Volume Fraction Of Silicone Oil Research Articles

Effect of hydrophobic modification of hydroxypropyl methylcellulose on silicone oil emulsions

ABSTRACTTo study the effect of hydrophobic modification of the emulsifier on the relationship between emulsion stability and polymer emulsifier concentration, silicone oil emulsions were prepared using hydroxypropyl methylcellulose (original HPMC) and HPMC stearoxy ether (hydrophobic HPMC) at concentrations around their overlap concentrations. Both HPMC types completely emulsified the silicone oil. However, the volume fraction of silicone oil in the emulsion prepared using hydrophobic HPMC was less than that that by the original HPMC, and the average oil droplet size in the former emulsion was less than that in the latter emulsion. Increasing HPMC concentration led to increase in both the amount of adsorbed polymer emulsifier and the storage moduli in the linear region, irrespective of which HPMC was used. Stress-strain sweep curves obtained by a rheo-optical method showed that emulsions stabilized by the hydrophobic HPMC flowed slowly, even beyond the yield stress, whereas emulsions prepared using the original HPMC flowed quickly beyond the yield stress. The storage moduli of the emulsions prepared by the hydrophobic HPMC were larger than those prepared using the original HPMC.

Styrene vapor mass transfer in a biotrickling filter: Effects of silicone oil volume fraction, gas-to-liquid flow ratio, and operating temperature

The addition of silicone oil as a non-aqueous phase (NAP) to the trickling liquid enhances the mass transfer of hydrophobic compounds from gas to liquid phase in biotrickling filters (BTFs). The present study investigated the effect of NAP volume fraction (ϕ; 0–20%), gas-to-liquid flow ratio (7.5, 16 and 32), and operating temperature (30 and 50°C) on styrene mass transfer in a BTF under abiotic conditions using a full-factorial experimental design. The BTF was packed with a mixture of pumice and steel pall rings. The inlet styrene concentration was 0.5–1.2gm−3 and EBRTs were set at 1 and 2min. The results were incorporated into a model to calculate the maximum fraction of styrene transferable from the gas to the aqueous phase (βS∗). The βS∗ was determined to be 0.208–1, depending on the operating conditions. Flow ratio and ϕ were the most significant factors affecting styrene mass transfer (p-value=0.0348 and p-value=0.0230, respectively). Temperature had no significant effect on the model (p-value=0.9322) at a 95% confidence interval. Styrene mass transfer was very sensitive to ϕ when ϕ<10%; at ϕ>10% the addition of silicone oil had a slight effect on βS∗.

ELECTRICAL PROPERTIES OF SILICONE OIL-WATER INTERFACE IN THE PRESENCE OF IONIC SURFACTANTS AND SALT: IMPORTANCE IN THE STABILITY OF OIL-IN-WATER EMULSIONS

Silicone oil emulsions are used in a variety of industries. Electrical properties of the oil-water interface play a very important role in the stability of these emulsions. This work reports studies on the stability of silicone oil-water emulsions in the presence of ionic surfactants and salt. It was found that the addition of salt has a profound effect on the electrical properties of the interface. The kinetics of the growth of oil droplets in the emulsion was studied in emulsions containing a low volume fraction of silicone oil. The growth of droplets followed second-order kinetics commensurate with binary coalescence of droplets. It was found that the surfactant concentration and the presence of salt had a significant effect on the size of the droplets as well as their rate of growth. The stability of emulsions was correlated with the electrical properties of the oil-water interface and adsorption of surfactant molecules at the interface.

Mass transfer coefficients of styrene into water/silicone oil mixtures: New interpretation using the “equivalent absorption capacity” concept

The physical absorption of styrene into water/silicone oil systems at a constant flow rate for mixtures of different compositions (silicone oil volume fraction ϕ=0%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, and 10%) was investigated in laboratory-scale bubble reactors using a dynamic absorption method. Experimental results previously analyzed assuming no contact between gas and silicone oil [10] were reconsidered by applying the “equivalent absorption capacity” concept characterized by the value of the styrene partition coefficient between air and the mixture (Hmix). The results indicate that silicone oil addition slightly hinders the styrene mass transfer rate compared to the air/water system. Moreover, a dramatic decrease in KLa values due to silicone oil addition is observed. In comparison with similar measurements available in the literature, it is noted that this decrease in KLa value could be related to the change in the partition coefficient ratio mR=Hwater/Hoil. Two explanations concerning the relationship between the change in a hydrodynamic parameter (KLa) and that in a thermodynamic parameter (mR) are proposed. Finally, it appears questionable to study the change in KLa in terms of silicone oil addition.

