Flory-Huggins Theory Research Articles

Flory-Huggins VOC Photonics Sensor Made of Cellulose Derivatives.

As a widespread air pollutant, volatile organic compounds (VOCs) are harmful to the human body's skin, nervous system, and respiratory system. Low-cost, extensive, and continuous detection of VOCs is of great significance to human health. We infiltrated and coated cellulose acetate on the inverse opal photonic crystal skeleton of methylcellulose-polyvinyl alcohol-graphene oxide to construct a degradable, high-toughness cellulose VOC sensor. Cellulose acetate enhances the response to VOCs and achieves a highly selective response to acetone vapor due to the smaller Flory-Huggins parameter with acetone. This work proposes a general, simple, easy-to-use, and highly selective photonic crystal VOC sensor development strategy. Calculated from the Flory-Huggins solution theory, a suitable polymer was selected to modify the inverse opal photonic crystal framework and achieve high selectivity detection.

Effects of inorganic salts in the casting solution on morphology of poly(vinyl chloride)/bentonite ultrafiltration membranes

Modified polyvinyl chloride (PVC) composite ultrafiltration (UF) membranes are prepared by blending bentonite and varying amounts of different salts such as KCl, NH4Cl, NaCl, CaCl2, and MgCl2 in the casting solution (CS). Thermodynamics of PVC- based systems during phase inversion are determined by locating the binodal curve using Flory–Huggins theory. The modelled binodal curves are validated with the experimental binodal curve obtained from the cloud points data and found in close agreement with each other for different PVC-based systems. The blending of salt in the CS has two contradictory effects on the phase inversion rate as well as membrane morphology. A polymer-solvent axis shift occurs in the PVC/bentonite system in the presence of salts, reducing the thermodynamic stability, and a porous membrane with a 'finger-like' structure is obtained. In contrast, the viscosity of CS increases when salt is present in the CS, resulting in an increase in kinetic hindrance, and a membrane with a spongy structure is obtained. Hence due to the trade-off relation of thermodynamic and kinetic properties, the optimum salt concentration in the CS was evaluated by tailoring these properties. All the membranes involving salt and bentonite in the CS possessed enhanced membrane performance compared to the membrane without salt in CS (i.e., P1-membrane), and the best performing membrane is obtained for 1.0 g KCl in the CS (i.e., PK1.0). An enhanced pure water flux (i.e., 415.55 L m−2 h−1), permeate flux (i.e., 251.08 L m−2 h−1), oil rejection (i.e., 97.25%), and fouling resistance ability (i.e., FRR: 74.85%) is obtained for PK1.0 membrane due to improved membrane hydrophilicity and surface roughness.

Ensuring patient safety by rational choice of color masterbatch for medical device applications—A case study investigating the properties of an ABS/SAN blend colored by different masterbatches based on styrenic polymers

AbstractThe coloration of plastics is an important quality feature of medical devices, and it is most frequently done by using masterbatches. This study investigates the influence of masterbatches with different carrier resins on the impact resistance and the morphology of an acrylonitrile‐butadiene‐styrene (ABS)/styrene‐acrylonitrile (SAN) blend. The experimental results were compared with thermodynamical models based on Hansen and Flory–Huggins theory. The models, as well as notched impact testing, indicated strong immiscibility and incompatibility when using a masterbatch carrier based on polystyrene (PS). Immiscibility was confirmed by morphology studies that revealed the formation of PS‐droplets with increasing masterbatch content. Masterbatches based on ABS and SAN showed no significant impact and theoretical calculations were in good accordance with mechanics and morphology. The proposed theoretical calculation of solubility between blend partners potentially allows a prediction for selecting a suitable masterbatch carrier.

