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A unique zig-zag banded morphology poly(e-caprolactone) (PCL), crystallized at high Tc = 46-47 °C and confined in thin films (

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.

Crystallized poly(nonamethylene terephthalate) (PNT) displays mirror-image and Fermat's-spiral ring-banded spherulites, respectively. The interior anatomy by SEM and AFM microscopic analyses shows that the lamellar arrangement of grating-board structures inside the 3D bulk banded PNT is correlated to top-surface topography of alternate ridge and valley bands. For the banded spherulites, tangential-oriented lamellae under the ridges and radial-oriented lamellae under the valleys are collectively arranged into mirror-image or spiral symmetry, where the tangential lamellae intersect at 90° angle with the branching radial lamellae. Moreover, the grating-layered structures of the tangential lamellae are viewed as the shish-crystals from which the kebab side-branches grow outwards in the radial direction. 3D models are proposed to illustrate the lamellar assemblies in both types of periodic bands. Morphological evolution and lamellar assembly with dual discontinuity are addressed to further establish 3-D models.

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.

Poly(butylene succinate) (PBSu) and poly(ethylene adipate) (PEA), isomeric to each other, are mixed in a miscible state, and PBSu crystallized at Tc’s where PEA is kept at a molten state. PBSu upon...

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.

A small-molecule compound, phthalic acid (PA), crystallized in the presence of poly(ethylene oxide) (PEO) with various compositions was utilized as a model to investigate the morphology and crystal assembly of periodically ordered structures in banded spherulites. After etching off PEO from crystallized solids, detailed crystal assembly in PA was analyzed by utilizing atomic-force microscopy (AFM) and scanning electron microscopy (SEM) to reveal the mechanisms of the formation of fractal-shaped banded spherulites. A novel banded pattern with fractal-shaped lamellar structures is found when the composition of PEO is at or above 20%, and this pattern significantly differs from the ordinary extinction–bright banded morphology of neat PA. The diluent PEO is regarded as the main factor in transforming the crystalline morphology from a compact banded pattern to a fractal-shaped banded pattern. The banded spherulites are composed of numerous fractal structures periodically branching out. Each fractal unit contains two portions: a main stalk (ridge) whose discrete crystalline aggregates are arranged along the radial direction and a fern-like dendrite (valley) whose crystals are arranged along the tangential direction. In situ monitoring of the growth process of the fractal-shaped banded spherulites proves the fractal-branching growth mechanism for the formation of banded spherulites. The periodically perpendicular intersection of discrete crystals results in the contrasting birefringence bands of banded spherulites. A periodic grating structure with fractal branching leads to such a novel pattern of banded PA spherulites.

Monitoring of nucleus geometry and growth into dual types of periodically ring-banded morphology in poly(nonamethylene terephthalate) (PNT), respectively, Type-1 and Type-2, are done with detailed analyses using polarized-light optical microscopy (POM) in-situ CCD recording, the periodic assembly morphologies are characterized using atomic-force microscopy (AFM) and scanning electron microscopy (SEM). Different annealing treatments (Tmax = 110, 120, 130 °C) are accomplished at a crystallization temperature of 85 °C, effects on the nucleus geometry, number (25–10%) and volume fractions (33–15%) of Type-2 among two types of banded PNT spherulites are expounded. Growth of a specific type of periodically banded PNT spherulite is initiated from either highly elongated sheaf-like or well-rounded nuclei, with the final grown lamellae being self-packed as multi-shell structures. Nucleation geometry and crystallization parameters collectively lead to development of multiple types of banded PNT spherulites of different relative fractions.

Polarized-light optical, atomic-force, electron scanning microscopies and X-ray techniques were applied to reveal and analyze a highly anisotropic crystal aggregation into Janus-face spherulites in poly(butylene succinate) (PBSu) induced by crystallization in presence of molten poly(ethylene oxide) (PEO) at Tc = 70 °C. The dual-face (i.e., Janus-face) PBSu spherulites are distinguished with various fractions of two different lamellar assemblies filling the spherulites’ two portions. The Janus-face PBSu crystals (straight dendritic and circularly ring-banded lamellae) become significant only when the PEO content is kept at 20–30 wt% in the blended PBSu/PEO mixtures at Tc = 70 °C, with no top-cover confinement. That is, existence of Janus-faced spherulite is highly kinetics-selective for favorable nucleation to highly anisotropic growth into co-existence of two faces. Mechanisms of unique nucleation and interior lamellae assembly into the peculiar Janus-face PBSu spherulites are analyzed and discussed.

