Thermodynamic Phase Behavior Research Articles

On the thermodynamic phase behavior of poly(N-vinylcaprolactam) solution in the presence of different ionic liquids

The influence of different Ionic Liquids (ILs) on the phase transition behavior of poly(N-vinylcaprolactam) (PVCL) solution is investigated by differential scanning calorimetry (DSC) and turbidity measurements, in combination with FT-IR spectroscopy. The DSC and turbidity results reveal that hydrophilic ILs at a concentration of 0.25 mol L−1 only slightly change the transition temperature. The LCST experiences an increase while the phase separation behavior disappears gradually as the concentration of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) increases from 0 to 1.0 mol L−1. In contrast, the addition of hydrophobic ILs, especially 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMIM][NTf2]), even at a low concentration, greatly raises the LCST, indicating the possibility of hydrogen bonding between [EMIM][NTf2] and PVCL. Finally, temperature-dependent FTIR spectra are employed to elucidate the dynamic mechanism of the different influences on the phase transition of PVCL. The hydrophilic ILs can change the state of the PVCL chains indirectly by varying their interaction with water molecules. For comparison, the formation of hydrogen bonds between the unsaturated C–H of [EMIM][NTf2] and the CO of PVCL results in a higher temperature and more energy to complete the phase transition. However, with the continual increasing of the concentration, extra [EMIM][NTf2] can not be well dispersed in water due to its hydrophobicity, so the LCST undergoes a decrease and finally reaches an equilibrium. Additionally, hydrophilic ILs tend to distribute in the solution, while hydrophobic ILs, especially [EMIM][NTf2], are prone to be wrapped in polymer chains of the aggregates after phase separation. Furthermore, both types of IL experience the process of hydrogen bond disruption and chain aggregation.

A New Alpha-function for the Peng-Robinson Equation of State: Application to Natural Gas

Cubic equations of state (EOSs) are simple and easy at calculation. One way of improving the accuracy of a cubic EOS is through the modification of temperature-dependent energy parameter by using alpha-function. The industrial applications of natural gas are very wide and as a result, prediction of thermodynamic properties and phase behavior of natural gas is an important part of design for such processes. In this work we develop a new α-function for the Peng-Robinson (PR) EOS with the parameters optimized especially for natural gas components. The parameters are generalized as a linear function of acentric factor. The results are compared to the predictions from original PR EOS and other α-functions in literature. It is shown that the new α-function presents a good accuracy with the average deviation of 1.42% for natural gas components.

A Negative-Flash Tie-Simplex Approach for Multiphase Reservoir Simulation

Summary Enhanced Oil Recovery (EOR) processes usually involve complex phase behavior between the injected fluid (e.g., steam, hydrocarbon, CO2, sour gas) and the in-situ rock-fluid system. Several fundamental questions remain regarding Equation-of-State (EOS) computations for mixtures that can form three, or more, phases at equilibrium. In addition, numerical and computational issues related to the proper coupling of the thermodynamic phase behavior with multi-component transport must be resolved to accurately and efficiently model the behavior of large-scale EOR processes. Previous work has shown that the adaptive tabulation of tie-simplexes in the course of a compositional simulation is a reliable alternative to the conventional EOS-based compositional simulation. In this paper, we present the numerical results of reservoir flow simulation with adaptive tie-simplex parameterization of the compositional space. We study the behavior of thermal-compositional reservoir displacement processes across a wide range of fluid mixtures, pressures, and temperatures. We show that our approach rigorously accounts for tie-simplex degeneration across phase boundaries. We also focus on the complex behavior of the tie-triangles and tie-lines associated with three-phase, steam injection problems in heterogeneous formations. Our studies indicate that the tie-simplex based simulation is a potential approach for fast EOS modeling of complex EOR processes.

Thermodynamic stability and phase behaviour of a liquid crystalline material: a theoretical model at molecular level

This article describes the thermodynamic stability and phase behaviour of a liquid crystalline material p-n-hexyloxybenzylidene-p-toluidine (6OBT) at a molecular level. The atomic net charge and dipole moment at each atomic centre have been evaluated using the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh–Schrodinger perturbation method along with multicentred-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a ‘6-exp’ potential function has been assumed for the short-range interactions. The total interaction energy values obtained through these computations have been used to calculate the probability of each configuration at room temperature (300 K), nematic–isotropic transition temperature (346.9 K) and above transition temperature (400 K) using the Maxwell–Boltzmann formula. Further, the Helmholtz free energy and entropy of each configuration has been computed during the different modes of interactions. An attempt has been made to understand the phase behaviour and stability of the molecule based on thermodynamic parameters introduced in this article.

