Phase and orientational ordering of low molecular weight rod molecules in a quenched liquid crystalline polymer matrix with mobile side chains

We study the phase diagram and orientational ordering of guest liquid crystalline (LC) rods immersed in a quenched host made of a liquid crystalline polymer (LCP) matrix with mobile side chains. The LCP matrix lies below the glass transition of the polymer backbone. The side chains are mobile and can align to the guest rod molecules in a plane normal to the local LCP chain contour. A field theoretic formulation for this system is proposed and the effects of the LCP matrix on LC ordering are determined numerically. We obtain simple analytical equations for the nematic/isotropic phase diagram boundaries. Our calculation show a nematic-nematic (N/N) first order transition from a guest stabilized to a guest-host stabilized region and the possibility of a reentrant transition from a guest stabilized nematic region to a host only stabilized regime separated by an isotropic phase. A detailed study of thermodynamic variables and interactions on orientational ordering and phases is carried out and the relevance of our predictions to experiments and computer simulations is presented.     

基于甲壳型液晶高分子的刚-柔型二嵌段共聚物的层状相:链伸展行为的研究

研究了一系列以聚己内酯(PCL)为柔性链段、甲壳型液晶高分子聚{2,5-二[(4-甲氧基苯基)氧羰基]苯乙烯}(PMPCS)为刚性链段的刚-柔型二嵌段共聚物(PCL-b-PMPCS)的微相分离结构.小角X射线散射(SAXS)和广角X射线衍射(WAXD)实验结果表明,当PMPCS为无定形态时,PCL-b-PMPCS的微相分离行为与柔-柔型二嵌段共聚物相似,其相形态主要取决于两段的体积分数.随温度升高,PMPCS链段采取伸展的棒状构象,形成六方柱状向列相(ΦHN),会诱导体系的微相分离结构出现"有序-有序"或"无序-有序"转变,使得在很宽的PMPCS体积分数(fPMPCS:40%~80%)内样品均呈现层状微相分离结构.我们对在200oC得到的层状相SAXS数据进行了一维相关函数分析,详细考察了层状相中PMPCS及PCL相区的厚度(LPMPCS、LPCL)与相应链段聚合度(NPMPCS、NPCL)的关系.对PMPCS相区,发现LPMPCS=0.2NPMPCS(nm).因棒状PMPCS链段与层的法线方向平行,该线性关系表明PCL-b-PMPCS的层状相为"单层近晶A相"结构,LPMPCS即为棒状PMPCS链段的长度,可通过控制PMPCS的聚合度予以精确控制.对PCL相区,则LPCL与NPCL近似有标度关系LPCL~NPCL0.85,说明处于熔融态的PCL链段受迫强烈伸展.进一步分析WAXD实验数据并计算每根PMPCS链段在层状相中的界面面积(S/X)可知,随NPMPS增大,PMPCS链段的液晶度从~20%增至~55%,S/X则从~2.4nm2增至~2.7 nm2.与此相应,PCL链段的伸展程度会略有降低,说明LPCL有较弱的NPMPCS依赖性.另一方面,LPCL与S/X的乘积与NPCL满足线性关系LPCL(S/X)=0.21NPCL(nm3),斜率即为PCL重复单元的体积.     

Morphological studies of blends of conjugated polymers and acceptor molecules using langevin dynamics simulations

We use coarse‐grained Langevin dynamics simulations of blends of generic conjugated polymers and acceptor molecules to show how architecture (e.g., side chains, backbone flexibility of oligomers) and the pair‐wise interactions between the constituents of the blend affect morphology and phase transition. Alkyl side chains on the conjugated oligomer backbones shift the liquid crystal (LC) transition temperature from that of bare conjugated backbones and the direction of the shift depends on backbone–backbone interactions. Rigid backbones and constrained side chains cause a layer‐by‐layer morphology of conjugated polymers and amorphous acceptors, whereas flexible backbones and unconstrained side chains facilitate highly ordered acceptor arrangement. Strong backbone–backbone attraction shifts LC transition to higher temperatures than weak backbone–backbone attraction, and strong acceptor–acceptor attraction increases acceptor aggregation. Pure macro‐phase separated domains form when all pair‐wise interactions in the blend are strongly attractive, whereas interconnected domains form at intermediate acceptor–acceptor attraction and strong polymer–polymer attractions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Synthesis and phase behavior of a polynorbornene‐based molecular brush with dual “jacketing” effects

