Crystallization Of Polystyrene Research Articles

Crystallization of syndiotactic polystyrene by immersion in liquid compounds

Amorphous syndiotactic polystyrene (SPS) films were found to crystallize under mild conditions below 75 °C only by immersion in liquid solvents. The crystallization and surface changes were systematically examined using wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The crystalline phases produced were strongly dependent on the solvent, i.e., the molecular volume size and the compatibility with SPS, which can be expressed as Fedor's solubility parameter (SP) value. The immersion of SPS in the solvents whose SPS solutions can form gels produced the SPS δ-clathrate crystalline phase, while immersion in the solvents whose SPS solutions crystallize the γ-crystalline phase produced the SPS γ-crystalline phase. Interestingly, when SPS amorphous films were immersed in most solvents whose SPS solutions crystallize the β-crystalline phase, the SPS γ-crystalline phase was produced instead of the β-crystalline phase. The solvents that could not produce any crystalline phase were only the solvents unable to dissolve SPS or the large solvent molecules whose SPS solutions crystallize the β-crystalline phase. If part of the structure of a solvent is compatible with SPS, it can go deep into the amorphous region of SPS and force SPS chains to form a helix conformation. However, some molecules larger than decylbenzene (252 Å3) were assumed unable to enter through a kind of mesh formed by SPS chains. We discuss why SPS was not dissolved, but instead crystallized, when the films were immersed in solvents.

Microcrystallization of Atactic Polystyrene Induced by Photooxidation Aging

AbstractPhotooxidation aging, hygrothermal aging, and hot‐air aging are carried out on atactic polystyrene (aPS) samples formed by injection molding. It is interesting that microcrystals of atactic polystyrene are only found in photooxidation aging. This work proposes that high molecular weight atactic polystyrene can crystallize under photooxidation aging. It is a good addition to the research on the aspect of crystallization of atactic polystyrene.

Acoustic Crystallization of 2D Colloidal Crystals.

2D colloidal crystallization provides a simple strategy to produce defined nanostructure arrays over macroscopic areas. Regularity and long-range order of such crystals is essential to ensure functionality, but difficult to achieve in self-assembling systems. Here, a simple loudspeaker setup for the acoustic crystallization of 2D colloidal crystals (ACDC) of polystyrene, microgels, and core-shell particles at liquid interfaces is introduced. This setup anneals an interfacial colloidal monolayer and affords an increase in average grain size by almost two orders of magnitude. The order is characterized via the structural color of the colloidal crystal, the acoustic annealing process is optimized via the frequency and the amplitude of the applied sound wave, and its efficiency is rationalized via the surface coverage-dependent interactions within the interfacial colloidal monolayer. Computer simulations show that multiple rearrangement mechanisms at different length scales, from the local motion around voids to grain boundary movements via consecutive particle rotations around common centers, collude to remove defects. The experimentally simple ACDC process, paired with the demonstrated applicability toward complex particle systems, provides access to highly defined nanostructure arrays for a wide range of research communities.

Improved Polymer Crystal Phase Field Model and Numerical Simulation

The existing phase field model of polymer crystallization contains many parameters that lack actual physical meaning. Although the value of these parameters can be adjusted to obtain results consistent with the experiment, it cannot correspond to the experimental conditions. In this paper, a new phase field model is established. By adjusting the latent heat, various forms of isotactic polystyrene crystals, such as dendrites, spherulites, lamellas, etc., can be simulated. Latent heat refers to the heat absorbed or released by a substance from one phase to another and has important physical meaning during the solidification process. The finite difference method was used to solve the model, and then the data were used to visualize. The simulation results were consistent with the experiment. Numerical simulation results under pure diffusion conditions show that the newly established phase field model can qualitatively predict the polymer growth process and provide a theoretical basis for the preparation and optimization of high-performance polymers. In order to make the simulation result closer to the actual growth of the crystal, the flow velocity is added in the simulation to make the melt convection. Under forced convection, the simulated polymer crystal image is no longer symmetrical.

Photoluminescence enhancement in monolayer MoS2 and self-assembled 3D photonic crystal heterostructures.

