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Fabrication of Mesoporous Nanofiber Networks by Phase Separation–Based Methods
Published in Ahmad Fauzi Ismail, Nidal Hilal, Juhana Jaafar, Chris J. Wright, Nanofiber Membranes for Medical, Environmental, and Energy Applications, 2019
Phase separation is a universal phenomenon observed in various materials, including metals, ceramics, and polymers (Papon et al. 2006). Specifically, phase separation in polymer solutions is commonly characterized by two descriptors, with the first one representing the factor causing phase separation (thermally induced, non-solvent-induced, evaporation-induced, and reaction-induced phase separations), and the second one illustrating the types of generated phases. In particular, the separation of a homogeneous phase into two liquid phases with different concentrations is denoted as a liquid-liquid phase separation (Lloyd et al. 1991). Similarly, the formation of a solid phase (usually as a result of crystallization of a certain component) in a uniform liquid phase is denoted as a solid-liquid phase separation (Lloyd et al. 1990). Since polymer solutions contain two components (i.e., polymer and solvent molecules), their phase separation features the processes of polymer and solvent molecule crystallization, which both correspond to solid-liquid phase separation.
Enzyme Catalysis
Published in Harvey W. Blanch, Douglas S. Clark, Biochemical Engineering, 1997
Harvey W. Blanch, Douglas S. Clark
(5) A complete treatment of the electrostatic potential difference is given in Haynes, C.A., Benitez, F.S., Blanch, H.W., and J.M. Prausnitz, AIChE Journal, 39(9), 1539 (1993). also minimizes the energy input required to achieve rapid phase dispersal during mixing. Following the mixing step, phase separation can be carried out by centrifugation (as is often done for the removal of cell debris) or by settling under gravity.
Recent developments and applications of the thermodynamics of surfactant mixing
Published in Molecular Physics, 2019
Jeffrey Penfold, Robert K. Thomas
The pseudophase approximation broadly replicates the main features of the adsorption data for DHDAB / C12E3. The model overestimates the amount of C12E3 at the surface for C12E3 rich solution compositions, and this could not be rectified using this pseudophase approximation model. However, the notable observations are that the solution aggregate mixing is highly nonideal and asymmetric, with a large synergistic interaction, i.e. large non-zero Cm and Dm parameters. In contrast, the surface is relatively close to ideal mixing. In Figure 6(a) the calculated curve for ideal surface mixing, but with the same highly nonideal bulk parameters, gives an indication of how close the surface is to ideal mixing. Hence the pattern of surface adsorption is being driven almost entirely by the bulk mixing. This is reinforced by the variation in the C12E3 monomer composition, which is also included in Figure 6(a). The variation in the micelle, or bulk aggregate, free energy of mixing is shown in Figure 6(b), and the tangent line in the figure shows that the mixture is close to phase separation over a narrow region from C12E3 mole fractions ∼0.3 to ∼0.45. In nonideal mixing a positive (repulsive) interaction parameter, > ∼ 2.0, and a large negative (attractive) interaction parameter are both indications of the proximity of phase separation. In these systems phase, separation means separation within the bulk aggregated phase or the formation of two separate phases. However, the published phase diagrams for DHDAB / C12E3 [27,40] do not give any particular indication of such mechanisms occurring.
Coexistence of nematic and chiral nematic phases of an achiral liquid crystal trimer possessing an octafluorobiphenyl unit
Published in Liquid Crystals, 2018
Atsushi Yoshizawa, Hirona Kato
Phase-separation phenomena in soft matter have attracted considerable attention because of its importance in the understanding of the molecular organisation [1–9]. Phase separation occurs usually in a mixture consisting of substances having different chemical structures. It occurs with difficulty in a single component, except in a few cases [10,11]. Phase separation observed for a liquid-crystalline mixture is coexistence of different phases which appear in the temperature sequence of the mixture. Recently, chiral nature in a liquid-crystalline phase of achiral molecules has been investigated extensively [7,12]. Chiral conglomerates consisting of domains with opposite handedness have been reported not only in liquid-crystalline phases [13–20] but also in isotropic liquids [21]. Rigid bent-core units are known to play an important role in the appearance of those frustrated phases. Furthermore, the twist-bend nematic phase (Ntb) was observed for members of achiral oligomers with a flexible odd-numbered methylene spacer [22–26]. Recently, achiral dimers were reported to exhibit Ntb phases and/or helicoidal smectic phases by Abberley et al [27]. One of the origins for the spontaneous mirror symmetry breaking is chiral synchronisation of transiently chiral molecules capable of adopting chiral conformations representing energy minima [7]. Biphenyl derivatives are mostly transiently chiral. Bulky substituents can enhance the rotational barriers, so that the enantiomerisation barrier separating the enantiomeric pairs increases. On the other hand, it is well known that rod-like nematic liquid-crystalline molecules are rotated with 90° between a twisted nematic cell where the rubbing direction on the bottom substrate is perpendicular to that on the upper substrate. We surmise that coupling between a transiently chiral unit and a surface anchoring effect can induce chiral conglomerates in a nematic phase.
Improved electro-optical and dielectric properties of polymer dispersed liquid crystal doped with disperse dye red 1 and carbon nanoparticles
Published in Liquid Crystals, 2023
Manoj M. Mhatre, Anuja Katariya-Jain, R. R. Deshmukh
The PDLC film can be constructed by two generalised processes, the emulsion method [12] and the phase separation method [13,14]. The emulsion method is based on the dispersion of LC material into a continuous aqueous solution having a film developing polymer. The LC is not soluble in this solution, therefore emulsion of oil-in-water (two-phase system) is formed. The coating of this emulsion on a conductive substrate and subsequent evaporation of water results in the LC/polymer composite system. Finally laminating the second conductive substrate onto this film leads to formation of final PDLC film device. However, the deformation of droplets from spherical to spheroids (shape anisotropy) as PDLC film forms greatly affects the electro-optical properties of the film. The phase separation method is opposite to the emulsion method as in it the LC is dissolved in a solution of organic fluid that contains a polymer phase. The phase separation method is broadly classified into three different types, namely, thermally-induced phase separation (TIPS), solvent-induced phase separation (SIPS), and polymerisation-induced phase separation (PIPS). We have used the PIPS method for the construction of the PDLC film, as it is clean, energy-saving and cost-effective with a fast processing time [15–21]. Also, the PIPS method offers great control over LC droplet morphology [22]. In the PIPS method, a low molecular weight monomer is used as a solvent for the LC. The LC material is homogeneously mixed with monomer and then polymerisation is induced through the application of ultraviolet (UV) radiation of appropriate wavelength and intensity. The phase separation occurs as the polymer chain grows resulting in the formation of a polymer matrix surrounding LC droplets. The curing temperature, the intensity of the UV light, types, and proportions of LC and monomer, rate of polymerisation and diffusion, LC solubility, and viscosity affect the size and optical structure of LC droplets [23–26].