国产bbaaaaa片,成年美女黄网站色视频免费,成年黄大片,а天堂中文最新一区二区三区,成人精品视频一区二区三区尤物

首頁> 外文學(xué)位 >Hydrodynamic simulations of colloidal gels: Microstructure, dynamics, and rheology.
【24h】

Hydrodynamic simulations of colloidal gels: Microstructure, dynamics, and rheology.

機(jī)譯：膠體的流體動力學(xué)模擬：微觀結(jié)構(gòu)，動力學(xué)和流變學(xué)。

獲取原文
獲取原文并翻譯 | 示例
  • 摘要
  • 著錄項
  • 相似文獻(xiàn)
  • 相關(guān)主題

摘要

The microstructure, dynamics, and rheology of colloidal suspensions with short-range depletion attraction and long-range electrostatic repulsion are studied using equilibrium predictions and a new algorithm for dynamic simulations. A focus is made on those combinations of attraction and repulsion that lead to the formation of gels. The effects of varying the strength of attraction epsilon A (0-50kT), range of attraction deltaA (0.05-0.18a), strength of repulsion epsilon R (0-54kT), and volume fraction &phis; (0.1-0.4) are investigated, where k is Boltzmann's constant, T is temperature, and a is the colloid radius. Hard-sphere thermodynamic perturbation theory is employed to predict equilibrium behavior. For &phis; ≤ 0.4, fluid phases are predicted at low epsilonA, while fluid-crystal coexistence is predicted above a certain value of epsilon A which decreases with increasing deltaA or &phis;, but increases with increasing epsilonR. A new algorithm called Fast Lubrication Dynamics (FLD) is developed as part of this work. This algorithm enables simulations including the effects of many-body hydrodynamic interactions, Brownian motion, and interparticle interactions at a speed more than 100 times faster than Stokesian Dynamics (SD) while retaining much of the relevant physics of SD. In addition, FLD is found to be nearly as fast as Brownian Dynamics (BD) due to the larger time steps allowed by FLD.;FLD simulations are performed to study the microstructural evolution of suspensions from a dispersed phase to other phases including fluids and gels. With increasing epsilonA, suspensions with short-range attraction undergo a transition from highly diffusive fluid phases to dynamically arrested gels in which particles are localized on length scales comparable to delta A. This transition first occurs by homogeneous nucleation and growth of crystalline structures which merge to form a space-spanning polycrystalline structure that coexists with a dilute fluid phase. With increasing epsilon A, the rate of nucleation increases, resulting in increasing polycrystallinity and smaller crystalline regions. For high epsilonA, a dilute fluid phase does not coexist and no crystalline structures are formed. The introduction of long-range repulsion inhibits crystallization and promotes one-dimensional cluster growth resulting in thinner structures which display greater positional fluctuations such that particles in gels are localized on length scales up to 7 times deltaA. In the presence of repulsion, for low epsilon A, small transient clusters are formed, while for high epsilon A, gels are formed by space-spanning clusters, but the time scale for gelation to occur increases exponentially with epsilonR. Comparisons with results of confocal microscopy experiments show significant differences which may be attributed to differences in initial conditions, inaccurately represented electrostatic interactions, and limitations of the simulated system size. Few changes are observed with different values of deltaA. With increasing &phis;, the average local structure around each