相界面张力对两相聚合物熔体中分散相粒子粗化速度的影响研究

多相高分子共混物熔体中微区的发展机理,决定着体系的最终相结构．所以研究共混物熔体或溶液中的微区聚结机理已越来越显得重要和必要．作者先前的研究工作表明［１～６］,通过简单共混得到的均匀共混体系（如ＰＰ／ＥＶＡｃ）,在一定的退火热处理条件下,会自组织形成梯度相结构,即分散相粒子尺寸及其浓度从样品中心到表面逐渐增大．作者认为,这一结构的形成主要与基板对共混体系粗化过程的影响作用有关．初步认为是由于体系分散相聚结过程中,共混组分对基板的选择性浸润析出而导致了这种特殊的结构,亦可称为基板诱导相结构的形成．…     

第三相界面对高分子共混物粗化过程的影响研究

共混物相分离的机理已有研究［１］．但对共混物分散相的粗化过程的研究则不多见．１９７７年,Ｃａｈｎ等［２］预言第三相界面与低分子共混物之间存在的浸润作用对相分离过程应有较大影响．近年Ｔａｎａｋａ等［３］的研究结果表明,在几何空间受限的条件下,含有小分子...     

高分子共混物梯度相结构形成过程中的界面效应

通过在高分子共混物内部引入不同的第三相界面,系统地研究了退火热处理条件下该界面对于共混物梯度相形态形成的影响.对具有一定初始粒径的共混物体系或初始近似为均相的共混体系,在第三相界面的诱导下,均能形成梯度相形态.探讨了诱导界面间距与体系相结构的关系.结果表明,当两个诱导界面间距小于所生成梯度层厚度的两倍时,梯度结构趋于交叠.继续减小诱导界面间距,则梯度结构趋于消失,诱导界面间共混物中分散相粒子快速长大,界面的诱导作用遍布整个样片,证实了我们所提出的“高分子共混物中二维条件下界面诱导加速分散相粒子粗化凝聚”的结论.     

Coalescence-induced coalescence and dimensional crossover during the phase separation in ternary surfactant/polymer/water mixtures

We studied the separation process in the ternary mixtures of nonionic surfactant (C(12)E(6), hexaethylene glycol monododecyl ether), polymer (PEG = poly(ethylene glycol)), and water. The separation process of PEG/water rich domains from the surfactant rich matrix was observed by the optical microscopy. From the morphological analysis, we determined the size of the domains as a function of time. On this basis we identified a dominating mechanisms of domains growth, that is the coalescence-induced coalescence mechanism. The coalescence (collision) event of two droplets induces a flow or a change of concentration distribution around droplets which pushes other droplets together inducing further growth. We also observed the evaporation-condensation (Lifshitz-Slyozov) mechanism of growth, but it did not affect the growth of large domains appreciably. We determined two regimes of the coalescence-induced coalescence associated with the dimensionality of the system. When the domains were smaller or comparable in size to the sample thickness we observe a three-dimensional growth. When the domains became larger than the sample thickness, a two-dimensional growth was observed. In the first regime, the size of the domains, L(t), grew linearly with t, while in the second regime, L(t) approximately t(0.3). In the binary, surfactant/water system, water domains grew by the geometrical coalescence-induced coalescence as L(t) approximately t in three dimensions.     

Formation and Release of Cobalt(II) Sorption and Precipitation Products in Aging Kaolinite-Water Slurries

A comprehensive simulation of the coarsening mechanism coalescence-induced coalescence (CIC) is developed to predictthe growth rate of inviscid droplets in a viscous matrix fluid. In CIC, the shape relaxations of coalescing droplets establish flow fields that drive other droplets into contact, thus creating a cascade of coalescence events. It is believed that CIC is responsible for droplet growth in some demixed polymer solutions, such as isotactic polypropylene (iPP) and diphenyl ether (DPE). A cascade of coalescence events is simulated using a three-dimensional molecular dynamics-like simulation of a dispersed two-phase isopycnic fluid system. The coalescence-induced flow is driven mostly by the strong gradients in curvature at the neck of a coalescing pair of droplets, and the flow is modeled analytically by approximating it as due to a ring of point forces. The resultant velocity of each droplet in the suspension is calculated by superimposing all of the coalescence-induced flow fields and applying Faxen's Law. The mean droplet size grows like t(xi), where t is the coarsening time and xi a growth exponent that increases with increasing minority phase volume fraction varphi. Good agreement with experimental values of xi (0.22/=0.23. It is also shown that the droplet size distribution broadens for semidilute suspensions (varphi/=0.54). A phenomenological kinetic theory of coalescence is proposed. It is believed that in nondilute emulsions, CIC can account for coarsening that has been attributed previously to more traditional coalescence mechanisms. Copyright 2000 Academic Press.     

