Symmetric Poly Research Articles

Role of Unimers to Polymersomes Transition in Pluronic Blends for Controlled and Designated Drug Conveyance.

This study investigates the nanoscale self-assembly from mixtures of two symmetrical poly(ethylene oxide)-poly(propylene oxide)-pol(ethylene oxide) (PEO-PPO-PEO) block copolymers (BCPs) with different lengths of PEO blocks and similar PPO blocks. The blended BCPs (commercially known as Pluronic F88 and L81, with 80 and 10% PEO, respectively) exhibited rich phase behavior in an aqueous solution. The relative viscosity (ηrel) indicated significant variations in the flow behavior, ranging from fluidic to viscous, thereby suggesting a possible micellar growth or morphological transition. The tensiometric experiments provided insight into the intermolecular hydrophobic interactions at the liquid-air interface favoring the surface activity of mixed-system micellization. Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) revealed the varied structural morphologies of these core-shell mixed micelles and polymersomes formed under different conditions. At a concentration of ≤5% w/v, Pluronic F88 exists as molecularly dissolved unimers or Gaussian chains. However, the addition of the very hydrophobic Pluronic L81, even at a much lower (<0.2%) concentration, induced micellization and promoted micellar growth/transition. These results were further substantiated through molecular dynamics (MD) simulations, employing a readily transferable coarse-grained (CG) molecular model grounded in the MARTINI force field with density and solvent-accessible surface area (SASA) profiles. These findings proved that F88 underwent micellar growth/transition in the presence of L81. Furthermore, the potential use of these Pluronic mixed micelles as nanocarriers for the anticancer drug quercetin (QCT) was explored. The spectral analysis provided insight into the enhanced solubility of QCT through the assessment of the standard free energy of solubilization (ΔG°), drug-loading efficiency (DL%), encapsulation efficiency (EE%), and partition coefficient (P). A detailed optimization of the drug release kinetics was presented by employing various kinetic models. The [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] MTT assay, a frequently used technique for assessing cytotoxicity in anticancer research, was used to gauge the effectiveness of these QCT-loaded mixed nanoaggregates.

Parameterization of minimal order strongly stabilizing controllers for two-link underactuated planar robot with single sensor

This paper investigates the minimal order of strongly stabilizing controllers for a two-link planar robot moving in a vertical plane with a single actuator and sensor, focusing on stabilizing the robot around its upright equilibrium point where both links are upright. By designing an output as the horizontal displacement of a point along the second link’s straight line, existing literature demonstrates that the robot’s strong stabilization problem is equivalent to that of a fourth-order linear plant, featuring two pairs of symmetric real poles and adjustable zeros. In contrast to an existing second-order strongly stabilizing controller tailored to a pair of symmetric real zeros around the origin within a given range, this paper achieves four main contributions. First, this paper obtains a parameterization of second-order strongly stabilizing controllers allowing the positive real zero in an expanded range. Second, this paper considers the plant with a pair of symmetric real zeros around the origin, a double origin zero, and a pair of conjugate imaginary zeros in a unified manner, and presents a more general parameterization of second-order strongly stabilizing controllers accommodating these three types of zeros in a more expanded range. Third, this paper provides a necessary and sufficient condition on these zeros (equivalently, all ranges of the observation point) for the existence of a second-order strongly stabilizing controller. Fourth, this paper demonstrates that a first-order stabilizing controller does not exist for the plant, regardless of its types of zeros, confirming that the minimal order of the strongly stabilizing controllers is two. This paper obtains all feasible regions for the parameters in each parameterization by explicitly expressing the range of each parameter using inequalities in a cascade structure, which makes the inequalities easy to check and verify. The results are applicable to both the Acrobot and Pendubot. The paper validates the theoretical findings through numerical investigations and simulations.

