Breakout Crystallization Research Articles

Resilient and reprocessable physical gels based on crystalline olefin block copolymer elastomer and mineral oil toward optically transparent electronic packaging

Due to the urgent demand of high-performance electronic packaging materials, thermoplastic elastomer physical gels (TPEG) have emerged as a promising alternative to traditional hydrogels and crosslinked rubbers due to their good thermal stability and reprocessability. In this work, olefin block copolymer (OBC) elastomer was blended with soft-block selective mineral oil (MO) to tune the mechanical property and transparency. It was found that the MO molecules can disperse well within amorphous phase with effective filling ratio ranging from 9.85 wt% to 44.82 wt%. The hard segments pack into spherulites and gradually develop into segregated crystals of ∼800 nm with the increase of MO concentration. Interestingly, fast quenching induces breakout crystallization morphology while thermal annealing at 130 °C can result in confined crystallization morphology with increased domain spacing due to the selective distributed MO since the corrected crystallinity remains constant and the crystal structure maintains as orthogonal crystals. Due to the combined effect of weak mesophase separation and decreased crystal size, OBC gels has an increased transparency up to 80% in visible region. The extensibility and cyclic property of OBC-based TPEG were finely tuned along with high transparency and excellent dielectric insulation property. Furthermore, the OBC gels are highly stable over a wide temperature and can be recycled. Overall, our work highlights the potential of thermoplastic elastomer physical gels as a sustainable and high-performance alternative for transparent electronics packaging materials.

Chemically crosslinked crystalline thermoplastic polyolefin elastomer with good elasticity and improved thermo-mechanical properties

Due to mechanical α-relaxation process, olefin block copolymer (OBC) has a limited heat resistance and thermo-mechanical property. In this work, peroxide-induced melt crosslinking was conducted to fabricate OBC elastomers with two types of crosslinks. It was found that orthogonal crystal structure forms in these chemically crosslinked elastomers. Interestingly, the crystallization peak temperature ( T c,p ) shifted to higher temperature after crosslinking, which is mainly due to the crystallization mode transition from confined crystallization to breakout crystallization. Based on CPMG method of LF- 1 H NMR and AFM nanomechanics, it was demonstrated that loosely crosslinked OBC achieves double crosslinks of one chemical crosslink and another well-interconnected crystalline crosslink. As a consequence, OBC elastomer with double crosslinks shows an obviously enhanced Young's modulus (∼13.5 MPa), improved high-temperature mechanical properties (∼2.2 MPa strength and ∼220% elongation at break @80 °C) and good damping property (tan δ = 0.42). Furthermore, a balanced reprocessability and elastic recovery can be reached by adjusting the quantity of chemical crosslinks. Therefore, our work can provide guidelines for structural design and related elasticity mechanisms for high performance thermoplastic polyolefin elastomer. • The preparation of a chemically crosslinked olefin block copolymer(OBC) elastomer by peroxide-induced crosslinking. • Breakout crystallization occurs in chemically crosslinked OBC elastomer. • Loose chemical crosslinks can balance reprocessability and elastic recovery. • Chemical crosslinking favors for enhancement of the thermo-mechanical properties.

3,4-Ethylenedioxythiophene (EDOT) End-Group Functionalized Poly-ε-caprolactone (PCL): Self-Assembly in Organic Solvents and Its Coincidentally Observed Peculiar Behavior in Thin Film and Protonated Media.

