水的玻璃化转变的研究

本文用我们液态低频力学谱方法对玻璃化转变研究领域中一个持续半个多世纪、十分令人困扰的热点水的玻璃化转变问题进行了研究。用表征玻璃化转变最直接的参量力学模量，首次实现对水的玻璃化转变过程的明确表征，得出水的玻璃化转变温度是163K，而不是长期一直认为的136K。另外，水的玻璃化转变表现出不同于传统玻璃化转变的反常耗散行为。研究还表明，水的玻璃化转变温度表现出重要的同位素效应，这是水的玻璃化转变奇异特征的一个反映，也是在玻璃化转变研究中首次观测到同位素效应。     

玻璃化转变机制的串模型与液态低频力学谱研究

本文对近期本课题组在玻璃化转变研究工作进行了扼要的总结.主要包括我们提出的玻璃化转变机制的串模型、发明的一种液态低频力学谱方法、以及用该方法对水的玻璃化转变的表征.     

水的玻璃化转变的研究

本文用我们液态低频力学谱方法对玻璃化转变研究领域中一个持续半个多世纪、十分令人困扰的热点水的玻璃化转变问题进行了研究.用表征玻璃化转变最直接的参量力学模量,首次实现对水的玻璃化转变过程的明确表征,得出水的玻璃化转变温度是163K,而不是长期一直认为的136K.另外,水的玻璃化转变表现出不同于传统玻璃化转变的反常耗散行为.研究还表明,水的玻璃化转变温度表现出重要的同位素效应,这是水的玻璃化转变奇异特征的一个反映,也是在玻璃化转变研究中首次观测到同位素效应.     

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。     

邻苯二甲酸二酯系玻璃材料中裂纹愈合效应研究

用最近发明的一种能够实时检测玻璃材料中应力诱导裂纹(stress cracking)和裂纹愈合(crack-healing)的新方法(RMS-L-CH)对邻苯二甲酸二甲酯、邻苯二甲酸二乙酯、邻苯二甲酸二丁酯和邻苯二甲酸二辛酯的系列玻璃材料中应力诱导裂纹和裂纹愈合效应进行了测量,对裂纹愈合效应的现象及其与玻璃化转变的关系进行了深入的研究与讨论.结果进一步验证了RMS-L-CH方法的有效性,并且表明该方法可能提供一种表征玻璃化转变过程和研究玻璃化转变机理的新手段.     

丙三醇浓溶液玻璃化转变与结构松弛参数DSC分析

利用差示扫描量热仪研究了5种高浓度丙三醇水溶液(60%、70%、80%、90%、100%)的玻璃化转变行为,以考察水分含量和升降温速率对其玻璃化转变行为和结构松弛参数的影响.采用4种线性升降温速率(10、15、20、25K/min)获得玻璃化转变的相关参数.利用GordonTaylor方程对玻璃化转变温度的分析结果表明,水对丙三醇增塑常数的计算结果与升降温速率和玻璃化转变温度的读取方法有很大关系.玻璃化转变过程的比热容变化不仅随水分含量的增加而增加,而且与升降温速率也有一定的依赖关系.结构松弛活化能的计算结果表明,随体系水分含量的增加,体系的结构松弛活化能和动力学脆度都逐渐降低.随水分含量的变化,热力学脆度和动力学脆度表现出相反的变化趋势.     

食品玻璃化保存的研究进展

简单介绍了玻璃化转变的基本理论,通过阐述玻璃化保存在水产品、速冻水果及速冻面制品中的应用来说明食品玻璃化保存的研究现状,并对目前食品的玻璃化保存所存在的主要问题进行了探讨。     

邻苯二甲酸二甲酯系材料的液态簧振动力学谱测量

用液态簧振动力学谱方法对邻苯二甲酸二甲酯、邻苯二甲酸二乙酯、邻苯二甲酸二丁酯和邻苯二甲酸二辛酯的系列样品进行了测量. 在升温过程中所测温区范围内，结果表明邻苯二甲酸二甲酯样品相继发生了动力学玻璃化转变、过冷液态的结晶、晶体—液态相变和挥发过程，而在邻苯二甲酸二乙酯、邻苯二甲酸二丁酯和邻苯二甲酸二辛酯样品中仅仅发生了动力学玻璃化转变和挥发过程. 上述实验结果与分析表明，液态簧振动力学谱方法是研究拥有液态过程的可靠和有效的方法，并且能够提供物质变化的丰富信息.     

