Orientador: Harry Westfahl Junior / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T09:45:51Z (GMT). No. of bitstreams: 1 HernandezJimenez_Marcela_D.pdf: 3260686 bytes, checksum: f15b800ff735b84b434b7b6317322209 (MD5) Previous issue date: 2007 / Resumo: Os polímeros líquido-cristalinos são estruturas macromoleculares compostas por blocos moleculares flexíveis e rígidos, que combinam propriedades típicas de polímeros e de cristais líquidos. Como ocorre nos copolímeros de blocos flexíveis, a macro-separação de fases originada pela incompatibilidade química entre os diferentes tipos de blocos é frustrada pela conectividade do polímero. Isto resulta na microsegregação de fases, ou formação de microdomínios, característicos de cada um dos blocos e dispostos de maneira auto-organizada. Os polímeros líquido-cristalinos de cadeia lateral (PLCCL) são copolímeros graftizados ou enxertados1, que caracterizam-se por possuir uma cadeia flexível contendo moléculas rígidas (mesógenos) liigadas à mesma em intervalos regulares, através de unidades metilénicas denominadas espaçadores. O acoplamento entre os mesógenos (moléculas rígidas responsâveis pela formação de fases líquido-cristalinas) e a cadeia principal nestes polímeros, origina-se de uma competição entre o ordenamento dos mesógenos dos grupos laterais e a entropia conformacional da cadeia principal. Neste trabalho propomos um modelo microscópico para PLCCL, que leva em conta a competição entre as interações isotrópicas de volume excluído e as interações anisotrópicas de Maier-Saupe. Os blocos flexíveis do PLCCL são tratados como cadeias Gaussianas, enquanto os mesógenos são tratados como bastões rígidos. Usando um desenvolvimento em séries de potências dos parâmetros de ordem, conhecido como aproximação Random Phase Approximation (RPA) calculamos o funcional de energia livre para os PLCCL em função de dois parâmetros de ordem, um relacionado às flutuações de densidade e outro relacionado às flutuações de orientação. Mostramos que a estabilidade da fase isotrópica, em relação a essas flutuações, depende da razão entre os potenciais das interações Flory-Huggins (isotrópicas) e Maier-Saupe (anisotrópicas). Neste caso, três fases termodinâmicas são evidenciadas. A primeira delas, corresponde a uma fase nemâtica similar à fase nemâtica dos cristais líquidos monoméricos. A segunda é uma fase na qual hâ uma modulação da densidade, mas não há orientação dos mesógenos, ou seja, uma fase paranemática com modulação de densidade. A terceira é uma superposição dos dois tipos anteriores, e portanto, sugere a existência de uma fase esmética. Numa anâlise mais detalhada da transição nemática-esmética, estudamos a instabilidade da fase nemática em relação à formação de fases esmética A e C. Essas análises foram efetuadas variando-se os parâmetros de geométricos do PLCCL, tais como grau de polimerização, tamanho dos mesógenos, tamanho do espaçador e espaçamento entre os grupos laterais. Os resultados obtidos com este modelo apresentam uma concordância qualitativa com as observações experimentais relatadas na literatura. 1 A palavra "graftizado" é uma tradução da palavra inglesa "grafted", aceita pelo Comitê Brasileiro para Assuntos de Química junto à IUPAC, vide referências [1,2] / Abstract: Polymeric liquid crystals are materials that combine properties of both polymers and liquid crystals. These polymers can be thought as block copolymers made of ftexible and rigid molecular blocks. As in flexible block copolymers, the macrophase separation originated from the repulsion between different blocks is frustrated by the connectivity constraint imposed by the architecture of the polymer. This frustration results in the formation of alternated microdomains, rich in the fiexible or rigid component (microphase separation). In Side-Chain Liquid-Crystalline Polymers (SCLCP) the mesogenic units are periodically attached to a ftexible polymer (backbone) through a polymeric chain called spacer. Because of the coupling effect of the spacer, there is a competition between the ordering of the mesogens in the side groups and the conformational entropy of the backbone. In this work we propose a microscopíc model for SCLCP that takes into account the competition between the isotropic excluded volume interactions and the anisotropic Maier-Saupe interactions. The flexible blocks are treated as ideal Gaussian chains while the mesogens are considered as rigid mesogenic rods. Using an series expansion on the arder parameters, known as Random Phase Approximation (RPA), we calculate the free energy functional for the SCLCP as a function of two order parameters, one related to density ftuctuations and another related to orientational fluctuations. We show that the stability of the isotropic pha..,e against these fluctuations depends on the relative strength between the Flory-Huggins and the