Search

Understanding interactions between nanoparticles and model membranes is relevant to functional nano-composites and the fundamentals of nanotoxicity. In this study, the effect of polyamidoamine (PAMAM) dendrimers as model nanoparticles (NP) on the mesophase behaviour of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) has been investigated using high-pressure small-angle X-ray scattering (HP-SAXS). The pressure-temperature ( p − T ) diagrams for POPE mesophases in excess water were obtained in the absence and presence of G2 and G4 polyamidoamine (PAMAM) dendrimers (29 A and 45 A in diameter, respectively) at varying NP-lipid number ratio (ν = 0.0002–0.02) over the pressure range p = 1–3000 bar and temperature range T = 20–80 °C. The p − T phase diagram of POPE exhibited the Lβ, Lα and HII phases. Complete analysis of the phase diagrams, including the relative area pervaded by different phases, phase transition temperatures (Tt) and pressures (pt), the lattice parameters (d-spacing), the pressure-dependence of d-spacing (Δd/Δp), and the structural ordering in the mesophase as gauged by the Scherrer coherence length (L) permitted insights into the size- and concentration-dependent interactions between the dendrimers and the model membrane system. The addition of dendrimers changed the phase transition pressure and temperature and resulted in the emergence of highly swollen lamellar phases, dubbed Lβ-den and Lα-den. G4 PAMAM dendrimers at the highest concentration ν = 0.02 suppressed the formation of the HII phase within the temperature range studied, whereas the addition of G2 PAMAM dendrimers at the same concentration promoted an extended mixed lamellar region in which Lα and Lβ phases coexisted. Statement of Significance Using high pressure small angle X-ray scattering in the pressure range 1–3000 bar and temperature range 20–60 °C, we have studied interactions between PAMAM dendrimers (as model nanoparticles) and POPE lipid mesophases (as model membranes). We report the pressure-temperature phase diagrams for the dendrimer-lipid mesophases for the first time. We find that the dendrimers alter the phase transition temperatures (Tt) and pressures (pt), the lattice parameters (d-spacing), and the structural order in the mesophase. We interpret these unprecedented results in terms of the fluidity of the lipid membranes and the interactions between the dendrimers and the membranes. Our findings are of fundamental relevance to the field of nanotoxicity and functional nanomaterials that integrate nanoparticles and organized lipid structures.

Positron Annihilation Lifetime Spectroscopy (PALS) has been employed to characterize the temperature dependence of the local free volume of hydrophobically-modified starch (HMS) – sucrose (S) blends as a function of blend composition and water content. The findings from PALS support the conclusions drawn from thermodynamic characterization using Differential Scanning Calorimetry (DSC) showing evidence of limited phase separation between the HMS and S phases, inferred from the drastic change in the temperature dependence of the average size of the local free volume element as a function of blend composition. The effect of water content on the average local free volume element size is in good agreement with previous studies on simpler carbohydrate polymer/low molecular weight inclusion blends, however, the width of the free volume distribution is also observed to be affected by water content. This is interpreted to be related to the heterogeneity of the free volume holes, which is higher for phase-separated systems comprising phases of different composition and molecular weight distribution. Wide angle X-ray scattering (WAXS) was employed to study the crystallinity of the blends, showing limited crystallinity is present in the blends at the highest water contents with origin in the corn starch (CS) added during processing, and not the HMS and S phases.

Stable suspensions of gold nanorods in 4-cyano-4′-pentylbiphenyl (5CB) have been prepared by capping the nanoparticles with polyethylene glycol (PEG). Small angle X-ray scattering has been used to characterize the orientational order of the gold nanorods and the properties of any aggregates. It was found that the nanorods had a very high degree of orientational order with respect to the director of the 5CB matrix and this could be redirected by an applied electric field at 2kHz. Two different PEG molecular weights were investigated and it was found that the lower (1.9kDa) gave exceptionally high order parameters, above 0.9.

The structure and phase behavior of colloidal solutions of monodisperse rod-shaped micelles, of different lengths (ca. 300–2100 nm) and formed from poly(ferrocenylsilane)-block-polyisoprene (PFS-b-PI) diblock copolymers, have been investigated using synchrotron small-angle X-ray scattering. The dimensions of the crystalline PFS core, solvated PI corona, and the overall radial polydispersity were measured, and relationships between the characteristics of the constituent copolymers and the internal structure of the self-assembled micelles have been established. In addition, the effects of micelle length, length distribution, concentration, composition, and block length on the liquid crystalline phase behavior of the micelles have been determined. It was found that micelle dispersions exist in three distinct phases: isotropic, nematic, and hexagonally packed, depending predominantly on their concentration and aspect ratio. The results have also highlighted the importance of the coronal composition and struct...

