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Kinetically sluggish growth of poly(e-caprolactone) at high Tc = 50 °C leads to a peculiar banding morphology, where thick-stacked lamellae self-assemble into camellia-petal-like bands with their outer rims divided into a ca. 10 lobs of round-shaped petals. The sluggish growth at Tc = 50 °C thick films is inductive and the thickened lamellae self-assemble into aggregates of peculiar and novel camellia-petal-shaped ring bands. Using novel morphology analyses via 3D-dissection approaches, the lamellae underneath the ridge bands are shown to be all perpendicular to the substrate plane, i.e. normally-oriented with respect to the substrate surface; whereas, the interior lamellae underneath the valley band are all flat-on and horizontal to the substrate plane. Stereo-depiction clearly demonstrates that the interior lamellae are periodically grating architectures with a fixed crossbar pitch of 20–30 μm of the interior lamellar assembly, matching with the optical inter-ring spacing of optical bands. The mechanisms of growth and assembly are probed in detail.

Lamellar assembly in unusual sector-face PLLA spherulites from crystallization of poly(l-lactic acid) (PLLA) diluted with amorphous poly(methyl methacrylate) (PMMA). The growth and morphology of the crystalline structures is studied using polarized optical microscopy (POM), atomic-force and scanning electron microscopies (AFM, SEM). Crystals are also analyzed using differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). The two alternate sectored faces differ dramatically in their optical birefringence and top-surface and interior lamellar assembly. By originating from the nucleus center, an explosive fan-like sector of high-birefringence lamellae is packed by fractal growth from an initial single stalk into hundreds of branches upon reaching the periphery, with the number of stalks increasing roughly by the Fibonacci sequence along the radial distance. The exploded pattern resembles a cross-hatch grating structure, and displays a cauliflower-like fractal-branching of optical birefringence blue/orange stripes. This finding suggests that growth with periodic branching is one of the main mechanisms to fill the ever-expanding space in the spherulitic 3D aggregates.

Extensive microscopic and thermal analyses and X-ray diffraction characterizations are conducted to investigate an unusual morphology and its evolution in extreme nonequimolar mixtures of poly(L-la...

Small-molecule phthalic acid (PA), confined in micrometer thin films, was crystallized in the presence of strongly interacting tannic acid (TA) to investigate crystal assembly and correlation between banded patterns and branching structures. Several compositions of the mixture of ethanol/water solutions and evaporation temperatures were also manipulated to investigate the kinetic effects on the morphology of PA crystals. With increasing evaporation rate, the morphology of PA crystals systematically changes from circular-banded spherulites to highly ordered grating-banded patterns. A unique periodic fractal-branch pattern with contrasted birefringent bands exists at intermediate evaporation rate, and this unique grating architecture has never been found in other banded crystals. Crystal assembly of these three periodic morphologies was analyzed by utilizing atomic-force microscopy (AFM) and scanning electron microscopy (SEM) to reveal the mechanisms of formation of hierarchical structures of PA. The detailed growth mechanisms of the novel fractal-branching assembly into circular- or grating-banded patterns are analyzed in this work.

Poly(butylene adipate) (PBA) self-aggregation into unique periodicity correlating to its interfacial photonic properties is probed in detail. Investigations on the unique periodic morphology and top-surface and interior architectures in specifically crystallized PBA are focused on its novel photonic patterns with periodic gratings. Detailed analysis of the interior lamellae from ringless to periodically ordered aggregates (crystallized at 33-35 °C vs. Tc = 30 °C) serves as ideal comparisons. Each interior arc-shape shell is composed of tangential and radial lamellae mutually intersecting at 90o angle. The interior layer thickness in SEM-revealed arc-shape shish-kebab shell is exactly equal to the optical inter-band spacing (≈6 µm). A 3D assembly mechanism of periodically banded PBA crystals is proposed, where the orderly arrays on top surfaces as well as the interior microstructures of strut-rib alternate-layered assembly resemble nature's photonic crystals and collectively account for the interfacial photonic properties in the ring-banded PBA crystal that is novel and has potential applications in future.

