Hydrophobic Substrates Research Articles

Recent advances in chemical durability and mechanical stability of superhydrophobic materials: Multi-strategy design and strengthening

• Recent advances of robust superhydrophobic materials is reviewed. • Multi-strategy design and strengthening of superhydrophobic materials is discussed. • Multifunctionality of robust superhydrophobic materials is shown. • Challenges and future solutions for robust superhydrophobic materials are proposed. Inspired by the lotus leaf effect, non-wetting artificial superhydrophobic surfaces demonstrate an enormous potential in numerous fields. However, limited by poor stability and durability, superhydrophobic surfaces are rarely available for practical applications. In this review, based on the wettability mechanisms and failure modes of superhydrophobic surfaces, it is proposed that the construction of highly stable superhydrophobic materials can be approached from four aspects, including structural design, chemical bonding, interfacial-strengthening of hydrophobic materials and substrates, and self-healing. We introduced in detail the design ideas, strengthening approaches, and characterization tools of highly stable superhydrophobic materials from the perspective of multi-strategy design and strengthening, and provided corresponding insights. Eventually, the development, current status, and prospects of highly stable and multifunctional superhydrophobic materials were also presented in detail. Recent advances and development prospects of durable superhydrophobic materials were summarized and discussed in this review, providing certain insights and design guidelines for the fabrication of stable superhydrophobic materials.

Lysosomal Targeting of β-Cyclodextrin.

β-Cyclodextrin (β-CD) and derivatives are approved therapeutics in >30 clinical settings. β-CDs have also shown promise as therapeutics for treatment of some lysosomal storage disorders, such as Niemann-Pick disease type C, and other disease states which involve metabolite accumulation in the lysosome. In these cases, β-CD activity relies on transport to the lysosome, wherein it can bind hydrophobic substrate and effect extraction. The post-translational attachment of N-glycans terminated in mannose-6-phosphate (M6P) residues is the predominant method by which lysosomal enzymes are targeted to the lysosome. In this work we covalently attach a synthetic biantennary bis-M6P-terminated N-glycan to β-CD and study the effect of the added glycans in a mammalian cell line. The formation of a host guest complex with a Cy5 fluorophore allows study of both cellular internalisation and transport to the lysosome by fluorescence microscopy. Results indicate that the rates of both internalisation and lysosomal transport are increased by the attachment of M6P-glycans to β-CD, indicating that M6P-glycan conjugation may improve the therapeutic effectiveness of β-CD for the treatment of disorders involving hydrophobic metabolite accumulation in the lysosome.

Nanorod-interlayered thin film composite membranes for ultrafast nanofiltration

Customizing high-performance nanofiltration membranes that can break the trade-off effect is critical to the development of membrane separation. Building an intermediate layer between the support and the selective layer to accelerate water transport is considered to be an effective solution to this issue. However, the synthesis of interlayered thin-film composite membranes (i-TFCs) on non-polar substrates with large pores and high porosity remains challenging. Here, we report a high-performance i-TFC membrane with FeOOH nanorods as interlayers. The porous and robust nanorods greatly increased the water transport paths and the mechanical strength of the membrane. Under the high pressure of 20 bar, the i-TFC membrane still remained a high salt rejection above 96 % while showing a high pure water permeance up to 48.9 L·m−2·h−1·bar−1. Furthermore, the presence of nanorods enhanced the hydrophilicity and compactness of the substrate, leading to the formation of a 23-nm thick polyamide layer without nanorod structures. The versatility of the strategy was also demonstrated with three different hydrophobic substrates. This work will thus provide further insights into the development of high-performance membranes for molecular separations.

High-Rate and Selective CO2 Electrolysis to Ethylene via Metal-Organic-Framework-Augmented CO2 Availability.