Counterion release in membrane–biopolymer interactions

When two oppositely charged macroions are brought into contact, a large fraction of the mobile counterions that previously surrounded each isolated macromolecule is released into the bulk solution, thereby increasing the counterions' translational entropy. The entropy gain associated with this counterion release mechanism is the driving force for various macroion binding processes, such as protein–membrane, protein–DNA, and DNA–membrane complexation. In this review we focus on the role of counterion release in the interaction between charged macromolecules and oppositely charged lipid membranes. The electrostatic interaction is generally coupled to other degrees of freedom of the membrane, or of the adsorbed macroion. Thus, for example, when a basic protein adsorbs onto a binary fluid membrane comprising anionic and neutral lipids then, in addition to the release of the mobile counterions to the bulk solution, the protein polarizes the membrane composition by attracting the charged lipids to its immediate vicinity. This process, which enhances the electrostatic attraction, is partly hampered by the concomitant loss of two-dimensional (2D) lipid mixing entropy, so that the resulting lipid distribution reflects the balance between these opposing tendencies. In membranes containing both monovalent and multivalent lipids, as is often the case with biological membranes, the peripheral protein preferentially interacts with (and thus immobilizes) the multivalent lipids, because a smaller number of these lipids are needed to neutralize its charge. The monovalent “counterlipids” are thus free to translate in the remaining area of the membrane. This entropy-driven counterlipid release mechanism in 2D is analogous to the extensively studied phenomenon of DNA condensation by polyvalent cations in 3D. Being self-assembled fluid aggregates, lipid bilayers can respond to interactions with peripheral or integral (whether charged or neutral) macromolecules in various ways. Of particular interest in this review is the interplay between electrostatic interactions, the lipid composition degrees of freedom mentioned above, and the membrane curvature elasticity, as will be discussed in some detail in the context of the thermodynamic stability and phase behavior of lipid–DNA complexes (also known as “lipoplexes”). This article is primarily theoretical, but the systems and phenomena considered are directly related to and motivated by specific experiments. The theoretical modeling is generally based on mean-field level approaches, specifically the Poisson–Boltzmann theory for electrostatic interactions, sometimes in conjunction with coarse grained computer simulations.

Influence of the interdigitated gel phase in mixtures of ether-linked and monofluorinated ester-linked phospholipids

To evaluate the influence of the hydrocarbon chain linkage on the thermodynamic phase behavior of spontaneously interdigitating lipids, mixtures of ether-linked 1,2-di-O-hexadecyl-phosphocholine (DHPC) and ester-linked 1-palmitoyl-2-[16-fluoropalmitoyl]sn-glycero-3-phosphocholine (F-DPPC) were studied. A combination of differential scanning calorimetry (DSC), fluorescence spectroscopy, and transmittance spectrophotometry was used. Small amounts of F-DPPC increase the pretransition temperature (Tp) between the interdigitated gel phase (LβI) and the ripple gel phase (Pβ′). There are some signs of immiscibility where the non-interdigitated lipid is present in the phase diagram. However, at around 20mol.% F-DPPC, the pretransition merges with the main transition and is no longer detectable as a separate entity. Additionally, the Tm hysteresis increases steadily with higher mole fractions of F-DPPC. These results support that incorporating F-DPPC progressively stabilizes the LβI phase of DHPC until the membrane is fully interdigitated below the main transition temperature (Tm). The mixtures of F-DPPC and DHPC are miscible once the membrane is entirely interdigitated in the gel phase. Therefore, the ability of both lipids to interdigitate is an important factor controlling gel phase miscibility. Our results also demonstrate that the gel phase behavior of DHPC is highly sensitive to changes in its environment.

ChemInform Abstract: Group Contribution Methodologies for the Prediction of Thermodynamic Properties and Phase Behavior in Mixtures

AbstractReview: 169 refs.