Dendritic spherulites are one type of diversified ways of crystal aggregations into micrometer-size consortia by kinetics-driven assembly from nanometer-size crystal plates (i.e., lamellae or single crystals). Crystallized polymers can exist in states of different degrees of order, which lead to the resulting assembled morphologies are of non-equilibrium supramolecular hierarchical patterns of crystal structures. Diffusion-controlled growth patterns emerge, which change the details of dendritic morphology depending on Tc (degree of super-cooling), polymer-diluent interactions, confinement. Investigation to the diversified patterns of lamellar assembly into polymer dendritic spherulites has come to several key conclusions. This article reviews and summarizes the top-surface-relief morphology and interior dissections of polymer dendritic spherulites, where the dendrites may be composed of ringed stripes or fibrous cilia crystals. The results yield interesting consistency for constructing workable mechanisms to account for each type of morphologies with respect to their molecular weights and crystallization kinetics conditions (i.e., Tc, space confinements, film thickness, blend interaction, as well as blend composition).

Towards the development of high-performance green composites, the surface functionalized cellulose nanocrystals (CNC) have been widely used as reinforcement along with biopolymer. In our previous work, it has been demonstrated that CNC grafted with PDLA (CNC-g-PDLA) could improve the crystal nucleation density and heat distraction ability of PLLA matrix via the PLLA/PDLA stereocomplex interaction. Herein, to understand the role of CNC-g-PDLA on the deformation behavior of PLLA/CNC-g-PDLA nanocomposites, the melt-quenched PLLA/CNC-g-PDLA nanocomposite was uniaxially stretched at 160 °C with various draw ratios. The stretched PLLA/CNC-g-PDLA composites allow us to discriminate the crystal transformation and crystal orientation of three individual components in the composites, that is, (i) PLLA matrix, (ii) PLLA/PDLA stereocomplex existed as interfacial phase, and (iii) CNC reinforcement. The results indicate that PLLA α′ and PLLA/PDLA stereocomplex crystals (βC) appear at the initial stage of drawing process. The disordered α′ transforms to ordered α and β forms gradually with increasing in draw ratio, whereas βC-crystals keep almost unchanged during the whole drawing process. The calculation on orientation function of various crystals suggests that the lamellaes of α form have the largest orientation degree along the stretching axis. Meanwhile,CNC nanoparticles and the βC crystals form the nano-dimensional shish kebab structure during stretching and present relatively low orientation. This study provides the physical insight to guide the preparation of high performance PLLA nanocomposites with hierarchical crystal and orientation structure.

Poly(3-hydroxybutyric acid-co-3-hydroxyl-valeric acid) (PHBV) crystallized in the presence of a polymeric diluent impurity is analyzed at specific crystallization temperatures (Tc) from 60 °C to 80 °C. 3D-dissected interior analysis for ring-banded spherulites evidently reveals that the alternate bands exist in not only top surface but also 3D interiors composted of grating-assembled lamellae. Aggregation of the lamellae, initially from two ends of nucleus sheaf-bundles, packs via crystal-by-crystal mode into either Archimedean single-spirals or Fermat's double-spirals, which constitute the “ridge” bands. Then from the ridge-band lamellae, secondary lamellae then branch out at 60–80° oblique angles, with irregular bending, twisting, or scrolling to accommodate in the confined space, to form the “valley” bands. Each new growth cycle repeats the fractal patterns of previous one. The periodic cycles repeat themselves in a fractal fashion to form a cross-lamellar structure, with “crossbar pitch” equal to its optical band spacing. Periodicity of aggregation in top surface and interior is depicted in detailed 3D assembly, beyond and distinguished from conventional planar analytical approaches, for novel mechanisms.

3D morphology of poly(3-hydroxybutyrate) (PHB), crystallized in the presence of diluents of poly(1,3-trimethylene adipate) and poly(ethylene oxide), is probed using a novel approach coupled with selective etching. For interpreting the mechanisms of crystal periodic aggregation, various microscopic techniques and synchrotron microbeam X-ray analysis are used to observe the top surface in connection with the 3D crystal assemblies. Periodic grating architectures, with the cross-bar pitch exactly matching with the optical band spacing, are proved in banded PHB. The crystals under the ridge branch out to spawn finer crystals orienting/bending horizontally underneath the valley band, repeating till species drainage or impingement. The grating structure in the banded PHB resembles many nature's iridescence crystals and is further proved by photonic reflection results as a critical breakthrough novel finding.