Here X-ray reflectivity has been used to determine the structure of liquid crystal monolayers for different cyanobiphenyl homologues supported on aqueous solutions of two different salt species. Sodium iodide induces homeotropic ordering for all of the monolayer forming liquid crystal homologues studied here, and forms a Stern layer of iodide ions at the liquid crystal cyano headgroup, similar to the case of lipids or surfactants supported on electrolyte solutions. The liquid crystal headgroups were also found to penetrate into the water surface when binding with iodide ions. Sodium bromide, however, does not form the same localisation of ions close to a liquid crystal monolayer, and instead appears to produce no noticeable change in the scattering length density of the liquid crystal monolayer compared to pure water. However, on further compression the X-ray reflectivity dramatically changes, revealing the emergence of the so-called “trilayer” structure for 5CB and 8CB. This transition occurs at a lower areal density for sodium bromide than for pure water, and unlike for the uncompressed film, a layer of bromide ions was found at the trilayer-water interface.

Self-assembled “cross” architectures are well-known in biological systems (as illustrated by chromosomes, for example); however, comparable synthetic structures are extremely rare. Herein we report an in depth study of the hierarchical assembly of the amphiphilic cylindrical P–H–P triblock comicelles with polar (P) coronal ends and a hydrophobic (H) central periphery in a selective solvent for the terminal segments which allows access to “cross” supermicelles under certain conditions. Well-defined P–H–P triblock comicelles M(PFS-b-PtBA)-b-M(PFS-b-PDMS)-b-M(PFS-b-PtBA) (M = micelle segment, PFS = polyferrocenyldimethylsilane, PtBA = poly(tert-butyl acrylate), and PDMS = polydimethylsiloxane) were created by the living crystallization-driven self-assembly (CDSA) method. By manipulating two factors in the supermicelles, namely the H segment-solvent interfacial energy (through the central H segment length, L1) and coronal steric effects (via the PtBA corona chain length in the P segment, L2 related to the degree of polymerization DP2) the aggregation of the triblock comicelles could be finely tuned. This allowed a phase-diagram to be constructed that can be extended to other triblock comicelles with different coronas on the central or end segment where “cross” supermicelles were exclusively formed under predicted conditions. Laser scanning confocal microscopy (LSCM) analysis of dye-labeled “cross” supermicelles, and block “cross” supermicelles formed by addition of a different unimer to the arm termini, provided complementary characterization to transmission electron microscopy (TEM) and dynamic light scattering (DLS) and confirmed the existence of these “cross” supermicelles as kinetically stable, micron-size colloidally stable structures in solution.

The intriguing twist-bend nematic (NTB) phase is formed, primarily, by liquid crystal dimers having odd spacers. Typically, the phase is preceded by a nematic (N) phase via a weak first-order transition. Our aim is to obtain dimers where the NTB phase is formed directly from the isotropic (I) phase via a strong first-order phase transition. The analogy between such behaviour and that of the smectic A (SmA)–N–I sequence suggests that this new dimer will require a short spacer. This expectation is consistent with the prediction of a molecular field theory, since the decrease in the spacer length results in an increase in the molecular curvature. A vector of odd dimers based on benzoyloxybenzylidene mesogenic groups with terminal ethoxy groups has been synthesised with spacers composed of odd numbers of methylene groups. Spacers having 5, 7, 9 and 11 methylene groups are found to possess the conventional phase sequence NTB–N–I; surprisingly, for the propane spacer, the NTB phase is formed directly from the I phase. The properties of these dimers have been studied with care to ensure that the identification of the NTB phase is reliable.

X-ray and neutron scattering investigations have been made on two series of liquid crystal dendrimers. The low generations (first to fourth) predominantly show smectic phases. The fifth generation shows a tendency to form columnar phases and two different types have been observed. The transition from smectic to columnar has been explained in terms of the distance between the dendritic core and the mesogenic units. As the generation number is increased, the distance increases until it becomes greater than the maximum length of the flexible spacers causing a change in molecular shape and the formation of columnar phases. Although the materials are nearly monodisperse, the small variation in the number of mesogens per molecule gives rise to some subtle structural effects. Two coexisting structures have been observed over large temperature ranges in some materials and small angle neutron scattering indicates that there is some microphase segregation which is a reversible function of temperature.

Amphiphilic carbosilane liquid-crystalline codendrimers with terminal mesogenic butoxybenzoate and phenolic groups have been synthesized for the first time. The structures and compositions of the synthesized codendrimers were characterized by NMR spectroscopy. The data from polarization optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering demonstrated that all codendrimers possessed mesomorphic properties. They form thin (Langmuir) films at the water-air interface. The surface pressure-surface area isotherms were plotted. The Langmuir-Blodgett films of different thicknesses were obtained by the vertical dipping method on the solid substrate. The film structures were studied by grazing incidence X-ray diffraction analysis.

