From Nucleation to Engineering of Crystalline Architectures at Air−Liquid Interfaces

Growing and making nano- and microcrystals

Thanks to recent technological advances in X-ray and micro-electron diffraction and solid-state NMR, structural information can be obtained by using much smaller crystals. Thus, microcrystals have become a valuable commodity rather than a mere stepping stone toward obtaining macroscopic crystals. Microcrystals are particularly useful for structure determination using serial data collection approaches at synchrotrons and X-ray free-electron lasers. The latter's enormous peak brilliance and short X-ray pulse duration mean that structural information can be obtained before the effects of radiation damage are seen; these properties also facilitate time-resolved crystallography. To establish defined reaction initiation conditions, microcrystals with a desired and narrow size distribution are critical. Here, we describe milling and seeding techniques as well as filtration approaches for the reproducible and size-adjustable preparation of homogeneous nano- and microcrystals. Nanocrystals and crystal seeds can be obtained by milling using zirconium beads and the BeadBug homogenizer; fragmentation of large crystals yields micro- or nanocrystals by flowing crystals through stainless steel filters by using an HPLC pump. The approaches can be scaled to generate micro- to milliliter quantities of microcrystals, starting from macroscopic crystals. The procedure typically takes 3-5 d, including the time required to grow the microcrystals.

Energetics and structures of the tilted phases of fatty acid Langmuir monolayers

Langmuir monolayers are monomolecular deep films composed of amphiphilic molecules which are typically confined to a water/air interface in a bi-dimensional structure. Due to the important applications in many research areas, they have been studied for many years. Their phase diagrams present several condensed phases, showing untilted or tilted structures at low values of surface pressure. In this paper, we present a novel density functional study on tilted phases of different fatty acid Langmuir monolayers. By means of this study, a further understanding of the physical chemistry properties and the nature of the formation of tilted monolayers can be achieved. Our calculations reveal that, regardless of the number of carbon atoms which form the apolar chain, the transversal (or conventional in the case of untilted phases) unit cell shows similar dimensions, ca. 4.9 × 6.8 Å, which is in fair agreement with the range of the observed data. The energy variation of the unit cell as a function of the inclination of the molecules, reveals an abrupt increase in values larger than 45° and 36° for NN- and NNN-tilt, respectively, in fair agreement with the experimental observation of L2h (NN) and L2' (NNN) phases of fatty acids. All of the fatty acids explored (from 10 to 19 carbon atoms) yield similar results. Finally, the energetics and structural changes of the monolayer along the variation of the area per molecule, obtained by enlarging in a-, b- or both axes of the untilted unit cell, have been explored. This study reveals that the untilted phases are energetically more stable at low values of area per molecule (high surface concentration), as it is expected. When the area per molecule values are increased, tilted phases (along NN or NNN-direction) with b/a ratio typical of herringbone (HB) or pseudo-herringbone (PHB) structures are found in the lowest energy configurations, which depend on how the distortion of the untilted unit cell is performed. For example, HB structures are the most stable when the molecules tilt along the enlarged axis of the untilted unit cell (a or b), meanwhile unit cell structures characteristic of PHB configurations occur in the opposite cases and at larger values of the area per molecule (low surface concentrations). All these predictions are in good agreement with the GIXD observations of the different phases of the phase diagram of fatty acid Langmuir monolayers.

Adaptability of monoglyceride-induced crystallization of K2SO4: effect of various anions and lipid chain splay

Understanding the interaction of a surfactant assembly with surrounding ionic compositions is critical in controlling the nanostructure formed by amphiphilic systems. In this study, we investigated the influence of specific anions upon the character of the crystallization process of a model inorganic salt (K2SO4) in an aqueous microdroplet (10-100 μm) in the presence of monolayers of monoelaidin (ME), monovaccenin (MV), monoolein (MO), and monolinolein (ML) assembled at a water-decanol interface. In particular, control monolayers of each monoglyceride at the water-oil interface did not accelerate nucleation (i.e., act as a template) of the crystallization of K2SO4. However, in the presence of 1-10 mM exogenous anions, certain types of monoglycerides did induce nucleation. The influence of the anions was consistent with the Hofmeister series. Monoglyceride monolayers in combination with chaotropic anions, such as SCN(-), imparted a euhedral crystal habit with a relatively lower C(onset), while kosmotropic anions showed less notable changes in the crystallization characteristics. However, this specific anion effect was seen only for monolayers of ME, MV, and MO but not for ML. This enhancement of nucleation-inducing ability upon addition of chaotropic anions appears to be related to the degree of chain splay: the larger the chain splay, the less anion efficiency in enhancing the templating capability. Our findings indicate that the improved nucleation-enhancing capabilities may originate from mutual interactions between anions and the monolayer, allowing the monoglyceride monolayers to adapt to a modulated self-assembled structure resulting in the greatest degree of control over K2SO4 crystallization.