particle in the gel changes very little while the gels becomes more dense, hindering collective motion and decreasing the length scales on which particles are localized.;BD simulations are also performed, and the results are compared with those of the FLD simulations. Remarkable agreement is observed for both the microstructure and dynamics, suggesting that the structural evolution and dynamics of colloidal suspensions with short-range attraction and long-range repulsion under quiescent conditions may not be very sensitive to the effects of hydrodynamic interactions.;FLD simulations are performed to study the rheological response of colloidal gels with a focus on the linear viscoelastic response. In addition to using ensemble averaging, we develop a new technique to improve the signal-to-noise ratio inherent in the stress of Brownian systems. By careful application of this technique, the average of two simulations sheared in opposite directions can yield a greater reduction in noise than does averaging over 10 times as many individual realizations. Steady shear and relaxation tests are performed, and the relaxation modulus G(t) is obtained from the stress response. The elastic modulus G'( w) and the viscous modulus G"(o)) are then obtained by Fourier transform of G(t). During steady shear, the stress increases with time and reaches a maximum as the gel strain softens and yields, after which the stress decreases and tends toward a steady-state value. (Abstract shortened by UMI.)
機(jī)譯：利用平衡預(yù)測和一種新的動態(tài)模擬算法，研究了具有短程耗盡吸引和長程靜電排斥的膠體懸浮液的微觀結(jié)構(gòu)，動力學(xué)和流變學(xué)。將重點(diǎn)放在導(dǎo)致凝膠形成的吸引和排斥的組合上。改變吸引εA的強(qiáng)度（0-50kT），吸引δA范圍（0.05-0.18a），排斥εR的強(qiáng)度（0-54kT）和體積分?jǐn)?shù)φ的影響。研究（0.1-0.4），其中k是玻爾茲曼常數(shù)，T是溫度，a是膠體半徑。硬球熱力學(xué)攝動理論被用來預(yù)測平衡行為。對于＆phis; ≤0.4時，在低epsilonA時會預(yù)測到液相，而在epsilon A的某個值以上時會預(yù)測到液晶共存，ε值隨deltaA或φ的增加而減少，但隨epsilonR的增加而增加。作為這項工作的一部分，開發(fā)了一種稱為快速潤滑動力學(xué)（FLD）的新算法。該算法可以進(jìn)行模擬，包括多體流體動力相互作用，布朗運(yùn)動和粒子間相互作用的影響，其速度比斯托克斯動力學(xué)（SD）快100倍以上，同時保留了SD的許多相關(guān)物理特性。此外，由于FLD允許的時間步長較大，因此發(fā)現(xiàn)FLD的速度幾乎與Brownian Dynamics（BD）一樣快;進(jìn)行FLD模擬以研究懸浮液從分散相到包括流體和凝膠在內(nèi)的其他相的微觀結(jié)構(gòu)演變。隨著epsilonA的增加，具有短距離吸引力的懸浮液會從高度擴(kuò)散的液相過渡到動態(tài)阻滯的凝膠，在該凝膠中，顆粒定位在與ΔA相當(dāng)?shù)拈L度尺度上。這種過渡首先通過均相成核和晶體結(jié)構(gòu)的生長而發(fā)生，并融合為形成與稀液相共存的跨空間多晶結(jié)構(gòu)。隨著εA的增加，成核速率增加，從而導(dǎo)致多晶度增加和較小的結(jié)晶區(qū)域。對于高εA，稀釋的液相不共存，并且不形成晶體結(jié)構(gòu)。引入長程排斥力可抑制結(jié)晶并促進(jìn)一維團(tuán)簇的生長，從而導(dǎo)致結(jié)構(gòu)變薄，從而顯示出較大的位置波動，從而使凝膠中的顆粒定位在高達(dá)7倍deltaA的長度尺度上。在存在排斥的情況下，對于低εA，會形成小的瞬態(tài)簇，而對于高εA，會由跨空間的簇形成凝膠，但是發(fā)生凝膠化的時間尺度隨epsilonR呈指數(shù)增長。與共聚焦顯微鏡實驗結(jié)果的比較顯示出顯著差異，這可能歸因于初始條件的差異，靜電相互作用的不準(zhǔn)確表示以及模擬系統(tǒng)尺寸的限制。使用不同的deltaA值觀察到的變化很小。隨著φ的增加，凝膠中每個粒子周圍的平均局部結(jié)構(gòu)變化很小，而凝膠變得更致密，阻礙了集體運(yùn)動并減小了粒子所在的長度尺度。;還進(jìn)行了BD模擬，結(jié)果是與FLD仿真相比。在微觀結(jié)構(gòu)和動力學(xué)方面都觀察到了顯著的一致性，這表明在靜態(tài)條件下具有短程吸引和長程排斥的膠體懸浮液的結(jié)構(gòu)演變和動力學(xué)可能對水動力相互作用的影響不是很敏感。為了研究膠體凝膠的流變響應(yīng)，著重于線性粘彈性響應(yīng)。除了使用集成平均以外，我們還開發(fā)了一種新技術(shù)來提高Brownian系統(tǒng)應(yīng)力中固有的信噪比。通過仔細(xì)應(yīng)用此技術(shù)，在相反方向剪切的兩個模擬的平均值可以比平均10倍以上的單個實現(xiàn)的平均值產(chǎn)生更大的噪聲降低。進(jìn)行穩(wěn)定的剪切和松弛測試，并從應(yīng)力響應(yīng)中獲得松弛模量G（t）。然后通過G（t）的傅立葉變換獲得彈性模量G'（w）和粘性模量G“（o））。在穩(wěn)定剪切過程中，應(yīng)力隨時間增加，并在凝膠應(yīng)變軟化和屈服時達(dá)到最大值。之后，應(yīng)力減小并趨于穩(wěn)態(tài)值（摘要由UMI縮短）。

著錄項

相似文獻(xiàn)

  • 外文文獻(xiàn)
  • 中文文獻(xiàn)
  • 專利
獲取原文

客服郵箱：kefu@zhangqiaokeyan.com

京公網(wǎng)安備：11010802029741號 ICP備案號：京ICP備15016152號-6 六維聯(lián)合信息科技 (北京) 有限公司?版權(quán)所有

  • 客服微信

  • 服務(wù)號