晶体粒径对碰撞成核的影响

从单个晶体运动中与结晶器内其他晶体及固体壁面碰撞过程的能量损失角度,描述了碰撞成核过程,建立了晶体粒径与成核速率的理论关系模型。结果表明,晶体的粒度对碰撞成核速率有很大的影响。并利用氯化钠晶体进行了碰撞成核实验,使用理论模型对实验结果进行拟合,进而验证了理论模型所预期的规律。指出在分析二次成核时,应充分考虑晶体粒度对成核影响的重要作用。该理论模型为实现工业结晶过程的仿真模拟提供了依据。     

大颗粒氯化钾聚结结晶及其粒径控制

利用聚焦反射光束测量技术（FBRM）测定了氯化钾在水中的溶解度,研究了在转速为250 r/min时,颗粒氯化钾晶体的制备及其粒径控制的规律,并考察了在此转速下溶液中氯化钾聚结过程中初级粒子、降温速率、过饱和度对聚结的影响。研究结果表明：氯化钾溶解度随温度升高而增大;降温速率越快,溶液瞬时过饱和度越大,越易爆发成核,产生的粒子数越多;初级粒子在每100 mL溶液的最佳添加量为0.05~0.1 g时,制备的晶体平均粒径可达1 900~2 000 μm,产品粒径较大,球形度也较好。     

齐聚物对PET结晶性能的影响

运用差示扫描量热法研究了不同齐聚物含量的聚对苯二甲酸乙二酯(PET)的非等温结晶过程。结果表明:随齐聚物含量的增加,PET的熔融结晶温度向低温偏移,过冷度增大,结晶热焓增加,结晶度先增大后减小;在相同的结晶温度下,随着齐聚物含量的增加,PET的结晶温度区域逐渐变宽,半结晶周期增大,结晶速率降低。     

Effect of thermodynamic parameters on prediction of phase behavior and process design of extractive distillation

Extractive distillation was investigated for separation of the minimum azeotrope of n-propanol/water,via the Aspen Plus simulation platform.Experimental data of n-propanol/water,which could pass the thermodynamic consistency test,were regressed to get suitable binary interaction parameters (BIPs) by the UNIQUAC thermodynamic model.The azeotrope system was heterogeneous in the simulation with built-in BIPs,which was contrary to the experimental data.The study focused on the effect of thermodynamic parameters on the prediction of phase behavior,and process design of extractive distillation.N-methyl-2-pyrrolidone (NMP) and ethylene glycol were used as solvents to implement the separation.Processes with built-in and regressed BIPs were explored,based on the minimum total annual cost (TAC).There were significant differences in the phase behavior simulation using different thermodynamic parameters,which showed the importance of BIPs in the design and optimization of extractive distillation.     

多孔球层内水的过冷与蓄冷特性

影响水过冷度的因素很多, 同样实验条件下水的过冷度并非一个定值, 多孔球层的存在对水的过冷度产生一定影响。对蒸馏水和不同球径的多孔球层介质进行了32次过冷度测定实验, 并对蒸馏水和多孔球层介质的蓄冷特性进行了实验研究。过冷度实验结果采用统计方法进行分析, 并用CCD相机和热像仪对过冷现象进行观察。结果表明:大温差降温条件下水的平均过冷度要小于阶梯缓慢降温条件下水的过冷度;多孔球层球径越小, 平均和峰值过冷度越小, 但直径为11 mm出现特例, 其平均过冷度比8 mm直径多孔球层要小, 峰值也比8 mm的小;多孔球层固体基底的存在大大缩短了蓄冷相变时间。     

超声波对三水醋酸钠相分离及结晶的影响

The effects of ultrasonic radiation on phase separation as well as the crystallization of sodium acetate trihydrate,a typical salt hydrate phase change material (PCM),were studied experimentally.It is shown that ultrasonic radiation may inhibit phase separation to a certain degree.The influence of ultrasonic radiation on crystallization is also found.The addition of PCM grain can inhibit supercooling effectively.The crystallization is related to the supercooling degree.Furthermore,the effects of ultrasonic radiation on inhibiting phase separation of salt hydrates are discussed based on theoretical analysis.     

