Scaling laws and internal structure for characterizing electrospun poly[(R)-3-hydroxybutyrate] fibers

Using chloroform/dimethylformamide (CF/DMF) co-solvent, electrospinning of poly[(R)-3-hydroxybutyrate] (PHB) solutions was carried out at ambient temperature. The effects of the applied voltage (V), flow-rate (Q), and solution viscoelastic properties on the Taylor cone, electrified jet, and fiber morphology were investigated. In addition, the electric field developed by the needle-plate electrode configuration was calculated using a finite element analysis to reveal the tip-to-collector (H) effect. Among the processing parameters (V, Q and H), it was found that Q played a key role in determining the jet diameter (d_j) and electrospun fiber diameter (d_f), and scaling laws existed between them, i.e., d_j-Q^0.61 and d_f-Q^0.33. The diameter reduction ratios of D_o/d_j (D_o is the needle diameter) and d_j/d_f were measured as 50-120 and 5-10, respectively; it suggested that major jet stretching took place in the straight electrified jet region, and further chain orientation could be gained by the subsequent process of jet whipping. By changing PHB concentrations from 5 to 15 wt%, the solution viscosity (η_o) was increased from 100 to 4900 cP, whereas the surface tension and solution conductivity remained unchanged; it provided a good model solution to exclusively reveal the η_o effect on the electrospinning process. Our results showed that the η_o-dependence of d_j and d_f also followed simple scaling laws: d_j-η_o^0.06, and d_f-η_o^0.39, with a prefactor depending on the processing variables, mainly the flow-rate. Regardless of the PHB concentrations used, the obtained PHB fibers showed a similar crystallinity fraction of ca. 0.63 and possession of major α-crystals together with a small amount of β-crystals with zigzag chain conformation.     

Correlation between processing parameters and microstructure of electrospun poly(D,l-lactic acid) nanofibers

Using dimethyl formamide as the solvent, electrospinning of poly(D,l-lactic acid) (PDLLA, d-lactide content:10%) solutions with various concentrations was performed by means of a heating jacket for controlling the solution temperature range from 25 to 104 °C. In addition, an IR emitter was used to control the surrounding temperature at ∼110 °C. The effects of solution properties and processing variables on the morphologies of the cone/jet/fiber were investigated, and the internal structure of the electrospun fibers was characterized using polarized FTIR, WAXD and DSC. A sufficient entanglement density existing in a given solution was an important requirement for successfully obtaining uniform fibers without beads. The log-log plot of specific viscosity (η_sp) versus PDLLA volume fraction (?_v) provided us with a useful guideline to determine the entanglement concentration (c_e) for preparing fiber-shaped electrospun products. The ?_v-dependence of η_sp varied from for a dilute solution to for a solution possessing entangled chains. From the incipient concentration of entanglements, the determined c_e was ∼10 wt%, which was in fair agreement with what was predicted theoretically by a simple relation of 2M_e/M_w, where M_e and M_w were the molecular weight between melt entanglements and the average molecular weight of PDLLA, respectively. To obtain uniform PDLLA fibers without beads, however, a minimum concentration of ∼1.9c_e was required for the entangled solutions possessing sufficient network strength to prohibit the capillary instability during jet whipping. The log-log plots of the jet diameter (d_j) and fiber diameter (d_f) versus zero shear viscosity (η_o) showed two scaling laws existing for the present solution, that is, and . For a given solution, an intimate relation between d_j and d_f was derived to be , regardless of the variations of processing variables applied. High-temperature electrospinning produced small diameter fibers because of the reduction of η_o, but the effect was gradually diminished for solution temperatures higher than 56 °C owing to the enhanced solvent evaporation.The as-spun nanofibers of this thermally slow-crystallizing PDLLA species were amorphous, and the Hermans orientation function calculated from the polarized FTIR results was ca. −0.063 regardless of the electrospinning conditions applied. This suggests that there was no preferential chain orientation developed in the nanofibers. In the heating in a DSC cell at a rate of 10 °C/min, however, rapid crystallization took place at 97 °C, followed by two well-separated melting endotherms centered at 121 and 148 °C, respectively. WAXD and FTIR results exhibited the exclusive presence of α-form crystals. These unique features were attributed to the occurrence of phase separation during electrospinning, which interrupted the chain orientation along the fiber during jet stretching, and yielded more trans-trans conformers with more extended chain structure to readily facilitate the cold crystallization during post-heating.     