Self-assembled photonic crystals (PCs) have promising applications in enhancing and directional manipulation of the photoemission due to their photonic bandgaps. Here, we employed self-assembled 3D polystyrene PCs to enhance the photoluminescence (PL) of monolayer molybdenum disulfide (MoS2). Through tuning the photonic bandgap of the polystyrene crystals to overlap with the direct emission band of monolayer MoS2, the MoS2/3D-PC heterostructure showed a maximum 12-fold PL enhancement, and Rabi splitting was also observed in the reflection spectrum. The heterostructure is expected to be useful in nanophotonic emitting devices.

Effect of MW Radiation on Thin-Film Polymer Membranes

To improve physical-chemical properties of thin-film membranes from nylon and nylon membranes with a surface layer of polystyrene (PS), nylon-PS, the processing of the latter was carried out with microwave radiation (microwave) at a frequency of 2450 MHz and a power of 300 W in air. As a result of exposure to microwave radiation, changes were found in the mass of the membranes depending on the processing time for nylon membranes, up to 0.34% and, for nylon-PS membranes, up to 0.67%. The results of scanning electron microscopy showed the formation of melted and compacted areas on the membrane surface. An increase in the hydrophilicity and specific performance of membranes as a result of treatment with microwave radiation has been established. A decrease in the roughness of the surface layer of membranes and changes in the structure of the nylon-PS membrane were revealed according to the results of scanning electron microscopy. Changes in the supramolecular structure of the nylon-PS membrane were confirmed by the results of Fourier-transform infrared spectroscopy: a shift of the base of the absorption band to characteristic vibrations of the C–H bond of the phenyl group of polystyrene has been detected. The phenyl groups in the polymer macro-molecule interfere with crystallization of polystyrene and a displacement of the peak base indicates structural changes in the macromolecule, which leads to an increase in the degree of crystallinity of PS. Under the influence of microwave radiation in PS, the orientation of the phenyl group changes: it is located, alternating, on opposite sides of the main chain, which contributes to an increase in the number of crystallization centers, streamlining the structure. An increase in the intensity of the absorption bands of the IR spectra after the treatment of the nylon membrane with microwave radiation is associated with the destruction of the defective regions of the surface layer of the membrane.

Chemical Stabilization of Hexanal Molecules by Inclusion as Guests of Nanoporous-Crystalline Syndiotactic Polystyrene Crystals

Chemical stabilization of air-unstable molecules, by their inclusion as guest of nanoporous-crystalline phases of syndiotactic polystyrene (s-PS), is for the first time revealed. FTIR analyses show that antimicrobial hexanal molecules are chemically stable for months when guest of s-PS cocrystalline phases, while they easily oxidize to hexanoic acid when they are simply dissolved in polymer amorphous phases. Formation of s-PS/hexanal cocrystalline forms is clearly demonstrated by polarized FTIR spectra and by X-ray diffraction patterns. Chemical stabilization is observed for hexanal molecules being guest of both nanoporous-crystalline forms of s-PS, i.e., for guest molecules isolated in the cavities of δ form or aligned along the channels of e form. Films exhibiting s-PS/hexanal clathrate forms are able not only to chemically stabilize the antimicrobial molecules but also to give their long-term release (with a diffusivity close to 2 × 10–14 cm2 s–1). Possible mechanisms of chemical stabilization by clath...

Formation of Periodically Modulated Polymer Crystals

We report novel morphologies with periodic height modulations of isotactic polystyrene (iPS) crystals, resulting from alternating stacks of correlated lamellae. Systematic experiments were performed on iPS films of several thicknesses (h) for varying degrees of undercooling, ΔT = Tm∞ – TC, where Tm∞ and TC are the equilibrium melting temperature and the crystallization temperature, respectively. We demonstrate that the spatial period (λ), i.e., the mean distance between neighboring stacks of lamellae, exhibits a power-law dependence on h and an exponential dependence on 1/ΔT. We propose that self-induced nucleation of stacked layers caused periodic deviation in the growth rate of iPS crystals, yielding periodic height modulations.

