Weakly Nonlinear Viscoelastic Nematodynamics

A weakly nonlinear viscoelastic theory is developed for nematic liquid crystalline (LC) polymers. A small transient elastic strain due to the change in length of macromolecular strands under stress and a director of unit length are employed in the theory as hidden variables. The theory allows describing anisotropic viscoelasticity and the evolution equation for the director in flows of relatively rigid LC polymers or in slow flows of LC polymers with flexible spacers. As shown, omitting the director gradient does not affect macroscopic predictions of the theory. In the infinitesimal case, the evolution equation for the director looks like the Ericksen equation, but with an additional relaxation term. Although the present theory is mostly applicable for thermotropic LC polymers it can also be used for concentrated lyotropic LC systems, as well as for analyzing flows of concentrated polymer suspensions and nanocomposites filled with uniaxially symmetric particles.     

羧基遥爪热致性主链液晶离聚物的合成与表征

以对羟基苯甲酸甲酯和1,4-丁二醇为主要原料,经熔融酯交换合成介晶基元双(对羟基苯甲酸)丁二醇酯(BBHB);以四氯乙烷为溶剂,采用溶液缩聚法将BBHB与适量的对苯二甲酰氯(TPC)反应,经Na2CO3溶液处理,合成端基为羧基的液晶离聚物。通过红外光谱等分析对它们的化学结构进行了表征。表明:所合成的液晶离聚物P1~P3为纹影织构,属于典型的向列型液晶,液晶相区间为100℃左右,羧基对液晶区间和玻璃化转变温度(Tg)、熔融温度(Tm)、相转变温度(Tc)影响不大。     

大分子自组装及其应用的研究与进展

综述了化学吸附、分子沉积、旋涂、慢蒸发溶剂和枝接成膜等 5种大分子自组装成膜方法 ,并介绍了其在液晶、非线性光学材料、聚合物表面改性等材料领域的应用及其表征研究。     

可控活性自由基聚合制备端基官能化聚合物研究进展

端基官能化聚合物是指那些在聚合物末端或悬垂端含有活性官能团的聚合物。它们可发挥交联剂或扩链剂的作用,从而制备出不同结构特点的嵌段聚合物、接枝聚合物、星型、超支化或树状聚合物。文章主要对引发转移终止剂(Iniferter)法、原子转移自由基聚合(ATRP)、氮氧自由基调控聚合(NMRP)和可逆加成-断裂链转移自由基聚合(RAFT)等可控活性自由基聚合方法在制备端基官能化聚合物中的应用进行了介绍。最后对可控活性自由基聚合在功能性聚合物制备中的应用前景进行了展望。     

Nanostructured Organic–Inorganic Composite Materials by Twin Polymerization of Hybrid Monomers

Forming two structurally different but associated polymer structures in a single step is a possible route for the production of nanostructured materials. By means of twin polymerization of specially constructed monomers consisting of two different covalently bonded building blocks (hybrid monomers), this route is realized. What is important is that two different macromolecular structures are formed from one monomer in a single process. The two polymers formed can be linear, branched, or cross‐linked structures. The molecular composition of the hybrid monomer defines the degree of cross‐linking of the corresponding macromolecular structures that is theoretically possible.     

Tunable Diffraction Gratings from Biosourced Lyotropic Liquid Crystals

Diffraction gratings are important for modern optical components, such as optical multiplexers and signal processors. Although liquid crystal (LC) gratings based on thermotropic LCs have been extensively explored, they often require expensive molecules and complicated manufacturing processes. Lyotropic LCs, which can be broadly obtained from both synthetic and natural sources, have not yet been applied in optical gratings. Herein, a facile grating fabrication method using a biosourced lyotropic LC formed by cellulose nanocrystals (CNCs), a material extracted from plants, is reported. Hydrogel sheets with vertically aligned uniform periodic structures are obtained by fixing the highly oriented chiral nematic LC of CNCs in polymer networks under the cooperative effects of gravity on phase separation and a magnetic field on LC orientation. The hydrogel generates up to sixth-order diffraction spots and shows linear polarization selectivity, with tunable grating periodicity controlled through LC concentration regulation. This synthesis strategy can be broadly applied to various grating materials and opens up a new area of optical materials from lyotropic LCs.     

