Preparation and functional evaluation of agarose derivatives

A facile microwave‐assisted one‐pot synthesis of sodium carboxymethylagarose and calcium carboxymethylagarose from Gracilaria dura agarose (Ag) has been described. The process is user friendly, and the highest degree of substitution was obtained within 15 min compared with the conventional method, which requires more than 3 h. Solubility and gelling behavior of the modified Ag products were found to be dependent on degree of substitution of the products. The characterizations were done by using Fourier transform infrared spectroscopy, ¹H‐ and ¹³C‐nuclear magnetic resonance spectroscopy, thermogravimetric analysis, scanning electron microscopy, Inductively coupled plasma spectrophotometry (ICP), rheology, conductometer analysis, and DNA gel electrophoresis. These agarose derivatives were easily soluble in water and exhibited low thermal hysteresis, improved conductivity, and improved the DNA resolution ability of the parent G. dura Ag hydrogels. These hydrogels may have potential applications in the areas including electrochemical devices, microbiology, biomedical, and pharmaceuticals fields. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40630.     

Cationic microgel emulsion with a high solid content by a multistep addition method in inverse microemulsion polymerization

The multistep addition of a monomer and initiator was developed to successfully synthesize cationic polyacrylamide microgels with solid contents (SCs) greater than 35% and cationic monomer concentrations of 0–40 mol % by inverse microemulsion polymerization. Two feed methods, three‐step nonuniform addition and five‐step uniform addition, were implemented to obtain microgel emulsions with 37% SC. The former addition method was designed according to the solubilization limit of the microemulsion before step polymerization, and that of the latter was a constant based on the remaining surfactant weight in the reactor. The product properties in the intermediate processes of these two methods were compared by dynamic light scattering and viscosity measurement. The results show that the products here were translucent microemulsions instead of milky ones when they were synthesized by a semicontinuous polymerization. Also, the particle sizes of these two methods were almost the same; this indicated that the oscillation phenomenon in continuous polymerization at a high SC was avoided. With the former feed method, the risk and operation cost in the synthesis process could be cut down greatly. Moreover, the viscosity of the cationic microgel emulsion conformed to the Krieger–Dougherty equation with a greater value of intrinsic viscosity than that of a hard‐sphere system because of an electroviscous effect. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40585.     

Rheological properties of collagen/hydroxypropyl methylcellulose (COL/HPMC) blended solutions

Collagen/HPMC blends with different HPMC content (HC) were investigated by dynamic responses, creep recovery, thixotropy, and morphological observation. Storage modulus, loss modulus, complex viscosity, and activation energy decreased with the increased HC, while the flow behavior index increased with the increased HC and the dynamic denaturation temperature reached the maximum as HC increased to 50%, indicating that the flowability and thermal stability of collagen solution were improved by the addition of HPMC. However, the blends with higher HC tended to have a relatively lower recovery capacity, and the hysteresis loop areas of the blends were lower than that of collagen (especially when HC > 50%). Additionally, the morphology of collagen/HPMC was examined by both of atomic force microscopy and scanning electron microscopy. By combining with these results, it seemed that the rheological and structural properties of collagen/HPMC were related to the hydrogen‐bond interaction and compatibility between collagen and HPMC molecules. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40042.     

Oscillatory shear rheology of dilute solutions of flexible polymers interacting with oppositely charged particles

Fluids with both attractions and repulsions among its constituents can exist in multiple states depending on nature of the interactions. An external flow can induce such systems to transition between the different states, such as the globule‐stretch transition for polymers in poor solvents. Brownian dynamics simulations of a dilute solution of polymers and colloids interacting via short‐ranged potentials are presented. For some values of the strength and range of interactions, compact structures of polymers and colloids are formed. An external flow is capable of pulling these globules apart, causing the polymers to stretch at a critical shear rate. In oscillatory shear, the shear rate can cycle between being above and below this critical shear rate leading to interesting dynamics. These dynamics are quantified using the rheological response in large amplitude oscillatory shear. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1365–1371, 2014     

风干与饱水状态下花岗岩单轴流变特性试验研究

对软弱岩石(体)的流变特性进行了许多研究，相比较而言。对坚硬(相对)完整岩石流变特性的研究则少得多。坚硬完整岩石的流变特性对岩土工程的影响在很多情况下可以忽略。但在长期恶劣环境作用下，例如。长期浸泡于水中呈水饱和状态。其影响则会大许多。因而了解坚硬完整的岩石在恶劣环境作用下的流变特性，是很有意义的。鉴于此。开展了花岗岩在饱水状态下流变特性的试验研究。并与其风干状态作了对比，在强度和变形特性方面获得了重要的资料。     

土质心墙堆石坝应力和变形研究

论述了考虑坝体流变和上游坝壳料浸水变形特性的土质心墙堆石坝应力和变形的计算方法，以黑河水库大坝为例，采用三维有效应力法对坝体的应力和变彤特性进行了分析研究，结合已有的坝体变形观测资料，反馈分析了坝体流变模型参数，并对坝体的后期变形进行了预测，重点研究了心墙应力、拱效应和心墙开裂等特性。     

灰色时效模型及在基坑锚拉墙位移预测中的应用

针对岩土工程的灰色理论，单纯从可测位移建立可预测的模型，未考虑工程荷载影响．在分析岩土流变模型的基础上，建立了反映岩土工程荷载与位移的时效关系的灰色流变模型GRM（m，n），并提出了采用最小二乘辨识模型的方法．将该模型辨识应用于辨识基坑锚拉墙中锚座位移随荷载变化时效关系并用于预测后期锚座位移，取得理想效果，验证了方法的可行性．     

饱和状态下硬岩三轴流变变形与破裂机制研究

利用岩石全自动流变伺服仪对饱和状态下坚硬大理岩和绿片岩进行了三轴压缩流变试验,基于得到的硬岩三轴流变试验结果,研究了硬岩在不同围压作用下的轴向应变以及侧向应变随时间的变化规律,从而为岩石工程流变数值分析时参数的辨识提供了可靠的试验依据。然后研究了硬岩轴向变形与侧向变形之间的关系,探讨了围压与粒径对岩石轴向以及侧向变形特性的影响规律,分析了岩石三轴流变过程中的塑性变形特性,讨论了流变应力水平对岩石侧向-轴向变形特性的影响规律。最后对不同围压作用下岩石流变破裂断口微细观特征进行了分析。