In this study, a series of well‐defined liquid crystalline molecular brushes with dual “jacketing” effects, polynorbornene‐g‐poly{2,5‐bis[(4‐methoxyhenyl)oxycarbonyl] styrene} (PNb‐g‐PMPCS), were synthesized by the “grafting through” method from ring opening metathesis polymerization of α‐norbornenyl‐terminated PMPCS. The rigid PMPCS side chain was synthesized by Cu(I)‐catalyzed atom transfer radical polymerization initiated by N‐[(2‐bromo‐2‐methylpropanoyl)ethyl]‐cis‐5‐norbornene‐exo‐2,3‐dicarboximide. The chemical structures of the molecular brushes were confirmed by ¹H NMR and gel permeation chromatography (GPC), and the thermal properties were studied by thermogravimetric analysis (TGA). GPC results reveal that the molecular brushes have relatively narrow polydispersities. TGA results show that the molecular brushes have excellent thermal stabilities. The PMPCS side chains in all the molecular brushes form the columnar nematic liquid crystalline phase, which is a little different from the behavior of linear PMPCS possibly due to the confinement or other effects of the brush architecture which leads to decreased order. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2116–2123     

Liquid crystalline side chain polymer with a poly (Geraniol-co-MMA) backbone and phenylbenzoate mesogenic group: synthesis and characterization

A new side chain liquid crystalline polymers have been synthesized and characterized in which [geraniol-co-MMA] polymer are used as a backbone linked via polymethylene spacer to phenyl benzoate mesogenic group. The polymer exhibits enantiotropic liquid crystallinity with nematic phase and does not exhibit side chain crystallization .A clear difference between the nature of the mesophase is evidenced between [Geraniol-co-MMA] main chain and methacrylate polymers .The LC polymer exhibit glass transition at 40 °C. In a comparative analysis, we discuss the relevance of polymer backbone in the synthesis of side chain liquid crystalline polymers.     

Liquid-crystalline ordering in polymer brushes

The mean-field theory of liquid crystalline (LC) ordering is developed for a polymer brush immersed in a solvent. Additional attraction between neighbouring parallel mesogenic segments of the grafted chains is taken into account. It is shown that LC ordering in this brush is connected with the loss of solubility and occurs as a discrete first-order phase transition which is similar or even identical to the transition in polymer solution.     

一种西佛碱侧链型液晶高分子的合成及表征

一种西佛碱侧链型液晶高分子的合成及表征邹友思，林国良，姚青青，戴李宗，潘容华（厦门大学化学系厦门３６１００５）关键词联苯，西佛碱，侧链型，液晶高分子，基团转移聚合Ｆｉｎｋｅｌｌｎａｎｎ等提出的柔性基去偶合概念’］已在侧链型液晶高分子的研究中得到了证实...     

