Showing papers by "Chalk River Laboratories published in 2004"
TL;DR: In this article, a literature survey is devoted to the problem of heat transfer of fluids at supercritical pressures including near critical region, and a discussion on the general trends of various thermophysical properties at near critical and pseudocritical points is also included.
415 citations
TL;DR: In this article, the state-of-the-art of heat transfer in nucleate pool-boiling is assessed and a literature review of the parametric trends points out that the major parameters affecting the Heat Transfer Coefficient (HTC) under poolboiling conditions are heat flux, saturation pressure, and thermophysical properties of a working fluid.
283 citations
15 Dec 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the formation of strain-induced martensite in austenitic stainless steel was studied, and the work hardening behavior was characterized, as well as the spatial distribution of the martensites as a function of prior strain.
Abstract: The strengthening that results from the low-temperature formation of strain-induced martensite in austenitic stainless steel was studied. Specifically, the work hardening behaviour was characterized, as well as the spatial distribution of the martensite as a function of prior strain. Neutron diffraction measurements revealed the degree of elastic strain partitioning between the austenite and martensite. It was found that a sufficiently high initial dislocation density leads to a localization of the martensite transformation in the form of a Luders front. The martensite acts as an elastic reinforcing phase as it supports a higher stress than the austenite tensile loading, even though the martensite co-deforms plastically with the austenite. A model was developed that predicts the volume fraction of martensite formed as a function of plastic strain. © 2004 Elsevier B.V. All rights reserved.
221 citations
TL;DR: In this article, the relation between spin fluctuations and superconductivity in a highly ordered sample of highly ordered samples of Cu using both polarized and unpolarized neutron inelastic scattering was described.
Abstract: We describe the relation between spin fluctuations and superconductivity in a highly ordered sample of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6.5}$ using both polarized and unpolarized neutron inelastic scattering. The spin susceptibility in the superconducting phase exhibits one-dimensional incommensurate modulations at low energies, consistent with hydrodynamic stripes. With increasing energy the susceptibility curves upward to a commensurate, intense, well-defined, and asymmetric resonance at 33 meV with a precipitous high-energy cutoff. In the normal phase, which we show is gapless, the resonance remains surprisingly strong and persists clearly in Q scans and energy scans. Its similar asymmetric spectral form above ${T}_{c}=59\mathrm{K}$ suggests that incoherent superconducting pairing fluctuations are present in the normal state. On cooling, the resonance and the stripe modulations grow in well above ${T}_{c}$ below a temperature that is comparable to the pseudogap temperature where suppression occurs in local and low-momentum properties. The spectral weight that accrues to the resonance is largely acquired by transfer from suppressed low-energy fluctuations. We find the resonance to be isotropically polarized, consistent with a triplet carrying $\ensuremath{\sim}2.6%$ of the total spectral weight of the Cu spins in the planes.
139 citations
TL;DR: In this paper, the authors examined the existing prediction methods for the heat transfer coefficient (HTC) under this boiling regime and concluded that within the investigated ranges of boiling conditions, working fluids and boiling surfaces, the Rohsenow and Pioro correlations are the most accurate among those assessed.
112 citations
TL;DR: The dynamic spin susceptibility, chi(")(omega), has been measured over the energy range of 2
Abstract: The dynamic spin susceptibility, chi(")(omega), has been measured over the energy range of 2
108 citations
TL;DR: In this article, a literature survey is devoted to hydraulic resistance of water and carbon dioxide flows at supercritical pressures, where the authors assess previous studies that were done in the area of hydraulic resistance and understand the specifics of pressure drop at these conditions.
105 citations
TL;DR: The structural parameters, thermal properties, and transport properties of three type I clathrates were determined by powder neutron diffraction as discussed by the authors at or below room temperature, which indicated strong resonant scattering of heat-carrying acoustic phonons via the rattling of the guests in the clathrate cages.