界面张力在基板诱导共混物分散相粒子粗化生长加速现象中的作用

通过相差显微镜和计算机图像处理来研究两相聚合物体系的粗化过程 .将具有不同聚比的乙烯 聚醋酸乙烯酯 (EVAc)共聚物与聚丙烯 (PP)共混 ,制备不同相界面张力的系列共混物薄膜 .观察了在玻璃基板的作用下 ,不同界面张力体系的分散相粒子粗化行为 ,发现界面张力在约 0 4 8·1 0 - 5N cm以上的体系中分散相粒子的粗化有明显的加速现象 ,粒子体积生长与时间关系的指数大于 1 0 ;而两相界面张力较低的情况下 ,选择具有不同表面极性的基板对同一体系试验 ,我们均未发现有粗化加速现象产生 ,且采用不同基板之间的试验结果差异很小 ,亦即当高分子共混物的相界面张力大于一定值时 ,仅与基板存在有关 ,粒子的粗化行为被加速     

Numerical simulation of phase separation of immiscible polymer blends on a heterogeneously functionalized substrate

The spinodal phase decomposition of an immiscible binary polymer blend system is investigated with numerical models in two-dimensional and three-dimensional (3D). The effect of the elastic energy is included. The mechanism of the evolution of the phase separation is studied and the characteristic length R(t) is shown to be proportional to t(13). In the case when the phase separation is directed by a heterogeneously functionalized substrate, the increase in the characteristic length is divided into two stages by a critical time. The R(t) approximately t(13) diagram can be fitted with a straight line in both the first and second stages. The slope of the fitting line significantly decreases after the critical time. The compatibility of the resulting pattern to the substrate pattern is also measured by a factor C(S). It is observed that there is also a critical time in the evolution of the compatibility for the cases with and without elastic energy. The critical time of C(S) is identical with the respective critical time of R(t). The lateral and vertical composition profiles functionalized substrate is observed with the 3D model. The difference mechanism of the cases with and without elastic energy is discussed.     

Dynamic Density Functional Theory for Sheared Polymeric Systems

Summary: Details of the dynamic density functional theory for sheared polymer systems are presented. The method is illustrated on polymer blends with and without compatibilizers. Shearing slows down coarsening of structures at later stages of phase separation, trapping the system in kineticly driven metastable states. Under certain conditions the system is found trapped in a metastable multiple sphere morphology, while under other conditions a sphere‐to‐string transition is observed. The results are sensitive to the (block co)polymer architecture.

The morphology of a symmetric polymer blend in a 32 × 32 box.     

Stochastic diffusion interactions and coarsening in a system of droplets growing from a supersaturated gas mixture

In this work we study diffusion interactions among liquid droplets growing in stochastic population by condensation from supersaturated binary gas mixture. During the postnucleation transient regime collective growth of liquid droplets competing for the available water vapor decreases local supersaturation leading to the increase of critical radius and the onset of coarsening process. In coarsening regime the growth of larger droplets is prevailing noticeably broadening the droplet size-distribution function when the condensation process becomes more intensive than the supersaturation yield. Modifications in the kinetic equation are discussed and formulated for a stochastic population of liquid droplets when diffusional interactions among droplets become noteworthy. The kinetic equation for the droplet size-distribution function is solved together with field equations for the mass fraction of disperse liquid phase, mass fraction of water vapor component of moist air, and temperature during diffusion-dominated regime of droplet coarsening. The droplet size and mass distributions are found as functions of the liquid volume fraction, showing considerable broadening of droplet spectra. It is demonstrated that the effect of latent heat of condensation considerably changes coarsening process. The coarsening rate constant, the droplet density (number of droplets per unit volume), the screening length, the mean droplet size, and mass are determined as functions of the temperature, pressure, and liquid volume fraction.     

