Absorption of Surfactants

The addition of the cationic surfactant cetylpyridinium chloride (CPC) to aqueous dispersions ofpolyNIPAM-co-AAc microgel particles leads to absorption of the CPC into the microgel particles [35]. Uptake of the surfactant depends on two distinct attractive interactions between the surfactant molecules and the microgel particles  

Similar results were observed with the uptake and release of an anionic surfactant into and from poly(NIPAM-co-2VP) microgel particles [36]. A comparison has also been made between the effect of added CPC on the hydrodynamic diameter of the free microgel particles in dispersion and the thickness, as determined from ellipso-metry measurements, of deposited monolayers of the same microgel particles on cationically-modified, oxidized silicon surfaces. The behavior of the microgel layers reflects the dispersion properties of the particles in the presence of CPC [35]. 

---

It has been shown that the exchange of counter ions for the ions of a surfactant can induce a sharp collapse of the polyelectrolyte gel. Simultaneously, a very effective absorption of surfactants from the solution is observed. Complexes of the networks with surfactants possess the ability to solubilize different organic substances. The later fact is of important practical interest, for example for removing surfactants and impurities from water. 

In a study of interaction between a small molecule and a macromolecule, equilibrium dialysis is a fundamentally important method and it has been applied to many studies. But in the case of surfactant ligands, it has a drawback as much as a week may be required to attain an equilibrium.5>33 Gel chromatography provides another technique for obtaining binding isotherm, but has been used mostly to determine an amount of binding saturation. It is supposed that absorption of surfactants into the gel phase may obstruct reaching equilibrium at lower surfactant concentrations. 

In 1956, Fuerstenau coined the term hemimicelle to describe the two-dimensional aggregates that he proposed were responsible for the rise through several orders of magnitude in the observed absorption of surfactant molecules on certain mineral oxide surfaces from aqueous solutions. The study on coadsorption of pinacyanol chloride (cyanine dye) with sodium p-(l-propylnonyl)-benzenesulfonate (dissolved in water) on AI2O3 surface reveals that surfactant adsorption is independent of the concentration of pinacyanol chloride, and the surfactant solution remains clear at total surfactant concentration ([SurfJx) below CMC, whereas the solid surface becomes dyed blue, the color characteristic of... 

Humectants and low vapor pressure cosolvents are added to inhibit drying of ink in the no22les. Surfactants or cosolvents that lower surface tension are added to promote absorption of ink vehicle by the paper and to prevent bleed. For improvements in durabiUty, additional materials such as film-forming polymers have been added. Ink developments are providing ink-jet prints with improved lightfastness, waterfastness, and durabiUty. As a result, such prints are beginning to rival the quaUty of electrophotographic prints. 

THE INFLUENCE OF SURFACTANTS NATURE AND CONCENTRATION ON THE ANALYTICAL SIGNAL IN THE ATOMIC ABSORPTION DETERMINATION OF LEAD, CADMIUM AND CHROMIUM... 

In the latter function, the reagent behaves as a surfactant and forms a cationic micelle at a concentration above the critical micelle concentration (1 x 10 4M for CTMB). The complexation reactions occurring on the surface of the micelles differ from those in simple aqueous solution and result in the formation of a complex of higher ligand to metal ratio than in the simple aqueous system this effect is usually accompanied by a substantial increase in molar absorptivity of the metal complex. 

Davies et al. (D9) have recently measured the rates of absorption of various gases into turbulently stirred water both with carefully cleaned surfaces and with surfaces covered with varying amounts of surfactants. That hydrodynamic resistances, rather than monolayer resistances, are predominant in their work is consistent with the high sensitivity of kL to very small amounts of surface contamination and also with the observation that a limit to the reduction in kL is found (D7, D9). This is in agreement with the results of Lindland and Terjesen (L9), who found that after a small concentration of surfactant had been used further additions caused but little change in terminal velocity (L9). 