28a-YC-7 アイソタクチックポリスチレンの結晶成長と膜厚

28a-YC-7 アイソタクチックポリスチレンの結晶成長と膜厚

Thermal effects on the strain-induced β to α form crystalline structural transition of solid-state syndiotactic polystyrene

Thermal effects on the strain-induced structural transition from β-form to α-form crystals of syndiotactic polystyrene (sPS) were investigated by changing the stretching temperature and the annealing temperature. When sPS was stretched at lower temperature (near the glass transition temperature (Tg) of sPS (∼130 °C)), the crystalline structural transition was incomplete, producing fragmented β-form and mesomorphic α-form crystals. Stretching at higher temperature facilitated the crystalline structural transition from β to α. For the sPS specimen stretched at 130 °C, the β-form crystals broke into small pieces, simultaneously creating mesomorphic α-form crystals. After annealing, the fragmented β-form crystals and the mesomorphic α-form crystals were reorganized to become complete crystals. The reorganization became more pronounced as the annealing temperature increased. The main role of the mechanical strain and the heat, therefore, could be the destruction of β-form crystals to produce fragmented β-form crystals and mesomorphic α-form crystals, and the formation of complete crystals, respectively.

Light-driven crystallization of polystyrene micro-spheres

We investigate the dynamic crystallization processes of colloidal photonic crystals, which are potentially invaluable for solving a number of existing and emerging technical problems in regards to controlled fabrication of crystals, such as size normalization, stability improvement, and acceleration of synthesis. In this paper, we report systematic high-resolution optical observation of the spontaneous crystallization of monodisperse polystyrene (PS) micro-spheres in aqueous solution into close-packed arrays in a static line optical tweezers. The experiments demonstrate that the crystal structure is mainly affected by the minimum potential energy of the system; however, the crystallization dynamics could be affected by various mechanical, physical, and geometric factors. The complicated dynamic transformation process from 1D crystallization to 2D crystallization and the creation and annihilation of dislocations and defects via crystal relaxation are clearly illustrated. Two major crystal growth modes, the epitaxy growth pattern and the inserted growth pattern, have been identified to play a key role in shaping the dynamics of the 1D and 2D crystallization process. These observations offer invaluable insights for in-depth research about colloidal crystal crystallization.

Nanograin nucleation at the growth front in melt crystallization of syndiotactic polystyrene

Melt-crystallization of syndiotactic polystyrene (sPS) is studied using simultaneous small/wide angle X-ray scattering (SAXS/WAXS). Emergence, intensification, and saturation of WAXS reflections within 120 s at isothermal crystallization temperature Tc = 250 °C after quenching from 300 °C illustrate crystallinity development through successive nucleation of instantaneously stabilized crystallites of lateral (hk0) coherence length Λ ≈ 75 nm. The corresponding SAXS profiles exhibit increased density heterogeneity due to formation of nanograins; fitting of time-resolved SAXS data with a model of arrayed disks reveals slightly thickened (lc = 7.4–8.4 nm) disks of radius R ≈ 9 nm and long period L ≈ 19 nm with polydisperse stacking number slowly enhanced from an average of 1.2 to 2.4. The moderate ratio of Λ/2R ≈ 4 indicates imperfect coalescence of nanograins in the lamellar assembly process. More importantly, with successively increased Tc from 250 to 260 °C the development of density heterogeneity of SAXS invariant Qinv is found to precede that of the WAXS-determined crystallinity Xc increasingly more, suggesting a precursor mesophase with non-crystalline nanograins. Avrami analysis for the developments of Xc and Qinv further reveals the same Avrami exponent n ≈ 3, consistent with heterogeneous nucleation of crystallites; the corresponding Avrami rate constant κ1/n(Tc) extracted from Xc is correlated to the crystal growth rates G(Tc) described by the Hoffman-Lauritzen theory with a common surface-nucleation rate constant Kg. A lateral surface energy σ ≈ 17 mJ m−2 can be deduced on the basis of Kg using previously determined fold surface energy σe ≈ 27 mJ m−2. Correspondingly, κ1/n(Tc) extracted from Qinv is described by a mesophase model proposed by Strobl with a zero-growth temperature of the nanograin mesophase ca. 30 K below the β-crystal melting point of sPS. Together, these results suggest that sPS melt-crystallization proceeds with nucleation of non-crystalline nanograins (SAXS-before-WAXS regime) at the crystal growth front, followed by crystallization of the nanograins with similar kinetics to sustain the growth front. Branching/twisting can occur at the lamellar growth front due to frustrated nanograin alignment, favoring the microscopically observed sheaf-like crystal morphology.

