The effects of melt annealing and counterpart's molecular weight on the thermal properties and phase morphology of poly(L‐lactide)‐based blends

The thermal properties and phase morphology of poly(L ‐lactide) (PLLA)‐based blends have been studied. Two poly(ethylene glycol)s (PEGs) with molecular weight (MW) of about 1,500 (1.5k) g/mol and 2,000,000 (2M) g/mol, respectively, were used as counterparts. The blends were annealed at a preselected temperature of 200 °C for either 2 min or 30 min before the characterizations. Both PEGs were determined to enhance the crystallizability of PLLA. After a 2‐min process of annealing, the PEG(1.5k)'s crystallization efficiency on PLLA has been noted to increase with the increase of its content. Conversely, PEG(2M)'s crystallization efficiency declined with the increase of its content. Extending the annealing time has evidently changed the PEGs' crystallization effect on PLLA. Moreover, the PEG(1.5k) has, to a greater extent, brought about the depression of PLLA's melting temperature by increasing its content, and this depression increased with the annealing time. The blends exhibited lower thermal stability than those of the parent components, particularly for the PEG(1.5k)‐included system with a higher PEG content. Regardless of the annealing time, the PEG(1.5k)‐included blends have shown homogeneous melt morphology under light microscope, whereas the PEG(2M)‐included blends have displayed phase‐separated melt morphology. In addition to the composition, PEG's MW and annealing time influence the crystalline morphology of the blends. The ringed PLLA spherulites have appeared mostly in the 2‐min annealed PEG(1.5k)‐included blends. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1497–1510, 2009     

Facile method to prepare monodispersed Ag/polystyrene composite microspheres and their properties

This article presents a facile method to prepare silver/polystyrene composite microspheres. In this approach, monodispersed polystyrene (PS) particles were synthesized with carboxyl acid groups on the surfaces of the PS particles via dispersion polymerization at first. With the addition of [Ag(NH₃)₂]⁺ to the PS dispersion, [Ag(NH₃)₂]⁺ was absorbed to the surfaces of the PS particles, and then by heating the system, [Ag(NH₃)₂]⁺ complex ions were reduced to silver to form the Ag/PS composite microspheres. In the synthesis of PS dispersion, PVP was used as dispersant to stabilize the PS particles, it also acted as reducing agent in the reduction of [Ag(NH₃)₂]⁺ complex ions to silver, so no additional reducing agent was needed. The resulting composite microspheres were characterized by TEM, SEM, XPS, and XRD. The catalytic properties and surface‐enhance Raman scattering (SERS) was studied as well. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4547–4554, 2009     

Eigenvalue spectra and geometric transformation of polyhedra

Starting from one fullerene, the three geometric transformations, cap, face dual and edge dual produce series of carbon clusters and deltahedra. The geometric relation between these polyhedra implies that their topological matrices and eigenvalue spectra must be relative. We have developed a matrix algebra method to research some polyhedra with high symmetry and one kind, two or three kinds of equivalent vertices such as C₆₀(I_h), resolve their exact eigenvalues, and proved this point.     

X-ray diffraction by thermotropic main-chain polymers with side groups. II. semiflexible polyesters

Semiflexible thermotropic aromatic polyesters with lateral groups were aligned magnetically and mechanically in monodomains after separation into high-molecular-weight (polymer) and low-molecular-weight (oligomer) fractions. Based on the x-ray intensity distributions recorded for a series of seven different substituents in the arylsulfonyl substituted group, a novel smectic structure was determined for H, F, Cl, OCH₃, and CH₃ in the para position while a normal nematic alignment prevailed when it contained Br or NO₂.     

Matrix Product State Simulations of Non-Equilibrium Steady States and Transient Heat Flows in the Two-Bath Spin-Boson Model at Finite Temperatures

Simulating the non-perturbative and non-Markovian dynamics of open quantum systems is a very challenging many body problem, due to the need to evolve both the system and its environments on an equal footing. Tensor network and matrix product states (MPS) have emerged as powerful tools for open system models, but the numerical resources required to treat finite-temperature environments grow extremely rapidly and limit their applications. In this study we use time-dependent variational evolution of MPS to explore the striking theory of Tamascelli et al. (Phys. Rev. Lett. 2019, 123, 090402.) that shows how finite-temperature open dynamics can be obtained from zero temperature, i.e., pure wave function, simulations. Using this approach, we produce a benchmark dataset for the dynamics of the Ohmic spin-boson model across a wide range of coupling strengths and temperatures, and also present a detailed analysis of the numerical costs of simulating non-equilibrium steady states, such as those emerging from the non-perturbative coupling of a qubit to baths at different temperatures. Despite ever-growing resource requirements, we find that converged non-perturbative results can be obtained, and we discuss a number of recent ideas and numerical techniques that should allow wide application of MPS to complex open quantum systems.     

Generalized ray expansion for pulse propagation and attenuation in fluid-saturated porous media

A theory suitable for studying pulses propagating through a layered fluid-saturated porous medium is presented. Biot's theory is used to describe the constitutive equation of a fluid-saturated porous solid. Since fast and slow compressional waves exist in a Biot solid even at normal incidence, there is mode conversion at the interface and, therefore, the transmission and reflection coefficients are 2x2 matrices. We use matrix methods in developing the solution of the wave propagation problem. A generalized ray expansion algorithm is obtained by using the Gauss-Seidel matrix iterative method. The arrivals of the fast and the slow waves are easily identified. A compact computational algorithm is developed using combinatorial analysis and the Cayley-Hamilton theorem.     

Consensus model for identification of novel PI3K inhibitors in large chemical library

Phosphoinositide 3-kinases (PI3Ks) inhibitors have treatment potential for cancer, diabetes, cardiovascular disease, chronic inflammation and asthma. A consensus model consisting of three base classifiers (AODE, kNN, and SVM) trained with 1,283 positive compounds (PI3K inhibitors), 16 negative compounds (PI3K non-inhibitors) and 64,078 generated putative negatives was developed for predicting compounds with PI3K inhibitory activity of IC₅₀ ≤ 10 μM. The consensus model has an estimated false positive rate of 0.75%. Nine novel potential inhibitors were identified using the consensus model and several of these contain structural features that are consistent with those found to be important for PI3K inhibitory activities. An advantage of the current model is that it does not require knowledge of 3D structural information of the various PI3K isoforms, which is not readily available for all isoforms.     

Challenges associated with the synthesis of unusual o-carboxamido stilbenes by the Heck protocol: Intriguing substituent effects, their toxicological and chemopreventive implications

The syntheses of fourteen unusual o-carboxamido stilbenes by the Heck protocol revealed surprising complexity related to intriguing substituent effects with mechanistic implications. The unexpected cytotoxic and chemopreventive properties also seem to be substituent dependent. For example, although stilbene 15d (with a 4-methoxy substituent) showed cytotoxicity on HT29 colon cancer cells with an IC(50) of 4.9 μM, the 3,4-dimethoxy derivative (15c) is inactive. It is interesting to observe that the 3,5-dimethoxy derivative (15e) showed remarkable chemopreventive activity in WRL-68 fetal hepatocytes, surpassing the gold standard, resveratrol. The resveratrol concentration needed to be 5 times higher than that of 15e to produce comparable elevation of NQO1.