The first series of carbosilane liquid crystal codendrimers with groups of different polarity has been synthesized. The chemical structure of the newly synthesized materials and the composition of the codendrimers were studied by NMR spectroscopy and MALDI-TOF MS. It was found that the codendrimers tend to form stable Langmuir films at the air-water surface. The influence of composition and generation number on surface pressure-surface area isotherms and film stability was studied. Brewster angle microscopy confirmed the different phase behavior for monolayers of different codendrimer composition and generation number. It was found that side groups of fifth-generation codendrimers do not segregate, unlike those of lower generations. Langmuir-Blodgett films on solid substrates were obtained by the vertical dipping method. X-ray diffraction showed that the codendrimers with 75% of hydrophobic mesogenic terminal groups formed ordered layers parallel to the substrate.

The structure of a ferroelectric liquid crystal mixture with an N∗ → SmC∗ transition in skew aligned cells has been studied by X-ray diffraction measurements of the layer normal distribution. The rubbing directions of the cells were set parallel, and skewed at ±9°, ±18° and ±40°. The cell with parallel alignment directions showed two sets of layers with normals twisted in-plane by ∼±20° from the rubbing direction. The layer normal distribution of each set of layers was consistent with a chevron-like structure but with an additional untilted region, probably at the apex. It was also observed that the tilt of the chevron arms was weakly temperature dependent, with their normals tilting out of the plane of the device by an angle of 9° to 12° on cooling. The cells with alignment skewed by ±9° and ±18° also showed chevron-like structures which are probably developed in the middle of the cell with each arms tilted by ∼20° and with normals slightly twisted in-plane by ±4° with respect to the mean rubbing directi...

The orientational order parameters P2, P4, and P6 have been determined by neutron scattering from a mixture of normal hydrogenous and deuterium labeled molecules in the nematic, smectic A and smectic C phases of the mesogen 2′,3′-difluoro-4-heptyl-4″-nonyl-p-terphenyl. Since the method relies on a knowledge of the molecular structure, the influence of different molecular conformations resulting from the terminal chains on the values determined was examined in detail. It was shown that the choice of conformation could significantly effect the resulting values of the order parameters. The order parameters were, therefore, determined by assuming a distribution of conformations for the alkyl chains. The relative contributions of these conformations were governed by the Flory rotational isomeric state model. The values for P2 were consistent with those determined by nuclear magnetic resonance but all the order parameters were generally much greater than those predicted by the Maier–Saupe theory.

Using a combination of neutron reflectivity and a surface force type apparatus, the hydration of polyelectrolyte multilayers, PEMs, is investigated under mechanical confinement. The samples consist of poly(styrenesulfonic acid), PSS, and poly(allylamine hydrochloride), PAH, which were formed by spin-coating with 11, 23, and 47 bilayers. The terminating layer polyelectrolyte of the PEMs was also varied. Selectively deuterating some layers and using a model that separately considers the last layer from the other strata representing the material structure of the PEM allow a low-resolution hydration distribution within the PEM to be determined. When swollen with H2O and unconfined, PSS-terminated PEMs are approximately 26% v/v water, and this decreases to 15% with an applied pressure of 5 bar. By comparison, PAH-terminated PEMs are 20% water when unconfined and dehydrate to 10% water at 5 bar. For all samples, the final adsorbed layer is significantly more hydrated at approximately 40% v/v. The water is generally uniformly distributed within the bulk of a PEM; however, there is a significant increase in hydration in the bilayers adjacent to the final layer in PAH-terminated PEMs. Also considered is an experiment where the inherent charge of the final adsorbed layer of a PEM is neutralized by compressing it with an oppositely charged PEM. This determines the hydration for an uncharged PEM and demonstrates that the influence of the potential of the final layer on a PEMs’ internal hydration is a perturbation. A detailed scheme is then presented whereby the amount and distribution of internal charge are directly responsible for the hydration of a PEM.

This paper presents a systematic study of two series of carbosilane liquid crystalline (LC) dendrimers from first to fifth generations bearing 8, 16, 32, 64 and 128 terminal chiral mesogenic groups...

A hexadecamer, first-generation, octasilsesquioxane liquid-crystalline dendrimer was synthesized by a platinum-catalyzed hydrosilylation reaction of the parent first-generation vinyl octasilsesquioxane dendrimer with a modified, laterally substituted mesogen. The structure and purity of the octasilsesquioxane substrate was confirmed by 1H, 13C, and 29 Si NMR spectroscopy, microanalysis, and size exclusion chromatography (SEC). The mesogenic substrate was found to exhibit only a chiral nematic phase, whereas the resulting hexadecamer dendrimer displays enantiotropic chiral nematic, disordered hexagonal columnar, and disordered rectangular columnar phases, with a glass transition below room temperature. The lateral or side-on attachment of the mesogen to the dendritic core was found to be a key design feature in the formation of the mesophases.

A systematic study of the influence of generation number on the phase behavior of LC dendrimers is presented. For this purpose, phase behaviors and structures of first to fifth generations of liquid crystalline (LC) carbosilane dendrimers with 8, 16, 32, 64, and 128 terminal cyanobiphenyl groups were investigated. Investigation of thermal behavior of the LC dendrimers by means of polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction experiments reveals smectic-type mesophases over a wide temperature region. It is shown that with increasing generation number the isotropization temperature increases whereas the enthalpy of this phase transition decreases. The strongest influence of spherical molecular architecture on the phase behavior of the LC dendrimers appears at high generations. In the case of LC dendrimer of the fifth generation, it leads to the formation of two levels of a structural organization. This dendrimer forms different supramolecular nanostructures of colum...

