Polymers

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393 KiB

Open AccessArticle

Richness of Side-Chain Liquid-Crystal Polymers: From Isotropic Phase towards the Identification of Neglected Solid-Like Properties in Liquids

by Laurence Noirez, Hakima Mendil-Jakani, Patrick Baroni and Joachim H. Wendorff

Polymers 2012, 4(2), 1109-1124; https://doi.org/10.3390/polym4021109 - 25 Apr 2012

Cited by 6 | Viewed by 7192

Abstract

Very few studies concern the isotropic phase of Side-Chain Liquid-Crystalline Polymers (SCLCPs). However, the interest for the isotropic phase appears particularly obvious in flow experiments. Unforeseen shear-induced nematic phases are revealed away from the N-I transition temperature. The non-equilibrium nematic phase in the [...] Read more.

Very few studies concern the isotropic phase of Side-Chain Liquid-Crystalline Polymers (SCLCPs). However, the interest for the isotropic phase appears particularly obvious in flow experiments. Unforeseen shear-induced nematic phases are revealed away from the N-I transition temperature. The non-equilibrium nematic phase in the isotropic phase of SCLCP melts challenges the conventional timescales described in theoretical approaches and reveal very long timescales, neglected until now. This spectacular behavior is the starter of the present survey that reveals long range solid-like interactions up to the sub-millimetre scale. We address the question of the origin of this solid-like property by probing more particularly the non-equilibrium behavior of a polyacrylate substituted by a nitrobiphenyl group (PANO2). The comparison with a polybutylacrylate chain of the same degree of polymerization evidences that the solid-like response is exacerbated in SCLCPs. We conclude that the liquid crystal moieties interplay as efficient elastic connectors. Finally, we show that the “solid” character can be evidenced away from the glass transition temperature in glass formers and for the first time, in purely alkane chains above their crystallization temperature. We thus have probed collective elastic effects contained not only in the isotropic phase of SCLCPs, but also more generically in the liquid state of ordinary melts and of ordinary liquids. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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694 KiB

Open AccessArticle

In Situ and Ex Situ Syntheses of Magnetic Liquid Crystalline Materials: A Comparison

by Ophelie Riou, Lacramioara Zadoina, Barbara Lonetti, Katerina Soulantica, Anne-Françoise Mingotaud, Marc Respaud, Bruno Chaudret and Monique Mauzac

Polymers 2012, 4(1), 448-462; https://doi.org/10.3390/polym4010448 - 10 Feb 2012

Cited by 11 | Viewed by 7462

Abstract

Magnetic hybrid liquid crystalline composites have been obtained either by thermal decomposition of a cobalt precursor in a solution containing a liquid crystal polymer or by dispersing preformed cobalt nanorods in a liquid crystal polymer matrix. The final materials are all mesomorphous and [...] Read more.

Magnetic hybrid liquid crystalline composites have been obtained either by thermal decomposition of a cobalt precursor in a solution containing a liquid crystal polymer or by dispersing preformed cobalt nanorods in a liquid crystal polymer matrix. The final materials are all mesomorphous and ferromagnetic. Their magnetic characteristics are compared as a function of the synthesis method. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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997 KiB

Open AccessArticle

Photomechanical Response of Composite Structures Built from Azobenzene Liquid Crystal Polymer Networks

by Kyung Min Lee and Timothy J. White

Polymers 2011, 3(3), 1447-1457; https://doi.org/10.3390/polym3031447 - 2 Sep 2011

Cited by 30 | Viewed by 8979

Abstract

Optically directed shape adaptive responses have been sought after for many decades in photoresponsive polymeric materials. A number of recent examinations have elucidated elucidated the unique opportunities of photomechanical responses realized in azobenzene-functionalized liquid crystalline polymer networks (both elastomers and glasses). This work [...] Read more.

Optically directed shape adaptive responses have been sought after for many decades in photoresponsive polymeric materials. A number of recent examinations have elucidated elucidated the unique opportunities of photomechanical responses realized in azobenzene-functionalized liquid crystalline polymer networks (both elastomers and glasses). This work summarizes and contrasts the photomechanical response of glassy polydomain, monodomain, and twisted nematic azo-LCN materials to blue-green irradiation. Building from this summary, the combinatorial photomechanical response observed upon irradiation of composite cantilevers is examined. Large scale shape adaptations are realized, with novel responses that may be of potential use in future employment of these materials in actuation. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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714 KiB

Open AccessArticle

Polarized Emission of Wholly Aromatic Bio-Based Copolyesters of a Liquid Crystalline Nature

by Kai Kan, Daisaku Kaneko and Tatsuo Kaneko

Polymers 2011, 3(2), 861-874; https://doi.org/10.3390/polym3020861 - 16 May 2011

Cited by 9 | Viewed by 8702

Abstract

A novel thermotropic liquid crystalline polymers poly{3-benzylidene amino-4-hydroxybenzoic acid (3,4-BAHBA)-co-trans-4-hydroxycinnamic acid (4HCA: trans-coumaric acid)} (Poly(3,4-BAHBA-co-4HCA)), was synthesized by the thermal polycondensation of 4HCA and 3,4-BAHBA, which was synthesized by a reaction of 3-amino-4-hydroxybenzoic acid (3,4-AHBA) with benzaldehyde. When [...] Read more.

