Structural Studies of Nonionic Dodecanol Ethoxylates at the Oil–Water Interface: Effect of Increasing Head Group Size

The conformation of charged surfactants at the oil-water interface was recently reported. With the aim to assess the role of the head group size on the conformation of the adsorbed layer, we have extended these studies to a series of non-ionic dodecanol ethoxylate surfactants (C12En, ethylene oxide units n from 6 to 12). The study was performed using neutron reflectometry to enable maximum sensitivity to buried interfaces. Similarly to charged surfactants, the interface was found to be broader and rougher compared to the air-water interface. Irrespectively of the head group size, the tail group region was found to assume a staggered conformation. The conformations of the head group were found to be significantly different compared to the air-water interface, moving from a globular to an almost fully extended conformation at the oil-water interface. The stretching of the head groups is attributed to the presence of some hexadecane oil molecules, which may penetrate all the way to this region. It is proposed here that the presence of the oil, which can efficiently solvate the surfactant tail groups, plays a key role in the conformation of the adsorbed layer and is responsible for the broadening of the interface

Surfactant mixtures at the oil–water interface

NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Colloid and Interface Science. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in JOURNAL OF COLLOID AND INTERFACE SCIENCE, VOL 398, (2013) DOI 10.1016/j.jcis.2013.01.06

Further Insights into the Catalytic Reduction of Aliphatic Polyesters to Polyethers

The synthesis of medium- and short-chain aliphatic polyethers is industrially limited to the ring-opening polymerization of cyclic ethers with a high ring strain, such as oxiranes, oxetanes, or tetrahydrofuran. This structural limitation can be overcome by the gallium bromide catalyzed reduction of different polyesters into their corresponding polyethers. Herein, the scope of applicable polyesters is broadened, while the influence of the polyester structure on the reduction system is examined. The reactivity as well as side reactions, i.e., overreduction leading to chain cleavage, are shown to depend on the distance of the ester groups in the repeating unit of the polyester. Two different reducing agents, namely triethylsilane and 1,1,3,3-tetramethyldisiloxane, are studied and compared in terms of reactivity and work-up procedures, showing advantages and disadvantages depending on the reduced polyester properties. The reaction conditions are optimized and the reduction can be scaled-up to 60 g polyester. All products are thoroughly characterized

Smart nanogels at the air/water interface: structural studies by neutron reflectivity

STFC for provision of consumables and subsistence and access to the ILL facility through the STFC managed UK contribution to the facility (EXP: 9-13-530, 9-11-1721 and 9-11-17446). The European Commission (FP7 Marie Curie Actions, NANOLEM, PIEF-GA-2013-627146 to KZ) and the Chinese Scholarship Council (studentship to HS) are gratefully acknowledged for financial support

Comparative adsorption of saturated and unsaturated fatty acids at the iron oxide/oil interface

A detailed comparison of the adsorption behavior of long straight chain saturated and unsaturated fatty acids at the iron oxide/oil interface has been considered using a combination of surface study techniques. Both depletion isotherms and polarized neutron reflectometry (PNR) show that the extent of adsorption decreases as the number of double bonds in the alkyl chains increases. Sum frequency generation spectroscopic measurements demonstrate that there is also an increase in chain disorder within the adsorbed layer as the unsaturation increases. However, for the unsaturated analogues, a decrease in peak intensity is seen for the double bond peak upon heating, which is thought to arise from isomerization in the surface-bound layer. The PNR study of oleic acid adsorption indicates chemisorbed monolayer adsorption, with a further diffuse reversible adsorbed layer formed at higher concentrations.Mary Wood is grateful for funding from the Oppenheimer Trust. The PNR data were collected using the V6 instrument at the Helmholtz-Zentrum Berlin (experiment number MAT-04-2131).This is the author accepted manuscript. The final version is available from the American Chemical Society via http://dx.doi.org/10.1021/acs.langmuir.5b0443

Comparative Adsorption of Saturated and Unsaturated Fatty Acids at the Iron Oxide/Oil Interface.

A detailed comparison of the adsorption behavior of long straight chain saturated and unsaturated fatty acids at the iron oxide/oil interface has been considered using a combination of surface study techniques. Both depletion isotherms and polarized neutron reflectometry (PNR) show that the extent of adsorption decreases as the number of double bonds in the alkyl chains increases. Sum frequency generation spectroscopic measurements demonstrate that there is also an increase in chain disorder within the adsorbed layer as the unsaturation increases. However, for the unsaturated analogues, a decrease in peak intensity is seen for the double bond peak upon heating, which is thought to arise from isomerization in the surface-bound layer. The PNR study of oleic acid adsorption indicates chemisorbed monolayer adsorption, with a further diffuse reversible adsorbed layer formed at higher concentrations.Mary Wood is grateful for funding from the Oppenheimer Trust. The PNR data were collected using the V6 instrument at the Helmholtz-Zentrum Berlin (experiment number MAT-04-2131).This is the author accepted manuscript. The final version is available from the American Chemical Society via http://dx.doi.org/10.1021/acs.langmuir.5b0443