Propylene Oxide Groups Research Articles

Hydrogen bond recombination regulated by strongly electronegative functional groups in demulsifiers for efficient separation of oil–water emulsions

Tight oil extraction and offshore oil spills generate large amounts of oil–water emulsions, causing serious soil and marine pollution. In such oil–water emulsions, the resin molecules are bound by π–π stacking and bind to interfacial water molecules via hydrogen bonds, which impede the aggregation between water droplets and thereby the separation of the emulsion. In this study, strongly electronegative oxygen atoms (in ethylene oxide, propylene oxide, esters, and hydroxyl groups) were introduced through poly(propylene glycol)-block-polyether and esterification with acrylic acid to attract negative charges in order to form electron-rich regions and enhance interfacial hydrogen bond recombination. The potential distribution in the demulsifier molecules and their space occupancy were regulated by the polymerization reaction to destroy the π–π stacking interaction between resin molecules. The results show that the binding energies (binding free energy and hydrogen bonding energy) of oxygen-containing demulsifier molecules with water molecules were higher than those of resin molecules with water molecules, resulting in the fission of the hydrogen bonds between resin and water molecules. The introduction of demulsifier molecules that occupied large interfacial space reduced the binding energy between resin molecules from −2176.06 to −110.00 kJ·mol−1. Noteworthy, the binding energy between demulsifier molecules and resin molecules was −1076.36 kJ·mol−1 lower than that between resin molecules (−110.00 kJ·mol−1), indicating the adsorption of the surrounding interfacial resin molecules by the demulsifier molecules and destruction of the π–π stacking between them, thus favoring the collapse of the interfacial structure of the oil–water emulsion and achieving its separation. This study provides important theoretical support for the treatment of oil-contaminated soil and offshore oil spill pollution.

Dilational Rheology of Extended Surfactants at the Air/Water and Oil/Water Interfaces: Effect of Propylene Oxide Group Numbers.

In this paper, the interfacial properties of extended surfactants with different oxypropylene (PO) groups were comprehensively investigated by using interfacial dilational rheology. The differences in molecular orientation, spatial configuration, and relaxation process were compared at the gas-water interface and oil-water interface. The influences of the PO groups on the interface viscoelasticity were analyzed, providing important theoretical support for the wide application of extended surfactants. Experimental results show that the lower number of PO groups in extended surfactants does not cause differences in their presence states on the interface; however, once it increases, the longer PO segment will spiral up in the direction perpendicular to the interface, forming a spatial configuration like a thin cylinder. Compared with air, the PO group has better solubility in the oil phase. The chain segment can still maintain a helical extension from the beginning to the end as a result. However, the upper layer of the thin cylinder will collapse to a certain extent at the surface. Moreover, the orientation of the hydrophobic side has a dynamic process of "tilting to upright" with the increase of adsorption amount or in response to interfacial dilation and compression. The increase of PO number or the insertion of oil molecules has little effect on dilational modulus, and the interfacial film strength is generally relatively low. That is to say, the better emulsifying and solubilizing ability of PO-containing extended surfactants may be more attributed to the matching steric effect at interface or better packing action in bulk phase than to higher film strength.

CO2 capture as bicarbonate using DMAPA with incorporation of surface activity

We present for the first time the CO2 capture and in-situ conversion into bicarbonate as a carbon-bearing product using an amine with built-in surface activity. The surface-active amine was 3-(dimethylamino)propylamine (DMAPA) modified with propylene oxide (PO) groups (DMAPA-xPO, x = 4, 6, 8, 12). Analysis of the CO2 capture capacity data with 13C Nuclear Magnetic Resonance (NMR) spectroscopy determined the bicarbonate concentrations and the generation mechanism during the CO2 capture influenced by the PO groups, establishing a relationship between CO2 solubility, pH of the solution, and steric effect. Results demonstrated the effectiveness of the built-in surface activity with an optimal PO level (DMAPA-6PO). DMAPA-6PO enhanced the bicarbonate generation by 54%, in comparison to DMAPA, under ambient conditions.

