Abstract: The influence of cholesterol and β-sitosterol on egg yolk phosphatidylcholine (EYPC) bilayers is compared. Different interactions of these sterols with EYPC bilayers were observed using X-ray diffraction. Cholesterol was miscible with EYPC in the studied concentration range (0-50 mol%), but crystallization of β-sitosterol in EYPC bilayers was observed at X â¥Â 41 mol% as detected by X-ray diffraction. Moreover, the repeat distance (d) of the lamellar phase was similar upon addition of the two sterols up to mole fraction 17%, while for X â¥Â 17 mol% it became higher in the presence of β-sitosterol compared to cholesterol. SANS data on suspensions of unilamellar vesicles showed that both cholesterol and β-sitosterol similarly increase the EYPC bilayer thickness. Cholesterol in amounts above 33 mol% decreased the interlamellar water layer thickness, probably due to "stiffening" of the bilayer. This effect was not manifested by β-sitosterol, in particular due to the lower solubility of β-sitosterol in EYPC bilayers. Applying the formalism of partial molecular areas, it is shown that the condensing effect of both sterols on the EYPC area at the lipid-water interface is small, if any. The parameters of ESR spectra of spin labels localized in different regions of the EYPC bilayer did not reveal any differences between the effects of cholesterol and β-sitosterol in the range of full miscibility.
Abstract: The formation of self-organized structures in poly(9,9-di-n-alkylfluorene)s â¼1 vol % methylcyclohexane (MCH) and deuterated MCH (MCH-d(14)) solutions was studied at room temperature using neutron and x-ray scattering (with the overall q range of 0.00058-4.29 Ã(-1)) and optical spectroscopy. The number of side chain carbons (N) ranged from 6 to 10. The phase behavior was rationalized in terms of polymer overlap, cross-link density, and blending rules. For N=6-9, the system contains isotropic areas and lyotropic areas where sheetlike assemblies (lateral size of >400 Ã) and free polymer chains form ribbonlike agglomerates (characteristic dimension of >1500 Ã) leading to a gel-like appearance of the solutions. The ribbons are largely packed together with surface fractal characteristics for N=6-7 but become open networklike structures with mass fractal characteristics for N=8-9, until the system goes through a transition to an isotropic phase of overlapping rodlike polymers for N=10. The polymer order within sheets varies allowing classification for loose membranes and ordered sheets, including the so-called β phase. The polymers within the ordered sheets have restricted motion for N=6-7 but more freedom to vibrate for N=8-9. The nodes in the ribbon network are suggested to contain ordered sheets cross-linking the ribbons together, while the nodes in the isotropic phase appear as weak density fluctuations cross-linking individual chains together. The tendencies for macrophase separation and the formation of non beta sheets decrease while the proportion of free chains increases with increasing N. The fraction of β phase varies nonlinearly, reaching its maximum at N = 8.
Abstract: Small-angle neutron scattering proved that molecules in aqueous solutions of pyridine, 2-methylpyridine and 2,6-dimethylpyridine form clusters. The clusters are dynamic aggregates consisting of hydrogen-bonded water-amine complexes. Strengthening of the hydrogen bonds between water and amine molecules due to the methyl groups in the ortho position in the pyridine ring makes the structures more stable, as was evidenced by relatively long times of the structural relaxation. The strong intermolecular forces affect the thermal expansion of the systems. No aggregates similar to those in aqueous systems are present in the methanolic ones. That points to the crucial role of water in the molecular clustering. A molecule of methanol, although capable of hydrogen bonding with the amines, cannot participate in larger structures because of the lack of protons that could form the enhanced network. Thus, even if the amine-methanol complexes occur, they are incapable of further association. It was shown that the co-operative nature of hydrogen bonds and the propensity of water to association are the main factors that determine the properties of aqueous systems.