Abstract: The structural parameters, thermal properties, and transport properties of three type I clathrates, namely ${\mathrm{Sr}}_{8}{\mathrm{Zn}}_{8}{\mathrm{Ge}}_{38}$, ${\mathrm{Sr}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Ge}}_{30}$, and ${\mathrm{Ba}}_{8}{\mathrm{Ga}}_{16}{\mathrm{Si}}_{30}$, have been determined at or below room temperature. The structural parameters of these clathrates were determined by powder neutron diffraction. Their lattice thermal expansion is two to four times greater than that of the diamond phases of silicon and germanium, consistent with more anharmonic lattice vibrations. From the temperature dependence of the isotropic atomic displacement parameters, the estimated rattling frequencies of guests in the large cages of these clathrates are in the range $50--60\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. The heat capacities of these three clathrate materials increase smoothly with increasing temperatures and approach the Dulong--Petit value around room temperature. The Gr\"uneisen parameter of these materials is constant between $100$ and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ but increases below $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, due to the dominance of the low-frequency guest-rattling modes. The room-temperature electrical resistivity and the Seebeck coefficient show that these materials are metallic. The temperature profile of the thermal conductivities and calculated phonon mean free paths of these materials show glasslike behavior, although they are crystalline materials, indicating strong resonant scattering of heat-carrying acoustic phonons via the rattling of the guests in the clathrate cages.
87 citations
TL;DR: In this article, the temperature dependence of both the diffuse and phonon scattering in PZN and PMN are compared and it is shown that both relaxors belong to the same universality class and discuss the relaxor transition in terms of the threedimensional Heisenberg model with cubic anisotropy in a random field.
Abstract: The relaxors $\mathrm{Pb}({\mathrm{Zn}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$ (PZN) and $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$ (PMN) have very similar properties based on the dielectric response around the critical temperature ${T}_{c}$ (defined by the structural transition under the application of an electric field). It has been widely believed that these materials are quite different below ${T}_{c}$ with the unit cell of PMN remaining cubic while in PZN the low-temperature unit cell is rhombohedral in shape. However, this has been clarified by recent high-energy x-ray studies which have shown that PZN is rhombohedral only in the skin while the shape of the unit cell in the bulk is nearly cubic. In this study we have performed both neutron elastic and inelastic scattering to show that the temperature dependence of both the diffuse and phonon scattering in PZN and PMN are very similar. Both compounds show a nearly identical recovery of the soft optic mode and a broadening of the acoustic mode below ${T}_{c}.$ The diffuse scattering in PZN is suggestive of an onset at the high-temperature Burns temperature similar to that in PMN. In contrast to PMN, we observe a broadening of the Bragg peaks in both the longitudinal and transverse directions below ${T}_{c}.$ We reconcile this additional broadening, not observed in PMN, in terms of structural inhomogeneity in PZN. Based on the strong similarities between PMN and PZN, we suggest that both materials belong to the same universality class and discuss the relaxor transition in terms of the three-dimensional Heisenberg model with cubic anisotropy in a random field.
84 citations
TL;DR: In this paper, a serendipitous match between the in-plane lattice constant of NCCO and the lattice constants of one of the decomposition products was found to cause the secondary phase to form an oriented, quasi-two-dimensional epitaxial structure.
Abstract: Extensive x-ray and neutron scattering experiments and additional transmission electron microscopy results reveal the partial decomposition of ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta}}$ (NCCO) in a low-oxygen-fugacity environment such as that typically realized during the annealing process required to create a superconducting state. Unlike a typical situation in which a disordered secondary phase results in diffuse powder scattering, a serendipitous match between the in-plane lattice constant of NCCO and the lattice constant of one of the decomposition products, ${(\mathrm{Nd},\mathrm{Ce})}_{2}{\mathrm{O}}_{3}$, causes the secondary phase to form an oriented, quasi-two-dimensional epitaxial structure. Consequently, diffraction peaks from the secondary phase appear at rational positions $(H,K,0)$ in the reciprocal space of NCCO. Additionally, because of neodymium paramagnetism, the application of a magnetic field increases the low-temperature intensity observed at these positions via neutron scattering. Such effects may mimic the formation of a structural superlattice or the strengthening of antiferromagnetic order of NCCO, but the intrinsic mechanism may be identified through careful and systematic experimentation. For typical reduction conditions, the ${(\mathrm{Nd},\mathrm{Ce})}_{2}{\mathrm{O}}_{3}$ volume fraction is approximately 1%, and the secondary-phase layers exhibit long-range order parallel to the NCCO ${\mathrm{CuO}}_{2}$ sheets and have a typical thickness of approximately $100\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. The presence of the secondary phase should also be taken into account in the analysis of other experiments on NCCO, such as transport measurements.
77 citations
TL;DR: In this article, the residual stress fields in pieces of quenched IN718 superalloy have been characterized by neutron diffraction, and the findings were rationalized with an elastic-plastic finite-element model that included temperature-dependent properties.