Effect of sulfur phase transition on polypropylene crystallization

ABSTRACT

The Polypropylene (PP) crystals can be regulated by inorganic additive. In this work, sulfur was blended with PP by dynamical in-situ dispersion to obtain good dispersion and refinement; meanwhile, during the non-isothermal crystallization of PP, the phase state of the dispersed sulfur phase changed from the liquid to the supercooled state, affecting the crystalline morphology and crystallization behavior of PP. The results showed that amorphous sulfur particles were present in the PP spherulites, which was obviously different from the traditional crystal morphology. The crystallization rate of the blend is found to increase with smaller sulfur content and due to the occurrence of the sulfur phase change; the crystallization activation energy are less than that of pure PP.     

粒度对氢氧化铝低温相变动力学的影响

利用综合热分析仪分析技术、激光粒度分析、扫描电镜和X射线衍射研究了粒度对氢氧化铝在低温相变转化成勃姆石过程的影响,并采用Kissinger方程、Ozawa方程和Crane方程进行了不同粒度的氢氧化铝在低温相变过程的动力学参数计算。结果表明：普通砂状氢氧化铝在相变过程有2个较为明显的吸热峰,将砂状氢氧化铝研磨至中位径D₅₀在12μm左右时,相变过程仍然有2个明显的吸热峰;当氢氧化铝中位径D₅₀在1μm左右的氢氧化铝,相变过程则只有1个吸热峰。根据Kissinger方程和Ozawa方程计算结果,随着粒度的降低,其相变活化能也相应的降低,说明降低氢氧化铝粒径,有利于勃姆石的制备。根据XRD图谱显示,低温煅烧后,样品的主要物相为勃姆石,此外还含有少量的三水铝石,粒径越细,煅烧后样品中勃姆石含量越高。     

Effect of calcium fluoride concentration on nylon 6,6 crystallization behavior and morphology

Nylon 6,6 (polyamide 6,6) heterogeneously nucleated with ca. 65 ppm calcium fluoride exhibits crystallization behavior and morphology characteristic of much higher levels of nucleating agent. This is shown using differential scanning calorimetry and polarized optical microscopy. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1675–1678, 1998     

Effect of solvents on closed-loop phase behavior of block copolymers

We studied the effect of solvent selectivity on the closed-loop phase behavior of a polystyrene-block-poly(n-pentyl methacrylate) copolymer. It was found that the lower disorder-to-order transition temperature (LDOT) and upper order-to-disorder transition temperature (UODT) consisting of the closed-loop were very sensitive to the selectivity of the solvent. With the addition of very small amounts of non-selective solvents such as di-n-octyl phthalate and dimethyl phthalate, the LDOT increased rapidly, whereas the UODT decreased dramatically; thus, the immiscibility loop was shrunk greatly. On the other hand, both the LDOT and UODT decreased with increasing amount of dodecanol, a highly selective solvent to poly(n-pentyl methacrylate) block. However, the decrease in the LDOT was greater than that of the UODT, leading to an increased immiscibility loop.     

Correlation between crystallization kinetics and melt phase behavior of crystalline-amorphous block copolymer/homopolymer blends

We show that the phase behavior of the strongly segregated blend consisting of a crystalline-amorphous diblock copolymer (C-b-A) and an amorphous homopolymer (h-A), which depends on the degree of wetting of A blocks by h-A, can be probed by the crystallization kinetics of the C block. A lamellae-forming poly(ethylene oxide)-block-polybutadiene (PEO-b-PB) was blended with PB homopolymers (h-PB) of different molecular weights to yield the blends exhibiting ‘wet brush’, ‘partially dry brush’, and ‘dry brush’ phase behavior in the melt state. The crystallization rate of the PEO blocks upon subsequent cooling, as manifested by the freezing (crystallization) temperature (T_f), was highly sensitive to the morphology and spatial connectivity of the microdomains governed by the degree of wetting of PB blocks. As the weight fraction of h-PB reached 0.48, for instance, T_f experienced an abrupt rise as the system entered from the wet-brush to the dry-brush regime, because the crystallization in the PEO cylindrical domains in the former required very large undercooling due to a homogeneous nucleation-controlled mechanism while the process could occur at the normal undercooling in the latter since PEO domains retained lamellar identity with extended spatial connectivity. Our results demonstrate that as long as the C block is present as the minor constituent the melt phase behavior of C-b-A/h-A blends can also be probed using a simple cooling experiment operated under differential scanning calorimetry (DSC).     