Jones-Ray effect on the organization of lysozyme in the presence of NaNO3 at an air/water interface: is it a cause or consequence?

Interfacial rheology confirms the Jones-Ray effect resulting from a synergy between lysozyme and NaNO₃ at an air/fluid interface.

Conformational transitions of cytochrome c in sub-micron-sized capsules at air/buffer interface

This work presents the design of sub-micron-sized capsules of Cytochrome c (cyt c) in the range 300-350 nm and the conformational transitions of the protein that occur when the films of these capsules spread at the air/buffer interface are subjected to repeated compression-expansion cycles. Steady state fluorescence, time-resolved fluorescence, and circular dichroic (CD) spectra have been used to study the highly compact native conformation (70% helicity) of the protein in the capsules and its stability has been analyzed using cyclic voltammetry. The capsules have been characterized using zeta sizer and high resolution transmission electron microscopy (HRTEM). Surface concentration-surface pressure (Γ-π) isotherms of the films of the capsules spread at air/buffer interface following compression-expansion show destabilizing effect on cyt c. FTIR and CD spectra of these films skimmed from the surface show that the protein transitions gradually from its native helical to an anomalous beta sheet aggregated state. This results from a competition between stabilizing hydrated polar segments of the protein in the capsule and destabilizing nonspecific hydrophobic interactions arising at the air/buffer interface. This 2D model could further our understanding of the spatial and temporal roles of proteins in confined spaces and also in the design of new drug delivery vehicles using proteins.

Conformational and H-bonding preferences for facile racemate crystallization of ribose

Recalcitrant crystallization and syrup formation are frequent features of natural sugars. This is the case of D-ribose, yielding low-quality crystals of mixed α- and β-pyranose anomers. However, large crystals of DL-ribose can be grown easily. The crystal structures of stable D-ribose forms I and II as well as DL-form II have been analyzed in terms of their compatibility with the molecular aggregation. The comparison of the potential energy of all conformers and their OH···O hydrogen-bonding patterns is consistent with the preferential racemate crystallization in terms of departures from the optimized isolated ribose molecule and its directional interactions. This analysis is aimed at rationalizing the interplay between the molecular structure and spontaneous crystallization of chiral compounds.

Energy Analysis of Competing Non-Covalent Interaction in 1:1 and 1:2 Adducts of Collidine with Benzoic Acids by Means of X-Ray Diffraction

The hydrogen bond pattern and the types of non-covalent interactions in the crystals of the 1:1 and 1:2 adducts of 2,4,6-trimethylpyridine and benzoic acids are studied using high-resolution X-ray diffraction. The geometries of the hydrogen bonds are estimated using a combined XRD/DFT approach that provides the geometrical parameters within the margin of error of neutron diffraction studies. The energies of the non-covalent interactions are estimated on the base of the experimental electron density distribution function. It is shown that the structures of the adducts are governed by the NOH and OHO hydrogen bonds. In turn, C-H...O contacts and stacking interactions define the packing of the adducts in the crystal. On the other hand, it is important to note that the latter interactions affect the competition of the former hydrogen bonds in some 1:2 adducts.

Effect of specific anion on templated crystal nucleation at the liquid-liquid interface