Electrospinning and characterization of highly sulfonated polystyrene fibers

Nanofibers of highly sulfonated (IEC ∼4.5 meq/g) polystyrene (SPS) were successfully electrospun. To accomplish this, the process of electrospinning this difficult-to-spin material was studied in detail. Fiber quality was optimized by manipulating the process and solution variables to fabricate continuous bead-free fibers. Bead-free fibers (average diameter 260 nm) were electrospun from 25 wt% SPS (500 kDa) in DMF at an electrode separation of 10 cm, an applied voltage of 16.5 kV and a flow rate of 0.3 mL/h. With increasing solution concentration, and thereby the solution viscosity, the morphology changed from beads to bead-on-string fibers to continuous cylindrical fibers. Beaded fibers and continuous bead-free fibers of SPS (500 kDa) could be spun at ∼2 C_e and 3.5 C_e, respectively, where C_e is the entanglement concentration determined from solution-viscosity measurements. The onset of formation of beaded fibers coincided with a sharp transition in the scaling of the storage modulus-concentration relationship.     

Electrospinning of Technical Lignins for the Production of Fibrous Networks

Abstract

Electrospinning is an effective strategy to produce micron and sub-micron diameter fibrous networks from a variety of polymeric systems. Using seven different technical lignins the effect of lignin structure on fiber formation by electrospinning was studied. Surprisingly, none of the technical lignins could be electrospun into continuous fibers, although beaded fiber formation was observed for the softwood Kraft lignin system at high concentration (>50 wt%). However, the addition of poly(ethylene oxide) dramatically affected the electrospinning behavior and fiber formation. For all of the technical lignins a clear transition from electrospray or beaded fibers to uniform fibers was observed upon addition of poly(ethylene oxide); the lignin concentration dependent on poly(ethylene oxide) content. In all of the systems a linear increase in fiber diameter with increasing lignin concentration was observed. At the same concentration, the various lignin solutions had varying viscosities and different electrospinning behavior, that is, fiber diameter and ability to form uniform fibers, suggesting lignin specific structures and intermolecular interactions are influencing solution properties and electrospinning behavior. In fact, specific viscosity versus concentration plots reveal scaling exponents’, η ～ c^7.4–7.8 consistent with a branched polymer participating in intermolecular interactions such as hydrogen bonding or association complexes.     

Investigation on process parameters of electrospinning system through orthogonal experimental design

Electrospinning is a very simple and versatile method of creating polymer‐based high‐functional and high‐performance nanofibers. But most of the investigations are not systematic and describe the electrospinning process without quantitative accuracy. Inconsistent and even opposite results have been reported, which has hindered the consistent interpretation of the experiments. Orthogonal experimental method was used to investigate qualitative and quantitative correlations between fiber characteristics (diameters and morphologies) and the processing and materials parameters. Uniform fibers can be obtained without any beads by proper selection of the processing parameters, and a lower glass transition temperature was observed for electrospun fibers than that of native polymer. Results of statistical analysis showed that significant influences were observed for polymer molecular weight and solution concentration on fiber diameters, and there were significant effects of polymer molecular weight, solution concentration, and solvent system on fiber morphologies. Meanwhile, solution concentration and polymer molecular weight, and polymer molecular weight and solvent system had obvious interaction effects. Regression analysis revealed quantitative relations of fiber diameters and beads percent, that is, Y₁ = 72.8X₁ ? 8.1X₂ + 138.8, Y₂ = ?3.2X₁ + 0.4X₂ + 60.5, where Y₁ is fiber diameter (nm), Y₂ beads percent (%), X₁ solution concentration (%, w/w), and X₂ polymer molecular weight (kDa). Validation test showed that the experimental values of fiber size and beads percent were in good agreement with the calculated ones. Based on these results, optimal conditions could be obtained for predetermined diameters and morphologies for electrospun fibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3105–3112, 2007     

Regeneration of Bombyx mori silk by electrospinning. Part 2. Process optimization and empirical modeling using response surface methodology

The response surface methodology was used to model and optimize the electrospinning parameters for the spinning of regenerated nanoscale silk fibers from domestic silkworm, Bombyx mori. Electric field and silk concentrations were chosen as variables to control fiber diameter at different spinning distances. Fiber diameter was correlated to these variables by using a second order polynomial function. The predicted fiber diameters were in agreement with the experimental results. Response surfaces were constructed to identify the processing window suitable for producing nanoscale fibers.     