Iridescent films constructed by self-assembly of rod-like cellulose nanocrystals (CNCs) are mechanically brittle and of poor thermal stability. Herein, we demonstrate that the toughness and thermal stability of vacuum filtered CNC iridescent films could be significantly improved by a simple alkali treatment. The results reveal that the NaOH treatment can simultaneously alter the condensed physical structure and surface chemical structure of CNCs in their liquid crystal state while the self-assembled CNC chiral nematic structure still well retained. To be specific, the CNC was transformed from a higher crystallinity of form I to a lower crystallinity of form II, and the sulfate groups of CNCs were erased by alkali treatment, resulting in the remarkable enhancement in mechanical and thermal properties of CNC iridescent films. Of note, the unprecedented improvements in both tensile strength and toughness of CNC iridescent film have been achieved by alkali treatment. A sandwiched model with interdigitated mol...

The dipyridamole is emissive in the solution state; however, the emission is weakened in the solid state due to the aggregation-caused quenching. The aggregation of dipyridamole can be prevented by synthesizing star-shaped poly(l-lactide) (SSPLLA) using dipyridamole core. During crystallization of the polymer, chromophore molecules were expelled out of crystalline lamellae and reside at the interface of crystalline and amorphous phase. The helical chains of poly(l-lactide) (PLLA) can induce the helicity to chromophore moieties during the crystallization of PLLA. The photoluminescence (PL) quantum yield measured for the semicrystalline polymer is 46%. When the polymer is melt-quenched to amorphous, PLLA chains remain in the random conformation, and no induced circular dichroism of dipyridamole was found. In the amorphous polymer, the dipyridamole molecules are scattered and show higher PL quantum yield ∼55%. Transparency of the polymer and the disruption of π-stacking of chromophore resulted in the higher ...

This investigation addresses the evolution of the microscopic and mesoscopic structures distribution, and micro-defects of carbon black (CB) filled natural rubber (NR) under uniaxial tensile condition during the fatigue process. NR was filled with three different grades of CB in order to understand the impact of the structural degree and specific surface areas of CB and fatigue degree on the Payne effect. It was found that the Payne effect was initially suppressed and then enhanced by increasing the degree of fatigue. The decrease of the storage modulus in the low strain area was attributed to the CB network destruction and the breakdown of the matrix cross-linking network in the early fatigue stage. However, by further increasing the degree of fatigue, the spatial rearrangement of CB aggregates with the orientation of molecular chains between adjacent CB aggregates will results in mechanical reinforcement before the appearance of micro-defects. Moreover, it has been demonstrated that the structural degree of CB has a stronger impact on the mesoscopic structures than the specific surface area of CB during the tensile fatigue process.

A completely novel 3D dissection approach is taken to re-investigate high-density polyethylene (HDPE) crystallized into periodic architectures in a wide range of Tc . This work first discovers that ring bands present in HDPE are crystallized in a quite wide Tc range (90-120 °C) all within regime-III growth. With further detailed analyses of the top-surface-relief patterns and 3D architectures of HDPE spherulites, this work has fully clarified the periodic morphology packed with alternate ways of single-crystal aggregates in correlation with the optical banding patterns. The proposed assembly mechanism sheds light that the periodic bands are actually composed of a cross-hatch grating structure in that the alternately perpendicular orientations from the ridge to valley bands being related to the interior radial to tangential lamellae. Such grating architectures in the interiors of HDPE can be viewed as a mimicry resembling shish-kebab lamellae self-aligned by Archimedean spiral-spins from the nucleus center.

