Characteristic features of the boiling of emulsions having a low-boiling dispersed phase

The results of investigation of heat transfer from thin wires to a boiling emulsion, the dispersed phase of which is formed from a liquid with a boiling temperature much lower than the boiling temperature of the dispersion medium, are presented. Two variants of boiling of such an emulsion are possible: boiling of the dispersed phase alone and simultaneous boiling of the dispersed phase and dispersion medium. In the present work, only the first variant has been studied; it is distinguished by the following most important features: high superheat of the dispersed-phase droplets ΔT_sup of the emulsion and a wide temperature range of bubble boiling (50–200°C). For conventional heat carriers (pure liquids and solutions), the value of ΔT_sup does not exceed 1–10°C, with the bubble-boiling interval lying within the range from 5 to 20°C. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 81–84, November–December, 2006.     

凸棒颗粒稳定的橄榄油／水型Pickering乳状液的制备条件及形成机理研究

选取凹凸棒作为乳化剂,系统研究pH、颗粒浓度、油相体积分数以及不同价态盐对橄榄油／水型Pickering乳状液稳定性的影响,结果表明,体系pH在4～9范围内可制备出稳定的乳状液;颗粒浓度的提高可增强乳液的分层和聚结稳定性;乳液液滴直径随油相体积分数的增加先增大后减小;无机盐的引入不会对乳液相及水相的体积产生影响,但对乳液液滴的尺寸分布影响显著,其中NaCl浓度的增加有利于乳状液液滴数均直径的增加,而CaCl2浓度增加时,乳状液液滴数均直径呈现先增大后减小的变化趋势。研究表明,凹凸棒可作为一种新型纳米乳化剂应用于绿色乳状液的制备。     

Results of experimental investigation of heat transfer with emulsions with low-boiling disperse phase

The results are given of a theoretical investigation of heat transfer from thin wires to emulsions in which the disperse phase is low-boiling compared to the dispersion medium. A special feature of heat transfer to such emulsions is observed in the mode of nucleate boiling, when only the droplets of the disperse phase of emulsion are boiling. The transition from the convective mode of heat transfer to nucleate boiling requires high values of temperature gradient ΔT = T _W ? T ₀ at which the temperature of the heat-transfer surface T _W is higher than the temperature T _S of saturated vapors of the disperse phase by 100 °C and more. Here, T ₀ is the temperature of the heat-transfer agent away from the heat-transfer surface. Note that, for pure liquids and solutions, the value of delay of the beginning of boiling ΔT _i = T _W ? T _S as a rule does not exceed 1–5 °C. Another feature of heat transfer to the emulsions being treated is a wide temperature range of the mode of nucleate boiling (over 100 °C); the upper limit of this temperature range is defined by the temperature of transition to film boiling of the dispersion medium of the emulsion being investigated that has already boiled by this instant of time. The value of delay of the beginning of boiling is affected significantly by additions of surfactants and adsorbents.     

Nanoemulsions containing octyl methoxycinnamate and solid particles of TiO2: preparation,characterization and in vitro evaluation of the solar protection factor

The objective of this work was to develop and evaluate the physical–chemical properties of oil-in-water nanoemulsions for application as nanocosmetics for sun protection. Oil-in-water dispersions were processed by ultrasound (US) to obtain small emulsion droplets. These emulsions were obtained in the presence of commercial nonionic surfactants based on polyoxides and avocado oil as the oil phase. The US generated small but unstable droplets. This problem was solved by using a different surfactant, with a longer ethylene oxide chain, able to promote stabilization by steric mechanisms. The light scattering technique was used to characterize the nanoemulsions by their dispersed droplets’ size, size distribution and variation of distribution with time (stability). Chemical and physical sunscreens – octyl methoxycinnamate (OMC) and titanium dioxide (TiO₂), respectively – were added to the stable system. The anti-UVB activity of the nanoemulsions and their components were evaluated by the method of Mansur et al. (1986) and spectral transmittance. The solar protection factor (SPF) was proportional to the OMC and TiO₂ concentrations. The in vitro OMC release was evaluated, and the presence of TiO₂ in the nanoemulsion did not affect the release profile, which showed the diffusion-dependent kinetics of the active ingredient in the formulation.     

