QSPR Study on the Glass Transition Temperature of Polyacrylates

Structural parameters of 22 polyacrylic compounds were computed at two levels using Hartree-Fock and DFT methods. Based on the experimental data of glass transition temperature （Tg）, four-parameter （energy of the lowest unoccupied molecular orbital （ELoMO）, the highest positive charge （Qmax^＋）, dipole moments（μ） and the next highest occupied molecular orbital （ENLOMO）） dependent equations were developed using structural parameters as theoretical descriptors. Especially, Tg dependent equation calculated at the HF/6-31G（d） level is more advantageous than others in view of their correlation and predictive abilities. This dependent equation was validated by variance inflation factors （VIF） and t-test methods.

Effects of C60 on the Glass Transition Temperature of Carbazole-based Photorefractive Polyphosphazenes

The bi-functional carbazole-based photorefractive polyphosphazenes with different content of C_（60）-doped were fabricated. The glass transition temperature（T_g） of these polymer composite materials was determined using a differential scanning calorimetric（DSC） method. According to the DSC measurement results with different heating rates, the variation of T_g and the active energy of glass transition（E_g） were analyzed in detail. The analysis results indicate that the transition region shifts to higher temperatures with increasing heating rate, and C_（60） content（below 1.0 wt%） can influence the T_g of photorefractive polyphosphazenes. The T_g first increases and then decreases with the C_（60） content（below 1.0 wt%）. The probable causes of the influence of C_（60） on T_g was proposed.

POLYMER CHAIN DIFFUSION AT A TEMPERATURE BELOW ITS BULK GLASS TRANSITION TEMPERATURE

In this study, it was examined whether the dynamics of polymer chains at a surface is different from that in thebulk, and if so, to what extent they differ in terms of surface glass transition temperature and diffusion coefficient. Obtainedresults clearly indicate that surface chains can travel for a relatively large distance in comparison with the characteristiclength scale of usual segmental motion even at a temperature below its bulk glass transition temperature, T_g^b. This isconsistent with our previous results that the surface glass transition temperature is much lower than the corresponding T_g^b.Also, it was experimentally revealed that there was a gradient of molecular motion in the surface region.

Creep performance of PVC aged at temperature relatively close to glass transition temperature

In order to predict the mechanical performance of the polyvinyl chloride （PVC） at a high operating temperature, a series of short-term tensile creep tests （one- tenth of the physical aging time） of the PVC are carried out at 63 ℃ with a small constant stress by a dynamic mechanical analyzer （DMA）. The Struik-Kohlrausch （SK） formula and Struik shifting methods are used to describe these creep data for various physical aging time. A new phenomenological model based on the multiple relaxation mechanisms of an amorphous polymer is developed to quantitatively characterize the SK parameters （the initial creep compliance, the characteristic retardation time, and the shape factor） determined by the aging time. It is shown that the momentary creep compliance curve of the PVC at 63℃ can be very well fitted by the SK formula for each aging time. However, the SK parameters for the creep curves are not constant during the aging process at the elevated temperatures, and the evolution of these parameters and the creep rate versus aging time curves at the double logarithmic coordinafes have shown a nonlinear phenomenon. Moreover, the creep master curves obtained by the superposition with the Struik shifting methods are unsatisfactory in such a case. Finally, the predicted results calculated from the present model incorporating with the SK formula are in excellent agreement with the creep experimental data for the PVC isothermally aged at the temperature relatively close to the glass transition temperature.

Prediction of Glass Transition Temperatures of Polyarylates Using a Support Vector Machine Model

A three-descriptor quantitative structure-property relationship （QSPR） model, based on the support vector machine （SVM） algorithm, was constructed to predict the glass transition temperatures （Tgs） ofpolyarylates with complex structures. A total of 50 polyarylates were randomly divided into three sets, viz., the training set （30 polymers）, validation set （10 polymers） and prediction set （10 polymers）. By adjusting various parameters by trial and error, the final optimum SVM model based on Austin Model 1 （AM1） calculation is a polynomial kernel with the parameters C of 100, ε of 1.00E-05 and d of 2. The root-mean-square （RMS） errors obtained from the training set, validation set and prediction set are 19.4, 12.8 and 15.5 K, respectively. Research results show that the proposed SVM model has better statistical quality than the previous models. Thus, applying the SVM algorithm to predict Tgs of polymers is feasible.