Studies of optical, photophysical, and thermal properties of poly(paraphenylenevinylene) (PPV) polymers with symmetric alkoxy side‐chain lengths for potential application in electronic devices

AbstractOptical, photophysical, and thermal properties of poly(paraphenylenevinylene) (PPV) derivatives of various symmetric alkoxyl substituents were studied with UV–vis and photoluminescence spectroscopy. Molar absorptivity coefficients of the symmetric monomers increased compared to that of hydroquinone and its derivatives. The symmetric polymers exhibited photoluminescence quantum yields in the range of 32%–39% and excited‐state lifetimes of 3.01–3.61 ns. The emission energy values for the calculated band gaps were in the range of 2.16–2.12 eV for the symmetric polymers. The photoluminescent characteristics of these compounds may show great potential in improving the emitting layers of electronic devices. The thermal behavior and heat changes of the symmetric dialkyl PPV polymers were monitored by TGA and DSC. Glass transition temperatures (Tg) for these polymers were observed as being in range of 67–108°C. The heat values of the symmetric dialkyl PPV polymers were found to be in range 220.41–599.98 J/g, and the entropy values of symmetric dialkyl PPV polymers were determined to be in range 0.567–1.754 J/ g °C.Highlights• Symmetric poly(phenylene vinylene) (PPV) derivatives were prepared.• UV–vis spectroscopy was used for optical absorption studies.• Photophysical properties were examined by photoluminescence spectroscopy.• TGA was used for the thermal behavior of symmetric dialkyl PPV polymers.• Heat changes of symmetric dialkyl PPV polymers were investigated by DSC.

An injectable thermosensitive hydrogel encapsulating tetramethylpyrazine nanocrystals alleviates angiogenesis and apoptosis in a choroidal neovascularization mouse model

Neovascular age-related macular degeneration (nAMD) is a leading global cause of blindness characterized by vascular endothelial growth factor (VEGF)-mediated choroidal neovascularization (CNV), in which aberrant pathological angiogenesis extends from the choriocapillaris into the subretinal region. However, the lifelong regime of intraocular anti-VEGF agents, as the front-line treatment for excessive angiogenesis, is not effective for all patients and can induce devastating ocular complications. Thus, it is crucial to develop an available, durable, and affordable drug system capable of overcoming ocular obstacles and enabling the sustained release of a drug to target CNV. Owing to its multitarget properties, tetramethylpyrazine (TMP) has been widely used in clinics for its anti-angiogenic, anti-inflammatory, antioxidant, and anti-fibrotic effects. Yet, its potential clinical use in ocular disorders has been hindered by its lipophilic properties and poor absorption. Herein, we developed and optimized an injectable thermosensitive polymeric hydrogel using the solvent evaporation drying method and the “cold” approach in turn for the controlled release and high drug-loading of TMP nanoparticles, facilitating the sustained release of TMP both in vitro and in vivo. The hydrogel-encapsulated TMP nanocrystals (NCs) were synthesized and characterized by zeta potential, dynamic light scattering, scanning and transmission electron microscopy, and rheometer. The payload of the hydrophobic drug TMP to the symmetrical poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) hydrogel (TMP-NCs-gel) had a porous structure (pore size, 10–200 mm), and the transparent in situ hydrogel system immediately transitioned from the liquid to gel phase when the phase transition temperature was reached. We also demonstrated that the TMP-NCs-gel ameliorated abnormal angiogenesis and repressed photoreceptor apoptosis in vivo without inducing toxicity. Furthermore, the TMP-NCs-gel were observed to accumulate in CNV lesions in vivo, confirming their targeting characterization. Overall, this advanced formulation, combining TMP and an in situ gel system, is promising for AMD treatment and may represent an effective therapeutic strategy for patients with CNV.