聚｛11-[(4′-正庚氧基-4-联苯基)羰基]氧-1-十一炔｝的相结构与相转变

采用示差扫描量热法(DSC)、一维(1D)、二维(2D)广角X-射线衍射(WAXD)和偏光显微镜(PLM)等研究手段对聚{11-[(4′-正庚氧基-4-联苯基)羰基]氧-1-十一炔}(PA-9,7)的本体相转变和相结构进行研究,并采用分子动力学方法对相结构进行模拟.结果表明,样品的相转变为近晶B相(SmB)近晶A相(SmA)各向同性态(Iso).在近晶B相中,侧链在层状结构中排列成具有六次对称性的准长程有序结构。     

Liquid Crystalline Polymers

History of Liquid Crystalline PolymersThe liquid crystalline(LC)state was first observed by Austrian botanist and chemist F.Reinitzer more than a century ago,and it was then confirmed in 1888 by German physicist O.Lehmann who named such a state of matter as"liquid crystal"in 1900.While low molecular mass(LMM)liquid crystals were successfully used in LC displays(LCDs),the development of LC polymers(LCPs)followed an independent path.Conceptually,LCPs are prepared with the incorporation of mesogenic groups that are responsible for the formation of LC mesophases,such as rod-like(calamitic)and discotic ones,into polymer chains.Depending on where the mesogens are attached,traditionally there are three major categories of LCPs.Main-chain LCPs(MCLCPs)have mesogens in the polymer backbone,while mesogens of side-chain LCPs(SCLCPs)are incorporated as side groups in a polymer with a relatively flexible main chain.In main-chain/side-chain combined LCPs(MCSCLCPs),mesogens are in both the backbone and side chains.Other classes of LCPs include mesogenjacketed LCPs(MJLCPs),dendronized LCPs,and LC networks(LCNs).     

In situ studies of phase transitions in thin discotic films

The crystalline to liquid crystalline (Cr-LC) phase transition in thin films of zone-cast hexa-peri-hexabenzocoronene sixfold substituted with dodecyl side chains (HBC-C12H25) has been studied in detail using grazing incidence X-ray diffraction (GID), electron diffraction (ED), and variable angle spectroscopic ellipsometry (VASE), When heating the material, a first minor transition is observed around 42 degrees C. This change is attributed to alterations of the crystalline alkyl chain packing, which only slightly changes the electronic properties of the material. At higher temperatures of about 90 degrees C, but still significantly below the previously reported transition temperature in bulk, the Cr-LC transition is observed. An accompanying large increase in optical anisotropy is compatible with the X-ray data, showing a transition from the as-cast herringbone-like crystalline state to a highly ordered discotic hexagonal columnar LC phase. The structural transition has the macroscopic effect of increasing the film thickness. The high structural order of the as-cast low-temperature phase is only partly recovered after cooling, and the phase transition exhibits a large hysteresis. From the ellipsometry data, the dielectric tensor of HBC-C12H25 was refined to unprecedented detail.     

Structure and internal dynamics of a side chain liquid crystalline polymer in various phases by molecular dynamics simulations: a step towards coarse graining

Side chain liquid crystalline polymer with relatively long spacer was modeled on a semiatomistic level and studied in different liquid crystalline phases with the aid of molecular dynamics simulations. Well equilibrated isotropic, polydomain smectic and monodomain smectic phases were studied for their structural and dynamic properties. Particular emphasis was given to the analysis on a coarse-grained level, where backbones, side chains, and mesogens were considered in terms of their equivalent ellipsoids. The authors found that the liquid crystalline phase had a minor influence on the metrics of these objects but affected essentially their translational and orientational order. In the monodomain smectic phase, mesogens, backbones, and side chains are confined spatially. Their diffusion and shape dynamics are frozen along the mesogen director (the one-dimensional solidification) and the reorientation times increase by one to one-and-half orders of magnitude. In this phase, besides obvious orientational order of mesogens and side chains, a stable detectable order of the backbones was also observed. The backbone director is confined in the plane perpendicular to the mesogen director and constantly changes its orientation within this plane. The backbone diffusion in these planes is of the same range as in the polydomain smectic phase at the same temperature. A detailed analysis of the process of field-induced growth of the smectic phase was performed. The study revealed properties of liquid crystalline polymers that may enable their future fully coarse-grained modeling.     

