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Abstract: Polyelectrolytes are polymers carrying either positively or negatively charged ionizable groups. The properties of these polymers in solutions and at charged surfaces depend on the fraction of dissociated ionic groups, solvent quality for polymer backbone, solution dielectric constant, salt concentration, and polymer–substrate interactions. In this review, we summarize the current development of theoretical models describing properties of polyelectrolyte solutions and adsorption of charged polymers at surfaces and interfaces. We discuss in detail the conformational properties of polyelectrolyte chains in dilute and semidilute solutions, the phenomenon of counterion condensation, the necklace structure of polyelectrolytes in poor solvent conditions for polymer backbone, the dynamics of polyelectrolyte solutions, the surface overcharging by adsorbed polyelectrolytes and its implication for assembled polyelectrolyte multilayers. [Copyright &y& Elsevier]

Two all-aromatic, high-performance poly(etherimide)s ODPA-P3 ( I ) and BPDA-P3 ( II ) are studied as a function of SWCNT loading. Polyetherimide I is amorphous but SWCNTs nucleate crystallization during imidization to produce a nanocomposite (nc- I ) with SWCNTs embedded in the crystals. This crystalline interphase, with a radial thickness of ∼8 nm, results in a substantial reinforcement efficacy. Melting the interphase and cooling nc- I yields an amorphous nanocomposite with an interphase thickness (3.6 nm) that is smaller and has a lower reinforcement efficacy. Polyetherimide II was used as a reference since SWCNTs reside in the amorphous fraction of its nanocomposite. Consequently, the reinforcement efficiency of the semi-crystalline nc- II and its amorphous analog (prepared by heating above the crystal melting point and cooling) remains unchanged. A crystalline interphase surrounding SWCNT-reinforced poly(etherimide)s appears to be critical in obtaining high reinforcement efficacies. Most high-performance polyimides and poly(etherimide)s are prepared using a thermal imidization step. Our work emphasizes that care has to be taken in selecting the final imidization temperature to avoid melting the crystalline interphase if one is targeting high modulus materials. [ABSTRACT FROM AUTHOR]

Stable microbubbles can be prepared by evaporation of a liquid core inside an expandable polymeric shell. To control the expansion temperature and the size of resulting microbubbles, we prepared polymeric microcapsules that contain multiple liquids in their core. One-step suspension polymerization allowed for encapsulation of at least two different liquids with near quantitative yield. The liquids may be miscible or immiscible, which directly affects the vapor pressure inside the capsule according to either Raoult's or Dalton's law, respectively. In the case of miscible liquids, e.g., perfluorohexane and perfluoropentane, both the vapor pressure and the expansion temperature vary within a range bounded by the properties of the neat liquids. For immiscible liquids, e.g. perfluoropentane and isopentane, the total vapor pressure is above this range as it equals to a sum of the individual pressures. Due to increased vapor pressure, encapsulation of two immiscible liquids significantly lowers the expansion temperature below the corresponding temperatures observed during expansion of microcapsules with neat perfluoropentane and isopentane cores. The microbubble diameter and shell thickness were controlled within ca. 10–50 μm and 0.1–3 μm, respectively, by varying the fractions and vapor pressure of the core fluids. We also showed that the effect of core composition on the expansion temperature was more significant than the effect of the shell thickness. Furthermore, one of the encapsulated materials may carry additional functions including imaging contrast, catalysis, and density compensation. To that end, these designer microcapsules may find applications in the fields of drug delivery, acoustic imaging, drilling, and self-healing materials. [ABSTRACT FROM AUTHOR]

In this study we contrast the behavior of an amorphous polyetherimide (ODPA-P3) with that of a semi-crystalline one (BPDA-P3) on introducing single-wall carbon nanotubes (SWCNTs; 0.1-4.4 vol.%). The SWCNTs act as a nucleating agent and induce crystallinity (up to 45%) in amorphous ODPA-P3; in BPDA-P3, the SWCNTs lower the onset of crystallization during thermal imidization, but decrease the overall degree of crystallinity. Tensile tests show that the yield strength is the same for both polyimides up to 0.3% SWCNT loadings. Above this concentration the yield strength for the BPDA-P3 nanocomposites remains constant whereas in the ODPA-P3 nanocomposites it increases from 80 to 126 MPa (1.2 vol.%). In the amorphous PEI, SWCNTs enhance the thermo-mechanical properties (Tg, storage- and elastic modulus, and yield strength), but in the semi-crystalline PEI there are little or no effects on the mechanical performance. [ABSTRACT FROM AUTHOR]

Reversible-addition fragmentation chain transfer (RAFT) polymerization enabled the synthesis of novel, stimuli-responsive, AB and ABA block copolymers. The B block contained oligo(ethylene glycol) methyl ether methacrylate (OEG) and was permanently hydrophilic in the conditions examined. The A block consisted of diethylene glycol methyl ether methacrylate (DEG) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (TMA). The A block displayed both salt- and temperature-response with lower critical solution temperatures (LCSTs) dependent on the molar content of TMA and the presence of salt. Higher TMA content in the AB diblock copolymers increased the critical micelle temperatures (CMT) in HPLC-grade water due to an increased hydrophilicity of the A block. Upon addition of 0.9 wt% NaCl, the CMTs of poly(OEG-b-DEG95TMA5) decreased from 50 °C to 36 °C due to screening of electrostatic repulsion between the TMA units. ABA triblock copolymers displayed excellent hydrogel properties with salt- and temperature-dependent gel points. TMA incorporation in the A block increased the gel points for all triblock copolymers, and salt-response increased with higher TMA composition in the A block. For example, poly(DEG98TMA2-b-OEG-b-DEG98TMA2) formed a hydrogel at 40 °C in HPLC-grade water and 26 °C in 0.9 wt% NaCl aqueous solution. These salt- and temperature-responsive AB diblock and ABA triblock copolymers find applications as drug delivery vehicles, adhesives, and hydrogels. [ABSTRACT FROM AUTHOR]

Objectives: We sought to identify factors contributing to racial disparity in the receipt of coronary angiography (CA).Background: Numerous studies have demonstrated that African American patients are less likely to receive needed diagnostic and therapeutic coronary procedures than white patients. This report summarizes the methods and findings of a study linking medical records with patient and physician interviews to address racial disparities in the utilization of CA.Methods: This is a retrospective, cross-sectional study conducted in three urban hospitals in Maryland. A total of 9,275 medical records were reviewed, representing all 7,058 cardiac patients admitted in a two-year period. We identified 2,623 patients who, according to American College of Cardiology guidelines, were candidates for receiving CA. A total of 1,669 patients (721 African Americans and 948 whites) and 74% of their physicians were successfully interviewed. Multivariate and hierarchical multivariate logistic regression were used to construct a model of receipt of CA within one year of the hospitalization.Results: The unadjusted odds of white patients receiving CA was three times greater than the odds for African American patients (odds ratio [OR] 3.0, 95% confidence interval [CI] 2.4 to 3.7). Adjusting for patients' clinical and social characteristics resulted in a 13% reduction in the OR for race. Adjusting for physician and health care system characteristics reduced the OR by 43%, to 1.7 (95% CI 1.3 to 2.4).Conclusions: Racial disparity in the utilization of CA is a function of differences in the health care system "context" in which African American and white patients obtain care, combined with differences in the specific clinical characteristics of patients. [ABSTRACT FROM AUTHOR]