快速冷却条件下银的比热及玻璃化过程的分子动力学模拟

本文采用以嵌入原子模型为基础的分子动力学方法对液态银快速冷却条件下的比热及玻璃化过程进行了模拟，得到了银的比热及其与温度的关系．同时，对快速冷却条件下银的结构特性以及动力学特性进行模拟和分析，结果表明在所模拟的冷却速率下，银在从 １２００ Ｋ冷却到 １０００ Ｋ的过程中发生了玻璃化转变，其玻璃化温度在 １０００ Ｋ左右．     

氟聚合物相态变化研究

相态变化主要有物理转变和化学反应两类。物理转变包括结晶／熔融、液晶转变等相转变、玻璃化转变；化学反应包括聚合、固化、交联、氧化和分解等。由于氟聚合物的使用环境温度与其的玻璃化转变温度比较接近，笔者主要借助DSC热分析仪、X射线衍射仪、红外原位反应池、高温高压反应池等仪器研究了氟聚合物在相态转化过程中的相关物理性能变化，探讨了相态转变时分子链锻是否会发生变化。     

The orientational glass transition in pentachloronitrobenzene: a study by differential scanning calorimetry and thermally stimulated currents

The orientational disorder that is a feature of the crystalline pentachloronitrobenzene above ∼−82 °C, can be frozen by cooling to produce an orientational glass. The number of degrees of freedom frozen on cooling, or released on heating, in this orientational glass transition is low, so that the heat capacity change associated with this transition is expected to be small. In the present work, we show that the calorimetric signature of this orientational glass transition is in fact very weak. Conversely, since the molecular motions associated with this relaxation drag strong dipoles, the technique of thermally stimulated depolarisation currents (TSDC) provides a very strong signature of this transition. The orientational glass transition in pentachloronitrobenzene was studied by TSDC and, from this study, it was shown that this orientational glass belongs to the class of very strong glasses in the fragility scale proposed by Angell.     

Is the dynamics of polystyrene films consistent with their glass transition temperature?

Experiments in the past 1.5 decades have found that the glass transition temperature of polymer films can be noticeably different from the bulk when the film thickness is decreased below ∼100  nm. On the other hand, many dynamic measurements have found results inconsistent with the observed change in the glass transition temperature. One frequently cited reason is that the dynamic properties being probed may not be directly related to the glass transition. Viscosity is a property traditionally used to characterize the dynamic slowing down occurring to a material at the glass transition. In this paper, we report experimental result showing that the viscosity of polystyrene films supported by oxide-coated silicon decreases with decreasing film thickness, consistent with the observed glass transition temperature of the films.     

Glass transition in ultrathin polymer films: calorimetric study

The ultrasensitive differential scanning calorimetry is used to observe the glass transition in thin (1-400 nm) spin-cast films of polystyrene, poly (2-vinyl pyridine) and poly (methyl methacrylate) on a platinum surface. A pronounced glass transition is observed even at a thickness as small as 1-3 nm. Using the high heating (20-200 K/ms) and cooling (1-2 K/ms in glass transition region) rates which are typical for this technique, we do not observe appreciable dependence of the glass transition temperature over the thickness range from hundreds of nanometers down to 3 nm thick films. The evolution of calorimetric data with film thickness is discussed in terms of broadening of transition dynamics and loss of transition contrast.     

Mechanical, vibrational, and dynamical properties of amorphous systems near jamming

Amorphous systems undergo the jamming transition when the density increases, temperature drops, or external shear stress decreases, as described by the jamming phase diagram which was proposed to unify different processes such as the glass transition, random close packing, and yielding under shear stress. At zero temperature and shear stress, the jamming transition occurs at a critical density at Point J. In this paper, we review recent studies of the material properties of marginally jammed solids and the glassy dynamics in the vicinity of Point J. As the only singular point in the jamming phase diagram, Point J exhibits special criticality in both mechanical and vibrational quantities. Dynamics approaching the glass transition in the vicinity of Point J show critical scalings, suggesting that the molecular glass transition and the colloidal glass transition are equivalent in the hard sphere limit. All these studies shed light on the long-standing puzzles of the glass transition and unusual properties of amorphous solids.     