Abstract: We report on the phase transitions, solution structure, and consequent effect on the photophysical properties of poly[3-(6-trimethylammoniumhexyl)thiophene] bromide (P3TMAHT) in aqueous sodium dodecylsulfate (SDS). Polythiophene was mixed with SDS or deuterated SDS to form P3TMAHT(SDS)(x) complex (x = the molar ratio of surfactant over monomer units) in D(2)O and studied by small-angle neutron and X-ray scattering (SANS/SAXS) and optical spectroscopy. At room temperature, P3TMAHT forms charged aggregates with interparticle order. The addition of SDS eliminates the interparticle order and leads to rod-like (x = 1/5) or sheet-like polymer-SDS aggregates (x = 1/2 to 1) containing rod-like (x = 1/5 to 1/2) or sheet-like (x = 1/2 to 1) polymer associations. Partial precipitation occurs at the charge compensation point (x = 1). Ellipsoidal particles without interparticle order, reminiscent of SDS micelles modified by separated polymer chains, occur for x = 2 to 5. Free SDS micelles dominate for x = 20. Structural transitions lead to a concomitant variation in the solution color from red (P3TMAHT) to violet (x = 1/5 to 1) to yellow (x > 2). The photoluminescence fingerprint changes progressively from a broad featureless band (x = 0) through the band narrowing and appearance of vibronic structure (x = 1/5 to 1) to the return to a blue-shifted broad emission band (x = 5). The polymer stiffness reaches a maximum for x = 1, which leads to minimization of the Stokes shift (0.08 eV). This work gives fundamental information upon how surfactant complexation can influence both the solution structure and photophysical properties of a water-soluble polythiophene.
Abstract: The intermolecular interaction of non-saturated (oleic acid) and saturated (stearic and myristic acids) mono-carboxylic acids in a non-polar organic solvent (deuterated benzene) is derived from the concentration dependence of the small-angle neutron scattering. The excluded volume repulsion dominates over the attraction (supposed due to van der Waals forces) for oleic and myristic acids. In turn, for stearic acid the attractive component is higher than the repulsive one; this results in a shift of the transition into the liquid crystalline state (because of molecule anisotropy) towards smaller concentrations and could explain early data on worse stabilization properties of stearic acid in ferrofluids compared to oleic and myristic acids.
Abstract: The effect of side chain length of Ï-conjugated poly(9,9-dialkylfluorene)s has been studied in semi-dilute (10 mg/mL) toluene solutions using small-angle neutron scattering (SANS) and 1H and 2H NMR spectroscopies. Under these conditions, SANS data indicate that poly(9,9-dinonylfluorene) and poly(9,9-dioctylfluorene) are dissolved down to the molecule level and appear as elongated one-dimensional chains (length >20â30 nm). In contrast, the shorter side chain polymers exhibit a self-association so that poly(9,9-diheptylfluorene) forms thin sheet-like (not, vert, similar1 nm) and poly(9,9-dihexylfluorene) thin (not, vert, similar1 nm) and thick sheet-like (>6 nm) aggregates. 1H NMR data, together with the density functional theory (DFT) calculations, however, show that this occurs without changes in the conformation of the polymer backbone.
Abstract: The structure of aqueous solutions of a prototype ionic liquid, the short alkyl chain 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) has been investigated by small-angle neutron scattering. Concentration fluctuations and Kirkwood-Buff integrals have been calculated, and the results are in good agreement with corresponding data calculated herein from vapor pressure measurements. The large concentration fluctuations and Kirkwood-Buff integral values indicate that the system is in the vicinity of phase separation, which is known to occur some 20 K below room temperature, at a salt mole fraction of around 0.075.
Abstract: Self-assembled polypeptide-surfactant complexes are usually infusible solids in the absence of solvent and do not allow fluidlike liquid crystallinity even when heated, which seriously limits their polymer-like applications in the solid state due to processing problems. This work is partly inspired by nature's liquid crystalline processing of silk and subsequent structural interlocking due to -sheet formation. We demonstrate here polypeptide-surfactant complexes that are fluidlike liquid crystalline at room temperature with hexagonal cylindrical self-assembly. The hexagonal structure with -helical polypeptide chains is then partially converted to lamellar self-assembly with -sheet conformation through thermal treatment. We use poly(L-lysine)-dodecylbenzenesulfonic acid complexes, PLL(DBSA)x (x = 1.0-3.0), where the branched dodecyl tails suppress the side-chain crystallization. In the stoichiometric composition, x = 1.0, there is one anionic DBSA molecule ionically complexed to each cationic lysine residue. Such a PLL(DBSA)1.0 is an infusible solid material at all temperatures until degradation. Introduction of additional DBSA, i.e., x = 1.5 or 2.0, plasticizes the material to be shear-deformable and birefringent. In organic solution, as witnessed by small-angle neutron scattering (SANS), the PLL(DBSA)x complexes form bottle-brush-like cylinders, which upon evaporation of the solvent self-assemble into hexagonal cylindrical morphology with -helical PLL secondary structure. Heating of PLL(DBSA)x with x = 1.0-2.0 up to the range 120-160 C leads to the formation of lamellar self-assembled domains with -sheet conformation of PLL, which coexist with the hexagonal self-assembled structures with -helical conformation, as shown by Fourier transform infrared spectroscopy (FTIR) and small-angle X-ray scattering (SAXS). Higher complexation ratio, i.e., x = 3.0, results in soft and shear-deformable hexagonally packed cylinders at room temperature, but heating irreversibly converts the PLL to a random coil conformation, which leads to a disordered structure. The present model studies show that in polypeptide-surfactant self-assemblies it is possible to change the properties of the material by thermal treatment due to irreversible structural and conformational transformations.