Synergism for lowering interfacial tensions between betaines and extended surfactants: The role of self-regulating molecular size

The synergism for reducing interfacial tensions (IFTs) between betaines and anionic extended surfactants with self-regulating ability was validated by experiments and molecular dynamics simulation. The IFTs of different betaines and different alkyl polypropylene ether sulfonates (APS) mixed solutions against decane and crude oil were investigated via the spinning drop method. The results demonstrate that the IFTs order of the three betaines is EDAS > ASB > XSB, which is consistent with their interfacial vacancies. Moreover, the interfacial activity of APS surfactants increases significantly and the IFTs decrease notably with the increase of propylene oxide (PO) numbers. For the betaines and APS surfactants mixed systems, the determining factor to reduce IFTs is not hydrophilic-lipophilic balance (HLB) but “size compatibility”. APS molecules can achieve a superior synergistic effect with different betaines by electrostatic attraction and size compatibility. The self-regulating characteristic of the flexible PO group enables the extended surfactants to exhibit certain synergistic effects with different betaines. What’s more, betaines and APS surfactants have a certain synergistic effect to reduce IFT values during a wide concentration ratio against crude oil. The findings of this study can help for better understanding of mixed surfactant solutions in enhanced oil recovery.

Self-assembly of anionic surfactant and its effect on oil–water interface: Implications for enhanced oil recovery

Surfactant micellization is a self-assembly process governed by complex interplay of solvent-mediated interactions. However, quantitative modeling of micelle formation and its effect on oil–water interface are not yet completely understood. In this work, dissipative particle dynamics simulations were used to investigate the self-assembly behavior of anionic surfactants of alcohol alkoxy sulfate (AAS) and its structural influence on the interfacial properties of oil–water at the mesoscopic scale. Our results indicate that with the increase of surfactant concentration, the morphology of surfactant aggregates varied from spherical micelles to rod-shaped micelles, and finally formed worm-like micelles. The larger the number of propylene oxide (PO) groups, the easier the formation of large micelles and the more tightness of formed micelles. On the oil–water interface, the interfacial tension of solutions decreased with increasing surfactant concentration below the critical micelle concentration, whereas a positive correlation was found for the tightness of surfactant arrangement. When surfactants formed micelles, the overall coverage area of AAS decreased and a lower root mean square end distance of individual PO group directly affected interfacial properties of AAS. The obtained results could provide a solid theoretical basis for the rational design of efficient surfactants in oil recovery and soft matter applications.

The mechanism for lowering interfacial tension by extended surfactant containing ethylene oxide and propylene oxide groups

In this work, the interfacial tensions (IFTs) of a series of alkyl ether carboxylates containing different ethylene oxide (EO) and propylene oxide (PO) groups (C12PO15EO5C, C12PO15EO10C and C12PO15EO15C) against n-alkanes were investigated. Based on the experimental and theoretic results, we find that for adsorbed extended surfactant molecules with both PO and EO groups, the PO group stretches towards the oil phase in a helical winding manner, which improves the size of hydrophobic part and decreases IFT. On the other hand, the whole EO group arranges in an “L” pattern with 4 EO flat at the interface and the others stretching into the water. The “dumbbell” type with the large size of the ionic head and PO group at both ends and the linear EO chain in the middle results in the high IFT values. Therefore, a sufficient PO number and few EO number are prerequisites for obtaining ultralow IFT. The addition of NaCl can decrease the size of anionic head and C12PO15EO5C solution can produce ultralow IFT against hydrocarbons at optimized salinity. However, electrolyte shows little effect on the IFTs of extended surfactants with “dumbbell” conformation at the interface because the size of linear EO group plays the crucial role. Our research has important implications for the in-depth understanding of extended surfactants and their application in high-salt reservoirs.