In this work, we have investigated the effect of potassium salts of different anions upon the crystal nucleation of K(2)SO(4) as interfacially templated by a surfactant monolayer of 1-octadecylamine (ODA), in an aqueous microdroplet system bounded by a liquid-liquid interface with 1-decanol. The salts used were K(2)HPO(4), KCl, KBr, KI, KNO(3), and KSCN, present at an initial concentration of 10 mM within an aqueous microdroplet containing K(2)SO(4) at an initial concentration of 287 mM. Supersaturation and subsequent crystallization were isothermally induced by droplet dissolution into the dehydrating decanol phase. The K(2)SO(4) solute crystallization behavior was studied by measurement of the calculated concentration of the solute in the microdroplet at the onset of crystallization, i.e., at the first perceptible microscopic appearance of a solid phase, and by crystal habit. Certain salts, e.g., K(2)HPO(4), had almost no influence on the templating ability of ODA, while the ability of ODA to template nucleation and direct the formation of regular crystal habit of K(2)SO(4) became appreciably disrupted in the presence of more chaotropic anions, such as SCN(-) or NO(3)(-). The propensity for anions to disrupt crystal templating was clearly seen to follow a Hofmeister trend. For crystallization events induced in the absence of ODA, however, these added salts had no influence on the outcome of the events. Microdroplets bounded by an ODA monolayer were also found to undergo droplet shrinkage into the surrounding dehydrating phase at a rate which generally depended upon the nature of the anion in the droplet, with chaotropic anions having an apparent effect of promoting shrinkage. Our findings suggest that the packing or ordering of an ODA monolayer at a liquid-liquid interface is strongly influenced by an interaction between anions in the aqueous phase and the surfactant monolayer at the liquid-liquid interface, which is manifested in its effect upon the crystal templating behavior. These intriguing results can have important implications for the understanding of biomineralization processes which occur in heterogeneous environments.

Formation of single-crystalline aragonite tablets/films via an amorphous precursor

Thin tablets and films of calcium carbonate have been grown at the air-water interface via an amorphous precursor route using soluble process-directing agents and a Langmuir monolayer based on resorcarene. By using appropriate concentrations of poly(acrylic acid-sodium salt) in combination with Mg2+ ion, an initially amorphous film is deposited on the monolayer template, which subsequently crystallizes into a mosaic film composed of a mixture of single-crystalline and spherulitic patches of calcite and aragonite. Of particular importance is the synthesis of single-crystalline "tablets" of aragonite (approximately 600 nm thick), because this phase generally forms needle-like polycrystalline aggregates when grown in vitro. To our knowledge, a tabular single-crystalline morphology of aragonite has only been observed in the nacreous layer of mollusk shells. Therefore, this in vitro system may serve as a useful model for examining mechanistic issues pertinent to biomineralization, such as the influence of organic templates on nucleation from an amorphous phase.

Adsorption of tentacled tetragonal star connectors, C4R4-Co-C5(HgX)5, on mercury

For future use in self-assembly of surface structures, the adsorption on the surface of mercury of a series of tetraphenylcyclobutadienecyclopentadienylcobalt double-decker sandwich complexes with five mercury and sulfur containing "tentacles" on the cyclopentadienyl deck has been examined by combined electrochemical and Langmuir trough techniques.

Aggregation-governed oriented growth of inorganic crystals at an organic template

X-ray studies performed during the growth of CdCO(3) and MnCO(3) crystals from supersaturated aqueous solutions, at fatty acid monolayer templates, reveal that the nucleates are nearly three-dimensional powders below a threshold supersaturation. However, at higher supersaturations, the crystals are preferentially oriented with the {0 1 2} direction vertical. Scanning electron microscope images of samples transferred to substrates show discrete crystals at low concentrations, while at higher concentrations the crystals self-aggregate to form linear chains and sheets. The authors speculate that preferential alignment at the organic-inorganic interface is enhanced as a consequence of oriented aggregation of crystals. The role of monolayer-ion interactions in governing the morphologies and the resulting orientation of the inorganic nucleate is discussed.

Arrangement of tris(phthalocyaninato) gadolinium triple-decker complexes with multi-octyloxy groups on water surface

A series of five carefully designed tris(phthalocyaninato) gadolinium triple-decker complexes [Pc(R)8]Gd[Pc(R')8]Gd[Pc(R'')8] (R=R'=R''=H; R=R'=H, R''=OC8H17; R=R''=H, R'=OC8H17; R=H, R'=R''=OC8H17; R=R'=R''=OC8H17) (1-5) were prepared and the film forming properties on water surface were systematically investigated. The limited mean molecular area obtained by pi-A isotherms revealed an "edge-on" conformation for all these compounds. UV-vis absorption spectra showed red-shifted Q bands, indicating the formation of J aggregates and effective intermolecular interaction in solid film. Phthalocyanine rings were found to take tilted orientation with respect to the normal of substrate according to the polarized absorption spectroscopic measurements. Low angle X-ray diffraction results provide direct evidence and therefore clearly clarify the point, for the first time, that unsymmetrical triple-decker molecules pack on the water surface with the unsubstituted phthalocyanine ring set close to the water surface and the substituted phthalocyanine ligand with octyloxy groups lies on the top.