Abstract: We report on the aggregate structure of a symmetrical A-B-A 9,9-dialkylfluorene/2-alkylaniline "coil-rod-coil" triblock copolymer (or PF/PANI11112-b-PANI11)--consisting of 2-dodecylanilines as A blocks and 9,9-di(3,7,11-trimethyldodecyl)fluorene)s as B blocks--mixed in deuterated toluene, chloroform, and methylcyclohexane. These mixtures contain micrometer scale aggregates. Small-angle neutron scattering data indicate that the interface between the aggregates and solvents manifests surface fractal-like structure. The upper and lower limit length scales which show fractal character are of the order of > 100 and 15 nm. The surface fractal dimension D(s) varies from 2.2 to 2.8. The data show that stiff polyfluorene (PF) segments (persistence length > or = 9.5 nm, diameter approximately 2 nm) of PF/PANI11112-b-PANI11 are dissolved down to the molecular level. Photoluminescence data indicate that most PF units are isolated from both polyaniline (PANi) units and each others. Together with the scattering data, this implies that the disordered interface consists of stiff isolated PF blocks linked together via domains of associated PANi blocks.
Abstract: Simulation (molecular dynamics and Car-Parrinello [Phys. Rev. Lett. 55, 2471 (1985)]) and diffraction (x-ray and neutron) studies on nitromethane are compared aiming at the determination of the liquid structure. Beyond that, the capabilities of the methods to describe liquid structure are discussed. For the studied liquid, the diffraction methods are performing very well in the determination of intramolecular structure, but they do not give detailed structural information on the intermolecular structure. The good agreement between the diffraction experiments and the results of molecular dynamics simulations justifies the use of simulations for the more detailed description of the liquid structure using partial radial distribution functions and orientational correlation functions. Liquid nitromethane is described as a molecular liquid without strong intermolecular interactions such as hydrogen bonding, but with detectable orientational correlations resulting in preferential antiparallel order of the neighboring molecules.
Abstract: Small-angle neutron scattering experiments and density measurements were carried out on dilute solutions of N,Nâ²-dimethylethyleneurea (DMEU) in heavy water in the aquamolality ranges 0.28â2.92 and 0.28â4.17, respectively, at 298.15 and 313.15 K. The results obtained for DMEU, the cyclic analogue of tetramethylurea (TMU), were compared with those reported for TMU solutions in the literature. Whereas in the aqueous solution of TMU the hydrophobic interaction increases with increasing temperature, the second osmotic virial coefficient obtained from the concentration dependence of the forward scattering intensities in the DMEU solution is temperature independent. In contrast with the TMU solution, the radius of gyration in the DMEU solution appears to be constant below the aquamolality of about 2. The molal volume second virial coefficient (Vxx), calculated from the densities of the solutions, is negative, which indicates that DMEU has a structure-making effect on water. In the TMU solution the value of Vxx was found to be more negative, which suggests that the water molecules are more structured in the hydration sphere of TMU than in that of DMEU molecule. The results of both the SANS and the volumetric studies on dilute solutions of DMEU lead to the conclusion that the pair-wise soluteâsolute interactions are weaker in DMEU than in TMU solutions.
Abstract: Aqueous solutions of tetramethylurea (TMU) were studied by small-angle neutron
and X-ray scattering at temperatures 10, 25 and 40oC in the TMU mole fraction
range of 0.0125 - 0.025. The scattering data indicate preferential attractive interac-
tion between the solute molecules, which becomes stronger as the temperature increases.