Laser induced rotation of trapped chiral and achiral nematic droplets

We study the response of optically trapped achiral and chiralized nematic liquid crystal droplets to linear as well as circular polarized light. We find that there is internal dissipation in rotating achiral nematic droplets trapped in glycerine. We also demonstrate that some chiralized droplets rotate under linearly polarized light. The best fit to our data on chiralized droplets indicates that rotational frequency of these droplets with radius R is approximately proportional to 1/R ², rather than to 1/R ³.     

Effect of Dextrose in the Internal Aqueous Phase on Formation and Stabiblity of W/O/W Multiple Emulsions

Abstract

The osmolarity of the internal aqueous phase of W/O/W multiple emulsions was varied by using different concentrations of dextrose in the internal phase. Evaluation of the stability of the emulsions was done by microscopic, viscometric and conductometric methods. Microscopic study indicated that as the dextrose concentration in the internal phase increased (0 – 2.50% W/V), the stability, in terms of coalescence of the internal droplets and rupture of the interfacial oily layer, increased from 12 hrs to 7-8 weeks. Viscometric evaluation showed the emulsions to exhibit Non-Newtonian flow and the apparent viscosities of freshly prepared emulsions increased from 8000 to 56,000 cps as the dextrose concentration was increased; the viscosity decreased as the emulsion aged. The amount of drug released as determined by the conductometric method, correlated with the viscosity and stability of the emulsions. The reduction of globule size of the primary (W/O) phase by use of a colloid mill increased the apparent viscosity significantly and thus improved the stability of the formulations.     

Chitosan Microspheres Prepared by Emulsification and Ionotropic Gelation

Abstract

An attempt was made to prepare chitosan microspheres by an emulsion-phase separation technique but without the usual use of glutaraldehyde as a cross-linking agent. Instead, ionotropic gelation was employed in a w/o emulsion. The effect of formulation factors was examined. The results showed that microspheres so formed were spherical, free-flowing, and had smooth surfaces. The rate of addition of counterions was important. Gelation of chitosan droplets should take place before the destabilizing effect of the counterions occurred. This effect is associated with the increase in aqueous phase volume when the counterion solution is incorporated.     

Undercooling and crystallization behaviour of antimony droplets

The level of liquid undercooling below the equilibrium melting point experienced typically in a bulk material is limited by the presence of potent heterogeneous nucleation sites. By subdividing the material into a collection of fine (10 to 150m) droplets the most potent nucleants are isolated into a small fraction of the droplet population, allowing the remainder to reach deep levels of undercooling prior to the onset of solidification. Droplet surface coating characteristics influence both the level and uniformity of the undercooling and, in addition, may alter the nucleation kinetics thereby encouraging the formation of a metastable crystalline phase from the undercooled liquid. An effective means of both creating a stable dispersion of fine droplets and influencing the surface coating is through the droplet emulsion technique. This approach has allowed the level of undercooling for pure antimony to be extended from 0.08 to 0.237T _m through proper control of droplet size, surface coating and applied cooling rate. The formation of a metastable simple cubic phase from the melt has been confirmed using both differential thermal analysis and X-ray diffraction techniques. The simple cubic phase is retained in droplets to temperatures approaching the melting point at a heating rate of 20° C min^–1. Drop tube treatment of emulsified samples has also been successful at producing the metastable simple cubic structure by containerless processing.     