A Novel Side‐Chain Liquid Crystal Elastomer Exhibiting Anomalous Reversible Shape Change

Liquid crystalline elastomers (LCEs) have been actively investigated as stimuli‐controlled actuators and soft robots. The basis of these applications is the ability of LCEs to undergo a reversible shape change upon a liquid crystalline (LC)‐isotropic phase transition. Herein, we report the synthesis of a novel LCE based on a side‐chain liquid crystalline polymer (SCLCP). In contrast to known LCEs, this LCE exhibits a striking anomalous shape change. Subjecting a mechanically stretched monodomain strip to LC‐disorder phase transition, both the length and width of the strip contract in isotropic phase, and both elongate in LC phase. This thermally induced behaviour is the result of a subtle interplay between the relaxation of polymer main chain oriented along the stretching direction and the disordering of side‐group mesogens oriented perpendicularly to the stretching direction. This finding points out potential design of LCEs of this peculiar type and possible applications to exploit.     

Liquid crystalline conjugated polymers and their applications in organic electronics

This article describes the syntheses and electro‐optical applications of liquid crystalline (LC) conjugated polymers, for example, poly(p‐phenylenevinylene), polyfluorene, polythiophene, and other conjugated polymers. The polymerization involves several mechanisms: the Gilch route, Heck coupling, or Knoevenagel condensation for poly(p‐phenylenevinylene)s, the Suzuki‐ or Yamamoto‐coupling reaction for polyfluorenes, and miscellaneous coupling reactions for other conjugated polymers. These LC conjugated polymers are classified into two types: conjugated main chain polymers with long alkyl side chains, namely main‐chain type LC polymers, and conjugated polymers grafting with mesogenic side groups, namely side‐chain type LC conjugated polymers. In general, the former shows higher transition temperature and only nematic phase; the latter possesses lower transition temperature and more mesophases, for example, smectic and nematic phases, depending on the structure of mesogenic side chains. The fully conjugated main chain promises them as good candidates for polarized electroluminescent or field‐effect devices. The polarized emission can be obtained by surface rubbing or thermal annealing in liquid crystalline phase, with maximum dichroic ratio more than 20. In addition, conjugated oligomers with LC properties are also included and discussed in this article. Several oligo‐fluorene derivatives show outstanding polarized emission properties and potential use in LCD backlight application. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2713–2733, 2009     

Perforated layer structures in liquid crystalline rod-coil block copolymers

We report a novel observation of the tetragonal perforated layer structures in a series of rod-coil liquid crystalline block copolymers (BCPs), poly(styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS). PMPCS forms rigid rods while PS forms the coil block. Differential scanning calorimetry (DSC), polarized light microscopy (PLM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and transmission electron microscopy (TEM) techniques were used to investigate these rod-coil molecules, and a perforated layer structure was observed at f(PMPCS) approximately 0.37 in relatively low molecular weight (M(w)) samples and approximately 0.5 in high M(w) PS-b-PMPCS. This substantial phase boundary shift was attributed to the rod-coil nature of the BCP. The perforation obeys a tetragonal instead of hexagonal symmetry. The "onset" of perforation was also observed in real space in sample PS(272)-b-PMPCS(93) (f(PMPCS) approximately 0.52), in which few PS chains punctuate PMPCS layers. A slight increase in f(PS), by blending with PS homopolymer, led to a dramatic change in the BCP morphology, and uniform tetragonal perforations were observed at f(PMPCS) approximately 0.48.     

Molecular Dynamic Simulation of Side-Chain Liquid Crystalline Elastomer Under Load

Summary: We present a molecular dynamic simulation of a side chain liquid crystalline elastomer (LCE) under load. The LCE is composed of a flexible tetrafunctional diamond like network with rod-like mesogens attached to the network. As a precursor of the LC elastomer a flexible polymer network in a low molecular liquid-crystal (LC) solvent was used. The phase behavior of the LCE under uniaxial stretching up to the deformations of λ = 1.5 and 2.0 at different densities was studied. As in the non-stretched case upon density increase an isotropic to nematic phase transition occurs. However, in contrast to thermotropic side chain LC elastomers the stress induced shift transition is not observed. The stretching slightly increases the anisotropy of translational diffusion of mesogens in the nematic state. The stress-strain dependence for LCE both in the isotropic and the nematic states is obtained. Elastic modulus increases at high values of order parameter.     