From SANS data, concentration fluctuations and Kirkwood-Buff integrals
have been calculated. The experimental data reveal a considerable solute-solute
attraction above 0.01 mole fraction of TMU. These findings indicate that in addition
tion to the usually assumed solute caging by water molecules, solute clustering of
hydrophobic nature should also be considered for this system.
Abstract: Aqueous solutions of 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol and 1,6-
hexanediol have been studied by small-angle neutron scattering over a wide
range of concentrations and temperatures. The structure of the solutions on the
mesoscopic length scale, corresponding to the intermolecular distances, was
analysed with the help of the KirkwoodâBuff formalism. 1,2-Hexanediol
solutions exhibited a strong attractive diolâdiol interaction, a weak diolâdiol
attraction was found for 1,6-hexanediol and 1,2-pentanediol, and an extremely
weak diolâdiol attraction was found in 1,5-pentanediol solutions. The general
tendencies are the following: aggregation is stronger as the length of the
hydrophobic hydrocarbon chain increases and the 1,2-diols exhibit much
stronger attraction then the 1,omega-diols. The temperature dependence of the
aggregation is weak for the 1,2-diols but strong for the 1,omega-diols, indicating in the
latter case the hydrophobic character of the interaction.
Abstract: The Kirkwood-Buff integrals of some binary aqueous alcohol mixtures are computed from the available vapor pressure measurements and compared with previous results as well as small angle neutron scattering experiments. The emphasis of the present report is on accuracy of the results that can be achieved by these two different types of measurements. This seems to be needed, mainly in view of the discrepancies between the various published results, as shown herein. It is argued that agreement in peak positions is more important than that in magnitude. In general, very good agreement is obtained by both methods, and sources of disagreements are discussed. The issue of the computer simulations of aqueous systems and the problematics related to correlations, microheterogeneity, and consequently the Kirkwood-Buff integrals are equally discussed herein.
Abstract: The small-angle neutron scattering (SANS) data of 12 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) dispersions at low lipid concentration (1 mg per 100-mg heavy water) prepared by 5, 9 and 29 extrusions through filters of pores with 50, 100, 200 and 400 nm diameter are presented. They were analyzed within a theory that permits the determination of both structural and hydration parameters of the bilayers as well as the portions of multilamellar vesicles in dispersions with negligible long-range order between the vesicles. The scattering length density profile across the bilayers is approximated by assuming a central hydrocarbon core surrounded by a water-accessible coat. It is modeled by two different forms of functions. In the boat model, the scattering length density of the coat changes linearly from core to water, whereas in the strip model it is constant across the water-accessible coat. It was found that the boat model reflects the reality better than the strip model. The decrease of the multilamellar vesicle portions, either with increasing the number of extrusions at same filter size and with decreasing the filter size, was characterized quantitatively.
Abstract: In the conventional setup of a small-angle neutron scattering instrument a nearly monochromatic neutron beam is formed by means of a mechanical velocity selector. We studied the influence of the wavelength distribution in the incident beam on the wavelength of the neutrons reaching the sample. The assumption that the wavelength spectrum behind the selector equals to the product of the incident spectrum of the thermalized neutrons and the transmission window of the selector predicts satisfactorily the wavelength measured at sample position. An approximate relation is given between the effective wavelength and the selector rotation speed. The described method of wavelength calibration can improve the precision of size determination in SANS experiment.
Abstract: The structure of polydispersed populations of unilamellar vesicles is studied by small-angle neutron scattering for three types of lipid systems, namely, single-, two-and four-component vesicular systems. Results of the numerical analysis based on the separated-form-factor model are reported.