Abstract: The residual stress fields in pieces of quenched IN718 superalloy have been characterized by neutron diffraction. The samples were in the form of cylindrical rods of length sufficient to ensure that steady-state conditions prevail at the midsection. Quenching the samples in air, water, and oil generated various residual stress fields. The interfacial heat-transfer coefficients were estimated using an inverse-modeling technique. The findings were rationalized with an elastic-plastic finite-element model that included temperature-dependent properties. The hoop and axial stresses are the most significant components of the stress field and arise from the plastic deformation occurring at the periphery of the cylindrical sections, the extent of which depends strongly upon the severity of the quench. The model is used to examine the residual stress fields to be expected in a turbine-disc forging of idealized geometry.
TL;DR: Using small-angle neutron scattering and dynamic light scattering, partial structural phase diagrams of lipid mixtures composed of the phosphatidylcholines dimyristoyl and dihexanoyl doped with calcium ions and DMPG are constructed, resulting in ULVs whose was found to be Clp dependent.
TL;DR: In this article, a solid solution La 2 Ni 1-x Co x O 4+δ (0.00 ≤ x ≤ 1.00), based on the K 2 NiF 4 structure was synthesized and studied for potential use as cathodes in solid-oxide fuel cells.
TL;DR: Spatially resolved neutron diffraction as a function of crystal depth in this paper reveals the presence of a distinct near-surface region where a strong distortion in the lattice exists.
Abstract: Spatially resolved neutron diffraction as a function of crystal depth in $\mathrm{Pb}({\mathrm{Mg}}_{1∕3}{\mathrm{Nb}}_{2∕3}){\mathrm{O}}_{3}$ reveals the presence of a distinct near-surface region where a strong distortion in the lattice exists A dramatic change in both the lattice constant and the Bragg peak intensity as a function of crystal depth is observed to occur in this region over a length scale $\ensuremath{\sim}100\phantom{\rule{03em}{0ex}}\ensuremath{\mu}\mathrm{m}$ This confirms a previous assertion, based on a comparison between high-energy x rays and neutrons, that such a near surface region exists in the relaxors Consequences to both single crystal and powder diffraction measurements and previous bulk neutron diffraction measurements on large single crystals are discussed
TL;DR: Neutron scattering measurements on the spin-ice candidate material Ho2Ru2O7 have revealed two magnetic transitions at T approximately 95 and approximately 1.4 K to long-range ordered states involving the Ru and Ho sublattices, respectively.
Abstract: Neutron scattering measurements on the spin-ice candidate material ${\mathrm{H}\mathrm{o}}_{2}{\mathrm{R}\mathrm{u}}_{2}{\mathrm{O}}_{7}$ have revealed two magnetic transitions at $T\ensuremath{\sim}95$ and $\ensuremath{\sim}1.4\text{ }\mathrm{K}$ to long-range ordered states involving the Ru and Ho sublattices, respectively. Between these transitions, the ${\mathrm{H}\mathrm{o}}^{3+}$ moments form short-ranged ordered spin clusters. The internal field provided by the ordered $S=1\text{ }\text{ }{\mathrm{R}\mathrm{u}}^{4+}$ moments disrupts the fragile spin-ice state and drives the ${\mathrm{H}\mathrm{o}}^{3+}$ moments to order. We have directly measured a slight shift in the ${\mathrm{H}\mathrm{o}}^{3+}$ crystal field levels at 95 K from the Ru ordering.
TL;DR: In this article, a combination of bulk magnetization, conversion electron Mossbauer spectroscopy, and polarized neutron reflectometry was used to show that in Pd/Fe multilayers at 4.5 K there is a slight $(\ensuremath{\sim}10%)$ enhancement of the Fe moment at the Pd /Fe interface, and that the PD is almost maximally polarized, with an average moment of $0.32{\ensureMath{\mu}}_{B}$ to a depth of about 20 \AA{} from the PdL
Abstract: A combination of bulk magnetization, conversion electron M\"ossbauer spectroscopy, and polarized neutron reflectometry is used to show that in Pd/Fe multilayers at 4.5 K there is a slight $(\ensuremath{\sim}10%)$ enhancement of the Fe moment at the Pd/Fe interface, and that the Pd is almost maximally polarized, with an average moment of $0.32{\ensuremath{\mu}}_{B}$ to a depth of about 20 \AA{} from the Pd/Fe interface. The Pd polarization is strongly temperature dependent.