Elasticity of Crystalline β-Sheet Monolayers

Designed amphiphilic beta-sheet peptides with the sequence Pro-Glu-(Phe-Glu)(n)-Pro (n = 2-7) were previously shown by grazing incidence X-ray diffraction (GIXD), to form ordered two-dimensional (2-D) monolayer structures at interfaces induced by the proline residues at peptide termini. The GIXD diffraction pattern was modeled with two coexisting lattice arrangements, suggesting structural flexibility exhibited in the multiple ways by which beta-strands and their amino acid side chains pack into ordered 2-D structures. Here, we find by in-situ GIXD measurements that the ordered beta-sheet assemblies may undergo a quasi-reversible compression and expansion cycle at the air-water interface. The diffraction measurements indicate that on compression the repeat distance that corresponds to the long axes of the peptide strands may decrease by up to 37% in length. Upon expansion the compressed beta-sheet assemblies revert elastically to their original conformation. The interstrand repeat distance along the peptide hydrogen bonds apparently does not change along the film compression and expansion. Based on the GIXD data, at surface pressures higher than approximately 3 mN/m, beyond the peptide limiting area per molecule, the compressibility is 7.4 +/- 0.6 m/N. The out-of-plane Bragg rod diffraction patterns imply that in the compressed state the beta-strands buckle up in reaction to the increase in surface pressure. At low surface pressure, the 2-D compressibility of the crystalline beta-sheet was estimated at approximately 32 m/N attributed to interdomain rearrangements.

Induction and Inhibition of Preferential Enrichment by Controlling the Mode of the Polymorphic Transition with Seed Crystals

Both induction and inhibition of "preferential enrichment", an unusual symmetry-breaking enantiomeric-resolution phenomenon observed upon simple recrystallization of a certain kind of racemic crystals from organic solvents, have been successfully achieved by controlling the mode of the polymorphic transition during crystallization with appropriate seed crystals. Such control of the polymorphic transition can be interpreted in terms of a novel phenomenon consisting of 1) the adsorption of prenucleation aggregates, 2) the heterogeneous nucleation and crystal growth of a metastable crystalline form, and 3) the subsequent polymorphic transition into the more stable form; these three processes occur on the same surface of a seed crystal. We refer to this phenomenon as an "epitaxial transition", which has been confirmed by means of in situ attenuated total reflection (ATR) FTIR spectroscopy in solution and the solid state, differential scanning calorimetry (DSC) measurements of the deposited crystals, and X-ray crystallographic analysis of the single crystals or the direct-space approach employing the Monte Carlo method with the Rietveld refinement for the structure solution from the powder X-ray diffraction data.

Formation of silver nanoparticles at the air-water interface mediated by a monolayer of functionalized hyperbranched molecules

Nanofibrillar micellar structures formed by the amphiphilic hyperbranched molecules within a Langmuir monolayer were utilized as matter for silver nanoparticle formation from the ion-containing water subphase. We observed that silver nanoparticles were formed within the multifunctional amphiphilic hyperbranched molecules. The diameter of nanoparticles varied from 2-4 nm and was controlled by the core dimensions and the interfibrillar free surface area. Furthermore, upon addition of potassium nitrate to the subphase, the Langmuir monolayer templated the nanoparticles' formation along the nanofibrillar structures. The suggested mechanism of nanoparticle formation involves the oxidation of primary amino groups by silver catalysis facilitated by "caging" of silver ions within surface areas dominated by multibranched cores. This system provides an example of a one-step process in which hyperbranched molecules with outer alkyl tails and compressed amine-hydroxyl cores mediated the formation of stable nanoparticles placed along/among/beneath the nanofibrillar micelles.