Helical twisting power of three-ring chiral molecules and polymerization in cholesteric electrolyte solutions

A series of chiral three-ring type compounds with rigid shape was employed as chiral inducers for induction of chiral cholesteric liquid crystal (cholesteric LC) from achiral nematic LC. Helical twisting power of the chiral compounds was estimated with the Cano wedge method. Cholesteric LC electrolyte solution was prepared by adding the chiral compounds. Subsequently, polymerization in the cholesteric LC was carried out to produce chiroptically active polymer films. This method is different from conventional methods for synthesizing chiral polymers because neither chiral monomers nor asymmetric catalysts are employed. Surface structure and optical properties of the polymer thus prepared were examined.     

An analysis of impact-induced deformation and fracture modes in amorphous glassy polymers

The finite deformation response of a planar block of polymer material subject to impact loading is analyzed using two constitutive models for glassy polymers, a reference Drucker–Prager type model and a physics-based macromolecular model, supplemented by a phenomenological model for craze initiation and widening. Full transient finite element analyses are carried out using a Lagrangian formulation of the field equations. The analyses allow an assessment of possible failure mechanisms under dynamic loading and the ability of the different models to predict such behavior. The results highlight the effect of the stress–strain behavior of polymers, notably the post-yield softening and large strain hardening, on localization of plastic flow. This behavior is adequately captured only by the macromolecular model.     

Shape-memory nanoparticles from inherently non-spherical polymer colloids

Samples of polymeric materials generally have no intrinsic shape; rather their macroscopic form is determined by external forces such as surface tension and memory of shear (for example, during extrusion, moulding or embossing). Hence, in the molten state, the thermodynamically most stable form for polymer (nano)particles is spherical. Here, we present the first example of polymer nanoparticles that have an intrinsic non-spherical shape. We observe the formation of high-aspect-ratio ellipsoidal polymer nanoparticles, of controlled diameter, made from main-chain liquid crystalline polymers using a mini-emulsion technique. The ellipsoidal shape is shown to be an equilibrium (reversible) characteristic and a direct result of the material shape memory when a liquid crystal nanoparticle is in its monodomain form.     

Assembling DNA into Advanced Materials: From Nanostructured Films to Biosensing and Delivery Systems

The past decade has witnessed a rapid expansion in the design and assembly of engineered materials for biological applications. However, such applications place limitations on the molecular building blocks that can be used. Requirements for polymer‐based building blocks include biocompatibility, biodegradability, and stimuli‐responsive behavior. Many traditional polymers used in materials science are limited in at least one of these areas, so new polymers need to be explored. As we outline here, DNA is one such polymer that shows promise in developing the next generation of ‘smart’ materials for biomedical and diagnostic applications.     

一种新的测量大分子缠结的方法——溶胀DSC法

从分子量、溶液浓度、测定状态、粘度、模量等多方面证明了聚合物溶胀DSC曲线尾部的小峰反映了大分子缠结,从而提出了一种新的测定固态聚合物中大分子缠结的方法—溶胀差示扫描量热法。这种方法能快速、方便地测量纤维和聚合物材料中的大分子缠结,且不受结晶、非晶和取向结构的影响。     

A functionally separated nanoimprinting material tailored for homeotropic liquid crystal alignment

In order to homeotropically align liquid crystals (LCs) at the nanosized surface grooves processed by nanoimprint lithography technology (NIL), we propose to design a hybrid-type homeotropic polymer material consisting of two distinct moieties with largely different thermo-mechanical properties and surface activity. Surface contact angle measurements and sum-frequency vibrational spectroscopy allow us to conclude that the polymer film is a functionally separated composite suitable for the homeotropic LC alignment processed by NIL. As one of the potential applications using the hybrid-type homeotropic polymer, we demonstrate that the nanoimprinted grooves at the polymer surface can achieve a zenithal nematic LC bistability.     

超支化聚合物的研究进展

超支化聚合物由于具有独特的特征和相对简单的合成方法，以及在材料科学上的用途而引起了科学家们强烈的兴趣。本文综述了超支化聚合物的基本合成方法以及共轭与非共轭两大类超支化聚合物。     

Magnetic-field-assisted formation of alignment polymer coatings in liquid crystal cells

We describe a new method for obtaining liquid crystal (LC) layers with planar orientation in plane-parallel cells, which is based on the technology of LC-polymer interface formation in solution under the action of an applied magnetic field. The azimuthal anchoring energy of LC at the polymer surface has been determined by measuring the angle of orientation of the nematic LC director on the substrate surface as a function of the magnetic field. The LC orientation provided by the proposed method is stable, and the anisotropy of LC anchoring is comparable with that achieved using well-known methods of alignment polymer film preparation by rubbing.     

