Hans Schott

Swelling kinetics of polymers

Abstract The equilibrium swelling of semicrystalline or crosslinked polymers and of their gels upon immersion in liquids has been investigated extensively. On the other hand, few studies have dealt with the kinetics of swelling. Swelling kinetics are important for designing controlled-release devices for drugs and agricultural pesticides based on swellable polymer matrices, and for predicting the release rates of the active ingredients. Theoretical considerations, based on diffusion-controlled swelling, show that first-order kinetics does not apply, even though deviations during the initial and even middle stages of the swelling process may be relatively small. Extensive studies of swelling rate and equilibrium swelling of supported and unsupported gelatin films have been published. The rate is controlled by stress relaxation in the swelling polymer network. The rate equations of these studies, which have also been reported to apply to cellulose, are shown to represent second-order kinetics with respect t...

Effect of Inorganic Additives on Solutions of Nonionic Surfactants

The effect of salts on the nonionic surfactant octoxynol 9 was studied by the changes they produced in its cloud point (CP): CP increases indicate salting in. The temperatures by which the sodium salts of water structure-breaking (chaotropic) anions increased the CP of 2.0% octoxynol solutions were measured as a function of salt concentration. The curves representing changes in CP versus salt molality rose to a maximum in a parabolic fashion, followed by steep decreases. Their ascending branches, corresponding to salting in, were caused by a disruption of the water structure due to the chaotropic effect of the anions combined with the effect of elevated CP temperatures. The descending branches were due to salting out by Na+. The net CP increases due to the chaotropic effect of the anions were calculated at each concentration by subtracting the CP decrease due to Na+from the observed CP increase of the respective Na+salts. With the exception of ClO4−, the plots of CP changes produced by the chaotropic anions rose in a nearly linear fashion to a maximum and then levelled off. The levelling off occurred at the salt concentration and CP temperature leading to the maximum disruption of the water structure of which each anion was capable. The chaotropic anions were ranked in the following order according to their capacity for increasing the CP: SCN−> I−> [Fe(CN)5NO]2−> ClO4−> BF4−. Even though the thiosulfate anion is a very soft Lewis base, it lowered the CP in direct proportion to its molality; i.e., it enhanced the structure of water and promoted salting out at all concentrations.

Salting in of nonionic surfactants by complexation with inorganic salts

Abstract The following cations were found to salt in polyoxyethylated compounds, raising the cloud point of aqueous solutions of i -octylphenol.10 EO and that of (EO) 400 previously reduced to 45° by the addition of sodium sulfate: H + , Pb 2+ , Cd 2+ , Mg 2+ , Ni 3+ , Al 3+ , Ca 2+ , and Li + . Only Na + , K + , and NH 4 + salted the polyoxyethylated compounds out, lowering their cloud points. The ether linkages act as ligands, possibly polydentate, for the cations. The capacity of cations to salt in polyoxyethylated compounds runs parallel with their capacity to form complexes with simple ethers such as ethyl ether, dioxane, and cineole, and to bind water in solid hydrates. All three phenomena are widespread.

Effect of inorganic additives on solutions of nonionic surfactants — XVI. Limiting cloud points of highly polyoxyethylated surfactants

Abstract As their degree of polyoxyethylation is increased, the cloud points (CPs) of three homologous series of nonionic surfactants (NSs) rise steeply at first but then level off, converging asymptotically to the temperature range of 114–118°C, which corresponds to the CP of polyethylene oxide with a molecular weight of 10 4 . Six of the 14 surfactants investigated were octoxynols, five were nonoxynols and three were polyoxyethylene dodecyl ethers. Ten had an average number of oxyethylene units per molecule p >20 and a CP>100°C. Three of these CPs were measured directly on 2.00% surfactant solutions sealed into ampoules. To avoid additional measurements under pressure, the other surfactants had their CPs lowered below the normal boiling point of their 2.00% solutions by adding the salting-out, CP-lowering salt NaNO 3 at various concentrations, measuring the depressed CPs and extrapolating them to zero salt concentration. The CPs decrease linearlv with increasing molality m of NaNO 3 up to ca. 2.5 m and more steeply at higher concentration. For a given concentration of NaNO 3 , larger p values result in more extensive salting out: The more highly polyoxyethylated a surfactant is, the greater the reduction in CP it undergoes. As p increases, the curves of CP in water versus p for the octoxynols and nonoxynols rise steeply and nearly linearly, reaching 100 and 103°C at p =16, and then begin to level off. The sharpest inflections are at p =22–25. The nonoxynol curve becomes horizontal at p ≅40 and 115°C while the octoxynol curve rises gently from 3°C below the nonoxynol curve to merge with it at p =90 and 114°C. The CPs of the three polyoxyethylene dodecyl ethers are slightly higher than those of the polyoxyethylated alkylphenols with comparable p values, peaking at 118°C. The most highly polyoxyethylated surfactant of each series contains 95% polyoxyethylene. Their CP range of 114–118°C equals that of polyethylene oxides with molecular weights between 8000 and 20 000. Published quantitative CP– p relations for polyoxyethylated NSs cover only CP values below 100°C and p values below 16. They fail to predict the levelling off of the CPs as the p values rise above 16.

Hydration of micellar nonionic detergents

Abstract The extent of hydration of micelles of polyoxyethylated detergents at room temperature was estimated from previously published and new data. The calculations were based on the relation between intrinsic viscosity, partial specific volume, and hydration, or on the difference between the volume of the hydrated micelles, obtained from intrinsic viscosity or ultracentrifugation, and the anhydrous micellar molecular weights, determined by light scattering or dye solubilization. The extent of hydration varied from 0.4 to 6.3 water molecules per micellar ether linkage, compared to 2.0 for aqueous solutions of model ethers. On the assumption that the micelles consist of a spherical hydrocarbon core and an outer spherical shell of polyoxyethylene chains, the plot of number of water molecules per ether linkage as a function of the ratio—volume of the polyoxyethylene shell to surface area of the hydrocarbon core—went through a maximum.