Influence of slot/pole number combinations and pole shaping on electromagnetic performance of permanent magnet machines with unbalanced north and south poles

AbstractThe influences of slot/pole number combinations on electromagnetic performances, including flux linkage, inductance, and torque ripple harmonic components etc., resulting from unbalanced characteristics between north and south poles in concentrated winding permanent magnet (PM) machines with symmetrical and asymmetric rotor pole shaping methods are theoretically analysed and experimentally validated in this paper. It shows that for the PM machines with odd number of coils per phase per submachine, including consequent pole (CP) and surface‐mounted PM (SPM) machines, the influences of unbalanced pole characteristics can lead to additional torque ripple harmonics due to additive effects in windings, but can be cancelled in other machines. Compared with symmetrical pole shaping method, asymmetric pole shaping method can result in lower torque ripple for CPPM machines with odd number of coils per phase per submachine, while symmetrical and asymmetric pole shapes have similar effects on torque ripple reduction for other CPPM machines and all the SPM machines. The findings have been validated by finite element analyses on 12‐slot/8‐pole, 12‐slot/10‐pole, 9‐slot/6‐pole, and 12‐slot/14‐pole machines, and by experiments with 12‐slot/8‐pole and 12‐slot/10‐pole CPPM prototypes.

Competitive Mechanism of Stereocomplexes and Homocrystals in High-Performance Symmetric and Asymmetric Poly(lactic acid) Enantiomers: Qualitative Methods.

To systematically explore the critical contributions of both molecular weights and crystallization temperature and chain length and molar ratios to the formation of stereocomplexes (SCs), our group quantitatively prepared a wide MW range of symmetric and asymmetric poly(lactic acid) (PLA) racemic blends, which contains L-MW PLLA with M n > 6k g/mol. The crystallinity and relative fraction of SCs increase with T c, and the SCs are exclusively formed at T c > 180 °C in M/H-MW racemic blends. When MWs of one of the enantiomers are over 6k and less than 41k, multiple stereocomplexation is clear in the asymmetric racemic blends and more ordered SCs form with less entanglement or the amorphous region compared to those for the MW of the enantiomers over 41k in the symmetric/asymmetric enantiomers. When the MW of the blends is more than 41k, SCs and homocrystals (HCs) coexist in the symmetric enantiomers and the multicomplexation can restrict the asymmetric enantiomers. This study provides a deep comprehensive insight into the stereocomplex crystallization mechanism of polymers and provides a reference value for future research attempting to prepare stereocomplex materials.

Solution and Solid-State Behavior of Amphiphilic ABA Triblock Copolymers of Poly(acrylic acid-stat-styrene)-block-poly(butyl acrylate)-block-poly(acrylic acid-stat-styrene)

A combination of statistical and triblock copolymer properties is explored to produce stable aqueous polymer dispersions suitable for the film formation. In order to perform an extensive structural characterization of the products in the dissolved, dispersed, and solid states, a wide range of symmetrical poly(acrylic acid-stat-styrene) x -block-poly(butyl acrylate) y -block-poly(acrylic acid-stat-styrene) x , poly(AA-st-St) x -b-PBA y -b-poly(AA-st-St) x , (x = 56, 108 and 140, y = 100-750; the AA:St molar ratio is 42:58) triblock copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) solution polymerization using a bifunctional symmetrical RAFT agent. It is demonstrated that the amphiphilic statistical outer blocks can provide sufficient stabilization to largely hydrophobic particles in aqueous dispersions. Such a molecular design provides an advantage over copolymers composed only of homoblocks, as a simple variation of the statistical block component ratio provides an efficient way to control the hydrophilicity of the stabilizer block, which ultimately affects the copolymer morphology in solutions and solid films. It was found by small-angle X-ray scattering (SAXS) that the copolymers behaved as dissolved chains in methylethylketone (MEK) but self-assembled in water into stable and well-defined spherical particles that increased in size with the length of the hydrophobic PBA block. These particles possessed an additional particulate surface structure formed by the statistical copolymer stabilizer block, which self-folded through the hydrophobic interactions between the styrene units. SAXS and atomic force microscopy showed that the copolymer films cast from the MEK solutions formed structures predicted by self-consistent field theory for symmetrical triblock copolymers, while the aqueous dispersions formed structural morphologies similar to a close-packed spheres, as would be expected for copolymer particles trapped kinetically due to the restricted movement of the blocks in the initial aqueous dispersion. A strong correlation between the structural morphology and mechanical properties of the films was observed. It was found that the properties of the solvent cast films were highly dependent on the ratios of the hard [poly(AA-st-St)] and soft (PBA) blocks, while the aqueous cast films did not show such a dependence. The continuous phase of hard blocks, always formed in the case of the aqueous cast films, produced films with a higher elastic modulus and a lower extension-to-break in a comparison with the solvent-cast films.