Complexation of tannic acid with polyoxypropylene diamine in water and application for the preparation of hierarchically structured functional surfaces

We rationalize that a water-soluble low molecular weight polyoxypropylene diamine (i.e., Jeffamine® D400 polyetheramine), capable of various types of noncovalent molecular interactions through its amine and propylene oxide groups, presents a simple yet versatile opportunity to form complexes with natural polyphenol of tannic acid (TA) and be exploited to engineer functional materials and surfaces. By investigating TA-D400 complexation behaviors in water, we demonstrate that mixing weakly acidic TA and neutral D400 solutions of stock concentrations above 1.0 mg/mL allowed easy formation of colloidally stable TA-D400 complexes. Such complexes were characterized as cationic nanoparticles of typical hydrodynamic diameters less than 300 nm. Mixing ratios were found to be less of an influencer on complexation. The TA-D400 intermolecular complexation was shown to be driven primarily by hydrophobic interaction in conjunction with ionic association. A simple immersion process can induce the formation of substrate-independent, hierarchically structured, and highly hydrophilic surfaces because of adsorption of TA-D400 complexes. Such functional surfaces not only can potentially modulate cell-material interactions shown by our brief in vitro fibroblast cell culture study, but also are feasible for in situ facile reduction of HAuCl4 to achieve integration of gold nanoparticles for function enrichment. This TA-D400 system adds a new option to the toolbox of polyphenol-mediated green technologies for surface engineering.

Stable Cycling of a 4 V Class Lithium Polymer Battery Enabled by In Situ Cross-Linked Ethylene Oxide/Propylene Oxide Copolymer Electrolytes with Controlled Molecular Structures.

Commercial lithium-ion batteries are vulnerable to fire accidents, mainly due to volatile and flammable liquid electrolytes. Although solid polymer electrolytes (SPEs) are considered promising alternatives with antiflammability and processability for roll-to-roll mass production, several requirements have not yet been fulfilled for a viable lithium polymer battery. Such requirements include ionic conductivity, electrochemical stability, and interfacial resistance. In this work, the ionic conductivity of the SPEs is optimized by controlling the molecular weight and structural morphology of the plasticizers as well as introducing propylene oxide (PO) groups. Electrochemical stability is also enhanced using ethylene oxide (EO)/PO copolymer electrolytes, making the SPEs compatible with high-Ni LiNixCoyMn1-x-yO2 cathodes. The in situ cross-linking method, in which a liquid precursor first wets the electrode and is then solidified by a subsequent thermal treatment, enables the SPEs to soak into the 60 μm thick electrode with a high loading density of more than 8 mg cm-2. Thus, interfacial resistance between the SPE and the electrode is minimized. By using the in situ cross-linked EO/PO copolymer electrolytes, we successfully demonstrate a 4 V class lithium polymer battery, which performs stable cycling with a marginal capacity fading even over 100 cycles.

Identification of more than 100 new compounds in the wastewater: Fate of polyethylene/polypropylene oxide copolymers and their metabolites in the aquatic environment

100 ethylene oxide (EO)/propylene oxide (PO) copolymer precursor and metabolites were detected in wastewater effluents. The homopolymers of EO and PO as well as the EO/PO copolymers are widely used as surfactants, e.g., for the production of cosmetics, pharmaceuticals and lubricants. Concomitantly, these compounds are discharged into the wastewater and the environmental fate of the PO homopolymers, also called polypropylene glycols (PPGs), and EO/PO copolymers is mostly unknown. In the present study, we identified hitherto unknown copolymer EO/PO homologous series and their metabolites in wastewater effluent. The identified compounds occur in homologous series and consist of PPGs and EO/PO copolymers, and their carbonylated, carboxylated and dicarboxylated metabolites. MBBR lab incubations of PPGs and EO/PO copolymers showed the successive degradation by cleavage of individual PO and EO groups, with high removal (>90%) in the initial 8 h for most of the copolymers. Carbonylated and carboxylated metabolites were degraded within 40 h. EO/PO copolymers with a higher number of EO and PO units showed a higher removal in MBBR and conventional activated sludge wastewater treatment plants. Polymers with lower molecular weight were initially formed by degradation of the EO/PO polymers. The mono-carboxylated metabolites were also detected in surface waters. Overall, our results provide new knowledge about degradation pathways of PO containing compounds and show the hitherto unnoticed occurrence of EO/PO copolymers and metabolites in the water cycle.

