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Droplet interactions in water-in-carbon dioxide (W/C) microemulsions formed with a perfluoropolyether-based surfactant for droplet volume fractions from 0.05 to 0.10 are studied with small-angle neutron scattering (SANS) to understand the mechanism of microemulsion stability. The water-to-surfactant ratio (Wo) is fixed at 12.5. Droplet interactions increase as the upper critical solution pressure is approached with decreasing pressure at constant temperature, increasing temperature at constant pressure, or increasing droplet volume fraction. These interactions are quantified in terms of the structure factor at zero momentum vector, S(0), and the correlation length, ξ, for an Ornstein−Zernicke structure factor, or the square-well depth for the structure factor of a square-well potential. Near the critical solution pressure, the interaction strength (A) approaches the value predicted for a hard-sphere fluid with a van der Waals attractive term. The observed interaction strength between droplets is larger in...

The melt-state phase behavior of isotactic polypropylene (i-PP) blended with a series of poly(ethylene/ethylethylene) random copolymers has been investigated using small-angle neutron scattering (SANS). These PEExx copolymers, where xx is the percentage of ethylethylene (EE) units, were prepared by hydrogenation of anionically polymerized polybutadienes with controlled amounts of 1,2 addition. Random phase approximation (RPA) fits to the scattering data for blends of i-PP with a deuterated, low molecular weight PEE90 at 180 °C indicate a statistical segment length for i-PP that is 10% less than that reported previously. Scattering from blends of i-PP with higher molecular weight PEE90 and PEE73 at 180 °C can be quantitatively fit using the RPA theory with χ as the only adjustable parameter, indicating melt miscibility. PEE46 and PEE62 are strongly and marginally immiscible, respectively, with i-PP at 180 °C. These results establish a “window” in EE content in which these random copolymers can form single ...

We have performed a series of small angle neutron scattering (SANS) experiments on blends of linear and branched polyethylenes to investigate the level of branching that is required to phase separate the system. These results confirm that the mixtures are homogenous for all compositions when the branch content is low (i.e., 2. In each case, the resolution of conventional SANS pinhole cameras (Qmin ∼ 10-3 A-1) is adequate to determine the state of mixing, even for systems with large domains.

The issue of multiple equilibrium phases in compositionally heterogeneous random copolymers has been addressed by a series of small-angle neutron scattering (SANS) experiments. An ethylene−hexene (EH) copolymer, representative of many linear low-density polyethylenes (LLDPE) has been shown to contain a dispersed minority phase (volume fraction, φ ∼ 0.02) consisting of highly branched, amorphous material. The dispersed phase is eliminated to a good approximation by xylene extraction, which removes the low molecular weight and highly branched molecules. The extracted material contains a much higher fraction of branched molecules and hence has a greater proportion of the dispersed phase (φ ∼ 0.2). These findings support the prediction of liquid−liquid phase separation for compositionally polydisperse LLDPEs, whereby the more highly branched molecules in the distribution may phase segregate, even if the overall branch content is low.

The effects of the addition of crown ether 1,4,7,10,13,16-hexaoxacyclooctadecane on the structure of aqueous solutions of surfactants sodium dodecyl sulfate and dodecyltrimethylammonium bromide have been studied by small angle neutron scattering. By modeling the scattering intensities, it was possible to derive, simultaneously, both structural properties and information on the distribution of crown ether between the micellar and aqueous phases. In the case of sodium dodecyl sulfate, an appreciable amount of crown ether was found to be localized in the micellar phase, though it was not possible to establish whether it was in the core or in the shell ; there was no evidence of crown ether localization in dodecyltrimethylammonium bromide micelles. The above observations indicate that although, at least in principle, the crown ether methylene groups could interact hydrophobically in the micellar core with the surfactant alkyl chains, the ability of crown ethers to form metal complexes might also lead, in sodium dodecyl sulfate solutions, to electrostatic interactions in the external palisade between the crown ether-sodium ion complex and the surfactant head groups. The absence of crown ether from dodecyltrimethylammonium bromide micelles indicates that the macrocyclic molecules interact with sodium dodecyl sulfate micelles via the formation of a complex between the sodium ion and the crown ether and rules out the possibility of hydrophobic interaction in the micellar core.

