Dynamics of phase separation in mesomorphic mixtures

Lansac, Yves; Fried, Floyd A.; Maïssa, P.

doi:10.1080/02678299508036699

Cited by 17 publications

(9 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The cross terms involving Γ φS in eqs 40-43 deserve comment, because they are not commonly included. Indeed, Lansac et al 13 have considered phase separation into coexisting isotropic and nematic phases without the cross terms. Although the terms appear with a coefficient q 2 in eq 40, this is not because of any conservation law.…”

Section: Resultsmentioning

confidence: 99%

“…In contrast, our equations are applicable to a broad class of rigid/flexible mixtures and can be carried into the nonlinear regime, where they provide a basis for numerical solutions. 12 Lansac et al 13 have also described the phase separation kinetics using two coupled equations of motion, but they neglect cross terms that originate from generalized currents in composition and orientation due to nonlocal forces. We believe that these neglected terms must be restored in order to achieve a realistic dynamical model of phase separation kinetics in rigid/flexible blends.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Phase Separation Kinetics of Rod/Coil Mixtures

Liu

Fredrickson

1996

Macromolecules

View full text Add to dashboard Cite

Equations of motion are presented that describe the kinetics of phase separation of mixtures of rods and coils into an isotropic phase rich in coils and a nematic phase rich in rods. The equations were derived using dynamical mean field theory and contain only a few pure-component parameters, such as the self-diffusion coefficients and molecular weights of the rods and coils. In such a system, both composition and orientation density evolve with time in a coupled fashion, so the presence of orientational order has a pronounced effect on the domain morphology at all but the latest stages of phase separation. The formalism presented here will provide insights into the control of domain morphology and properties of bicontinuous polymeric structures produced by quenching spinodal decomposition processes.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Phase Separation Kinetics of Rod/Coil Mixtures

Liu

Fredrickson

1996

Macromolecules

View full text Add to dashboard Cite

show abstract

“…To capture these thermodynamic and kinetic effects, we use a Cahn-Hilliard framework that allows composition and orientational density to evolve in a coupled fashion as functions of position and time following a temperature quench [13]. In contrast to earlier studies that treat orientational den-sity as a scalar order parameter [14,15], this framework includes the orientational density's second-order tensorial nature [16]. Although it is instructive to study the case of two coupled scalar order parameters (Model C [17]), a scalar cannot capture the direction of nematic order.…”

mentioning

confidence: 99%

Effect of ordering on spinodal decomposition of liquid-crystal/polymer mixtures

et al. 1999

View full text Add to dashboard Cite

Partially phase-separated liquid-crystal/polymer dispersions display highly fibrillar domain morphologies that are dramatically different from the typical structures found in isotropic mixtures. To explain this, we numerically explore the coupling between phase ordering and phase separation kinetics in model two-dimensional fluid mixtures phase separating into a nematic phase, rich in liquid crystal, coexisting with an isotropic phase, rich in polymer. We find that phase ordering can lead to fibrillar networks of the minority polymer-rich phase.Mixtures of liquid crystals with a small amount of polymer (polymer-stabilized liquid crystals [1][2][3], or PSLC's) show promise for electro-optic devices such as light shutters and displays [4][5][6][7], because the polymer tends to form a network that aligns the liquid crystal [8]. Since polymers and liquid crystals tend to be immiscible, the dispersions are prepared by mixing a small amount of miscible monomer with the liquid crystal and photopolymerizing. As the polymers grow, the system phase separates into an ordered phase rich in liquid crystal and an isotropic phase rich in polymer. Long before the system reaches equilibrium, however, the polymerization "freezes" the mixture into a crosslinked network of polymer-rich domains. Thus, the fabrication of PSLC's involves interplay among three kinetic processes: polymerization, phase separation, and phase ordering. Depending on the time scales that control these processes, a rich variety of morphologies have been observed [9][10][11][12]. Because of the number of nonequilibrium processes involved, however, there is little theoretical understanding of the factors that control the domain morphology. In this Letter, we focus on the interplay between phase separation (PS) and phase ordering (PO) kinetics in mixtures of short, rigid polymers (rods) and long, flexible polymers (coils), as a first step towards rational design and control of the network morphology.It is well known that thermodynamic factors such as the anisotropy of the isotropic/nematic interfacial tension can influence domain morphology, leading to anisotropic domain shapes. However, there are also kinetic factors that control domain morphology, such as the anisotropic diffusion coefficient of a rod. To capture these thermodynamic and kinetic effects, we use a CahnHilliard framework that allows composition and orientational density to evolve in a coupled fashion as functions of position and time following a temperature quench [13]. In contrast to earlier studies that treat orientational density as a scalar order parameter [14,15], this framework includes the orientational density's second-order tensorial nature [16]. Although it is instructive to study the case of two coupled scalar order parameters (Model C [17]), a scalar cannot capture the direction of nematic order. Because a vector does not have head/tail symmetry, it is crucial to retain the tensor order parameter to obtain domain anisotropy [18].To assess the effects of phase ordering, we study two sy...

show abstract

“…1 Phase separation in LC-polymer mixtures has thus been thoroughly studied, experimentally [2][3][4] and theoretically. [5][6][7][8][9][10] For LC mixtures of exclusively low molar mass components the situation is different. It is not uncommon to see reports of a single clearing temperature of multicomponent mixtures such as E7, which develops the nematic LC phase (exhibiting no long-range order beyond the orientational one).…”

Section: Introductionmentioning

confidence: 99%