A SAFT equation of state for the quaternary H2S–CO2–H2O–NaCl system

Phase equilibria and thermodynamic properties of the quaternary H2S–CO2–H2O–NaCl system were studied using a statistical associating fluid theory (SAFT)-based equation of state (EOS) at temperatures from 0 to 200°C (373.15–473.15K), pressures up to 600bar (60MPa) and concentrations of NaCl up to 6mol/kgH2O. The understanding of the physical–chemical properties of this system is critical for predicting the consequences of co-injection of CO2 and H2S into geological formations (geological carbon sequestration) as an option for mitigating the global warming trend. Equation of state parameters were generated from regression of available and reliable experimental data and incorporation of existing parameters for some subsystems. Densities were predicted and compared with available experimental results. Using the EOS developed in this study, we predicted equilibrium compositions in both liquid and vapor phases, fugacity coefficients of components, the equilibrium pressures at a given composition of the H2O-rich phase in electrolyte solutions with NaCl varying from 0 to 4mol/kgH2O, and the aqueous solution densities. These predicted values are tabulated and available as supplementary data in the electronic version online. These predictions provide information and guidance for future experiments regarding the thermodynamic properties and phase behaviors in the H2S–CO2–H2O–NaCl system.

Statistical Analysis of Supercooling in Fuel Gas Hydrate Systems

The recently developed high pressure automated lag time apparatus (HP-ALTA) was applied to the study of the formation and growth of interfacial gas hydrate films for three gases; methane (C1), 90% methane/10% propane gas mix (C1/C3), and synthetic gas mix (SGM). The effects of gas pressure and cooling rate were studied for each gas. Some degree of supercooling was observed in all cases. The probability distributions of formation temperature (Tf) were often found to be bimodal, due to the formation of either gas hydrate or ice in sequential experimental runs. The width of the Tf distribution of ice was about 3–4 K. In contrast, the width of the Tf distribution of gas hydrates was about 20 K which reflects the importance of mass transfer (gas diffusion) processes in nucleation. Differences in hydrate and ice nucleation probability distributions were observed for different gases, reflecting differences in both thermodynamic equilibrium phase behavior and hydrate formation mechanisms. For all gases studied, Tf generally increased with increasing gas pressure. A minimum threshold pressure for hydrate formation was observed, with magnitude decreasing in the order C1 > SGM > C1/C3. The effect of cooling rate on gas hydrate nucleation probability was also studied. The median of the distribution of Tf (Tf50) was found to decrease with an increased cooling rate, consistent with the increases in effective induction time as samples were cooled more slowly. Our results clearly highlight the value in collecting large data sets which can be used to assemble probability distributions when studying intrinsically stochastic processes such as gas hydrate nucleation and growth.

Investigation of the relationships between the thermodynamic phase behavior and gelation behavior of a series of tripodal trisamide compounds

Download options Please wait... Supplementary files Supplementary information PDF (296K) Article information DOI https://doi.org/10.1039/C2SM25415H Article type Paper Submitted 23 Feb 2012 Accepted 26 Apr 2012 First published 15 May 2012 Download Citation Soft Matter, 2012,8, 6483-6492 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Investigation of the relationships between the thermodynamic phase behavior and gelation behavior of a series of tripodal trisamide compounds L. Feng and K. A. Cavicchi, Soft Matter, 2012, 8, 6483 DOI: 10.1039/C2SM25415H To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Li Feng Kevin A. Cavicchi

Dimensional crossover and scaling behavior of a smectic liquid crystal confined to controlled-pore glass matrices