High-rate conversion of carbon dioxide (CO2 ) to ethylene (C2 H4 ) in the CO2 reduction reaction (CO2 RR) requires fine control over the phase boundary of the gas diffusion electrode (GDE) to overcome the limit of CO2 solubility in aqueous electrolytes. Here, a metal-organic framework (MOF)-functionalized GDE design is presented, based on a catalysts:MOFs:hydrophobic substrate materials layered architecture, that leads to high-rate and selective C2 H4 production in flow cells and membrane electrode assembly (MEA) electrolyzers. It is found that using electroanalysis and operando X-ray absorption spectroscopy (XAS), MOF-induced organic layers in GDEs augment the local CO2 concentration near the active sites of the Cu catalysts. MOFs with different CO2 adsorption abilities are used, and the stacking ordering of MOFs in the GDE is varied. While sputtering Cu on poly(tetrafluoroethylene) (PTFE) (Cu/PTFE) exhibits 43% C2 H4 Faradaic efficiency (FE) at a current density of 200mA cm- 2 in a flow cell, 49% C2 H4 FE at 1 A cm- 2 is achieved on MOF-augmented GDEs in CO2 RR. MOF-augmented GDEs are further evaluated in an MEA electrolyzer, achieving a C2 H4 partial current density of 220mAcm-2 for CO2 RR and 121mAcm-2 for the carbon monoxide reduction reaction (CORR), representing 2.7-fold and 15-fold improvement in C2 H4 production rate, compared to those obtained on bare Cu/PTFE.

Fabrication of free standing graphene oxide membranes for efficient adsorptive removal of cationic dyes

Free standing graphene oxide membranes (FSGOMs) were prepared by controlled infra-red irradiation of aqueous GO dispersions on hydrophobic Si substrate and evaluated for their adsorption ability towards methylene blue (MB) class cationic dyes. The intactness and morphological characteristics of FSGOMs are determined by precursor GO dispersion medium and GO mass accumulated in membrane. The MB adsorption ability of FSGOMs was examined at different membrane weights, MB concentrations, ambience of interaction, initial pH, heat treatment conditions and these results were analyzed in light of corresponding morphological and vibrational features. Disintegration of FSGOMs in aqueous medium liberate plentiful GO layers enriched with unsaturated chemical bonds, which are prone to react with tertiary amine nitrogen, sulphur entities of MB molecules through electrostatic/π-π interactions and assist in MB adsorption. FSGOMs displayed superior adsorption efficiency towards MB as compared to rhodamine B, rhodamine 6G, malachite green dyes, which is attributed to relatively smaller size, planarity and alignment of MB molecules with GO layers and their affinity towards diverse GO functionalities. The demonstrated solid state FSGOM based procedure facilitate to provide platform for substantial adsorption of variety of cationic dyes, limits generation of secondary liquid waste and has significant potential in waste water purification applications.

Importance of Substrate Pore Size and Wetting Behavior in Gas Diffusion Electrodes for CO2 Reduction

We study the effect of substrate pore size and wetting behavior on the performance of polymer-based Ag gas diffusion electrodes (GDEs) for electrochemical CO2 reduction. We find a strong correlation between the pore size of the substrate and the GDE product selectivity and performance stability during CO2 electrolysis. We attribute this correlation to the GDE’s wetting behavior, in particular, to its resistance to aqueous electrolyte penetration. We quantify this resistance by the water entry pressure, that is, the minimum pressure required to push water through a hydrophobic porous substrate, which depends on the pore size of the substrate and on the hydrophobicity of the substrate polymer. While substrates with low water entry pressure yield GDEs that exhibit poor CO selectivity and stability, high water entry pressure substrates lead to greatly improved Faradaic efficiency toward CO (up to 95% at 100 mA/cm2) and remarkably longer performance stability (97% of initial CO selectivity retained after >40 h). We also assess the sensitivity to surface Cu contaminants and find that substrates with high water entry pressures lead to GDEs that are more resilient to impurities, with an almost unvaried selectivity even when contaminated with >1 at % Cu vs Ag. On this basis, we propose the water entry pressure as a metric to assess GDE quality. These results highlight how acting on the substrate is a powerful and scalable handle for improving the performance of GDEs for the electrochemical CO2 reduction.

Asymmetric freezing behaviors of inclined impact of water droplets on cold hydrophobic surfaces

Solidification of impacting water droplets on surfaces impairs the performance and safety of various applications. Prior studies mostly focused on the freezing behaviors of normal impact of water droplets on cold surfaces. In this work, we explore the freezing morphologies and self-peeling behaviors of water droplets when impacting cold hydrophobic substrates with an inclination angle (45°). To improve the coupling between the solidification and drop-scale hydrodynamics, we thus conducted the experiments in a regime where the heat transfer rate is significantly enhanced for fast solidification. In contrast to hydrophilic surfaces, the final freezing morphologies on hydrophobic surfaces are easier to exhibit a rivulet, whose length has a non-monotonic relation with Weber number. The rivulet morphologies can be transited into an asymmetric fingering pattern when Weber number is high enough. More intriguingly, we observe the asymmetric self-peeling behaviors of water droplets upon impacting cold inclined surfaces, where both ice titled direction and degree are highly dependent on Weber number. Moreover, the maximum ice deflection at the edge is found to agree well with a scaling law.