Thermodynamic analysis of oligomeric blends by applying the Kirkwood-Buff theory of solutions

The accurate prediction of the thermodynamic properties of oligomeric blends and, in general, binary liquid mixtures from atomistic simulations is a challenging task. In this work we develop a methodology for the full thermodynamic analysis of oligomeric blends and the extraction of the Flory-Huggins interaction parameter from the Gibbs energy of mixing, combining Flory-Huggins thermodynamics with Kirkwood-Buff theory of solutions. We perform a series of Molecular Dynamics (MD) simulations of 2-methylpentane/n-heptane mixtures, at various mole fractions. Firstly we validate the forcefield we apply in our MD simulations, comparing the density and excess volume we obtain against the corresponding experimental estimates found in the literature. Then we calculate the Kirkwood-Buff integrals in the isothermal-isobaric (NpT) ensemble, applying the particle fluctuations method, and we extract the component activity coefficients, the excess Gibbs energy, the excess enthalpy, and the excess entropy of mixing as functions of the mole fraction. Finally we calculate the Flory-Huggins interaction parameter χ by interpreting the Gibbs energy of mixing in the framework of Flory-Huggins theory, and explore its dependence on composition. All results are compared against experimental measurements in order to evaluate our methodology. Agreement is found to be very good.

Dynamic tunability of phase-change material transition temperatures using ions for thermal energy storage

Thermal energy storage (TES) based on phase-change materials (PCMs) has many current and potential applications, such as climate control in buildings, thermal management for batteries and electronics, thermal textiles, and transportation of pharmaceuticals. Despite its promise, the adoption of TES has been limited, in part due to limited tunability of the transition temperature, which hinders TES performance for varying use temperatures. Transition temperature tuning of a material using an external stimulus, such as pressure or an electric field, typically requires very large stimuli. To circumvent this problem, here, we report on the dynamic transition temperature tunability of a PCM using ions. We achieve a transition temperature tunability up to 6°C in polyethylene glycol (PEG) by using the salt lithium oxalatodifluoroborate at a low voltage of 2.5 V, which may enable simpler and safer devices/system designs. We also explain the thermal properties of the salt/PCM solution using the Flory-Huggins theory. Dynamically tunable T m (15°C–21°C) of phase change materials with 2.5 V perturbation A dual-ion battery approach using ions to modulate T m of the phase-change materials Combination of thermal energy storage with electrical energy storage in one device Demonstration of higher thermal utilization of the dynamically tunable PCM Lau et al. develop a dynamic tunable phase-change material (PCM) that uses ions to tune the T m , based on the dual-ion battery concept. With static T m PCM, utilization at ambient temperature is limited, whereas for tunable PCM, where T m closely aligns with ambient temperature, higher energy storage is possible.

Triphasic Polymer Particles Assembled via Microphase Separation with Multiple Functions.

This work investigated a unique type of triphasic colloidal particles composed of an azo polymer (PCNAZO), a fluorescent pyrene-containing polymer [P(MMA-co-PyMA)], and a poly(dimethylsiloxane)-based polymer (H2pdca-PDMS), focusing on the synthesis, forming mechanism, morphology control, and functions. The triphasic particles with well-defined morphologies were assembled through the microphase separation of the components in dichloromethane (DCM) droplets in an aqueous medium, induced by the gradual evaporation of the organic solvent. The real-time fluorescence emission spectra of the pyrenyl moieties and in situ microscopic observations show that the formation of the triphasic particles undergoes the segregation of the PCNAZO-rich phase, separation between P(MMA-co-PyMA)-rich and H2pdca-PDMS-rich phases, coalescence, and solidification in the dispersed droplets. The structure formation is due to the strong phase separation of the polymers as revealed by the calculations based on the Flory-Huggins theory. The morphologies and phase boundaries of the particles are found to be controlled by the interfacial energy between the phases and processing conditions. The triphasic particles thus obtained possess a series of interesting functions stemming from the polymers and the triple-compartmentalized structures. After being deposited on a substrate, the H2pdca-PDMS parts can tightly adhere on the surface, caused by the spreading nature of the polymer when slightly swelled by DCM. Upon irradiation with a linearly polarized laser beam at 488 nm, the azo polymer compartments show a significant elongation along the electric vibration direction of the polarized light, accompanied by the cooperative deformation of the H2pdca-PDMS pads. When dispersed in water and adhered on the substrate surface, the triphasic particles exhibit tunable colors originating from the fluorescence of the pyrenyl fluorophores and light absorption of the azo chromophores. The real-time investigation methods developed here could lead to the deep understanding of the structure formation process in the confined volume and be applied in phase-separation study of other polymers as well.