Foam stability of flotation frothers under dynamic and static conditions

The objective of this paper is to provide a detailed understanding of the relationship between frother type and foam stability under dynamic and static conditions. The dynamic foam stability for eighteen non-ionic frothers from different frother families was assessed using foaminess, which quantified the ratio of foam height to the gas superficial velocity. For all tested frothers, the foaminess increased as the concentration was increased. The static foam stability was assessed by measuring the half-life and the decay rate of the foams at different superficial gas velocities and concentrations. The foam stability results showed that for aliphatic alcohols, the greater the number of hydrocarbon groups, the more stable the foam was under dynamic and static conditions. For polypropylene glycols, increasing the number of propylene oxide groups increased foaminess and half-life, however, a further increase in the number of propylene oxide groups (m > 7) led to a decrease in foaminess. There was not a clear relationship between the number of propylene oxide groups and the maximum foam half-life. Interestingly, the foam decay rate coefficient increased by increasing the number of propylene oxide groups. For propylene glycol methyl ethers, foaminess, foam half-life and decay rate coefficient increased with an increase in the number of propylene oxide groups.

Enhanced recovery of a viscous oil with a novel surfactant

Steam-based recovery methods are usually employed to recover heavy and viscous oils, but they are not efficient in deep and thin oil reservoirs. Chemical flooding is studied here to improve recovery of a viscous oil (about 300 cp at the reservoir temperature of 70 °C) from a thin, high permeability, unconsolidated reservoir. A large number of novel short-hydrophobe based surfactants were designed and synthesized. As these surfactants do not require expensive aliphatic alcohols for their synthesis, they are likely to be less costly than conventional anionic surfactants. Only phenol hydrophobe-based non-ionic surfactants with varying number of propylene oxide (PO) and ethylene oxide (EO) groups are discussed in this paper. These surfactant molecules were investigated for their aqueous stability, interfacial tensions (IFT) with a viscous crude oil, and oil recovery from sandpack or sandstone cores. Surfactant phase behavior experiments with viscous crude oil showed low IFT (not ultralow) for single surfactant systems. A chemical formulation using only a single surfactant (Phenol-7PO-15EO) was chosen for corefloods in sandpacks and sandstone cores. Water flood recovered about half of the original oil and reduced the oil saturation to about 48% in the high permeability sandpacks. The tertiary surfactant polymer flood with Phenol-7PO-15EO increased the cumulative recovery to 99% for sandpacks. The oil recovery was insensitive to injection brine salinity in the range studied. As the permeability decreased, the tertiary oil recovery decreased. Surfactant-polymer formulations with this surfactant can be recommended for high permeability sandstone reservoirs with viscous oils, but not for sub-Darcy sandstones.

Thermophoresis in self-associating systems: probing poloxamer micellization by opto-thermal excitation.

Due to its exquisite sensitivity to interfacial properties, thermophoresis, i.e., particle motion driven by thermal gradients, can provide novel, exclusive, and often surprising information on the structural properties of colloidal or macromolecular fluids and on particle/solvent interactions at the nanoscale. Here, by using an all-optical thermal excitation technique, thermal lensing, we show that thermophoresis can be profitably exploited to investigate the self-association of an amphiphilic block copolymer, poloxamer P407, which takes place above a concentration-dependent critical micellization temperature (cmt). In particular we show that, around and above the cmt, the direction of the poloxamer thermophoretic motion displays a remarkable double sign inversion, which is fully correlated with a peak in the thermal expansivity of the solution marking the progressive dehydration of the propylene oxide groups of P407 and their incorporation into the micellar core. This rather puzzling behaviour of the thermophoretic mobility and of the Soret coefficient in the P407 micellization region can tentatively be explained by properly taking into account the temperature-dependent balance between micellized and nonassociated poloxamer chains.