Physical and chemical degradative effects of etching agents on polymer spherulites have been explored thoroughly to understand the etching mechanism as well as to perceive the polymer crystal structure and assembly. Interior lamellae of an aromatic polyester, poly(trimethylene terephthalate) (PTT), crystallized into a well-defined periodic-birefringent spherulitic structure, are subjected to sequence-assorted etching agents of basic methylamine (MA) vapor, acidic permanganate (KMnO4) reagent, inorganic acids mixture (H2SO4:H3PO4), and organic dichloroacetic acid (DCA). The chemistry involved in reactions between the selected etchants with the polymer spherulites was probed and their synergistic effects on exposing the interior 3D assembly were assessed. The exposed circumferential alignment of rod-like polycrystals interconnected by nanofibrils signifies the hidden interfaces between the lamellae that are assembled in a periodic grating structure to form banded PTT spherulites.

Using poly(3-hydroxybutyrate) (PHB) of two molecular weights and various other polymeric or blend systems, this study has shed a critical clue that cracks are inclined to be guided by interior lamellae via interior inter-lamellae discontinuity and interfaces that exist between the successive ring bands or radial/tangential lamellae. Advanced interior dissection analysis on the aggregated spherulites of several polymers further proves that the cracks occur at the interface between the valley and ridge bands of the ringed spherulites, where interfaces with discontinuous lamellae exist with either impingement or intersection. Propagation of the cracks follows the spiral or circular lamellae assembly into similarly spiral or circular concentric patterns, Such updated views via interior lamellae dissection and analysis on PHB's or other polymers' banded spherulites provide avenues for cracks to develop upon cooling contraction. The mechanism of spiral/circular cracks' formation is well proven in this work, which is related to the inner arrangement/assembly of the periodic spiral lamellae into banded types; by contrast, without such lamellae periodicity, cracks tends to be randomly irregular.

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.

Wide-angle and small-angle X-ray scattering measurements were performed simultaneously using an X-ray beam 1 μm in size to detect the inner structure of a spherulite of poly(ethylene adipate) [PEA, –(O(CH2)2OCO(CH2)4CO–)n–]. The lamellae were found to twist periodically by 180° in the area between the neighboring bright rings observed in the polarized optical microscope image of the spherulite. However, as known from the discontinuity between the repeated lamellar zones discovered by Woo et al. (Macromolecules, 45:1375–1383, 2012), the twisted lamellae must not be assumed to be continuously twisted long plates spreading out over the spherulite. Rather, these lamellae should be considered to have limited areas of ~7 μm in length along the radial direction and with disconnected end zones. The present X-ray scattering data revealed the structural relation between the repeated arrays of the disconnected lamellar blocks and the 180° twisting phenomenon, which occurs only in the finite and disconnected flat-on lamellar zones. Designer supramolecular polymers are a growing field of polymer materials. The designability and flexibility in their structures and functionality have attracted a great deal of attention in polymer science, as well as in supramolecular chemistry. These polymeric structures are formed from one or more molecular components via reversible bonds; therefore, monomeric and polymeric states are in equilibrium on the relevant experimental timescale. The dynamic nature of supramolecular polymers in terms of chain lifetime and conformational flexibility are determined by external conditions. This adaptivity can result in stimuli-responsive structures and properties. This article describes the use of our host–guest structures based on a calix[5]arene, a bisporphyrin, and a self-assembled capsule in the synthesis of supramolecular polymers.

Sophisticated dissection into the interiors of the three different birefringent types of poly(l-lactic acid) (PLLA) spherulites via delicate fracturing across the thickness sections, coupled with proper etching techniques, was adopted to reveal the correlations between the diversified birefringence patterns and interior lamellae assembly. The three types of spherulites are circularly ringed spherulite (type 1), hexagon-shaped axialite (type 2), and circularly core–stripe dendrites (type 3). Such morphological diversification originates from different nuclei geometries. For all three different types (circularly ringed, hexagonal, and core–stripe) of PLLA aggregation into spherulites or dendrites/axialites, the dissected inner lamellar arrangement shares universal commonality of intersecting at a 60° angle in the intersection between different lamellar species, with distinct discontinuity in the grating structures being characteristic of all three types of aggregated PLLA spherulites. This kind of grating a...

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).

Nature tends to assemble hierarchical structures in similar ways to achieve compactness and functions. This work probes the interior lamellae assembly of crystalline spherulites of poly(ethylene adipate) (PEA) with striking birefringence patterns versus some known biological structures for optical color diffraction. Three-dimensional dissecting onto interior lamellar structures of spherulites in poly(ethylene adipate) (PEA) in bulk forms crystallized at 28 ± 3 °C were studied in correlation with thin-film forms. Interior morphology in bulk PEA samples revealed periodic hemisphere or arc-shaped layers resembling corrugate boards with liner-flute medium alteration. Interior spherulites clearly expose that the lamellae within the intralayer are kebabs (plates) in the radial direction while the interlayer region are thin sheaths (fibrils) composed of cilia-like lamellae in the tangential direction. The interior repetitive lamellar assembly of PEA banded spherulites in displaying periodic optical birefringence...