Maier-Saupe interactions. Three different thermodynamic phases are found within this model. The first one is a nematic phase similar to the nematic phase of low molar mass liquid crystals. The second one is a phase with modulated density without mesogen orientation, being this a paranematic phase. The third phase is characterized by both density modulation and orientational order, suggesting the formation of a smectic phase. In a more detailed analysis of the nematic-smectic transition, we studied the stability of the nematic phase against the formation of smectic A and smectic C phases. This analysis was performed for different values of the geometrical parameters of the molecule, such as degree of polymerization, length of the spacer, length of the meso.gen and spacing between side groups. The results obtained are in qualitative agreement with experimental data found in literature / Doutorado / Física da Matéria Condensada / Doutor em Ciências

Thermal and morphological studies of the segmented multiblock copolyesters containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol and dimethyl-1,4-cyclohexane dicarboxylate were carried out using differential scanning calorimetry, small angle X-ray scattering, wide angle X-ray diffraction and dynamic mechanical analysis. Molecular origins of the thermal transitions appearing in copolyesters were assigned by the copolyester analysis at different temperatures. The hard segments in copolyesters underwent short-range and long-range ordering (crystallization) during cooling or annealing above glass transition temperature, as concluded from thermal and wide angle X-ray diffraction analysis. Annealing process affected the ordering in hard segments and annealing temperatures of 160 °C and above led to increased microphase mixing. The small angle X-ray scattering studies confirmed the microphase separated morphology of copolyesters and supported the argument of increased microphase mixing in copolyesters annealed at higher temperatures. The amount of sulfonate containing co-monomer and its presence in either hard or soft microphase affected the morphology of the copolyesters. Introduction of the sulfonate groups led to increased microphase mixing in copolyesters as well as destruction of long-range order in the hard segments. / Master of Science

The foundational studies of this dissertation concern the characterization of segmented polyurethanes and polyureas synthesized without the use of chain extenders'molecules that are typically used to promote a microphase separated morphology that gives these materials their useful characteristics. Polyurethanes in which a single asymmetric diisocyanate comprising the whole of the hard segment were found to display poor microphase separation. Conversely, polyurethanes in which a single symmetric diisocyanate composed the hard segment were found to display good microphase separation. The more efficient packing of the symmetric hard segments also led to an increase in hard segment connectivity and hence higher values of storage moduli in these systems. When hydroxyl-terminated diisocyanates were replaced with amine-terminated diisocyanates, polyureas were formed. Here too, diisocyanate symmetry was found to play a key role with symmetric diisocyanates leading to better microphase separation. In addition, the polyurea materials displayed broader service temperature windows than their polyurethane counterparts as the relatively stronger bidentate hydrogen bonding replaced monodentate hydrogen bonding in these materials. A thread-like, microphase separated morphology was visually confirmed using atomic force microscopy. Other techniques such as ambient temperature tensile testing, and wide and small angle x-ray scattering were employed to confirm the presence of the microphase separated structure. The investigation into the effects of diisocyanate chemistry and its symmetry was broadened to incorporate non-chain extended polyurethane materials with different soft segment molecular weights, as well as polyurethanes that did contain chain extenders. Once again the effect of using symmetric versus asymmetric diisocyanates was evident in the structure–property behavior of these systems, with symmetric diisocyanates forming materials that displayed better microphase separation and more connectivity of their hard domains. Lastly, in a departure from the segmented copolymer area, a study was conducted into the influence of casting variables on the solid-state structure of synthetic polypeptide films based on glutamate chemistry. The effect of solvent evaporation was determined to play a key role in the morphology of these polypeptide films. Measured small angle light scattering patterns were compared to computer calculated patterns to reveal information about the structure, shape, and length scale of the polypeptide structure. / Ph. D.