Prediction of microemulsion phase behavior from surfactant and co-solvent structures

A predictive model was developed that captures quantitative structure-property relationships between the molecular structures of surfactants and co-solvents and microemulsion phase behavior. Both the optimum salinity and the optimum solubilization ratio (and thus the interfacial tension) are modeled as a function of both monovalent and divalent cations in the brines. A dataset consisting of 685 microemulsion phase behavior experiments with 24 unique crude oils, 85 surfactants (internal olefin sulfonates, alkylbenzene sulfonates, alcohol alkoxy sulfates and alcohol alkoxy carboxylates) and 18 co-solvents (alcohols and alcohol alkoxylates) was used for the model development and validation. Variations in the type of hydrophobe (carbon number, degree of branching, polydispersity, and aromaticity), number of propylene oxide groups, number of ethylene oxide groups, and the type of head group (sulfonate, benzene sulfonate, sulfate, carboxylate, hydroxyl) were studied. The oils were characterized using their equivalent alkane carbon number. The model includes the effect of soaps generated from the neutralization of acidic crude oils. The interfacial concentration of co-solvent is calculated using the pseudophase model. Previous models for optimum salinity have not included the effects of divalent cations, soap, and co-solvents among other limitations. Most importantly, the new model can be used to predict interfacial tension as well as optimum salinity and provide a better understanding of the impact of molecular structures on microemulsion phase behavior. The model is sufficiently accurate to provide a useful guide to experimental testing programs for the development of chemical formulations for enhanced oil recovery and other similar applications requiring low interfacial tension.

Phase equilibria and the surface tension of polypropylene polyol series in water/methanol mixtures: A consideration of structural effects

The phase equilibria and surface tension of a polypropylene polyol (PPP) series was studied in aqueous solvent systems. The PPP series was composed of ethylene oxide (EO) and propylene oxide (PO) groups, exhibiting specific interactions with both water and alcohols. Binary and ternary liquid-liquid equilibria (LLE) of the PPP series were determined via thermo-optical analysis (TOA) methods, which represented closed-loop miscibility in water and Treybal Type 1 behavior in water and methanol (MeOH), respectively. The surface tension of the ternary PPP1/water/MeOH system was measured using a well-known plate method. The dendritic characteristics of the PPP series were reflected through modeling using lattice cluster theory (LCT) for complex structures of the polymer. The phase diagrams and surface tension of the PPP series were described from binary to ternary systems based on LCT incorporated with Guggenheim's treatment using predetermined parameters. The calculated results of both systems were in good agreement with the experimental data using the same interaction energy parameters.

Critical Microemulsion Concentration and Molar Ratio of Water-to-Surfactant of Supercritical CO2 Microemulsions with Commercial Nonionic Surfactants: Experiment and Molecular Dynamics Simulation

The critical microemulsion concentration (cμc) and the molar ratio of water-to-surfactant (W0) of supercritical CO2 (scCO2) microemulsion that uses different nonionic hydrocarbon surfactants (LS-36, LS-45, LS-54, DYNOL-604, TMN-6) were examined at temperatures from 35 to 45 °C and pressures up to 19 MPa. The results show that the cμc mainly depends on the structure of the surfactant. The surfactant with more hydrophilic structure, such as the ethylene oxide (EO) group and hydroxyl, tends to produce a higher cμc. In addition, the cμc increases with the increase of the ratio of ethylene oxide (EO) group number to the propylene oxide (PO) group number of the surfactant. The capacity of the microemulsion system to dissolve water, which is characterized by W0, is related to the concentration and structure of surfactant. It is found that a higher solubility of surfactant in CO2 favors the system to dissolve water at lower pressure. At higher pressure, the stronger hydrophilicity of surfactant and the higher sur...

