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The morphology and thermal stability of different sectors in solution- and melt-grown crystals of star-branched polyesters with poly(ε-caprolactone) (PCL) arms, and of a reference linear PCL, have been studied by tapping-mode atomic-force microscopy (AFM). Real-time monitoring of melt-crystallization in thin films of star-branched and linear PCL has been performed using hot-stage AFM. A striated fold surface was observed in both solution- and melt-grown crystals of both star-branched and linear PCL. The presence of striations in the melt-grown crystals proved that this structure was genuine and not due to the collapse of tent-shaped crystals. The crystals of the star-branched polymers had smoother fold surfaces, which can be explained by the presence of dendritic cores close to the fold surfaces. The single crystals of linear PCL grown from solution showed earlier melting in the {100} sectors than in the {110} sectors, whereas no such sectorial dependence of the melting was found in the solution-grown crystals of the star-branched polymers. The proximity of the dendritic cores to the fold surface yields at least one amorphous PCL repeating unit next to the dendritic core and more nonadjacent and less sharp chain folding than in linear PCL single crystals; this evidently erased the difference in thermal stability between the {110} and {100} sectors. Melt-crystallization in thin polymer films at 53-55°C showed 4 times faster crystal growth along b than along a, and more irregular crystals with niches on the lateral faces in star-branched PCL than in linear PCL. Crystal growth rate was strictly constant with time. Multilayer crystals with central screw dislocation (growing with or without reorientation of the b-axis) and twisting were observed in both classes of polymers. [ABSTRACT FROM AUTHOR]

The radiative lifetime of single 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindodicarbocyanine molecules, embedded in a polymer thin film, has been characterized. At room temperature the chemically identical molecules exhibit strong fluctuations in their fluorescence lifetime. The possible conformational origin of these fluctuations has been addressed by semi-empirical quantum-chemical calculations. Specifically, the impact of conformational effects induced by thermal motion on the transition energy and the value of the transition dipole moment has been studied. The results indicate that the strong fluctuations cannot be explained by pure thermally activated conformational changes. Since quenching mechanisms are not responsible for the observed fluctuations, we suggest that molecular segmental dynamics of the surrounding polymer play a key role in determining the lifetime fluctuations. [Copyright &y& Elsevier]

Describes the construction and applications of an inexpensive, small temperature control device based on the Peltier electrocooling effect. Cold-stage; Atomic force microscopy; Polymers; Phase transitions.

Abstract: Ultrafine fibers were spun from polyacrylonitrile (PAN)/N,N-dimethyl formamide (DMF) solution as a precursor of carbon nanofibers using a homemade electrospinning set-up. Fibers with diameter ranging from 200nm to 1200nm were obtained. Morphology of fibers and distribution of fiber diameter were investigated varying concentration and applied voltage by scanning electric microscopy (SEM). Average fiber diameter and distribution were determined from 100 measurements of the random fibers with an image analyzer (SemAfore 5.0, JEOL). A more systematic understanding of process parameters was obtained and a quantitative relationship between electrospinning parameters and average fiber diameter was established by response surface methodology (RSM). It was concluded that concentration of solution played an important role to the diameter of fibers and standard deviation of fiber diameter. Applied voltage had no significant impact on fiber diameter and standard deviation of fiber diameter. [Copyright &y& Elsevier]

The morphology of poly(propylene oxide) (PPO) crystals grown from the melt was investigated. The spherulites of the optically pure S polymers displayed a regular pattern of concentric rings as observed by polarizing optical microscopy, while the stereocopolymer developed irregularly banded, or non-banded spherulites depending on the degree of undercooling. The organization of the lamellar crystals within the spherulites was examined by means of atomic force microscopy (AFM). For all cases, the lamellar structures appeared to adopt an alternating flat or edge-on orientation. Examination of the morphology of single crystals in the melt of the stereocopolymer revealed truncated-lozenge crystals, which were elongated in shape. Results from crystallization kinetics, obtained by in situ AFM observations, showed that the elongated habit is related to differences in the growth rates of the {2 0 0} and {1 1 0} facets. Interestingly, the melt-grown RS-PPO crystals developed a curved asymmetrical three-dimensional shape. Based on these observations it can be proposed that the chiral nature of the chain is transmitted to higher structural levels of ordering in the crystal aggregates. [Copyright &y& Elsevier]

The correlation between impact resistance and crystalline morphology was studied on specimens prepared from three different polypropylene (PP) homo- and copolymers, obtained by injection molding. The crystalline morphology was varied using three different nucleating agents. Linear elastic fracture mechanics was applied for the description of fracture resistance. The results indicate that morphological characteristics strongly influence the mechanical performance of the polymers. According to Young's theory for yielding, the resistance to crack initiation, represented by KIc, correlates with the thickness of the lamellae. This suggests that the onset for yield can be described by a dislocation mechanism. The total energy absorbed during impact, GIc, is a complex function of the morphology with no single identifiable morphological characteristic that dominates its value. The heterogeneous, dispersed morphology of the PP block copolymer initiates an additional energy absorption mode compared to the homo-polymer and the random-copolymer. [ABSTRACT FROM AUTHOR]