Phase biaxiality in nematic liquid crystalline side-chain polymers of various chemical constitutions

In a previous deuterium NMR study conducted on a liquid crystalline (LC) polymer with laterally attached book-shaped molecules as the mesogenic moiety, we have revealed a biaxial nematic phase below the conventional uniaxial nematic phase (Phys. Rev. Lett. 2004, 92, 125501). To elucidate details of its formation, we here report on deuterium NMR experiments that have been conducted on different types of LC side-chain polymers as well as on mixtures with low-molar-mass mesogens. Different parameters that affect the formation of a biaxial nematic phase, such as the geometry of the attachment, the spacer length between the polymer backbone and the mesogenic unit, as well as the polymer dynamics, were investigated. Surprisingly, also polymers with terminally attached mesogens (end-on polymers) are capable of forming biaxial nematic phases if the flexible spacer is short and thus retains a coupling between the polymer backbone and the LC phase. Furthermore, the most important parameter for the formation of a biaxial nematic phase is the dynamics of the polymer backbone, as the addition of a small percentage of low molar mass LC to the biaxial nematic polymer from the original study served to shift both the glass transition and the appearance of detectable biaxiality in a very similar fashion. Plotting different parameters for the investigated systems as a function of T/Tg also reveals the crucial role of the dynamics of the polymer backbone and hence the glass transition.     

Synthesis and properties of comb polymers with semirigid mesogen‐jacketed polymers as side chains

A series of novel comb polymers, poly{2,5‐bis[(4‐methoxyphenyl)oxycarbonyl]styrene}‐g‐polystyrene (PMPCS‐g‐PS), with mesogen‐jacketed rigid side chains were synthesized by the “grafting onto” method from α‐yne‐terminated PMPCS (side chain) and poly(vinylbenzyl azide) (backbone) by Cu(I)‐catalyzed 1,3‐dipolar cycloaddition click reaction. The α‐yne‐terminated PMPCS was synthesized by Cu(I)‐catalyzed atom transfer radical polymerization initiated by a yne‐functional initiator. Poly(vinylbenzyl azide) was prepared by polymerizing vinylbenzyl chloride using nitroxide mediated radical polymerization to obtain poly(vinylbenzyl chloride) as the precursor which was then converted to the azide derivative. The chemical structure and architectures of PMPCS comb polymers were confirmed by ¹H NMR, gel permeation chromatography, and multiangle laser light scattering. Both surface morphologies and solution behaviors were investigated. Surface morphologies of PMPCS combs on different surfaces were investigated by scanning probe microscopy. PMPCS combs showed different aggregation morphologies when depositing on silicon wafers with/without chemical modification. The PMPCS comb polymers transferred to polymer‐modified silicon wafers using the Langmuir‐Blodgett technique showed a worm‐like chain conformation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Influence of a liquid crystalline block on the microdomain structure of block copolymers