Dynamic interfacial tensions of alkyl alcohol polyoxypropylene–oxyehtylene ether sulfonate solutions

Abstract The dynamic interfacial tensions (IFTs) of a series of branched alkyl ether sulfonates with different number of ethylene oxide (EO) groups and propylene oxide (PO) groups, C 8 PO 3 EO 3 S, C 8 PO 3 EO 6 S, C 8 PO 6 EO 3 S and C 8 PO 6 EO 6 S, against n-alkane have been investigated by spinning drop interfacial tensiometer. The influences of surfactant concentration and salinity on IFT were expounded. The effect of alkyl chain carbon number (ACN) of the oil phase on the IFT has also been investigated. The experimental results show that the dynamic IFTs of C 8 PO 3 EO 6 S and C 8 PO 6 EO 3 S decrease and then reach a plateau with time, shown as an L-shaped; on the other hand, the dynamic IFTs go through minima and show V-shaped for C 8 PO 3 EO 3 S and C 8 PO 6 EO 6 S solutions at high bulk concentration. Moreover, V-shaped curve also appears at low bulk concentration for C 8 PO 3 EO 3 S and C 8 PO 6 EO 6 S with addition of NaCl. An increase in the length of alky chain of the oil molecules will enhance V-shaped phenomenon as well. This research suggests that the ratio of PO groups to EO groups is a key factor for controlling interfacial properties. Under optimal conditions, the transient and equilibrium ultralow IFTs can be obtained by C 8 PO 6 EO 6 S and C 8 PO 6 EO 3 S solutions respectively. Previous studies have shown that the interfacial concentration of surfactant monomers and the cross-sectional area of surfactant molecule at the interface are the two most important factors in dominating ultralow IFT. A mechanism base on the variation of cross-sectional area of surfactant molecule due to the PO groups looping away from the aqueous phase into the oil phase has been provided for understanding the ultralow IFT property for anionic–nonionic surfactants.

Surfactant (in situ)–Surfactant (Synthetic) Interaction in Na2CO3/Surfactant/Acidic Oil Systems for Enhanced Oil Recovery: Its Contribution to Dynamic Interfacial Tension Behavior

The effect of synthetic surfactant molecular structure on the dynamic interfacial tension (DIFT) behavior in Na2CO3/surfactant/crude oil was investigated. Three surfactants, a nonionic (iC17(EO)13), an alcohol propoxy sulfate (C14–15(PO)8SO4), and sodium dodecyl sulfate (SDS) were considered in this study. Sodium tripolyphosphate (STPP) was added to ensure complete compatibility between brine and Na2CO3. In Na2CO3/iC17(EO)13/oil and Na2CO3/C14–15(PO)8SO4/oil systems, a strong synergistic effect for lowering the dynamic interfacial tension was observed, in which the dynamic IFT are initially reduced to ultralow transient minima in the range 1.1 × 10−3–6.6 × 10−3 mNm−1 followed by an increment to a practically similar equilibrium value of 0.22 mNm−1 independent of Na2CO3 concentration (for iC17(EO)13) and to decreasing equilibrium values with increasing alkali concentrations (for C14–15(PO)8SO4). The observed difference in the equilibrium IFT for the two systems suggest that in both systems, the mixed interfacial film is efficient in reducing the dynamic interfacial tension to ultralow transient minima (~10−3 mNm−1) but the mixed film soap-iC17(EO)13 is much less efficient than the mixed film soap-C14–15(PO)8SO4 in resisting soap diffusion from the interface to the bulk phases. In both systems, the synergism was attributed, in part, to the intermolecular and intramolecular ion–dipole interactions between the soap molecules and the synthetic surfactant as well as to some shielding effect of the electrostatic repulsion between the carboxylate groups by the nearby ethylene oxide (13 EO) and propylene oxide (8 PO) groups in the mixed interfacial monolayer. SDS surfactant showed a much lower synergism relative to iC17(EO)13 and C14–15(PO)8SO4, probably due to the absence of ion–dipole interactions and shielding effect in the mixed interfacial layer at the oil–water interface.