End-group functionalization of homopolymers is a valuable way to produce high-fidelity nanostructured and functional soft materials when the structures obtained have the capacity for self-assembly (SA) encoded in their structural details. Herein, an end-functionalized PCL with a π-conjugated EDOT moiety, (EDOT-PCL), designed exclusively from hydrophobic domains, as a functional “hydrophobic amphiphile”, was synthesized in the bulk ROP of ε-caprolactone. The experimental results obtained by spectroscopic methods, including NMR, UV-vis, and fluorescence, using DLS and by AFM, confirm that in solvents with extremely different polarities (chloroform and acetonitrile), EDOT-PCL presents an interaction- and structure-based bias, which is strong and selective enough to exert control over supramolecular packing, both in dispersions and in the film state. This leads to the diversity of SA structures, including spheroidal, straight, and helical rods, as well as orthorhombic single crystals, with solvent-dependent shapes and sizes, confirming that EDOT-PCL behaves as a “block-molecule”. According to the results from AFM imaging, an unexpected transformation of micelle-type nanostructures into single 2D lamellar crystals, through breakout crystallization, took place by simple acetonitrile evaporation during the formation of the film on the mica support at room temperature. Moreover, EDOT-PCL’s propensity for spontaneous oxidant-free oligomerization in acidic media was proposed as a presumptive answer for the unexpected appearance of blue color during its dissolution in CDCl3 at a high concentration. FT-IR, UV-vis, and fluorescence techniques were used to support this claim. Besides being intriguing and unforeseen, the experimental findings concerning EDOT-PCL have raised new and interesting questions that deserve to be addressed in future research.

Nanoconfinement-Induced β-Phase Formation Inside Poly(vinylidene fluoride)-Based Block Copolymers.

The electroactive properties of poly(vinylidene fluoride) (PVDF) are a direct consequence of its crystalline phases. Although poorly understood, nanostructuring PVDF in confined geometries can drastically change its crystallization behavior. Therefore, we synthesized a variety of PVDF-based triblock copolymers to gain a better understanding of the melt crystallization and explore how crystallization is affected by the morphology and chemical nature of the amorphous block. Differential scanning calorimetry, small-/wide-angle X-ray scattering, and transmission electron microscopy gave us excellent insights into the morphology and the corresponding crystalline phases. We find that crystallization of PVDF inside spherical nanodomains occurs via a homogeneous nucleation mechanism leading to a large undercooling and the formation of the thermodynamically favorable ferroelectric β-phase. On the contrary, when confined crystallization occurs inside a lamellar morphology, or in the case of breakout crystallization, a heterogeneous nucleation process leads to the formation of the nonferroelectric α-phase. Furthermore, favorable melt interactions between both blocks induce crystallization into the polar γ-phase at moderate cooling rates.

Cold Crystallization of PDMS and PLLA in Poly(l-lactide-b-dimethylsiloxane-b-l-lactide) Triblock Copolymer and Their Effect on Nanostructure Morphology

Poly(l-lactide-b-dimethylsiloxane-b-l-lactide) (PLLA-b-PDMS-b-PLLA) triblock copolymer was synthesized by ring-opening polymerization of l-lactide using bis(hydroxyalkyl)-terminated PDMS as a macroinitiator. The block copolymer was immiscible in the melt, and the melt morphology was preserved upon cooling the melt to −120 °C. It was also observed that at moderate cooling rates PDMS and PLLA blocks remain in the amorphous phase at temperatures below −120 °C. The breakout and preservation of the nanostructure morphology of the triblock copolymer have been investigated by variable temperature small-angle and wide-angle X-ray scattering (SAXS and WAXS) during heating. The crystallization and melting of PDMS block occurred within the confined space entrenched by the amorphous PLLA block in the temperature range from −120 to 40 °C by preserving the microphase-separated morphology. At around the glass transition temperature of PLLA (∼45 °C), chain stretching of PLLA and PDMS took place, resulting in the sudden increase of the lamellar long period. In this temperature region, amorphous PLLA transiently transformed to the mesophase structure that resulted in the increase of PLLA domain thickness. At higher temperature, the morphological perturbation was induced by the breakout crystallization of PLLA block. In addition, the effect of isothermal cold crystallization temperatures on the polymorphic behavior of PLLA in PLLA-b-PDMS-b-PLLA triblock copolymers was also investigated. It was found that the polymorphic behavior of PLLA was not influenced much by the presence of PDMS blocks. The disordered (α′) and ordered (α) forms are formed at low and high cold crystallization temperatures, respectively, similar to the PLLA homopolymer.