This work utilized an in-house synthesized aryl polyester, poly (decamethylene terephthalate) (PDT), to investigate the crystal assembly of unique camellia-flower-like extinction bands periodically assembled in spherulites formed at specific Tc's or driven by other kinetic factors. These extinction PDT bands at high Tc's (110–125 °C) and confined in thin films are packed by parallel flat plates of single-crystal-like dimensions in nanometer to micrometer scales (measuring 4 μm × 4 μm x 20 nm) self-assembled as terrace-like shingles that are bordered with an optically extinct boundary. The valley corresponds to where most amorphous ingredients accumulate and the growth precipitates suddenly from tip of ridge to near the substrate, resulting in an optical extinction border. All ridges (convex bands) are composed of discrete crystal plates aligned as roof-shingle stacks along the circumferential bands, and the crystals do not traverse across the bands. These lamellae on ridge bands are discrete and do not twist at all or rotate 360° angle continuously extending from nucleus to periphery. The circular-extinction bands of PDT of nanometer films (300–400 nm) are composed of parallel lamellae with the terrace alignment pointing along the circumferential direction; the epicycloid-extinction bands of thicker PDT specimens (2000–3000 nm) are assembled with single-crystal plates of lozenge shapes and aligned in growth-preferred directions to form petal-like tips.

Novel approaches and fractal-branching models are proposed to provide an evidence-supported mechanism of hierarchal lamellae assembly with regular periodicity in ring-banded poly(ϵ-caprolactone) (PCL) crystallized in bulk forms from PCL/poly(phenyl methacrylate) mixtures. Crystallized specimens are examined with two different film-thickness levels. For interior analysis, specimens are fractured in delicate ways to study correlations of the architectures on top-surface vs. interior lamellae, and how these crystal species self-assemble to display morphological repetitive fractals with optical-banding periodicity. 3D self-assembly of alternate horizontal and vertical lamellar bundles with fractal-branching leads to varieties of architectures of ring-banded aggregates packed with lamellar branches at periodic intervals.

Two triblock ABA copolymers poly( l -lactide- b -dimethylsiloxane- b - l -lactide) (PLLA- b -PDMS- b -PLLA) and poly( l -lactide- b -ethylene glycol- b - l -lactide) (PLLA- b -PEG- b -PLLA) containing poly( l -lactide) were synthesized by ring opening polymerization of l -lactide using bis(hydroxyalkyl) terminated PDMS and hydroxyl end-capped polyethylene glycol as macroinitiators, respectively. Both the triblock copolymers were melt-quenched to −40 °C to prepare the amorphous samples. The melt morphology of the triblock copolymers was preserved upon cooling the melt to −40 °C. PLLA and PDMS blocks are immiscible in the melt, and the amorphous triblock copolymer shows two distinct glass transition temperatures ( T g ) on heating. On the other hand, PLLA and PEG segments are miscible and the triblock copolymer shows the single T g . Structural evolution of PLLA during heating of the amorphous ABA triblock copolymers has been investigated by measuring the variable temperature small-angle and wide-angle X-ray scattering (SAXS and WAXS) and FTIR spectra. In the case of PLLA- b -PDMS- b -PLLA triblock copolymer (immiscible system), the mesophase of PLLA was found to appear just above the T g of PLLA block (∼45 °C), and on further heating the mesophase changed to the regular α form at around 90 °C. On the other hand, in PLLA- b -PEG- b -PLLA (miscible system), the mesophase of PLLA was found to appear at lower temperature i.e. −20 °C, because of the enhanced molecular mobility of PLLA chains in the presence of PEG. However, irrespective of the mesophase formation temperature, the ordered α form has appeared at around 90 °C. In this way, during heating of the amorphous triblock copolymers, the PLLA block was found to crystallize into the ordered α form always through the mesophase just above the T g of PLLA. These results are helpful in understanding the regularization process of semicrystalline polymers in different environments.

