Phase-separated Polymer Research Articles

Predicting the visco-elastic properties of polystyrene/SIS composite blends using simple analytical micromechanics models

This paper is concerned with the prediction of the viscoelastic properties of rubber filled polymer blends. The question asked was as follows. Can the temperature dependent viscoelastic properties of phase separated polymer blends be adequately predicted using only a rational two phase micromechanics based analytical model with no empirical fitting parameters? In particular can this be achieved using only a knowledge of the individual bulk phase properties and the blend microstructure, but without any further detailed polymer physics knowledge such as the presence of an interphase region or any additional nanoscale structures within the separated rubber phase with the properties different from those of the two bulk phases?Blends of a polystyrene matrix containing phase separated rubber inclusions (a polystyrene-polyisoprene-polystyrene triblock polymer (SIS)) were manufactured in a range of blend fractions (up to 20 vol % of the triblock co-polymer). Experimental measurements, for the storage modulus G′ and the loss tangent tanδ, of both the individual phases and the blends, were made using dynamic mechanical tests over a range of temperatures from −50 to +70 °C.Numerical predictions, of the same properties, were first obtained using the generalised self-consistent Christensen and Lo model which uses a simple representative volume element (RVE) of an isolated sphere of the minority rubber component in a surrounding sheath of polystyrene matrix embedded in a homogeneous effective medium. The agreement between the Christensen and Lo model and the experimental measurements, for G′ and tanδ, was found to be excellent for rubber contents up to 10%. For a 20% rubber content, an improved prediction was obtained by altering the RVE to include the observed effect of having a polystyrene central core in a number of the dispersed rubber zones at this rubber fraction, using the Hervé and Zaoui generalization of the Christensen and Lo model. Although conjoined (and therefore non-spherical) zones became more prevalent at the highest rubber content, use of the Tandon and Weng model showed that this shape anisotropy would not be expected to affect the viscoelastic properties.

Preparation of Flattened Cross-Linked Hollow Particles by Suspension Polymerization in a Solid Dispersion Medium.

Flattened cross-linked hollow poly(divinylbenzene) (PDVB) particles with encapsulated n-hexadecane (HD) were successfully prepared through suspension polymerization using the self-assembling of phase-separated polymer (SaPSeP) method, in which the solid dispersion medium was gelled by gellan gum and compressed. The solid phase induced by gellan gum can be easily changed to a liquid state by heating, allowing the obtained particles to be easily recovered after polymerization. When the polymerization was conducted in the solid dispersion medium without compression, spherical hollow PDVB/HD composite particles were obtained. In contrast, when the polymerization was conducted with the compression of the solid dispersion medium, flattened hollow PDVB/HD composite particles were obtained. The shape of the flattened hollow polymer particles was controlled by changing the compression ratio of the solid phase, and the size could also be controlled by changing the DVB/HD droplet size using the Shirasu porous glass membrane-emulsification technique. Furthermore, flattened hollow particles larger than 20 μm in size were obtained, but it was difficult to obtain spherical hollow particles of such large size using the SaPSeP method.

感熱性高分子水溶液の相分離・ゲル化・レオロジー

The recent status of studies on temperature–sensitive water-soluble polymers is briefly reviewed. The concept of cooperative dehydration, defined as simultaneous dissociation of the water molecules bound to a polymer chain in correlated sequences, has been applied to study the collapse transition and LCST phase separation of temperaturesensitive polymer, poly(N–isopropylacrylamide), in water and in mixed solvents of water and methanol. The transition becomes sharper as the cooperativity of (de)hydration increases. The sharp depression by the LCST co–nonsolvency in the mixed solvents is shown to be caused by the competitive hydrogen bonding of water and methanol seeking for hydrogen–bonding sites on the polymer chains. The degree of hydration and of methanol binding, preferential adsorption coefficients, LCST cloud–point depression are theoretically calculated and compared with the experiments. The shifts of LCST induced by added salts (salting–in and salting-out effect) are briefly discussed from the viewpoint of competing polymer hydration and ionic hydration, with focus on anion binding.