Effect of graphene oxide in the formation of polymeric asymmetric membranes via phase inversion

Membrane morphology of integrally skinned asymmetric membranes made by phase inversion can be tailored by precise control of the thermodynamic properties of the casting solution. In this work, the morphology of polyethersulfone (PES) and polyvinylidene fluoride (PVDF) membranes containing graphene oxide (GO) and their phase separation behavior have been studied. The Flory-Huggins theory and the Hansen solubility parameters have been used to construct theoretical binodal lines for ternary and quaternary systems, which have been validated by conducting cloud titration experiments. Moreover, the effect of different solvents on the morphology of PES membranes is discussed through the thermodynamic and kinetic properties of the casting solutions. Nontoxic solvents dimethyl sulfoxide (DMSO) and dihydrolevoglucosenone (Cyrene™) induce PES/GO membranes with finger-like pores and cellular voids, respectively. The addition of GO in the PES and the PVDF casting solutions increases their thermodynamic instability, leading to thinner selective top layers and higher porosities, up to a point where the high viscosity of the GO-containing solutions hinders the solvent-nonsolvent demixing. The highest porosity and pure water flux (PWF) occurs at 0.1 wt% GO for PES/GO/DMSO and at a loading of 0.3 wt% GO for systems PES/GO/Cyrene and PVDF/GO.

Effect of carbon nanotubes in ferroelectric liquid crystals

ABSTRACT Effect of carbon nanotubes (CNTs) in ferroelectric liquid crystal (FLC) is studied using a combination of Flory-Huggins theory and Landau theory. An appreciable change in polarisation, tilt angle and dielectric susceptibility behaviour in the chiral smectic C phase of the smectic-A to chiral smectic-C transition has been observed for CNTs- doped FLC system. We discussed these changes by theoretical calculations followed by plotting and discussing various topologies in the phase diagrams. Theoretical results based on this model show good agreement with experiment.

Negatively thermodynamic toughening in double network hydrogel towards cooling-triggered multi-shape memory effect

This paper explores fundamental mechanisms of negatively thermodynamic toughening during microphase separations of double network (DN) hydrogels, which have dynamically coordinating components with adjustable swelling behavior and designable multi-shape memory effect (multi-SME). Based on the Flory–Huggins theory and Fick’s second law, a thermodynamic model is formulated to study the diffusive dynamics, cooling-triggered multi-SME and mechanical toughness of the DN hydrogels. The negatively thermodynamic toughening effect of the DN hydrogels is strongly dependent on their water concentration, hydrophobic transition and microphase separation. Finally, effectiveness of this new model is demonstrated by applying it to predict dual-SME, quadruple-SME and cooling-triggered shape memory behaviors of DN hydrogels. This study provides a methodology for the design of shape memory DN hydrogels with tunable, giant and programmable cooling-triggered multi-SME.

Effect of bore fluid composition on poly(lactic-co-glycolic acid) hollow fiber membranes fabricated by dry-jet wet spinning

Poly(lactic-co-glycolic acid) (PLGA) is a widely used polymeric biomaterial due to its excellent biocompatibility and biodegradation. Asymmetric PLGA hollow fiber membranes (HFMs) have been extensively used as porous tubular scaffolds for tissue engineering, e.g. for nerve conduits and artificial blood vessels. PLGA HFMs are generally fabricated through a dry-jet wet spinning process, and the porous morphology of PLGA HFMs induced by polymer/solvent/nonsolvent ternary phase inversion plays a key role in their biomedical performance. In this study, PLGA was dissolved in dimethyl sulfoxide (DMSO) as the dope fluid, and deionized water with different DMSO contents was used as the bore fluid. The influence of bore fluid composition on the HFM morphology and performance was investigated by measuring phase separation time, porosity, mechanical properties, and in vitro hydrolytic degradation. The results indicated that with increased bore fluid DMSO content, the inner and outer diameters, as well as the wall thickness of the HFMs, decreased significantly; also, the inner surface became more porous and the inner surface pore size and porosity increased. Cross-sectional SEM images showed that the middle layer of the five-layered microstructure gradually changed from large voids to finger-like microvoids when the DMSO content in bore fluid increased from 0% to 60%. Furthermore, the HFMs resulting from higher DMSO content in bore fluid had a lower porosity, a faster degradation rate, a higher Young's modulus, and a lower suture retention strength. More importantly, the in vitro cell culture on the inner surface of PLGA HFMs showed that PC12 cells cultured on HFMs prepared with 60% DMSO bore fluid exhibited better cell adhesion, longer neurite length, and alignment along the HFM longitudinal axis. A ternary phase diagram and the Flory-Huggins theory were applied to analyze HFM morphological formation. The study contributes to understanding of the mechanism of HFM porous morphology formation and should guide potential application of PLGA HFMs as tissue engineering scaffolds.