A NEURAL NETWORK STUDY ON GLASS TRANSITION TEMPERATURE OF POLYMERS

In this paper, an artificial neural network model is adopted to study the glass transition temperature of polymers. In our artificial neural networks, the input nodes are the characteristic ratio C-infinity, the average molecular weight M-e between entanglement points and the molecular weight M-mon of repeating unit. The output node is the glass transition temperature T-g, and the number of the hidden layer is 6. We found that the artificial neural network simulations are accurate in predicting the outcome for polymers for which it is not trained. The maximum relative error for predicting of the glass transition temperature is 3.47%, and the overall average error is only 2.27%. Artificial neural networks may provide some new ideas to investigate other properties of the polymers.

Molecular Dynamic Simulation Study on Glass Transition Temperature of DGEBA-THPA/SWCNTs Composites

Molecular dynamic (MD) simulations were carried out to predict the thermo-mechanical properties of the cured epoxy network composed of diglycidyl ether bisphenol A (DGEBA) epoxy resin and tetrahydrophthalic anhydride (THPA) curing agent and their single-walled carbon nanotubes (SWCNT) reinforced the epoxy matrix composites. Different characters such as the density of the materials and mean square displacements (MSDs) were calculated to estimate the glass transition temperatures (Tgs) of of the materials. 365 K and 423 K of the Tgs were obtained respectively, whereas the latter is much higher than the former. The simulation results indicated that the incorporation of SWCNTs in the epoxy matrix can significantly improve the Tg of the cured epoxy. The approach presented in this study is ready to be applied more widely to a large group of candidate polymers and nanofillers.

Effect of latex conversion on glass transition temperature

We have synthesized styrene-acrylic latex and investigated the effect of such reaction conditions as the dosage of initiator, surfactant and stirring speed on monomer conversion and glass transition temperature (Tg) of polymer by means of orthogonal experiment, then we get the best reaction conditions. Test results prove that the glass transition temperature of the polymer is directly related to the monomer con- version. The improvement of monomer conver- sion can make the glass transition temperature close to the theoretical value. In the case of high final conversion, we can predict the glass transition temperature of the polymers of different composition according to the theoretical relation effectively.

High temperature strain glass in Ti–Au and Ti–Pt based shape memory alloys

Strain glass is a frozen short-range strain ordered state found in shape memory alloys recently, which exhibits novel properties around the ideal glass transition temperature T_(0). However, the T_(0) of current strain glass systems is still very low, limiting their potential applications and experimental studies. In this paper, we reported two new strain glass systems with relatively high T_(0). In Ti_(50)Au_(50-x)Cr_(x) alloys, the strain glass appears at x = 25, and exhibits a T_(0) of 251 K, while in Ti_(50)Pt_(50-y)Fey alloys, the strain glass takes place at y = 30, and shows a T_(0) of 272 K. Both of them are comparable with the highest T_(0) value reported so far. Moreover, the phase diagrams of main strain glass systems in Ti-based alloys were summarized. It is found that the influence of the martensitic transformation temperature of the host alloy on the T_(0) of the strain glass is limited. This work may help to design new strain glass systems with higher T_(0) above ambient temperature.

Understanding the alkyl effect of geminal dinitropropyl ester energetic plasticizers on hydroxyl terminated polybutadiene(HTPB):Simultaneous tuning on low temperature behavior and processability

Geminal dinitropropyl ester plasticizers(DNPEPs) possess excellent energetic performances which provide good potentials as insensitive plasticizer. In this study, we design and synthesize DNPEPs with different alkane chain parts, and systematically investigate their structure-property relationships.Results show that DNPEPs have impact sensitivities all higher than 25.2 J, thermal decomposition temperatures all higher than 254 ℃, and glass transition temperatures(T_(g)) lower than-90 ℃.Furthermore, the effects of DNPEPs as plasticizer are studied on hydroxyl terminated polybutadiene(HTPB) in detail, including the viscosity, glass transition temperatures and others. It is noteworthy that 2,2-dinitropropyl nonanoate(DNPNc) among these DNPEPs exhibits the most expected simultaneous tuning effects on both viscosity and T_(g) of HTPB systems, providing favorable potentials to replace the conventional plastizers as dioctyl sebacate(DOS) in the HTPB based propellants and explosives.

Molecular Dynamics Simulation of Glass Transition Behavior of Polyimide Ensemble

The effect of chromophores to the glass transition temperature of polyimide ensemble has been investigated by means of molecular dynamics simulation in conjunction with barrier analysis. Simulated Tg results indicated a good agreement with experimental value. This study showed the MD simulation could estimate the effect of chromophores to the Tg of polyimide ensemble conveniently and an estimation approach method had a surprising deviation of Tg from experiment. At the same time, a polyimide structure with higher barrier energy was designed and validated by MD simulation.

