高分子凝胶体积相变中的氢键作用

我们把关联模型(association models)推广应用到高分子凝胶体系,研究高分子与溶剂分子间的氢键和溶剂分子与溶剂分子间的氢键在高分子凝胶体积相变中的作用.首先通过分析凝胶体积分数与温度的关系发现,由于两种氢键作用,随着温度变化高分子凝胶出现连续、不连续体积相变,结果表明在体积相变过程中两种氢键都起着重要作用.其次,对不同氢键分数条件下的旋节线的研究发现,对于高分子凝胶体积相变中出现的UCST和LCST(上临界共溶温度和下临界共溶温度)现象也是由于高分子与溶剂分子间氢键和溶剂分子与溶剂分子间氢键共同作用的结果.     

线性高分子体系中高分子链间排除体积效应的模型化

提出了线性高分子体系中高分子链间排除体积效应的一个它回避模型，并且针对具体的四个模型系统进行了计算机模拟. 计算结果表明：1)线团的均方末端距〈R²〉与行走步数(N)仍然保持着与无规线团模型一样的线性关系；2)但与无规线团相比，线团的空间尺寸被压缩；3)与两侧方向的回避相比，在行走的前进方向的回避而导致的压缩效应更加明显. 关键词： 排除体积效应 回避行走 无规线团 线性高分子     

表面催化反应模型中关联噪声诱导非平衡相变

建立含有关联噪声的双分子-单分子(DM)表面催化反应延迟反馈模型,该模型能同时显示一级和二级非平衡动力学相变,即在一级和二级非平衡动力学相变之间的反应窗口展现.讨论双分子在DM延迟反馈模型中两种吸附机制,即局域和随机吸附模型.研究结果表明:1)外部噪声及两噪声关联性致使反应窗口的宽度收缩;2)内部噪声对非平衡动力学相变行为的影响依赖两噪声关联性,即当两噪声负关联,内部噪声致使反应窗口的宽度变宽;而当两噪声正关联时,内部噪声致使反应窗口的宽度收缩;3)关联噪声致使反应窗口变化对DM模型中一级和二级非平衡动力学相变研究具有重要的科学意义.     

非共沸混合物分离过程热质传递模型研究

本文对R32/R125/R134a三元非共沸混合制冷剂在实现变组成容量控制的组成调节装置中的分离器即填料塔中的传热传质过程进行了理论分析,建立了初步的热质传递模型.对热质传递模型的计算结果进行了分析比较,说明本文建立的热质传递模型是合适正确的.     

非稳态人口温度下相变材料蓄热性能研究

太阳能辐射强度随时间发生变化,造成蓄热单元入口处传热流体温度呈现非稳态变化。为了分析非稳态的入口温度对相变材料蓄热特性的影响,假设传热流体入口温度1 h内随时间呈线性变化,并且1 h内的平均温度恒定在60℃。讨论了入口温度随时间线性增加及线性降低两种变化形式,对相变材料的熔化速率、熔化分数、蓄热量、固液界面位置等参数的影响。结果表明,当1 h内平均入口温度不变,而初始入口温度在30～90℃的范围内变化时,随初始入口温度增加,尽管熔化速率增加,熔化时间从42.75 min减小到20.58 min;但1 h内的总蓄热量却从72.6 kW减小到45.3 kW。     

双源共蒸法制备非均匀膜的模型分析

探讨了双源共蒸法制备非均匀薄膜的堆积模型，并给出了非均匀膜的沉积速率与两种膜料沉积速率的关系.当两种膜料的沉积单分子大小近似相等或者小分子沉积速率远大于大分子时，可以近似认为混合介质膜的沉积速率等于两种膜料的沉积速率之和；当两种膜料的沉积单分子大小不满足近似相等且两种膜料的沉积速率可比较时，非均匀膜的沉积速率不能简单地用两种膜料的沉积速率之和来近似，它将随两种膜料沉积单分子的大小不同和沉积速率比不同按照不同的规律变化，并在文中给出了不同情况下的非均匀膜的沉积速率变化规律. 关键词： 非均匀膜 共蒸法 模型     

动态外场作用下Ising自旋体系的非平衡动态相变

系统地考察了Ising自旋体系的动力学方程对三种不同性质的驱动外场（正弦波 、方波和锯齿波）的动态响应及其相应的非平衡动态相变特征.在正弦波和方波的驱动场 作用下，体系存在分别对应于低温对称破缺的铁磁有序态和高温对称顺磁无序态的动态非平衡转变，相应的动态转变相界上存在区分连续转变和非连续转变的三临界点；而锯齿波驱动 场情形下体系始终维持对称性破缺的有序态.体系动态转变表现出的上述差异与作用外场的驱动特征有关.确定了表征相应动态相变相界的临界驱动外场振幅h0C和频率 ωc、体系的温度tc, 并给予了分析讨论 关键词： Ising自旋体系 非平衡动态相变 对称性 平均场     