Optical tracking of relaxation dynamics in semi-dilute hydroxypropylcellulose solutions as a precise phase transition probe.

Phase separation of thermo-responsive polymers in solution is a complex process, whose understanding is essential to screen and design materials with diverse technological applications. Here we report on a method based on dynamic light scattering (DLS) experiments to investigate the phase separation of thermo-responsive polymer solutions and precisely define the transition temperature (TPS). Our results are applied on hydroxypropylcellulose (HPC) solutions as an important biosourced green water-soluble polymer. As determined by DLS, the amplitudes of the fast and slow modes of relaxation dynamics evolve as temperature gets closer to the phase transition point eventually leading to phase separation. The evolution of relaxation modes with temperature is markedly different for concentrations below the overlap concentration (c*) (dilute regime), above c* (semi-dilute regime) and above the entanglement concentration (ce). In the three cases though, the fast and slow mode amplitudes undergo a sharp transition in a narrow temperature range, defining accurately the phase separation locus. The results agree with turbidimetric analysis for the phase transition determination but with a better precision. Our results also show that the one-phase dynamics and phase separation dynamics in the two-phase region are only in continuity for c > ce, revealing mechanistic details about the HPC phase separation process. Above TPS we identify a temperature range where the intensity autocorrelation function has a single-exponential shape. In the latter regime, we monitor the growth kinetics of polymer domains and provide clues to rationalize the stabilizing effects of the interfaces leading to the arrested-like phase separation behavior observed for HPC.

Macroscopic and tunable nanoparticle superlattices.

We describe a robust method to assemble nanoparticles into highly ordered superlattices by inducing aqueous phase separation of neutral capping polymers. Here we demonstrate the approach with thiolated polyethylene-glycol-functionalized gold nanoparticles (PEG-AuNPs) in the presence of salts (for example, K2CO3) in solutions that spontaneously migrate to the liquid-vapor interface to form a Gibbs monolayer. We show that by increasing salt concentration, PEG-AuNP monolayers transform from two-dimensional (2D) gas-like to liquid-like phase and eventually, beyond a threshold concentration, to a highly ordered hexagonal structure, as characterized by surface sensitive synchrotron X-ray reflectivity and grazing incidence X-ray diffraction. Furthermore, the method allows control of the inplane packing in the crystalline phase by varying the K2CO3 and PEG-AuNPs concentrations and the length of PEG. Using polymer-brush theory, we argue that the assembly and crystallization is driven by the need to reduce surface tension between PEG and the salt solution. Our approach of taking advantage of the phase separation of PEG in salt solutions is general (i.e., can be used with any nanoparticles) leads to high-quality macroscopic and tunable crystals. Finally, we discuss how the method can also be applied to the design of orderly 3D structures.

A multi-fluid model for microstructure formation in polymer membranes.

We develop a multi-fluid model for a ternary polymer solution using the Rayleighian formalism of Doi and Onuki, and give an efficient pseudo-spectral method for solving both the diffusion and momentum equations that result. Subsequently, we find that the numerical simulation is capable of describing systems at the micron length-scale and easily reaches millisecond time-scales. In addition, we characterize the model thermodynamics and kinetics including the (i) phase behavior, (ii) structure of the interfaces, (iii) mutual diffusion coefficients, (iv) bulk spinodal decomposition kinetics with and without hydrodynamics and (v) spinodal decomposition in the presence of an interface with a non-solvent bath. We obtain good qualitative agreement with the expected thermodynamic and kinetic behavior. We also show that a linear stability analysis of the diffusion equation quantitatively predicts the fastest growing mode obtained from simulation and gives insight into the phase separation process relevant for the evolution of microstructure in phase-separating ternary polymer solutions.