Orientation analysis of individual electrospun PE nanofibers by transmission electron microscopy

A systematic orientation analysis of individual electrospun polyethylene (PE) nanofibers was performed by transmission electron microscopy (TEM). PE nanofibers with a wide diameter distribution, ranging from 150 nm to several micrometers, and a variety of morphologies, including cylindrical, beaded- and ribbon-like fibers, were produced by the high-temperature solution electrospinning. In each fiber, crystalline orientation and its morphology were investigated by TEM. In the cylindrical fibers, development of fiber structure was strongly related to the fiber diameter. Depending on the diameter, three different structural models based on 1) the random-oriented crystalline structure, 2) the shish-kebab structure, and 3) the fibrillar structure composed of extended-chain crystals were proposed. In addition, orientation analysis of beaded fibers and that of ribbon-like fibers was also performed.     

Air filtration performance of nanofiber membranes with different morphologies produced by green electrospinning

To further target product development with low environmental impact, an integral green electrospinning (G-ES) approach has been adopted through the simultaneous application of various strategies, such as the use of biopolymers, reduction of energy use to avoid melting temperatures, and selection of non-toxic solvents and surfactants. Green solubility spinnability maps for cellulose acetate (CA), poly ε-caprolactone (PCL), and polyvinyl alcohol (PVA) are presented. Green electrospinning (G-ES) allows the production of new morphologies for CA and PCL nanofiber membranes. In this work, CA exhibits a ribbon-like morphology, PCL shows a honeycomb-like morphology and PVA cylindrical fibers. Membrane morphologies are compared with filtration efficiency (FE) for particle size of 1.0 μm and quality factor (Q_F) at a volumetric flux of 27.63 cm⁻¹. For CA is between 83% and 96% and high Q_F = 0.31–0.38 Pa⁻¹, PCL is 92% and 99% and high Q_F = 0.28–0.21 Pa⁻¹ and for PVA between 96% and 99% and high Q_F = 0.14–0.08 Pa⁻¹. These results suggest that the hierarchical nanofiber structure improves filtration performance because of the reduction in pressure drop and increase in PM interception. CA ribbon-like fibers favored air filtration performance, followed by PCL honeycomb-like fibers.     

Properties of aligned poly(L‐lactic acid) electrospun fibers

Poly(L‐lactic acid) (PLLA)‐aligned fibers with diameters in the nano‐ to micrometer size scale are successfully prepared using the electrospinning technique from two types of solutions, different material parameters and working conditions. The fiber quality is evaluated using scanning electron microscopy (SEM) to judge fiber diameter, diameter uniformity, orientation, and appearance of defects or beads. The smoothest fibers, most uniform in diameter and defect free, were found to be produced from 10% w/v chloroform/dimethylformamide solution using an accelerating voltage from 10–20 kV. Addition of 1.0% multiwalled carbon nanotubes (MWCNT) into the electrospinning solution decreases fiber diameter, improves diameter uniformity, and slightly increases molecular chain alignment. The fibers were cold crystallized at 120°C and compared with their as‐spun counterparts. The influences of the crystalline phase and/or MWCNT addition were examined using fiber shrinkage, temperature‐modulated calorimetry, X‐ray diffraction, and dynamic mechanical analysis. Crystallization increases the glass transition temperature, T_g, slightly, but decreases the overall fiber alignment through shrinkage‐induced buckling of the fibers when heated above T_g. MWCNT addition has little impact on T_g, but significantly increases the orientation of crystallites. MWCNT addition slightly reduces the dynamic modulus, whereas crystallization increases the modulus in both neat‐ and MWCNT‐containing fibers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41779.     

Electrospinning of linear homopolymers of poly(methyl methacrylate): exploring relationships between fiber formation, viscosity, molecular weight and concentration in a good solvent