Two Laponite clays, of general formula [Mn+]x/n [Lix Mg6-x Si8 O20 Fy (OH)4-y], were prepared with different Li+ levels (0.57 and 0.70% w/w) and F- levels (9.5 and 9.9% w/w). The clays were characterized by measurements of nitrogen adsorption isotherms, cation exchange capacity, and conductometric titration data. The clay with higher Li+ and F- levels had a higher (more negative) face charge and a lower (less negative) edge charge. Small-angle X-ray scattering (SAXS) data obtained from dilute aqueous dispersions indicate that both clays are of similar particle size (diameter ca. 40 nm and thickness ca. 3.5 nm). Experimental structure factors for concentrated Laponite dispersions were calculated using the ratio of scattered X-ray intensities from concentrated and dilute dispersions. Maxima in the experimental structure factors were observed at scattering angles of 0.14−0.2 nm-1 under favorable solution conditions (pH ≥ 9 and ionic strength ca. 5 × 10-3 mol dm-3) for one of the Laponite clays. These results...

For the first time a series of liquid crystalline dendrimers of generations 1–4 containing 8, 16, 32 and 64 terminal methoxyphenyl benzoate mesogenic groups respectively have been synthesised. Mesogenic groups were attached to the carbosilane dendritic matrices with terminal allyl groups through -OOC-(CH2)10-Si(CH3)2OSi(CH3)2- spacer by a hydrosilylation reaction. Structure and purity of all new compounds were confirmed by 1H-NMR spectros-copy and GPC analysis. Phase behaviour of LC dendrimers was investigated by means of polarising optical microscopy, DSC and X-ray methods. All LC dendrimers synthesised display mesophases of smectic types as well as crystalline phases over wide temperature region. Possible structure and arrangement of molecules of LC dendrimers in these mesophases are discussed.

We have studied the structure of two series of liquid crystalline dendrimers based on the carbosilane dendritic matrix. Generations 1 to 5 have been investigated for the series with cyanobiphenyl mesogenic groups and generations 1 to 4 for the series with methoxyphenyl benzoate mesogenic groups. Generations 1 to 4 of both series show a diffraction pattern corresponding to a simple smectic phase with disordered layers indicating that the tendency of the mesogenic units to form smectic layers overcomes the restrictions imposed by the globular dendritic core of the molecule. The variation of layer spacing with temperature and generation number indicates that there are subtle differences in the packing of the mesogens in the different samples. The 5th generation of the dendrimers with cyanobiphenyl groups shows the same smectic structure below 40[ddot]C but at higher temperatures there is some in-plane structure that suggests that columns may be formed. This can be rationalised in terms of the molecu...

The Small Angle Neutron Scattering (SANS) from specifically deuterated samples of side-chain liquid crystal polymers has been used to determine the dimensions of the backbone both parallel and perpendicular to the director as well as the degree of polymerisation. It has been possible to determine the effect of molecular weight on the chain dimensions in the smectic phase. There is strong anisotropy of the backbone conformation and it becomes stronger as the molecular weight increases. This means that the tendency for the chains to be confined between the smectic layers is stronger for larger molecular weight polymers.

The structure of a liquid crystalline (LC) carbosilane dendrimer of the fifth generation bearing 128 terminal cyanobiphenyl mesogenic groups has been studied. This dendrimer was synthesized by a hydrosilylation reaction and then the cyanobiphenyl mesogenic groups were chemically linked to the dendritic matrix via a-OOC-(CH2)10-Si(CH3)2OSi(CH3)2-spacer. Structural studies carried out by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction methods revealed unusual phase behaviour. At room temperature the dendrimer forms a lamellar (smectic A) phase which develops in-plane ordering above 40C.This is due toa tendency to form columns ofmolecules which areprobably perpendicular to the layers. Above 121C the material transforms into another more disordered mesophase which is probably a disordered hexagonal columnar phase. The proposed structures and molecular packing in these different types of mesophase are discussed.

The incoherent quasi-elastic neutron scattering from the heptyl and octyl derivatives of the acta-alkylphthalocyanines, CnPcH2, in their crystalline and liquid crystalline (discotic columnar) phases has been measured. Diffusive motion is observed on the 10-10 to 10-12 s timescale. This is interpreted as alkyl chain motion. A detailed comparison of the mesophase data for C7PcH2 has been made with the predictions of the rotational isomeric state model, and an 2 extra motion on this timescale has been invoked, which probably is a localized translational motion. A small discontinuity in the elastic fraction of the quasi-elastic scattering is consistent with a change in the molecular tilt at the transition between the two Dhd phases.