Unusual Lower Critical Solution Temperature Phase Behavior of Poly(benzyl methacrylate) in a Pyrrolidinium-Based Ionic Liquid.

Polymer/ionic liquid systems are being increasingly explored, yet those exhibiting lower critical solution temperature (LCST) phase behavior remain poorly understood. Poly(benzyl methacrylate) in certain ionic liquids constitute unusual LCST systems, in that the second virial coefficient (A2) in dilute solutions has recently been shown to be positive, indicative of good solvent behavior, even above phase separation temperatures, where A2 < 0 is expected. In this work, we describe the LCST phase behavior of poly(benzyl methacrylate) in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide for three different molecular weights (32, 63, and 76 kg/mol) in concentrated solutions (5–40% by weight). Turbidimetry measurements reveal a strong concentration dependence to the phase boundaries, yet the molecular weight is shown to have no influence. The critical compositions of these systems are not accessed, and must therefore lie above 40 wt% polymer, far from the values (ca. 10%) anticipated by Flory-Huggins theory. The proximity of the experimental cloud point to the coexistence curve (binodal) and the thermo-reversibility of the phase transitions, are also confirmed at various heating and cooling rates.

Theoretical and experimental validation of praziquantel with different polymers for selection of an appropriate matrix for hot-melt extrusion

The selection of an appropriate matrix for the preparation of amorphous extrudate in hot-melt extrusion (HME) deals with the study of various solid-state properties of drugs and polymers. Therefore, it is necessary to have an appropriate knowledge of drug-polymer miscibility, the interaction between the drug-polymer on mixing, and Gibb's free thermal energy of mixing to screen polymers through thermodynamic phase diagrams, to be suitable amorphous matrix system for HME. Here, we evaluated the possibility of three different polymers, namely, Eudragit®EPO, polyvinyl alcohol (PVA), Kollicoat®IR (KIR) with Praziquantel (PZQ), with proper validation of the Flory-Huggins theory and construction of the phase diagram using the melting point depression approach to determine a suitable matrix for HME. The solubility parameter theoretical calculation approach was used as a preliminary study to validate the miscibility of PZQ with three different polymers. Theoretical and experimental validation studies using the Flory-Huggins interaction parameter value using the melting point depression approach and the effect of PZQ loading on the interaction parameter were systematically validated to predict thermodynamic phase diagrams and Gibbs free energy of mixing for screening these polymers for the preparation of amorphous extrudate. Using the phase diagram, the thermal processing temperature for the HME was determined using a T-φ phase diagram to obtain an appropriate matrix. The obtained extrudates were further validated through physical appearance, microscopic structure, thermal and functional group characterizations, followed by the PZQ assay. Thus, considering the solid-state properties, the processing parameters of HME were selected to obtain stable extrudates and an appropriate matrix for PZQ loading.

Prediction of the Miscibility of PBAT/PLA Blends.

Designing polymer structures and polymer blends opens opportunities to improve the performance of plastics. Blending poly(butylene adipate-co-terephthalate) (PBAT) and polylactide (PLA) is a cost-effective approach to achieve a new sustainable material with complementary properties. This study aimed to predict the theoretical miscibility of PBAT/PLA blends at the molecular level. First, the basic properties and the structure of PBAT and PLA are introduced, respectively. Second, using the group contribution methods of van Krevelen and Hoy, the Hansen and Hildebrand solubility parameters of PBAT and PLA were calculated, and the effect of the molar ratio of the monomers in PBAT on the miscibility with PLA was predicted. Third, the dependence of the molecular weight on the blend miscibility was simulated using the solubility parameters and Flory–Huggins theory. Next, the glass transition temperature of miscible PBAT/PLA blends, estimated using the Fox equation, is shown graphically. According to the prediction and simulation, the blends with a number-average molecular weight of 30 kg/mol for each component were thermodynamically miscible at 296 K and 463 K with the possibility of spinodal decomposition at 296 K and 30% volume fraction of PBAT. This study contributes to the strategic synthesis of PBAT and the development of miscible PBAT/PLA blends.