Mesoporous carbon-vanadium oxide films by resol-assisted, triblock copolymer-templated cooperative self-assembly.

Unlike other crystalline metal oxides amenable to templating by the combined assemblies of soft and hard chemistries (CASH) method, vanadium oxide nanostructures templated by poly(ethylene oxide-b-1,4-butadiene-b-ethylene oxide) (OBO) triblock copolymers are not preserved upon high temperature calcination in argon. Triconstituent cooperative assembly of a phenolic resin oligomer (resol) and an OBO triblock in a VOCl3 precursor solution enhances the carbon yield and can prevent breakout crystallization of the vanadia during calcination. However, the calcination environment significantly influences the observed mesoporous morphology in these composite thin films. Use of an argon atmosphere in this processing protocol leads to nearly complete loss of carbon-vanadium oxide thin film mesostructure, due to carbothermal reduction of vanadium oxide. This reduction mechanism also explains why the CASH method is not more generally successful for the fabrication of ordered mesoporous vanadia. Carbonization under a nitrogen atmosphere at temperatures up to 800 °C instead enables formation of a block copolymer-templated mesoporous structure, which apparently stems from the formation of a minor fraction of a stabilizing vanadium oxynitride. Thus, judicious selection of the inert gas for template removal is critical for the synthesis of well-defined, mesoporous vanadia-carbon composite films. This resol-assisted assembly method may generally apply to the fabrication of other mesoporous materials, wherein inorganic framework crystallization is problematic due to kinetically competitive carbothermal reduction processes.

In Situ Study of the Breakout Crystallization in the Poly(butadiene)-block-Poly(ε-caprolactone) Thin Film

Despite its wide occurrence in soft confined block co-polymers, breakout crystallization remains poorly understood and is difficult to control. In this work, thin films of cylinder-forming poly(butadiene)-block-poly(ε-caprolactone) (PB-b-PCL) diblock co-polymers, with PCL being the minority block, have been chosen as the study subject. We demonstrate a new route to study the breakout crystallization by obtaining the microphase separation structure within terraced lamellae first and then in situ tracking down the lamellar coalescence, resulting from the development of the crystal growth front. We find that the crystal growth front has sucked materials from the surrounding amorphous lamellae, which lead to the decrease of the lamellar zones and coalescence of the microphase separation structure. Dividing the breakout crystallization into parallel breakout and vertical breakout, we illustrate that it is the crystallization-driven molecular diffusion that make the molecules overcome the topography constraint and grow into large-scale spherulite. Moreover, the results show that the polymer microphase separation structure has a significant influence on the crystal nucleation and greatly retarded the crystal growth rate. With a well-designed microphase separation structure within terraces and an easily tunable atomic force microscopy in situ imaging technique, an intensive study of the breakout crystallization and concomitant microdomain coalescence has been offered.

Effect of molecular weight and film thickness on the crystallization and microphase separation in polystyrene-block-poly(L-lactic acid) thin films at the early stage

We investigated the effects of molecular weight and film thickness on the crystallization and microphase separation in semicrystalline block copolymer polystyrene-block-poly(L-lactic acid) (PS-b-PLLA) thin films, at the early stage of film evolution (when Tg < T < TODT) by in situ hot stage atomic force microscopy. For PS-b-PLLA 1 copolymer which had lower molecular weight and higher PLLA fraction, diffusion-controlled break-out crystallization started easily. For PS-b-PLLA 2 with higher molecular weight, crystallization in nanometer scales occurs in local area. After melting of the two copolymer films, islands were observed at the film surface: PS-b-PLLA 1 film was in a disordered phase mixed state while PS-b-PLLA 2 film formed phase-separated lamellar structure paralleling to the substrate. Crystallization-melting and van der Waals forces drove the island formation in PS-b-PLLA 1 film. Film thickness affected the crystallization rate. Crystals grew very slowly in much thinner film of PS-b-PLLA 1 and remained almost unchanged at long time annealing. The incompatibility between PS and PLLA blocks drove the film fluctuation which subsequently evolved into spinodal-like morphology.