The conformation of the backbone in the side chain liquid crystal polymer poly\[omega (4-methoxybiphenyl-4-yloxy)butyl methacrylate] has been studied in the smectic C and nematic phases. Small angle neutron scattering experiments were performed on mixtures of molecules with perdeuteriated backbones and unlabelled molecules. The polymer is found to adopt an oblate conformation in the smectic C phase. The components of the radius of gyration parallel and perpendicular to the director are determined as a function of temperature from Guinier plots of the SANS data. The radii of gyration do not vary across the smectic phase and are found to be Rg,||=(27+/-1)A, Rg, =(42+/-1)A. These results are compared with recent SANS results for other side chain liquid crystal polymers.

The long range orientational order in the nematic phase of 4,4′‐dimethoxyazoxybenzene (PAA) has been studied using small angle neutron scattering (SANS) from mixtures of protonated and perdeuterated molecules. Unlike spectroscopic methods, the determination of the complete set of orientational order parameters is, in principle, possible using this technique. The orientational order parameters were extracted from the anisotropic single molecule scattering isolated at small scattering angles. These order parameters were compared to those extracted from previous neutron scattering measurements, to second rank order parameters extracted from NMR, and to those predicted from the Maier–Saupe theory of nematic ordering. It was found that only the second and fourth rank terms in the expansion of the single molecule scattering in a basis of Legendre functions are statistically significant, which means that the order parameters P2 and P4 only could be obtained. For the semirigid nematogen PAA, the Maier–Saupe theory is found to underestimate P2 and its dependence on the reduced temperature T/TNI where TNI is the nematic–isotropic (NI) transition temperature. The theoretical values of P4 are, however, in remarkably good agreement with the measured values. Order parameters extracted from NMR are found to be slightly lower than those determined from the SANS experiment, and we also make comparisons with earlier neutron scattering results. Singlet orientational distribution functions are reconstructed from the measured order parameters using the maximum entropy method.

The 4-substituted tris(3,5-dimethylpyrazolyl)borato compounds [Mo(CO)2 (NO){HB(4-R-dmpz)3}] (R  Me, Et, Bun and C5H11) and [MoCl2(NO){HB(4-R-dmpz)3}] (R  Me or Bun) have been prepared and characterized spectroscopically and electrochemically. X-ray crystal structural determination of [Mo(CO)2(NO){HB(4-R-dmpz)3}] (R  Bun) revealed that the n-butyl chains attached to the 4-position of the pyrazolyl rings were oriented, overall, in a random fashion, although the first and second C atoms of each chain extended in a star-shaped configuration, similar to that observed in [Mo(CO)2(NO){HB(4-bzdmpz)3}] (4-bzdmpz = 4-benzyl-3,5-dimethylpyrazolyl).

The smectic A to smectic C* transition of a commercial ferroelectric mixture (SCE13 and its racemic mixture) has been studied within a surface stabilised cell using X-ray ‘rocking curve’ techniques. An unusual distribution of the layer orientation in the smectic A phase implies the existence of a tilted structure. This phenomenon in the smectic A phase is believed to be a result of an unusual temperature dependence of the layer thickness and a comparison with a typical material is reported.

A series of side-chain liquid crystal polymers have been screened for successhl deposition using the Langmuir Blodgett method. It was found that the best materials had glass transitions below room temperature. The behaviour of the spread film of one material was studied in detail using surface isotherms, surface potential, X-ray and neutron reflection techniques. It was found to undergo a phase transition from a thin, low density film to a thicker, more dense one as the surface pressure was increased. This corresponds to a reorientation of the mesogenic units so that about half of them point upwards. At higher pressure a transition to a multilayer occurs on the water surface. In the surface pressure range where deposition is possible, neutron reflection shows that the spread film has a stratum of close packed mesogenic units outermost and the total thickness (38 A) agrees very well with the smectic layer spacing in the bulk. This similarity in structure could explain the ease of deposition.

Self-assembled disc-shaped clusters of hexagonally packed, thiol-functionalized gold nanorods are prepared and dispersed in thermotropic nematic liquid crystals. The resultant hybrid complex fluids exhibit colloidal anisotropy with very high orientational order and are characterized by SAXS as shown in the figure. Precise, reconfigurable control of the cluster orientation at very low electric field strengths (0.18 V μm(-1) ) is achieved.

The Langmuir monolayer and Langmuir-Blodgett (LB) deposition behaviour of asymmetrically substituted 1,4-bis(6-hydroxyhexyl)−8,11,15,18,22,25-hexa-octylphthalocyanine (1) and a phthalocyanine dimer (2) and trimer (3) have been investigated. The materials were also deposited onto glass by the spin coating (SC) technique. The spin coated films were exceptionally smooth, even and free from crystallites. X-ray reflectivity measurements reveal varying degrees of order. Unpolarized UV-visible absorption spectra of the films deposited by the two techniques were closely similar. The LB technique has the advantage of introducing some degree of anisotropic ordering of the molecules within the films of the monomer and dimer whereas the SC method has the advantage of convenience.