Bio-inspired monomers functionalized with nucleobase or ionic group allowed synthesis of supramolecular polymers using free radical polymerization and controlled radical polymerization techniques. Comprehensive investigations for the structure-property-morphology relationships of these supramolecular polymers elucidated the effect of noncovalent interactions on polymer physical properties and self-assembly behaviors. Reverse addition-fragmentation chain transfer (RAFT) polymerization afforded acrylic ABC and ABA triblock copolymers with nucleobase-functionalized external blocks and a low-Tg central block. The hard-soft-hard triblock polymer architecture drove microphase-separation into a physically crosslinked hard phase in a low Tg matrix. Hydrogen bonding in the hard phase enhanced the mechanical strength and maintained processability of microphase-separated copolymers for thermoplastics and elastomers. A thermodynamically favored one-to-one stoichiometry of adenine and thymine yielded the optimal thermomechanical performance. Intermolecular hydrogen bonding of two thymine units and one adenine unit allowed the formation of base triplets and directed self-assembly of ABC triblock copolymers into remarkably well-defined lamellae with long-range ordering. Acetyl protected cytosine and guanine-containing random copolymers exhibited tunable cohesive strength and peel strength as pressure sensitive adhesives. Post-functionalization converted unprotected cytosine pendent groups in acrylic random copolymers to ureido-cytosine units that formed quadruple self-hydrogen bonding. Ureido-cytosine containing random copolymers self-assembled into nano-fibrillar hard domains in a soft acrylic matrix, and exhibited enhanced cohesive strength, wide service temperature window, and low moisture uptake as soft adhesives. A library of styrenic DABCO salt-containing monomers allowed the synthesis of random ionomers with two quaternized nitrogen cations on each ionic pendant group. Thermomechanical, morphological, and rheological analyses revealed that doubly-charged DABCO salts formed stronger ionic association and promoted more well-defined microphase-separation compared to singly-charged analogs with the same charge density. Bulkier counterions led to enhanced thermal stability, increased phase-mixing, and reduced water uptake for DABCO salt-containing copolymers, while alkyl substituent lengths only significantly affected water uptake of DABCO salt-containing copolymers. Step growth polymerization of plant oil-based AB monomer and diamines enabled the synthesis of unprecedented isocyanate-free poly(amide hydroxyurethane)s, the first examples of film-forming, linear isocyanate-free polyurethanes with mechanical integrity and processability. Successful electrospinning of segmented PAHUs afforded randomly orientated, semicrystalline fibers that formed stretchable, free-standing fiber mats with superior cell adhesion and biocompatibility. / Ph. D.

abstract: Polyurea is a highly versatile material used in coatings and armor systems to protect against extreme conditions such as ballistic impact, cavitation erosion, and blast loading. However, the relationships between microstructurally-dependent deformation mechanisms and the mechanical properties of polyurea are not yet fully understood, especially under extreme conditions. In this work, multi-scale coarse-grained models are developed to probe molecular dynamics across the wide range of time and length scales that these fundamental deformation mechanisms operate. In the first of these models, a high-resolution coarse-grained model of polyurea is developed, where similar to united-atom models, hydrogen atoms are modeled implicitly. This model was trained using a modified iterative Boltzmann inversion method that dramatically reduces the number of iterations required. Coarse-grained simulations using this model demonstrate that multiblock systems evolve to form a more interconnected hard phase, compared to the more interrupted hard phase composed of distinct ribbon-shaped domains found in diblock systems. Next, a reactive coarse-grained model is developed to simulate the influence of the difference in time scales for step-growth polymerization and phase segregation in polyurea. Analysis of the simulated cured polyurea systems reveals that more rapid reaction rates produce a smaller diameter ligaments in the gyroidal hard phase as well as increased covalent bonding connecting the hard domain ligaments as evidenced by a larger fraction of bridging segments and larger mean radius of gyration of the copolymer chains. The effect that these processing-induced structural variations have on the mechanical properties of the polymer was tested by simulating uniaxial compression, which revealed that the higher degree of hard domain connectivity leads to a 20% increase in the flow stress. A hierarchical multiresolution framework is proposed to fully link coarse-grained molecular simulations across a broader range of time scales, in which a family of coarse-grained models are developed. The models are connected using an incremental reverse–mapping scheme allowing for long time scale dynamics simulated at a highly coarsened resolution to be passed all the way to an atomistic representation. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2020

