Effect of cosolvents on the phase separation of polyelectrolyte complexes.

Evidence is shown that cosolvent mixtures control the coacervation of mixtures of oppositely charged polyelectrolytes. Binary and ternary solvent mixtures lead to non-monotonic solubility as a function of the average dielectric constants of the solvent mixtures. These data are rationalized by considering both electrostatic-driven phase separation and solvophobic-driven phase separation using group contribution effects on solubility parameters. These estimates are introduced into an effective Flory-Huggins interaction parameter within the framework of Voorn-Overbeek theory with variable dielectric constants and temperature dependences. Despite its simplicity, the model recovers salient experimental observations not only on their coacervate stabilities, but also on their lower critical solution temperature behaviors. These observations highlight the importance of weak van der Waals interactions in determining the phase behaviors of polyelectrolyte complexes relative to electrostatic correlations.

Building Ultrastrong, Tough and Biodegradable Thermoplastic Elastomers from Multiblock Copolyesters via a "Reserve-Release" Crystallization Strategy.

Simultaneously attaining high strength and toughness has been a significant challenge in designing thermoplastic elastomers, especially biodegradable ones. In this context, we present a class of biodegradable elastomers based on multiblock copolyesters that afford extraordinary strength, toughness, and low-strain resilience despite expedient chemical synthesis and sample processing. With the incorporation of the semi-crystalline soft block and the judicious selection of block periodicity, the thermoplastic materials feature low quiescent crystallinity ("reserve") albeit with vast potential for strain-induced crystallization ("release"), resulting in their significantly enhanced ultimate strength and energy-dissipating capabilities. Moreover, a breadth of mechanical responses of the materials - from reinforced elastomers to shape-memory materials to toughened thermoplastics - can be achieved by orthogonal variation of segment lengths and ratios. This work and the "reserve-release" crystallization strategy herein highlight the double crystalline multiblock chain architecture as a potential avenue towards reconciling the strength-toughness trade-off in thermoplastic elastomers and can possibly be extended to other biodegradable building blocks to deliver functional materials with diverse mechanical performances.

Polyzwitterion fast and slow mode behavior are coupled to phase separation as observed by dynamic laser light scattering.

A model zwitterionic polysulfobetaine, poly(3-(acrylamidopropyl-dimethyl-ammonium) propyl-1-sulfonate) (pAPAPS), phase separates upon cooling and exhibits an upper critical solution temperature (UCST) behavior with no added salt in deuterium oxide solutions. Dynamic light scattering measurements indicate the presence of distinct fast and slow diffusive modes, where the fast mode is interpreted as a collective diffusion coefficient and the slow mode is attributed to the diffusion of multi-chain dynamic clusters. The relative population of fast and slow modes varies systematically with temperature and concentration. A clustering temperature (T*) was assigned when the slow mode first appeared upon cooling. The slow mode then increases in relative scattering amplitude as the phase boundary is approached. The fast mode exhibits a concentration dependence above T* consistent with the virial expansion in the collective diffusion. The sign of the virial coefficient (kd) is negative, even in the good solvent region above the expected Flory temperature (Θ ≈ 39 °C), a behavior distinct from synthetic neutral polymers in organic solvents. The onset of multi-chain clustering at T < T* coincides with the poor solvent regime (T < Θ). Attractive dipolar interactions due to the zwitterionic sulfobetaine groups in pAPAPS are suggested as the origin of the multi-chain clusters with no salt. Upon the addition of 100 mM NaCl, the slow mode is suppressed, and the hydrodynamic radius is consistent with polyzwitterion chain dimensions in a dilute solution. We find that concentration dependent diffusion is highly linked to the theta temperature and the emergence of dynamic clusters as the polymer goes from good to poor solvent on approach to the UCST. The slow mode in the semidilute regime is reported along with preliminary small-angle neutron scattering data that show salt reduces clustering and leads to predominantly chain scattering.

Temperature dependent single-chain structure of poly[3-(acrylamidopropyl-dimethyl-ammonium) propyl-1-sulfonate] via small-angle neutron scattering.