TL;DR: Using neutron diffraction and a specially constructed high pressure cell suitable for aligned multibilayer systems, the much observed anomalous swelling regime in dimyristoyl- and dilauroyl-phosphatidylcholine bilayers, DMPC and DLPC is studied.
Abstract: Using neutron diffraction and a specially constructed high pressure cell suitable for aligned multibilayer systems, we have studied, as a function of pressure, the much observed anomalous swelling regime in dimyristoyl- and dilauroyl-phosphatidylcholine bilayers, DMPC and DLPC, respectively. We have also reanalyzed data from a number of previously published experiments and have arrived at the following conclusions. ~a! The power law behavior describing anomalous swelling is preserved in all PC bilayers up to a hydrostatic pressure of 240 MPa. ~b! As a function of increasing pressure there is a concomitant decrease in the anomalous swelling of DMPC bilayers. ~c! For PC lipids with hydrocarbon chains >13 carbons the theoretical unbinding transition temperature T ! is coupled to the main gel-to-liquid crystalline transition temperature TM . ~d! DLPC is intrinsically different from the other lipids studied in that its T ! is not coupled to TM . ~e! For DLPC bilayers we predict a hydrostatic pressure ( .290 MPa) where unbinding may occur.
01 Aug 2004-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: The first gas-fed ion source for radiocarbon AMS applications (without sputtering) has been operated at the Woods======Hole NOSAMS Facility as discussed by the authors, where the ion source was operated on CO_2 at a flow rate of about 200 µ1 per minute, negative carbon ion beams up to 20 µA.
Abstract: The first gas-fed ion source for radiocarbon AMS applications (without sputtering) has been operated at the Woods
Hole NOSAMS Facility. A three-year, off-line test program resulted in positive carbon ion currents up to 1 mA and
negative ion currents up to 80 µA. Recently, the compact, permanent-magnet microwave plasma ion source and
magnesium vapor charge-exchange canal were coupled to the recombinator injector of the 2.5 MV Tandetron. When
the ion source was operated on CO_2 at a flow rate of about 200 µ1 per minute, negative carbon ion beams up to 20 µA
were obtained, at an energy of 35 keV. Radiocarbon measurements were performed on standard reference gases and the
dynamic response to square-wave pulses of gas was determined. Time constants in the ion source are less than 1 s, which
should allow analysis of chromatographic peaks of CO_2 with very little broadening. A combustion device has been
constructed to generate CO_2 for direct injection into the source. Argon carrier gas is used to buffer the pressure at one
atmosphere in the sample gas injector. A dedicated ion-beam injector, with higher angular acceptance and higher
transmitted currents, is being constructed for the AMS system.
TL;DR: In this article, the erbium moments on the 2d and 4e sites of the orthorhombic Er3Cu4X4 (X = Si, Ge, Sn) system were studied using both 119 Sn and 166 Er M¨ ossbauer spectroscopy, combined with neutron diffraction.
Abstract: Magnetic ordering of the orthorhombic Er3Cu4X4 (X = Si, Ge, Sn) system has been studied using both 119 Sn and 166 Er M¨ ossbauer spectroscopy, combined with neutron diffraction. We observe two distinct ordering events for the erbium moments on the 2d and 4e sites (TN (Er 2d) > TN (Er 4e)) and confirm that the Er 2d moments are larger than those on the Er 4e site. Comparison of neutron diffraction with 166 Er M¨ ossbauer spectroscopy shows that the ordering of the Er 4e moments is far from complete, even at 0.7 TN, causing neutron diffraction analysis to severely underestimate the Er 4e moments in the Er3Cu4X4 system.
TL;DR: Interestingly, deuterated HPC ethers, prepared for neutron reflectivity measurements, exhibit monolayer properties significantly different from those of their hydrogenated analogues, which indicates that these LB films do not possess an internal periodic structure and the initial layer-by-layer organization is lost by large interlayer diffusion.
