Factors influencing droplet size distribution in SPG membrane emulsification

Membrane emulsification is a new emulsification method proposed in 1988 by Nakashima and Shimizu [1]. This method enables the production of highly uniform droplets of controlled mean sizes [2]. The additional advantage over traditional processes is a low mechanical stress, because small droplets are directly formed by pressing the dispersed phase through the pores into the flowing continuous phase (Fig. 1). Due to uniform pores, the wide spectrum of available mean pore sizes (0.05-30 μm) [3], and the possibility of surface modification, the Shirasu-porous-glass (SPG) membrane is a suitable membrane for mechanical emulsification. The aim of this work was to investigate the influence of the mean pore size of the SPG membranes and the various operating parameters on the droplet size distribution

Preparation of emulsions with a narrow particle size distribution using microporous α-alumina membranes

O/W emulsions with the smallest spans of particle size distribution (PSD) [span = (d 90 − d 10)/d 50] reported until now for ceramic α‐alumina membranes (0.42–0.56) were prepared using a 1.4‐µm membrane cleaned thoroughly after use in an ultrasonic bath. The smallest span values of 0.42–0.48 were achieved at transmembrane pressures 2.6–3.5 times greater than the capillary pressure. A narrow particle size distribution with a span of 0.48–0.49 was obtained at a wall shear stress of 0.55 Pa, provided that the dispersed phase flux was not above 4.6 L m2 h−1. The span and mean droplet size were remarkably constant over the 1–10 vol.% range of dispersed phase content. Membrane cleaning by ultrasonication was one of the critical conditions for successful operation. If the membrane was cleaned only by the cleaning in place (CIP) method, emulsions with a span value in the range of 0.7–1.4 were obtained

Comparison of O/W emulsions produced using cross-flow SPG membranes and a microfluidizer

The oil-in-water emulsions consisting of vegetable (rape seed) oil as the dispersed phase and 2 wt % Tween 80 dissolved in demineralized water as the continuous phase were produced using Shirasu-porous-glass (SPG) membranes and Microfluidizer (Microfluidics Corp., Newton, MA, USA). The mean pore size of the membranes used was in the range of 0.4-6.6 μm and the wall porosity 53-60 %. The hydraulic membrane resistance was inversely proportional to the square of the mean pore size according to the equation: Rm = 0.056dp -2, where Rm and dp are in m-1 and m, respectively. The shear stress at the membrane surface was 8 Pa and the transmembrane pressure was 10 % higher than the cappilary pressure. Using SPG membranes under these conditions, the emulsions with a mean droplet size 3.5 times larger than the mean pore size and the span of the droplet size distribution of 0.26-0.45 were produced. Therefore, the SPG technology is very suitable for producing emulsions with a narrow droplet size distribution over a wide range of mean droplet sizes (0.2-30 μm) using small mechanical stresses. On the other hand, a Microfluidizer is more appropriate device for producing emulsions with a very low mean droplet size (0.08-0.2 μm). However, the span of the droplet size distribution curves for the emulsions produced using Microfluidizer typically range between 0.91 and 2.7

Production of monodispersed food O/W emulsions using Shirasu porous glass (SPG) membrane emulsification

The O/W emulsions containing Tween 80 dissolved in demineralized water as the continuous phase and rapeseed oil as the dispersed phase were prepared using different emulsification methods. The influence of operating conditions on droplet size distribution (DSD) was discussed and compared

Influence of process parameters on droplet size distribution in SPG membrane emulsification and stability of prepared emulsion droplets

SPG membranes were used to prepare monodispersed O/W and W/O/W emulsions over a wide range of membrane wall shear stress (0.37–40 Pa), dispersed phase content (1–20 vol.%) and transmembrane pressure. Although the most uniform droplets were prepared at the membrane wall shear stress of 30 Pa, a monodispersed O/W emulsion can be even obtained at the wall shear stress of 0.37 Pa, corresponding to laminar flow regime of continuous phase inside the membrane tube. The minimum droplet size somewhat decreased with time, probably due to gradual activation of smaller pores. There was no significant difference in the size distribution curve of pure oil droplets of O/W emulsions and W/O drops of W/O/W emulsions, if they were both prepared under the same conditions. No significant change in droplet size distribution of prepared O/W emulsions was observed during the storage time of up to 159 days

Production of O/W emulsions using SPG membranes, ceramic α-aluminium oxide membranes, microfluidizer and a silicon microchannel plate - a comparative study