Lyotropic numbers of anions from cloud point changes of nonionic surfactants

Abstract The Hofmeister or lyotropic series arrange ions according to their ability to salt out polymers [1] and also according to their effects on various bulk, surface and interfacial properties of water, aqueous solutions and colloidal dispersions [2]. The quantitative assignment of lyotropic numbers to individual ions is based on a cumbersome procedure involving flocculation of agar or gelatin sols [3,4]. Nonionic surfactants owe their solubility to hydration of the polyoxyethylene moiety, which decreas with increasing temperature. On heating, they precipitate reversibly at the cloud point (CP). The CP is raised and lowered by salting-in and salting-out electrolytes, respectively (5–7). The CP shift values of anions were found to be related by a smooth curve to their lyotropic numbers. In view of the rapidity and accuracy of measuring CPs and determining the effect of anions thereon, anionic CP shift values can be used to obtain lyotropic numbers.

The effect of protein denaturants on the cloud point of a nonionic surfactant

Abstract The effect of various protein denaturants (11 urea and thiourea derivatives, acetamide, and guanidinium chloride) on the cloud point of a nonionic surfactant was investigated. In the range of 0.1–0.5 m , all but one additive increased the cloud point in direct proportion to their concentration. The proportionality constant b between cloud point increase and additive molality is a measure of the effectiveness of the additives to salt the surfactant in. It was proportional to the excess partial molal heat capacity of the additives at infinite dilution, which discloses the effect of the additives on the structure of water. Small b values were found for additives with negative excess heat capacities, which are structure breakers. The increase in b with increasing number and/or size of the alkyl groups in urea and thiourea is ascribed to increased micellar binding.

Deflocculation of swelling clays by nonionic and anionic detergents

Abstract The deflocculation of sodium montmorillonite suspensions by two polyoxyethylated nonionic detergents and polyethylene glycol was studied by measuring turbidity, viscosity, and sedimentation volume. Maximum deflocculation was produced by the nonionic detergents at the composition at which the insertion of two closepacked detergent layers between adjacent lattice layers of the clay was complete. At higher nonionic: clay ratios, some flocculation occurred. The extinction coefficient of clay suspensions increased on dilution as well as on addition of the nonionics. Dilution at constant detergent: clay ratio increased the extinction coefficient to the same extent as dilution of suspensions containing only clay. The relative viscosity of suspensions increased linearly with clay concentration at constant detergent: clay ratio. With the clay concentration expressed as volume fraction, the maximum slope or intrinsic viscosity observed for suspensions of clay without detergent was 177. Deflocculation involved reduction of lateral dimensions as well as of thickness. Two anionic detergents did not interact with the clay.

Adsorption of a nonionic surfactant by cotton

Abstract The adsorption and desorption of polyoxyethylated 1-dodecanol containing an average of 14 ethylene oxide (EO) units on cotton was studied over a concentration range of two decades in distilled water at 25°C. The method consisted in equilibrating cotton fabric or chopped fiber with surfactant solutions and determining the equilibrium surfactant concentration by surface tension or by the cobalt blue colorimetric analysis. Surface tension is more affected by surfactant molecules of few EO units, whereas the colorimetric method emphasizes the more highly polyoxyethylated surfactant molecules; the observed discrepancy between the two methods (10%–30%) was caused by preferential adsorption of surfactant of shorter EO chain length onto cotton. The adsorption was almost completely reversible. The adsorption isotherm leveled off at 35 mg. surfactant/100 g. cotton near the critical micelle concentration. In view of the specific surface area of cotton, this level of adsorbed surfactant is of the order of the amount required to cover the cotton completely with a close-packed monolayer of surfactant molecules lying flat against the substrate.

A linear relation between the cloud point and the number of oxyethylene units of water-soluble nonionic surfactants valid for the entire range of ethoxylation

The following linear equation correlates the cloud point (CP) of water-soluble polyoxyethylated nonionic surfactants (NSs) with the average number p of oxyethylene units per molecule: (p - p0)/CP = a + b(p - p0). Here p0 is the smallest value of p that confers solubility in cold water: In a homologous series of NSs, it belongs to the surfactant with CP = 0 degrees C. Plots of CP versus p for five representative homologous series of NSs consist of three segments: A steeply ascending, nearly straight line, a transition region that ranges from p = 15-22 to p = 20-28, and a nearly horizontal plateau that approaches asymptotically the CPs of polyethylene glycols with molecular weights between 30,000 and 4400. These CPs range from 113 to 130 degrees C. Most CPs for NSs were taken from the literature or measured on commercially available samples; eight CPs above 100 degrees C were measured on newly synthesized surfactants. Previously published linear equations correlating CP with p cover only NSs with p < 16 and CPs < 100 degrees C: They apply only to the ascending segment of the CP versus p plots. Our equation covers the entire plots and applies to the full range of NSs, including extensively polyoxyethylated NSs with p > or = 100. It can be used for selecting specific NSs for high-temperature applications. The hydrophile-lipophile balance of the surfactant with p = p0 oxyethylene units, namely, HLB0, is a novel quantitative measure of the hydrophobicity of the hydrocarbon moiety of the relevant homologous NS series. Its value reflects the size, composition, and structure of the hydrocarbon moiety.