Amount Of Ionic Surfactant Research Articles

Initiation mechanism of ultrasonically irradiated emulsion polymerization

AbstractThe emulsion polymerization of some monomers can occur without the conventional free radical initiators under ultrasonic irradiation. However, the initiation mechanism is still under controversy. In this paper, the sources of free radicals arising from ultrasonically initiated emulsion polymerization were investigated. Experimental results show that ionic surfactants play a very important role in obtaining a high polymer yield. While monomer conversion is very low in the absence of surfactants or in the presence of nonionic surfactants, it increases significantly upon addition of a little amount of ionic surfactant. FTIR and a radical trapping experiment confirm that the free radicals involved in the irradiation process originate from the decomposition of the ionic surfactants. Under ultrasonic irradiation, ionic surfactants undergo bond scission between the alkyl and ionic group, where the bond is the weakest along the chain. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2617–2624, 2005

Surfactant Adsorption at Solid−Aqueous Interfaces Containing Fixed Charges: Experiments Revealing the Role of Surface Charge Density and Surface Charge Regulation

The charge on the solid−liquid interface affects both the amount of ionic surfactant and the organization of the surfactant adsorbed at the solid−liquid interface. For most solids, the surface charge is not fixed; it is regulated by the adsorption or desorption of ions. The aim of this work is to study surfactant adsorption to surfaces that have a controlled and fixed density of covalently bound surface charges. The desired surface charge density is achieved by the use of gold−thiol self-assembled monolayers (SAMs) of different ω-groups (−OH and −N+(CH3)3). The mole fraction of −N+(CH3)3 on the mixed SAM dictates the density of covalently bound charges. The charge on −N+(CH3)3 is fixed and does not self-regulate, but the total surface charge can be changed through adsorption of other ions. We have studied the adsorption of sodium dodecyl sulfate (SDS) to the interface between these model surfaces and aqueous solutions of SDS. Atomic force microscopy (AFM) of the adsorbed surfactant reveals no surface micelles above the critical micelle concentration, cmc, over a wide variety of −N+(CH3)3 densities. This leads us to hypothesize that lateral mobility of ions other than surfactant at the interface is important for the formation of surface micelles of ionic surfactants. Adsorption isotherms of SDS (with no added salt) measured by surface plasmon resonance (SPR) show a plateau region that ends at about cmc/25. In this plateau region, the surface excess of SDS is equal to the known fixed surface charge. There is a second plateau region above the cmc. In this concentration range, the surface excess is approximately twice the fixed surface charge. Desorption experiments starting above the cmc show rapid desorption of SDS into water until the surface excess is equal to the fixed surface charge. The rapid desorption is followed by a much slower desorption.

Small-Angle Neutron Scattering and Fluorescence Studies of Mixed Surfactants with Dodecyl Tails

The mixed micelles formed in solutions of the anionic surfactant sodium dodecylsulfate (SDS) and the nonionic surfactant dodecylmalono-bis-N-methylglucamide (DBNMG) were studied by surface tension, fluorescence, and small-angle neutron scattering. Measurements of the critical micelle concentration (CMC) by surface tension and fluorescence show that these two surfactants mix nonideally. The experimental values of the CMCs for surfactant mixtures for all compositions are less than the ideal prediction proposed by Clint (J. Chem. Soc. 71, 1327 (1975)). Regular solution theory (for example, Penfold et al., Langmuir 11, 2498 (1995)) can be used to calculate the composition of the micelle at the CMC. The micellar composition thus calculated differs significantly from that at higher total surfactant concentrations, the latter being much closer to the stoichiometric composition. The polarity of the micellar environment, as perceived by a solubilized fluorescence probe, is identical for both the single-component and the mixed micelles. The scattering data show that the mixed micelles are comparable in size to the pure nonionic micelle and slightly larger than the anionic micelle. Parallel studies with deuterated SDS showed no evidence of segregation or local ordering within the mixed micelle. The effective charge on the mixed micelle is determined by the amount of ionic surfactant within the micelle. Addition of 0.1 M NaCl to these systems has no effect on the CMC, micelle ellipticity, and aggregation number—a behavior very different from that observed for simple SDS solutions.

Investigation of surfactant alkyl chain length and counterion effects on the thermogelling EHEC system

Ethylhydroxyethylcellulose (EHEC) forms a reversible thermogelling system in water in the presence of ionic surfactants. In an effort to minimise the amount of ionic surfactant needed to produce a thermogelling system with timolol in salt form, we have examined in detail the system with respect to the alkyl chain length and counterion of the ionic surfactant. Two salts of timolol were also investigated, timolol (hydrogen)maleate and timolol chloride. It was found that in order to form a gel with a small amount of ionic surfactant, a number of criteria have to be fulfilled, e.g., (i) the ionic drug should typically be a co-ion to the ionic surfactant, (ii) the counterion of the drug and the ionic surfactant should preferably be inorganic and with a low polarisability and (iii) the ionic surfactant should have a low CMC but a Krafft temperature not higher than room temperature.

The effect of electrolytes on the cloud point of mixed solutions of polypropylene glycol and ionic surfactants

The cloud points of polypropylene glycol (PPG) in the presence of small amounts of ionic surfactants, including dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and sodium cetyl sulfate (SCS) have been determined. The results show that the cloud point of PPG will be elevated if a certain amount of ionic surfactant is added. The longer the hydrocarbon chain length of the ionic surfactant homologues, the stronger the effect is, and the effect of anionic surfactants is stronger than that of cationic surfactants with the same hydrocarbon chain length. On the other hand, the cloud point remains unaltered on addition of the same amount of inorganic salt. However, when salts are added to the PPG solution in the presence of a certain amount of ionic surfactants, the cloud point decreases in a ratio depending on the concentration of salts, the nature of the ions and, particularly, the valency of the ions with charges opposite in sign to the charges of the surface-active ion. For systems of 0.01% PPG + SCS and 0.1% PPG + SCS, the valency of the cation of salts is decisive, and the order of the effect is: 1/3 LaCl 3 > 1/2 CaCl 2, > NaCl. For the system of 0.1% PPG + CTAB, the valency of the anion of electrolytes plays the dominant role, and the order of the depressing effect is: 1/3 K 3Fe(CN) 6 > 1/2 Na 2SO 4 > NaBr. For the system of 0.01% PPG + CTAB, a striking phenomenon was observed, i.e. the cloud point was enhanced rather than decreased by the addition of electrolytes. An explanation in terms of the enhancing adsorption of surface-active ions on the PPG chains due to the addition of electrolytes was suggested.