The structural and thermodynamic phase behavior of the thermotropic liquid crystal dodecylcyanobiphenyl (12CB) confined in controlled-pore glasses (CPGs) has been studied by means of high-resolution calorimetry and small-angle X-ray scattering. Non-treated CPG matrices have been used with a characteristic pore size R ranging from nanometre to micrometre scale. Even in the case of the strongest confinement the isotropic-to-smectic-A (I-SmA) transition was pronounced. Both the smectic pretransitional ordering and the broadening of the specific heat capacity anomaly were relatively weak. This signals the secondary importance of the surface interaction potential and of the disorder upon phase behavior. We claim that the surface interaction is dominated by the coupling between surface-frozen and volume liquid crystal molecules. This coupling is weak due to the flexible long alkyl chains which dominantly influence the phase behavior of 12CB. The depression of the phase transition temperature Tc is dominated by smectic elastic compressibility distortions. The observed anomalous Tc(R) dependence is explained by allowing surface rearrangement processes. In severely-confined samples the 1st order I-SmA phase transition tends to be replaced by a 2nd order one. This phenomenon is attributed to a dimensional-crossover which, in 12CB samples, is not masked by surface interactions as it is in case of similar liquid crystals with shorter alkyl chains. The observed behavior is explained using scaling and dimensional analysis within the Landau–Ginzburg–de Gennes mesoscopic approach.

Influence of the Interdigitated Gel Phase in Mixtures of Ether-Linked and Monofluorinated Ester-Linked Phospholipids

To evaluate the thermodynamic phase behavior of 1,2-di-O-hexadecyl-phosphocholine (DHPC) and 1-palmitoyl-2-[16-fluoropalmitoyl]sn-glycero-3-phosphocholine (F-DPPC) mixtures, a combination of differential scanning calorimetry (DSC), fluorescence spectroscopy, and spectrophotometry was used. DHPC is the ether-linked analogue of DPPC and has a pretransition between the interdigitated gel phase (LβI) and the ripple gel phase (Pβ′). F-DPPC is identical to DPPC except for a single fluorine substitution on the terminal carbon of the sn-2 chain.

Effects of cholesterol on phospholipid membranes: Inhibition of the interdigitated gel phase of F-DPPC and F-DPPC/DPPC

Unlike the parent phospholipid, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), the monofluorinated analog, 1-palmitoyl-2-(16-fluoropalmitoyl)sn-glycero-3-phosphocholine (F-DPPC), spontaneously forms an interdigitated gel phase (LβI) below the main transition temperature (Tm). We have examined the effects of introducing cholesterol to F-DPPC and 1:1 F-DPPC/DPPC membranes using a combination of DSC, optical density, fluorescence intensity and polarization, 31P NMR, and X-ray diffraction techniques. Cholesterol increases the fluidity of the gel phase, broadens the main transition, and decreases the main transition enthalpy. However, these results also reveal that there is an unusually large degree of phase coexistence between the LβI and non-interdigitated gel phases when cholesterol is added. Cholesterol encourages this phase segregation by partitioning into the thicker non-interdigitated domains. At higher cholesterol concentrations, the majority or all of the LβI phase of F-DPPC and 1:1 F-DPPC/DPPC is eliminated and is replaced by a non-interdigitated liquid-ordered (lo) phase with properties similar to DPPC/cholesterol. Consequently, cholesterol mitigates the influence the CF moiety has on the thermodynamic phase behavior of F-DPPC. Our findings demonstrate that there are multiple characteristics of cholesterol-rich membranes that disfavor interdigitation.

PC-SAFT characterization of crude oils and modeling of asphaltene phase behavior

Asphaltenes are the heaviest and most polarizable components of crude oil. The phase behavior of these polydisperse components is important in both the upstream and downstream processing of crude oil because of their potential to precipitate, deposit and plug pipelines and production equipment. Predicting flow assurance issues caused by asphaltenes requires the ability to model the phase behavior of asphaltenes as a function of temperature, pressure, and composition. In this work we present a detailed procedure to characterize crude oil and plot asphaltene phase envelope, using the Perturbed Chain form of the Statistical Associating Fluid Theory (PC-SAFT). This work also demonstrates that the proposed procedure can model the asphaltene thermodynamic phase behavior better than using a cubic equation of state typically used in the industry, even with compositional data as low as C9+.The results obtained with the proposed characterization method show a remarkable matching with the experimental data points for both the bubble point and asphaltene precipitation onset curves. A wide range of temperatures, pressures and gas injection percentages have been tested. In this work, the concept of lower asphaltene onset pressure is also clarified and a new representation of asphaltene phase plot is presented. The results obtained in this work are very promising in providing better tools to model asphaltene phase behavior.