O/W emulsions consisting of rapeseed oil as the dispersed phase and 2 wt.% Tween 80 dissolved in demineralized water as the continuous phase were prepared by using different emulsification methods, such as membrane emulsification (ME) with Shirasu porous glass (SPG) and α-aluminium oxide (α-Al2O3) membranes, microfluidization (MF) and microchannel (MC) emulsification. The influence of operating conditions and membrane structure on the emulsification process and the emulsion properties was investigated and compared. Under the same conditions and for the same pore size, the SPG membrane enabled to obtain more uniform droplets (span=0.26–0.45) than α-Al2O3 membrane. However, the span of the droplet size distribution of 0.51–0.59 for the α-Al2O3 membrane at the wall shear stress of 8 Pa and the dispersed phase flux up to 9 l m−2 h−1 was significantly smaller than that reported elsewhere for the same membrane type, which was due to careful membrane cleaning by ultrasonication. The calculated maximum proportion of active pores for unhindered droplet growth was higher for the α-Al2O3 than for SPG membrane, due to the smaller porosity and smaller mean droplet/pore size ratio for the α-Al2O3 membrane. At the same Δptm/pcap ratio, the actual proportion of active pores was also higher for this membrane, due to the smaller thickness of active layer. The microfluidization is a suitable method for producing O/W emulsions with a very small mean droplet sizes of 0.085–0.30 μm, that cannot be attained by membrane or microchannel emulsification. However, the span of the droplet size distribution was in the range between 0.91 and 2.7

Metabolic Changes in the Visual Cortex Are Linked to Retinal Nerve Fiber Layer Thinning in Multiple Sclerosis

OBJECTIVE: To investigate the damage to the retinal nerve fiber layer as part of the anterior visual pathway as well as an impairment of the neuronal and axonal integrity in the visual cortex as part of the posterior visual pathway with complementary neuroimaging techniques, and to correlate our results to patients' clinical symptoms concerning the visual pathway. DESIGN, SUBJECTS AND METHODS: Survey of 86 patients with relapsing-remitting multiple sclerosis that were subjected to retinal nerve fiber layer thickness (RNFLT) measurement by optical coherence tomography, to a routine MRI scan including the calculation of the brain parenchymal fraction (BPF), and to magnetic resonance spectroscopy at 3 tesla, quantifying N-acetyl aspartate (NAA) concentrations in the visual cortex and normal-appearing white matter. RESULTS: RNFLT correlated significantly with BPF and visual cortex NAA, but not with normal-appearing white matter NAA. This was connected with the patients' history of a previous optic neuritis. In a combined model, both BPF and visual cortex NAA were independently associated with RNFLT. CONCLUSIONS: Our data suggest the existence of functional pathway-specific damage patterns exceeding global neurodegeneration. They suggest a strong interrelationship between damage to the anterior and the posterior visual pathway

Pripremanje emulzija tipa voda-u-ulju pomoću hidrofobnih mikroporoznih šupljih vlakana

The preparation of fine and monodispersed water-in-oil (w/o) emulsions by utilizing hydrophobic polypropylene hollow fibers with 0.4 µm pores was investigated in this work. The experiments have been carried out using demineralized water as the disperse phase, mineral oil Velocite 3 as the continuous phase, and polyglycerol polyricinoleate (PGPR 90) in the concentration range of 2.5-10 wt% as the oil-soluble emulsifier. The size of water droplets in the resulting emulsions and the droplet size distribution strongly depended on the disperse phase content, the transmembrane pressure difference and the emulsifier concentration. The stable emulsions with a very narrow droplet size distribution and the mean droplet size lower than 0.27 μm were produced using 10 wt% PGPR 90 at the pressure difference below 30 kPa.Stabilne monodisperzne emulzije vode u mineralnom ulju su dobijene propustanjem vode pod pritiskom kroz mikropore polipropilenskih supljih vlakana u kontinualnu fazu koja je recirkulisala unutar vlakana. Fluks disperzne faze kroz membranu u prisustvu kontinualne faze unutar vlakana je 3-4 puta manji od fluksa koji se dobija kada se i unutar vlakana nalazi voda, sto ukazuje da je pri emulgovanju vrlo veliki procenat pora blokiran uljem i kao takav ne ucestvuje u permeaciji vode kroz membranu. Srednja velicina emulgovanih kapi raste sa porastom transmembranske razlike pritisaka a opada sa porastom koncentracije emulgatora (poliglicerol-poliricinoleata). Ako se emulgovanje vrsi pri razlici pritisaka manjoj od 30 kPa i pri koncentraciji emulgatora od 10 mas% mogu se dobiti emulzije sa vrlo uskom raspodelom velicina emulgovanih kapi i srednjom velicinom kapi manjom od 0,27 urn