Surfactants suspension stabilization

Because the core of an aqueous micelle is extremely hydrophobic, it has the abiHty to solubiHze oil within it, as weU as to stabilize a dispersion. These solubilization and suspension properties of surfactants are the basis for the cleansing abiHty of soaps and other surfactants. Furthermore, the abiHty of surfactants to stabilize interfacial regions, particularly the air—water interface, is the basis for lathering, foaming, and sudsing. 

Ether carboxylates are used not only in powdered detergents but in liquid laundry detergents for their hard water stability, lime soap dispersibility, and electrolyte stability they improve the suspension stability and rheology of the electrolyte builder [130,131]. Formulations based particularly on lauryl ether carboxylate + 4.5 EO combined with fatty acid salt and other anionic surfactants are described [132], sometimes in combination with quaternary compounds as softeners [133,163]. Ether carboxylates show improved cleaning properties as suds-controlling agents in formulations with ethoxylated alkylphenol or fatty alcohol, alkyl phosphate esters or alkoxylate phosphate esters, and water-soluble builders [134]. 

A cosolvent, typically ethanol, may be used to bring drug into solution. A small number of surfactants (sorbitan trioleate, oleic acid, and lecithin) may be dispersed in propellant systems and can aid in suspension stability and in valve lubrication. 

The choice of carrier liquid is primarily based on the suspension stability for colloids or solvent goodness for macromolecule solutions. Moreover, surface-charged colloidal particles are also sensitive to ionic strength and addition of surfactants. 

Kollidon 30 is also used for this purpose. It can be combined with all conventional suspension stabilizers (thickeners, surfactants, etc.). 

Typical suspension stabilizers for the production of EPS are water-soluble, surface-active macromolecules, such as poly (vinyl alcohol) (PVA), hydroxyethyl-cellulose (HEC) and polyvinylpyrrolidone (PVP), or natural products, such as gelatin [36-40], and insoluble inorganic powders, such as tricalcium phosphate (TCP), also called picketing stabilizer , mostly in combination with surfactants called extenders [33-35,44], or a combination of these [129]. The differences and specialties of these stabilizing mechanism are described briefly below ... 

Surfactants which stabilize the alumina suspensions either maintains or increases the copper removal rate when polished with these slurries, as compared to the corresponding surfactant-free slurries. This is maintained in the presence of added chemistries (hydrogen... 

Sedimentation ratio is often used to assess suspension stability. Byron reported the sedimentation ratios for a 1% sodium fluoresein suspension formulation with different amounts of surfactant (sorbitan trioleate) after standing for 20 days at room temperature. The suspension formulation with the lowest sedimentation ratio had thebest-flocculated system. However, all formulations were easily redispersible one complete revolution of the container was sufficient to produce a homogeneous dispersion. There was no clear difference in the times taken to reach apparent sedimentation equilibrium. Physical stability of the formulation was determined according to ... 

Suspension stability is governed by the same forces as in other disperse systems such as emulsions. There are differences, however, as coalescence obviously cannot occur in suspensions the adsorption of stabilising polymers and surfactants may also occur in a different... 

The adsorption or incorporation of molecules, such as surfactants and polymers, can create a steric repulsion that prevents aggregation [288-290]. This can also increase suspension stability, important for metered-dose inhaler formulations [291]. Lung surfactant coating on the surface of poly(lactic-co-glycolic) acid microparticles has been shown to dramatically improve dry powder aerosol performance by reducing particle-particle interactions [134,292],... 

The main formulation challenge with HFA pMDI has been the poor solubility of the surfactants that were used in CFC products. Most pMDI formulations are suspensions of fine powder in propellant, and in order to obtain acceptable dose uniformity these suspensions usually require surfactants to stabilize them. The inability to use conventional surfactants has therefore led to a range of diverse formulation approaches. These encompass drug solubilization using cosolvents (Qvar is an example), new surfactants, coating particles with surfactant, and particle engineering (Fig. 3). However, as is the case with most... 

Petcoke water slurries were prepared at mass ratios ranging from 30 70 to 70 30. EnerSol determined that mixtures of up to 50 50 were pumpable and fed without problems to the RRT reactor. Mixtures with higher petcoke concentrations were difficult to maintain in suspension. Experimentation with surfactants and stabilizers resulted in a pumpable mixture at 65% petcoke and 35% water. 

Liquid scrubbing is also known as one of the most efficient methods for very fine-particle collection, but they are gathered in the form of a suspension that can be rather used for nasal, pulmonary, or parenteral delivery. The suspension stability is often a delicate issue because no chemical or biological degradation shall occur, nor particle decantation, which requires the use of complex mixtures, including a buffer (especially for biomolecules), preservatives (antimicrobial, antioxidant, etc.), and surfactants. Several systems have been described (37,86-88) ... 

Instead of low Mw surfactants or in combination with those natural or semisynthetic colloids are used in suspension polymerization of PVC and in emulsion polymerization of vinyl acetate homo- and co-polymers as protective colloids also called suspension stabilizers or suspending agents. 

U.S. 5302323 (1994) Hartung et al. (Abbott Lab.) 0.5-2.5% selenium sulfide two suspending agents di(hydrogenated) tallow phthalic acid amide and one selected from hydroxypropylbmethylcellulose and Mg Al silicate pH 4.0-6.5 buffer system with Na citrate and citric acid at least 18% anionic surfactant Improved pH stability, suspension stability, lathering, and conditioning (three-in-one)... 

The amount of substance present in the micellar state, cmjc = mnmic / NA may exceed the concentration of it in the molecular solution by several orders of magnitude. The micelles thus play a role of a reservoir (a depot) which allows one to keep the surfactant concentration (and chemical potential) in solution constant, in cases when surfactant is consumed, e.g. in the processes of sol, emulsion and suspension stabilization in detergent formulations, etc. (see Chapter VIII). A combination of high surface activity with the possibility for one to prepare micellar surfactant solutions with high substance content (despite the low true solubility of surfactants) allows for a the broad use of micelle-forming surfactants in various applications. 

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