Non-ionic solutes

Gibbs equation of surface concentration This equation relates the surface tension (y) of a solution and the amount (T) of the solute adsorbed at unit area of the surface. For a single non-ionic solute in dilute solution the equation approximates to... 

Electro-osmosis has been defined in the literature in many indirect ways, but the simplest definition comes from the Oxford English Dictionary, which defines it as the effect of an external electric held on a system undergoing osmosis or reverse osmosis. Electro-osmosis is not a well-understood phenomenon, and this especially apphes to polar non-ionic solutions. Recent hterature and many standard text and reference books present a rather confused picture, and some imply directly or indirectly that it cannot take place in uniform electric fields [31-35]. This assumption is perhaps based on the fact that the interaction of an external electric held on a polar molecule can produce only a net torque, but no net force. This therefore appears to be an ideal problem for molecular simulation to address, and we will describe here how molecular simulation has helped to understand this phenomenon [26]. Electro-osmosis has many important applications in both the hfe and physical sciences, including processes as diverse as water desahnation, soil purification, and drug delivery. 

S. Murad, R. Madhusudan, J. G. Powles. A molecular simulation to investigate the possibility of electro-osmosis in non-ionic solutions with uniform electric fields. Mol Phys 90 671, 1997 R. Madhususan, J. Lin, S. Murad. Molecular simulations of electro-osmosis in fluid mixtures using semi-permeable membranes. Eluid Phase Equil 150 91, 1998. 

A. Ben-Naim and Y. J. Marcus, Solvation thermodynamics of non-ionic solutes, Chem. 

Vesicles are permeable to apolar non-ionic solutes, and, if ionic, can bind counterions at the inner and outer surfaces. Permeability to ions depends critically upon vesicle structure. 

The fractional ionization, a, of ionic micelles is increased by hydrophobic non-ionic solutes which decrease the charge density at the micellar surface and the binding of counterions (Larsen and Tepley, 1974 Zana, 1980 Bunton and de Buzzaccarini, 1982). Consistently, microemulsion droplets are less effective at binding counterions than otherwise similar micelles. 

To investigate ionic equilibria so as to obtain information about the interactions of ions with each other, with non-ionic solutes and with the solvent. 

Just as in aqueous solutions, the activity of solute i (acl) in non-aqueous solutions is related to its (molar) concentration (sj by aCii = yCiiCi, where g is the activity coefficient that is defined unity at infinite dilution. For non-ionic solutes, the activity coefficient remains near unity up to relatively high concentrations ( 1 M). However, for ionic species, it deviates from unity except in very dilute solutions. The deviation can be estimated from the Debye-Hiickel equation, -log yci = Az2 /1/2/ (1+aoBf1 2). Here, I is the ionic strength and / (moll-1), a0 is the ion size parameter... 

According to eqn.(3.90), k is proportional to the concentration of the pairing ion, with the proportionality constant being determined by the distribution coefficient for the neutral molecule (Kxy) and by the dissociation constant for this molecule into the two separate ions X and Y (K ). The first factor is affected by the same parameters as retention in the LC of non-ionic solutes (section 3.2). The latter factor will be determined by the nature of the solute ion and the pairing ion and by the composition (ionic strength, pH, modifier content) of the aqueous phase. 

From the analysis of the specifications in Table 12.2, IPC - MS hyphenation requires (1) specific optimization of mobile phase composition, selecting only volatile components, (2) devising strategies to minimize eluent fiow, and (3) an interface to make IPC effluent amenable to MS detection. The goals of the interface are (1) separation of the analyte from the bulk eluent, (2) ion evaporation for ionic species or ionization of non-ionic solutes, and (3) fragmentation and quantitative transfer of analyte fragments to the mass analyzer. 

For a non-ionic solute, it is plausible to attribute the viscosity reduction to more shorter ranged interactions such as the dipole-dipole interaction This suggests... 

Retention behaviour of non-ionic. solutes in rever.sed-plui.se chromatography... 

In the case of dissolved substances, the standard state of a solute is that in which the effective concentration , known as the activity, is unity. For non-ionic solutes the activity and molarity are usually about the same for concentrations up to about 1M, but for an ionic solute this approximation is generally valid only for solutions more dilute than 0.001-0.0 lAf, depending on electric charge and size of the particular ion. 

Disperse Red 13 (DR) was irradiated by UV at 253.7 nm in solutions containing different non-ionic solutions. Figure 28 shows the decay curves of DR in water and various surfactant solutions. In general, the photodegradation rates of DR follows pseudo first-order kinetics. The decay rates of DR, therefore, can be determined by the integrated first-order decay expression ... 

Non-ionic solutes which can enter the micelle increase a, because they reduce the density of charged head groups at the micellar surface, and therefore its ability to attract counterions. 

This equation is formally similar to Eqn. 2 for micellar binding of non-ionic solutes. In this treatment /8, i.e., [N, ]/([D] — cmc), has the formal limits of 0 and 1, but the lower limit will never be reached because counterions are always present in solution, even when [surfactant] < cmc, and the upper limit would be reached only at [surfactant] well above the solubility limit. 

Both explanations are reasonable. Critical micelle concentrations are decreased by addition of both electrolytes and hydrophobic non-ionic solutes to water [15]. But submicellar aggregates could coexist in solution with monomeric and micellized surfactant, although their concentration is probably low [2,23]. They could interact with, and be stabilized by, hydrophobic substrates. 

The application of relaxation measurements to non-ionic solutes, also incidentally showing up solvent effects, is illustrated by some results on... 

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