A novel thermotropic liquid crystalline polymers poly{3-benzylidene amino-4-hydroxybenzoic acid (3,4-BAHBA)-co-trans-4-hydroxycinnamic acid (4HCA: trans-coumaric acid)} (Poly(3,4-BAHBA-co-4HCA)), was synthesized by the thermal polycondensation of 4HCA and 3,4-BAHBA, which was synthesized by a reaction of 3-amino-4-hydroxybenzoic acid (3,4-AHBA) with benzaldehyde. When the 4HCA compositions of Poly(3,4-BAHBA-co-4HCA)s were above 55 mol%, the copolymers showed a nematic, liquid crystalline phase. Differential scanning calorimetry (DSC) measurements of the copolymers showed a high glass transition temperature of more than 100°C, sufficient for use in engineering plastics. Furthermore, the copolymers showed photoluminescence in an N-methylpyrrolidone (NMP) solution under ultraviolet (UV) light with a wavelength of 365 nm. Oriented film of Poly(3,4-BAHBA-co-4HCA) with a 4HCA composition of 75 mol% emitted polarized light, which was confirmed by fluorescent spectroscopy equipped with parallel and crossed polarizers. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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353 KiB

Open AccessArticle

Mechanism Studies of LCP Synthesis

by Anne Buyle Padias and Henry K. Hall, Jr.

Polymers 2011, 3(2), 833-845; https://doi.org/10.3390/polym3020833 - 4 May 2011

Cited by 19 | Viewed by 13772

Abstract

The LCP (Liquid Crystal Polymer) known as Vectra is synthesized by acidolysis of 4-hydroxybenzoic acid with 6-hydroxy-2-naphthoic acid. The apparently simple acidolysis mechanism for LCP polycondensation is in fact a complex blend of mechanisms. Kinetics of model reactions and of actual polycondensations followed [...] Read more.

The LCP (Liquid Crystal Polymer) known as Vectra is synthesized by acidolysis of 4-hydroxybenzoic acid with 6-hydroxy-2-naphthoic acid. The apparently simple acidolysis mechanism for LCP polycondensation is in fact a complex blend of mechanisms. Kinetics of model reactions and of actual polycondensations followed second-order kinetics and their rate constants were comparable. In the latter stages, ketene loss leads to phenolic ends, while decarboxylation provides phenyl ester ends. Accordingly, the mechanism changes to phenolysis. A quinone methide intermediate may also intervene, as revealed by kinetics studies and MALDI-TOF spectroscopy. Tailor-made matrices and synthesis of alternating well-defined oligomers assisted our studies. Nucleophilic aromatic substitutions may play a role, and we speculate on possible chain polycondensation. Esterolysis may be a useful alternative to LCP synthesis. Complications caused by ketene loss can be averted by the use of methoxycarbonyloxy monomers. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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665 KiB

Open AccessArticle

Structural Analysis of Aromatic Liquid Crystalline Polyesters

by Henry Hall, Samiul Ahad, Robert Bates, Maria Bertucci, Cristina Contreras, Alexandru Dospinoiu, Guangxin Lin, Nancy Singletary and Arpad Somogyi

Polymers 2011, 3(1), 367-387; https://doi.org/10.3390/polym3010367 - 27 Jan 2011

Cited by 4 | Viewed by 10780

Abstract

Laboratory preparations of liquid crystalline prepolymers, distillates accompanying prepolymers, final polymers, and sublimates accompanying final polymers were examined. NaOD/D₂O depolymerization of prepolymers and polymers back to monomers with integration of the ¹H NMR spectra showed up to 6% excess of [...] Read more.

Laboratory preparations of liquid crystalline prepolymers, distillates accompanying prepolymers, final polymers, and sublimates accompanying final polymers were examined. NaOD/D₂O depolymerization of prepolymers and polymers back to monomers with integration of the ¹H NMR spectra showed up to 6% excess of carboxyls over phenol groups, caused partly by loss of the low-boiling comonomer hydroquinone through distillation during prepolymerization and leaving anhydride units in the polymer chain. ESI⁻ MS and MS/MS of hexafluoroisopropanol extracts of the prepolymer detected small molecules including some containing anhydride groups; ESI⁺ MS showed the presence of small cyclic oligomers. ¹H NMR (including TOCSY) spectra provided more quantitative analyses of these oligomers. The final polymerization increases the length of the polymer chains and sublimes out the small oligomers. Anhydride linkages remaining in the polymer must make LCP’s more susceptible to degradation by nucleophilic reagents such as water, alkalis, and amines. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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Review

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1372 KiB

Open AccessReview

Current Advances in the Carbon Nanotube/Thermotropic Main-Chain Liquid Crystalline Polymer Nanocomposites and Their Blends

by Henry Kuo Feng Cheng, Tanya Basu, Nanda Gopal Sahoo, Lin Li and Siew Hwa Chan

Polymers 2012, 4(2), 889-912; https://doi.org/10.3390/polym4020889 - 23 Mar 2012

Cited by 51 | Viewed by 11023

Abstract

Because of their extraordinary properties, such as high thermal stability, flame retardant, high chemical resistance and high mechanical strength, thermotropic liquid crystalline polymers (TLCPs) have recently gained more attention while being useful for many applications which require chemical inertness and high strength. Due [...] Read more.