磷石膏在低浓度硫酸中的溶解及相态变化

湿法磷酸生产过程副产大量磷石膏,因其含有较多杂质而无法直接利用,目前可采用硫酸酸浸处理提高磷石膏品质。为弄清酸浸过程中石膏的溶解性能和结晶形态的变化,本文探讨了在0～80 ℃、0～30%的硫酸浓度条件下,磷石膏在硫酸溶液中的溶解度大小、结晶形貌、物相组成及结晶水含量的变化情况。实验结果表明,磷石膏在硫酸溶液中的溶解度随温度升高而升高,在80 ℃时达最大;随浓度升高呈先升后降的变化,在硫酸浓度为10%时溶解度最大。硫酸浓度小于10%时,磷石膏中二水硫酸钙溶解,但无新相生成,其形貌变化不大;硫酸浓度大于10%时,二水硫酸钙溶解,同时再结晶转化成无水硫酸钙,最终导致磷石膏形貌和相态发生了改变,溶解度随硫酸浓度升高而降低。     

温敏性两亲嵌段共聚物相行为的耗散粒子动力学模拟

采用耗散粒子动力学模拟研究了由温敏性聚N-异丙基丙烯酰胺(PNIPAM)与聚己内酯(PCL)构成的两亲嵌段共聚物(PCL-PNIPAM-PCL)在水溶液中自组装的动力学过程及微相分离现象,考察了溶液浓度及温度对其相行为的影响。模拟发现不同体积分数的嵌段共聚物在水溶液中呈现出不同的自组装形貌,如球状胶束、柱状胶束、层状胶束等。温度对其在水溶液中的形貌及相变行为有着显著的影响。当温度较低时,PCL-PNIPAM-PCL于稀溶液中可形成稳定的以PCL为核,PNIPAM为壳的球形核壳胶束;而当温度升高到某一值时,在低温时所形成的球形核壳胶束将因温度的升高而转变为表面由PCL组成的多个不连续微区的多隔段胶束。这种温敏现象在耗散粒子动力学模拟中尚属首次被发现。另外,模拟中所得到的该体系的低临界溶解温度与实验测得的值也符合良好。对这一温敏现象作了较深入和细致的解释。本文工作表明耗散粒子动力学能用来研究温度对温敏性两亲嵌段共聚物相行为的影响并揭示其中的机制和一般规律。     

Effects of kinetics coefficients on ternary phase separation during the wet spinning process

A new Monte Carlo diffusion model is employed to simulate the phase separation of the ternary system during wet spinning process. Our results illustrate the thermodynamics parameters are the primary factors in morphology determination during the phase separation process. Meanwhile by varying kinetic parameters different fiber structures ranging from dust-like, finger-like to sponge-like morphologies are obtained. The morphological patterns are discussed in relation to the rate of particle exchange and the phase diagram. On the basis of the systematical simulation experiments we propose how the competition between segment–solvent and solvent–nonsolvent exchange determines the ultimate fiber morphologies in spinning solution.© 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Crystallization behavior of hydrogenated sunflowerseed oil: Kinetics and polymorphism

Kinetics of crystallization of hydrogenated sunflowerseed oil was studied by means of an optical method. Two different aspects were examined: the effects of preheating of the molten liquid on induction time of isothermal crystallization and the effects of cooling rate on the crystallization behavior. Induction time for crystallization was markedly dependent on the crystallization temperature and the cooling rate selected. Morphology, polymorphism and chemical composition of the crystals were examined. At all crystallization temperatures, β′-form was found for the first occurring crystals. Long spacings were also similar in all cases and corresponded to a double chainlength arrangement. The chemical composition of the crystals showed no differences at either cooling rate. However, the melting behavior was different. At a slow cooling rate, fractionation occurred, and differential scanning calorimetry diagrams had a broad second endotherm with three peaks, none of which were completely resolved. The polymorphic transformation rate from β′ to β was slower when induction times were longer.     

Influences of processing on the phase transition and crystallization of polypropylene cast films

Phase transition and changes of properties of isotactic polypropylene (i‐PP) cast films with the processing conditions have been investigated by wide‐angle X‐ray diffraction, two‐dimensional small‐angle X‐ray scattering, and atomic force microscopy. It was found that chill roll temperature was a major factor, which influenced the formation of mesomorphic phase and its transition to spherulitic structure. Only mesomorphic phase was observed in the films produced under a chill roll temperature of below 40°C. When the roll temperature was increased to 60°C, mesomorphic phase coexisted with spherulitic crystal structure, and totally transformed to monoclinic structure at the roll temperature of 80°C. Differential scanning calorimetry, tensile, and optical tests were also performed on the films. The results showed that the observed structure changes were closely related to the thermal behavior, tensile, and optical properties of the PP films. The influence of die temperature on the films was also discussed, but the effect was much less than chill roll temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41100.     