太阳能建筑用石蜡/CNTs相变乳液的制备及光-热性能研究

结合建筑结构在太阳能领域的蓄热控温特点,采用"两步法"制备出适用于太阳能蓄热的新型石蜡/CNTs相变乳液,通过纳米粒度电位仪和布鲁克旋转黏度仪分析了CNTs掺量对相变乳液技术性能的影响,确定最佳CNTs掺量;再采用差示扫描量热仪、导热系数测定仪、自制太阳光-热转换装置及紫外/可见/近红外分光光度计探究相变乳液的热物性能和光-热转换性能。结果表明,随着CNTs掺量的增大,相变液滴的粒径分布和运动黏度发生较为明显的变化,综合考虑相变乳液的稳定性及泵送性,推荐石蜡相变乳液中CNTs的最佳掺量控制为0.6%。由于石蜡具有较高的相变储热性能及CNTs具有较大的导热系数,掺加石蜡/CNTs能够显著增强相变乳液的导热性能和光-热转换能力,完全可用于建筑结构中以达到对太阳光辐射的蓄热与调温作用。     

Tunable photonic crystals from emulsion containing magnetic nanoparticles

We report a simple approach to synthesize emulsion of oleic acid (OA) containing Fe₃O₄-OA nanoparticles as magnetic building block of photonic crystals by combined chemical co-precipitation and emulsification technology. The emulsion droplets exhibit dominant size distribution of 80-110 nm and superparamagnetic behavior. A high loading fraction of magnetic compounds Fe₃O₄ in emulsion of 72% was achieved by the approach. Upon application of a magnetic field, the emulsion droplets in water facilely self-assemble into photonic crystals, and the stop bands could be tuned in ranging visible spectrum by moving position of magnet. The method to synthesize emulsion with high magnetic loading fraction should facilitate preparation of tunable photonic crystals and expand their application.     

Heat capacity and pressure at phase separation and solidification of3He in hcp4He

We have measured heat capacity and pressure of 0.45% and 0.9%³He-⁴He mixtures at pressures between 25 bar and 33 bar and temperatures between 20 mK and 250 mK. The data show the latent heats and the pressure changes associated with the phase separation (or remixing) and with the liquification (or solidification) of the resulting droplets in the hcp matrix. Above about 31 bar, the phase separation and the liquid-solid phase transition are separately observable. From these data, as well as from the heat capacity of the liquid droplets, we conclude that the droplets are filled with almost pure³He showing bulk behavior and that only a part of the separated³He is liquified. The amount of the liquid depends on the history of the sample. The phase separation is reproducible and lasted for many hours. In the pressure range of the hcp-L₁-L₂ univariant the sample moves along the univariant for a limited temperature range.     

Preparation and characterization of β-elemene-loaded microemulsion

Intravenously injectable emulsion of β-elemene was studied in detail. Both blank and β-elemene-loaded microemulsions were prepared using a simple water titration method. The pseudoternary phase diagram was constructed for the optimization of microemulsion. The loading capacity test, dilutability test, and especially the influence of antioxidants were conducted for further optimization of β-elemene-loaded microemulsion. Transmission electron microscope showed intact and spherical microemulsion droplets. Conductivity and viscosity measurements were used to study the phase behaviors of β-elemene-loaded microemulsions, providing convincing explanation. In vitro release study showed that β-elemene was steadily released until 12?h, which most fitted the first order.     

Influences of combustion improver content and motionless time on the stability of two-phase emulsions

The heavy molecular bonds of liquid fuels can be broken with the assistance of a nitromethane fuel additive by virtue of its explosive and flammable properties to obtain greater heat release. Because of the immiscibility between nitromethane and petro-diesel, two-phase emulsions of nitromethane dispersed in the oil phase of a mixture of diesel and biodiesel were prepared. The experimental results show that microwave irradiation produced an emulsion with a larger number of dispersed nitromethane droplets in the continuous oil mixture, a smaller mean droplet size, and lower turbidity than magnetic stirring, and thus was a better method for preparation of the two-phase emulsion. The increase in the nitromethane weight fraction increased the number of dispersed nitromethane droplets and the emulsion turbidity. In addition, allowing the emulsion preparation to remain motionless for a longer period of time after either method resulted in an obvious reduction in the emulsification stability (ES).     

