sodium-dodecyl-sulfate and n-hexadecane

The Oil Transfer Technique (OTT) was developed by Taisne et al. [1] to measure coalescence during emulsification and has been applied since in several studies. One of the main drawbacks of this technique is that it only gives a qualitative measure of coalescence. This paper proposes a new evaluation method of OTT experimental results for estimating qualitative coalescence rates, e.g. for investigating the scaling of coalescence with emulsification parameters (such as homogenizing pressure, and emulsifier concentration). The method is based on comparison with simulated OTT experiments using bivariate Population Balance Equation models. Simulations have been performed under a wide variety of conditions in order to investigate the influence of assumptions on coalescence and fragmentation kernels. These investigations show that the scaling of coalescence rates could be determined accurately when the scaling of efficient residence time of drops in the active region of homogenization is known. The proposed evaluation method is also exemplified by analyzing OTT data from two previously published studies.

Topics: Alkanes; Computer Simulation; Emulsifying Agents; Emulsions; Hydrocarbons, Brominated; Kinetics; Lactoglobulins; Models, Chemical; Muramidase; Oils; Sodium Dodecyl Sulfate; Thermodynamics; Water

It is often proposed that oil solubilization in anionic and nonionic micelles proceeds by different mechanisms, with diffusion of the oil molecule thought to control the former, and the latter interfacially controlled. In order to investigate this hypothesis, the effect of aqueous phase viscosity, salt, and surfactant concentration during the solubilization process was studied. The progressive decrease in average droplet size of nearly monodisperse emulsions during solubilization in SDS or Tween 20 micellar solutions was monitored by light scattering, and the change in turbidity was measured by UV-vis spectrophotometer. The solubilization rates were analyzed using a population balance approach to calculate the mass transfer coefficients. Increasing the aqueous viscosity by adding sucrose reduced the mass transfer coefficients of n-tetradecane and n-dodecane but had a smaller effect on n-hexadecane. The strong dependence of the solubilization rate for the shorter chain length alkanes on aqueous viscosity supported a mechanism in which the oil undergoes molecular diffusion before being taken up by micelles. The dependence of the solubilization kinetics on surfactant concentration appeared consistent with this mechanism but yielded a slower micellar uptake rate than previously predicted theoretically. As the solute chain length increased in nonionic surfactant solutions, an interfacial mechanism mediated by micelles appeared to contribute substantially to the overall rate. Addition of salt only slightly increased the solubilization rate of n-hexadecane in SDS solutions and, thus, indicated a weak role of electrostatic interactions for ionic surfactants on the overall mechanism.

Topics: Alkanes; Emulsions; Kinetics; Micelles; Nephelometry and Turbidimetry; Oils; Sodium Dodecyl Sulfate; Solubility; Solutions

The effect of long-chain alcohols (C(n)OH for n=8, 10, 12, 14, 16, 18) on the partitioning of sodium dodecyl sulfate (SDS) to the oil/water interface in oil-in-water macroemulsions was investigated and related to emulsion droplet size and total interfacial area (TIA) contributed by SDS. Alcohols were solubilized in hexadecane and emulsified in SDS solutions. Ultrafiltration was carried out in centrifuge tubes having nanoporous filters with a 30,000 molecular weight cutoff (MWCO), so that emulsion droplets would not pass through, and only SDS that is in the bulk water phase as monomers or micelles (i.e., not at the interface) could pass through. The results showed a chain-length compatibility effect; the maximum amount of SDS partitioned to the interface when dodecanol (C(12)OH) was added to the oil. The results also showed that partitioning of SDS is affected only when dodecanol is added. All other alcohols had no significant influence on SDS partitioning to the oil/water interface. Droplet size measurements revealed a minimum in droplet size for emulsions with added C(12)OH. In order to explain the results, it was proposed that the penetration of alcohol molecules into the interfacial film occur at the interface, resulting in more cohesive molecular packing at the interface, and the minimum droplet size and maximum partitioning of SDS at the oil/water interface for C(12)OH/SDS emulsion system. The TIA provided by the SDS molecules, as determined from our ultrafiltration method, was two orders of magnitude greater than that calculated from the droplet size measured by light scattering. Possible explanations for this disparity are discussed.

Topics: Alkanes; Dodecanol; Emulsions; Fatty Alcohols; Membranes, Artificial; Molecular Weight; Oils; Particle Size; Scattering, Radiation; Sodium Dodecyl Sulfate; Solubility; Surface Properties; Surface-Active Agents; Ultrafiltration; Water; Wettability

The aim of this investigation was to determine whether sublethal concentrations of chlorhexidine (Cx), hexetidine (Hx), cetylpyridinium chloride (Cc), sodium dodecyl sulfate (SDS), sanguinarine (Sg), sodium fluoride (NaF), and ammonium fluoride (NH4F) could affect hydrophobicity and adhesion of Streptococcus sanguis and Streptococcus mutans to saliva-coated hydroxyapatite (S-HA). Determination of the minimum inhibitory concentrations (MICs) showed that both species were susceptible to all agents tested. Growth in the presence of sub-MIC concentrations of Cx, SDS, Cc, NaF, or NH4F did not change significantly the hydrophobicity of S. sanguis cells when compared to the control which lacked any agent. However, growth in the presence of Hx or Sg resulted in a significant reduction in their hydrophobicity. Sub-MIC levels of SDS or Sg in the growth medium resulted in S. mutans cells with increased affinity for hexadecane compared with the control. The adherence of S. sanguis was changed significantly only by Hx or Sg, resulting in less cells adhering to S-HA. However, S. mutans cells previously incubated with NaF, NH4F, or Sg showed a higher adherence to S-HA than the control. The mechanisms of interference with adherence are at present not completely understood. Thus, antimicrobial agents at sub-MIC concentrations can interfere selectively with hydrophobicity and/or adhesion of oral streptococci.

Topics: Adsorption; Alkaloids; Alkanes; Ammonium Compounds; Anti-Infective Agents, Local; Bacterial Adhesion; Benzophenanthridines; Cetylpyridinium; Chlorhexidine; Dental Plaque; Durapatite; Fluorides; Hexetidine; Humans; Isoquinolines; Quaternary Ammonium Compounds; Saliva; Sodium Dodecyl Sulfate; Sodium Fluoride; Streptococcus mutans; Streptococcus sanguis; Surface Properties; Water

The adherence of Streptococcus sanguis to saliva-coated hydroxylapatite was markedly reduced by treatment of the cells with trypsin. In Scatchard plots of adherence data, protease-treated S. sanguis did not exhibit the characteristic positive slopes, suggesting that trypsin prevented cooperative interactions between the cells and artificial pellicle. Trypsin also reduced the tendency of S. sanguis to bind to hexadecane and to octyl-Sepharose. When sodium dodecyl sulfate was used to elute S. sanguis from columns of octyl-Sepharose, it was observed that the elution profiles of trypsin-treated cells were more complex than those of control cells. Water and salts were incapable of removing the cells from octyl-Sepharose. The results suggest that adherence to saliva-coated hydroxylapatite, binding to hexadecane and to octyl-Sepharose depend on trypsin-susceptible cell surface molecules.

Topics: Adhesiveness; Alkanes; Bacterial Proteins; Durapatite; Hydroxyapatites; Membrane Proteins; Saliva; Sepharose; Sodium Chloride; Sodium Dodecyl Sulfate; Streptococcus sanguis; Trypsin