Ratio of dielectric strength of structural and secondary relaxation close to the glass transition for PPGE and DGEBA

Here, dielectric spectroscopy is used in the fre- quency range from 10-2 Hz up to 107 Hz and we found dynamics of the primary α-and intermolecular Johari–Goldstein β-processes are strongly correlated in diglycidyl-ether of bis-phenol-A and poly phenyl glycidyl-ether (PPGE) over a wide temperature from 193 to 345 K and pressure P range from 0.1 to 600 MPa. In contrast with the widespread opinion of statistical independence of these processes the α-β mutual dependence is quantitatively confirmed in [1] analysing the temperature and pressure behavior of the α-and (JG) β-processes the investigation of the ratio of dielectric strength of two processes close to Tg evidence that the importance of secondary dy namics in relaxing external electric stresses increase in glass formers at high pressures with respect to that of the structural relaxation. We suggest that the thermal agitation, acting above Tg is at the basis of the observed result.

基于玻璃化转变的稻谷干燥变温控制系统设计与试验

针对稻谷在变温干燥过程中变温节点不明确、温度波动范围大和响应时间慢等问题,该研究设计了一种基于玻璃化转变的稻谷变温干燥控制系统。根据稻谷玻璃化转变曲线,确定变温控制策略,运用Logistic回归分析建立混配阀门开度和稻谷温度之间的控制模型并通过最小二乘法辨识模型参数。利用遗传算法对模糊隶属度函数进行优化,目标函数值迭代至0.118收敛,寻得最优幅宽。在Simulink仿真试验中,稻谷温度设定为42℃时,模糊PID控制的响应时间为66.43 s,且超调量为3.600%,优化后的模糊PID控制响应时间为37.06 s,且超调量为0.120%;在150 s加入5 s的外部信号干扰,优化后的模糊PID控制比模糊PID控制的调节时间少4.19 s且超调量减小0.050%;在稳态时输入升温信号,优化后的模糊PID控制比模糊PID控制的调节时间少16.79 s且超调量低0.338%。利用自主研制的干燥试验台进行变温试验,在变温响应试验中,优化后的模糊PID控制比模糊PID控制在目标温度和梯度升温调节时间中分别缩短了37.56 s和18.63 s;在温度稳定性试验中,稻谷温度变化范围为41.9~42.1℃,平均相对误差小于0.4%,变异系数小于0.5%;在建三江国家农业高新技术示范区浓江农场进行生产性验证,优化后的模糊PID控制系统响应时间小于30 s,稳态温度误差在±0.15℃,平均相对误差小于0.5%。测试数据表明变温干燥控制系统性能稳定,满足实际干燥作业的生产工艺需求。

籼粳杂交稻变温-缓苏干燥工艺优化及蛋白结构研究

为提升稻谷干燥品质,本实验以籼粳杂交稻为对象,通过爆腰率、整精米率、能耗、干燥时间进行评价,结合单因素、响应面分析优化干燥工艺;同时采用差示扫描量热仪、傅里叶红外光谱、荧光光谱等技术手段,探究了变温-缓苏干燥对籼粳杂交稻蛋白结构及热特性的影响。结果显示:变温-缓苏干燥(变温区间30~60℃)在升温温度5℃、风速1 m/s、缓苏比0.6条件下可使稻谷始终保持在玻璃态,干燥后的爆腰率和整精米率比恒温组(60℃)分别降低79.89%和提高39.54%。在此条件下稻谷蛋白质发生极性减弱、分子间聚集现象,提高了蛋白质热稳定性,α-螺旋含量由16.21%提升至17.64%;扫描电镜结果表明,变温-缓苏干燥未对蛋白质表面结构造成明显影响。实验探究并验证了杂交稻谷变温-缓苏干燥机制,为杂交稻谷高品质干燥研究提供了理论和实践参考。

龙眼果粉的水分吸附特性研究

以龙眼果粉为对象,利用静态测量法测定其在不同温度下的吸湿等温线,探究在不同含水率下龙眼果粉的X射线衍射图谱及玻璃化转变温度,并通过数学方程计算其热力学特性参数,以揭示龙眼果粉的水分吸附特性。结果表明,龙眼果粉的吸湿等温线为Ⅲ型等温线,Peleg模型是龙眼果粉吸湿等温线的最佳拟合模型。在水分活度(water activity,A_(w))>0.69时,龙眼果粉水分吸附量显著增加,导致糖类晶体结构消失。龙眼果粉的吸附过程符合熵焓互补理论,其吉布斯自由能为1586.6 J/mol>0,表明可通过控制环境条件来控制龙眼果粉的吸附过程。干基含水率从0.054 g/g上升到0.350 g/g时,龙眼果粉的玻璃化转变温度起始点从14.6℃降低至-26.5℃,其终点从39.1℃下降至-5.8℃。25℃下龙眼果粉的理论最佳贮藏A_(w)为0.086,对应的干基含水率为0.0495 g/g。该研究结果可为龙眼果粉贮藏条件的选择提供参考。

