using BLM are also studied. It is observed that transport of LS can be enhanced by increasing the temperature and stirring speed of feed phase. Stirring of strip phase has no appreciable effects on the transport of LS. With increase in initial feed concentration the initial rate of the transport of LS is higher but continues for a longer time. Recovery of LS is much higher in co-transport mode in comparison to counter transport mode. Application of 1.25 M NaOH as stripping solution gives high recovery (70%) and high strip flux (70% of feed flux).     

Determination of the second critical micelle concentration of benzyldimethyltridecylazanium chloride in aqueous solution by acoustic and conductometric measurements

Density, speed of sound, and conductivity of benzyldimethyltridecylazanium chloride as a cationic surfactant in aqueous solutions have been measured as a function of concentration at atmospheric pressure and at five temperatures (293.15, 298.15, 303.15, 308.15, and 313.15) K. Isentropic compressibility values have also been calculated from the experimental density and speed of sound results. The critical micelle concentration (cmc) values of investigated cationic surfactant were evaluated by using conductivity measurements. The speed of sound, isentropic compressibility and also the conductivity values of the solutions have been employed to determine the second critical micelle concentrations (2nd cmc). The temperature dependence of the speed of sound and isentropic compressibility is shown to be sensitive to the aggregation process. The 2nd cmc values of the surfactant obtained at different temperatures by conductivity, speeds of sound and isentropic compressibility data are in agreement with each other.     

Quasielastic neutron scattering study of dynamics of CaCl2 aqueous solution confined in Vycor glass

Quasielastic neutron scattering was used to probe the diffusion of water molecules in 2.3 molal CaCl(2) solution confined in 100% hydrated Vycor glass in the temperature range of 220 to 260 K. We observed a gradual transition from the restricted diffusion regime at lower temperatures to unrestricted diffusion regime at higher temperatures. The diffusion parameters were compared with the data on pure water confined in Vycor available in the literature. We found that the effect of dissolved ions onto the diffusion dynamics of the water molecules in the solution was amplified by confinement by at least an order of magnitude compared to bulk form, even though the dissolved ions were found to have little effect on the spatial characteristics of the restricted diffusion process of water molecules. At 260 K, the local diffusion coefficient of water molecules in the H(2)O-CaCl(2) confined in Vycor was only 6% of the value reported for pure water confined in Vycor.     

Dependence of size and morphology on shear flow for PS-based amphiphilic block copolymer micelles in aqueous solution

This contribution focuses on the impact of shear flow on size and nanostructure of PS-based amphiphilic block copolymer (BC) micelles by varying the stirring rate and copolymer composition.The results show that the vesicles formed from diblock copolymer (di-BC) of PS-b-PAA remain with vesicular morphology,although the average size decreases,with the increase of stirring rate.However,the multi-compartment micelles (MCMs) formed from tri-block copolymer (tri-BC) of PS-b-P2VP-b-PEO are quite intricate,in which the copolymer first self-assembles into spheres,then to clusters,to large compound micelles (LCMs),and finally back to spheres,as stirring rate increases from 100 r/min to 2200 r/min.Formation mechanism studies manifest that vesicles form simultaneously as water is added to the di-BC solution,termed as direct-assembly,and remain with vesicular structure in the flowing process.While for the PS-b-P2VP-b-PEO copolymer,spherical micelles at initial stage can further assemble into clusters and LCMs,termed as second-assembly,due to the speeding-up-aggregation of the favorable stirring.As a result,an invert V-relationship between tri-BC micelle dimension and stirring rate is observed in contrast to the non-linear decreasing curve of di-BC vesicles.It is by investigating these various amphiphilic BCs that the understanding of shear dependence of size and morphology of micelles is improved from self-assembly to second-assembly process.     

Liquid crystal-forming aqueous hydroxypropyl cellulose solutions: Effects of surfactants on the turbidity and shear viscosity

The effects of type and concentration of surfactant on the turbidity and viscometric behavior for dilute and concentrated aqueous hydroxypropyl cellulose (HPC) solutions were examined. Two anionic surfactants, sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS), caused the cloud point of the dilute system to increase, but a nonionic and two cationic surfactants did not do so markedly. The transmittance for the dilute system increased with surfactant. The transmittance and viscometric behavior for the concentrated system were strongly dependent on the phase of the system: In the single-phase (isotropic and anisotropic), the transmittance and viscosity increased with SDBS, but, in the biphasic region, the behaviors were not as simple. An attempt was made to explain the transmittance and viscometric behavior in the single-phase on the basis of the change in apparent molecular weight and in order of HPC molecules. The phase transformation appeared to become less sensitive to temperature with SDBS. © 1993 John Wiley & Sons, Inc.     

One-step controlled synthesis of anisotropic gold nanostructures with aniline as the reductant in aqueous solution

We report a general and versatile method for controlled synthesis of anisotropic gold nanostructures through the reduction of HAuCl4 by aniline in aqueous solution, without the need for an additional stabilizer or capping agent. In this approach, the reduction kinetics of AuCl-4 can be altered by simply adjusting the initial pH and temperature, inducing the formation of a wide variety of anisotropic nanostructures such as dispersed or multilayered plates, wires with networked or paramecium-like structures, and ginger-shaped particles. AFM, TEM, XRD, EDX, FTIR, and UV-vis-NIR measurements were used to characterize the resulting gold nanostructures. Investigation reveals that in situ formed polyaniline serves effectively as a capping agent to direct the shape of gold nanostructures during the slow growth process. These as-synthesized gold nanostructures exhibit strongly shape-dependent optical properties. This facile approach may be extended to the synthesis of some other anisotropic metal nanostructures such as platinum or palladium.     

Determination of nanocellulose fibril length by shear viscosity measurement

The lengths of ten types of cellulose nanofibrils were evaluated by shear viscosity measurement of their dilute dispersions. Aqueous dispersions of surface-carboxylated cellulose nanofibrils with a uniform width of ~3 nm were prepared from wood cellulose by 2,2,6,6-tetramethylpiperidine-1-oxyl-mediated oxidation and successive mechanical treatment. Cellulose nanofibril samples with different average lengths were prepared by controlling the conditions of the oxidation or mechanical treatment. The viscosity-average lengths, L _visc, of the nanofibrils were calculated by applying the shear viscosities of the dilute dispersions to an equation for the dilute region flow behavior of rod-like polymer molecules. The obtained L _visc values ranged from 1,100 to 2,500 nm and showed a linear relationship to the length-weighted average length, L _w, measured by microscopic observation; the relation was described as L _visc = 1.764 × L _w + 764. The influences of the electric double-layer of the nanofibrils and surface-carboxylate content on the value of L _visc were also investigated.     

Density,viscosity, and excess properties of aqueous solution of diethylenetriamine (DETA)

Densities and viscosities of aqueous DETA solutions were measured for the entire concentration range and for the temperature range between (293.15 and 363.15) K. The excess molar volume was determined from the experimental density data whereas the excess Gibbs free energy and the excess entropy of flow were determined from the experimental viscosity data by implementing the theory of rate processes of Eyring. A Redlich–Kister equation was applied to correlate the excess properties such as: the excess molar volume and the excess Gibbs free energy of flow as functions of the DETA mole fraction and temperature. The results showed that the model agree very well with the experimental data. In comparison with AEEA and DEA, the excess properties of DETA are higher than these amines.