Interaction of a partially fluorinated alcohol (F8H11OH) with biomembrane constituents in two-component monolayers

The interaction of (perfluorooctyl)undecanol (F8H11OH) with dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylglycerol (DPPG), and cholesterol (Ch) has been investigated in two-component monolayers at the air–water interface. The thermodynamic properties and phase behavior of the monolayers have been systematically elucidated employing isotherm measurements and several methods at the mesoscopic and microscopic scales. Addition of F8H11OH induces strong condensation in DPPC and DPPG monolayers. The magnitude for the Gibbs free energy and the interaction parameter between the two components for the DPPC/F8H11OH and DPPG/F8H11OH systems are twice as large as those for the Ch/F8H11OH system. Judging from the evidence that disordered/ordered transition pressures and collapse pressures for the binary monolayers change with molar fraction of F8H11OH, F8H11OH was (partially) miscible with all the compounds investigated. The miscibility of the two components in the monolayer is also supported by the in situ (Brewster angle and fluorescence microscopies) and ex situ (atomic force microscopy after transfer on a mica plate) morphological aspects. The present study reports firstly on the interaction between Ch and the fluorinated amphiphile by simply employing the monolayer technique. The molecular function of Ch in pulmonary surfactants and lipid rafts is now extensively investigated. To our knowledge, Ch does not interact strongly with lipid components in biomembranes. However, this study indicates that the partially fluorinated amphiphile has some affinity for Ch. This study provides a fundamental insight into the molecular function of biomembrane components and support for biomedical use of fluorinated materials.

Modeling pVT Properties and Phase Equilibria for Systems Containing Ionic Liquids Using a New Lattice-Fluid Equation of State

The cations or anions of ionic liquids (ILs) usually have long alkyl chains or chainlike structures. Therefore, ILs can be reasonably considered as fluids containing neutral chainlike molecules. Lattice-based molecular thermodynamic models generally used for polymer systems can be applied to describe the thermodynamic properties and phase behavior of IL systems. In our previous work, a new lattice-fluid equation of state (LF EoS) was developed and successfully applied to normal fluid systems (Xu et al., Fluid Phase Equilib. 2008, 265, 112.). In this work, this LF EoS is further extended to model the pVT properties and phase equilibria of IL systems. The molecular parameters of ILs in this EoS were determined by correlating the experimental pVT data of pure ILs. It is shown that the pVT behavior of IL mixtures can be fairly well predicted by these parameters. The vapor−liquid equilibria (VLE) of binary IL−solvent systems were calculated by using an adjustable binary parameter, κ12. For liquid−liquid equilibria (LLE) of binary IL systems, a parameter Cr describing the effect of the mixture composition on the chain-length parameter r is further used, and satisfactory correlation is obtained. The upper critical solution temperature (UCST) can be predicted successfully. Moreover, the EoS reproduces the solubility data for carbon dioxide (CO2) in various ILs covering a wide range of pressures (0−100 MPa), and it describes the global behavior of trifluoromethane (CHF3) and IL mixtures. The results reveal that the LF EoS is well-suited for the calculation or prediction of the thermodynamic properties of systems containing ILs.

Liquid Crystalline Phase Behavior of Protein Fibers in Water: Experiments versus Theory

We have developed a new method allowing the study of the thermodynamic phase behavior of mesoscopic colloidal systems consisting of amyloid protein fibers in water, obtained by heat denaturation and aggregation of beta-lactoglobulin, a dairy protein. The fibers have a cross section of about 5.2 nm and two groups of polydisperse contour lengths: (i) long fibers of 1-20 microm, showing semiflexible behavior, and (ii) short rods of 100-200 nm long, obtained by cutting the long fibers via high-pressure homogenization. At pH 2 without salt, these fibers are highly charged and stable in water. We have studied the isotropic-nematic phase transition for both systems and compared our results with the theoretical values predicted by Onsager's theory. The experimentally measured isotropic-nematic phase transition was found to occur at 0.4% and at 3% for the long and short fibers, respectively. For both systems, this phase transition occurs at concentrations more than 1 order of magnitude lower than what is expected based on Onsager's theory. Moreover, at low enough pH, no intermediate biphasic region was observed between the isotropic phase and the nematic phase. The phase diagrams of both systems (pH vs concentration) showed similar, yet complex and rich, phase behavior. We discuss the possible physical fundamentals ruling the phase diagram as well as the discrepancy we observe for the isotropic-nematic phase transition between our experimental results and the predicted theoretical results. Our work highlights that systems formed by water-amyloid protein fibers are way too complex to be understood based solely on Onsager's theories. Experimental results are revisited in terms of the Flory's theory (1956) for suspensions of rods, which allows accounting for rod-solvent hydrophobic interactions. This theoretical approach allows explaining, on a semiquantitative basis, most of the discrepancies observed between the experimental results and Onsager's predictions. The sources of protein fibers complex colloidal behavior are analyzed and discussed at length.