Surface structure analysis of thin dewetted polymer blend films

The surface structure of thin polymer blend films of deuterated polystyrene (dPS) and polyparamethylstyrene (PpMS) after annealing above the glass transition temperature was investigated. With scanning force microscopy (SFM) the surface topography originated by a dewetting process is detected. The sample surface is covered with small droplets consisting of several polymer molecules. Utilizing grazing incidence small angle neutron scattering (GISANS) the topographical information as well as the in‐plane composition is probed. For thin confined blend films a substructure of the droplets resulting from an additional phase separation process at different length scales is detected.     

动力学因素对热诱导相分离法制备亲水性乙烯-丙烯酸共聚物微孔膜结构的影响

选择 3种不同丙烯酸含量的乙烯 丙烯酸共聚物 (EAA)为原材料 ,二苯醚 (DPE)为稀释剂 ,研究了淬冷温度、粗化时间等影响液滴生长的动力学因素对热诱导相分离法 (TIPS)制备EAA DPE亲水性高分子微孔膜结构的影响 .淬冷温度的高低决定了EAA DPE体系是发生液 液相分离还是固 液相分离 ,而产生相分离的机理不同将影响稀释剂液滴的生长 ,最终影响微孔膜的孔径 .实验结果表明 ,在相同粗化时间的条件下 ,随着EAA1 41 0 DPE、EAA3 0 0 2 DPE、EAA3 0 0 3 DPE三体系冷却温度的逐渐升高 ,孔径逐渐变大 .在结晶温度以下 ( 0℃、3 0℃、60℃ )粗化时间相同时 ,温度对微孔膜的孔径影响较小 ,例如 0℃和 3 0℃的恒温条件粗化 1 0min,微孔膜的孔径在 1～ 3 μm之间 ;在 60℃的恒温条件粗化 1 0min ,微孔膜的孔径在 3～ 5 μm之间 .而在 90℃的恒温条件粗化相同的时间 ,由于体系始终处于结晶温度线以上 ,体系始终处在液 液相分离区域 ,最终得到微孔膜的孔径达到了 6～8μm .在结晶温度以下 ( 3 0℃ )进行恒温粗化 ,由于体系的过冷程度很大 ,液滴相的粗化过程被抑制住 ,所以粗化时间对微孔膜的孔径影响不大 ;而在结晶温度以上 ( 90℃ )进行恒温粗化时 ,则是随着粗化时间的延长 ,微孔膜的孔径逐渐变大     

Three-dimensional numerical simulations of lamellar structure via two-step surface-directed phase separation in polymer blend films

Lamellar structure via two-step surface-directed phase separation in polymer blend films is numerically investigated in three-dimensional (3D) space, which is more physically appropriate for the experimental situation than that in two-dimensional (2D) space [L.-T. Yan and X. M. Xie, J. Chem. Phys. 128, 034901 (2008)]. The 3D phase morphology and its evolution dynamics in both critical and off-critical conditions have been studied. The wetting layer formation mechanism during the second quench has been concerned. The effects of noise on the ordered phase structures have also been examined. The simulated results in 3D space give a more certain evidence that the lamellar structure can be induced by the surface or interface when the system is in the equilibration state with very shallow quench depth first and then imposed on a further quench depth in the unstable region of the phase diagram. It is found that the lamellar structure can also be induced in the polymer blends with off-critical condition. The simulated results demonstrate that the formation of the lamellar structure can present two basic processes and obey logarithmic growth law at the initial and metaphase stages. The results also show that a stronger thermal noise corresponds to a smaller region with the lamellar structure.     

