Miscibility in Cross-Linked Polymer−Solvent Systems with Nematic Interactions

Benmouna, Farida; Maschke, Ulrich; Coqueret, Xavier; Benmouna, M.

doi:10.1021/ma990517z

Cited by 15 publications

(15 citation statements)

References 37 publications

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“…Volume phase transitions of a liquid crystalline gel immersed in a nematogen [168][169][170][171][172] are also closely related to the phase separations stated in this chapter, where the liquid crystalline ordering induces the volume change of the gel. Polymer-clay nanocomposites are a new class of organic-inorganic hybrid materials, which have good thermal stability in a liquid crystalline phase [173].…”

Section: Discussionmentioning

confidence: 63%

Thermodynamics of Flexible and Rigid Rod Polymer Blends

Matsuyama

2010

Encyclopedia of Polymer Blends

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Binary mixtures of a flexible polymer and a low molecular weight liquid crystalline molecule, or a rigid rod-like molecule, are of interest because of their important technological applications in high modulus fibers, nonlinear optics, and electro optical devices. These blends are basic materials for recent new technologies of liquid crystal displays [1,2]. The performances of these systems are closely related to phase separations and conformations of polymer chains dissolved in a liquid crystalline phase. One of the main problems is to examine the location of various phases such as isotropic, nematic, and smectic phases, depending on temperature and concentra tion. To understand the thermodynamics and thermal instability of these blends, it is important to consider the co-occurrences between liquid crystalline ordering and phase separations.Generally, polymer chains exhibit a variety of flexibility, from flexible to rigid rodlike polymers. Polymer blends containing a liquid crystalline ordering have received considerable attention. The volume of literature on the theories and experiments of liquid crystallinity in polymer blends is now very extensive. There are many theoretical models for liquid crystalline polymers, such as the Flory lattice model [3][4][5][6][7][8], wormlike chain model [9][10][11], and Onsager virial theory [12] for rigid rods. An example of a recent review of liquid crystalline polymers is the text book of Donald and Windle [13].In this chapter we introduce the thermodynamics, or phase behavior, of binary mixtures of a flexible polymer and a rigid rod-like molecule. Here the flexible polymer means that liquid crystalline ordering does not occur in the constituent pure polymer. We first describe the fundamentals of a nematic phase, based on the Onsager theory for a rigid rod, where the entropy-induced nematic ordering is discussed. This will be the basis of the following sections. In Section 2.3, we focus on the phase separations of mixtures of a flexible polymer and a rigid rod-like molecule, or a low molecular weight liquid crystalline molecule, in a thermal equilibrium state. We introduce recent theoretical models to describe phase behavior, combining the Flory-Huggins Edited by Avraam I. Isayev

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Section: Discussionmentioning

confidence: 63%

Thermodynamics of Flexible and Rigid Rod Polymer Blends

Matsuyama

2010

Encyclopedia of Polymer Blends

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“…These results were subject to the incompressibility condition φ p = 1 − φ s and the fact that we were dealing with UV‐cured samples in the absence of solvent where φ 0 = 1. On the basis of these considerations, one can calculate the phase diagram using the standard procedure of chemical potentials described previously 27, 28…”

Section: Resultsmentioning

confidence: 99%

“…Interest in crosslinked polymers and low‐molecular‐weight liquid crystals (LMWLCs) is relatively new 26–28. Crosslinked networks present substantial advantages over linear polymers by providing a higher mechanical strength and a better thermal stability.…”

Section: Introductionmentioning

confidence: 99%

“…These considerations remain essentially valid if the small molecules are nematogens with some rearrangements required due to the nematic ordering. This work can be viewed as part of the systematic studies undertaken in our laboratory to explore the physical properties of composite materials made of polymers and LMWLCs such as polymer‐dispersed liquid crystals (PDLCs) 27–30. Two main problems emerge when one deals with these materials with regard to their performances in terms of aging, thermal stability, mechanical strength, electrooptical responses, and relaxation processes.…”

Section: Introductionmentioning

confidence: 99%

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Swelling of crosslinked polyacrylates in isotropic and anisotropic solvents

Bouchaour

Benmouna

Coqueret

et al. 2003

J of Applied Polymer Sci

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ABSTRACT:The purpose of this study was to examine the swelling and deswelling of photochemically crosslinked poly(n-butylacrylate) networks in isotropic and anisotropic solvents. The phase diagrams were established in terms of composition and temperature for five isotropic solvents, acetone, cyclohexane, methanol, tetrahydrofuran, and toluene, and two low-molecular-weight nematic liquid crystals, 4-cyano-4Ј-n-pentyl-biphenyl and an eutectic mixture of cyanoparaphenylenes. Networks were formed by ultraviolet curing in the presence of 0.5 wt % difunctional monomer (hexane diol-di-acrylate) and 0.5 wt % photoinitiator (Darocur 1173). Immersion in excess solvent allowed us to measure the solvent uptake by weight and to determine the size increase by optical microscopy in terms of temperature. We calculated weight and diameter ratios considering the swollen-to-dry network states of the samples. Phase diagrams were analyzed with the phantom network model according to the Flory-Rehner theory of rubber elasticity, and for the anisotropic solvents, modeling was supplemented with the Maier-Saupe theory of nematic order for free energy. The polymer-solvent interaction parameter was deduced as a function of temperature, but the values were in discrepancy with Fedors's model of solubility parameters, which overestimated the interaction.

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“…For a crosslinked polymer, µ 1 is given by the first term in Eq. , but µ 2 has to be adapted to the network, which can be viewed as a single molecule (N 2 = 1) . Then one can write:

μ_{2} = g - ϕ_{1} \frac{d g}{d ϕ_{1}}

…”

Section: Chemical Potentials and Fitting Proceduresmentioning

confidence: 99%

Phase Diagrams of PolyAcrylic Networks and Liquid Crystal E7

Boudraa

Youcef

Bedjaoui

et al. 2014

Macromolecular Symposia

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Summary Equilibrium phase diagrams of polymer networks and a nematic liquid crystal blend were investigated. The polymer network used was PolyABu (poly(n‐butyl‐acrylate)), obtained by exposure to UV radiation of initial solutions composed of a reactive monomer, a small amount of a crosslinking agent, and a photoinitiator. Experimental phase diagrams were established using polarizing optical microscopy, and the results were analyzed within the predictions of the combined Flory‐Rehner theory of rubber elasticity and the Maier‐Saupe theory of nematic ordering.

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Miscibility in Cross-Linked Polymer−Solvent Systems with Nematic Interactions

Cited by 15 publications

References 37 publications

Thermodynamics of Flexible and Rigid Rod Polymer Blends

Thermodynamics of Flexible and Rigid Rod Polymer Blends

Swelling of crosslinked polyacrylates in isotropic and anisotropic solvents

Phase Diagrams of PolyAcrylic Networks and Liquid Crystal E7

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