The process of melting in poly(ethylene oxide) (PEO) is followed in real-time at elevated temperatures by atomic force microscopy (AFM) using a simple hot stage apparatus. AFM imaging of the morphology above the onset of melting revealed the dynamics of a complex melting process. The observed melting behavior of PEO is associated with the existence of separate dominant and subsidiary morphological entities. The morphological observations revealed that the melting process is not explained by a mechanism of crystal reorganization (melting–recrystallization–remelting or crystal thickening. The kinetic data shows that the crystal dimensions decrease proportional to time indicating a nucleation controlled melting process. The crystals melt instantaneously on heating and reveal a spread in the rates of melting of the radial {120} faces. This variation in rate of retrogression of the crystals is assumed to be related to a lamellar thickness distribution of the melt grown crystals. [Copyright &y& Elsevier]

We report on the crystallization of poly(lactic acid) (PLA) films in the presence of a sorbitol-based nucleating agent; 1,2,3-tridesoxy-4,6:5,7-bis-O-[(4-propylphenyl) methylene]-nonitol (TBPMN). Dispersion of the nucleating agent was performed by solution-mixing and melt-blending. Crystallization behavior was studied by differential scanning calorimetry (DSC). The structure and morphology were characterized by wide-angle X-ray scattering (WAXS), optical imaging, and atomic force microscopy (AFM). A significant impact of the nucleating agent was observed at or above a threshold concentration of 2 wt%, which was assigned to the solubility limit of TBPMN. The degree of crystallinity reached up to 39.6 % with 2 wt% TBPMN. An influence of the dispersion method was observed on the peak temperature of crystallization (T cp). While T cp decreased slightly for solution-mixed films, a sigmoidal trend was noted for melt-blended samples. Under isothermal conditions at 100 °C, the crystallization half-time was lowered from 6.5 min to 1.0 min. Avrami analysis pointed to the formation of 2-dimensional or 3-dimensional crystalline domains; WAXS data revealed α- and α' -crystals, depending on the dispersing method. AFM imaging showed a nanosized fibrillar network of the nucleator within the PLA matrix, demonstrating that TBPMN acted as a soluble self-assembly nucleator. • The crystallization of polylactic acid films in the presence of a sorbitol-based nucleating agent is reported. • Dispersion of the nucleating agent was performed by solution-mixing and melt-blending. • Under isothermal conditions at 100 °C, the crystallization half-time was lowered from 6.5 min to 1.0 min. • AFM imaging showed a nanosized fibrillar network of the nucleator within the PLA matrix. • TBPMN (the sorbitol-based nucleator) acted as a soluble self-assembly nucleator. [ABSTRACT FROM AUTHOR]

Abstract: The lateral habit, unit cell structure and melting behaviour of single crystals of poly(ε-caprolactone) (PCL) prepared by the rapid expansion of a supercritical solution technique was studied by AFM at ambient and higher temperatures and by grazing-incident X-ray scattering using a synchrotron source. After dissolving PCL in a solution of supercritical CO2 and 0.1 vol.% chloroform, an extremely fast phase transfer from a supercritical to a gas-like state occurred during expansion into atmospheric conditions, leading to a temporary temperature drop to below −50 °C at the silica surface where the crystals were deposited. Single crystals of a hitherto unreported rectangular lateral habit were observed. Six-sided crystals were also observed, but they were fewer than the rectangular crystals and in addition the angles between the lateral faces were different from the theoretical angles between adjacent {110} faces and {110} and {100} faces. X-ray scattering indicated a polymorphic structure also including the orthorhombic (110) and (200) diffraction peaks. Distinct low angle peaks essentially along the c-axis indicated a stacking on a very fine scale (3.7–4.7 nm) within the crystals. The equatorial diffraction peaks indicated a less dense packing of the PCL stems. Rectangular single crystals with a height according to AFM of 11–27 nm melted between 40 and 45 °C, which is lower than the melting points (55 °C) recorded for the distorted six-sided crystals. The unusual conditions for crystallisation used gave the polymer molecules a severe limitation to rearrange from the initial random coil state. The facetted crystals consisted of a stack of 4 nm thick blocks; these blocks most probably constituted a regular variation in molecular packing, i.e. molecular order. The pronounced changes in the angles between adjacent faces from those observed in mature PCL crystals and the wide-angle X-ray scattering data indicated the presence of conformational disorder in the crystals. [Copyright &y& Elsevier]

Abstract: A comparative study of the structure and morphology of nylon-12 and 10-polyurethane (10-PUR) lamellar crystals, was carried out. Lamellar crystals were obtained by isothermal crystallization from diluted solution. Electron diffraction of lamellae combined with WAXS data recorded from crystal sediments indicated that nylon-12 crystallized in either α-form or γ-form according to the solvent chosen for crystallization. The α-form was the crystal modification predominant in doubly oriented films of nylon-12 prepared by epitaxial crystallization. On the contrary, 10-PUR invariably crystallized in α-form regardless crystallization conditions. The α-form of nylon-12 and 10-PUR shared the same crystal structure with hydrogen-bonded sheets made of antiparallel chains and stacked with progressive shifting along both b and c directions. Lamellar crystals of nylon-12 in γ-form and 10-PUR in α-form displayed similar morphological features but only the former appeared to be sensitive to temperature. Upon heating the nylon-12 crystals near to melting, the real-time WAXS analysis evidenced the occurrence of a partial γ-to-α crystal transition, and in situ AFM observations revealed the appearing of more or less regular ridges on the crystal surface. None of these changes were observed in 10-PUR crystals when subjected to similar treatment. [Copyright &y& Elsevier]

