Electron diffraction studies of supersonic jets. IV. Conformational cooling of n‐butane

Expansions through small tapered nozzles (∼10−2 cm inlet diameter) have produced conformational cooling of gas phase n‐butane to estimated conformational temperatures as low as 180 K. Relaxation into the lower energy trans form was seen with neat butane and with addition of up to ∼30% helium or neon. Thin plate nozzles of comparable diameter do not seem to produce the same effects, presumably because the more rapid cooling they bring about is accompanied by many fewer collisions. Conformational analyses carefully checked for and took into account butane cluster scattering, which if present and ignored, artificially increases the apparent trans mole fraction. At higher concentrations of monatomic carrier gas the cluster scattering becomes strong enough to interfere seriously with the determination of conformational composition. Analysis of the present data and a reanalysis of earlier, conventional, gas electron diffraction data both gave the room temperature trans mole fraction as 64% (3σ=9%) in agreement with a recent spectroscopic inference of 68%.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70828/2/JCPSA6-78-3-1270-1.pd

Electron diffraction studies of supersonic jets. III. Clusters of n‐butane

Expansions of n‐butane from small nozzles were observed to generate large clusters, provided that enough helium or neon carrier gas accompanied the butane to remove the heat of condensation rapidly and to produce low temperatures. Although expansions of neat n‐butane led to substantial conformational cooling under some circumstances, clusters were never seen without carrier gas. Both thin‐plate and tapered glass nozzles yielded clusters. Diffraction patterns of the clusters are characteristic of a liquidlike structure perhaps as cold as 100 K. No evidence for inclusion of carrier gas atoms in the clusters was found. Cluster scattering signals are stronger and show less noise than those which could be expected from bulk liquid by x‐ray or neutron diffraction. Their interference terms are dominated by nearest neighbor intermolecular C...H contacts. Information about the distribution of these contacts has not yet been deduced in computer simulations of liquid butane but should soon become available for comparison.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70517/2/JCPSA6-78-3-1265-1.pd

The interfacial structure of polymeric surfactant stabilised air-in-water foams

Small-angle neutron scattering was used to probe the interfacial structure of nitrogen-in-water foams created using a series of tri-block polymeric surfactants of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (EOx–POy–EOx) range, from which the nature of the polymeric interface could be characterised. The data follow a pronounced Q−4 decay, along with a number of inflexions and weak but well-defined peaks. These characteristics were well-described by a model embodying paracrystalline stacks of adsorbed polymer layers, whose formation is induced by the presence of the air–water interface, adsorbed at the flat air–water (film lamellae) interface. A minimum of approximately five paracrystalline polymer layers of thickness of the order of 85–160 Å, interspersed with somewhat thicker (400 Å) films of continuous aqueous phase were found to best fit the data. The thickness of the layer (L) was shown to follow a relationship predicted by anchor block dominated polymer adsorption theories from non-selective solvents, L EO1PO1/3. The insight gained from these studies should permit a more rational design of polymeric stabilisers for hydrophilic polyurethane foams

Segregation versus interdigitation in highly dynamic polymer/surfactant layers

Many polymer/surfactant formulations involve a trapped kinetic state that provides some beneficial character to the formulation. However, the vast majority of studies on formulations focus on equilibrium states. Here, nanoscale structures present at dynamic interfaces in the form of air-in-water foams are explored, stabilised by mixtures of commonly used non-ionic, surface active block copolymers (Pluronic®) and small molecule ionic surfactants (sodium dodecylsulfate, SDS, and dodecyltrimethylammonium bromide, C12TAB). Transient foams formed from binary mixtures of these surfactants shows considerable changes in stability which correlate with the strength of the solution interaction which delineate the interfacial structures. Weak solution interactions reflective of distinct coexisting micellar structures in solution lead to segregated layers at the foam interface, whereas strong solution interactions lead to mixed structures both in bulk solution, forming interdigitated layers at the interface

Construction and physiochemical characterisation of a multi-composite, potential oral vaccine delivery system (VDS)

An increasing human population requires a secure food supply and a cost effective, oral vaccine delivery system for livestock would help facilitate this end. Recombinant antigen adsorbed onto silica beads and coated with myristic acid, was released (∼15% (w/v)) over 24 h at pH 8.8. At pH 2, the myristic acid acted as an enteric coating, protecting the antigen from a variety of proteases. The antigen adsorbed onto silica particles, coated in myristic acid had a conserved secondary structure (measured by circular dichroism (CD) spectroscopy) following its pH-triggered release. Small angle neutron scattering (SANS) was used to measure the thickness of the adsorbed antigen, finding that its adsorbed conformation was slightly greater than its solution radius of gyration, i.e. 120–160 Å. The addition of myristic acid led to a further increase in particle size, with scattering data consistent with an acid thickness slightly greater than a monolayer of fully extended alkyl chains and a degree of hydration of around 50%. Whilst adsorbed onto the silica and coated in myristic acid, the protein was stable over 14 days at 42 °C, indicating a reduced need for cold chain storage. These data indicate that further investigation is warranted into the development of this technology

Probing competitive interactions in quaternary formulations

Hypothesis The interaction of amphiphilic block copolymers of the poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) group with small molecule surfactants may be “tuned” by the presence of selected alcohols, with strong interactions leading to substantial changes in (mixed) micelle morphology, whilst weaker interactions lead to coexisting micelle types. Experiments The nature and the strength of the interactions between Pluronic P123 (EO20PO70EO20) and small molecule surfactants (anionic sodium dodecylsulfate, SDS, C12SO4Na), (cationic dodecyltrimethylammonium bromide, C12TAB) and (non-ionic polyoxyethylene(23)lauryl ether, Brij 35, C12EO23OH) is expected to depend on the partitioning of the short, medium and long chain alcohols (ethanol, hexanol and decanol respectively) and was probed using tensiometry, pulsed-gradient spin-echo nuclear magnetic resonance (PGSE-NMR) and small-angle neutron scattering (SANS). Findings The SANS data for aqueous P123 solutions with added alcohols were well described by a charged spherical core/shell model for the micelle morphology. The addition of the surfactants led to significantly smaller, oblate elliptical mixed micelles in the absence of alcohols. Addition of ethanol to these systems led to a decrease in the micelle size, whereas larger micelles were observed upon addition of the longer chain alcohols. NMR studies provided complementary estimates of the micelle composition, and the partitioning of the various components into the micelle