Solute dynamics in a block copolymer: effect of additives and temperature

The solute dynamics in a symmetrical poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) (PEO-PPO-PEO) triblock copolymer, P-123 were studied in aqueous and saline solutions as a function of additives, temperature using spectroscopic techniques. We have chosen a hydrophobic solute Coumarin-6 (C-6) as probe to study the photophysics and rotational dynamics in the above systems. We found that the rotational dynamics of C-6 is hindered in saline solution compared to that in aqueous solution of P-123. Therefore, in the saline solution of P-123, C-6 faced more restricted environment compared to the aqueous solution of P-123. In the absence of saline, at a temperature higher than cmt, we observed that addition of 0.02 M n-hexanol decreases the rotational relaxation time compared to that in P-123. Whereas, addition of 0.02 M n-hexylamine the rotational relaxation remains almost same compared to that in P-123. Therefore, n-hexanol affect more on the solute dynamics compared to n-hexylamine because of its preferential partitioning in the micellar phase owing to its greater hydrophobic ranking compared to n-hexylamine. In the saline solution we observed that addition of 0.02 M n-hexanol on P-123 solution affect more on the rotational dynamics of C-6 compared to the addition of 0.02 M n-hexylamine.

Phase Control of Colloid-like Block Copolymer Micelles by Tuning Size Distribution via Thermal Processing

The formation of a Frank–Kasper (FK) phase in a one-component block copolymer (bcp) has been attributed to the sufficiently large conformational asymmetry parameter that leads to the deformation of the micellar core into the polyhedral shape templated by the Voronoi cells for relieving the packing frustration of the coronal blocks. Here we present the insight into the evolution of body-centered cubic (BCC) and Laves C14 phases from the corresponding metastable liquidlike packing (LLP) phases in a conformationally symmetric poly(2-vinylpyridine)-block-poly(dimethylsiloxane) (P2VP-b-PDMS) forming the colloid-like micelle with a hard P2VP core and a soft PDMS corona at the temperature of micelle ordering (Tgcorona < Ta < Tgcore). Different thermal processing conditions were applied to produce four distinct types LLP phase characterized by different average micelle size and size dispersity. The LLP phase was found to transform to BCC, C14 and a reorganized LLP phase with increasing polydispersity of particle size, showing the existence of a proper range of size dispersity for the formation of the Laves phase. The real-space analysis of the local environments of the particles revealed that the C14 phase can accommodate the particles with a broader range of interparticle distance and a less uniform local environment, such that the PDMS coronal blocks of the micelles with greater size dispersity suffered a lower degree of packing frustration when they organized into a C14 lattice. In view of the colloid-like nature of the micelle, a size fractionation process found in the crystallization of polydisperse colloidal particles was proposed as the mechanism for directing the effective development of C14 phase from the LLP phase. Due to the metastable nature of the ordered phases, their order–disorder transition temperatures were found to depend strongly on the structures of the LLP phases from which they developed and a strong memory effect underlying the phase transitions was identified.