Phase Equilibrium and Interdiffusion in Blends of Polystyrene with Polyacrylates.

The solubility and interdiffusion of polystyrene (PS) with polymethyl acrylate (PMA), polyethyl acrylate (PEA), polybutyl acrylate (PBA), and polyethylhexyl acrylate (PEHA) have been studied by the optical interferometry method. Phase state diagrams are plotted. It is shown that they are characterized by the upper critical solution temperatures (UCST), which are localized in the temperature range above 450 K. Pair interaction parameters and their temperature dependences are determined and analyzed. Extrapolation of the temperature dependence of the interaction parameter was used to construct the dome of binodal curves and determine the spinodal curves in the framework of the Flory–Huggins theory. The diffusion coefficients of polystyrene into polyacrylates and polyacrylates into polystyrene are calculated. The dependences of the interdiffusion coefficients on the concentration, temperature, polystyrene molecular weight, and the number of carbons in the side chain of polyacrylate are analyzed. The numerical values of the interdiffusion coefficients of PS-1 into polyacrylates at 433 K change as −8.5 → −6.7 → −6.4 in the homologous series PMA → PEA → PBA. The coefficients of friction are calculated and the effect of change in the matrix structure on the diffusion of polystyrene in them is estimated.

High-Pressure Dielectric Studies-a Way to Experimentally Determine the Solubility of a Drug in the Polymer Matrix at Low Temperatures.

In this work, we employed broad-band dielectric spectroscopy to determine the solubility limits of nimesulide in the Kollidon VA64 matrix at ambient and elevated pressure conditions. Our studies confirmed that the solubility of the drug in the polymer matrix decreases with increasing pressure, and molecular dynamics controls the process of recrystallization of the excess of amorphous nimesulide from the supersaturated drug–polymer solution. More precisely, recrystallization initiated at a certain structural relaxation time of the sample stops when a molecular mobility different from the initial one is reached, regardless of the temperature and pressure conditions. Finally, based on the presented results, one can conclude that by transposing vertically the results obtained at elevated pressures, one can obtain the solubility limit values corresponding to low temperatures. This approach was validated by the comparison of the experimentally determined points with the theoretically obtained values based on the Flory–Huggins theory.

Trileucine as a dispersibility enhancer of spray-dried inhalable microparticles

The formation of trileucine-containing spray-dried microparticles intended for pulmonary delivery was studied in depth. A single-particle method was employed to study the shell formation characteristics of trileucine in the presence of trehalose as a glass former, and an empirical correlation was proposed to predict the instance of shell formation. A droplet chain instrument was used to produce and collect monodisperse particles to examine morphology and calculate particle density for different levels of trileucine. It was observed that the addition of only 0.5 mg/mL (10% w/w) trileucine to a trehalose system could lower dried particle densities by approximately 1 g/cm3. In addition, a laboratory-scale spray dryer was used to produce batches of trileucine/trehalose powders in the respirable range. Raman spectroscopy demonstrated that both components were completely amorphous. Scanning electron microscopy and time-of-flight secondary ion mass spectrometry were used to study the particle morphologies and surface compositions. For all cases with trileucine, highly rugose particles with trileucine coverages of more than 60% by mass were observed with trileucine feed fractions of as little as 2% w/w. Moreover, it was seen that at lower trileucine content, smaller and larger particles of a polydisperse powder had slightly different surface compositions. The surface activity of trileucine was also modeled via a modified form of the diffusion equation inside an evaporating droplet that took into account initial surface adsorption and eventual surface desorption due to droplet shrinkage. Finally, using the Flory-Huggins theory, it was estimated that at room temperature, liquid-liquid phase separation would start when the trileucine reached an aqueous concentration of about 18 mg/mL. Besides the surface activity of trileucine, this low concentration was assumed to explain the substantial effect of trileucine on the morphology of spray-dried particles due to early phase separation. The methodology proposed in this study can be used in the rational design of trileucine-containing microparticles.