We report on the phase behavior and microdomain structure of two types of diblock copolymers containing a liquid crystal (LC) block joined to a flexible coil block. Consideration of the symmetry groups of the liquid crystalline phases and of the block copolymer microdomain structures provides a rationale for predicting the possible types of liquid crystalline block copolymer morphologies. Both previously reported and newly discovered structural types are identified. Possible organizational schemes are developed for the mesogens and periodic disclination defects with respect to the intermaterial dividing surfaces separating the liquid crystalline and flexible coil domains. The first type of copolymer investigated has a rod-like LC block whereas the second type copolymer has a side chain LC block. Five different rod-coil diblocks based on poly(hexyl isocyanate-b-styrene) P(HIC-b-S) were synthesized by anionic polymerization. Wavy lamellae, zig-zag and arrowhead microdomain morphologies corresponding to smectic-C and smectic-O structures were observed depending on the composition. These layered phases have the director (PHIC chain axis) tilted at various orientations with respect to the layer normal. Side-chain LC diblocks based on functionalized poly(isoprene-b-styrene) P(I-b-S) were also investigated. These polymers were synthesized using polymer analogous chemistry from P(I-b-S) precursors. Three different mesogenic groups were attached to the PI blocks: one based on biphenyl benzoate and two based on azobenzene. The microdomain structures found for the functionalized poly(isoprene side-chain LC-b-styrene) P(ILC-b-S) diblocks are typical of traditional coil-coil diblocks (lamellae and cylinders). However, these morphologies possess an additional smectic layering of the mesogens within the microdomains of the LC block. In the case of the rod-coil diblocks, the transformation from an initially isotropic state to the final microphase separated solid state occurs via nematic and then smectic liquid crystalline states, whereas for the side-chain LC-coil cases, the microphase separation transition occurs prior to development of orientational order. The long-range microdomain order of LC block-coil block copolymers can extend over very large distances due to the influence of the orientational ordering of the LC block.     

Simulation of Copolymer Bottle-Brushes

Summary: The structure of bottle-brush polymers with a rigid backbone and flexible side chains is studied in three dimensions, varying the grafting density, the side chain length, and the solvent quality. Some preliminary results of theoretical scaling considerations for one-component bottle-brush polymers in a good solvent are compared with Monte Carlo simulations of a simple lattice model. For the simulations a variant of the pruned-enriched Rosenbluth method (PERM) allowing for simultaneous growth of all side chains in the Monte Carlo sampling is employed. For a symmetrical binary (A,B) bottle-brush polymer, where two types (A,B) of flexible side chains are grafted with one chain end to the backbone in an alternating way, varying repulsive binary interactions between unlike monomers and the solvent quality, it is found that phase separation into an A-rich part of the cylindrical molecule and a B-rich part can occur only locally. Long range order (in the direction of the backbone) does not occur, and hence the transition from the randomly mixed state of the bottle-brush to the phase-separated structure is strongly rounded, in contrast to the corresponding mean field predictions of a sharp transition to a “Janus cylinder” phase-separated structure. This lack of a phase transition can be understood from an analogy with spin models in one dimension. By estimating the correlation length for this phase separation along the backbone as a function of side chain length and solvent quality, we present strong evidence that no sharp phase transition occurs.     

Nonionic diethanolamide amphiphiles with unsaturated C18 hydrocarbon chains: thermotropic and lyotropic liquid crystalline phase behavior

The neat and lyotropic liquid crystalline phase behavior of three nonionic diethanolamide amphiphiles with C18 hydrocarbon chains containing one, two or three unsaturated bonds has been examined. This has allowed the effect of degree of unsaturation on the phase behavior of diethanolamide amphiphiles to be investigated. Neat linoleoyl and linolenoyl diethanolamide undergo a transition from a glassy liquid crystal to a liquid crystal at ～-85 °C, while neat oleoyl diethanolamide undergoes a transition at ～-60 °C to a liquid crystalline material before re-crystallizing at -34 °C. Oleoyl diethanolamide then undergoes a third transition from a crystalline phase to a smectic liquid crystalline phase at ～5 °C. In the absence of water, the transition temperature from a smectic liquid crystal to an isotropic liquid decreases with increasing unsaturation. The addition of water results in the formation of a lamellar phase (L(α)) for all three amphiphiles. The lamellar phase is stable under excess water conditions up to temperatures of at least 70 °C. Approximate partial binary amphiphile-water phase diagrams generated for the three unsaturated C18 amphiphiles indicate that the excess water point for each amphiphile occurs at ～60% (w/w) amphiphile.