Reaction of [HB(bdmpz)3]–, obtained by reaction of 4-benzyl-3,5-dimethylpyrazole (Hbdmpz) with KBH4, with [M(CO)6](M = Mo or W) and p-MeC6H4SO2N(NO)Me afforded [M(CO)2(NO)-{HB(bdmpz)3}](M = Mo or W). The molybdenum carbonyl was converted into [Mo(NO)-{HB(bdmpz)3}X(Y)](X = Y = Cl, I or OC6H4Me-p; X = Cl, Y = OMe or OC6H4Me-p) the spectral and electrochemical properties of which are virtually identical to those of [Mo(NO){HB(dmpz)3}X(Y)](Hdmpz = 3,5-dimethylpyrazole), indicating that the addition of a benzyl group has no significant electronic effect in the new species. However, a crystal and molecular structure determination of [Mo(CO)2(NO){HB(bdmpz)3}] revealed that the molecule has a highly symmetrical structure, the CH2groups of the benzyl groups in the tris(pyrazolyl)borate ligand being disposed in a star-shaped configuration where the phenyl rings adopt an ‘inverted’ bowl-like structure with the BH group inside and the Mo(CO)2(NO) group outside the bowl. The arrangement of the 4-benzyl groups with respect to the pyrazolyl rings and the H–B ⋯ Mo three-fold axis is strongly reminiscent of an inverted three-legged ‘Isle of Man’ symbol.

The monolayer and LB film-forming properties of 20 structurally related amphiphilic octa-substituted phthalocyanine derivatives have been assessed. The molecular packing within examples of the films has been probed by visible-region spectroscopy and low-angle X-ray diffraction methods. Among derivatives where the aliphatic substituents are attached by ether linkages, there is a variation in the behaviour according to the length of the chains and whether or not the chains are branched. Films are not highly ordered but may contain domains of ordered structure, giving rise to a red-shifted absorption band in the visible spectrum. Analogues where the chains are attached by carbon–carbon bonds show superior monolayer behaviour and are excellent materials for deposition as LB films. Furthermore, there is good evidence from the spectra that change in the length of the alkyl chains provides a means of controlling the type of molecular packing within the films.

Application of the technique of specular neutron reflection to the study of adsorbed layer structure is illustrated for the case of β-casein at the air—water interface in the presence and absence of nonionic water—soluble surfactant C12E6. Guinier analysis of reflectivity data for a 5 × 10−3 wt% solution of pure β-casein in air-contrast-matched water (8 vol% D2O) at pH 7.0 gives a time-independent adsorbed amount of 2.05 ± 0.10 mg/m2 and an adsorbed layer thickness of 1.65 ± 0.07 nm; these values are found to increase quite substantially as the pH is reduced towards the protein's isoelectric point. In the presence of surfactant the loss of reflectivity is a direct measure of protein displacement from the interface because the hydrogenated surfactant is almost contrast matched to the aqueous phase. At a C12E6 concentration in the range 2–2.5 × 10−4 wt% (surfactant: protein molar ratio, R ≈ 2.2), there is roughly half the protein lost from the interface but little change in adsorbed layer thickness as inferred from the slopes of the Guinier plots. Protein is effectively completely removed from the surface for R ≳ 10. These results are in semi-quantitative agreement with complementary competitive adsorption data for β-casein in soya oil-in-water emulsions.

Structural studies of a series of laterally attached side chain liquid crystalline polysiloxanes have been made by X-ray diffraction. All but one exhibit a nematic phase with SC-like short range ordering. The diffraction has been interpreted in terms of a model in which the mesogenic units form a ‘jacket’ around the polymer backbone. The backbone conformation has been studied by small angle X-ray scattering from oriented samples of mesomorphic solutions and by infrared dichroism measurements on oriented samples of the polymers. In both cases the results were consistent with the mesogens being oriented parallel to the backbone which is consistent with the ‘mesogen jacket’ model.

Three side chain liquid crystal polymers have been studied by neutron scattering methods. We have compared the three compounds, all with a polysiloxane backbone, a four-atom flexible spacer, (CH2)3O, and a benzoate ester mesogenic unit. However, the mesogenic unit was terminated by one of three different groups. The hexyloxy and cyano derivatives gave smectic A phases and the methoxy gave a nematic. Small angle neutron scattering measurements of mixtures of deuteriated and hydrogenous versions of the same polymer have been used to determine the dimensions and anisotropy of the backbone. The anisotropy was found to be similar in the smectic and nematic phases and suggested a tendency for the polymer backbone to be confined between the layers of mesogenic units. The SANS results show two different characteristic sizes. One is attributed to the size of a single polymer molecule. The other indicates density fluctuations on a scale larger than one polymer molecule. The local packing of the mesogenic u...