Thermoreversible Morphology and Conductivity of a Conjugated Polymer Network Embedded in Block Copolymer Self‐Assemblies

Self‐assembly of block copolymers provides numerous opportunities to create functional materials, utilizing self‐assembled microdomains with a variety of morphology and periodic architectures as templates for functional nanofillers. Here new progress is reported toward the fabrication of thermally responsive and electrically conductive polymeric self‐assemblies made from a water‐soluble poly(thiophene) derivative with short poly(ethylene oxide) side chains and Pluronic L62 block copolymer solution in water. The structural and electrical properties of conjugated polymer‐embedded self‐assembled architectures are investigated by combining small‐angle neutron and X‐ray scattering, coarse‐grained molecular dynamics simulations, and impedance spectroscopy. The L62 solution template organizes the conjugated polymers by stably incorporating them into the hydrophilic domains thus inhibiting aggregation. The changing morphology of L62 during the micellar‐to‐lamellar phase transition defines the embedded conjugated polymer network. As a result, the conductivity is strongly coupled to the structural change of the templating L62 phase and exhibits thermally reversible behavior with no signs of quenching of the conductivity at high temperature. This study shows promise for enabling more flexibility in processing and utilizing water‐soluble conjugated polymers in aqueous solutions for self‐assembly based fabrication of stimuli‐responsive nanostructures and sensory materials.     

A designers' guide to engineering polymer technology

The influence of polymers on modern product design is unprecedented and in many cases is the only material suitable. Today, the range of polymer materials is vast and, at the same time, bewildering to designers new to these materials. This article contains an essential summary of salient information on polymer technology formatted for use by engineering designers considering product designs which comprise of or contain parts made from polymer materials. The information is structured around materials, processes, properties and applications for thermoplastics, thermosets and rubbers.     

Synthesis and polymerization of substituted ammonium sulfonate monomers for advanced materials applications

Sulfonated polymers have found use as ion-exchange membranes for use in fuel cells, water purification, electroactive devices, and inorganic materials templating and synthesis. Improving the materials for these applications and opening up new applications requires the ability to synthesis targeted or more complex sulfonated polymers, which includes tailoring the chemistry (copolymerization across a wider range of solubility) and/or polymer architecture (block, graft, nanoparticle). This article will summarize the recent work using sulfonated monomers with substituted ammonium counterions as a versatile route for enabling this goal. Two main benefits of these monomers are as follows. First, they are useful for preparing amphiphilic copolymers, which is a challenge using traditional acidic or alkali salt forms of sulfonated monomers. Second, sulfonated polymers with substituted ammonium counterions are useful polymers for obtaining unique material properties, such as organo-gelation of low polarity solvents or obtaining ionic liquid polymers for the fabrication of solid polymer electrolytes.     

Wrinkled liquid-crystalline microparticle-enhanced photoresponse of PDLC-like films by coupling with mechanical stretching

Photoresponsive behaviors are studied in hybrid liquid-crystalline (LC) films prepared with light-responsive LC polymer microparticles as dopants using photoinert polymers as a host material. Upon mechanical stretching, both topological shape change and mesogenic alignment occur in the LC polymer microparticles, enabling the polymer-dispersed LC (PDLC)-like films to bend toward a light source upon UV irradiation. The rough morphologies of the hydrophobic LC microparticles enhance their interactions with hydrophilic polymer substrates. The bilayer-like structures of the hybrid film formed in the fabrication processes are responsible for the photomechanical behavior, which is reversibly controlled by combing light irradiation with the stretching processes.     

聚合物凝聚态中大分子链的形态

从教学的角度,论述了凝聚态中大分子链形态理论的发展,指出应该用辩证的方法,引导学生去分析问题,并把理论模型结合材料实际进行学习。     

Synthesis,processing sand properties of thermotropic liquid-crystal polymers

Thermotropic liquid-crystal polymers for high-performance applications are typically based on wholly aromatic polyester and polyamide architectures. The linear character of the aromtic monomers produces polymer chains with stiff, extended conformations. As a result, the chains organize themselves into a nematic melt and readily orient in response to processing flow fields. The close coupling between chain orientation and flow fields produces both a rich variety of materials and a high degree of controllability of their structure and properties (such as the tensile strength, elastic modulus and coefficient of thermal expansion). In this paper, we describe synthetic efforts to develop liquid-crystal polymer structures and the relationships between chain molecular structure, processing, and properties of this class of polymers in two distinct processing situations: Injection molding and fiber formation. The special importance of the orientational flow field in developing high orientation and excellent mechanical properties will be highlighted.