Abstract: We report on the solubilization, phase behavior, and self-organized colloidal structure of a ternary water-polyfluorene-surfactant (amphiphile) system comprised of polyelectrolytic poly{1,4-phenylene[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) in nonionic pentaethylene glycol monododecyl ether (C12E5) at 20 degrees C. We show in particular how a high amount (milligrams per milliliter) of polyfluorene can be solubilized by aqueous C12E5 via aggregate formation. The PBS-PFP and C12E5 concentrations of 0.31 x 10(-4)-5 x 10(-4) M and 2.5 x 10(-4)-75 x 10(-4) M, respectively, were used. Under the studied conditions, the photoluminescence (PL), surface tension, static contact angle, and (pi-A) isotherm measurements imply that D2O-PBS-PFP(C12E5)x realizes three phase regimes with an increasing molar ratio of surfactant over monomer unit (x). First, for x < or = 0.5, the mixture is cloudy. In this regime polymer is only partially dissolved. Second, for 1 < or = x < or = 2, the solution is homogeneous. In this regime polymer is dissolved down to the colloidal level. Small-angle neutron scattering (SANS) patterns indicate rigid elongated (polymer-surfactant) aggregates with a diameter of 30 A and mean length of approximately 900 A. The ratio between contour length and persistence length is less than 3. Third, for x > or = 4, the solution is homogeneous and there is cooperative binding between polymer and surfactant. Surface tension, contact angle, and surface pressure remain essentially constant with increasing x. A PL spectrum characteristic of single separated polyfluorene molecules is observed. SANS curves show an interference maximum at q approximately 0.015 A(-1), indicating an ordered phase. This ordering is suggested to be due to the electrostatic repulsion between polymer molecules adsorbed on or incorporated into the C12E5 aggregates (micelles). On dilution the distance between micelles increases via 3-dimensional packing. In this regime the polymer is potentially dissolved down to the molecular level. We show further that the aggregates (x = 2) form a floating layer at the air-water interface and can be transferred onto hydrophilic substrates.
Abstract: The Kirkwood-Buff integrals of acetone-water mixtures are determined using two experimental techniques: small-angle neutron scattering and vapor pressure measurements, in order to test the precision and reliability that can be achieved. The data are then compared with those previously reported by different authors, which tend to show considerable variation between them. The various possible sources of inaccuracies are pointed out, both from experimental origins and from the numerical treatment of the data. Comparison with recent simulation results allows to critically compare different models and provide some information about the microstructure of the aqueous mixture.
Abstract: We report on an experimental study of the self-organization and phase behavior of hairy-rod pi -conjugated branched side-chain polyfluorene, poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl]-i.e., poly[2,7-(9,9-bis(2-ethylhexyl)fluorene] (PF2/6) -as a function of molecular weight (M(n)) . The results have been compared to those of phenomenological theory. Samples for which M(n) =3-147 kg/mol were used. First, the stiffness of PF2/6 , the assumption of the theory, has been probed by small-angle neutron scattering in solution. Thermogravimetry has been used to show that PF2/6 is thermally stable over the conditions studied. Second, the existence of nematic and hexagonal phases has been phenomenologically identified for lower and higher M(n) (LMW, M(n) < M(*)(n) and HMW, M(n) > M(*)(n) ) regimes, respectively, based on free-energy argument of nematic and hexagonal hairy rods and found to correspond to the experimental x-ray diffraction (XRD) results for PF2/6 . By using the lattice parameters of PF2/6 as an experimental input, the nematic-hexagonal transition has been predicted in the vicinity of glassification temperature (T(g)) of PF2/6 . Then, by taking the orientation parts of the free energies into account the nematic-hexagonal transition has been calculated as a function of temperature and M(n) and a phase diagram has been formed. Below T(g) of 80 degrees C only (frozen) nematic phase is observed for M(n)< M(*)(n) = 10(4) g/mol and crystalline hexagonal phase for M(n) > M(*)(n) . The nematic-hexagonal transition upon heating is observed for the HMW regime depending weakly on M(n) , being at 140-165 degrees C for M(n) > M(*)(n). Third, the phase behavior and structure formation as a function of M(n) have been probed using powder and fiber XRD and differential scanning calorimetry and reasonable semiquantitative agreement with theory has been found for M(n) >or=3 kg/mol. Fourth, structural characteristics are widely discussed. The nematic phase of LMW materials has been observed to be denser than high-temperature nematic phase of HMW compounds. The hexagonal phase has been found to be paracrystalline in the (ab0) plane but a genuine crystal meridionally. We also find that all these materials including the shortest 10-mer possess the formerly observed rigid five-helix hairy-rod molecular structure.
Abstract: We report results of small-angle neutron scattering (SANS) measurements on aqueous solutions of 1,7-heptanediol in the molarity range 0.11 - 1.5 mol dm-3 at room temperature. The experimental data show aggregation of the diol molecules within the whole studied concentration range. The scattering curves could be accurately described by the structural model of random concentration fluctuations. The results suggest that 1,7-heptanediol molecules in aqueous solution aggregate in a rather loose way.