Because of their extraordinary properties, such as high thermal stability, flame retardant, high chemical resistance and high mechanical strength, thermotropic liquid crystalline polymers (TLCPs) have recently gained more attention while being useful for many applications which require chemical inertness and high strength. Due to the recent advance in nanotechnology, TLCPs are usually compounded with nanoparticles to form particulate composites to enhance their properties, such as barrier properties, electrical properties, mechanical properties and thermal properties. Carbon-based nanofillers such as carbon nanotube (CNT), graphene and graphene oxide are the most common fillers used for the TLCP matrices. In this review, we focus on recent advances in thermotropic main-chain liquid crystalline polymer nanocomposites incorporated with CNTs. However, the biggest challenges in the preparation of CNT/TLCP nanocomposites have been shown to be inherent in the dispersion of CNTs into the TLCP matrix, the alignment and control of CNTs in the TLCP matrix and the load-transfer between the TLCP matrix and CNTs. As a result, this paper reviews recent advances in CNT/TLCP nanocomposites through enhanced dispersion of CNTs in TLCPs as well as their improved interfacial adhesion with the TLCP matrices. Case studies on the important role of chemically modified CNTs in the TLCP/thermoplastic polymer blends are also included. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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821 KiB

Open AccessReview

Nanoparticle-Liquid Crystalline Elastomer Composites

by Yan Ji, Jean E. Marshall and Eugene M. Terentjev

Polymers 2012, 4(1), 316-340; https://doi.org/10.3390/polym4010316 - 30 Jan 2012

Cited by 74 | Viewed by 13102

Abstract

Liquid crystalline elastomers (LCEs) exhibit a number of remarkable physical effects, including a uniquely high-stroke reversible mechanical actuation triggered by external stimuli. Fundamentally, all such stimuli affect the degree of liquid crystalline order in the polymer chains cross-linked into an elastic network. Heat [...] Read more.

Liquid crystalline elastomers (LCEs) exhibit a number of remarkable physical effects, including a uniquely high-stroke reversible mechanical actuation triggered by external stimuli. Fundamentally, all such stimuli affect the degree of liquid crystalline order in the polymer chains cross-linked into an elastic network. Heat and the resulting thermal actuation act by promoting entropic disorder, as does the addition of solvents. Photo-isomerization is another mechanism of actuation, reducing the orientational order by diminishing the fraction of active rod-like mesogenic units, mostly studied for azobenzene derivatives incorporated into the LCE composition. Embedding nanoparticles provides a new, promising strategy to add functionality to LCEs and ultimately enhance their performance as sensors and actuators. The motivation for the combination of nanoparticles with LCEs is to provide better-controlled actuation stimuli, such as electric and magnetic fields, and broad-spectrum light, by selecting and configuring the appropriate nanoparticles in the LCE matrix. Here we give an overview of recent advances in this area with a focus on preparation, physical properties and actuation performance of the resultant nanocomposites. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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996 KiB

Open AccessReview

Optical and Physical Applications of Photocontrollable Materials: Azobenzene-Containing and Liquid Crystalline Polymers

by Akira Emoto, Emi Uchida and Takashi Fukuda

Polymers 2012, 4(1), 150-186; https://doi.org/10.3390/polym4010150 - 9 Jan 2012

Cited by 92 | Viewed by 15414

Abstract

Photocontrol of molecular alignment is an exceptionally-intelligent and useful strategy. It enables us to control optical coefficients, peripheral molecular alignments, surface relief structure, and actuation of substances by means of photoirradiation. Azobenzene-containing polymers and functionalized liquid crystalline polymers are well-known photocontrollable materials. In [...] Read more.

Photocontrol of molecular alignment is an exceptionally-intelligent and useful strategy. It enables us to control optical coefficients, peripheral molecular alignments, surface relief structure, and actuation of substances by means of photoirradiation. Azobenzene-containing polymers and functionalized liquid crystalline polymers are well-known photocontrollable materials. In this paper, we introduce recent applications of these materials in the fields of mechanics, self-organized structuring, mass transport, optics, and photonics. The concepts in each application are explained based on the mechanisms of photocontrol. The interesting natures of the photocontrollable materials and the conceptual applications will stimulate novel ideas for future research and development in this field. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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