喷雾干燥颗粒表面形貌形成过程粗粒化模拟

喷雾干燥制粒有着广泛的应用。颗粒表面形貌的调控对提升颗粒品质起到至关重要的作用。本研究旨在建立分子尺度粗粒化模型,描述蒸发诱导下溶质的自组装行为,预测不同干燥条件下表面形貌的演变过程。文中建立的粗粒化网格Monte Carlo模型可以处理球形固体溶质,并充分考虑各物质之间相互作用及相变过程。开发的分析方法可以定量蒸发过程中液体残留率、颗粒分布与组装形貌。通过初步的二维系统模拟可以发现,溶剂不断蒸发过程中溶质逐渐移动,形成各种自组装结构。溶剂化学势越小,液体残留率越低。随着初始溶质浓度升高,最终溶质组装形貌从点状变为网状结构。不同的物质间相互作用也会导致紧密或松散的溶质分布。     

碳纳米管在炭纤维表面的可控自组装

采用催化化学气相沉积法将碳纳米管(CNTs)原位生长于炭纤维(CF)表面并自组装成不同形貌的CNTs/CF杂化结构。使用扫描电子显微镜、拉曼光谱仪对制备的纳米/微米杂化结构进行微观形貌分析和结构表征。结果显示,随着温度的升高,碳纳米管在炭纤维表面由均匀分布状态转变为取向生长状态,并且长度及石墨化程度均不断增加。结合碳纳米管结构参数的变化,使用纳米悬臂梁模型解释了这一杂化结构的形成机理。模型分析表明,杂化结构的形貌转变是由不同温度下在炭纤维表面生长的碳纳米管的结构参数不同所造成的,因此可以通过调整相关结构参数控制碳纳米管在炭纤维表面的自组装过程。     

ε-CL-20在二元混合溶剂中晶体形貌的分子动力学模拟

利用分子动力学模拟的方法探究了乙酸乙酯与二溴甲烷组成的二元溶剂在298.15 K,1 atm下对ε-CL-20晶体形貌的影响。通过修正附着能模型(MAE)模型探究了溶剂-晶体相互作用,用分子动力学模拟预测了不同组成的乙酸乙酯/二溴甲烷混合溶剂中ε-CL-20的晶体形貌并与实验获得ε-CL-20的晶体形貌进行了对比。结果表明,实验获得的晶体形貌与模拟结果一致,且晶面粗糙度越大,溶剂-晶体相互作用越强。此外,还通过均方位移(MSD)分析了溶剂分子在不同晶面的扩散系数,探究了溶剂扩散速率对不同晶面的影响,并利用径向分布函数(RDF)分析了溶剂分子与晶体分子间相互作用的组成。     

离子型表面活性剂水溶液自组装胶团模型研究

以表面活性剂为模板的仿生合成中,模板的自组装特性是关键环节;利用试验优选合适的表面活性剂用于仿生合成,耗费时间长,成本高。因此,我们从热力学角度出发,考虑了尾基转换自由能、尾基变形自由能、胶团中心-水界面自由能、头基空间相互作用、头基离子间相互作用的影响,建立了单一离子型表面活性剂自组装模型,用于仿生合成过程中优选表面活性剂。利用该模型可直接预测离子型表面活性剂自组装的临界胶团浓度、胶团聚集数和胶团尺寸分布,并用试验数据进行了验证,二者吻合较好。     

耦合粗粒化离散颗粒法和多相物质点法的气固两相流模拟

在气固两相流动的模拟中严格处理颗粒运动和颗粒相互作用时,欧拉?拉格朗日(EL)方法比欧拉?欧拉(EE)方法更具优势。但传统的EL方法仅能处理少量颗粒。将颗粒群作为单个计算颗粒处理可扩大模拟规模,粗粒化离散颗粒法(CG-DPM)和多相物质点法(MP-PIC)是其中两种主要方法,分别更适用于稠密和稀疏的颗粒流体系统。将两种方法耦合建立了更通用、准确和有效的EL方法,比较了不同耦合参数下流型、固相分率分布等定量信息,确定了最佳耦合参数。     