升降温速率对低温保护剂溶液结晶性质的影响

引言细胞和组织的低温保存是现代低温生物医学的重要研究内容,对于保存稀缺物种、器官移植有着重要意义。目前,成功实现低温保存的细胞和组织包括红细胞、胚胎、皮肤、精子等。卵母细胞是哺乳动物最重要的生殖细胞之一,卵母细胞低温保存对于保护濒危物种、保存优良动物品种、使人类突破生育年龄限制等方面有重大意义。卵母细     

水相添加剂对热可膨胀聚合物微球颗粒结构和膨胀特性的影响

通过戊烷发泡剂存在下的偏氯乙烯-丙烯腈-甲基丙烯酸甲酯(VDC-AN-MMA)悬浮共聚制备包覆型热可膨胀聚合物微球,考察氯化钠、柠檬酸和重铬酸钾等水相添加剂对聚合物微球颗粒结构和热膨胀特性的影响。结果表明氯化钠、柠檬酸和重铬酸钾的添加均可起到降低聚合过程中形成难膨胀聚合物细微粒子的作用,当氯化钠添加量为4%(质量分数,基于单体,下同)、柠檬酸添加量为2.5%～5.0%、重铬酸钾添加量为0.05%～0.1%时,制备的可膨胀聚合物微球具有粒径分布窄、形态规整、聚合物对发泡剂包覆效果好等特点;加热后未膨胀聚合物微粒数目少,膨胀均匀,膨胀温度区间宽。     

Phase equilibrium and crystallization behavior of mixed lipid systems

As complex lipid systems, the phase and crystallization behavior of mixtures of a high-melting milk fat fraction with a low-melting milk fat fraction or canola oil was studied. A turbidity technique was developed to estimate solubility and metastability conditions of these lipid mixtures. Both solubility and metastability of the high-melting milk fat fraction in liquid lipids increased exponentially with temperature. At a given equilibration temperature, liquid phases and solid fractions with nearly identical melting profiles and TAG compositions were obtained regardless of the original concentration of the lipid mixture. The maximum melting temperature (MMT), as measured by DSC, of the liquid phase increased dramatically in the equilibrium temperature range of 27.5–35.0°C but did not change at temperatures below and above this range (down to 25.0°C and up to 40°C in this study). The content of long-chain TAG (C₄₆−C₅₂) increased and short-chain TAG (C₃₆−C₄₀) decreased in the liquid phases as the equilibrium temperature increased. A plot of the TAG group ratio (i.e, long-short-chain TAG) vs. equilibrium temperature was generated to illustrate the phase behavior of the complex lipid system and to represent a solubility curve, from which the supersaturation level for crystallization kinetics was determined. Higher supersaturation and lower temperature resulted in higher nucleation and crystallization rates. Compared to the system with a low-melting milk fat fraction, mixtures of the high-melting milk fat fraction with canola oil had higher nucleation and crystallization rates due to the lower solubility found for this system.     

Effect of cooling rate on crystallization behavior of milk fat fraction/sunflower oil blends

The effect of cooling rate (slow: 0.1°C/min; fast: 5.5°C/min) on the crystallization kinetics of blends of a highmelting milk fat fraction and sunflower oil (SFO) was investigated by pulsed NMR and DSC. For slow cooling rate, the majority of crystallization had already occurred by the time the set crystallization temperature had been reached. For fast cooling rate, crystallization started after the samples reached the selected crystallization temperature, and the solid fat content curves were hyperbolic. DSC scans showed that at slow cooling rates, molecular organization took place as the sample was being cooled to crystallization temperature and there was fractionation of solid solutions. For fast cooling rates, more compound crystal formation occurred and no fractionation was observed in many cases. The Avrami kinetic model was used to obtain the parameters k _n and n for the samples that were rapidly cooled. The parameter k _n decreased as supercooling decreased (higher crystallization temperature) and decreased with increasing SFO content. The Avrami exponent n was less than 1 for high supercoolings and close to 2 for low supercoolings, but was not affected by SFO content.