Les polyuréthanes segmentés thermoplastiques (TPUs) sont des matériaux élastomères thermoplastiques qui couvrent une large gamme d’applications. Ces matériaux possèdent intrinsèquement une aptitude à la nano-structuration car ils présentent dans leur structure macromoléculaire une alternance de segments rigides et de segments souples thermodynamiquement immiscibles en dessous d’une certaine température (température de micro-mélange). Ainsi, en refroidissant à partir de l’état fondu, une micro-séparation de phase, dont la cinétique dépend de la température, se produit. De plus, l’application d’une déformation avant cette structuration modifie sa cinétique. Ainsi, en vue d’appréhender l’effet de la mise en oeuvre sur certaines propriétés de ces matériaux, il s’avère intéressant d’étudier l’influence de l’histoire thermomécanique sur la structuration. Cette étude repose sur l’observation du comportement de cristallisation et/ou de séparation de phase de cinq polyuréthanes commerciaux de nature chimique différente, en fonction de différentes conditions thermiques et mécaniques appliquées en milieu modèle ou en conditions de mise en oeuvre réelles. Les techniques utilisées sont principalement rhéologiques, rhéo-optiques et par diffusion de rayons X aux petits angles (SAXS). Ces différentes analyses permettent d’affirmer que les contraintes appliquées dans le fondu des matériaux avant leur solidification modifient de façon drastique la cinétique de structuration mais aussi leur morphologie résultante. En effet, une orientation particulière des entités structurées au sein des matériaux peut être engendrée par des contraintes appliquées en fonction de leur intensité. Cette morphologie résultante particulière joue également un rôle sur les propriétés mécaniques finales des matériaux. / Thermoplastic segmented polyurethanes are an important class of thermoplastic elastomers which cover a wide range of applications. These materials are multi-block copolymers composed of alternating “hard” and “soft” segments which are respectively below and above their glass transition temperature under ambient conditions. TPUs exhibit a twophase microstructure which arises from the thermodynamic incompatibility between the hard and soft segments. This microphase separation is often combined with the crystallization of either or both segments. The mechanical properties of these polymers will depend upon the overall multiblock length and the hard block sequence length and how they affect the material morphology. Our goal is to understand how the polyurethane final properties can be affected by the processing stresses (extrusion, injection…). In this scope, experiments were performed using a rheometer or an optical microscope coupled with a shearing hot stage. A preshear controlled treatment was applied and its effect on the material structuration was followed. These characterizations highlighted the enhancement of phase separation kinetics by the shear. For instance, for presheared samples, phase separation and/or crystallization of the hard segments occur ten times faster than for non-sheared ones. Moreover, SAXS experiments carried out on samples structured from several conditions illustrated perpendicular arrangements of crystalline domains perpendicularly to the flow direction. Finally, this particular morphology induced by shear modifies the materials final mechanical properties

Segmented copolymers are a commercially important class of materials that are utilized in a wide variety of applications. In these systems a relatively large number of variables such as backbone chemistry, segment molecular weight, and the overall molecular weight of the copolymer can be independently controlled to engineer materials with targeted properties. Such versatility also means that a large number of variables can influence the morphology and therefore, properties and performance of segmented copolymers. In this dissertation, the influence of selected variables on the solid state structure-property behavior of segmented poly(ether-block-amide), polyurethane, polyurethaneurea, and polyurea copolymers is explored. The specific variables which have been utilized singly or in conjunction with others are hard segment crystallizability, crystallization conditions, hard segment content, soft segment type and molecular weight, nature of hydrogen bonding, extent of inter-segmental hydrogen bonding, segment symmetry, and chain architecture. In poly(ether-block-amide)s, it was found that the morphology of both the crystalline and the amorphous phase depend upon the polyamide content of the sample and, as expected, the crystallization conditions. A comparison of polydimethylsiloxane based segmented polyurethanes with their polyurea counterparts demonstrated that for a constant hard segment content the soft segment molecular weight particularly governs the extent of microphase separation in these materials. The nature of hydrogen bonding, monodentate or bidentate, also strongly influences their mechanical response. Remarkably, the polyurea sample with a polydimethylsiloxane molecular weight of 7000 g/mol and a hard segment content of 25 wt % exhibited a remarkable service temperature window (for rubber-like behavior) of ca. 230°C (from -55°C to 175°C) whereas it was ca. 200°C wide (from -55°C to 145°C) for the equivalent polyurethane sample. The extremely high chemical