New Insights into the Effects of Physical Aging on Glass Transition of Polystyrene by FTIR

A new method to detect the glass transition was used to investigate the effects of physical aging on the glass transition of polystyrene by Fourier transform infrared (FTIR) spectroscopy. The results showed that the onset point of the glass transition shifted to higher temperature with aging, but the end point didn't change. It was demonstrated that this method was of great use in determining the glass transition temperature of aged polymeric samples. For each aged sample, the four bands assigned to the vibrational modes of the main chain groups and the side groups of polystyrene showed the same transition regions, indicating that the main chain and the side groups were aging synchronously. The rates of increase of the relative peak areas for the four investigated bands during the glass transition decreased with aging with the increased rates of the relative peak areas for the two bands assigned to side group decreasing less than those of main chain, which seemed to indicate the dominance of the side group in aging process.     

Glass transition and relaxation processes in supercooled water

Many of water's peculiar physical properties are still not well understood, and one of the most important unresolved questions is its glass transition related dynamics. The consensus has been to accept a glass transition temperature (T(g)) around 136 K, but this value has been questioned and reassigned to about 165 K. We find evidence that the dielectric relaxation process of confined water that has been associated with the long accepted T(g) of water (130-140 K) must be a local process which is not related to the actual glass transition. Rather, our data indicate a glass transition at 160-165 K for bulk water and about 175 K for confined water (depending on the confining system).     

Mechanical spectrum study of glass transition by a composite method

Normalized mechanical spectra of glycerol, 1,2-propanediol carbonate and poly(vinyl chloride)/di(2-ethyl-hexyl) phthalate (PVC/DOP) blends were studied in the temperature range from 100 to 300 K by a composite method. The dynamic glass transition was observed, which exhibits a peak of temperature-dependent loss modulus. The peak moves toward higher temperature with higher measuring frequency, which accords with the relaxation feature of the dynamic glass transition. Another characteristic temperature can be marked in the mechanical spectrum by the onset of storage modulus change, which is labeled as T_gm. T_gm is found to be nearly equal to the calorimetric glass transition temperature in glycerol, 1,2-propanediol carbonate and di(2-ethyl-hexyl) phthalate. As we expected, this onset temperature in the mechanical spectrum has an intimate relation with the calorimetric glass transition of materials, and it can be regarded as a representative when the calorimetric glass transition temperature is not available. Finally, normalized mechanical spectra of PVC/DOP blends with different PVC content were obtained and mechanical glass transition temperatures T_gm were determined.     

非晶材料玻璃转变过程中记忆效应的热力学

低温下处于非平衡态的非晶材料升温到玻璃转变以上,要先后发生弛豫和回复最终达到平衡过冷液态,其中弛豫过程中释放的能量在回复过程中以等量的方式获取,表现出明显记忆行为.本文基于氧化物、金属与小分子等多种非晶形成体系,全面探讨了在围绕玻璃转变的一个冷却加热循环过程中的焓弛豫特征,建立了弛豫谱,发现弛豫焓在数值上与熔化焓密切相关.基于弛豫焓与非晶材料动力学Fragility之间的关联,展示了非晶体系在动力学极限(m=175)条件下的玻璃转变热力学基本特征,与热力学二级相变进行了对比.研究深化了对非晶弛豫与玻璃转变热力学的理解.     

Intrinsic Features of an Ideal Glass

In order to understand the long-standing problem of the nature of glass states, we perform intensive simulations on the thermodynamic properties and potential energy surface of an ideal glass. It is found that the atoms of an ideal glass manifest cooperative diffusion, and show clearly different behavior from the liquid state. By determining the potential energy surface, we demonstrate that the glass state has a flat potential landscape, which is the critical intrinsic feature of ideal glasses. When this potential region is accessible through any thermal or kinetic process, the glass state can be formed and a glass transition will occur, regardless of any special structural character. With this picture, the glass transition can be interpreted by the emergence of configurational entropies,as a consequence of flat potential landscapes.