The structure of ultrathin cellulose acetate membranes, known as active layer membranes, has been investigated using small-angle neutron scattering. These membranes are known to have structural and functional similarity to the surface or "skin" layer in commercial reverse-osmosis (RO) membranes and hence are useful model systems for understanding the structure of the RO membrane skin layer. Active layer membranes were studied after swelling them with either DzO or CD30D. The results in both cases clearly indicated the presence of very small (10-20 A) porous structures in the membrane. The presence of such pores has been a subject of long-standing controversy in this area. The data was analyzed using a modified Debye-Bueche analysis and the resultant membrane structure was seen to agree well with structural information from electron microscopic studies. Finally, a possible explanation for the differences in scattering observed between the DzO swollen membranes and the CD30D swollen membranes has been presented.

Pore structure in cellulose acetate ultrafiltration (UF) and reverse-osmosis (RO) membranes has been studied using small-angle neutron scattering. Scattering experiments were carried out on dry membranes as well as on membranes swollen with deuterated solvents (D[sub 2]O and CD[sub 3]OD). In addition, the RO membranes were studied both before and after annealing (a process of heating a membrane in a water bath at [approximately]75 C to improve its separation properties). The pore surface in UF membranes was found to be smooth and nonfractal, as evidenced by the fourth power law behavior at high Q. Values of average pore sizes obtained for dry and solvent swollen membranes agree well with pore sizes obtained by other methods. For cellulose acetate RO membranes in their dry state, the unannealed membrane appears to consist of two discrete pore size distributions in the intermediate and high Q region while the annealed membrane contains a much wider distribution of pore sizes. These results give a good account of the changes occurring in the structure of RO membranes as a result of annealing, and agree well with the prediction of other authors.

Crystalline morphologies of poly(e-caprolactone) (PCL) and deuterated polycarbonate (d-PC) blends were studied by SANS and SAXS. Measurements were conducted at both room temperature and temperatures above the melting point (60°C) of PCL. Due to the different contrast between the phases for neutrons and X-rays, SANS exhibited a monotonic drop in intensity with increasing scattering angle while SAXS showed lamellar (peak) scattering. A two-correlation length model provided an excellent fit for the SANS data over the entire composition range

Mini-emulsified lateres of anionically polymerized deuterated and protonated polystyrene (DPS=185 000, HPS= 00 000) were prepared by direct mini-emulsification. Films containing 6% deuterated particle were annealed at 144 o C for various periods of time. The average depth of penetration of the deuterated polystyrene chains and tensile strength buildup were characterized during the course of annealing. When the present results were compared with those of the conventional emulsion polymerized system, the directly mini-emulsified later had greater interdiffusion rates and higher tensile strength than the emulsion polymerized latex system at similar annealing times

SANS measurements of deuterated polystyrene in undeuterated polystyrene solvents that vary in molecular weight are reported. The second virial coefficients decrease with increasing molecular weight of the solvent as is expected, but the functional dependence of this decrease is not in accord with Flory-Huggins theory or simple modifications of it. The results are qualitatively similar to earlier work of Kirste and Lehnen on the poly(dimethylsiloxane) system

Melange de PEO avec PMMA protone ou deuterie. PMMA est incorpore dans la phase amorphe entre les lamelles cristallines

Small-angle neutron scattering (SANS) experiments on solutions of polystyrene (PSH) and its deuterated homologue (PSD) in deuterated toluene have been performed over a wide range of concentration. Several redundant measurements demonstrated that the high-concentration technique of extracting single-chain scattering functions is highly reliable. Radii of gyration and screening lengths were fitted to power laws and were found to be R/sub g//sup 2/ approx. c/sup -0.156/ and xi approx. c/sup -0.70/. The results differ significantly from predictions by scaling theory, though the dependence of xi on c is in good accord with that previously found by other researchers. These experiments were also analyzed by using recent theoretical results of Muthukumar and Edwards. Measurements at different concentrations yielded a reasonably consistent value of the excluded volume interaction parameter. 41 references, 10 figures, 7 tables.