The mesophase behaviour of a number of non-peripherally octa-substituted phthalocyanine derivatives has been studied by optical microscopy, differential scanning calorimetry (DSC) and X-ray diffraction. A homologous series of straight chain alkoxymethyl derivatives has exhibited both rectangular and hexagonal columnar mesophases, with the rectangular phases being favoured by the shorter chains. Two branched chain derivatives were found to give rectangular columnar phases at room temperature. A detailed analysis of the X-ray data has shown some differences from the analogous n-alkyl compounds. It has been deduced that the increased polarizability and flexibility of the ether linkage allows the disc-like molecules to approach more closely face to face with correspondingly thicker columns.

Thermotropic mesomorphism has been observed in a highly substituted and asymmetrically shaped tetrabenzotriazaporphyrin (TBTAP) derivative. TBTAP has a ring system closely related to that of phthalocyanine, however the single maso-carbon provides an additional site for the attachment an alkyl chain. The TBTAP mesogen has a pentadecyl group at this site as well as a bulky neopentoxy substituent attached to each of the four peripheral benzo-portions of the macrocycle. Optical texture (focal-conic fan) and X-ray diffraction studies suggest that the TBTAP has a mesophase with a lamellar structure analogous to that of the smectic A phase of rod-like molecules. Such a mesophase has not been observed previously from discotic compounds.

Reaction of tran.s-4-alkyloxy-4′-stilbazoles (n-OPhVPy) with silver dodecylsulphate (AgDOS) led to the complexes [Ag(n-OPhVPy)2][DOS] which showed thermotropic mesomorphism. All homologues from met...

A selection of novel materials exhibiting smectic polymorphism has been studied by X-ray diffraction. The smectic A and smectic C phases were generally identified from the diffraction patterns of mag netically aligned samples in Lindemann tubes. Some of the crystal smectic phases were identified by indexing the diffraction lines from the powder patterns. However it was not possible to distinguish between the hexatic phases (i.e., SB, SF and SI) by diffraction from magnetically aligned samples in Lindemann tubes because sufficiently large monodomains could not be obtained. We therefore prepared monodomain, free-standing films and recorded diffraction patterns. The distribution of scattered X- ray intensity amongst the six equatorial spots is characteristic of the phase if the beam is perpendicular to the smectic layers. However, if the beam is not perpendicular, identifying the phase is more complicated. We have therefore calculated the diffraction pattern expected for any unit cell and angle of i...

Discotic columnar mesophase behaviour exhibited by ten metal-free and copper 1,4,8,11,15,18,22,25- octa-alkylphthalocyanines has been characterised by optical microscopy, differential scanning calorimetry, x-ray diffraction and electronic absorption spectroscopy. Compounds with side-chains as short as hexyl exhibit one or more mesophases, and a total of three different mesophases are apparent for the series as a whole. The highest temperature mesophase is assigned as Dhd. At lower temperatures, some compounds develop a second mesophase of hexagonal symmetry, whereas others form a mesophase of rectangular symmetry. One example shows all three mesophases.

Molecular assemblies within Langmuir–Blodgett (LB) films of 1,4,8,11,15,18-hexaoctyl-22,25-bis(carboxypropyl)phthalocyanine (1a) copper 1,4,8,11,15,18-hexanonyl-22,25-bis(carboxypropyl)phthalocyaninate (1b) and 1,4,8,11,15,18-hexadecyl-22,25-bis(carboxypropyl)phthalocyanine (1c) have been examined using X-ray diffraction, RAIRS and polarised optical spectroscopy. The LB films are constructed as bilayers by Y-type deposition and the resulting assemblies give rise to visible-region absorption spectra closely similar to those of crystallised films of octaalkylphthalocyanines. When heated, the molecular assemblies within the LB films of 1a and 1b reorganise irreversibly to a form in which the bilayer spacing is reduced. The transition from one type of packing to another is sharp for the film of 1a but occurs over a wide temperature range for the film of 1b. Heating the film of 1c to 140 °C modifies the packing but in this case a further modification occurs on cooling.

Neutron reflection was used to measure the buildup of layers at a solid surface as the smectic phase is approached from higher temperatures in a nematic liquid crystal. The liquid crystal was 4-octyl-4'-cyanobiphenyl (8CB), and the solid was silicon with one of five different surface treatments that induce homeotropic alignment: (i) silicon oxide; (ii) a cetyltrimethylammonium bromide coating; (iii) an octadecyltrichlorosilane monolayer; (iv) an n-n-dimethyl-n-octadecyl-3- aminopropyltrimethyloxysilyl chloride monolayer; and (v) a lecithin coating. The development of surface smectic layers in the nematic phase of 8CB was followed by measuring specular reflectivity and monitoring the pseudo-Bragg peak from the layers. The scattering data were processed to remove the scattering from short-ranged smecticlike fluctuations in the bulk nematic phase from the specular reflection. The pseudo-Bragg peak at scattering vector Q approximately 0.2 A(-1) therefore corresponded to the formation of long-range smectic layers at the surface. The amplitude of the smectic density wave decayed with increasing distance from the surface, and the characteristic thickness of this smectic region diverged as the transition temperature was approached. It was found that the characteristic thickness for some of the surface treatments was greater than the correlation length in the bulk nematic. The different surfaces gave different values of the smectic order parameter at the surface. This suggests that the interaction with the surface is significantly different from a "hard wall" which would give the same values of the smectic order parameter and penetration depths similar to the bulk correlation length. Comparison of the different surfaces also suggested that the strength and range of the surface smectic ordering may be varied independently.