Synchrotron radiation phase-contrast computed tomography study on self-assembly of polystyrene colloidal crystals via solvent evaporation

The colloidal crystals of polystyrene (PS) spheres were assembled from the emulsion of PS by an in situ solvent evaporation method. The local internal 3D structure of the fabricated colloidal crystals was noninvasively characterized with synchrotron radiation phase-contrast computed tomography. The satisfactory contrast difference was obtained and the shapes of the spheres were clearly reconstructed. Based on the slice images, the two-stage mechanism of crystallization process for in situ evaporation was suggested. In the initial stage, stable nucleation and growth result in formation of an ordered face-centered cubic structure with the sphere volume fraction 70.2%, which is very close to the maximum sphere packing volume fraction 74%. In the second stage, the sphere concentration in suspension decreased too much to support an adequate sphere transfer through the solvent flux to the growth front. The transformation from square to hexagonal lattice did not therefore complete under the same evaporation rate. This incompleteness results in formation of local ordered structure with randomly arranged hexagonal and square packing with a slightly low volume fraction of 68.41%.

Isothermal crystallization of syndiotactic polystyrene induced by graphene nanosheets and carbon nanotubes: a comparative study

Composites of sPS filled with different contents of graphene nanosheets (GNS) are prepared by coagulation method. Two types of GNS with different thicknesses (denoted as G1 and G10) are studied to unveil the effect of aspect ratio on the crystallization kinetics of the composite. Atomic force microscopy and transmission electron microscopy (TEM) show that G1 is a wrinkled sheet with an average thickness of ~2 nm and that G10 is a smooth flake with a thickness of ~50 nm; both possess a basal dimension of ~5 μm. TEM studies on the melt-quenched composites reveal that G1 has a more uniform dispersion in the sPS matrix than G10. Short lamellae of sPS are observed in the G10-filled composites with GNS content higher than 0.5 wt.%. The results of wide-angle X-ray diffraction show that the produced sPS crystallites are in β form under severe cooling conditions in liquid N2. Regardless of the GNS content and type, the glass transition and equilibrium melting temperature of the sPS matrix are unchanged at ~96 and ~290 °C, respectively. Both G1 and G10 nanofillers are good nucleating agents for the heterogeneous nucleation of sPS. With increasing GNS loading, the isothermal crystallization rate of sPS increases. G10 is more effective than G1 in inducing sPS crystallization despite the higher concentration required to form the GNS network. Compared with 1D CNT nanofiller, 2D GNS is less effective in enhancing sPS crystallization through surface-induced nucleation because of the geometrical difference between the two materials.

Two-dimensional colloidal crystal assisted formation of conductive porous gold films with flexible structural controllability

Two-dimensional (2D) colloidal crystals of polystyrene (PS) particles were used as a structure-controlling template to fabricate conductive Au films with an ordered array of nanoholes. The fabrication mainly involved the functionalization of the supporting substrate with polyelectrolyte (PE) functional layers, self-assembly of Au nanoparticles, and electroless deposition of gold. The self-assembly of Au nanoparticles and electroless deposition of gold were macroscopically monitored using ultraviolet–visible (UV–vis) spectroscopy based on the changes in both the extinction spectra of Au nanoparticles and the optical responses of ordered arrays of PS particles. By scanning electron microscopy (SEM) characterization, it was found that Au nanoparticles were assembled into a film structure with orderly dispersed nanoholes and the deposition of gold was confined to the preformed Au nanoparticle films. During the formation of Au films, PE layer structure, Au nanoparticle size and heating treatment applied to the PS template could influence the structures of conductive porous Au films such as the hole diameter, film thickness, and hole diameter/wall thickness ratio (D/W). In addition, this paper also described electrochemical cyclic voltammetry (CV) employed to demonstrate the porosity of the ultimate Au films.