石蜡乳状液潜热输送材料的研究进展

石蜡乳状液潜热输送材料是由相变石蜡与水乳化而成的悬浮液,具有较大的热客,能量储存密度及输送密度远高于相同温差下的水,因此可以使循环流量大幅降低,从而降低循环能耗,实现节能.根据相变石蜡材料及应用背景不同,分别综述了低温石蜡乳状液潜热输送材料、高温石蜡乳状液潜热输送材料的研究现状.指出了石蜡乳状液潜热输送材料在导热性能和稳定性等方面存在的共性问题,并探讨了解决措施:纳米颗粒强化传热是提高其导热性能的有效方法,研制纳米级相变石蜡微乳液是提高稳定性的有效途径.     

Designing Internal Hierarchical Porous Networks in Polymer Monoliths that Exhibit Rapid Removal and Photocatalytic Degradation of Aromatic Pollutants

This paper describes the preparation of 3D polymer monoliths containing internal hierarchical porosity. The porous networks are fabricated based on Pickering high‐internal‐phase emulsions (HIPEs) stabilized by microporous β‐cyclodextrin‐based polymer particles (CDPs) as the emulsifier; CDPs are facilely synthesized by the polyaddition reactions without the need for catalysts. The designed Pickering agents enable to form a bicontinuous internal phase in 8:2 cyclohexane–water v/v, and the oil droplets in the continuous water phase is found to be fairly stable up to 1 month. Furthermore, the addition of acrylamide and N,N'‐methylenebis(acrylamide) results in polymer networks after in situ thermal polymerization at 60 °C in the water phase, and the monoliths include both interconnected macropores from the HIPE template and micro‐ and mesopores from the CDPs embedded at the interface. The porous monoliths rapidly absorb a variety of solvents taking advantage of multiscale porosity and amphiphilicity. Furthermore, the materials can be efficiently used for the removal of aromatic pollutants and then reused after washing and drying without the deterioration of performance. Also, they exhibit high photocatalytic capability and good recyclability as being used as a catalytic support when embedded with titanium dioxide (TiO₂).     

Formulation and characterization of liquid crystal systems containing azelaic acid for topical delivery

Purpose: The aim of this study is to prepare and characterize azelaic acid (AzA) containing liquid crystal (LC) drug delivery systems for topical use.

Methods: Two ternary phase diagrams, containing liquid paraffin as the oil component and a mixture of two nonionic surfactants (Brij 721P and Brij 72), were constructed. Formulations chosen from the phase diagrams were characterized by polarized light microscopy, rheological analyses, differential scanning calorimetry (DSC), and small angle x-ray scattering spectroscopy.

Results: Polarized light microscopy proved that except the oil/water emulsion (O/W E), other formulations showed lamellar LC structure. In vitro release studies indicated that the fastest release was achieved by the Lamellar LC (LLC) and O/W E systems, whereas slower release was obtained from the emulsion containing lamellar LC (E-LLC) and distorted lamellar LC (D-LLC) systems. Results of rheological measurements both supported the results of in vitro release studies and showed that the emulsion containing the LC (E-LLC) system had the most stable structure. The formulations and their effect on stratum corneum (SC) were evaluated by DSC studies. The lamellar LC (LLC), emulsion containing lamellar liquid crystal (E-LLC), and O/W E formulations had an effect on both lipid and protein components of SC, whereas distorted lamellar liquid crystal (D-LLC) system had an effect on only the lipid components of SC.

Conclusions: LLC systems could be considered promising for the topical delivery of AzA.     