Styrene absorption in water/silicone oil mixtures

The absorption of styrene in water/silicone oil systems at a constant flow rate for emulsion compositions ranging from 0% to 20% was investigated using a dynamic absorption method. It was found that the mass transfer for air/water/silicone oil systems is roughly double than those determined for air/water systems whatever the silicone oil percentage (ϕ). This result, mainly due to the high value of the partition coefficient ratio (mR=Hwater/Hoil=257), was in agreement with the enhancement factor models proposed in the literature. Considering the volumetric mass transfer coefficient, it was shown that change in KLa versus ϕ depended on the mass transfer model used for its determination. By using the “equivalent absorption capacity” concept developed by Dumont et al. [18] (CEJ 162 (2010) 927–934; doi:10.1016/j.cej.2010.06.045), a dramatic decrease in the KLa with increasing silicone oil volume fraction was observed in relation to the decrease in the value of the partition coefficient Hmix. Conversely, considering a styrene mass transfer pathway in series (gas→water→oil), the KLa values for gas/water/silicone oil systems were roughly double the KLa for gas/water systems and did not depend on the mixture composition. The styrene mass transfer performances were also analyzed using the modeling framework proposed by Hernandez et al. [17] (CEJ 172 (2011) 961–969; doi:10.1016/j.cej.2011.07.008). This model confirmed the ability of a water/silicone oil mixture to increase the styrene mass transfer by a factor of 2 and verified that the change in Hmix versus ϕ followed the trend predicted by the theory (although the Hmix values determined from this model were significantly lower than the theoretical values).

Normal-mode spectrum of finite-sized granular systems: The effects of fluid viscosity at the grain contacts

We investigate the effects of adsorbed films on the attenuative properties of loose granular media occupying a finite-sized rigid container that is open at the top. We measure the effective mass, M[over ̃](ω), of loose tungsten particles prepared under two different sets of conditions: (i) We lightly coat tungsten grains with a fixed volume fraction of silicone oil (polydimethylsiloxane, PDMS), where the liquid viscosity is varied for individual realizations, and (ii) in the other set of experiments we vary the humidity. On a theoretical level, we are able to decompose the effective mass into a sum over the contributions from each of the normal modes of the granular medium. Our results indicate that increasing either the PDMS viscosity or the humidity, as the case may be, markedly increases the damping rate of each normal mode relevant to our measurements. However, there is appreciable damping even in the absence of any macroscopic film. With a notable exception in the case of the highest humidity in the humidity-controlled experiments, all the relevant modes are weakly damped in the sense of a microscopic theory based on damped contact forces between rigid particles.

Hydrophobic VOC absorption in two-phase partitioning bioreactors; influence of silicone oil volume fraction on absorber diameter

A methodology to determine the diameter of an absorber contacting a gas phase and two immiscible liquid phases (water/silicone oil mixture) is presented. The methodology is applied to a countercurrent gas/liquid randomly packed column for the absorption of three VOCs (toluene, dimethyl sulfide, or dimethyl disulfide). Whatever the silicone oil volume fraction, Eckert's generalized pressure drop correlation was used. The results present the change in the column diameter through the change in the dimensionless ratio D(ϕ)/D(ϕ=1) versus the silicone oil volume fraction for the same operating conditions. For toluene and dimethyl disulfide, characterized by Hvoc,silicone oil values equal to 2.3 and 3.4Pam3mol−1, respectively, it is highlighted that it is unwise to use water/silicone oil mixtures for mass transfer. In these cases, the contact between the polluted air and pure silicone oil requires roughly the same amount of silicone oil as for a (90/10v/v) water/silicone oil mixture, but enables a 2-fold decrease in the column diameter. For dimethyl sulfide, which is characterized by a larger partition coefficient value (Hvoc,silicone oil=17.7Pam3mol−1), the mass transfer operation should not be considered because large amounts of silicone oil are required (whatever the silicone oil volume fraction), which is not acceptable from an economic point of view.The feasibility of using a bioscrubber for the treatment of hydrophobic pollutants depends mainly on the partition coefficient Hvoc,silicone oil. VOC absorption in TPPB should therefore be restricted to pollutants characterized by a Hvoc,silicone oil value of around 3 to 4Pam3mol−1 or less. In this case, absorption can be efficiently carried out in a biphasic air/silicone oil system.