Gas-Flow-Induced Reorientation to Centimeter-Sized Two-Dimensional Colloidal Single Crystal of Polystyrene Particle

Centimeter-sized two-dimensional (2D) colloidal single crystals of polystyrene (PS) particles were fabricated at the water/air interface by capillary-modulated self-assembly. Different from previous reports, in this work, emulsifier was used to facilitate the stress release during 2D colloidal crystal formation by adjusting the interparticle lateral interactions. With the assistance of compressed nitrogen flow, 2D hexagonal colloidal single crystals of centimeter size were obtained under appropriate emulsifier concentrations. A new method was also developed to transfer the 2D colloidal crystals from the air/water interface to the desired substrate without obvious disturbance. This new transferring method was proven not to be sensitive to surface wettability nor curvature, thus 2D colloidal single crystals with large areas could be obtained on different kinds of substrate.

A phase-field model for simulating various spherulite morphologies of semi-crystalline polymers

A modified phase-field model is proposed for simulating the isothermal crystallization of polymer melts. The model consists of a second-order phase-field equation and a heat conduction equation. It obtains its model parameters from the real material parameters and is easy to use with tolerable computational cost. Due to the use of a new free energy functional form, the model can reproduce various single crystal morphologies of polymer melts under quiescent conditions, including dendritic, lamellar branching, ring-banded, breakup of ring-banded, faceted hexagonal, and spherulitic structures. Simulation results of isotactic polystyrene crystals demonstrate that the present phase-field model has the ability to give qualitative predictions of polymer crystallization under isothermal and quiescent conditions.

Effects of Temperature and Template Surface on Crystallization of Syndiotactic Polystyrene in Cylindrical Nanopores

Crystallization of syndiotactic polystyrene (sPS) in anodized aluminum oxide (AAO) templates is investigated by FTIR. Nanopore surfaces of AAO templates are modified with n-hexyltrimethoxysilane to produce templates with alkyl surfaces, and effects of crystallization temperature and surface property of the template on the degree of crystallinity of sPS in nanopores of various sizes are studied. When isothermally crystallized at 245–260 °C, while the crystallinity in the bulk barely varies, in pristine and modified nanopores it increases substantially with degree of supercooling, which may be attributed to more surface-induced crystallization at lower temperatures. For all crystallization temperatures and pore sizes studied, sPS exhibits much lower crystallinity in the surface-modified templates, likely due to suppression of surface nucleation by the lower energy surfaces. This work reveals the significant role surface plays in polymer crystallization in nanotemplates and may aid the design and fabrication...

Crystallization of Syndiotactic Polystyrene Monitored by Angular Distributions of Polarized Fluorescence

The method to measure polarized fluorescence by rotating a sample around the excitation light (PFR) was applied to observe the initial stage of crystallization of syndiotactic polystyrene (SPS) induced by the exposure of naphthalene (NP) vapors. At room temperature, no crystallization of SPS appeared when the stretched films were exposed by NP vapors. PFR clearly evidenced that the NP molecules were not distributed uniformly but rather with a sort of orientation in the oriented amorphous SPS. NP molecules were clathrated in SPS films in the case of the exposure at 80°C. However, the exposure of NP vapors at 60°C was found to produce SPS/NP clathrate cocrystalline structure with only a small amount but rather mainly produce a trans-planar mesomorphic phase. In this initial stage, the wide angle X-ray diffraction revealed diffuse and unclear, whereas PFR was effective to determine orientation and distribution of the NP molecules. The NP molecules staying in the amorphous region were shown to be oriented due to the formation of a trans-planar mesomorphic phase, and their main arrangements were first determined by PFR.

Monitoring nonisothermal crystallization of thermoplastic polymers using a quartz crystal resonator

A new monitoring device for the nonisothermal crystallization of thermoplastic polymers, polyethylene, polypropylene, polystyrene, and polyamide, is developed utilizing a quartz crystal resonator, and its performance is evaluated by comparing the measurements with the results of DSC thermoanalysis and microscopic observation. The experimental results of four different polymers indicate that the variation of resonant freency of the quartz crystal resonator is a good means to monitor the crystallization process. Though the measurements of melting and crystallization are close to the DSC outcome, more deviation is observed with the new device. The change in crystalline morphology during the crystallization process is also detected from the slope changes of the frequency decrease. In comparison with the microscopic observation of polymer films, it is found that the processes of nucleation and crystal growth in nonisothermal crystallization can be explained with the variation of the resonant frequency of the quartz crystal resonator. In addition, crystallization kinetics is modeled with the Avrami equation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011