Abstract: The knowledge on linear aliphatic polyurethanes n-PUR has increased significantly due to a series of works made in these last years and published in recent literature. An overview of 12-polyurethane (12-PUR) embracing its synthesis, thermal properties, crystal structure and crystallization is given in this paper. The purpose is to provide a representative example able to reflect comprehensively the state of the art reached for the whole family. The synthesis of 12-PUR was accomplished in good yield and with acceptable molecular weight from 12-amino-1-dodecanol by applying a two-step method without isolation of the isocyanate alcohol precursor. 12-PUR is a semicrystalline polymer with an equilibrium melting temperature of 157°C. It adopts a layered crystal structure similar to the α-form of nylons with chains in fully-extended conformation and arranged in hydrogen-bonded sheets in the antiparallel mode. This structure is thermally stable up to melting and is unable to undergo Brill transition. 12-PUR crystallized from dilute solution affording well-shaped lamellar crystals with a thickness of 8–9nm and from the melt yielding either banded or fibrillar spherulitic textures displaying negative birefringence. Isothermal crystallization of 12-PUR from the melt took place with heterogeneous nucleation, while both crystallization rate and the finally attained crystallinity degree were highly depending on crystallization temperature. [Copyright &y& Elsevier]

In this Letter, we address nanoscale heterogeneity in polymer mobility. Single molecule fluorescence lifetime fluctuations are exploited as a probe for local segmental dynamics in polymer films. Wide distributions in polymer mobility are observed, which depend on film fabrication, treatment and amount of solvent contained. Upon solvent evaporation mobile regions disappear, while more immobile regions settle, effectively increasing the glass transition temperature. Besides insight in polymer nanoscale dynamics and heterogeneity, our results bear specific relevance to photodynamic studies on single chromophores, where routinely polymer matrices are used for immobilization. [Copyright &y& Elsevier]

Inverse gas chromatography (IGC) was applied to the surface energy study of surfaces of toner particles. The dispersive component of the surface energy was determined for three toner materials by infinite dilution IGC. The values obtained were comparable to the values obtained from contact angle experiments. Previous adhesion experiments by atomic force microscopy suggested that the toner is a hydrophilic material with multiple adsorption energy sites. Both aspects were at least qualitatively confirmed by finite concentration IGC. Several indications for surface heterogeneity were found: (i) the difference between the dispersive component of the surface energy determined by IGC and the unexpectedly low total surface energy as determined by droplet analysis, (ii) the strong tailing behavior of the peaks of the injected polar probes, (iii) the decrease of the net retention volume with increasing n-pentane concentration, and finally (iv) the broad energy site distribution function with a dominant site at 28 kJ/mol, as determined by finite concentration IGC for n-pentane as molecular probe. [ABSTRACT FROM AUTHOR]

Cast, segmented polyetherurethanes with 30 and 50% hard-segment content (HSC), respectively, were studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Multi-phase segregation was observed in both samples on two levels (micro and nano) of structural organization. Spherulites with a prominent radial structure, built of branched fibrils and globules, were captured on the micrometer level. The use of AFM enabled us to investigate the nanostructure in the polyurethanes studied here. In the sample with low (30%) HSC, nano-scale phase separation was observed by AFM in areas outside the crystalline aggregates. The morphology in these domains exhibited short, rodlike hard domains embedded in the matrix of the soft segments. The other sample (50% HSC) contained four identifiable morphological features. These included spherulites, globules, bundles of lamellae, and nanophase-separated, rodlike hard domains, embedded in the soft-segment matrix. [ABSTRACT FROM AUTHOR]

Abstract. Several symmetrical and asymmetrical long-chain diethylalkanoat disulfides were synthesized and characterized. The differences in the chain lengths of the disulfides ranged between zero and five methylene units. Self-assembled monolayers of these disulfides formed on Au(111) surfaces were studied by atomic force microscopy (AFM) in order to obtain information about the origin of the image contrast. Domains with hexagonal lattices (lattice constants 5.2-5.3 Angstrom) were detected for all derivatives, independent of the chain length differences. This indicates that the contrast arises roughly at a depth of 4-8 Angstrom in the monolayers at imaging forces between 0.2 and 3 nN. For SAMs of diethylalkanoat disulfides, the image contrast is therefore not entirely due to the terminal functional groups of the molecules, but is due to the lattice formed by the closely packed alkane chains in the bulk part of the monolayer. These results are of general importance with respect to the interpretation of AFM images of organic monolayers. [ABSTRACT FROM AUTHOR]