Most classical crystallization analyses on top surfaces of thin films could not adequately reveal the inner assembly of banded spherulites. Interior dissections by fracturing across various spherulite planes should be conducted to justify the inner lamellar assembly underneath the periodic bands. In this study, self-assembly of poly(dodecamethylene terephthalate) (P12T) into banded spherulites has been explored using powerful microscopy approaches. Results interestingly show a hierarchical ordered sequence of tangentially and radially oriented crystals into alternating polycrystalline layers. The layer width of the inner bands exactly matches with the optical inter-ring spacing (ca. 5 μm), proving emphatically that the interior lamellar assembly accurately accounts for the optical patterns of periodic rings.

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.

Surface topology and interior crystals of highly anisotropic Janus-faced spherulites from crystallization of semicrystalline poly(l-lactic acid) (PLLA) with amorphous poly(methyl methacrylate) (PMMA) have been characterized using polarized optical, atomic-force, and scanning electron microscopes. The morphologies in the two faces differ dramatically in optical birefringence, growth rates, as well as crystal dimensions and assembly. Dissection into the interior lamellar arrangement of the optically asymmetric spherulites is conducted via fracturing and selective etching with a proper solvent. Large α′-form platelet lamellae, along the direction of the sheaf-nuclei, grow faster, periodically bend or branch out, appearing as densely fan-like dendritic region(s) with strong birefringence. As opposed to this, the α-form nanosize rod-like lamellae grow more slowly in the perpendicular direction, with each rod slanting at an angle to the substrate, appearing as a bivalve-shaped region of weak birefringence. Both...

Unique interior dissection coupled with selective etching techniques for exposing the interiors of poly(trimethylene terephthalate) (PTT) banded spherulites. Three banded PTT spherulite types are present, originating from different nuclei geometries and corresponding to different assemblies of interior lamellae, but all possess similar multishell spheroid layered structures, each with their layer thickness exactly equal to the optical interband spacing. Interior lamellae are alternatingly intersected with mutually perpendicular orientations and clear discontinuity, which evidently disagrees with the conventional models of continuous helical twisting for banding. Interior 3D lamellae assemblies also have been fittingly correlated with top-surface banding patterns.

Using in-house synthesized poly(dodecamethylene terephthalate) (P12T) as a model, periodic extinction-banded spherulites melt-crystallized at high Tcs (100–115 °C) are expounded in terms of growth mechanism. The extinction-banded spherulites wildly differing from the usual blue/orange double ring-banded spherulites are composed of all flat-on discrete single-crystalline lamellae packed like roof shingles (or fish scales) along the circularly curved bands and the lamellae in the extinction bands are flat with a lozenge shape with no continuous twisting at all. For P12T films of more than 10 µm crystallized at Tc = 105–115 °C, no periodic bands were seen, and all spherulites were ringless, where periodic growth precipitation of crystals to extinction does not occur until impingement. Extinction bands in the P12T spherulites with the inter-ring spacing steadily decrease with decreasing film thickness, because for thinner films (submicrons to 2 µm), draining or depletion of available molten species takes place more frequently, leading to bands of smaller inter-ring spacing. The petal-like extinction bands are discussed and analyzed in detail using 3D AFM imaging. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

Thorough microscopy analyses are done on dissecting 3D interiors of poly(nonamethylene terephthalate) (PNT) banded spherulites. Growth of a specific type (Type-I) of banded spherulites is initiated from highly elongated sheaf-like nuclei, with asymmetrically grown lamellae packed as a multi-shell structure, leading to resemblance of a dual-face spheroid. Top-surface bands are characterized with discrete/unconnected dots of crystals aligned as zig-zag circles, which correspond to interior layered lamellae ends surfacing to top. Thus, the banded spherulites display not only inter-band discontinuity, but also discontinuity among the dotted crystals aligned on the top-surface ridges. 3D analysis exhibits that the banded spherulites possess a Janus-face morphology of compounded shell-and-kink lamellae assembly with dual discontinuities.

Poly(L-lactic acid) (PLLA) interacts with solvents of different interaction strengths and crystallizes, upon solvent evaporation, into spherulites with various birefringence patterns. The top surface-relief morphologies associated with interior lamellae assembly in solvent-evaporated PLLA confined films are probed using atomic force, scanning electron, and polarized-light microscopy techniques. For PLLA crystallized upon solvent evaporation, the type of solvent, solvent evaporation rate and evaporation temperature lead to a wide variety of morphologies with complex optical birefringence patterns. PLLA crystallized by solvent evaporation in open atmosphere with tetrahydrofuran (THF) as the solvent exhibits a one-ring or two-ring birefringence-banded morphology at 26–30 °C, and its lattice belongs to α-crystals without occurrence of complexation with any solvent molecules. When PLLA is cast from solvents other than THF or temperatures outside the range of 26–30 °C, no banded spherulites are formed. The topography of the banded PLLA spherulites demonstrates that the dendritic petal-like lamellae are arranged in multi-layered tree-branch patterns. In addition, inside the spherulites, the lamellae are arranged in a radial direction, and a layered structure is seen from the lateral view.