A series of seven linear homopolymers of poly(methylmethacrylate) ranging from 12,470 to 365,700 g/mol M_w, were utilized to further explore scaling relationships between viscosity and concentration in a good solvent at 25 °C and to investigate the impact of these relationships on fiber formation during electrospinning. For each of the polymers investigated, chain dimensions (hydrodynamic radius and radius of gyration) were measured by dynamic light scattering to determine the critical chain overlap concentration, c^*. The experimentally determined c^*, was found to be in good agreement with the theoretically determined value that was calculated by the criteria c^*∼1/[η], where the intrinsic viscosity was estimated from the Mark-Houwink parameters, K and a (at 25 °C in dimethyl formamide) obtained from the literature. The plot of the zero shear viscosity vs. c/c^* distinctly separated into different solution regimes, viz. dilute (c/c^*<1), semidilute unentangled (1<c/c^*<3) and semidilute entangled (c/c^*>3). The crossover between semidilute unentangled and semidilute entangled regimes in the present investigation occurred at c/c^*∼3, which, therefore, marked the onset of the critical chain entanglement concentration, c_e, according to the procedure utilized by Colby and co-workers [Colby RH, Rubinstein M, Daoud M. J de Phys II 1994;4(8):1299-310. [52]]. Electrospinning of all solutions was carried out at identical conditions to ascertain the effects of solution concentration, molecular weight, molecular weight distribution and viscosity on fiber formation and morphological features of the electrospun material. Only polymer droplets were observed to form from electrospinning of solutions in the dilute concentration regime due to insufficient chain overlap. As the concentration was increased, droplets and beaded fibers were observed in the semidilute unentangled regime; and beaded as well as uniform fibers were observed in the semidilute entangled regime. Uniform fiber formation was observed at c/c^*∼6 for all the narrow MWD polymers (M_w of 12,470-205,800 g/mol) but for the relatively broad MWD polymers (M_w of 34,070 and 95,800 g/mol), uniform fibers were not formed until higher concentrations, c/c^*∼10, were utilized. Dependence of fiber diameter on concentration and viscosity was also determined, viz. fiber dia∼(c/c^*)^3.1 and respectively. These scaling relationships were in general agreement with that observed by Mckee et al. [McKee MG, Wilkes GL, Colby RH, Long TE. Macromolecules 2004;37(5):1760-67. [33]].     

Performance of nanofiber/microfiber hybrid air filter prepared by wet paper processing

High-performance air filters composed of a hybrid structure of nanofiber/microfiber were fabricated using wet paper processing. Two types of nanofibers (NF) with average diameters of 180 and 234?nm were mixed with a suspension of microfibers (11.5 and 11.7?µm) in various mixing fractions. Then, the suspension was filtered to fabricate hybridized fiber sheets with a known nanofiber/microfiber composition. The effects of NF diameter and mixing fraction on the performance of the hybrid filters were experimentally investigated. With increasing NF fraction, both the particle collection efficiency and the pressure drop increased. The quality factor (Q_f) was used to evaluate the performance of the prepared filters. As predicted by the single fiber filtration theory, the experimentally obtained Q_f was almost independent of the mixing fraction of the NF. The collection efficiency and pressure drop of the hybrid filters could be controlled by the NF fraction at the same Q_f. Moreover, the inhomogeneity factor of fiber packing (δ) did not significantly affect Q_f over the δ range from 3 to 23 for our filters. This implies that the lower particle capturing efficiency due to heterogeneous packing could be compensated by a decrease in the pressure drop, resulting in the same Q_f value. Therefore, Q_f for particles smaller than 100?nm, which are in the diffusion-controlled regime, can be increased by reducing the NF diameter.

Copyright © 2019 American Association for Aerosol Research     

The effects of solution properties and polyelectrolyte on electrospinning of ultrafine poly(ethylene oxide) fibers

The effects of solution properties and polyelectrolyte on the electrospinning of poly(ethylene oxide) (PEO) solutions were investigated. Ultrafine PEO fibers without beads were electrospun from 3, 4, 7 and 7 wt% PEO solutions in chloroform, ethanol, (dimethylformamide) DMF and water, respectively. At these concentrations, the values of [η]C were ∼10 for all solutions. The average diameters of PEO fibers were ranged from 0.36 to 1.96 μm. The higher the dielectric constant of solvent was, the thinner PEO fiber was. The average diameters of electrospun PEO fibers from PEO/water solutions were decreased and their distributions were narrowed by adding 0.1 wt% poly(allylamine hydrochloride) (PAH) and poly(acrylic acid sodium salt) (PAA) due to the increased charge density in solutions. The addition of PAH and PAA lowered the minimum concentration for electrospinning of a PEO/water solution to 6 wt%.     