Insect tricks: two-phasic foot pad secretion prevents slipping

Many insects cling to vertical and inverted surfaces with pads that adhere by nanometre-thin films of liquid secretion. This fluid is an emulsion, consisting of watery droplets in an oily continuous phase. The detailed function of its two-phasic nature has remained unclear. Here we show that the pad emulsion provides a mechanism that prevents insects from slipping on smooth substrates. We discovered that it is possible to manipulate the adhesive secretion in vivo using smooth polyimide substrates that selectively absorb its watery component. While thick layers of polyimide spin-coated onto glass removed all visible hydrophilic droplets, thin coatings left the emulsion in its typical form. Force measurements of stick insect pads sliding on these substrates demonstrated that the reduction of the watery phase resulted in a significant decrease in friction forces. Artificial control pads made of polydimethylsiloxane showed no difference when tested on the same substrates, confirming that the effect is caused by the insects’ fluid-based adhesive system. Our findings suggest that insect adhesive pads use emulsions with non-Newtonian properties, which may have been optimized by natural selection. Emulsions as adhesive secretions combine the benefits of ‘wet’ adhesion and resistance against shear forces.     

Heat exchange with different schemes for introducing the heat-exchange agent into a furnace

The effect of the scheme for introducing the heat-exchange agent into a furnace for heat exchange in a selective nonisothermal gaseous medium is investigated taking into account the heat loss due to convection depending on the emissivity of the metal and the furnace lining.Notation T temperature - Er specific resulting radiative flux - q_c convective heat flux density - q_Me overall density of the resulting heat flux to the metal - emissivity - a_g0 absorbing capability of the gas relative to the radiation of the lining - a_g4 same for the metal - a _go /a+b+c absorbing ability of a layer of gas a+b+c... relative to the radiation of the lining - a_gj/ikmnp absorbing ability of the gas layer i+k + m + n + p with radiation from layer j - A emissivity of the walls - l _ef effective length of a ray path - coefficient of convective heat transfer - k heat-exchange coefficient from the internal surface of the lining with temperature T_o in the medium with temperature T_m - B fuel expenditure - Q_H ^P heat of combustion - v volume of the combustion fuel products per 1 m³ of gas - c_g specific heat capacity of the gas - h overall height of the channel - x instantaneous height coordinate in the channel The indices for the temperatures and heat fluxes are as follows: 0, lining; 4, metal; 1, 2, and 3, gas zones; m, media.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 4, pp. 692–698, October, 1980.     

The Tricritical Point

Analysis of critical phenomena in bodies with the tricritical point, based on the Gibbs equations for the critical state, is performed. The generalized Gibbs equations allow for the difference in the symmetry of the phases, which is characteristic of bodies with the tricritical point. Successive analysis enables one to clarify all characteristics of the critical state of the class of bodies being treated, whose singularity is that their phase diagram contains regions of phase transitions of both the first and second kind, and to establish the regularity of variation of the properties in the vicinity of the tricritical point. In particular, it is demonstrated that the specific heat C _V goes to infinity at the tricritical point following the logarithmic law (along the critical isochore), and the sound velocity vanishes. In the regions of phase transitions of the second kind, the specific heat C _p reaches an infinitely high value at the transition point T _s at p = const also following the logarithmic law. The line of phase equilibrium is a cubic parabola. In the critical state, the second variation of the internal energy ₂ E(S, V) is zero; and, in the vicinity of the line of phase transitions of the second kind, it varies as (T – T _c)². In the critical state, the heat conductivity goes to infinity, etc.     

NMR Study of Solid 3He Droplets In Phase-Separated 3He-4He Mixtures

We report measurements on solid ³ He droplets embedded in a solid ⁴ He matrix. A feature of our experiments is that the mixture crystals, of 1% ³ He concentration, are grown under constant pressure conditions to minimise the formation of defects. Upon cooling the mixture isotopic phase separation is clearly observed in both pressure and NMR data. At a pressure of 36 bar the ³ He separates as solid droplets. NMR measurements on these droplets indicate values of T ₁ and T ₂ similar to those in bulk solid ³ He at the same pressure in the temperature-independent régime. Measurements of the bounded diffusion in the droplets indicate a spin diffusion coefficient similar to that in bulk solid ³ He at the same pressure. These measurements also show the size of the droplets to be a few microns.