Responsive polyzwitterionic materials have become important for a range of applications such as environmental remediation and targeted drug delivery. Much is known about the macroscopic phase-behaviors of such materials, but how the smaller scale single-chain structures of polyzwitterions respond to external stimuli is not well understood, especially at temperatures close to their phase boundaries. Such chain conformation responses are important in directing larger-scale associative properties. Here, we study the temperature dependent single-chain structure of a model polysulfobetaine, poly[3-(acrylamidopropyl-dimethyl-ammonium) propyl-1-sulfonate], using small angle neutron scattering. In the absence of salt, we find that temperature has a large effect on solvent quality with a decreasing trend from good solvent conditions at 50 °C to poor solvent at 10 °C (a temperature just above the cloud point of 7.6 °C) and an estimated theta temperature of 39 °C. When 100 mM NaCl is present, the solvent quality is good with weak temperature dependence. Without salt present, the polymer chain appears to have a nearly Gaussian coil conformation and the backbone becomes slightly more rigid as the temperature is lowered to the cloud point as determined by the Debye-local rod model on a Kratky plot. The addition of salt has a notable effect on the intra-chain correlations where an increase in chain dimensions to a swollen coil conformation and an increase in chain rigidity is observed at 100 mM NaCl in D2O, however, with a negligible temperature dependence.

Research on the Derated Power Data Identification Method of a Wind Turbine Based on a Multi-Gaussian-Discrete Joint Probability Model.

This paper focuses on how to identify normal, derated power and abnormal data in operation data, which is key to intelligent operation and maintenance applications such as wind turbine condition diagnosis and performance evaluation. Existing identification methods can distinguish normal data from the original data, but usually remove power curtailment data as outliers. A multi-Gaussian-discrete probability distribution model was used to characterize the joint probability distribution of wind speed and power from wind turbine SCADA data, taking the derated power of the wind turbine as a hidden random variable. The maximum expectation algorithm (EM), an iterative algorithm derived from model parameters estimation, was applied to achieve the maximum likelihood estimation of the proposed probability model. According to the posterior probability of the wind-power scatter points, the normal, derated power and abnormal data in the wind turbine SCADA data were identified. The validity of the proposed method was verified by three wind turbine operational data sets with different distribution characteristics. The results are that the proposed method has a degree of universality with regard to derated power operational data with different distribution characteristics, and in particular, it is able to identify the operating data with clustered distribution effectively.

Molecular Mass Dependence of Interfacial Tension in Complex Coacervation.

The interfacial tension of coacervates, the liquidlike phase composed of oppositely charged polymers that coexists at equilibrium with a supernatant, forms the basis for multiple technologies. Here we present a comprehensive set of experiments and molecular dynamics simulations to probe the effect of molecular mass on interfacial tension γ, far from the critical point, and derive γ=γ_{∞}(1-h/N), where N is the degree of polymerization, γ_{∞} is the infinite molecular mass limit, and h is a constant that physically corresponds to the number of monomers of one chain within the coacervate correlation volume.

Recyclable and Dual Cross-Linked High-Performance Polymer with an Amplified Strength-Toughness Combination.

Supramolecular chemistry has provided versatile and affordable solutions for the design of tough, flexible polymers. However, application of supramolecular chemistry has been limited to the production of rigid, high-performance polymers due to weak segment mobility. This paper describes a new method of toughening rigid high-performance polymers using the synergistic effect between dual Cu2+ -coordination bonds as a crosslink. These dual Cu2+ -coordination cross-linked high-performance polymers are a class of rigid polymers with an outstanding combination of strength and toughness. The distinct lifetimes and binding strengths of the dual Cu2+ -coordination bonds in a rigid polymer network elicit different dynamic behaviors to improve its energy dissipation and mechanical properties. Moreover, the reformation and removal of Cu2+ -coordination bonds by pyrophosphoric acid endows these cross-linked high-performance polymers with recyclability.

Applicability of the Generalized Stokes-Einstein Equation of Mode-Coupling Theory to Near-Critical Polyelectrolyte Complex Solutions.

