Using neutron reflectometry we have resolvedto high resolutionthe internal structure of self-assembled polyelectrolyte multilayer films and have developed a detailed molecular picture of such systems by analyzing the data with a composition-space refinement technique. We show that such surface films consist of stratified structures in which polyanions and polycations of individual layers interdigitate one another intimately. Nevertheless, the deposition technique leads to results that are predictable, if well-defined and constant environmental conditions are maintained during the preparation. For alternating layers of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), adsorbed onto atomically flat surfaces, a roughening of successively deposited layers leads to a progressively larger number of adsorption sites for consecutive generations of adsorbed polymer, and thus to an increase in layer thicknesses with an increasing number of deposited layers. Because of the interpenetration of adjacent polyelectrolyte species, however, this increase settles quickly into an equilibrium thickness. In fully hydrated films (100% relative humidity), water occupies ≥40% of the volume within the films. About twice as much water (by volume) is associated with PSS as with PAH. Incorporated inorganic salt plays a minor role only, if any. The equilibrium thickness of the deposited layer structure may be fine-tuned via the ionic strength, I, of the solutions used for the preparation. We show that the dependence of the thickness d lp per layer pair on I is linear, with a sensitivity, Δd lp/ΔI = 16 Å × L/mol. Concurrently with the layer thickness the interface roughness σ between adjacent layers increases:  σ ∼ 0.4 × d lp. In contrast to the ionic strength of the deposition solutions, the degree of polymerization of the polyanions used in the preparation plays a minor role only in determining the overall structure of the deposited films. The results reported here are quantitatively consistent with those of a recent study (Tarabia et al. J. Appl. Phys. 1998, 83, 725−732), if one assumes that the hydration of the polyelectrolyte molecules in the sample films investigated in the two studies is similar.

Studies are presented on the two-dimensional (2-D) crystalline packing arrangements of enantiomerically pure and racemic α-amino acid RHC(NH3 +)CO2 - monolayers on water and on glycine aqueous solutions, as determined by synchrotron grazing incidence X-ray diffraction. The amphiphiles have been designed such that their racemic mixtures form 2-D crystals which are either heterochiral (for R = C n H2 n +1−, n = 10, 12, 16) due to the tendency for herringbone chain arrangements via glide symmetry or homochiral (for R = C n H2 n +1CONH(CH2)4−, n = 11, 17, 21) by virtue of hydrogen bonding by translation of the amide group in the chains leading to a spontaneous separation into islands of opposite chirality. The two different crystalline motifs led to a correlation between their packing arrangements and induced oriented nucleation of 3-D crystals of α-glycine by these monolayers. The relevance of the present results to the possibility of ordering and spontaneous segregation of racemates of the natural hydrophobic α-amino acids at the air-solution interface is discussed.

In this paper, a set of complementary techniques was used to characterize surface and bulk structures of an anisotropic Soy Protein Isolate (SPI)-vital wheat gluten blend after it was subjected to heat and simple shear flow in a Couette Cell. The structured biopolymer blend can form a basis for a meat replacer. Light microscopy and scanning electron microscopy provided a detailed view of structure formation over the visible surfaces of the SPI-gluten blend. Protein orientation in the direction of the flow was evident and fibrous formation appeared to exist on the macro- and micro-scale. Furthermore, according to texture analysis, the structured biopolymer obtained from the Couette Cell after processing at 95 °C and 30 RPM for 15 min has high tensile stress and strain anisotropy indices (∼2 and ∼1.8, respectively), comparable to those of raw meat (beef). The novel element in this work is the use of the neutron refraction method, utilizing spin-echo small angle neutron scattering (SESANS), to provide a look inside the anisotropic biopolymer blend complementing the characterization provided by the standard techniques above. With SESANS, it is possible to quantify the number of fibre layers and the orientation distribution of fibres. For a specimen thickness of 5 mm, the obtained number of fibre layers was 36 ± 4 and the standard deviation of the orientation distribution was 0.66 ± 0.04 radians. The calculated thickness of one layer of fibres was 138 μm, in line with SEM inspection.

Monolayers of the long-chain alcohols on water promote nucleation of ice. In order to determine the minimum size of crystalline alcohol monolayer domains that induce ice nucleation, we reduced their size in two distinct ways. One approach encompassed embedding the pure hydrocarbon alcohol, C n H2 n +1OH (n = 20, 31), into a matrix of an immiscible monolayer of perfluoro alcohol C10F21C2H4OH, which is inert as an ice nucleator. The second set of experiments involved the introduction of random defects into the monolayer crystalline domains of C29H59OH through the use of the fully miscible guest alcohol molecule, C31H63OH, as additive. By these methods we estimated that ∼450 water molecules are necessary to form a stable ice cluster at the onset of induced ice nucleation at a temperature just below 0 °C.

An overview will be given of new instruments using Larmor precession of polarized neutrons in precession regions with inclined front and end faces. These instruments concern small angle scattering, neutron reflectometry and high-resolution diffraction. The advantages of the first application, spin echo small angle scattering (SESANS), with respect to conventional SANS, is the range of applicability and orders of magnitude higher available intensity. The reflectometry application makes it possible to measure the momentum dependent intensity without hindrance of the waviness of the sample also with the high intensity of SESANS. The high resolution application enables one to measure very high resolution diffraction (10 −5 relative in momentum space) without angular of wavelength confinement of the beam, thus with very high intensity.

Abstract:The formation of Langmuir monolayers at the air-water interface has long been believed to be limited to amphiphilic molecules containing a hydrophobic chain and a hydrophilic headgroup. Here we report the formation of crystalline mono-and multilayer self-assemblics of oligothiophenes, a class of aromatic nonamphiphilic molecules, selfaggregated at the air-water interface. As model systems we have examined the deposition of quaterthiophene ( S , ) , quinquethiophene (SJ, and sexithiophene (S,) from chloroform solutions on the water surface. The structures of the films were dctermined by surface pressure-area isotherms, by scanning force microscopy (SFM) after transfer of the films onto atomically smooth mica, by cryo-transmission electron microscopy (Cryo-TEM) on vitreous ice, and by grazing incidence synchrotron X-ray diffraction (GID) directly on the water surface. S, forms two polymorphic crystalline multilayers. In polymorph K. of structure very similar to

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The volume distribution of precipitates in high-strength low-alloy (HSLA) steels has been studied using small-angle neutron scattering (SANS) at high temperatures. Three samples with different niobium concentrations (0.00, 0.05, and 0.10 wt pct) were slowly heated from a temperature of 910 ЊC to 1200 ЊC. With increasing temperatures, the scattered intensity strongly decreases as the precipitates gradually dissolve or coarsen. A comparison between the particle distribution of the three different materials suggests that the particles with a radius below 10 nm mainly correspond to Nb(C,N) precipitates and the larger particles to MnS precipitates. Subsequent cooling from 1200 ЊC to 910 ЊC only leads to a small increase in the scattered intensity. Quenching from the austenite to the ferrite phase and reheating to the austenite phase, however, produces a large increase in the formation of the small precipitates with a radius below 10 nm.