微波作用下反应结晶制备碱式碳酸镁

采用等初末温度比较法和等温法分别在微波及水浴加热下反应结晶合成了碱式碳酸镁颗粒。用扫描电镜（SEM）、X射线衍射（XRD）以及粒度分析表征不同阶段样品的晶体结构、表面形貌和粒度分布,用化学分析（滴定法）跟踪反应结晶过程中镁离子浓度的变化。实验结果表明：所得晶体由纳米片自组装而成,微波场对碳酸镁结晶具有促进作用,即微波对碳酸镁结晶中初级纳米颗粒的组装具有促进作用,可提高碱式碳酸镁的生长速率,增大颗粒粒度,但没有改变产物晶习;不同温度下碱式碳酸镁转变路径不同,较高温度时无定形颗粒直接组装成碱式碳酸镁,较低温度时将出现正碳酸镁中间态,经由不同相转变历程的碱式碳酸镁纳米片微观形貌和组装方式并不相同。     

分子动力学模拟研究两亲聚合物与疏水纳米粒子自组装核-壳结构

基于Martini力场采用粗粒化分子动力学模拟研究了Pluronic嵌段共聚合物在疏水纳米表面自组装膜结构,考察了Pluronic嵌段共聚合物结构对自组装单分子膜结构的影响。模拟结果发现Pluronic聚合物在疏水纳米表面自组装形成了以纳米材料为核,聚合物为壳的特殊核-壳结构。聚合物的浓度和结构都会影响该壳层结构,在浓度较低时,聚合物EO嵌段卷曲地附着在疏水纳米颗粒表面,类似形成层状的壳层结构;随着浓度的提高,EO嵌段伸向溶剂相,形成星形自组装膜结构。增加Pluronic共聚物相对分子质量,吸附在纳米材料的聚合物壳层厚度也逐渐增加。随着聚合物PO摩尔的增加,吸附在纳米材料表面的PO嵌段由“S”形或“W”形吸附逐渐变成“U”形吸附。这可能因为随着聚合物浓度的提高,有限的纳米颗粒表面不足以提供足够多的吸附位点导致聚合物吸附构型转变。     

分子动力学模拟研究两亲聚合物与疏水纳米粒子自组装核-壳结构

基于Martini力场采用粗粒化分子动力学模拟研究了Pluronic嵌段共聚合物在疏水纳米表面自组装膜结构,考察了Pluronic嵌段共聚合物结构对自组装单分子膜结构的影响。模拟结果发现Pluronic聚合物在疏水纳米表面自组装形成了以纳米材料为核,聚合物为壳的特殊核-壳结构。聚合物的浓度和结构都会影响该壳层结构,在浓度较低时,聚合物EO嵌段卷曲地附着在疏水纳米颗粒表面,类似形成层状的壳层结构;随着浓度的提高,EO嵌段伸向溶剂相,形成星形自组装膜结构。增加Pluronic共聚物相对分子质量,吸附在纳米材料的聚合物壳层厚度也逐渐增加。随着聚合物PO摩尔的增加,吸附在纳米材料表面的PO嵌段由"S"形或"W"形吸附逐渐变成"U"形吸附。这可能因为随着聚合物浓度的提高,有限的纳米颗粒表面不足以提供足够多的吸附位点导致聚合物吸附构型转变。     

金属Pd掺杂ZnO纳米材料的制备及其气敏性能研究

以氯化锌、尿素、聚乙烯吡咯烷酮为原料,不同配比的乙醇和水为反应溶剂,用水热法制备出尺寸、形貌不同的ZnO纳米材料。采用X射线衍射(XRD)、场发射扫描电镜(FESEM)、透射电镜(TEM)研究产物的组成、结构及形貌。表征结果显示三种不同反应条件分别生成了刺球状、雪片状和片球状三种不同形貌的ZnO,经过自组装过程在ZnO材料表面掺杂上纳米Pd颗粒,气敏性能测试结果表明:负载纳米Pd颗粒的ZnO灵敏度比纯ZnO灵敏度有不同程度的提高,研究表明金属Pd颗粒掺杂的ZnO为丙酮传感器的理想材料。     

氧化铁纳米薄膜自组装制备与原子力显微镜表征

单晶硅表面上自组装单层有机分子巯基硅烷单层膜,将这层巯基原位氧化成为磺酸基,在氢氧化铁溶胶形成过程中同时放入带有磺酸基层的硅基底进行薄膜组装,由于溶胶颗粒极小、分布均匀,可以得到表面粗糙度仅为0.164nm、颗粒小于10nm的均匀的氧化铁薄膜,并采用原子力显微镜(AFM)进行了表面形貌的表征.     