incompatibility between the polydimethylsiloxane of sufficiently high molecular weight and urethane or urea segment is expected to generate a relatively sharp interface between the soft matrix and the dispersed hard domains. Therefore, a polyether co-soft segment was incorporated in a controlled manner along the chain backbone, which resulted in inter-segmental hydrogen bonding between the ether and the urea segments. The consequent segmental mixing gave rise to a gradient interphase, which led to a significant improvement in the tensile strength, and elongation at break in selected polydimethylsiloxane segmented polyurea copolymers. The importance of the hydrogen bonding network in model polyurethaneurea copolymers was also explored by utilizing LiCl as molecular probe. It has been demonstrated that hydrogen bonding plays an important role, over and above microphase separation, in promoting the long-range connectivity of the hard segments and the percolation of the hard phase through the soft matrix. The incorporation of hard segment branching in these polyurethaneurea also reduced the ability of the hard segments to pack effectively and establish long-range connectivity. The disruption of the percolated hard phase resulted in a systematic softening of the copolymers. The role of chain architecture in governing the structure/property/processing of segmented was also investigated by comparing highly branched segmented polyurethaneureas with their linear analogs. These copolymers were based on poly(propylene oxide) or poly(tetramethylene oxide) as the soft segments The highly branched copolymers utilized in this dissertation were able to develop a microphase morphology similar to their linear analogs. Particularly noteworthy, and surprising, was the observation of weak second order interference shoulder in the respective small angle X-ray scattering profiles of the highly branched samples based on poly(propylene oxide) of MW 8200 and 12200, indicating the presence of at least some level of long-range order of the hard domains in these samples. Tapping-mode atomic force microscopy phase images of these two samples clearly confirmed the small angle X-ray scattering results. In addition to the strain induced crystallization of the poly(tetramethylene oxide) MW 2000 g/mol based linear polyurethaneureas, the highly branched analog of this sample also exhibited similar behavior at ambient temperature and uniaxial deformation of ca. 400 % strain. Wide angle X-ray scattering confirmed the above observation. The reduced ability of the branched polymers to entangle resulted in slightly poorer mechanical properties, such as tensile strength, elongation at break, and stress relaxation as compared to their linear analogs. However, primarily due to their reduced entanglement density, the branched polyurethaneureas had significantly lower ambient temperature solution viscosity as compared to their linear polyurethaneurea analogs. Therefore, these highly branched polyurethaneureas can be more easily processed than the latter materials. Finally, it was demonstrated that non-chain extended segmented polyurethane and polyurea copolymers in which the hard segment is based on only a single diisocyanate molecule may well exhibit properties, such as the breadth of the service window, the average plateau modulus, stiffness, tensile strength, and elongation at break that are similar to chain extended segmented copolymers that possess distinctly higher hard segment content. A careful control of the hard segment symmetry and the nature of the hydrogen bonding is necessary to achieve such improved performance in the non-chain extended systems. Therefore, the results of this study provide new direction for the production of thermoplastic segmented copolymers with useful structural properties. / Ph. D.

<p>Soft matter systems exhibiting spatially modulated patterns on a mesoscale are characterized by many long-lived metastable phases for which relaxation to equilibrium is difficult and a satisfactory thermodynamic description is missing. Current dynamical theories suffer as well, because they mostly rely on an understanding of the underlying equilibrium behavior. This thesis relates the study of two canonical examples of modulated systems: microphase and cluster crystal formers. Microphases are the counterpart to gas-liquid phase separation in systems with competing short-range attractive and long-range repulsive interactions. Periodic lamellae, cylinders, clusters, etc., are thus observed in a wide variety of physical and chemical systems, such as multiblock copolymers, oil-water surfactant mixtures, charged colloidal suspensions, and magnetic materials. Cluster crystals in which each lattice site is occupied by multiple particles are formed in systems with steep soft-core repulsive interactions. Dendrimers have been proposed as a potential experimental realization. In order to access and understand the equilibrium properties of modulated systems, we here develop novel Monte Carlo simulation methods. A thermodynamic integration scheme allows us to calculate the free energy of specific modulated phases, while a [N]pT ensemble simulation approach, in which both particle number and lattice spacing fluctuate, allows us to explore their phase space more efficiently. With these two methods, we solve the equilibrium phase behavior of