Influence of functionalized side chains of polythiophene diblock copolymers on the performance of CdSe quantum dot hybrid solar cells

The incorporation of functional groups into the side chains of polythiophenes can improve the phase separation of polymer : nanoparticle hybrid solar cells (HSCs).

Size-Tunable Low Molecular Weight Pectin-Based Electrospun Nanofibers Blended with Low Content of Poly(ethylene oxide)

Pectin, a natural plant polysaccharide, holds great potential for biomedicine. Developing low molecular weight (Mw) pectin-based nanofibers is desirable for biomedical applications in which fast degradation and elimination of polymer from the body are required. Here, we report the first work on fabricating low Mw pectin-based nanofibers through electrospinning, among which the content of carrier polymer, poly(ethylene oxide) (PEO), can be minimized to 10%. Surfactant (Triton X-100), high polymer concentration and cosolvent were essential to electrospin bead-free nanofibers at low PEO content. The size of pectin nanofibers was dependent on polymer concentration and cosolvent. The presence of cosolvent inhibited the crystallization of PEO, but enhanced the crystallization of pectin. Meanwhile, glycerol as cosolvent could lead to phase separation of polymers. This work provides a new prospective for the fabrication of low Mw pectin nanofibers suitable for in vivo applications with the demand of fast degradation.

束状ゲルファイバーによる細胞接着制御

Hydrogels have attracted much attention for their biocompatibility and tunable properties for use in tissue engineering and regenerative medicine. Cellular adhesion and organization can be controlled by the microstructure of the scaffold. Here, we describe a new cellulose-based bundled hydrogel fiber fabricated by a dynamic microfluidic gelation system that utilizes a phase-separated polymer blend solution and a co-flow microfluidic device. In addition, multi-walled carbon nanotubes were embedded to enhance the mechanical and electrical properties of the gel fibers. Using normal human dermal fibroblasts, we demonstrated the bundled gel fibers facilitate cellular attachment and orientation. These results demonstrate that the bundled gel fiber may be useful in tissue engineering applications as a cell scaffold with tunable properties.

Angle-independent colored materials based on the Christiansen effect using phase-separated polymer membranes

Angle-independent colored materials based on Christiansen effect was successfully prepared using phase-separated polymer membrane and thermotropic liquid crystal. Because this system displays angle-independent color and can act as a multi-color polymer-dispersed liquid crystal, I believe that this system may be applicable for energy-saving multi-color displays.

Reversible Monolayer/Spheroid Cell Culture Switching by UCST-Type Thermoresponsive Ureido Polymers.

Multicellular spheroids have been studied in the fields of oncology, stem cell biology, and tissue engineering. In this study, we found a new polymer material for thermo-controlled spheroid/monolayer cell culture switching. The polymers that have pendant ureido groups (ureido polymers) exhibited upper critical solution temperature-type phase separation behavior. Cells in monolayer culture were converted to spheroids by the addition of ureido polymers below phase separation temperature (Tp). Time-lapse observations indicated that cells began to migrate and aggregate to form the spheroids to avoid contact with phase-separated polymer (coacervates) on the surface of the culture dish. We supposed that the coacervates seemingly suppressed interaction between cell and the dish surface or extracellular matrices. By increasing culture temperature above Tp, the spheroids began to collapse into a monolayer of cells due to dissolution of the coacervates. These results indicated that cell morphology could be repeatedly switched by changing the culture temperature in the presence of ureido polymers.