PNIPAM线性链与凝胶在二元溶剂中相变的变温NMR研究

通过对聚N-异丙基丙烯酰胺（PNIPAM）水溶液和凝胶在水和甲醇混合溶剂中的¹H NMR谱图以及弛豫时间(T₁与T₂)等多种NMR参数随温度变化的研究,发现PNIPAM大分子的基团质子NMR信号、溶剂的弛豫时间都可以用来灵敏表征PNIPAM在二元溶剂中的相变行为. 在PNIPAM凝胶中,温度升到LSCT以上,溶剂峰由单峰变为双峰,分别对应于受限在大分子网络内的受限溶剂和排除到大分子网络外的自由溶剂,两者的弛豫时间存在明显差异. 在PNIPAM溶液中,溶剂峰在相变前后并没有显著变化. 通过PNIPAM溶胀在water/alcohol混合溶剂中的相变研究进一步证实了PNIPAM与不同溶剂之间的相互作用强弱.      

Polyakov-loop拓展的夸克介子模型中的Roberge-Weiss相变研究

${\mathbb{Z}}_3$-QCD是具有严格中心对称性的类QCD理论,研究其在特殊条件下的性质有助于理解QCD退禁闭相变。本文应用三种味道的Polyakov-loop拓展的夸克介子模型作为${\mathbb{Z}}_3$-QCD的低能有效理论,研究了不同中心对称性破缺模式下的Roberge-Weiss(RW)相变。为保证RW周期性,本文采用味道依赖的虚化学势$(\mu_{\rm{u}},\mu_{\rm{d}},\mu_{\rm{s}})={\rm{i}}T(\theta-2C\pi/3,\theta,\theta+2C\pi/3)$,其中${\mathbb{Z}}_3$-QCD是具有严格中心对称性的类QCD理论,研究其在特殊条件下的性质有助于理解QCD退禁闭相变。本文应用三种味道的Polyakov-loop拓展的夸克介子模型作为${\mathbb{Z}}_3$-QCD的低能有效理论,研究了不同中心对称性破缺模式下的Roberge-Weiss(RW)相变。为保证RW周期性,本文采用味道依赖的虚化学势$(\mu_{\rm{u}},\mu_{\rm{d}},\mu_{\rm{s}})={\rm{i}}T(\theta-2C\pi/3,\theta,\theta+2C\pi/3)$,其中$0\!\leqslant\!{C}\!\leqslant1$。传统的和夸克反馈效应改进的两种不同Polyakov-loop势被分别用于相应的计算。研究表明,当$N_{\rm{f}}\!=\!3$,$C\!\ne\!1$时,RW相变出现在$\theta=\pi/3$(mod $2\pi/3$)处,其强度随$C$值的减小而加强;当$C\!=\!1$,$N_{\rm{f}}\!=\!2\!+\!1$时,RW相变位置出现反常,变为$\theta=2\pi/3$(mod $2\pi/3$);而当$C\!=\!1$,$N_{\rm{f}}\!=\!1\!+\!2$时,RW相变点又返回$\theta\!=\!\pi/3$(mod $2\pi/3$)。上述几种情形的RW相变端点均为三相点。研究发现,夸克反馈效应使得RW相变强度减弱,退禁闭相变温度变低,但并未改变前述的定性结论。     

热解碳化学气相沉积中的多重定态和非平衡相变的研究

讨论在热解碳化学气相沉积过程中出现的多重定态和非平衡相变这一典型的非平衡物理现象的机理和发展趋势.通过理论分析和实验结果的分析发现热解碳化学气相沉积的化学反应是一个典型的非平衡化学反应,其中在沉积过程中出现的生成碳黑的过程是一个典型的非平衡相变.在这一非平衡化学反应中,自由基的反应模型符合Schlogl模型.在这一非平衡化学反应中,有线性区和非线性区,线性区的产物是热解碳,而非线性区是碳黑.在线性区,反应速率方程是唯一的、线性的,而在非线性区,反应速率方程是多重的、非线性的. 关键词： 非平衡化学反应 非平衡相变 化学气相沉积 Schlogl模型 热解碳     

Static and time-dependent properties of polymer gels around the volume phase transition

Recent progress in the study of the volume phase transition of polymer gels is reviewed. The phenomenological theories of swelling equilibrium and phase transition of gels are summarized, and some basic experimental results on poly-N-isopropylacrylamide (NIPA) gels are compared with the prediction from these theories. Special attention is paid to the elastic properties of the gel network near the volume phase transition. The effect of external stresses on the swelling and the phase transition is analyzed. Some anomalous and unique characteristics revealed in NIPA gels such as shape- and size-dependent swelling and phase transition properties, curious phase coexistence, and domain structure are presented. Experimental results on some time-dependent phenomena such as phase separation, spinodal decomposition, and pattern formation are also presented and discussed. Some problems inherent to gels from biological bodies are briefly discussed.     