二胺型苯并噁嗪改性双酚A环氧树脂及其玻璃纤维复合材料性能研究

为了延长环氧树脂漆的适用期,提高其耐热性,使用苯并噁嗪树脂对其进行共混改性。以溶液共混方式制备了环氧树脂漆(EP)与苯并噁嗪树脂(BZ)的共混树脂体系(E/B-x),讨论了BZ的加入对共混树脂的黏度、流变特性、凝胶化活化能、固化行为、表面特性及玻布增强复合材料的耐热性、力学性能的影响。结果表明:BZ的加入使共混树脂的黏度明显降低,凝胶温度及凝胶活化能增加,迟滞了EP的固化反应,延长了其适用期;少量BZ的加入不会改变EP的玻璃化转变温度(Tg),当BZ加入量达到40份时,与EP复合材料相比,E/B-40复合材料的干态和湿态Tg分别提高了12.6%和11.7%;随BZ加入量的增加,复合材料的弯曲强度先下降后上升,E/B-40复合材料的弯曲强度和弯曲模量可达569 MPa和27.9 GPa,与EP复合材料相当。

玻璃态液氮速冻对蓝莓品质特性的影响

以‘北村’蓝莓为研究对象,构建蓝莓的状态图确定其特征玻璃化转变温度T_(g)’,在此基础上以蓝莓T_(g)’为冻结终点,对蓝莓进行超低温冰箱冷冻(-80℃)(记为RF-80℃组)、液氮浸渍速冻(-80、-100、-120℃)(记为LN-80℃、LN-100℃、LN-120℃组)处理,测定冷冻曲线、汁液流失、硬度、营养物质含量、细胞膜完整性、酶活性、微观结构等指标,探究液氮速冻结合T_(g)’对蓝莓品质特性的影响。结果表明,蓝莓T_(g)’为-52.55℃;与RF-80℃组相比,液氮速冻蓝莓的品质保持效果更佳,液氮速冻蓝莓的冷冻时间显著缩短,果实解冻后汁液流失减少,硬度保持得更好;可溶性固形物含量、可滴定酸含量、抗坏血酸含量和花青素含量与鲜果更接近;相对电导率和丙二醛含量更低,细胞膜的完整性破损程度更低;过氧化物酶和多酚氧化酶活性更低;微观结构的紧密型和完整性更强。液氮速冻的环境温度越低,冷冻效果越好,LN-120℃处理将冷冻蓝莓的品质劣化降至最低。综上所述,液氮速冻能够显著提高冷冻速率,结合T_(g)’有助于保持良好的冷冻蓝莓品质,研究结果可为蓝莓冷冻加工条件的选择提供理论基础。

紫胶树脂玻璃化转变温度的测定及其对贮存稳定性的影响

作为聚合物的紫胶树脂应该具有玻璃化转变温度(T g),但始终未能明确,确切的T g将能够解释紫胶树脂的贮存不稳定性问题并指导其贮存温度条件。为验证其玻璃化转变温度,通过聚合物的玻璃化转变研究方法及理论,应用X射线衍射法(X-ray Diffraction,XRD)、差示扫描量热法(Differential Scanning Calorimetry,DSC)和动态热机械分析法(Dynamic Thermomechanical Analysis,DMA)对紫胶树脂的玻璃化转变T g值进行了验证实验。由XRD图及2.93%的结晶度计算结果证实紫胶树脂属非晶态聚合物,其5次DSC二次升温扫描曲线中表现出0.071 J/(g·K)的平均比热容差,结合其DMA曲线中的储能模量在36.0℃处的拐点、耗能模量在19.5℃处、损耗因子在36.9℃处的峰值温度,共同证实了紫胶树脂存在玻璃化转变及T g,其T g值在DSC和DMA测试条件下分别为27.3℃和36.0℃;根据紫胶树脂的玻璃化转变及T g温度,对其贮存不稳定性问题的解释为:当贮存温度低于其T g时,由于物理老化作用会导致其性质变异,但仍可相对较长时间贮存,当温度高于其T g时,由于接有活性端基的链段可以运动使得紫胶树脂更易发生活性端基间反应,致使紫胶树脂的贮存时间缩短,利用此点可指导紫胶及紫胶树脂的贮存温度条件,即应低于其T g温度。