Abstract: Langmuir-Blodgett films of a series of cellulose ethers are investigated by X-ray and neutron reflectometry. Two types of samples are considered: simple alkyl ethers of cellulose and derivatives obtained by the alkylationof (2-hydroxypropyl)cellulose (HPC). All of the cellulose ethers form stable monolayers at the air-water interface. Significant differences are, however, found in the surface pressure-area compression isotherms. Ethers prepared from HPC typically exhibit larger limiting molecular areas and higher surface pressures than the corresponding simple cellulose ethers. The ease of monolayer transfer to hydrophobic silicon substrates differs greatly from one type of molecule to another. Successful transfer conditions are found only for ethers that form stable monolayers at sufficiently high surface pressures. Surprisingly, deuterated HPC ethers, prepared for neutron reflectivity measurements, exhibit monolayer properties significantly different from those of their hydrogenated analogues. Although essentially identical limiting molecular areas are found, the surface pressure corresponding to a characteristic plateau transition in the compression isotherm is found to decrease by about 8-10 mN m - 1 upon side chain deuteration. X-ray reflectivity results show a linear increase of film thickness with the number of deposited layers, indicating a regular and reproducible transfer. Observed average layer spacings are, however, significantly smaller than the calculated length of fully extended side chains. Neutron reflectivity curves recorded for composite LB films composed of both deuterated and hydrogenated polymers exhibit regular Keissig fringes, but no Bragg peak. This result indicates that these LB films do not possess an internal periodic structure and the initial layer-by-layer organization is lost by large interlayer diffusion.
TL;DR: Neutron activation analysis (NAA) in combination with mainly high-performance liquid chromatography (HPLC) has been developed for the determination of low levels of five arsenic species, namely As(III), As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and arsenobetaine (AsB) in water samples.
Abstract: Neutron activation analysis (NAA) in combination with mainly high-performance liquid chromatography (HPLC) has been developed for the determination of low levels of five arsenic species, namely As(III), As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), and arsenobetaine (AsB) in water samples. Organically bound arsenic (OBAs) and total arsenic have also been determined. In addition to anion-exchange HPLC, solid phase extraction and open-column cation-exchange chromatographic methods have also been used. The detection limits of the method have been found to be 0.005 ng·cm−3 for OBAs, 0.02 ng·cm−3 for AsB, DMA, MMA, As(III), and As(V) and 0.12 ng·cm−3 for total arsenic.
TL;DR: In this article, the authors reported dimensional changes in three dimensions for cold-worked Zr-2.5 Nb pressure tube material irradiated to a fast fluence of 174 × 10 24 nm −2, E ǫ> 1 MeV at a nominal temperature of 250 −C.
TL;DR: In this article, the magnetic moment of uncovered and V-covered Fe films in the thickness range from 0.3 to 0.5 was determined using polarized neutron reflectometry (PNR).
Abstract: We used polarized neutron reflectometry (PNR) to determine the absolute magnetic moment of uncovered and V-covered Fe films in the thickness range from $0.3\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}5.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The films were prepared by molecular beam epitaxy on a V(100) buffer layer grown on a MgO(100) crystal. The magnetic moment shows a linear dependence on the Fe film thickness with a reduction (compared to the Fe bulk value) of the magnetic moment equivalent to $0.1\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ bulk Fe for the V-covered films and a reduction equivalent to $0.03\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ bulk Fe for the uncovered Fe films. For the case of the $\mathrm{V}∕\mathrm{Fe}∕\mathrm{V}$ samples we observe a much smaller reduction of the magnetic moment than reported for experiments on $\mathrm{Fe}∕\mathrm{V}$ multilayers. As theoretical calculations show a strong decrease of the magnetic moment for an interface alloy we conclude that the larger reduction of the magnetization in $\mathrm{Fe}∕\mathrm{V}$ multilayers is due to an increase in interface roughness with increasing film thickness. For the uncovered Fe(100) films we find a much smaller reduction of the magnetic moment than in earlier in situ PNR experiments on $\mathrm{V}(110)∕\mathrm{Fe}(110)$ where we observed a reduction equivalent to $0.4\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ bulk Fe.
TL;DR: In this paper, a new experimental/numerical technique for controlling phase interface motion, acceleration and temperature gradients during pure material solidification was developed, where the required time-dependent boundary conditions were predicted with an inverse numerical method, in order to produce the desired interfacial motion.
TL;DR: A new Os-containing, pillared perovskite, La5Os3MnO16, has been synthesized by solid state reaction in sealed quartz tubes.
TL;DR: In this paper, the structural response of buddingtonite [N(D/H)4AlSi3O8] on cooling has been studied by neutron diffraction, and data have been collected from 280 K down to 11 K, and the crystal structure refined using the Rietveld method.