Control of droplet size of polymer–diluent blends through thermally induced phase separation

The effects of process conditions and molecular structure of polymer and diluent on the droplet size of membranes formed by thermally induced phase separatiom (TIPS) process were examined. The observed upper critical solution temperature–type phase boundaries of nylon‐12 blended with poly(ethylene glycol) (PEG) and nylon 12 diluted with poly(ethylene glycol) dimethyl ether (PEGDE) and their interaction energy densities calculated using the Flory–Huggins theory suggest that the nylon‐12/PEGDE blends are less stable than the nylon‐12–PEG blends. Infrared spectra confirmed that the difference in phase stability might come from specific interactions of the hydroxyl terminal groups of PEG with the amide groups from nylon‐12, which are not be feasible in the nylon‐12–PEGDE blends. The phase stability of diluent PEG blended with various nylons that are different in the number of methyl groups in the repeat unit was ranked in the order of: nylon‐6–PEG blend < nylon‐12–PEG blend < nylon‐11–PEG blend. We also noted that the phase‐separated droplets grew by both coalescence and the Oswald ripening process after the onset of phase separation. As a result, the cubic exponent of average droplet radius (R³) plotted against time satisfied the linear relationship. As the blends became less stable, the droplet growth rate increased and larger equilibrium droplets formed at a constant quenching depth. The TIPS membranes with desired pore structure could be prepared by controlling the molecular structure of components as well as by varying processing conditions such as quenching depth and annealing time. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3042–3052, 2000     

The dewetting dynamics of the polymer thin film by solvent annealing

The slippage effect of the polymer chains is investigated in the dewetting process of the polymer solution film. The solvent-induced dewetting is used in our experiments to study the dynamics of hole growth in the dewetting process of the polymer solution film. Our results show that in the case of the low molecular weight polystyrene (PS) film, the slippage effect of the polymer chains is not displayed and the radius of the holes is R approximately exp(t/tau); in the case of the higher molecular weight PS film, the slippage effect of the polymer chain is not valid in the case of the thin film and that is valid in the case of the thick film, and the dynamic process of hole growth divides into three stages (R approximately t, and then R approximately t(x) (23相似文献   

Phase separation mechanism in gelling aqueous biopolymer mixture probed by light scattering

Using time-resolved static and dynamic light scattering (DLS) we have studied the kinetics of phase separation in an aqueous gelatin/maltodextrin mixture upon fast cooling. The time evolution of the droplet radius is modelled for the monodisperse case under reaction-limited and diffusion-limited conditions and compared with the observed evolution of the mode associated with the droplet diffusion. For quenches to above the gelatin ordering temperature, nucleation and rather reaction-limited than diffusion-limited growth and late-stage coalescence of droplets with diameters up to 90 μm were concluded. Quenches to well below the gelatin ordering temperature seem to induce diffusion-limited growth or (delayed) spinodal decomposition (SD) to a phase-separated microstructure with slow late-stage coarsening. In deep quenches, a second slow SD or diffusion-limited cluster aggregation (DLCA) process becomes apparent from the evolution of the static structure factor; the process seems to be related to the maltodextrin gelation in the composite.     

Using two-dimensional time resolved light scattering to study the cure reaction induced phase separation process of epoxy-amine-polyethersulfone blend with secondary phase separation

<正>The generalized two-dimensional correlation analysis based on time-resolved light scattering patterns(2D TRLS) has been employed to study the phase separation process of an epoxy-amine-polyethersulfone blend in which the secondary phase separation takes place.The results of the 2D TRLS provided more detailed information that was not readily observed in the 1D TRLS patterns.(i) During the first process of phase separation,the sequential order of coarsening in size of the domains among the larger and smaller ones has been reversed between the diffusion regime and the hydrodynamic regime. (ii) The change of the larger domains in size,due to the hydrodynamic flow in the late stage of the first phase separation process,keeps on taking place earlier than that of the new domains appeared in the secondary phase separation process. (iii) During the secondary phase separation process the size growth of the smaller domains takes place earlier than that of the larger ones,probably due to the assumption that the coarsening mode could decrease the interface tension more quickly.     