Comparison of Techniques for Drying Cellulose Nanocrystal Pickering Emulsions into Oil Powders

A recent push for surfactant-free products driven by environmental awareness has propelled the use of bio-based materials in place of petroleum-derived components. However, both the formulation and processing need to be considered for scale-up feasibility and environmental sustainability. This work investigated the drying of corn oil-in-water emulsions stabilized by cellulose nanocrystals (CNCs), methyl cellulose (MC), and tannic acid via freeze drying, spray freeze drying, and spray drying. All three techniques produced oil powders with low moisture content and high encapsulated oil content (>90%). The oil powders could be redispersed in water by hand shaking to reform the original emulsion and could be stored dry for weeks without oil leakage (in the fridge). The release of oil from the powders on hydrophobic substrates (at room temperature) was controlled by changing the CNC and MC stabilizer content; the spray freeze dried samples were the most tunable. The three drying techniques imparted different surface morphologies that were linked to powder redispersibility and oil release properties. The lack of freezing (and associated ice crystal growth) in spray drying minimized oil droplet agglomeration, and it was the fastest, most scalable, and least energy-intensive drying technique of the three, but it was also the most sensitive to emulsion concentration and susceptible to instabilities associated with high temperature and shear stress. It was demonstrated that essential oils with a range of interfacial tensions and volatilities (e.g., jojoba, lavender, tea tree oil) could also be encapsulated in spray dried oil powders. This general encapsulation strategy can be tailored based on the drying technique selected, uses plant-based industrially-produced feedstocks, works with commercially relevant oils, and will hopefully contribute to the development of sustainable emulsions and oil powders for food, pharmaceutical, agricultural, and cosmetic applications.

Stretchable, adhesive and antibacterial mussel-inspired cellulose nanocrystal/pectin biomass-based multifunctional tough hydrogels

The multifunctional biocompatible hydrogels have attracted widespread attention in biomedical applications such as the fields of biomimetic tissues, wound dressings and biosensors. But it is a great challenge to facilely develop a hydrogel with favorable mechanical strength, adhesion performance, anti-swelling behavior, antibacterial activity and biocompatibility at the same time. Inspired by the mechanical reinforcement mechanism of double network and nanocomposite hydrogels as well as the adhesion mechanism of mussel, tannic acid-coated cellulose nanocrystals ([email protected])/pectin/polyacrylic acid nanocomposite hydrogels (TPP hydrogels) are reported in this work. The obtained TPP hydrogels exhibited high stretchability with the fracture strain of more than 1400%, and excellent elasticity and fatigue resistance. Additionally, the abundant catechol groups on [email protected] nanoparticles endow TPP hydrogels with good adhesiveness and can adhere to various hydrophilic and hydrophobic substrates such as wood, glass, polytetrafluoroethylene and biological tissues. Moreover, TPP hydrogels also exhibited the significant anti-swelling properties expressed that the equilibrium swelling ratio of the tested TPP hydrogel was only 19.25% as much as that of the polyacrylic acid hydrogel. In addition, TPP hydrogels displayed favorable antibacterial properties against Escherichia coli and Staphylococcus aureus, and can effectively support the adhesion, growth and proliferation of mouse fibroblasts for showing cytocompatibility. All the results imply that TPP hydrogels have promising potential in biomedical application.

Constructing anti-scaling and anti-wetting polyvinyl alcohol layers through spray-coating with improved water permeability in membrane distillation

Membrane scaling and wetting severely hinder the implementation of membrane distillation (MD) in hypersaline wastewater treatment. In this study, Janus membranes with high water flux and anti-scaling/wetting capacities were successfully fabricated by spray-coating polyvinyl alcohol (PVA) layers on hydrophobic membrane substrates (SCJMs). The surface properties and wastewater treatment performances of SCJMs were systematically investigated and compared with those of Janus membranes fabricated via frame-coating methods (FCJMs). Compared with the FCJMs, the PVA layers formed on the SCJM surface were defect-free, more uniform in thickness, and had larger evaporation areas; consequently, they exhibited higher water fluxes. Further investigation of the flux-enhancement mechanisms of the SCJMs using Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and polarizing microscope analyses revealed that spray-coating promoted the crosslinking of PVA polymer networks and facilitated water molecule transport. In addition, although the PVA layer of the SCJMs exhibited higher crystallinity, the crystal particles were smaller in size, and the crystal domains exhibited a lower resistance to water transport compared to those of the FCJMs. Fabrication conditions such as spraying time and distance were also optimized to further enhance the performance of the SCJMs, which exhibited great potential for application in the efficient MD-based desalination of hypersaline wastewater.