Surface-induced breakout crystallization in cylinder-forming P(I-b-EO) diblock copolymer thin films

We have found very slow crystallization in thin films of cylinder-forming poly(isoprene-b-ethyleneoxide) (P(I-b -EO)) diblock copolymers with PEO being the minority block. The film was crystallized at room temperature after melting at 62 °C. Imaging methods were combined with X-ray reflectometry and grazing-incidence small-angle X-ray scattering and diffraction. Initially, hexagonally packed, amorphous PEO cylinders lie in the film plane. After 148 days, crystallized, finger-like terraces were observed over the entire film surface. The terrace height is 20% higher than the repeat distance in the as-prepared film. Thus, at the film surface, the cylinders have been destroyed by crystalline lamellae lying in the film plane. The PEO chain stems are perpendicular to the substrate surface and are once-folded and fully interdigitated. The substrate-near layers still consist of the hexagonally packed, amorphous PEO cylinders within the PI matrix.

Crystallization of Molecular Brushes with Block Copolymer Side Chains

A series of three cylindrical molecular brushes with poly(e-caprolactone)-b-poly(n-butyl acrylate) side chains were investigated with regard to the effect of the intramolecular confinement on the crystallization behavior of the PCL core block. While the length of the PCL block was maintained (nPCL = 50), the degree of polymerization of the PBA corona block, prepared by atom transfer radical polymerization, was varied from nPBA = 0 (PCL brush) to nPBA = 52 and 163. The crystallization behavior of the studied polymers was shown to be different in thin films and bulk samples. In thin films, the brushlike macromolecules were fully extended and remained segregated due to the steric repulsion of the adsorbed PBA corona. Under the constraint of the backbone extension, crystallization of the PCL core led to formation of a characteristic spinelike morphology. In bulk samples, the core−shell confinement did not prohibit breakout crystallization, leading to the formation of a spherulitic morphology similar to linear...

Crystallization-induced switching of the morphology of poly(ethylene oxide)-block-polybutadiene micelles

We studied the morphology of micelles formed by a well-defined poly(1,2-butadiene)-block-poly(ethylene oxide) diblock copolymer (PB-b-PEO). Dissolved in n-heptane at 70 °C, that is, above the melting point of PEO, spherical micelles are formed due to the selectivity of the solvent for the PB-block. If the solutions are cooled down to low temperatures, the liquid PEO-block crystallizes within the cores of the spherical micelles that remain stable. If, however, the solutions are quenched to 30 °C, the spherical micelles aggregate to a novel meander-like structure within several minutes. In its final state, the meander-like super-structure is crystalline, as revealed by time-resolved wide-angle X-ray scattering. The super-structure is shown to result from crystallization-induced aggregation of spherical micelles. Moreover, crystallization leads to well-defined angles between subsequent aggregating units. A quantitative Avrami-type analysis of the crystallization kinetics demonstrates that the formation of the meander-type structure resembles a 2D growth process combined with a breakout crystallization, showing an Avrami-exponent of 2.5. In contrast to this, crystallization at low temperatures resembles a confined crystallization with a low Avrami-exponent of 0.7. All data demonstrate that the morphology of block copolymers having a crystallizable block can be switched by the competition of aggregation and crystallization.