Magnetic Equivalent Circuit Modelling of Synchronous Reluctance Motors

This paper proposes a modelling technique for Synchronous Reluctance Motors (SynRMs) based on a generalized Magnetic Equivalent Circuit (MEC). The proposed model can be used in the design of any number of stator teeth, rotor poles, and rotor barrier combinations. This technique allows elimination of infeasible machine solutions during the initial machine sizing stage, resulting in a lower cohort of feasible machine solutions that can be further optimized using finite element methods. Therefore, saturation effects, however, are not considered in the modelling. This paper focuses on modelling a generic structure of the SynRM in modular form and is then extended to a full SynRM model. The proposed model can be iteratively used for any symmetrical rotor pole and stator teeth combination. The developed technique is applied to model a 4-pole, 36 slot SynRM as an example, and the implemented model is executed following a time stepping strategy. The motor characteristics such as flux distribution and torque of the developed SynRM model is compared with finite elemental analysis (FEA) simulation results.

Aggregation behavior of symmetric poly(n‐butyl acrylate)‐block‐poly(acrylic acid) on subphases of different ionic strengths

AbstractInfluences of subphase pH value and ionic strength (NaCl concentration) on the aggregation behavior of a symmetric diblock polyelectrolyte poly(n‐butyl acrylate)‐block‐poly(acrylic acid) (PnBA‐b‐PAA) at the air/water interface and its Langmuir–Blodgett (LB) films were studied. With the increase of subphase pH value, surface pressure–molecular area isotherms of PnBA‐b‐PAA monolayers shift toward smaller area due to the gradually enhanced ionization and underwater solubility of hydrophilic PAA chains. All the initial LB films transferred from different subphases with/without NaCl (before monolayer compression) exhibit the densely mixed structures of worm‐like aggregates and circular micelles, which indicates that the aggregate formation belongs to the spontaneous mechanism. The micelle core diameters in the LB films increase with the increase of subphase pH value, owing to the enhanced PAA chain solubility and PnBA block aggregation. Under acidic condition, micelle cores are slightly larger upon addition of NaCl due to the enhanced underwater solubility of the uncharged PAA chains triggered by their possible interaction with Cl−. Under neutral/alkaline conditions, micelle cores are also larger upon addition of NaCl, which is attributed to the electrostatic shielding effect of Na+. Upon compression, the LB films prepared under neutral/alkaline conditions exhibit the predominantly large circular micelles.

Suppression of Torque Ripple for Consequent Pole PM Machine by Asymmetric Pole Shaping Method

Consequent-pole (CP) permanent magnet (PM) machines have attracted considerable interest as a means of reducing machine cost through a marked reduction in the volume of PM required to meet a particular torque specification. However, the presence of a large torque ripple that can result from the CPPM structure can hinder their adoption in some applications, especially for the dominant third-order torque ripple. Although several design-specific modifications have been proposed to ameliorate torque ripple, the generalized principles underpinning this behavior have not been fully established. In this article, it will be illustrated that an aggregation of the fluctuations in inductance, back electromotive force, and cogging torque contributes to increased torque ripple. Meanwhile, an asymmetric pole shaping method is proposed to reduce the torque ripple, taking the dominant third-order torque ripple as an example. Both simulated and experimental results of the 12-slot&#x002F;8-pole prototypes show that compared to the symmetrical pole shaping model and the plain pole model, the proposed asymmetric shaping method is effective in reducing torque ripple.

Tammann Analysis of the Molecular Weight Selection of Polymorphic Crystal Nucleation in Symmetric Racemic Poly(lactic acid) Blends

Tammann Analysis of the Molecular Weight Selection of Polymorphic Crystal Nucleation in Symmetric Racemic Poly(lactic acid) Blends

Direct and indirect effects of membrane pore size on fouling development in a submerged membrane bioreactor with a symmetric chlorinated poly (vinyl chloride) flat-sheet membrane