Robust graphene field-effect transistor biosensors via hydrophobization of SiO2 substrates

The interfacial adhesion energy between graphene and underlying substrates is considerably important for robust graphene biosensors because water molecules can intercalate underneath graphene when submerged, possibly detaching graphene from substrates. This study investigated the robustness of graphene field-effect transistor arrays fabricated on hydrophobic and hydrophilic SiO2 substrates. Although the graphene sheets delaminated from hydrophilic substrates within minutes of submersion in a buffer solution, they remained stable on hydrophobic substrates for several days. This result agreed with the estimated thermodynamic work of adhesion in water, which improved significantly from −17.3 to 17.7 mJ m−2 through the hydrophobization process of the substrates.

Effect of Substrate Microstructure and Hydrophobicity on Ag Gas Diffusion Electrodes for Electrochemical CO2 Reduction

Electrochemical CO2 reduction (CO2RR) is a very promising way to convert detrimental CO2 emissions into sustainable fuels and chemicals, and move us closer to a circular economy.1 To compete with traditional fuel/chemical production routes, we need to develop electrocatalysts that are highly active, selectivity towards a desired product, and stable. Thanks to the use of gas diffusion electrodes (GDEs) that provide gaseous CO2 close to the catalyst, high activities can be achieved.2,3 However, product selectivity and stability must still be improved before practical application. An emerging strategy in this regard is to control the local environment surrounding a catalyst, i.e. the concentration of the various products and reagents therein.4 In this work, we achieve such control by varying the microstructure of substrates later used to fabricate GDEs by Ag deposition. By systematically studying the CO2RR performance, we observe a clear correlation between the pore size of the GDEs and their product selectivity, stability, and even resilience to Cu impurities.5 We rationalize it with the different effective hydrophobicity of the GDEs, which control the extent of electrolyte penetration within the electrode and depends on both substrate chemistry and pore size. We show that a higher effective hydrophobicity correlates with higher Faradaic efficiency towards carbon monoxide production (FECO up to 95 % at 100 mA/cm2) and longer stability (~100 % retention after a 1 hour electrolysis at 100 mA/cm2). These results show the importance of the substrate's microstructural properties in GDE for CO2RR, and highlight a new strategy to achieve control over selectivity and stability of these electrodes.

Degradation of long-chain alkanes through biofilm formation by bacteria isolated from oil-polluted soil

Three bacteria, Novosphingobium sp. S1, Gordonia amicalis S2 and Gordonia terrae S5, were isolated from a crude oil polluted soil and investigated for their ability to utilize long-chain alkanes (C16-C30). The strains were able to use n-hexadecane, n-octadecane and paraffins as carbon and energy source, although at different extents. Growth with alkanes, resulted in the formation of a biofilm at the alkane-water interface. Growth was shown to occur only if cells had access to the alkane-water interface suggesting that biofilm formation was required to assimilate these hydrophobic substrates. The interfacial access to alkanes is also supported by the ability of the strains to adhere to n-hexadecane, with Gordonia amicalis S2 and Gordonia terrae S5 exhibiting a much stronger adhesion than Novosphingobium sp. S1. None of the strains released biosurfactant into the culture medium which is consistent with an interfacial access to alkanes. LC-MS analyses revealed the release into the extracellular medium of 8-hydroxyhexadecanedioic acid by Novosphingobium sp. S1 and Gordonia amicalis S2, and 8-hydroxyhexadecanoic acid and 7-hydroxyhexadecanoic by Gordonia terrae S5. The production of these hydroxylated carboxylic acids substantiates the degradation of n-hexadecane by the strains although their physiological significance remains to be elucidated.

Wafer-Scale Full-Coverage Self-Limiting Assembly of Particles on Flexible Substrates.