VOC absorption in a countercurrent packed-bed column using water/silicone oil mixtures: Influence of silicone oil volume fraction

A calculation procedure to determine the influence of the silicone volume fraction on the physical absorption of VOCs in water/silicone oil mixtures is presented ( η silicone oil = 5 mPa s). It is based on the “equivalent absorption capacity” concept previously developed by Dumont et al. (2010) [1] and applied to a countercurrent gas–liquid absorber. The calculation procedure is first applied to three VOCs: dimethylsulphide (DMS), dimethyldisulphide (DMDS) and toluene, and then generalised to other VOCs. The influence of VOC partition coefficients ( H voc,water and H voc,solvent) and the ratio m R = H voc,water/ H voc,solvent is shown. For VOCs having a much higher affinity for silicone oil than for water ( m R > 20 as for DMDS and toluene), it is preferable to use pure silicone oil rather than water/silicone oil mixtures for absorption.

Adaptation of a Mycobacterium strain to phenanthrene degradation in a biphasic culture system: influence on interfacial area and droplet size

A phenanthrene-degrading Mycobacterium sp. strain 6PY1 was grown in an aqueous/organic biphasic culture system with phenanthrene as sole carbon source. Its capacity of degradation was studied during sequential inoculum enrichments, reaching complete phenanthrene degradation at a maximim rate of 7 mg l(-1) h(-1). Water-oil emulsions and biofilm formation were observed in biphasic cultures after four successive enrichments. The factors influencing interfacial area in the emulsions were: the initial phenanthrene concentration, the initial inoculum size, and the silicone oil volume fraction. The results showed that the interfacial area was mainly dependent on the silicone oil/mineral salts medium ratio and the inoculum size.

Rheological properties of silicone oil emulsions stabilized by poly( N-isopropyl acryl amide)s

Oil in water emulsions were prepared by dispersion of silicone oil into aqueous solutions of poly( N-isopropyl acryl amide) (PNIPAM) as a function of concentration for three different molecular weights of PNIPAM. The resulting emulsions were characterized by the measurements of visual observation, microscopic observation, adsorbed amounts of PNIPAM, and rheological properties, such as stress–strain sweep curves, shear viscosities, and dynamic moduli. Added silicone oil was almost emulsified by PNIPAM above an overlapping polymer concentration C *, leading to a volume fraction of silicone oil in the emulsion higher than 0.74, irrespective of the molecular weight, and the emulsions showed no coalescence and they were stable. The emulsions prepared at twice C * showed solid-like viscoelastic responses and stronger shear-thinning flow, and moreover the emulsion prepared by the highest molecular weight of PNIPAM only indicated a clear yield stress. On the other hand, below C * all added oil was not emulsified by PNIPAM and the volume fraction of the emulsified oil was decreased with a decrease in the concentration of PNIPAM. The emulsions prepared at C = 0.5 g/100 mL, which is lower than C * for two lower molecular weight PNIPAM samples indicated viscoelastic responses and weak shear-thinning flow.

Characteristics of Electrorheological Responses in an Emulsion System

The characteristics of electrorheological (ER) responses in an emulsion system have been examined for the first time. The emulsion system consists of a chlorinated paraffin oil and a silicone oil; these two liquids have similar dielectric constants, but the former liquid is 1000 times more conductive than the latter liquid. The mismatch in electric properties between the dispersed phase and the dispersing medium can be reversed in an emulsion by inverting the phase distribution. Transient ER responses in the emulsion system have been studied over a range of shear rates following step changes (on/off) of an external dc electric field. The relative response strength characterizing the ER effect increases with the field strength and with the volume fraction of silicone oil, but decreases with increasing shear rate imposed. The paraffin oil-in-silicone oil emulsion exhibits a response much stronger than that observed in the phase-reversed silicone oil-in-paraffin oil emulsion. No negative ER response is detected in the silicone oil-in-paraffin oil emulsion. With an optical microscope, very different microscopic response characteristics are observed for the phase-reversed emulsions under static conditions, and this can be explained according to the leaky dielectric liquid model of Taylor.