超快扫描量热技术表征高分子结晶动力学

高分子结晶行为是高分子材料加工过程研究的热点,因为高分子组分和加工工艺控制着高分子结晶及其产物性能。差示扫描量热仪(DSC)是研究高分子结晶动力学常规手段。但是,普通DSC所能达到的最快降温速率一般无法抑制较快的样品结晶,结晶行为将在等温结晶动力学测试之前发生,因此可进行等温结晶的研究温度范围局限于较低结晶过冷度的高温区域。近年来,具有超快速升降温扫描速率和精准控温的快速扫描芯片量热仪(FSC,其商业化版本Flash DSC 1)得到了广泛应用。FSC可以抑制高分子样品在升降温过程中的结晶成核,避免对之后的结晶动力学测试产生影响。因此FSC技术将高分子结晶动力学的研究温度区间延伸至具有较大过冷度的低温区,加深了我们对高分子结晶成核机理以及高分子工业加工过程的理解。本文首先介绍了由初级成核方程描述的高分子结晶动力学原理,初级成核自由能位垒(?G~*)和扩散活化能位垒(?U)分别控制了高低温区的结晶动力学。我们还总结了FSC技术的发展,包括氮化硅薄膜芯片技术、快速扫描量热仪、商业化Flash DSC 1在不同高分子结晶熔融行为研究中的应用。然后介绍表征高分子等温结晶动力学的方法,其中包括样品制备、质量估算、消除热历史、临界扫描速率的确定等,并举例介绍FSC在高分子结晶动力学研究中的应用,涵盖高分子总结晶动力学、结晶成核动力学、高分子焓松弛对结晶成核的影响、FSC联用技术等方面。应用举例中对应形貌和结晶信息,分析了通过FSC测试得到的结晶成核动力学特点。另外通过比较不同结构特点的高分子,总结了我们对结晶动力学行为的基本理解。总之,FSC技术是一种能够提供相转变动力学和热力学信息的高效工具,特别是应用于分析只能在快速扫描中得到的样品结构变化信息。同时我们希望本文能够帮助读者考虑超快扫描量热技术在其他材料研究上的应用,包括合金、药物、生物大分子等。     

原位聚合聚乙烯/蒙脱土纳米复合材料的结晶行为

用DSC研究了HDPE与MMT负载的催化剂熔融共混和原位聚合得到的两种纳米复合材料的熔融、 结晶行为和等温结晶动力学.  结果表明, HDPE与熔融共混样品的结晶度、 平衡熔点、 球晶生长速率和结晶能力大体相同; 原位聚合得到的HDPE/MMT纳米复合材料的结晶度和平衡熔点高于纯HDPE; 在相同过冷度条件下熔融结晶速率和结晶能力低于纯HDPE, 而在相同结晶温度Tc下, 熔融结晶速率和结晶能力则高于纯HDPE.  纯HDPE的晶体生长侧向单位面积表面自由能最小, 其次是熔融共混样品, 原位聚合样品最大, 且随ＭＭＴ含量的增加逐渐升高.     

用DSC研究稀土顺式聚丁二烯的低温结晶与熔融行为

采用示差扫描量热仪研究了稀土顺式聚丁二烯(PB)等温过程的结晶及其熔融行为. 结果表明,在等温结晶的后期存在晶型完善的过程,而且随着等温结晶温度的提高,结晶速率均下降. PB的熔融总是在比等温结晶温度高约2 ℃处开始,而且在10 ℃/min的升温速率下,DSC曲线不仅显示出很宽的熔融温度范围,而且在低温处还出现了小肩峰,说明等温结晶后体系中具有在该升温速率下不同稳定性的晶体. 通过不同温度下的等温结晶曲线,分别采用结晶度趋于零(Xc=0)时的熔点和结晶时间无限长(t-1c＝0)时的熔点,用Hoffman-Weeks方法得到顺式聚丁二烯的平衡熔点T∞m位于9～17.6 ℃之间.     

聚丁二酸丁二醇酯的自成核结晶行为

利用差示扫描量热仪(DSC)研究了自成核对聚丁二酸丁二醇酯(PBS)的结晶行为的影响. 研究结果表明, PBS的有效自成核温度处理区间为118～120 ℃. PBS经自成核处理后结晶温度提高, 可以在100~118 ℃温度区间内迅速结晶. 同时, 研究了自成核处理后样品在100～104 ℃范围内的等温结晶行为、动力学过程及熔融行为. 结果表明, 随着等温结晶温度的升高, 结晶速率变慢, 熔融曲线出现多重熔融峰. Hoffman-Weeks方程分析结果表明, 自成核处理对PBS的平衡熔点没有影响. Avrami等温结晶动力学方程适合分析自成核处理样品的等温结晶动力学过程, 获得其动力学参数K与n, 其中n值偏大的原因在于自成核的样品结晶生长点增多. 根据Arrhenius方程, 计算获得PBS自成核处理后等温结晶活化能为-286 kJ/mol.     