Drying of a system of multiple solvents: Modeling by the reaction engineering approach

Drying is a very important industrial operation in society. In drying, solute may dissolve in an aqueous solvent, a nonaqueous solvent or a mixture of solvents. Many mathematical models have been published previously to model drying of solute in water. The reaction engineering approach (REA) is known to be an easy‐to‐use approach. It can describe well many drying cases of water removal. Currently, no simple lumped model has been attempted to describe drying of porous materials containing a mixture of solvents. In this study, for the first time, REA is constructively implemented to model drying in a mixture of one aqueous and one nonaqueous solvent. The REA is applied here to model the drying of polyvinyl alcohol/methanol/water under constant and time‐varying environmental conditions. Similar to the relative activation energy of water, that of methanol is generated through one accurate drying run. For modeling the time‐varying drying, the relative activation energies are the same as those for modeling convective drying under constant ambient conditions but combined with the equilibrium activation energies at the corresponding humidity, methanol concentration, and temperature for each drying period. The REA is accurate to model drying of a solute in nonaqueous solvent as well as in a mixture of noninteracting solvents. In the future, spatially distributed REA for nonaqueous or mixtures of both aqueous and nonaqueous solvent will be explored for fundamental understanding and for practical application. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2144–2153, 2016     

Impact of agitated drying on the powder properties of an active pharmaceutical ingredient

In this study, the impact of agitated drying on the physical and bulk powder properties of an active pharmaceutical ingredient (API) is presented. The effects of different agitated drying conditions such as agitation rate, drying temperature, drying time pre-agitation, drying time during agitation and number of solvent wash cycles on the bulk density, millability, flow and specific surface area is reported. The crystal morphology is altered from fibrous needles to agglomerates when switching from tray to agitated drying. An increase in bulk density and specific surface area was evident when using agitated drying compared to tray drying as hard coarse granules were produced with an increase in the number of fine particles < 10 μm. The bulk density was found to increase with an increase in agitation speed, drying time and number of solvent wash cycles used during filtration. Controlling both fine and coarse particle size of the granules for this API during agitated drying was difficult to achieve due to the fibrous crystal habit. However, the increase in the bulk density observed has the potential to facilitate improvements in the ease of drug product development. In the case of this system further particle size control was required through the use of dry milling.     

The role of solute conformation,solvent–solute and solute–solute interactions in crystal nucleation

The induction time for nucleation can differ based on the solutions used to conduct a crystallization, which can in turn impact the efficiency and economics of a crystallization process, the crystal size distribution, the morphology and ultimately functionality of the final product. Establishing a link between the nucleation pathway/solution structure and nucleation induction time is essential to achieve improved comprehension of the process of crystal nucleation from solution. In this study, the role of solute conformation, solvent–solute interaction, and solute–solute interaction in nucleation was examined using tolbutamide as a model compound in toluene and toluene–alcohol solutions. Through a combination of induction time experiments, attenuated total reflection Fourier transformed infrared spectroscopy, nuclear magnetic resonance spectroscopy, molecular dynamics simulations, and quantum chemical calculations, it was found that not only solvent–solute interactions but also solute–solute interactions and structural similarities between molecular self-assemblies in the solution and synthons in the crystal structure, can significantly influence the nucleation induction time.     

Migration during Convective Drying. I-Theoretical

A model is proposed which makes possible the mathematical treatment of the movement of solute resulting from the evaporation of solvent from the surface of a capillary network. It is considered useful in predicting the migration of solute in the capillaries of a textile material during the constant–rate period of convective drying. Within the limits of certain simplifying assumptions, the concentration depth profiles are defined as a function of time by the solution to the equation of Fick's second law of diffusion satisfying defined boundary conditions.     

