Effects of molecular weight and polydispersity of poly (3-hexylthiophene) in bulk heterojunction polymer solar cells

This paper reports the effect of the molecular weight (MW) and polydispersity (PD) of poly (3-hexylthiophene) (P3HT) in bulk heterojunction polymer solar cells (BHJ-SCs). The P3HT with low MW and broad PD exhibited higher crystallinity compared to that with high MW and narrow PD. Due to the improved crystallinity, the BHJ-SCs based on P3HT with low MW and broad PD showed performance with a power conversion efficiency of 3.8% with short-circuit currents of −9.90 mA/cm².     

A hierarchical algorithm for predicting the linear viscoelastic properties of polymer melts with long-chain branching

The hierarchical model proposed earlier [Larson in Macromolecules 34:4556–4571, 2001] is herein modified by inclusion of early time fluctuations and other refinements drawn from the theories of Milner and McLeish for more quantitative prediction. The hierarchical model predictions are then compared with experimental linear viscoelastic data of well-defined long chain branched 1,4-polybutadienes and 1,4-polyisoprenes using a single set of parameter values for each polymer, which are obtained from experimental data for monodisperse linear and star polymers. For a wide range of monodisperse branched polymer melts, the predictions of the hierarchical model for monodisperse melts are very similar to those of the Milner–McLeish theories, and agree well with experimental data for many, but not all, of the branched polymer samples. Since the modified hierarchical model accounts for arbitrary polydispersity in molecular weight and branching distributions, which is not accounted for in the Milner–McLeish theories, the hierarchical algorithm is a promising one for predicting the relaxation of general mixtures of branched polymers.     

Polymeric microspheres as support to co-immobilized Agaricus bisporus and Trametes versicolor laccases and their application in diazinon degradation

The laccase enzymes of Agaricus bisporus and Trametes versicolor were successfully covalently co-immobilized on poly(glycidyl methacrylate) microspheres. The enzyme load reached after the co-immobilization of both enzymes was 6.75 U g⁻¹ carrier. The resulting biocatalyst showed the combined properties of both immobilized enzymes, increasing their optimum pH and temperature ranges. The storage and operational stabilities were also improved after co-immobilization. In presence of mediator (ABTS) the organophosphate pesticide diazinon was 100% biodegraded after 48 h of reaction with 0.2 U/mL of co-immobilized enzymes (at the two maximum activity pH values: 2.0 and 3.0). In the absence of a mediator, the degradation percentages were above 88%. Data showed that, compared with single enzymatic immobilization, the co-immobilization of the two laccases is an easy, efficient, and low cost alternative to expanding the range of work of the biocatalyst, thereby improving the stability and some biochemical properties to generate a powerful alternative for pesticide degradation in a wide range of conditions.     

Effect of molecular weight and its distribution on the spinodal for polydisperse polymer solutions

The Flory–Huggins interaction parameter χ(r_i) is considered as dependent on the chain length of a polymer. Therefore, a modified free energy expression of Flory–Huggins theory is obtained for the polydisperse polymer solutions. Based on this modified free energy expression and the thermodynamics of Gibbs, the expression of spinodal for polydisperse polymer solutions is obtained. For a given χ(r_i) according to de Gennes, the spinodals are calculated for polydisperse polymer solutions at different molecular weights and their distributions. It is found that all the interested variables r_n, r_w, r_z and molecular weight distribution have an effect on the spinodal for polydisperse polymer solutions, where the effect of changing r_w is much greater than that of changing r_n, r_z and molecular weight distribution.     

Kinetics of emulsion copolymerization of methylmethacrylate and ethylacrylate: effect of type and concentration of initiator in unseeded polymerization system

The free radical emulsion copolymerization of methylmethacrylate (MMA) and ethylacrylate (EA) initiated by a water-soluble initiator (potassium persulphate, KPS) at 50 °C in the presence of anionic emulsifier above critical micelle concentration under constant stirring speed in an inert atmosphere is investigated. The effect of blend of KPS and oil-soluble initiators [KPS+2,2^′-azobisisobutyronitrile (AIBN)] is also examined. The order of the interval-II polymerization rate (R_p) is found to be 0.76±0.03 in KPS initiation alone and 0.72±0.04 in presence of fixed concentration of AIBN under similar experimental condition. On the other hand, interestingly, the rate of polymerization is found to be propotional to the 0.40th power of the AIBN concentration in presence of fixed concentration of KPS. The kinetic features of the present investigation indicate that probably the radical desorption is relatively facile and also the cage effect may be operative under high conversions (i.e. in polymer particles) in this MMA/EA emulsion copolymerization system. It is also found that the polydispersity index of polymer is being influenced by the type and concentration of initiators.     

Towards more controlled poly(n-butyl methacrylate) by atom transfer radical polymerization

The homogeneous controlled/‘living’ free radical polymerization of n-butyl methacrylate in toluene or o-xylene at 90 °C, in bulk and in solution, using the novel combination of the catalyst bis-triphenylphosphine iron(II)chloride tetrahydrate (FeCl₂ · 4H₂O(PPh₃)₂) with ethyl 2-bromoisobutyrate ((CH₃)₂CBrCO₂Et)) and α,α-dichloroacetophenone (CHCl₂COPh) as initiators has been investigated. The rate of polymerization initiated by the two initiators exhibited first-order kinetic with respect to the monomer. A linear increase of the number-average molecular weight (M_n) versus monomer conversion was observed for these systems. Among the two initiation systems, ethyl 2-bromoisobutyrate gave the fastest polymerization rate. A system with Fe³⁺ added at the beginning of the polymerization was examined and the lowest polydispersity (M_w/M_n∼1.2) was found when 10% Fe³⁺, relative to Fe²⁺ was added.     

A Monte Carlo ray tracing study of polarized light propagation in liquid foams

A Monte Carlo ray tracing scheme is used to investigate the propagation of an incident collimated beam of polarized light in liquid foams. Cellular structures like foam are expected to change the polarization characteristics due to multiple scattering events, where such changes can be used to monitor foam dynamics. A statistical model utilizing some of the recent developments in foam physics is coupled with a vector Monte Carlo scheme to compute the depolarization ratios via Stokes-Mueller formalism. For the simulations, the incident Stokes vector corresponding to horizontal linear polarization and right circular polarization are considered. It is observed that bubble size and the polydispersity parameter have a significant effect on the depolarization ratios. This is partially owing to the number of total internal reflection events in the Plateau borders. The results are discussed in terms of applicability of polarized light as a diagnostic tool for monitoring foams.     

油酸囊泡尺度多分散性及二元醇对其pH窗口的影响

以油酸(OA)为模型脂肪酸, 依据目测激光丁达尔现象在pH滴定曲线上划分相区, 确定OA囊泡化pH窗口为8.2~10.1. 利用光学显微镜、 激光共聚焦显微镜和冷冻刻蚀-透射电子显微镜共同表征了OA囊泡的形貌及粒径, 发现体系中微米和亚微米级的多层囊泡以及纳米级的单层囊泡共存, 呈现尺度多分散性. 用不同链长的短链二元醇辅助OA形成囊泡, 结果表明, 短链二元醇有助于脂肪酸囊泡(FAV)的pH窗口拓宽, 拓宽的方向取决于表面氢键作用方式或疏水插入方式. 在酸性条件下二元醇与FAV相互作用后, 在囊泡表面残留的自由羟基越多, 越有助于拓宽其酸性pH窗口.