As a popular bioplastic, poly ( l -lactic acid) (PLLA) still faces some drawbacks mainly related to its low crystallization rate and heat distortion resistance. Herein, we demonstrate a facile and promising route to solve these problems by compositing PLLA with poly( d -lactide) grafted cellulose nanocrystal (CNC-g-PDLA) which can be synthesized via ring-opening polymerization of d -lactide on the CNC surface. The grafting density of PDLA on the CNC surface has been quantified by newly developed spectral method using FTIR technique. Moreover, the non-isothermal and isothermal crystallization behavior of PLLA/CNC-PDLA composites has been investigated by DSC, POM and WXRD. Our results show that the addition of small amount of CNC-g-PDLA could enhance the crystallization rate of PLLA significantly due to the heterogeneous nucleation effect of CNC and the presence of stereocomplex crystals. In addition, the specific stereocomplex interaction in the interphase of PLLA matrix and modified CNC particles results in great improvement of both storage modulus and the heat distortion resistance of the PLLA/CNC-g-PDLA nanocomposites. This study provides a way to design advanced PLLA-based nanocomposites with fast matrix crystallization ability and excellent heat distortion resistance.

The chiral liquid crystal self-assembly behavior of cellulose nanocrystals (CNC) opens a fantastic way to design functional nanocomposites with advanced optical properties. Herein, we demonstrate that crack free, large size thermal reduced graphene (TRG)/CNC composite films with highly ordered, layered structures at the submicrometer level can be obtained through a vacuum-assisted self-assembly (VASA) technique. The results show that the addition of a small amount of TRG (≤0.5 wt%) is compatible with the self-assembly of CNC under flow field. Benefiting from the homogeneous dispersion of TRG in the chiral nematic phase of CNC, the resultant TRG/CNC films present uniformly metallic iridescence, which can be reversibly changed by the hydration or dehydration process similar to the water response of beetles Tmesisternus isabellae's elytra. Moreover, the TRG/CNC composite film with only 0.3 wt% TRG loading exhibits high electrical conductivities. This study demonstrates that it is feasible to combine the intriguing self-assembly ability of CNC with the extraordinary optical and electrical properties of graphene for constructing multifunctional biomimetic materials and sensors.

The classical model of continuous helix-twist lamellae versus a novel corrugate-grating assembly in accounting for long-debated issues of periodic optical banding in poly(ethylene adipate) (PEA) polymer spherulites is critically assessed, by comparing and checking against a series of scientific evidence based on experimental data of scanning electron microscopy (SEM), ultrathin microbeam small-angle & wide-angle X-ray scattering (SAXS/WAXD), and optical microscopy. Analyses show that grating-structured model fits perfectly with all results. The novel proposition of grating-structured lamellae with a crossbar pitch fits perfectly with the experimental optical band spacing, and the interior morphology dissection is fully supported by the literature-reported microbeam X-ray data.

It is worthy to understand the reinforcement of nanoparticle in rubber blends in application prospect because of its dispersion and distribution. The dielectric and mechanical methods were used to study the reinforcement impact of the carbon black (CB) in NR/NBR blends, based on the percolation and reinforcement theories. Results indicated that the CB aggregates had dispersed in NBR phase and the reinforcement effect was dependent on both CB concentration and the rubber blend ratio. It has been observed that the CB particles diffused and filling in the NBR reinforcement network at 50:50 ratio of NR/NBR blend, CB particles assembled as supernanosphere at 70:30 ratio and CB particles wrapped/covered supernanosphere at 90:10 ratio. The highest elongation at break was observed in 90:10 ratio of NR/NBR. The new observations are conducive to providing guidelines for producing high mechanical performance and low conductivity percolation threshold elastomers via a maturely industrial method for a wide range of application.

In this study, lactic acid monomer or dimer is grafted onto CNC by a simple esterification reaction. The quantitative solid-state 13C NMR spectrum suggests that more than 87% of all the available OH groups on the surface of CNC are substituted by lactic acid. Such modified CNC (CNC-g-LA) exhibits excellent thermostability and nano-sized dispersion in chloroform. Benefit from this character, fully biobased PLLA/CNC-g-LA nanocomposite could be prepared simply by a solution-casting method. The crystallization behavior of obtained nanocomposites has been systematically investigated by differential scanning calorimetry (DSC). The results show that the crystallization rate of PLLA is distinctly enhanced. Moreover, the mechanical properties of nanocomposites are also improved remarkably by the addition of CNC-g-LA because of its excellent dispersion and compatibility with PLLA matrix. This study provides a green and facile way to modify CNC for fabricating bio-nanocomposites with fast crystallization rate and improved mechanical properties.