Abstract: The structural response of buddingtonite [N(D/H)4AlSi3O8] on cooling has been studied by neutron diffraction. Data have been collected from 280 K down to 11 K, and the crystal structure refined using the Rietveld method. Rigid-body constraints were applied to the ammonium ion to explore the structural properties of ammonium in the M-site cavities at low-temperature. Low-temperature saturation is observed for almost all the lattice parameters. From the present in situ low-temperature neutron diffraction studies, there is no strong evidence of orientational order–disorder of the ammonium ions in buddingtonite.
TL;DR: In this paper, the authors evaluated the fracture toughness of pressure tubes made from Zr-2.5Nb by various fabrication routes to evaluate the response of their fracture toughness (represented by crack growth resistance, dJ/da) at 250°C to irradiation by fast neutrons (E > 1 MeV).
Abstract: Specimens of pressure tubes made from Zr-2.5Nb by various fabrication routes were irradiated in research reactors to evaluate the response of their fracture toughness (represented by crack growth resistance, dJ/da) at 250°C to irradiation by fast neutrons (E > 1 MeV). The reference route consists of melting Kroll sponge and some recycled material, primary hot-working, extrusion at 815°C, and cold-working 27 %. Tubes made from ingots that were melted four times (quadruple melting) are initially tougher than tubes made from ingots that have been melted twice (double melting), and after irradiation the former retain close to 50 % of their original crack growth resistance while the latter retain less than 30 % of theirs. The high toughness and its retention in the quadruple melted material are attributed to low concentrations of chlorine. Tubes made from electrolytic powder contain fluorine rather than chlorine. Fluorine is less damaging than chlorine. Crack growth resistance and its retention with irradiation of tubes made from electrolytic powder are intermediate between those of tubes made from quadruple and double melted sponge. Lowering the amount of cold-work is beneficial, and the toughness of tubes made with less than 27 % cold-work correlates well with strength, both before and after irradiation. Lowering the extrusion temperature produces strong, tough tubes, but these tubes lose much of their crack growth resistance with irradiation. This loss in toughness is not associated with material chemistry but with a high sensitivity to strength.
TL;DR: In this article, the authors investigated the effect of fine-size effects in stacks of phospholipid bilayers, in the fluid L α phase, using samples oriented on silicon substrates, and found that at full hydration all samples have the same repeat spacing, irrespective of their thickness.
Abstract: Finite-size effects in stacks of phospholipid bilayers, in the fluid L α phase, are investigated using samples oriented on silicon substrates. Recently in this journal, such effects have been suggested as the probable cause of reduced lamellar repeat spacings in very thin samples made up of a few (<10) bilayers. Our systematic studies on samples of different thicknesses do not support this conclusion. At full hydration all samples are found to have the same repeat spacing, irrespective of their thickness. At lower hydrations, on the other hand, very thin samples, consisting of only a few bilayers, have a slightly larger spacing.
TL;DR: In this article, the pore invasion, and not repeated nucleation, dominates the freezing process in these rocks, which implies that microscopic advance of crystallographically coherent ice occurs through pore network and not by the direction of bulk heat flow.
Abstract: [1] Crystallographic textures are presented of ice formed in situ by directional cooling of saturated porous rocks. The observations of texture demonstrate that pore invasion, and not repeated nucleation, dominates the freezing process in these rocks. This implies that microscopic advance of crystallographically coherent ice occurs through the pore network. The textures are governed by the permeability of the pore network and not by the direction of bulk heat flow. The anisotropy of permeability provides a mechanism for grain competition during ice growth, as crystals with fast growth directions aligned favorably to the maximum permeability are favored.
TL;DR: Using neutron diffraction, it is found that the repeat spacing of stacks containing up to a few tens of bilayers depends on their thickness, with d increasing with decreasing D.
Abstract: Thin stacks of lipid multibilayers supported on rigid silicon and mica substrates are found to exhibit finite-size effects. Using neutron diffraction we find that the repeat spacing (d) of stacks containing up to a few tens of bilayers depends on their thickness (D), with d increasing with decreasing D. Differences in d are larger in the low-temperature L'{sub {beta}} phase consisting of rigid bilayers than in the high-temperature L{sub {alpha}} phase where the bilayers are more flexible. Various scenarios that may be responsible for this counterintuitive observation are discussed.