Multicore-shell nanofiber architecture of polyimide/polyvinylidene fluoride blend for thermal and long-term stability of lithium ion battery separator

Li-ion battery, separator, multicoreshell structure, thermal stability, long-term stability. A nanofibrous membrane with multiple cores of polyimide (PI) in the shell of polyvinylidene fluoride (PVdF) was prepared using a facile one-pot electrospinning technique with a single nozzle. Unique multicore-shell (MCS) structure of the electrospun composite fibers was obtained, which resulted from electrospinning a phase-separated polymer composite solution. Multiple PI core fibrils with high molecular orientation were well-embedded across the cross-section and contributed remarkable thermal stabilities to the MCS membrane. Thus, no outbreaks were found in its dimension and ionic resistance up to 200 and 250 °C, respectively. Moreover, the MCS membrane (at ~200 °C), as a lithium ion battery (LIB) separator, showed superior thermal and electrochemical stabilities compared with a widely used commercial separator (~120 °C). The average capacity decay rate of LIB for 500 cycles was calculated to be approximately 0.030 mAh/g/cycle. This value demonstrated exceptional long-term stability compared with commercial LIBs and with two other types (single core-shell and co-electrospun separators incorporating with functionalized TiO2) of PI/PVdF composite separators. The proper architecture and synergy effects of multiple PI nanofibrils as a thermally stable polymer in the PVdF shell as electrolyte compatible polymers are responsible for the superior thermal performance and long-term stability of the LIB.

Optimized phase separation in low-bandgap polymer:fullerene bulk heterojunction solar cells with criteria of solvent additives

We investigate a correlation between the type of solvent additives (SAs) with specific criteria such as aromatic additives (AAs) and non-aromatic additives (NAAs) and phase separation in the bulk heterojunction (BHJ) films comprising low-band gap polymer and fullerene derivatives. When AAs are used as SAs, the geometrical structures (π-π and lamellar stacking) of aggregated polymer chains do not significantly change. However, NAAs increase the lamellar stacking distance through a strong interaction with non-aromatic segments of polymers. Therefore, a well-phase separated BHJ morphology with the finer fibrils is developed, thereby leading to balanced charge mobilities and a reduced charge recombination in BHJ solar cells. Finally, the optimized solar cell exhibits a high power conversion efficiency of 7.9%.

Versatile synthesis of high performance, crosslinked polymer microcapsules with encapsulated n-hexadecane as heat storage materials by utilizing microsuspension controlled/living radical polymerization (ms CLRP) of ethylene glycol dimethacrylate with the SaPSeP method

When encapsulated n-hexadecane (HD) in polymer microcapsules is used for heat storage material, two problems that are the decreasing of latent heat (J/g-capsules, J/g-HD) and the generating of supercooling (ΔTs: °C) should be overcome. In previous studies, it was suggested that more polar polymer capsule shell and larger particle size were useful to improve the two problems, respectively. Based on the idea, first, 6-μm-sized, polar poly(ethylene glycol dimethacrylate) (PEGDM) particles with encapsulated HD were prepared by microsuspension conventional radical polymerization (ms CRP) with Self-assembly of Phase-Separated Polymer (SaPSeP) method that the authors proposed. As expected, the heat of solidification of the encapsulated HD (ΔHs* = 220 J/g-HD) was almost the same as that of pure HD (ΔHso = 230 J/g-HD) but the supercooling was still observed (ΔTs = 10 °C). Larger PEGDM particles (11- and 42-μm in diameter) prepared by the ms CRP “included” HD in the inside, but did not “encapsulate” it ideally, because they had porous structures. Ideal large PEGDM microcapsules (31 μm in diameter) with “encapsulated” HD were successfully prepared by utilizing microsuspension activators generated by electron transfer atom transfer radical polymerizations (ms AGET ATRP), which is one of controlled/living radical polymerization. They had excellent heat storage abilities (ΔHs = 105 J/g-capsules; ΔHs* = 210 J/g-HD; ΔTs = 6 °C).