Membrane bioreactors (MBRs) have been recognized as a promising wastewater treatment technique because of their superior solid–liquid separation performance; however, fouling development remains a concern. In this study, the relationship between membrane pore size and fouling development is investigated using originally prepared chlorinated polyvinyl chloride (CPVC) flat-sheet membranes with different pore sizes in MBRs; further, the mechanism of fouling development is demonstrated. Under the conditions in this study, the optimal membrane pore size for suppressing fouling development was determined to be in the range of 0.31–0.57 µm. It was also demonstrated that irreversible fouling is closely related to the capture of protein-like compounds inside the membrane; in contrast, it was considered that reversible fouling is caused by gel and cake layers formed on the membrane surface. Moreover, it was indicated that the membrane pore size directly and indirectly affected both reversible and irreversible fouling through the mutual relationship with other membrane characteristics such as the surface roughness. Finally, it is concluded that the optimal membrane pore size for suppressing fouling development is determined by the total filtration resistance caused by irreversible and reversible fouling phenomena.

Electrochromic polymer with asymmetric substituents – Inhibit aggregation and modify respond speed

The asymmetric structure could improve the electronic properties of molecules through changing the molecular packing style. In this paper, a conjugated molecule EDOT-BE-1F (5,5′-(2-fluoro-5-(hexyloxy)-1,4-phenylene)bis(2,3-dihydrothieno[3,4–b] [1,4]dioxine)) was constructed based on the asymmetric chains (hexoxyl group and fluorine atom) para-substituted para-phenylene, and polymerized to poly(EDOT-BE-1F) by electrochemical method. The asymmetric chains endow molecule possess compromised configuration, making poly(EDOT-BE-1F) display different film morphology, hydrophobic property and molecular aggregation from symmetric polymers. The electrochromic result demonstrate that the asymmetric poly(EDOT-BE-1F) could achieve color change between red and blue with the fast respond time (0.9 s) and high coloration efficiency (305C−1 cm2). Through the comparison of asymmetric poly(EDOT-BE-1F) and symmetric poly(EDOT-BE-O), we found the decreased molecular aggregation has positive influence on respond speed and coloration efficiency of polymer during reduction process, however, displays no obvious help on that of polymer during oxidation process. The relationship between molecular aggregation and electrochromic properties of conjugated polymer is discussed in detail. The result prove that the asymmetric chains could effectively modify the molecular aggregation and balance the charge transport and ion migration, which provide a simple method to modify the performance of polymer.

Fast‐converging robust PR‐P controller designed by using symmetrical pole placement method for current control of interleaved buck converter‐based PV emulator

AbstractIn this study, the interleaved buck converter‐based photovoltaic (PV) emulator current control is presented. A proportional‐resonant‐proportional (PR‐P) controller is designed to resolve the drawbacks of conventional PI controllers in terms of phase management, which means balancing currents evenly between active phases to avoid thermally stressing and provide optimal ripple cancelation in the presence of parameter uncertainties. The resonant path of the controller (PR) with a constant proportional unity gain is designed considering the changing dynamics of a notch filter by pole placement method (adding mutually complementary poles to the notch transfer function) at PWM switching frequency. The proportional gain path (P) of the controller is used to determine the compatibility of the controller with parameter uncertainty of the phases and designed by utilizing loop‐shaping method. The proposed controller shows superior performance in terms of 10 times faster‐converging transient response, zero steady‐state error with significant reduction in current ripple. Equal load sharing that constitutes the primary concern in multiphase converters is achieved with the proposed controller. Implementing of robust control theory involving comprehensive time and frequency domain analysis reveals 13% improvement in the robust stability margin and 12‐degree bigger phase toleration with the PR‐P controller. In addition to these, the proposed unconventional design process of the controller reduces the computational complexity and provides cost‐effectiveness and simple implementation. Moreover, implementing of auxiliary resistor‐capacitor (RC) circuits parallel with the inductors to sense the current in each phase removes the need for current measurement sensors that contribute to overall cost of the system.