Finite volume effects on the QCD chiral phase transition in the finite size de-pendent Nambu-Jona-Lasinio model

The effective Lagrangian of a finite volume system should, in principle, depend on the system size. In the framework of the Nambu-Jona-Lasinio(NJL) model, by considering the influence of quark feedback on the effective coupling, we obtain a modified NJL model so that its Lagrangian depends on the volume. Based on the modified NJL model, we study the influence of finite volume on the chiral phase transition at finite temperature, and find that the pseudo-critical temperature of crossover is much lower than that obtained in the normal NJL model. This clearly shows that the volume dependent effective Lagrangian plays an important role in the chiral phase transitions at finite temperature.     

扫描力显微术在高聚物薄膜玻璃化转变研究中的应用

简述了高聚物薄膜玻璃化转变的复杂性，并结合文章作者的的一些研究结果介绍了扫描力显微术(SFM)在研究高聚物玻璃化转变中的一些方法，包括观察高聚物薄膜形貌的变化，测量其摩擦力、粘附力和弹性模量等物理量的变化，最后指出SFM是研究高聚物薄膜玻璃化转变的有力工具。     

Ferrimagnetism and metal–insulator transition in an organic polymer chain

The ferrimagnetism and quantum phase transition of a bipartite lozenge periodic Anderson-like organic polymer, in which the localized f electrons hybridize with the odd site conduction orbitals, are investigated by means of Green＇s function theory. The ground state turns out to be gapless ferrimagnetism. At a finite temperature, the ferrimagnetic-to- paramagnetic phase transition takes place. The Kondo screenings and Ruderman-Kittel-Kasuya-Yosida （RKKY） inter- action can reduce and increase the transition temperature, respectively. Two Kondo screenings compete with each other, giving rise to the localized f electron spin screened antiferromagnetically. Accordingly, in a magnetic field, all spins are aligned along the chain easily, which is associated with metal-insulator transition. Furthermore, in a temperature-field plane, we reveal the gapless and spin polarized phases, which are characterized by susceptibility and specific heat, and whose behaviours are determined by the competition between the up-spin and down-spin hole excitations.     

Phase transition in polymer gels due to local heating by illumination of light

The volume phase transition in gels induced by visible light and its related properties are presented, the mechanism of which is based on local heating of a polymer network by illumination of light. The gels consist of a covalently cross-linked copolymer network of thermosensitive N-isopropylacrylamide and a chromophore. Without light illumination, the gel volume changes sharply, but continuously at approximately 34°C when the temperature is varied. At a fixed temperature of an appropriate value, a discontinuous volume transition is observed when the light intensity is gradually changed. The phase transitions can be understood in terms of the temperature increment at the immediate vicinity of polymer chains due to the local heating via light absorption and subsequent thermal dissipation of light by the chromophore. The results can be qualitatively described by the Flory-Huggins mean-field equation of state of gels. In order to make clear the mechanism of the light-induced phase transition in the present system, we measured the light transmitting properties and the swelling as well as shrinking kinetics. These preliminary results are described semi-qualitatively by making use of a simple phenomenological model.     

Comblike polymer electrolyte with main chain glass transition near room temperature

A new amorphous comblike polymer (CBP) based on methylvinyl ether/maleic anhydride altering copolymer backbone and on oligooxyethylene side chain was synthesized. The dynamic mechanical properties of CBP and its Li salt complexes were investigated by means of DDV-ll-EA type viscoelastic spectrometry. Results showed that there were two glass transitions (-transition and β-transition) in the temperature range from − 100 to 100 °C. The β-transition was assigned to oligo-PEO side chains and the temperature of β-transition increases with increasing Li salt content. The -transition was assigned to the main chain of CBP. The temperature of the -transition (T) is also dependent upon the Li-salt content, but not monotonie. The value of T lies between 30–45 °C in the Li salt concentration range studied, near room temperature. It was found that the CBP-Li salt complexes showed an unusual dependence of ionic conductivity on Li salt content. There are two peaks in the plot of the ionic conductivity vs. Li salt concentration, which has been ascribed to the movability of the CBP main chain at ambient temperature. The temperature dependence of the ionic conductivity indicated that the Arrhenius relationship was not obeyed, and the plot of log σ against 1/(T − T₀) showed the unusual dual VTF behavior when using side chain glass transition temperature (T_β) as T₀.     

The phase transition of the directed polymer on disordered hierarchical lattices

The directed polymer on disordered hierarchical lattices is studied using an exact renormalization scheme. The phase transition is studied and a hyperscaling relation is derived. The fixed distributions of the renormalized energies are obtained numerically. The specific heat and associated exponents are computed from the fixed distributions.