five schematic modulated-phase-forming spin and particle models, including the axial next-nearest-neighbor Ising (ANNNI) model, the Ising-Coulomb (IC) model, the square-well linear (SWL) model, the generalized exponential model of index 4 (GEM-4) and the penetrable sphere model (PSM). Interesting new physics ensues. In the ANNNI layered regime, simple phases are not found to play a particularly significant role in the devil's flowers and interfacial roughening plays at most a small role. With the help of generalized order parameters, the paramagnetic-modulated critical transition of the ANNNI model is also studied. We confirm the XY universality of the paramagnetic-modulated transition and its isotropic nature. With our development of novel free energy minimization schemes, the determination of a first phase diagram of a particle-based microphase former SWL is possible. We identify the low temperature GEM-4 phase diagram to be hybrid between the Gaussian core model (GCM) and the PSM. The system additionally exhibits S-shaped doubly reentrant phase sequences as well as critical isostructural transitions between face-centered cubic (FCC) cluster solids of different integer occupancy. The fluid-solid coexistence in the PSM phase diagram presents a crossover behavior around T~0.1, below which the system approaches the hard sphere limit. Studying this regime allows us to correct and reconcile prior DFT and cell theory work around this transition.</p> / Dissertation

The phase behavior of chiral block copolymers (BCPs*), namely, BCPs with at least one of the constituent block is formed by chiral monomers, is studied both experimentally and theoretically. Specifically, the formation of a unique morphology with helical sense, the H* phase, where the chiral block forms nanohelices hexagonally embedded in the matrix of achiral block, is investigated. Such unique morphology was first observed in the cast film of polystyrene-b-poly(L-lactide) (PS-b-PLLA) from a neutral solvent dichloromethane at room temperature with all the nanohelices being left-handed, which would switch to right-handed if the PLLA block changes to PDLA. Further studies revealed that such morphology only forms when the chiral PLLA block possesses certain volume fraction (from 0.32 to 0.36), and the molecular weight exceeds certain critical value (around 20,000 to 25,000 g/mol). Achiral phases such as lamellae, gyroid, cylinder, and sphere will form if the above criteria are not satisfied. Even though the unique H* phase has been extensively studied and utilized for many applications, many fundamental and important questions remain unanswered for such BCP* system. Specifically, how does the molecular level chirality transfer from the several-angstrom scale of the lactide monomer to the tens-of-nanometer size scale of the H* domain morphology? Why is the chirality transfer not automatic for this BCP* system? Is H* phase a thermodynamic stable or metastable phase? Are there other novel phases other than the H* phase that could form within the BCP* system? We aimed at providing answers to the abovementioned questions regarding the formation of chiral H* phase, which is no longer limited to the PS-b-PLLA/PDLA system. We divided our studies into both experimental and theoretical parts. In the experiments, we studied the effect of solvent casting conditions, including solvent removal rate and polymer-solvent interactions, on the formation of the H* phase in PS-b-PLLA/PDLA BCPs*. In addition, we monitored the morphological evolution during solvent casting using time-resolved x-ray scattering technique. We found that good solubility towards both PS and PLLA/PDLA blocks are required for the formation of the H* phase, and microphase separation has to happen prior to crystallization of chiral block. Most importantly, we found that crystalline ordering is not necessary for the H* phase formation. This result led us to propose melt-state twisted molecular packing as the underlying driving force for such helical phase to form, and began our work on the theory for BCPs*. First we built the theoretical tool by incorporating the orientational segmental interactions into the self-consistent field theory (SCFT) for BCPs. As a demonstration, we constructed the phase diagrams for one-dimensional (1D) and two-dimensional (2D) phases, for achiral BCPs with different orientational stiffness. We found that orientational stiffness could serve as another parameter to introduce asymmetry into BCP systems, in addition to conformational and architectural asymmetry. This model was further applied to study the phase behavior of BCPs*, and two phase diagrams were constructed. Another chiral phase, wavy lamellae (L* phase), was observed for BCPs*. The H* phase was found to be a thermodynamic stable phase, as long as the segregation strength ����and chiral strength ��! exceed certain critical values. Energetically favorable cholesteric texture was observed for the chiral segment packing inside the H* phase, which is believed to drive such unusual morphology to form. A simple geometrical argument based on bending of cylindrical microdomain and twisted packing of the bended microdomain can be given to explain the nonlinear chiral sensitivity of BCP* morphology, which further explains the non-automatic feature of chirality transfer in such system.

No description available.