聚-4-乙基苯酚抗氧剂对聚丙烯结晶行为的影响

通过差示扫描量热仪(DSC)和X射线粉末衍射仪(XRD)研究了聚-4-乙基苯酚抗氧剂对聚丙烯结晶行为的影响。 分别用Jeziorny法和Mo法处理非等温结晶动力学。 同时用Friedman法和Kissinger法计算其结晶活化能。 最后由结晶活化能与结晶温度的变化曲线求得Hoffman-Lauritzen参数成核速率常数(K_g)和迁移活化能(U^*)值,进而求得折叠链端表面自由能(σ_e)和分子链段折叠功(q)。 结果表明,抗氧剂的加入,使聚丙烯的结晶峰温度向低温区移动,结晶半峰宽变大,半结晶时间(t_1/2)增大,Jeziorny法所得的结晶速率常数(Z)降低,Mo法所得反映结晶速率快慢的参数F(T)提高,在相同结晶转化率下,结晶活化能负值变小。 Hoffman-Lauritzen参数K_g、U^*、σ_e和q值均增大。 所有变化均表明聚-4-乙基苯酚抗氧剂对PP的结晶有抑制作用。     

基板受限条件下聚合物薄膜厚度对结晶的影响研究

通过溶液铸膜方法,用匀胶机(spin-coater)在铝箔基板上制备出一系列具有不同厚度的结晶聚合物聚羟基丁酸酯(PHB)和聚ε-己内酯(PCL)超薄膜.经退火处理后,用差热扫描量热仪(DSC)测试了薄膜厚度对其结晶熔点T_m和结晶温度T_c的影响.结果表明,结晶熔点T_m随超薄膜厚度的减小逐渐减小;在减至一定的厚度时,熔点有突升,至极大值后,随膜厚继续减小熔点又会骤降.而结晶温度T_c则一直随膜厚的减小而逐渐降低.可以认为,结晶聚合物的分子在基板受限作用下,主要是熔融熵的变化导致了熔点的上述变化,而受限条件下的扩散控制结晶使结晶温度降低.     

高分子结晶和熔融行为的Flash DSC研究进展

近年来,作为常规示差扫描量热仪(DSC)技术的发展,商业化的快速扫描芯片量热技术(fast-scan chip-calorimeter,FSC)对推动高分子结晶学研究进展发挥了重要的作用.本文首先介绍了闪速示差扫描量热仪Flash DSC的研发历程及其对高分子结晶样品的测试技术,然后举例介绍了其在高分子结晶和熔融行为研究中的一些应用,包括总结晶动力学、晶体成核动力学、成核剂和填料对结晶的影响、共聚单元对结晶的影响、多重熔融峰的鉴定、折叠链片晶的不可逆和可逆熔化、以及极性大分子晶体的熔融等.Flash DSC极大地扩展了扫描温度速率范围,使得其研究的时间窗口能与实际高分子材料加工过程和计算机分子模拟的时间窗口相互匹配,所提供的综合信息有助于我们更好地理解高分子结晶、退火和熔融行为的微观机理.     

聚碳酸亚丙酯对聚(β-羟基丁酸酯-β-羟基戊酸酯)结晶行为的影响

用FTIR和DSC研究了PHBV及其与聚碳酸亚丙酯(PPC)熔融共混样的熔融结晶行为和等温结晶动力学.结果表明,PHBV与PPC熔融共混过程中发生了酯交换反应,两组分间存在一定的相互作用.PPC虽然能降低PHBV结晶折迭链的表面自由能,但同时也能够降低PHBV的结晶度、球晶径向生长速率、平衡熔点和结晶能力.     

聚2-吡咯烷酮的非等温结晶动力学

用差示量热扫描热分析仪(DSC)测试了不同降温速率下聚2-吡咯烷酮(PPD)样品的温度-热焓曲线,样品黏均分子量为2.2×10~4,熔点为272℃。采用Jeziorny法、Ozawa法和莫志深法分析了PPD的非等温结晶动力学。结果表明,在给定降温速率范围内,Ozawa法不适用于描述PPD的非等温结晶动力学过程,Jeziorny法只适用于描述PPD的主结晶阶段,而莫志深法能很好地描述整个结晶过程。Jeziorny法处理结果表明,PPD主结晶阶段的Avrami指数(n)为1.68~1.78,晶体生长为准二维生长。莫志深法处理结果表明,在单位结晶时间里达到某一相对结晶度所需的降温速率随相对结晶度的增加而增大。用Kissinger方程求得PPD的非等温结晶活化能为-31.9kJ/mol。     

己内酯和2,2-二羟甲基丁酸共聚酯的非等温结晶动力学研究

采用示差扫描量热仪(DSC) 研究了具有生物相容性及可降解性P(BHB-CL)超支化共聚酯的非等温熔融结晶过程, 分别采用Avrami 方程、Ozawa 方程和Mo方程对P(BHB-CL)共聚酯的非等温动力学数据进行比较分析, 计算了相关的非等温结晶动力学参数, 并利用Kissinger方程计算其非等温结晶活化能. 结果表明, Mo方程更适合描述P(BHB-CL)共聚酯的非等温结晶过程.     