Structure-dependent re-dispersibility of graphene oxide powders prepared by fast spray drying

The graphene oxide powder (GOP) obtained from the spray drying process often exhibits poor re-dispersibility which is considered due to the partial reduction of GO sheets. The reduction of drying tem-perature can effectively increase the re-dispersibility of GOP, but result in a decreased drying efficiency. Herein, we found that the re-dispersibility of GOP is strongly affected by its microstructure, which is determined by the feed concentration. With the increase of feed concentration, the GO nanosheet assem-bly varies from the disordered stacking to relatively oriented assembly, making the morphology of the GOP transform from ball-like (the most crumpled one) to flake-like (the least crumpled one), and the 0.8 mg·ml-1 is the threshold concentration for the morphology, structure, and re-dispersibility change. Once the feed concentration reaches 0.8 mg·ml-1, the appearance of the nematic phase in droplet ensures the relatively oriented assembly of GO sheets to form the layered structure with a low crumpling degree, which greatly improves the polar parts surface tension of the solid GOP, making the GOP easier to form hydrogen bonding with water during the redispersion process, thus stabilizing dispersion. This work pro-vides useful information for understanding the relationships between the morphology, microstructure, and final re-dispersibility of GOPs.     

Influence of pore structure and impregnation–drying conditions on the solid distribution in porous support materials

Deposition of solids within porous materials from a drying solution is an important phenomenon in numerous natural and industrial processes. A profound knowledge about influences of different parameters on the solid distribution in the material is required for an effective targeted impregnation process. Experimental investigations and simulations are used to study the influence of pore structure, drying conditions, and solute concentration on the solid distribution in porous support materials after impregnation and drying. It is found that low drying rates lead to strong solid accumulation at the material surface, whereas high drying rates reduce the solute transport to the surface and result in more uniform solid distributions. A small pore diameter and distribution width reduce solute migration during drying and lead to uniform solid distributions without being influenced by the drying conditions. A higher initial concentration of the impregnation solution causes pronounced surface accumulation, while low initial solute concentrations result in more uniform distributions. Fundamental effects during drying are captured in an existing pore network model by adaption of experimental pore structures and impregnation–drying conditions, resulting in a good general agreement of experiments with simulations.     

Fluidized bed spray granulation: Investigation of the coating process on a single sphere

The coating and granulation of solid particles in a fluidized bed is a process which converts pumpable and atomizable liquids (solutions, slurries, melts) into granular solids in one step by means of drying. The solution to be processed is sprayed onto a fluidized bed. Particle growth can take place either via surface layering or agglomeration. In the case of surface layering the atomized droplets deposit a thin layer of liquid onto the seed particles. The solvent is then evaporated by the hot fluidizing, leaving behind the dissolved material on the surface. Although fluidized bed spray granulation and film coating have been applied in industry for several years, there is still a lack of understanding of the physical fundamentals and the mechanisms by which spherical granules are formed. Hence a new method was developed which allows the direct observation of the subsequent particle-forming mechanisms such as droplet deposition, spreading, wetting and drying. The authors present a laboratory scale apparatus in which a single freely suspended particle can be coated under well defined and constant coating and drying conditions. With this device, particle-growth-rate and the development of particle morphology were measured and investigated under various experimental conditions.     

Nanostructures generated from photopolymerization of poly(ethylene glycol) diacrylate templated from hexagonal lyotropic liquid crystals

The use of lyotropic liquid crystals (LLC) as a template to form periodic nanostructures in polymer materials is a promising technology. In this study, cross‐linked poly(ethylene glycol) diacrylate nanostructured materials were prepared by photopolymerization in LLC hexagonal phases. Polarized light microscopy and small‐angle powder X‐ray diffraction were used to understand the original LLC order retention on photopolymerization, and scanning electron microscope was used to investigate the morphology under different purifying solvents and drying conditions. A Quantachrome Autosorb 1 system was used to study the pore size distribution of samples. It was found that the LLC hexagonal structure was retained to a great extent after photopolymerization. The formation of nanostructures was affected by purifying solvent and drying condition. The nanostructure synthesized from LLC with favorably aligned nanopores will find increasing applications in gas and water filtration, biology, and health science. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

反渗透过程溶质脱除率方程

<正>溶解扩散理论、摩擦模型和表面力-孔流模型假设稳态时膜中溶质通量恒定“-”。本文分 析了该假设存在的理论依据,并基于膜的吸附-扩散模型’‘’建立了反渗透过程溶质脱除率方 程。     

Diffusion behaviour of the lead—acetate system

Variations in polarographic diffusion current constants for the lead—acetate system at constant ionic strength are shown to correlate with published equilibrium data. There is evidence that different types of solute—solute and solute—solvent interactions can be detected and distinguished by means of diffusion parameters.