The synthesis of the first inorganic-organic hybrid liquid crystal dendrimers based on carbosilazane cores, which exhibit enantiotropic nematic and smectic C and columnar phase behaviour is presented and the liquid-crystalline phase properties and the phase structures are discussed.

The structure of adsorbed layers of the disordered milk protein β-casein at the air-water interface determined by specular neutron reflectivity measurements is presented and compared with results obtained from self-consistent-field modelling of a β-casein look-alike molecule at a solid-water interface. Changes in the layer structure with substrate pH in the range pH 5.5-7.0 have been determined experimentally and have been estimated theoretically. At pH 7 the neutron reflectivity data are fitted using a two-layer model of the adsorbed protein film consisting of a thin ( 10 A) protein-rich region (φ 0.95) at the interface and a thicker (45 A), more diffuse (φ 0.15), layer extending into the bulk aqueous phase. On reducing the substrate pH towards the protein isoelectric point, a thickening of the adsorbed layer is observed which is attributed to secondary adsorption of protein parallel to the monolayer observed at pH 7. The thicknesses of both layers in the fitted model, and the volume fraction of protein in the diffuse layer, increase to accommodate the extra protein. A model, linear chain polyelectrolyte consisting of apolar, polar (uncharged) and polar (pH-dependent charge) residues is constructed in a sequence which mirrors the known primary structure of β-casein. The adsorption behaviour of this casein look-alike at a solid-water interface is modelled using the self-consistent-field theories of Scheutjens and Fleer, under similar conditions of pH as for the specular neutron reflection experiments. Total segment density profiles are obtained which show very good qualitative agreement with the experimental results. At neutral pH, the monolayer profile φ(z) falls off in a smooth fashion from very high values at the interface (φ=0.95) to values close to the bulk concentration over about 50 A. On reducing the pH, the adsorbed amount is seen to increase, with the additional material appearing as a shoulder on the φ(z) profile, as observed in the neutron experiments.

The structures of the third and fifth generation of a liquid crystal dendrimer have been studied as a function of temperature and pressure using X-ray diffraction. The third generation LC dendrimer showed a crystal to smectic transition and increasing pressure simply increased the transition temperature. The fifth generation showed two different rectangular columnar phases and one hexagonal columnar phase. The application of pressure did not induce either of the rectangular phases to transform to a simple smectic phase, suggesting that they are slightly modified smectic phases. The hexagonal phase was more easily suppressed by the application of pressure, suggesting that the molecules are splayed into a disc-like conformation and become more cylinder-like under pressure.

The liquid-crystal properties are reported for a series of multinuclear phthalocyanines containing either two or three macrocyclic ring units. All but one of the compounds, the ‘dimer’ with the shortest spacer group between the two rings, exhibit discotic columnar mesophase behaviour. On cooling from the isotropic liquid the liquid-crystalline dimers show two distinct mesophases and the trimers one. Phase-transition temperatures are dependent upon the length of the linkages and whether or not copper is inserted into the macrocycle. The materials become very viscous, if not glass-like, when cooled to room temperature but retain the mesophase features defined by X-ray diffraction measurements.

Reaction of 4-alkoxydithiobenzoates (n-odtb, where n refers to the number of carbon atoms in the alkoxy chain) with divalent salts of nickel, palladium and zinc leads to complexes of the formula [M(n-odtb)2] where M = Ni, Pd and [Zn2(n-odtb)4] which are mesomorphic. The shortest-chain homologues of the Ni and Pd complexes show a nematic phase while at longer chain lengths, an SC phase is observed. Most homologues of the zinc complexes show a nematic phase with an SC phase appearing only for the longest homologues. The gold(III) complexes [AuX2(n-odtb)] are also mesomorphic and show the SA phase. Single-crystal X-ray structure determinations have been carried out for [Pd(8-odtb)2], [Zn2(4-odtb)4] and [Zn2(8-odtb)4], showing the first to be planar and the last two dinuclear with pseudo five-co-ordinate zinc atoms.

X-ray and neutron diffraction measurements of the intensity of the 00/ Bragg reflections from the smectic layers in hydrogenous and partly deuterated isobutyl 4-(4′-phenyl-benzylideneamino)cinnamate are reported. A model calculation has been used to deduce from these intensities, the configuration and orientational order of the molecules. The orientations of the long molecular axes are well ordered with P2 > 0.9 in S E, S B and S A phases and there is no appreciable interdigitation of the molecules of adjacent layers. These results are compared with those obtained from incoherent quasielastic neutron scattering experiments.