Electrospinning of thermoplastic polyurethane microfibers and nanofibers from polymer solution and melt

Electrospinning technique was used to produce ultrafine fibers from thermoplastic polyurethane (TPU). A direct comparison between melt and solution electrospinning of TPU was provided for the evaluation of process–structure relationship. It was found that the deposition rate of melt electrospinning (0.6 g h^?1) is four times higher than that of solution electrospinning (0.125 g h^?1) for TPU under the same processing condition. However, the average fiber diameters of solution electrospun TPUs (220–280 nm) were much lower than those of melt electrospun TPUs (4–8 μm). The effect of processing variables including collection distance and electric field strength on the electrospun fiber diameter and morphology was also studied. The findings indicate that increasing the electric field strength yielded more electrical forces acting on polymer jet and resulted in a decrease in fiber diameter as a result of more fiber drawing in both solution and melt electrospun fibers. It was also demonstrated that increasing the collection distance led to an improvement in the solidification of melt electrospun fibers and thus less fused fibers were obtained. Finally, a close investigation of fiber structures revealed that melt electrospun TPU fibers had smooth surface, whereas solution electrospun TPU fibers showed high intensity of cracks on the fiber surface. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

An investigation into the influence of electrospinning parameters on the diameter and alignment of poly(hydroxybutyrate‐co‐hydroxyvalerate) fibers

Electrospinning is an effective technology for the fabrication of ultrafine fibers, which can be the basic component of a tissue engineering scaffold. In tissue engineering, because cells seeded on fibrous scaffolds with varying fiber diameters and morphologies exhibit different responses, it is critical to control these characteristics of electrospun fibers. The diameter and morphology of electrospun fibers can be influenced by many processing parameters (e.g., electrospinning voltage, needle inner diameter, solution feeding rate, rotational speed of the fiber‐collecting cylinder, and working distance) and solution properties (polymer solution concentration and conductivity). In this study, a factorial design approach was used to systematically investigate the degree of influence of each of these parameters on fiber diameter, degree of fiber alignment, and their possible synergetic effects, using a natural biodegradable polymer, poly(hydroxybutyrate‐co‐hydroxyvalerate), for the electrospinning experiments. It was found that the solution concentration invoked the highest main effect on fiber diameter, whereas both rotational speed of the fiber‐collecting cylinder and addition of a conductivity‐enhancing salt could significantly affect the degree of fiber alignment. By carefully controlling the electrospinning parameters and solution properties, fibrous scaffolds of desired characteristics could be made to meet the requirements of different tissue engineering applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology, structure and properties of conductive PS/CNT nanocomposite electrospun mat

The morphologies and properties of Polystyrene (PS)/Carbon Nanotube (CNT) conductive electrospun mat were studied in this paper. Nanocomposite fibers were obtained through electrospinning of PS/Di-Methyl Formamide (DMF) solution containing different concentrations and types of CNTs. The dispersion condition of CNTs was correlated to morphologies and properties of nanocomposite fibers. A copolymer as an interfacial agent (SBS, Styrene-butadiene-styrene type) was used to modify the dispersion of CNTs in PS solution before electrospinning. The results showed that the presence of the copolymer significantly enhances CNT dispersion. The fiber diameters varied between 200 nm and 800 nm depending on CNT type, polymer concentration and copolymer. The final morphological study of the fibers showed that CNT addition caused a decrease in beads formation along fiber axis before percolation threshold. However, addition of CNTs above percolation increased the beads formation, depending on the dispersion condition. The presence of SBS modified the dispersion, reduced the fiber diameter and the number of bead structures. Electrical conductivity measurements on nanocomposite mats of 15-300 μm in thickness showed an electrical percolation threshold around 4 wt% MWCNT; while the samples containing SBS showed higher values of conductivities below percolation compared to the samples with no compatibilizer. Enhancement in mechanical properties was observed by the addition of CNTs at concentrations below percolation.     

Preparation of 0.4Li2MnO3·0.6LiNi1/3Co1/3Mn1/3O2 with tunable morphologies via polyacrylonitrile as a template and applications in lithium‐ion batteries