American Society for Testing and Materials, Standard for Qualitative Classification of Surfactants by Infrared Absorption, D2357-74 (Reapproved 1989). 1916 Race St., Philadelphia, PA 19103. 

For example, for alkyl (8-16) glycoside (Plantacare 818 UP) non-ionic surfactant solution of molecular weight 390 g/mol, an increase in surfactant concentration up to 300 ppm (CMC concentration) leads to a significant decrease in surface tension. In the range 300 < C < 1,200 ppm the surface tension was almost independent of concentration. In all cases an increase in liquid temperature leads to a decrease in surface tension. This surface tension relaxation is a diffusion rate-dependent process, which typically depends on the type of surfactant, its diffusion/absorption kinetics, micellar dynamics, and bulk concentration levels. As the CMC is approached the absorption becomes independent of the bulk concentration, and the surfactant... 

M Kraml, J Dubuc, D Beall. Gastrointestinal absorption of griseofulvin. I. Effect of particle size, addition of surfactants and corn oil on the level of griseofulvin in the serum of rats. Can J Biochem Physiol 40 1449-1451, 1962. 

The absorption of drugs from the rectal [32] cavity has been studied in some detail. Muranishi et al. [34] have shown that a significant increase in the absorption and lymphatic uptake of soluble and colloidal macromolecules can be achieved by pretreating the rectal mucosal membrane with lipid-nonionic surfactant mixed micelles. They found no evidence of serious damage of the mucosal membrane. Davis [30] suggested that the vaginal cavity could be an effective delivery site for certain pharmaceuticals, such as calcitonin, used for the treatment of postmenopausal osteoporosis. 

Penetration enhancers are low molecular weight compounds that can increase the absorption of poorly absorbed hydrophilic drugs such as peptides and proteins from the nasal, buccal, oral, rectal, and vaginal routes of administration [186], Chelators, bile salts, surfactants, and fatty acids are some examples of penetration enhancers that have been widely tested [186], The precise mechanisms by which these enhancers increase drug penetration are largely unknown. Bile salts, for instance, have been shown to increase the transport of lipophilic cholesterol [187] as well as the pore size of the epithelium [188], indicating enhancement in both transcellular and paracellular transport. Bile salts are known to break down mucus [189], form micelles [190], extract membrane proteins [191], and chelate ions [192], While breakdown of mucus, formation of micelles, and lipid extraction may have contributed predominantly to the bile salt-induced enhancement of transcellular transport, chelation of ions possibly accounts for their effect on the paracellular pathway. In addition to their lack of specificity in enhancing mem-... 

Nevertheless, there are reports on enhancement of ocular drug absorption by bile salts [33], surfactants [200], and chelators [149], Newton et al. [35] demonstrated that Azone, an enhancer widely tested in transdermal drug delivery [201], increased the ocular absorption of cyclosporine, an immunosuppressant, by a factor of 3, thereby prolonging the survival of a corneal allograft. In 1986, Lee et al. [34] reported that 10 pg/mL cytochalasin B, an agent capable of condensing the actin microfilaments, increased the aqueous humor and iris-ciliary body concentrations of topically applied inulin (5 kDa) by about 70% and 700%, respectively, in the albino rabbit. 

S Hirai, T Yashiki, H Mima. (1981). Mechanisms for the enhancement of the nasal absorption of insulin by surfactants. Int J Pharm 9 173-184. 

Choi and Funayama [19] also measured sodium atom emission from sodium dodecylsulfate (SDS) solutions in the concentration range of 0.1-100 mM at frequencies of 108 kHz and 1.0 MHz. The sodium line intensity observed at 1 MHz was nearly constant in the concentration range from 3 to 100 mM and was considerably higher than that at 108 kHz. This frequency dependence of the intensity is opposite that for NaCl aqueous solution. The dynamical behavior of the absorption and desorption of surfactant molecules onto the bubble surface may affect the reduction and excitation processes of sodium atom emission. This point should be clarified in the future. 

---