Behavior of thermosensitive graft copolymer with aromatic polyester backbone and poly-2-ethyl-2-oxazoline side chains in aqueous solutions

Thermoresponsive graft copolymers with alkylene-aromatic polyester main chain and poly-2-ethyl-2-oxazoline side chains were synthesized. Two copolymer samples which differed in grafting density (0.5 and 0.7) were studied using dynamic and static light scattering and turbidimetry in aqueous solutions at concentration 0.0053?g?cm^?3. Hydrodynamic radii of scattering objects and their contribution to light scattering were obtained as a function of temperature in a wide temperature interval. Temperatures of phase separation were found out. Effect of grafting density on the copolymer behavior in aqueous solutions upon heating was determined. In particular, the phase separation temperature reduces with the decreasing grafting density.     

Simulating Light Scattering Behavior of Branched Molecules

Monte Carlo simulations reveal long chain branching (LCB) topology based on kinetics of systems like low‐density polyethylene (ldPE). Examining the topologies computed shows the majority of branch arms to be short as compared to backbone length, while also a significant branch‐on‐branch fine structure is observed. Until now, predicting scattering function P ⁻¹(θ) from LCB has only been successful for structures like simple combs or stars. Topologies in graph theoretical form are used to predict scattering function P ⁻¹(θ) and by summating intramolecular distances, accounting for branching and excluded volume. Experimental size exclusion chromatography with multiangle light scattering can be brought in line with the predicted branching character. Branching is less than predicted due to a different fine structure in ldPE leading to stronger size contraction.     

Molecular and conformational properties of comb-like polymers with ionically bound side chains studied in organic solvent

Conformational and dynamo-optical properties of a homologous series of poly(cetyltrimethylammonium 2-acrylamido-2-methylpropane sulfonates) with molecular masses ranging from 80 to 700?kDa were studied in chloroform solutions by viscometry, dynamic light scattering, sedimentation, and flow birefringence. The Mark–Kuhn–Houwink Equations for this polymer in chloroform were obtained; the values of hydrodynamic diameter and the Kuhn segment length as well as the value of intrinsic anisotropy of polarizability of the monomer unit were defined.     

New evaporative light scattering detector for high temperature gel permeation chromatography

A new evaporative light scattering detector (ELSD) for the analysis of polyolefins by high temperature gel permeation chromatography (GPC) was recently introduced by Agilent Technologies. For the first time, we investigated the possibility to use this detector to measure the molecular weight distributions (MWD) of different type of polyolefines (polypropylene, linear, and low-density polyethylene). These samples were previously characterized by GPC with a differential refractive index (DRI) detector by several companies, in an interlaboratory study conducted by International Union of Pure and Applied Chemistry.^[1 Luruli, N. 2010. PHASE 1: IUPAC SEC/GPC Round Robin Project Report: Repeatability and Reproducibility of Sample Preparation and Analysis in High-Temperature SEC, http://media.iupac.org/projects/2005/2005-011-3-400_rpt-phase1_110510.pdf [Google Scholar]^] The excellent baseline stability of ELSD as compared with DRI was reflected in a better reproducibility of the measured average molecular weights. More importantly, after applying required corrections to linearize the response of the ELSD as a function of concentration, we obtained similar results as previously obtained with DRI for the MWD of analyzed resins, covering typical applications of polyolefins.     

以腐植酸为对象开展稳态和时间分辨荧光实验教学

腐植酸是天然有机质的重要组成部分,其结构复杂且具有多种荧光发射特征。我们结合目前环境科学领域腐植酸或其他天然有机质的研究重点,利用腐植酸开展稳态和时间分辨荧光综合实验教学。本实验可以使学生全面掌握分子荧光分析中拉曼散射、激发光能量对荧光发射影响、荧光寿命和内滤效应等知识。     

Synthesis of Cu2O/Ag Composite with Visible Light Photocatalytic Degradation Activity for in situ SERS Analysis

A multifunctional Cu₂O/Ag micro-nanocomposite, which has the characteristics of high catalytic activities under the visible light and high surface-enhanced Raman scattering (SERS) activity, was fabricated via a facile method and employed for the in situ SERS monitoring of the photocatalytic degradation reaction of crystal violet. Through the variation of the AgNO₃ concentration, Ag content on the Cu₂O template can be controllably tuned, which has great influence on the SERS effect. The results indicate that Ag nanoparticles form on the Cu₂O nanoframes to obtain the Cu₂O/Ag nanocomposite, which can act as an excellent bifunctional platform for in situ monitoring of photocatalytic degradation of organic pollutions by SERS.     

Remarks on the Born approximation and the Factorization Method

In this paper, we compare the far-field operators for the full nonlinear inverse scattering problem with the Born approximation as its linearization. The Factorization Method shows that both operators share the same behavior with respect to illposedness of the inverse problem. The results are derived for acoustic and electromagnetic scattering problems and the corresponding problem in electrical impedance tomography.     

Computation of waveguide scattering matrix near thresholds

A waveguide occupies infinite strip with one or several narrows on a two-dimensional (2D) plane and is governed by the Helmholtz equation with Dirichlet boundary condition. On the waveguide continuous spectrum, which coincides with a half-axis, a scattering matrix is defined. At each point of the continuous spectrum this matrix has finite size, which changes at thresholds. The thresholds form a sequence of positive numbers increasing to infinity. Approximate calculation of the scattering matrix in a threshold vicinity requires special treatment. We discuss and compare two methods of numerical approximation to the scattering matrix near a threshold.