Crystallization and melting behaviors of polystyrene- b-poly(ethylene- co-butene) block copolymers

Non-isothermal and isothermal crystallization behaviors of polystyrene- b-poly(ethylene- co-butene) (PSt- b-PEB) block copolymers with different compositions and chain lengths were investigated by differential scanning calorimetry (DSC). The results show that crystallization of PEB block is strongly dependent on the composition. Crystallization temperature ( T c), melting temperature ( T m) and fusion enthalpy (Δ H f) increase rapidly with PEB volume fraction ( V E) for block copolymers with V E below 50%, but there is little change when PEB block becomes the major component. Glass transition temperature ( T g) of the PSt block and order–disorder transition temperature ( T ODT) of block copolymers also have a weak effect. The isothermal crystallization kinetics results show that Avrami exponent ( n) was strongly dependent on the composition and crystallization temperature. For the block copolymers with V E below 38.7 vol%, the values of n vary between 0.9 and 1.3, indicating that crystallization is confined. For the PSt- b-PEB block copolymers with V E higher than 50%, fractionated crystallization behavior is usually observed. A two-step isothermal crystallization procedure is applied to these block copolymers. It is found that breakout crystallization occurs at higher T c, but confined at lower T c. Two overlapped melting peaks are observed for the block copolymers with fractionated crystallization behavior after two-step crystallization, and only the higher melting peak corresponding to breakout crystallization can be used to derive equilibrium melting temperature.

Crystallization of block copolymers in restricted cylindrical geometries

Using Tapping Mode atomic force microscopy, we studied crystallization of polymers in confined cylindrical geometries of micro-phase separated asymmetric diblock copolymers, deposited in thin films onto solid substrates. We observed that in most cases crystallization occurs separately and independently in each cylinder of the mesophase pattern. We followed the kinetics of the crystallization process with time and found an influence of the lateral size of the cylindrical morphology on the rate of crystallization. The present data are compared to previous results on spherical mesophase patterns. The growth rate within one single cylinder was found to be not necessarily constant. Depending on the amount of crystallized material and the molecular weight, structural relaxations of the crystals can have very strong influence on the amorphous matrix and can even lead to the destruction of the mesophase pattern, allowing for break-out crystallization. As a consequence of break-out crystallization, crystallization kinetics changed considerably since the crystal growth was not limited anymore to the confinement imposed by the cylinders.

Crystallization behavior of oxyethylene/oxybutylene diblock and triblock copolymers

The crystallization behavior of poly(oxyethylene)-b-poly(oxybutylene) block copolymers with different compositions, morphologies and architectures (EmBn diblock copolymers and EmBnEm, BnEmBn triblock copolymers) were investigated and the effect of volume fraction and architecture on the crystallization temperature (Tc) in non-isothermal crystallization was determined. It is found that the EmBn diblock copolymers having long E blocks exhibit similar crystallization temperatures, irrespective of volume fraction and morphology, but for the block copolymers with shorter E blocks the crystallization temperature increases with both the volume fraction, φE, and the length, m, of the E block. Some block copolymers with extremely low Tc, which fall into the temperature range normally associated with homogenous nucleation, were chosen for time-resolved small-angle X-ray scattering (SAXS) and isothermal crystallization kinetics experiments. The results show that breakout crystallization occurs in all these block copolymers. Therefore, unlike EmBn/Bh blends, there is no obvious relationship between Tc and crystallization behavior in neat block copolymers and homogeneous nucleation does not definitely lead to confined crystallization. The values of χc/χODT for all the block copolymers with hex and bcc morphology were also calculated. It is found that all the block copolymers have χc/χODT<3, in agreement with the previously reported critical value and consistent with their breakout crystallization behavior.

