A sorption balance-based method to study the initial drying of dispersion droplets

The initial drying of dispersion samples with varying geometries and surface areas was continuously recorded in a sorption balance at different temperatures and relative humidities. The samples were applied as small (5–20 mg) droplets on glass. We were able to show a linear dependence of the evaporation rate on the exposed surface area of the samples if the evaporative cooling was taken into account. The method outlined in the present paper facilitates scaling and comparison of results obtained from drying experiments with different-sized dispersion samples.     

Yield stress measurements and microstructure of colloidal kaolin powders clusterized and dispersed in different liquids

Rheologicat measurements of four colloidal kaolin powders dispersed in water, paraffinic oil and liquid rubber have been done at solid concentration （9 （VS/VL） in the range 8-33%. In quasi-static conditions the yield stress τ° values were derived. An S-shaped relationship between τ° and （9 exists, that allows to evaluate the percolation threshold θc values. In water θc ranges between 29% and 33%, while it is between 17% and 21% in oil and in liquid rubber. In water the microstructure units, i.e. the primary clusters among kaolin crystallites, are denser and bigger than the ones in the two other liquids. Furthermore, in quasistatic condition, the aqueous microstructure units have less tendency to cling together to form a network that can span all over the liquid phase. The different kaolin dispersions at θ equal to 22% are characterized by yield stress ranging between 7.S Pa and 59 Pa in water, 66-250 Pa in oil and 230-770 Pa in liquid rubber. It has been found that for any kaolin types the log τ°/ θ evaluated near to the percolation threshold is a conservative parameter of the three different liquids. These results are useful to design colloidal dispersions with selected microstructure.     

Order in amorphous polystyrenes as revealed by electron diffraction and diffraction microscopy

Ordered regions ranging in size between 15 and 45 Å have been established in several atactic polystyrenes of various molecular weights (4800; 51,000; and 1,800,000) as well as in an amorphous isotactic polystyrene by means of electron diffraction and high-resolution diffraction microscopy. The order is due to long-chain polymer molecules which tend to align more-or-less parallel to one another with a constant average spacing. The orderly chain packing can be disturbed upon cross-linking by electron irradiation, the disturbance being manifested in the irreversible changes in the d spacing and broadening of one of the diffuse rings which is inter-molecular in origin. From the results obtained, the high-resolution diffraction microscopy technique appears to have the potential for resolving the question regarding the presence of order in unoriented amorphous polymers. The technique can also differentiate between a broadened diffuse ring due to small crystallites and another due to paracrystals containing numerous defects.     

Experimental study of the relative effect of pressure drop and flow rate on the droplet size downstream of a pipe restriction

An experimental setup consisting of a 100?mm inner diameter pipeline, a butterfly valve with inner diameter of 100?mm, and oil and water pumping capacities of up to 20?m³/h were used to study droplet breakup in two-phase oil–water flow. The tests were performed at atmospheric pressure and under ambient temperatures. A particle-sizing camera was used to quantify droplet sizes. Combinations of different flow rates, water cuts, and pressure drops were tested to determine the relative effects of flow rate and pressure drop over a valve on the droplet breakup process. The test matrix was designed so that it should be possible to determine if the droplet sizes produced were independent of the flow rate. The fluid system consisted of a water phase and a mineral oil with viscosity of 4?mPa?·?s. Two different droplet breakup models were compared against the measured droplet sizes. The two models considered turbulence and droplet acceleration through the restriction respectively as the main contributor for droplet breakup.     

Poly(ethylene terephthalate)/carbon black composite fibers prepared by electrospinning

Poly(ethylene terephthalate)(PET)/carbon black(CB) composite fibers with improved mechanical properties in tensile modulus and tensile strength are prepared by eletrospinning. Stable dispersions suitable for electrospinning are obtained by dispersing melt pre-compounded PET/CB composites in hexafluoroisopropanol. The fiber morphology and CB dispersion are investigated by FESEM and TEM. The addition of CB has no obvious effect on fiber diameter, and the average fiber diameters for all the samples are around 2-3 μm. CB in the fibers is in the form of submicron-sized clusters. The thermal properties of the PET/CB composite fibers are evaluated by DSC, showing almost unchanged melting temperature and crystallinity. Uniaxial tensile tests are used to measure the mechanical properties of the PET/CB composite fiber mats. The fiber mats containing 1 wt%-8.5 wt% CB have significantly improved tensile modulus compared to neat PET fiber mat, showing reinforcing effect of CB. The electrical conductivity of the fiber mats has also been tested.     