(Invited) The Implications of Cation Clustering in Anion Exchange Membranes on Conductivity and Mechanical Properties

The potential of anion exchange membrane (AEM) fuel cells to provide inexpensive compact power from a wider variety of fuels than is possible with a proton exchange membrane (PEM) fuel cell, has continued to drive the research interest in this area. Alkaline catalysis in fuel cells has been demonstrated with non-precious metal catalysts, and with a variety of fuels beyond H2 and methanol. Alkaline fuel cells (AFCs), based on aqueous solutions of KOH, have serious drawbacks associated with system complexity and carbonate formation. Anion exchange membrane (AEMs) fuel cells have a number of advantages over both PEM fuel cells and traditional AFCs; however, although anionic conductivity in AEMs can be comparable to PEMs the chemical stability of membrane attached cations in hydroxide is still not always sufficient for practical applications. Recently, it has been recognized that a number of advanced cations, may give AEMs the needed chemical stability. In some circumstances simple trimethyl benzyl ammonium cations are stable up to 60oC allowing us to being to study hydroxide and water transport in these systems. We use in-plane conductivity and multi-nuclear PFGSE to measure self-diffusion coefficients of the water and where possible, the ion, i.e. F-, carbonate and bicarbonate. Together with temperature and RH dependent SAXS we couple this information with the morphological changes in the materails. By their nature these organic cations form dipoles, which have a tendency to interact, see Figure below for a trimethylbenzyl cation with bromide for illustrative purposes. For maximum ion transport the cation should be distributed along the polymer chain, however, cation clustering is a common phenomena. It occurs in phase separated diblock polymers when an attempt is made to raise the IEC, no net increase is observed in ionic conductivity above a certain IEC. In many other less structured polymers it occurs in the fully humidified state when the distributed disordered cations order in agglomerates at a disorder/order Tδ. This Tδ is often observed in the operating temperature range expected for a device, in both DMA, DSC, and broadband electric spectroscopy. Interestingly, even though the SAXS clearly shows an agglomeration on the nano-scale, little difference is seen in the bulk conductivity with temperature. However, steric hindernce effects are expected to discourage aggregation, and may allow the cation to tune all properties of the AEM. As these phenomena are so prevalent in AEM materials the implications and science behind them are being investigated by us and will be discussed in this presentation. The implications of more complex cations proposed for stability in AEMs will be described. Figure 1

High-temperature functional analysis of bitumen modified with composite of nano-SiO2 and styrene butadiene styrene polymer

ABSTRACTIn recent decades, researchers have always considered the production of modified bitumen that could perform suitably in both high and low temperatures. One bitumen modifier is styrene butadiene styrene (SBS) polymer. Because bitumen modified with styrene butadiene styrene polymer does not show expected field performance in high and low temperatures largely due to phase separation of bitumen and polymer, the present research study is an attempt to use the composite of nano-SiO2 and styrene butadiene styrene polymer in modification of bitumen and analyze its high-temperature performance. The study revealed that adding nano-SiO2 to bitumen modified with SBS polymer resulted to an improvement of complex modulus, phase angle, resistance potential against rutting, storage modulus, loss modulus, and high-temperature functional performance in general. Additionally, the study uncovered that adding nano-SiO2 with 3% and 4% of bitumen weight, compared with other composites, considerably improved the high-temperature functional performance of bitumen modified with styrene butadiene styrene polymer. As 4.5%SBS+4%nano-SiO2 could not estimate less than 3 Pa.sec rotational viscosity in 135°C, 4.5%SBS+3%nano-SiO2 is offered as the optimal composite. The study is the first one in its own type in the world and is, therefore, innovative.

Modelling and numerical simulation of phase separation in polymer modified bitumen by phase-field method

In this paper, a phase-field model with viscoelastic effects is developed for polymer modified bitumen (PMB) with the aim to describe and predict the PMB storage stability and phase separation behaviour. The viscoelastic effects due to dynamic asymmetry between bitumen and polymer are represented in the model by introducing a composition-dependent mobility coefficient. A double-well potential for PMB system is proposed on the basis of the Flory-Huggins free energy of mixing, with some simplifying assumptions made to take into account the complex chemical composition of bitumen. The model has been implemented in a finite element software package for pseudo-binary PMBs and calibrated with experimental observations of three different PMBs. Parametric studies have been conducted. Simulation results indicate that all the investigated model parameters, including the mobility and gradient energy coefficients, interaction and dilution parameters, have specific effects on the phase separation process of an unstable PMB. In addition to the unstable cases, the model can also describe and predict stable PMBs. Moreover, the phase inversion phenomenon with increasing polymer content in PMBs is also well reproduced by the model. This model can be the foundation of an applicable numerical tool for prediction of PMB storage stability and phase separation behaviour.