Simulations of the Upper Critical Solution Temperature Behavior of Poly(ornithine-co-citrulline)s Using MARTINI-Based Coarse-Grained Force Fields.

Poly(ornithine-co-citrulline)s are ureido-based polymers, which were shown to exhibit tunable upper critical solution temperature (UCST) behavior, a property that can be exploited to develop thermoresponsive nanoparticles for controlled drug delivery systems. To gain insight into the driving forces that govern the formation and dissolution processes of poly(ornithine-co-citrulline) nanoparticles, a molecular dynamics (MD) simulation study has been carried out using MARTINI-based protein coarse-grained models. Multi-microsecond simulations at temperatures ranging from 280 to 370 K show that the fully reparametrized version 3.0 of MARTINI force field is able to capture the dependence on temperature of poly(ornithine-co-citrulline) aggregation and dissolution, while version 2.2 could not account for it. Furthermore, the phase separation observed in these simulations allowed us to extrapolate a phase diagram based on the Flory-Huggins theory of polymer solution, which could help in future rational design of drug delivery nanoparticles based on poly(amino acid)s.

Effect of different good solvents in flash nano-precipitation via multi-scale population balance modeling-CFD coupling approach

A computational and modeling approach is used to highlight the key factors that affect polymer nanoparticles (NP) formation in flash nano-precipitation (FNP), when the good solvent, e.g., acetone, is replaced by acetonitrile, tetrahydrofuran and tert-butanol. A population balance model is coupled with computational fluid dynamics to study the kinetics effects on FNP. The mean NP size is predicted in terms of mean radius of gyration via the Flory law of real polymers. The effect of different good solvents is modeled in terms of solute–solvent interactions, using the Flory–Huggins theory and Hansen solubility parameters. Promising results show how the proposed methodology is able to investigate the role played by different good solvents, analyzing single factors at the time. A deep insight into both the dynamics of mixing and the dynamics of aggregation is therefore reached and the main mechanisms involved are pointed out, showing a good agreement with experimental data.

Blends of Polyisoprene with Model Styrene–Olefin Copolymers: Mixing Energetics in Blends versus Block Copolymers

Most theoretical treatments of polymer mixing thermodynamics assume that the phase behavior of both polymer blends and block copolymers is controlled by the same Flory segmental interaction parameter, χ—a quantity which is proportional to the interaction energy density, X. However, there are few comparative experimental studies on this point. This work presents a systematic experimental comparison between the interaction energy densities measured on model polydiene–polyolefin blends (Xblend) and analogous block copolymers (XBC). Experimental cloud point temperature (Tcl) curves for blends of polyisoprene (PI) with selectively saturated poly(butadiene-r-styrene) (hSBR) random copolymers are fit to the Flory–Huggins theory, and the resultant values of Xblend are corrected for critical fluctuations and for end-group contributions, wherever significant. The temperature-dependent PI/hSBR Xblend(T) and previously reported PI–hSBR XBC values show satisfactory agreement at all levels of styrene incorporation, reinforcing the conclusion that random incorporation of styrene units into the saturated polybutadiene chain significantly enhances its compatibility with PI.

A New Era in Engineering Plastics: Compatibility and Perspectives of Sustainable Alipharomatic Poly(ethylene terephthalate)/Poly(ethylene 2,5-furandicarboxylate) Blends.

The industrialisation of poly(ethylene 2,5-furandicarboxylate) for total replacement of poly(ethylene terephthalate) in the polyester market is under question. Preparation of high-performing polymer blends is a well-established strategy for tuning the properties of certain homopolymers and create tailor-made materials to meet the demands for a number of applications. In this work, the structure, thermal properties and the miscibility of a series of poly(ethylene terephthalate)/poly(ethylene 2,5-furandicarboxylate) (PET/PEF) blends have been studied. A number of thermal treatments were followed in order to examine the thermal transitions, their dynamic state and the miscibility characteristics for each blend composition. Based on their glass transition temperatures and melting behaviour the PET/PEF blends are miscible at high and low poly(ethylene terephthalate) (PET) contents, while partial miscibility was observed at intermediate compositions. The multiple melting was studied and their melting point depression was analysed with the Flory-Huggins theory. In an attempt to further improve miscibility, reactive blending was also investigated.