Insights Into Crowding Effects on Protein Stability From a Coarse-Grained Model

Proteins aggregate and precipitate from high concentration solutions in a wide variety of problems of natural and technological interest. Consequently, there is a broad interest in developing new ways to model the thermodynamic and kinetic aspects of protein stability in these crowded cellular or solution environments. We use a coarse-grained modeling approach to study the effects of different crowding agents on the conformational equilibria of proteins and the thermodynamic phase behavior of their solutions. At low to moderate protein concentrations, we find that crowding species can either stabilize or destabilize the native state, depending on the strength of their attractive interaction with the proteins. At high protein concentrations, crowders tend to stabilize the native state due to excluded volume effects, irrespective of the strength of the crowder-protein attraction. Crowding agents reduce the tendency of protein solutions to undergo a liquid-liquid phase separation driven by strong protein-protein attractions. The aforementioned equilibrium trends represent, to our knowledge, the first simulation predictions for how the properties of crowding species impact the global thermodynamic stability of proteins and their solutions.

Structural, Mineralogical, and Rheological Properties of Methane Hydrates in Smectite Clays

Smectite clays are widely dispersed in deep ocean sediments and can be subdivided into two representative clay types, Cheto- and Wyoming-montmorillonites. In this study, we measured the thermodynamic phase behavior of methane hydrates intercalated at various concentrations of these clays and found the relatively weak promotion tendency when compared to that of pure methane hydrate stability. The structure and morphology of intercalated methane hydrate (IMH) samples were analyzed using the MAS NMR, RAMAN, LT-XRD, and Cryo-FE-SEM. The 27Al and 29Si solid-state MAS NMR spectra of IMH Cheto and Otay clays represent that the structural stability is preserved during the IMH formation, which is also indicated with the XRD pattern showing no structural transformation but different d-spacing values due to clay−water suspension and IMH. In addition, Cryo-SEM images of IMH samples show that IMH Otay clays provide well-developed methane hydrate (MH) morphology, compared to the IMH Cheto clay.

Impact Of Ceramide3 On POPC Host Membranes: A Study On Structure And Thermodynamics

The uppermost layer of skin epidermis exhibits a very peculiar lipid composition consisting mostly of long-chain ceramides of asymmetric chain length. The functional impact of ceramides on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes was investigated using natural phytosphingosine type ceramide3 (Cer3) as a model system. Results will be presented on structure and thermodynamic phase behavior of the composite model system for three mole ratios Cer3/POPC (5:95; 10:90; 15:85). All methods applied so far (SAXS; DSC; confocal microscopy) reveal non-ideal miscibility of the two compounds with macroscopic separation of coexisting lamellar phases of different rigidity. Two major transition regions were identified: at low temperature(Tm1) and at high temperature(Tm2). They were attributed to POPC rich and Cer3 rich domains respectively. A slight increase in the d-spacing and as well a shift of Tm1 towards higher values indicate a solidifying effect of Cer3 on POPC host membranes. At low concentration the Cer3 rich domain (Tm2) exhibits normal thermodynamic behavior with freezing point depression due to the presence of POPC. The continuous shift in Tm1 together with a loss of transition cooperativity for the POPC rich domain hints towards a modification of the bilayer elasticity due to the presence of the Cer3. The overall heat content of the composite system increases with the amount of Cer3 present, signifying a stronger attractive interaction among the lipids. The Cer3 rich phase is almost dehydrated. Giant vesicles (GUVs) exhibit fluid-gel domain coexistence with the typical smooth and flat face facets as signatures of the more fluid and the more rigid membrane regions.