Abstract: Solutions of pyridine in heavy water were studied by small-angle neutron scattering at 25 °C in the pyridine mole fraction range of 0.02 - 0.25. From the experimental data Kirkwood-Buff integrals and the closeness to phase separation parameters were calculated and compared with those obtained for pyridine - light water solutions from thermodynamic data available in the literature. The detailed analysis shows that a significant clustering of similar species occurs in the solution. In spite of the strongly non-ideal behavior these solutions are still far away from macroscopic phase separation.
Abstract: Three-layer nanoparticles were prepared by radiation-induced polymerization of 1-10 g/L of methyl methacrylate dissolved in a 0.1 wt % D(2)O solution of polystyrene-poly(methacrylic acid) (PS-PMA) micelles. According to NMR and small-angle neutron scattering (SANS), most of the poly(methyl methacrylate) (PMMA) is adsorbed at the core-shell interface of the particles. A small fraction of shorter PMMA probably sticks to outer parts of the PMA chains. The absorption kinetics and equilibria of benzene and chloroform were studied by NMR and SANS time-resolved experiments. The diffusion front in the PS core is very narrow but quite broad in the PMMA sheet suggesting, thus, a less compact state of PMMA. According to SANS, the diffusion kinetics is almost independent of the PMMA sheet thickness. In contrast to it, the absorption capacity, reflected by both SANS and NMR, increases markedly with the PMMA content in the particle. The maximum amount of solubilized compound depends on its positive interaction with PMMA (expressed by the chi parameter) but is restricted by the growing interface tension between swollen PMMA and D(2)O. In accordance with this conclusion, a particle saturated with benzene can absorb chloroform only at the expense of a part of benzene expelled into the surrounding medium and vice versa. Starting with 10 g PMMA/L (10 times the weight of the original micelles), the particles become unstable when being swollen with a good solvent.
Abstract: Small-angle neutron scattering studies on 1-propanol -- heavy water mixtures were performed in the mole fraction range of 0.02 - 0.6 at 20C. From the experimental data the Kirkwood-Buff integrals were calculated and compared with those obtained by SAXS and from thermodynamic data. It was demonstrated that SANS is a suitable method to determine the Kirkwood-Buff integrals in liquid mixtures.
Abstract: Quasi-elastic neutron scattering measurements (QENS) were performed on aqueous solutions of 3-picoline (3-methyl pyridine) at room temperature. H-D substitution on both the solute and the water was used to separate the dynamics of the two species. The analysis of the translational diffusive motion at different concentrations shows that at high picoline content the diffusion coefficient of water decreases strongly and becomes similar to that of the solute, indicating strong coupling between the motions of the solute and the solvent. Activation energies characteristic of the dynamic behavior of the methyl group were determined from 1H spin-lattice relaxation rate measurements for H2O and D2O solutions of 3-picoline above 310 K.
Abstract: The molecular and crystal structure of 2-methylpyridine or 2-picoline (1), melting point 206 K, was obtained from single crystal X-ray diffraction data by low-temperature crystallization of the liquid in a thin capillary on the diffractometer SMART 1000 CCD in a cold N2 gas stream. The molecule has almost Cs symmetry with all atoms in a plane except two hydrogen atoms of the CH3 group. Molecular geometry parameters obtained from the X-ray data and corrected for libration effect are in good agreement with those obtained from our ab initio calculations. Interesting peculiarity of the crystal packing of (1) is the CâHÏ intermolecular contact with short HX distance 2.64 Ã, which can bring about the packing motif of (1) (X is the center of the aromatic ring, C is a carbon atom of the ring).
Abstract: The mixture of 3-methylpyridine (3MP) and heavy water was studied in the concentration range of 0.25-4 mol% at 25 degrees C and 50 degrees C by small-angle neutron scattering. Measurements on the water-rich side of the closed-loop phase diagram showed that the aggregation of 3MP molecules sets in already at very small concentrations. It indicates the presence of effective attractive interactions between the solute molecules, which lead to phase separation at higher concentrations.
Abstract: A SANS study revealed the orientational stabilisation of the smectic structure by non-mesogenic polymer networks dispersed in a liquid crystal matrix. In the present experiment, hydrophobic silica particles were dispersed in liquid crystal 8CB. The Bragg reflections from smectic layers show that the alignment of the layers is perfect if the system is cooled down in a magnetic field. After annealing without magnetic field and cooling down to smectic A phase, the previous alignment of the liquid crystal is recovered. Temperature and concentration dependence of the effect has been analysed by recording the diffraction pattern from smectic layers.