Aggregation behavior of heteroleptic tris(phthalocyaninato) dysprosium complexes with different alkoxy chains in monolayer or multilayer solid films

Three heteroleptic tris(phathlocyaninato) dysprosium triple-decker complexes with different alkoxy groups at the peripheral positions of the medium phthalocyanine ligand (Pc)Dy[Pc(OCnH(2n+1))8]Dy(Pc) (n = 4, 8, 16) (I-III) {Pc = unsubstituted phthalocyaninate; Pc(OC4H9)8 = 2,3,9,10,16,17,23,24-octakis(butyloxy)phthalocyaninate; Pc(OC8H17)8 = 2,3,9,10,16,17,23,24-octakis(octyloxy)phthalocyaninate; Pc(OC16H33)8 = 2,3,9,10,16,17,23,24-octakis(hexadecyloxy)phthalocyaninate} have been synthesized, and their aggregate behaviors in monolayer and multilayer solid films have been comparatively studied. The pure compounds and their 1:4 mixtures with stearic acid (SA) have been found to form a stable monolayer at the air/water interface with a tilted edge-on orientation of (Pc)Dy[Pc(OCnH(2n+1))8]Dy(Pc) molecules. In the pure monolayers of the three triple-decker compounds, wirelike molecular aggregates were observed by high-resolution transmission electron microscopy (HRTEM). Adding SA has been found to prevent triple-decker compounds (Pc)Dy[Pc(OC4H9)8]Dy(Pc) (I) and (Pc)Dy[Pc(OC8H17)8]Dy(Pc) (II) from forming large aggregates, and small domains with a diameter of ca. 10 nm were observed in the mixed monolayers. HRTEM studies revealed that two crystalline phases with rectangular and hexagonal lattice structure are present in the small domains. However, both pi-A isotherms and HRTEM studies indicated that the mixed monolayer of compound (Pc)Dy[Pc(OC16H33)8]Dy(Pc) (III) with SA did not show a difference from the corresponding pure monolayer. The SA molecules were pressed into the cavity above the phthalocyanine ring formed by the eight long hexadecyloxy side chains of the medium macrocycle ligand in III. The multilayer LB films of all of these triple deckers fabricated by the vertical dipping method showed very good layered structure as revealed by the multiple-order diffraction peaks in low-angle X-ray diffraction (LAXRD) patterns.

Thermodynamic and structural properties of phospholipid langmuir monolayers on hydrosol surfaces

Measurements of Langmuir pressure/area isotherms, rheology, grazing incidence X-ray diffraction (GIXD), and grazing incidence diffuse X-ray scattering out of the specular plane (GIXOS) have been used to investigate the influence of a hydrosol containing charged mineral nanoparticles on the thermodynamic and structural properties of a DPPC monolayer. The mineral adsorption layer that is formed via electrostatic interaction underneath the lipid layer alters the thermodynamic properties of the phospholipid monolayer in terms of maximal achievable compression, compressibility, and phase behavior. Modifications appear in the latter case as a coolinglike effect. Rheology measurements of the bulk viscoelastic properties revealed a stabilizing effect of the transient bulk network on the surfactant layer. The lipid chain lattice is found to be reorganized and adapted to the internal atomic structure of the mineral particles. A model for the superposition of Bragg rods from the lipid chains and the minerals is applied to separate these scattering contributions. In the vicinity of the mineral particles, the (2) reflection for DPPC on a liquid substrate was found, indicating strongly suppressed fluctuations at the surface. An estimation of the Debye-Waller factor associated with the lipid layer organization is used to quantify the damping of fluctuations within the lipid matrix due to the rigidifying and stabilizing effect of the mineral particles.

Nanocrystal induced organization of a langmuir phospholipid monolayer

The influence of crystal surface charge on the thermodynamic and structural behavior of phospholipid monolayers has been investigated. We present how charged nanocrystals in the vicinity of an inherently nonordered lipid membrane provoke strong effects on the molecular arrangement within the monolayer. Apart from the induction of phase shifts and nucleation processes, the molecules were forced to adopt an ordered phase. A very recently developed X-ray scattering method is used for the first time to replace time-consuming specular reflectivity measurements. We conclude on the potential effects of crystal surface charge on cellular membranes.

The structure and phase diagram of Langmuir films of alcohols on mercury

The coverage-dependent phase behavior of molecular films of alcohols (CH3(CH2)n-2CH2OH, denoted as CnOH) on mercury was studied for chain lengths 8 < or = n < or = 28, using surface tensiometry and surface specific X-ray methods. Phases with surface-normal-oriented molecules are found at high coverage, showing the CS, S, and LS phases found also on water. Phases comprising surface parallel molecules, which do not exist on water, are found here at low coverage. For the lowest coverage a two-dimensional gas phase is found, followed, upon increasing the coverage, by an n-dependent sequence of condensed phases of up to four layers of surface-parallel molecules before converting to the surface-normal phases. In contrast with the surface-normal phases, all of the surface-parallel phases are found to lack long-range order in the surface-parallel direction. Adsorption energies are derived from the phase diagram for the alkyl chain and the alcohol headgroup.