A Novel Asymmetric-Magnetic-Pole Interior PM Machine With Magnet-Axis-Shifting Effect

This article proposes a novel asymmetric-magnetic-pole interior permanent magnet (AMP-IPM) machine, which is geometrically characterized by a combination of dual-layer reluctance and flat-type PM rotor structures. The design concept of “asymmetric-magnetic-pole” is introduced to achieve a magnet-axis-shifting effect, namely, the magnet <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis is shifted to make PM and reluctance torque components approximately maximize at similar current angles. Consequently, the resultant torque can be further improved without increasing magnet usage. The machine topology is first introduced. The electromagnetic characteristics of the proposed AMP-IPM machine are then investigated and compared with those of the benchmark conventional IPM machine with symmetrical magnetic poles, with similar sizing and PM usage. Finally, an AMP-IPM machine prototype is manufactured and tested, which confirms the feasibility of the proposed AMP design for the torque performance improvement.

Sinter-free inkjet-printed PEDOT:PSS/WO3/PEDOT:PSS flexible valency change memory

With the rapid proliferation of consumer electronics in our day to day lives, there is an ever increasing demand for flexible electronic devices which are low cost, easy to fabricate and deliver reliable performance. In this work, we report fabrication of symmetric poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/WO3/PEDOT:PSS memory cells by inkjet printing on transparent, flexible polyethylene naphthalate (PEN) substrates. The cells show resistive switching behavior with two stable resistance states. The current conduction across the interface between the PEDOT:PSS electrode and dielectric WO3 is determined by localized filamentary features which is space charge limited in the high resistance state, facilitated through the migration of oxygen vacancies at low voltages (<2 V) whereas Schottky emission dominates the current conduction for higher voltages (>2 V). The cells show good retentivity and endurance (>6000 cycles). The cells are entirely sinter free and no electroforming is required to activate them. These characteristics make them suitable for the next generation of flexible non-volatile memory devices.

Graphoepitaxy of Symmetric Six-Arm Star-Shaped Poly(methyl methacrylate)-block-Polystyrene Copolymer Thin Film.

The authors perform directed self-assembly based on graphoepitaxy of symmetric six-arm star-shaped poly(methyl methacrylate)-block-polystyrene copolymer [(PMMA-b-PS)6 ] thin film. The affinity between each block and the trench wall is adjusted by using polymer brushes or selective gold (Au) deposition. When the surface of the trench is strongly selective for the PMMA block, (n+0.75)L0 thick (n is the number of the lamellae, L0 is lamellar domain spacing) lamellae parallel to the trench wall are formed at each side, while nanotubes are formed away from the trench wall. However, for a trench grafted with PS brushes, nanotubes are formed beside (n+0.25)L0 thick lamellar layers. By adjusting the trench width (W) and the affinity between the block and the wall, various dual nanopatterns consisting of lines and nanotubes are fabricated. Moreover, when the trench wall is selectively deposited by Au, asymmetric dual nanopattern is formed, where different numbers of lines exist on each side wall, while nanotubes are formed in the middle of the trench. The observed morphologies depending on the commensurability condition between W and L0 are consistent with predictions by self-consistent field theory.

Influence of Charge Fraction on the Phase Behavior of Symmetric Single-Ion Conducting Diblock Copolymers.

A series of symmetric poly[(oligo(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) propyl sodium sulfonate methacrylate)]-block-polystyrene (PsOEGMA-PS) diblock copolymers were synthesized as a model system to probe the effect of charge fraction on the phase behavior of charged-neutral single-ion conducting diblock copolymers. Small-angle X-ray scattering (SAXS) experiments showed that increasing the charge fraction does not alter the ordered phase morphology (lamellar) but increases the order-disorder transition temperature (TODT) significantly. Additionally, the effective Flory-Huggins interaction parameter (χeff) was found to increase linearly with the charge fraction, similar to the case of conventional salt-doped diblock copolymers. This indicates that the effect of counterion solvation, attributed to the significant mismatch between the dielectric constant of each block, provides the dominant effect in tuning the phase behavior of this charged diblock copolymer. We therefore infer that electrostatic cohesion (local charge ordering induced by Coulombic interactions), which is predicted to suppress microphase separation and lead to asymmetric phase diagrams, only plays a minor role in this model system.