Samples of 0.4Li₂MnO₃·0.6LiNi_1/3Co_1/3Mn_1/3O₂ (LMO) with tunable morphologies were synthesized via polyacrylonitrile (PAN) as a template. The starting PAN/N,N‐dimethylformamide (DMF) ratios, including 1:9, 1:10, 1:12, and 1:14, were optimized for the fiber morphologies and electrochemical performance. Through electrospinning, metal salts were well dispersed in the PAN fibers. The crystal structure and morphologies of the PAN/LMO fibers were characterized by X‐ray diffraction, scanning electron microscopy, and thermal analysis. Along with the decrease in the concentration of PAN in the precursor, the diameters of the PAN/LMO fibers decreased. On the other hand, at the highest and lowest concentrations, 1:9 and 1:14, of PAN with DMF, micrometer PAN fibers were electrospun, whereas ratios of PAN to DMF of 1:10 and 1:12 resulted in the electrospinning of millimeter‐long fibers of PAN. In the interface of PAN and metal salts, LMOs were grown and accompanied the decomposition of PAN, and the crystal morphologies of LMO quite depended on the diameter and length of the PAN/LMO nanofibers. During heat treatment, the morphologies of the PAN fibers controlled the removal of small molecules and the crystal morphologies of LMOs. The charge/discharge results indicate that LMO with a tubular structure delivered a capacity of 262.3 mAh/g at a cutoff voltage of 2.5–4.8 V at a 0.1 C rate. Benefitting from a unique hollow and nanocrystalline architecture, it also exhibited good rate and cycling performances. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43022.     

Synthesis of ultra-fine α-Al2O3 fibers via electrospinning method

Ultra-fine Al₂O₃ fibers were synthesized via electrospinning technique using PVP/ethanol polymer solution and aluminium acetate sol followed by calcinations at higher temperature. The formation, crystalline phase, surface morphology, fibers diameter and surface area of alumina ultra-fine fibers were characterized using FT-IR, TGA/DTA, XRD, SEM, TEM and BET analytical techniques. The results show that pure and crystalline α-Al₂O₃ ultra-fine fibers were formed with fiber diameter in the range of 100–500 nm and BET surface area of the fibers were found to be 40 m²/g.     

超细二氧化硅纤维/橡胶复合材料的结构与性能研究

通过静电纺丝技术制备了直径为300~500 nm的超细二氧化硅纤维,制备的纤维进一步研磨和超声处理得到二氧化硅短纤维,然后将其填充到胎面胶中,分析了不同取向的二氧化硅纤维对胎面胶物理机械性能与动态力学性能的影响。结果表明：二氧化硅纤维在胎面胶基体中有着良好的分散,可以明显提高复合材料的100%定伸模量。在动态性能上,当纤维取向方向与分子链方向一致时,其60~80oC损耗因子最小。当纤维取向方向与分子链方向垂直时,0~-20oC损耗因子最大。因此该二氧化硅纤维作为一种新型增强填料在胎面胶上有着良好的应用前景。     

Controlling the deposition of light‐emitting nanofibers/microfibers by the electrospinning of a poly(p‐phenylene vinylene) polyelectrolyte precursor

Poly(p‐phenylene vinylene) (PPV) nanofibers with disordered, helical, and yarn morphologies were controllably prepared by the electrospinning of a cationic polyelectrolyte precursor in an ethanol solution followed by thermal conversion. Through the tuning of the precursor solution properties and processing variables, the factors affecting the morphology of PPV fibers were studied. The diameter of these PPV nanofibers decreased with a decrease in the precursor concentration, and gradual blueshifts and changes in the relative intensity of the vibronic components in photoluminescence spectra were observed. These nanofibers with excellent fluorescent properties are potentially interesting for many applications such as micro‐ and nano‐optoelectronic devices and systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

CHARACTERISTICS OF MICROMETER AND SUBMICROMETER SIZE O/W EMULSIONS PRODUCED BY RAMOND SUPERMIXER®

A novel motionless mixer named the Ramond Supermixer® (RSM®) was employed to produce O/W emulsions composed of micrometer and submicrometer-size droplets. Liquid paraffin as dispersed phase, aqueous sucrose solution as continuous phase, and anionic sodium dodecyl sulfate as emulsifying agent were used as the model emulsification system. Pressure drop, droplet size distribution, Sauter mean diameter (d ₃₂), and geometric standard deviation of the droplet size distribution (σ_g) were investigated under the various combinations of process variables; superficial liquid velocity, number of mixing units, number of passages through RSM®, dispersed phase viscosity (η_d), continuous phase viscosity (η_c), and dispersed phase volume fraction. Different modes of droplet size variations with process variables were obtained, with respect to micrometer- and submicrometer-size ranges, and theoretical explanations are forwarded. For the micrometer-size range, maximum droplet diameter (d _max) was proportional to d ₃₂. For the submicrometer-size range, d _max varied with d ₃₂ in the range of 1.53–2.19-fold, and a correlation is proposed with K (=η_d/η_c); d ₃₂ and σ_g were well correlated with the process variables. Furthermore, a semi-empirical mechanistic model was developed for the formation of droplets obtained under inertial sub-range to interpret the effect of process variables.