We examine whether the mode-coupling theory of Kawasaki and Ferrell (KF) [Kawasaki, K. Kinetic Equations and Time Correlation Functions of Critical Fluctuations. Ann. Phys. 1970, 61 (1), 1-56; Ferrell, R. A. Decoupled-Mode Dynamical Scaling Theory of the Binary-Liquid Phase Transition. Phys. Rev. Lett. 1970, 24 (21), 1169-1172] can describe dynamic light scattering (DLS) measurements of the dynamic structure factor of near-critical polyelectrolyte complex (PC) solutions that have been previously shown to exhibit a theoretically unanticipated lower critical solution temperature type phase behavior, i.e., phase separation upon heating, and a conventional pattern of static critical properties (low angle scattering intensity and static correlation, ξs) as a function of reduced temperature. Good qualitative accord is observed between our DLS measurements and the KF theory. In particular, we observe that the collective diffusion coefficient Dc of the PC solutions obeys the generalized Stokes-Einstein equation (GSE), Dc = kBT/6πηξs, where ξs is specified from our previous measurements and where η is measured by capillary rheometry under the same thermodynamic conditions as in our previous study of these solutions, allowing for a no-free-parameter test of the GSE. We also find that even the wavevector (q)-dependent collective diffusion coefficient Dc(q), measured by varying the scattering angle in the DLS measurements over a large range, is also well-described by the mean-field version of the KF theory. We find it remarkable that the KF theory provides such a robust description of collective diffusion in these complex charged polyelectrolyte blends under near-critical conditions given that charge fluctuations and association of the polymers might be expected to lead to physical complications that would invalidate the standard model of uncharged fluid mixtures.

Finely tunable dynamical coloration using bicontinuous micrometer-domains.

Nanostructures similar to those found in the vividly blue wings of Morpho butterflies and colorful photonic crystals enable structural color through constructive interference of light waves. Different from commonly studied structure-colored materials using periodic structures to manipulate optical properties, we report a previously unrecognized approach to precisely control the structural color and light transmission via a novel photonic colloidal gel without long-range order. Nanoparticles in this gel form micrometer-sized bicontinuous domains driven by the microphase separation of binary solvents. This approach enables dynamic coloration with a precise wavelength selectivity over a broad range of wavelengths extended well beyond the visible light that is not achievable with traditional methods. The dynamic wavelength selectivity is thermally tunable, reversible, and the material fabrication is easily scalable.

Ultra-small angle neutron scattering to study droplet formation in polyelectrolyte complex coacervates.

Associating soft matter such as surfactants, polymers, proteins, and liposomes, may form structures with dimensions not readily accessible by optical methods. Scattering methods can provide detailed information about the mechanism of associative phase separation including nucleation density, size, and shape. Ultra-small angle neutron scattering, a reciprocal space method, provides sensitivity to submicron to micron-scale structures in a non-invasive manner and described in the context of nucleation and growth of dilute droplets formed by a temperature jump into the meta-stable region of polyelectrolyte complex coacervates.

Tuning Net Charge in Aliphatic Polycarbonates Alters Solubility and Protein Complexation Behavior.

A synthetic strategy yielded polyelectrolytes and polyampholytes with tunable net charge for complexation and protein binding. Organocatalytic ring-opening polymerizations yielded aliphatic polycarbonates that were functionalized with both carboxylate and ammonium side chains in a post-polymerization, radical-mediated thiol-ene reaction. Incorporating net charge into the polymer architecture altered the chain dimensions in phosphate buffered solution in a manner consistent with self-complexation and complexation behavior with model proteins. A net cationic polyampholyte with 5% of carboxylate side chains formed large clusters rather than small complexes with bovine serum albumin, while 50% carboxylate polyampholyte was insoluble. Overall, the aliphatic polycarbonates with varying net charge exhibited different macrophase solution behaviors when mixed with protein, where self-complexation appears to compete with protein binding and larger-scale complexation.

Unprecedented toughening high-performance polyhexahydrotriazines constructed by incorporating point-face cation-π interactions in covalently crosslinked networks and the visual detection of tensile strength.

We described a new concept for the design of high-performance supramolecular thermosets by incorporating point-face cation-π interactions in covalently crosslinked networks. Our findings showed an unprecedented increase in tensile strength and extensibility at once, a previously unknown behavior for stiff high performance polymers.

A novel carboxylic-functional indole-based aerogel for highly effective removal of heavy metals from aqueous solution via synergistic effects of face-point and point-point interactions.

A new type of carboxylic-functional indole-based aerogel (CHIFA) has been successfully prepared via a facile sol-gel technology, which possessed a highly effective removal of heavy metals from aqueous solution through the synergistic effects of face-point and point-point interactions.

Cation-π induced lithium-doped conjugated microporous polymer with remarkable hydrogen storage performance.

A cation-π induced lithium-doped conjugated microporous polymer, Li+-PTAT, was constructed. It was proved that the point to face cation-π interactions between Li+ and indole can endow the resulting Li+-PTAT with high Li+ content and without agglomeration, which further leads to its encouraging hydrogen storage capacity.