Computer simulation of crystallization kinetics and morphology in fiber-reinforced thermoplastic composites. II. Three-dimensional case

A three-dimensional computer simulation has been used to predict crystallization kinetics and crystalline morphology in composite materials that are based on crystallizable thermoplastics. Reinforcing fibers in three-dimensional simulations show similar behavior to those in two-dimensional simulations; fibers suppress crystallization relative to an unreinforced polymer since they constrain spherulitic growth by an impingement mechanism, and also enhance crystallization by providing added surface nucleation sites. The effects of varying controlling parameters on crystallization kinetics and morphology are qualitatively the same as those observed in the two-dimensional case. The relative bulk and fiber nucleation denisities, in addition to the fiber volume fraction, fiber diameter, and spherulitic growth rate control the crystallization kinetics and crystalline morphology that develop in reinforced thermoplastic composites. It is more difficult to achieve the transcrystalline morphology in slices of three-dimensional composites than it is in two-dimensional composites because nuclei in 3-D systems are not constrained to positions in or near a 2-D plane. © 1993 John Wiley & Sons, Inc.     

The equilibrium melting temperature and isothermal crystallisation kinetics of cyclic poly(butylene terephthalate) and styrene maleimide (c-PBT/SMI) blends

The equilibrium melting point ( $ T_{\text{m}}^{0} $ ) and isothermal crystallisation kinetics of cyclic poly(butylene terephthalate) (c-PBT) and styrene maleimide (SMI) blends prepared by solid dispersion and in situ polymerisation of cyclic butylene terephthalate oligomers (CBT) within SMI were investigated. This c-PBT/SMI blend is a miscible semicrystalline–amorphous blend system. The $ T_{\text{m}}^{0} $ of c-PBT/SMI blends was determined using the Hoffman and Weeks method, while Avrami crystallisation kinetic model have been applied to study their isothermal crystallisation kinetics. It was found that $ T_{\text{m}}^{0} $ decreased with increasing SMI content in the blend compositions. All the crystallisation exotherms were obtained from differential scanning calorimetry under isothermal experimental conditions. The average value of Avrami exponent, n, is in the range of 2.4–2.8 for the primary crystallisation process for c-PBT and its blends, which suggest that heterogeneous nucleation of spherulites occurred and growth of spherulites was between two-dimensional and three-dimensional.     

Gas sorption and luminescence properties of a terbium(III)-phosphine oxide coordination material with two-dimensional pore topology

The structure, stability, gas sorption properties and luminescence behaviour of a new lanthanide-phosphine oxide coordination material are reported. The polymer PCM-15 is based on Tb(III) and tris(p-carboxylated) triphenylphosphine oxide and has a 5,5-connected net topology. It exhibits an infinite three-dimensional structure that incorporates an open, two-dimensional pore structure. The material is thermally robust and remains crystalline under high vacuum at 150 °C. When desolvated, the solid has a CO(2) BET surface area of 1187 m(2) g(-1) and shows the highest reported uptake of both O(2) and H(2) at 77 K and 1 bar for a lanthanide-based coordination polymer. Isolated Tb(III) centres in the as-synthesized polymer exhibit moderate photoluminescence. However, upon removal of coordinated OH(2) ligands, the luminescence intensity was found to approximately double; this process was reversible. Thus, the Tb(III) centre was used as a probe to detect directly the desolvation and resolvation of the polymer.     

Crystallization of condensation droplets on a liquid surface

Highly ordered microporous two-dimensional membranes have been obtained from polymer solutions (Widawski et al. (1994) Nature 369: 397–399). Recently, a mechanism for the formation of such membranes was proposed, involving water vapour condensation (induced by the rapid evaporation of the volatile solvent) onto the surface of solutions and the formation of floating water droplets. Unfortunately, the droplets growth process was not observed, and consequently only qualitative information was reported. In the present paper, results of light-scattering experiments with this system are reported. The formation of water droplets growing at the surface of the solution has been observed and the evolution with time of the mean droplet radius has been found to be described by a power law with an exponent of 1/3, proving that no coalescence processes occur. This particular behaviour is attributed to the precipitation of the polymer at the water/solution interface and to the formation of a mechanically resistant polymer layer encapsulating each droplet. In this way, water droplets behave like solid particles, allowing compact sheets to be formed. The presence of important surface currents is believed to promote the formation of “polycrystal” and “monocrystal” patterns. Received: 4 January 1999 Accepted in revised form: 15 February 1999