New surfactant developments for chemical enhanced oil recovery

Abstract Recent advancements in surfactants for chemical enhanced oil recovery (EOR) are presented. For oils with a high equivalent alkane carbon number (EACN), surfactants with very large hydrophobes are needed to obtain the ultra-low interfacial tensions needed to reduce the residual oil saturation to nearly zero. The need increases at high temperature. Furthermore, these large hydrophobes need to be branched to promote formation of microemulsions with low to moderate viscosity as opposed to gels or other viscous structures that cause high surfactant retention. We show that such surfactants can be made from more than one type of hydrophobe in the form of either alkoxy sulfates or carboxylates. The carboxylates have the advantage of better stability at high temperature. Both the sulfates and carboxylates can be easily tailored to specific reservoir conditions and oils by adjusting the number of ethylene oxide (EO) or propylene oxide (PO) groups in the surfactant. A new correlation has been developed using an extensive data set taking into account the effects of PO number, EO number, temperature, brine salinity and the EACN of the oil on the optimum hydrophobe size. These new developments have enabled us to address a much wider range of conditions of oil characteristics, reservoir temperature, salinity and hardness level. Furthermore, the new surfactants are competitive in cost with previous EOR surfactants. Thus, these new developments have greatly advanced the commercial potential of chemical EOR.

Bacterial resistance of self-assembled surfaces using PPOm-b-PSBMAn zwitterionic copolymer – Concomitant effects of surface topography and surface chemistry on attachment of live bacteria

Three well-defined diblock copolymers made of poly(sulfobetaine methacrylate) (poly(SBMA)) and poly(propylene oxide) (PPO) groups were synthesized by atom transfer radical polymerization (ATRP) method. They were physically adsorbed onto three types of surfaces having different topography, including smooth flat surface, convex surface, and indented surface. Chemical state of surfaces was characterized by XPS while the various topographies were examined by SEM and AFM. Hydrophilicity of surfaces was dependent on both the surface chemistry and the surface topography, suggesting that orientation of copolymer brushes can be tuned in the design of surfaces aimed at resisting bacterial attachment. Escherichia coli, Staphylococcus epidermidis, Streptococcus mutans and Escherichia coli with green fluorescent protein (E. coli GFP) were used in bacterial tests to assess the resistance to bacterial attachment of poly(SBMA)-covered surfaces. Results highlighted a drastic improvement of resistance to bacterial adhesion with the increasing of poly(SBMA) to PPO ratio, as well as an important effect of surface topography. The chemical effect was directly related to the length of the hydrophilic moieties. When longer, more water could be entrapped, leading to improved anti-bacterial properties. The physical effect impacted on the orientation of the copolymer brushes, as well as on the surface contact area available. Convex surfaces as well as indented surfaces wafer presented the best resistance to bacterial adhesion. Indeed, bacterial attachment was more importantly reduced on these surfaces compared with smooth surfaces. It was explained by the non-orthogonal orientation of copolymer brushes, resulting in a more efficient surface coverage of zwitterionic molecules. This work suggests that not only the control of surface chemistry is essential in the preparation of surfaces resisting bacterial attachment, but also the control of surface topography and orientation of antifouling moieties.

Effect of some operational variables on bubble size in a pilot-scale mechanical flotation machine

This work aims to provide a relationship of how the key operational variables of frother type and impeller speed affect the size of bubble (D32). The study was performed using pilot-scale equipment (0.8 m3) that is up to two orders of magnitude larger than equipment used for studies performed to date by others, and incorporated the key process variables of frother type and impeller speed. The results show that each frother family exhibits a unique CCC95-HLB relationship dependent on n (number of C-atoms in alkyl group) and m (number of propylene oxide group). Empirical models were developed to predict CCC95 from HLB associated with other two parameters α and β. The impeller speed-bubble size tests show that D32 is unaffected by increased impeller tip speed across the range of 4.6 to 9.2 m/s (representing the industrial operating range), although D32 starts to increase below 4.6 m/s. The finding is valid for both coalescing and non-coalescing conditions. The results suggest that the bubble size and bubble size distribution (BSD) being created do not change with increasing impeller speed in the quiescent zone of the flotation.