Control of Polymer Phase Separation by Roughness Transfer Printing for 2D Microlens Arrays.

Great efforts have been devoted to the control of phase separation between blended polymers in terms of the advantages for engineering functional topologies. A simple and straightforward pathway through roughness transfer printing (RTP) is proposed to realize the control of polymer phase separation. The additional roughness difference, which is introduced by trace agarose transferred from a hydrogel stamp, offers a great effect on the rate of nucleation and coalescence orientation of polymethylmethacrylate (PMMA) protrusions grown from a polydimethylsiloxane (PDMS) network. Using a particular topography of agarose stamp and a proper growth time in toluene atmosphere, a 2D microlens array with high uniformity is obtained that shows great potential for optical applications. Moreover, the control of polymer phase separation was successfully extended to the collection and identification of fingerprints with a high degree of replication.

Preparation and characterization of ECTFE hollow fiber membranes via thermally induced phase separation (TIPS)

Abstract A porous poly (ethylene-chlorotrifluoroethylene) (ECTFE) membrane was prepared and evaluated in this study. Initially, solvent screening revealed diethyl phthalate (DEP) and glycerol triacetate (GTA) as proper solvents for the preparation of homogenous ECTFE solutions with the required properties for fabricating a hollow fiber membrane. The thermodynamic phase diagrams for both systems (ECTFE/DEP and ECTFE/GTA) showed a liquid–liquid (L-L) phase separation region, which is needed for a bicontinuous structure, prior to solid–liquid (S-L) phase separation (polymer crystallization). The ECTFE hollow fiber membranes were prepared by a thermally induced phase separation (TIPS) method using a unary solvent (DEP or GTA). The morphologies of hollow fiber membranes were observed by scanning electron microscopy (SEM) and it was observed that a bicontinuous structure was formed through L-L phase separation. The effect of the solvent types on properties of the prepared membrane such as water permeability and mechanical strength was discussed in detail. Moreover, the spherulite growth rate and crystallization degree were measured to assess the differences in the mechanical properties of the membranes prepared using DEP and GTA. In this study, with a polymer concentration of 20 wt%, the membrane showed a superior water flux and comparable mechanical properties with the ECTFE membranes already reported in published papers. Furthermore, the chemical resistance properties of ECTFE hollow fiber membranes were evaluated using the harsh treatments.

Influence of the processing method and antimicrobial agents on properties of starch‐gelatin biodegradable films

AbstractBiodegradable films based on corn starch (CS), bovine gelatin (BG), glycerol as a plasticizer, and lysozyme or N‐α‐lauroyl‐l‐arginine ethyl ester monohydrochloride (LAE) as antimicrobial agents were obtained by both extension‐drying (casting) of the aqueous dispersions and melt blending and compression moulding. Microstructural analyses revealed the lack of miscibility between CS and BG, which implied polymer phase separation, with the formation of domains rich in each polymer, with different arrangements for casting and melt blending processes. Thermoprocessed films were more permeable to water vapour (60% − 115%) and oxygen (70% − 355%) compared to the corresponding cast films and exhibited lower stiffness (50% − 75%) and resistance to break (17% − 33%) and greater extensibility (150% − 190%) than casting films. LAE improved the water vapour barrier and reduced the oxygen barrier of both kinds of films, whereas the opposite effect was observed for lysozyme. Antimicrobial activity against Listeria innocua was observed for formulations containing LAE processed by both casting and compression moulding, all of which exhibited a bactericidal effect. © 2016 Society of Chemical Industry