Fatty acid Langmuir films on liquid mercury: X-ray and surface tension studies

The structure and phase behavior of liquid-mercury-supported molecular films of fatty acids (CH3(CH2)n-2COOH, denoted CnOOH) were studied for molecular lengths 7 < or = n < or = 24, by surface tensiometry and X-ray methods. Two qualitatively different film structures were found, depending on coverage. For high coverage, the film consists of a monolayer of roughly surface-normal molecules, showing a pressure-dependent sequence of structures similar, though not identical, to that of the corresponding water-supported Langmuir films. At low coverage, phases consisting of surface-parallel molecules are found, not observed on the aqueous subphases employed to date. In this range, a two-dimensional (2D) gas followed by a single and, for 14 < or = n < or = 24, also by a double layer of surface-parallel molecules is found as coverage is increased. Depending on chain length, the flat-lying phases have a crystalline 2D-ordered, a smectic-like 1D-ordered, or a disordered in-plane structure consisting of molecular dimers. The structure and thermodynamics of the films are discussed.

Neutron reflectivity and external reflection FTIR studies of DL-aspartic acid crystallization beneath nylon 6 spread films

The crystallization of DL-aspartic acid beneath nylon 6 spread films has been studied for 150% supersaturated systems using neutron reflectivity and external reflection FTIR. The neutron reflectivity data showed the gradual incorporation of DL-aspartic acid within a nylon 6 spread film layer over a period of 6-8 h, culminating in over 50 vol % of the "film" layer comprising DL-aspartic acid. Accumulation of further DL-aspartic acid material to produce microscopic/macroscopic surface crystals occurred, but on a more limited scale, resulting in approximately 1-5% surface coverage of crystals over the same period. External reflection FTIR studies revealed very weak bands attributable to DL-aspartic acid in surface regions devoid of visible crystals, in agreement with the neutron reflectivity studies. In regions with visible crystals, much larger and sharper DL-aspartic acid bands were seen. Changes in the intensity of the nylon 6 NH stretch band were often observed during the visible crystallization and dissolution of DL-aspartic acid and were consistent with the reversible accumulation of nylon 6 around the growing crystals.

Enantioselective Crystal Growth of Leucine on a Self-Assembled Monolayer with Covalently Attached Leucine Molecules

Enantioselective crystal growth of leucine occurs on a solid surface modified with a self-assembled monolayer depending on the chirality of the enantiomer attached, as evidenced by the X-ray diffraction method.

Polar head group interactions in mixed Langmuir monolayers

We have investigated the miscibility in the mixed monolayers of cholesterol (Ch)-octyl cyano biphenyl (8CB) and cholesteryl acetate (ChA)-8CB using surface manometry and epifluorescence microscopic techniques. The main skeleton is the same both in Ch and ChA, whereas the polar head group is alcohol in Ch and ester in ChA. The 8CB molecule has a polar cyano as a terminal group and we probe its interaction with the polar group of Ch or ChA molecules in the mixed monolayers. Both Ch-8CB and ChA-8CB mixed monolayers exhibit two collapse pressures. In the case of the Ch-8CB mixed monolayer, the lower collapse pressure varies after 0.6 mole fraction (MF) of Ch in 8CB and the higher collapse pressure is nearly independent of composition. In ChA-8CB mixed monolayer, the lower collapse pressure varies continuously with the composition of ChA while the higher collapse pressure is nearly independent of the composition of ChA. In both these mixed monolayers, above the lower collapse pressure, 8CB gets squeezed out of the monolayer and forms multilayers. We find that in the case of Ch-8CB there is a phase separation in the monolayer occurring in the range of 0.15-0.9 MF of Ch. However, in ChA-8CB, the monolayer phase is miscible in all the proportions (except at very high concentration of ChA) below the lower collapse pressure. We attribute this better miscibility in the ChA-8CB compared to the Ch-8CB to the role played by the ester and cyano polar head group interactions.