SAXS/WAXS/DSC studies on crystallization of a polystyrene- b-poly(ethylene oxide)- b-polystyrene triblock copolymer with lamellar morphology and low glass transition temperature

Crystallization of a polystyrene- b-poly(ethylene oxide)- b-polystyrene (S–EO–S) triblock copolymer, S 40EO 136S 40, with lamellar morphology in the melt and low glass transition temperature ( T g=47 °C) of the S block was studied. The triblock copolymer was cooled from ordered melt and isothermal crystallization was conducted at crystallization temperatures ( T c) near the T g of the S block. It is found that crystallization behavior of S 40EO 136S 40 strongly depends on T c. When T c is far below T g, an Avrami exponent n=0.5 is observed, which is attributed to diffusion-controlled confined crystallization. As T c slightly increases, the Avrami exponent is 1.0, indicating that crystallization is confined and crystallization rate is determined by the rate of homogeneous nucleation. When T c is just below the T g of the S block, crystallization tends to become breakout and accordingly Avrami exponent changes from 1.0 to 3.2. Crystallinity and melting temperature of the EO block in breakout crystallization are slightly higher than those in confined crystallization. Time-resolved small and wide angle X-ray scattering (SAXS/WAXS) were used to monitor isothermal crystallization of S 40EO 136S 40. It shows that the long period is constant in confined crystallization, but it gradually increases during breakout crystallization. WAXS result reveals that confined or breakout crystallization has no effect on the crystal structure of the EO block.

Isothermal Crystallization Kinetics and Melting Behavior of Poly(oxyethylene)-b-poly(oxybutylene)/Poly(oxybutylene) Blends

Poly(oxyethylene-b-oxybutylene) block copolymers of various chain lengths (EmBn) were blended with poly(oxybutylene) homopolymer (Bh), materials having different segregation strengths and morphologies (lamellae, cylinder, and sphere) were obtained. The isothermal crystallization kinetics and melting behavior of the blends were studied using differential scanning calorimetry (DSC) and synchrotron small-angle X-ray scattering (SAXS), respectively. Two types of crystallization are identified: confined crystallization occurring at lower temperature with Avrami exponent close to 1.0, having a strong dependence of crystallization halftime on crystallization temperature and a smooth change of q* in crystallization; breakout crystallization occurring at higher temperature with an Avrami exponent much bigger than 1.0 and a step change in q*. The relative segregation strength χc/χODT has an important influence on the crystallization mechanism, and confined crystallization is observed at χc/χODT > 3 whereas breakou...

Morphological Confinement on Crystallization in Blends of Poly(oxyethylene-block-oxybutylene) and Poly(oxybutylene)

Three poly(oxyethylene-block-oxybutylene) diblock copolymers, E76B38, E114B56, and E155B76, were blended with poly(oxybutylene) homopolymer, B14 and B28, such that lamellae (lam), gyroid (gyr), hexagonally packed cylinders (hex), and body-centered-cubic (bcc) spheres were obtained in the melt. The nonisothermal crystallization on cooling of the blends was investigated with synchrotron small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). In general, two classes of behavior are observed. In confined crystallization the morphology of the melt is retained, and crystals have limited dimensions. In breakout crystallization the melt morphology is destroyed, and a new lamellar morphology is formed. The morphological state (confinement in or breakout of melt morphology) during crystallization was evaluated by the change of the position of the first-order peak (q*) in SAXS and the crystallization temperature (Tc). Breakout of morphology was observed in all E76B38/B14 blends and E114B56/B28 and E155B76/B28 blends with lam morphology, while confined crystallization occurred in E155B76/B28 blends with hex and bcc morphologies and E114B56/B28 blends with bcc morphology. Confined crystallization was also observed in low E content E114B56/B28 blends with hex morphology. These findings lead to two conclusions: (i) the tendency of confined crystallization varies with morphology and decreases in the order bcc > hex > lam, and (ii) confinement on crystallization tends to increase with the extent of segregation between the two blocks. The DSC results show that the crystallization temperature of the blends varies with morphology and chain length of the block copolymers. A much lower Tc was observed for the blends exhibiting confined crystallization behavior, and this phenomenon is explained by a homogeneous nucleation mechanism. The morphology over a larger scale was also examined by polarized light microscopy, and spherulite formation was only observed in the blends where the morphology was easily broken out during crystallization.