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Surfactants in Cosmetic Products
Published in Heather A.E. Benson, Michael S. Roberts, Vânia Rodrigues Leite-Silva, Kenneth A. Walters, Cosmetic Formulation, 2019
Ricardo Pedro, Kenneth A. Walters
The molecular structure of the hydrophobic chain, the polarity of the hydrophilic group and the ‘environment’ (composition, pH, temperature, presence of co-solutes, etc.) of the solution dictate surfactant solubility. While many surfactants have appreciable solubility in water, such a characteristic can change significantly with changes in the hydrophobic group. In general, the aqueous solubility of ionic substances increases as the water temperature rises, dependent on the energy of their crystalline reticulum and its heat of hydration. Ionic surfactants frequently undergo a sudden and discontinuous increase in their solubility at a specific temperature, which is known as Krafft temperature, TK or Krafft point. Below the Krafft point, the solubility of the surfactant is determined by the crystalline energy and heat of hydration of the system, in other words, it is a thermodynamic-driven process. The concentration of the surfactant monomeric species in solution (an individual dissolved surfactant molecule) is limited to an equilibrium value determined by such properties. Above the Krafft temperature the solubility of the monomer increases and reaches a point at which another sudden change takes place with the formation of aggregate species.
Pharmacology for venous and lymphatic diseases
Published in Ken Myers, Paul Hannah, Marcus Cremonese, Lourens Bester, Phil Bekhor, Attilio Cavezzi, Marianne de Maeseneer, Greg Goodman, David Jenkins, Herman Lee, Adrian Lim, David Mitchell, Nick Morrison, Andrew Nicolaides, Hugo Partsch, Tony Penington, Neil Piller, Stefania Roberts, Greg Seeley, Paul Thibault, Steve Yelland, Manual of Venous and Lymphatic Diseases, 2017
Ken Myers, Paul Hannah, Marcus Cremonese, Lourens Bester, Phil Bekhor, Attilio Cavezzi, Marianne de Maeseneer, Greg Goodman, David Jenkins, Herman Lee, Adrian Lim, David Mitchell, Nick Morrison, Andrew Nicolaides, Hugo Partsch, Tony Penington, Neil Piller, Stefania Roberts, Greg Seeley, Paul Thibault, Steve Yelland
Detergent sclerosants are surfactants normally used for reducing surface tension.1−5 They are adsorbed at the cell membrane to disrupt the normal architecture of the lipid surface causing it to desquamate in sheets. They are amphiphilic organic compounds with a hydrophilic head end which is attracted to water and a hydrophobic tail end away from water. At a certain concentration, they clump into spheres called micelles and this is termed the critical micelle concentration. An ionic surfactant such as STS has a critical temperature termed the Krafft temperature below which it does not form micelles and above which solubility increases greatly as large amounts of surfactant can be incorporated into micelles. A non-ionic surfactant such as polidocanol does not have a Krafft point but ex hibits a cloud point which is the temperature above which its solubility decreases so that it precipitates as a ‘cloud’. Because of this, some practitioners add small quantities of STS to polidocanol to improve its micellar function, as addition of an ionic to a non-ionic surfactant will raise its cloud point. However, the biological activity of surfactants is now known to be due to monomers in solution, with micelles functioning as a reservoir to replenish surfactant adsorbed from solution.
Fecal microbiota transplantation: a review on current formulations in Clostridioides difficile infection and future outlooks
Published in Expert Opinion on Biological Therapy, 2022
Adèle Rakotonirina, Tatiana Galperine, Eric Allémann
Alternatively, the use of saturated monoglycerides as an encapsulation matrix to incorporate probiotics in ice cream was described by Marino et al. [94]. Briefly, long-chain saturated monoglycerides develop a highly hydrated lamellar phase, which jellifies when cooled below the Krafft temperature. They obtained multiphase droplets where the monoglyceride layer forms a protective gel system containing hydrophobic and hydrophilic layers, allowing the introduction of hydrophilic, lipophilic or amphiphilic molecules to enhance bacterial viability. While the encapsulation matrix effectively protected Lactobacillus rhamnosus during freeze-drying and storage, homogenization parameters still need to be optimized to minimize the mechanical stress applied to the cells. In regard to this topic, stability studies of the formulation in ice cream over 14 days were detailed and showed that the use of milk fat is an effective way of protecting probiotics, since they observed a loss of viability of 0.8 log CFU [100].