Self-limiting assembly of particles represents the state-of-the-art controllability in nanomanufacturing processes where the assembly stops at a designated stage, providing a desirable platform for applications requiring delicate thickness control such as optics, electronics, and catalytic systems. Most successes in self-limiting assembly are limited to self-assembled monolayers (SAMs) of small molecules on inorganic, chemically homogeneous rigid substrates (e.g., Au and SiO2) through surface-interaction mechanisms. Similar mechanisms, however, cannot achieve a uniform assembly of particles on flexible polymer substrates. The complex configurations and conformations of polymer chains create a surface with nonuniform distributions of chemical groups and phases. In addition, most assembly mechanisms require good solvent wettability, where many desirable but hard-to-wet particles and polymer substrates are excluded. Here, we demonstrate a collision-based self-limiting assembly (CSA) to achieve wafer-scale, full-coverage, close-packed monolayers of hydrophobic particles on hydrophobic polymer substrates in aqueous solutions. The kinetic assembly and self-limiting processes are facilitated and controlled by the combined acoustic and shear fields. We envision many applications in functional coatings and showcase their feasibility in structural coloration. Importantly, such functional coatings can be repaired using CSA, and both particles and polymer substrate can be recycled.

YfeX - A New Platform for Carbene Transferase Development with High Intrinsic Reactivity.

Carbene transfer biocatalysis has evolved from basic science to an area with vast potential for the development of new industrial processes. In this study, we show that YfeX, naturally a peroxidase, has great potential for the development of new carbene transferases, due to its high intrinsic reactivity, especially for the N-H insertion reaction of aromatic and aliphatic primary and secondary amines. YfeX shows high stability against organic solvents (methanol and DMSO), greatly improving turnover of hydrophobic substrates. Interestingly, in styrene cyclopropanation, WT YfeX naturally shows high enantioselectivity, generating the trans product with 87 % selectivity for the (R,R) enantiomer. WT YfeX also catalyzes the Si-H insertion efficiently. Steric effects in the active site were further explored using the R232A variant. Quantum Mechanics/Molecular Mechanics (QM/MM) calculations reveal details on the mechanism of Si-H insertion. YfeX, and potentially other peroxidases, are exciting new targets for the development of improved carbene transferases.

Robust polyamide-PTFE hollow fibre membranes for harsh organic solvent nanofiltration

Polymeric membranes have been extensively studied for organic solvent nanofiltration (OSN) but many fail to show sufficient chemical resistance in strong solvents like dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). This study focuses on harnessing the outstanding chemical resistance of polytetrafluoroethylene (PTFE), to develop polyamide-PTFE thin film composite (TFC) membranes that are resistant to such aprotic solvents. A defect-free polyamide thin film layer was successfully synthesized on the microfiltration PTFE hollow fibre substrates, overcoming challenges such as large and uneven pore size, and hydrophobicity of the PTFE substrates. A simple polydopamine (PDA) coating was carried out to improve the substrate’s hydrophilicity prior to the polyamide synthesis via interfacial polymerization (IP). Polyethyleneimine (PEI) and trimesoyl chloride (TMC) were used as the monomers and a two-time IP method was employed to obtain a defect-free polyamide coating. The synthesized membranes showed high acetonitrile (ACN) and DMF permeabilities of 7.94 and 3.70 lm−2h−1bar−1, respectively, with acid fuchsin (585 Da) rejections of > 90 %. The molecular weight cut-off (MWCO) of the membranes could be further reduced to ∼300 Da by the addition of piperazine (PIP) monomers. The membranes also showed excellent stability and performance in a 72-hour OSN test performed in DMF indicating their great potential in effective molecular separation in harsh solvents. This study demonstrates how a simple modification and coating technique can transform commercially available microfiltration PTFE hollow fibres into durable and high value OSN membranes.

Polyacrylic acid ultra‐thin films: Influence of cross‐linking structure via hyperthermal hydrogen‐induced cross‐linking

AbstractThe facile technology of hyperthermal hydrogen‐induced cross‐linking (HHIC) has recently been employed to efficiently cross‐link the typical surface modification material of poly acrylic acid (PAA) on polymer substrates, such as polylactic acid substrates, parylene C substrates and hydrophobic polypropylene substrates. This paper systematically studied the HHIC induced self‐cross‐linking of PAA without polymer substrates. It was found that the H was cleaved not only from the CH, but also from the surface functional group COOH, evidenced by both X‐ray photoelectron spectroscopy (XPS) measurement and the water contact angle test. We explained the self‐cross‐linking process as a result of both CC bonding and COOC bonding. Meanwhile, it was also found that PAA on different substrates can also be cross‐linked by secondary electron generated by X‐ray radiation during XPS analysis, which could be the main reason for wide variations of different reported XPS results.