Rheological studies of fumed silica–polydimethylsiloxane suspensions

In this study, dynamic mechanical measurements and transmission electron microscopy are used to examine the behavior of fumed silica/polydimethylsiloxane (PDMS) suspensions. The work focuses on three aspects: (i) the modulation of the interactions between silica and PDMS through a controlled silylation of the silica surface; (ii) the effect of the process used to graft the silica surface; (iii) the effect of the silica volume fraction used in the dispersions. A relation between the silica grafting ratio, the aggregate size and the rheological properties has been established and the results have interpreted through a model of fractal clusters.     

聚苯胺水基胶体分散液及其复合物的研究 Ⅱ紫外光谱及导电性能

利用紫外可见光谱研究了聚苯胺（ＰＡｎ）在水基胶体分散液中掺杂与脱掺杂过程，证实了ＰＡｎ的掺杂与脱掺杂是完全可逆的过程．当ｐＨ＝３５时，开始脱掺杂，当ｐＨ＝６０时，脱掺杂已基本结束．ＰＡｎ颗粒的大小也对紫外光谱有影响．当聚苯胺颗粒尺寸达到纳米量级时（１００ｎｍ），复合膜光谱吸收峰明显兰移，表现出了表面效应和量子尺寸效应．聚苯胺／聚乙烯醇复合膜的电导率不仅受聚苯胺含量的影响，同时也受复合膜中聚苯胺颗粒聚集状态的影响．较小的聚苯胺颗粒，使复合膜具有较低的渗滤阈值．     

聚苯胺水基胶体分散液及其复合物的研究 Ⅰ制备、表征及复合物的表观形貌、力学性能

以聚乙烯醇（ＰＶＡ）为稳定剂（ｓｔｅｒｉｃｓｔａｂｉｌｉｚｅｒ）利用分散聚合（ｄｉｓｐｅｒｓｉｏｎｐｏｌｙｍｅｒｉ ｚａｔｉｏｎ）的原理，成功地制备出了稳定的聚苯胺（ＰＡｎ）水基胶体分散液．聚苯胺颗粒的大小受聚合条件如稳定剂浓度、单体浓度、温度以及搅伴状态等的影响．ＰＶＡ通过物理作用吸附在ＰＡｎ颗粒的表面，起到阻止ＰＡｎ颗粒进一步团聚的作用．但这种作用力较弱．ＰＡｎ颗粒的原始尺寸大小约为２０ｎｍ．由此原始颗粒组成了尺寸在１００ｍｍ～２００ｍｍ左右的稳定颗粒     

Efficient Synthesis of Hydrolytically Degradable Block Copolymer Nanoparticles via Reverse Sequence Polymerization-Induced Self-Assembly in Aqueous Media

Hydrolytically degradable block copolymer nanoparticles are prepared via reverse sequence polymerization-induced self-assembly (PISA) in aqueous media. This efficient protocol involves the reversible addition-fragmentation chain transfer (RAFT) polymerization of N,N′-dimethylacrylamide (DMAC) using a monofunctional or bifunctional trithiocarbonate-capped poly(ϵ-caprolactone) (PCL) precursor. DMAC monomer is employed as a co-solvent to solubilize the hydrophobic PCL chains. At an intermediate DMAC conversion of 20–60 %, the reaction mixture is diluted with water to 10–25 % w/w solids. The growing amphiphilic block copolymer chains undergo nucleation to form sterically-stabilized PCL-core nanoparticles with PDMAC coronas. ¹H NMR studies confirm more than 99 % DMAC conversion while gel permeation chromatography (GPC) studies indicate well-controlled RAFT polymerizations (M_w/M_n≤1.30). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) indicate spheres of 20–120 nm diameter. As expected, hydrolytic degradation occurs within days at 37 °C in either acidic or alkaline solution. Degradation is also observed in phosphate-buffered saline (PBS) (pH 7.4) at 37 °C. However, no degradation is detected over a three-month period when these nanoparticles are stored at 20 °C in deionized water (pH 6.7). Finally, PDMAC₃₀-PCL₁₆-PDMAC₃₀ nanoparticles are briefly evaluated as a dispersant for an agrochemical formulation based on a broad-spectrum fungicide (azoxystrobin).