Distinct impact of substrate hydrophilicity on performance and structure of TFC NF and RO polyamide membranes

Substrate properties have profound impacts on the structure and performance of both thin-film composite (TFC) nanofiltration (NF) and reverse osmosis (RO) polyamide (PA) membranes. Some studies have previously investigated the impact of substrate hydrophilicity on PA formation and TFC membrane performance. However, the observed phenomena and explanations remain contradictory in literature. Herein, we performed interfacial polymerization (IP) reactions of both piperazine (PIP)-trimesoyl chloride (TMC) and m-phenylenediamine (MPD)-TMC systems on substrates with different hydrophilicity. We found that the TFC RO membrane showed higher water permeance and NaCl rejection on the relatively hydrophobic substrate, while the TFC NF membrane favored the relatively hydrophilic substrate. The critical importance of interfacial degassing and local monomer concentration was highlighted to dissect the distinct impact of substrate hydrophilicity. For the MPD-TMC system, interfacial nanobubble generation was inhibited because of the decreased local MPD concentration and heat production for the more hydrophilic substrates, resulting in a decrease in the roughness feature and compromised water permeance of RO membranes. In contrast, interfacial degassing was not a dominant mechanism in the PIP-TMC system due to the slower reaction rate of PIP-TMC than MPD-TMC. Consequently, the PA layer of NF membrane became thinner and looser when the substrate became more hydrophilic, resulting from the diluted local PIP concentration. Our study unveils the fundamental relationship among substrate hydrophilicity, PA structure, and separation performance of both TFC NF and RO PA membranes, providing important guides on their design and synthesis.

Chemical structure change of lignin extracted from bamboo biomass by maleic acid

Maleic acid (MA) is an effective solvent for lignin extraction from raw biomass under mild conditions through acidolysis and hydrophobic interaction. To improve the valorization of lignin, the lignin extracted with MA was subjected to successive organic solvent fractionation to make the narrow Mw and Mn distribution and the homogeneity structure of lignin fragments. After successive organic solvent fractionation, the dispersity index (Đ) of lignin reduced from 2.86 to 1.25, and the purity and homogeneity were greatly improved. The phenolic hydroxyl content of lignin extracted by ethyl acetate was the highest (2.45 mmol/g), and the aliphatic-OH concentration was the lowest (0.65 mmol/g). While the βO4 bonds were partially cleaved, more hydrophobic substrates with CC linkages were recovered by ethyl acetate. Lignin fragments with a variety of main structures and functional groups were obtained effectively with successive fractionation. This method supplied broad prospects for the preparation of lignin and its applications in epoxy resin, rubber, thermoplastic additives and polymer raw materials.

Optimization of the primary purification process of extracting sphorolipid from the fermentation broth to achieve a higher yield and purity

Abstract Sophorolipid (SL) is a surface-active glycolipid biosurfactant with promising industrial applications. It is synthesised by fermentation of hydrophobic and hydrophilic substrates using selected non-pathogenic yeasts. However, its applications are limited by high production costs and ineffective product recovery in downstream purification stages. Natural sophorolipids are produced in six to nine different hydrophobic sophorosides, where the carboxyl end of the fatty acid is either free, which is known as the acidic or open form, or it can be esterified internally to produce the lactonic form. The present study deals with the screening and selection of suitable solvents for the extraction of acidic and lactonic SL from fermentation broth. The optimisation study involves exhaustive extraction with the six different immiscible solvents ethyl acetate, butyl acetate, methylene dichloride, methyl tert.-butyl ether, methyl iso-butyl ketone and methyl ethyl ketone. The partition coefficient (Kd), which is the ratio of the solute concentration in the organic layer compared to the aqueous layer, determines the performance measurement of the extraction process in terms of yield and purity of the desired solute. The factors that influence exhaustive extraction were the broth to solvent ratio and the extraction stages. The optimal extraction conditions for the highest possible yield were a broth to solvent ratio of 1:1 and a number of extraction steps of 2. Methylene dichloride showed better results in terms of yield and selectivity in the extraction of acidic and lactonic SL from the fermentation broth compared to the other solvents investigated. For lactonic SL, the highest Kd value determined was 36.6 and for acidic SL the highest Kd value was 1.14.