Miscibility and crystallinity of poly(3-hydroxybutyrate)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends

With the objective of developing new biodegradable materials, the miscibility and the crystallinity of blends of poly(3-hydroxybutyrate), P(3HB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), P(3HB-co-3HV), have been studied. P(3HB) (300 kg mol⁻¹)/P(3HB-co-3HV)–10% 3HV (340 kg mol⁻¹) blends were prepared by casting in a wide range of proportions, and characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The experimental values for the glass transition temperatures (T_g) are in good agreement with the values provided by the Fox equation, showing that the blends are miscible. It was observed that the T_g and the melting temperature (T_m) decreases with the increase in the P(3HB-co-3HV)–10% 3HV content, while the crystallization temperature (T_c) increases. FT-IR analyses confirmed the decrease on the crystallinity of P(3HB)/P(3HB-co-3HV)–10% 3HV blends with higher copolymer contents. Bands related to the crystallinity were changed, due to the copolymer content that produced miscible and less crystalline blends.     

Crystallization of a polyamide 11/organo-modified montmorillonite nanocomposite at rapid cooling

Fast scanning chip calorimetry (FSC) has been used for analysis of the crystallization behavior of a polyamide 11/organo-modified montmorillonite (PA 11/OMMT) nanocomposite. The addition of OMMT leads to a significant increase of the crystallization temperature of the polymer matrix only on cooling faster than about 10⁰ K s^–1. In case of slow cooling at rates typically used in standard differential scanning calorimetry (DSC), the nucleating effect of OMMT on crystallization of PA 11 is negligible. The critical cooling rate to suppress crystallization of PA 11 and to completely vitrify the relaxed melt increases at least by one order of magnitude due to the addition of OMMT. Furthermore, the enthalpy of crystallization is nearly independent on the cooling conditions in the analyzed cooling rate range from 10^–2 to 2?×?10³ K s^–1 in PA 11/OMMT nanocomposites. Isothermal crystallization experiments confirmed that the nucleating effect of OMMT on the crystallization of PA 11 increases with supercooling, being therefore of particular importance at cooling conditions relevant in polymer processing. The evaluation of the kinetics of crystallization of the PA 11/OMMT nanocomposite by FSC and DSC in a wide range of cooling rates/supercooling has been completed by analysis of the effect of OMMT on the α/δ’ polymorphism of PA 11 and the spherulitic superstructure.     

Nonisothermal crystallization kinetics of amorphous Te51.3As45.7Cu3

The structure and kinetics of the crystallization reaction of amorphous Te_51.3As_45.7Cu₃ were studied under nonisothermal conditions using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Two exothermic changes were reported. Five isoconversional methods, of Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Tang, Starink, and Vyazovkin, were used to determine the variation of the activation energy for crystallization with temperature, E(T). The results show that the activation energy for crystallization associated with the first peak first decreases with increasing temperature and then increases. Different behaviour was observed for the second peak, where an increase of E with temperature followed by a decrease. The effect of heating rate on the reaction model, g(), was also different for the two crystallization peaks.     

Thermal and topographical characterization of polyester- and styrene/acrylate-based composite powders by scanning probe microscopy

The thermal properties of two conventional polyester-based toners and a chemically prepared styrene/acrylate toner with different thermal histories were studied by scanning probe microscopy (SPM) and differential scanning calorimetry (DSC). The thermal transition temperatures detected by SPM agreed with the results of the DSC measurements. The validity of SPM for detecting thermal transitions was further confirmed by studying two amorphous reference polymers with different glass transition points (T_g) and three crystalline reference polymers with different melting points (T_m). When the toner sample was heated by the SPM probe above the glass transition temperature of the toner powder (T_probe > T_g), changes occurred in the surface topography and roughness causing different levels of local sintering of the particles. A set of roughness parameters calculated from the SPM image data were used to quantify the most essential features of toner surfaces. Environmental scanning electron microscopy (ESEM) was used to study the penetration depth of heat dissipated by the SPM probe. The probe-annealing was compared with oven-annealing in order to establish the effect of thermal history on the thermal properties of the materials.     

聚β-羟基丁酸酯顺丁烯二酸酐接枝共聚物的等温结晶动力学和熔融行为

采用DSC方法对聚 β 羟基丁酸酯顺丁烯二酸酐接枝共聚物 (PHB g MA)的等温结晶动力学和熔融行为进行了研究 .结果表明 ,顺丁烯二酸酐的引入使得聚 β 羟基丁酸酯的结晶能力下降 ,但是并没有改变它的结晶成核机理和生长方式 .随着接枝率的增加 ,结晶活化能增加 .等温结晶后的PHB g MA表现出双熔融行为 ,这是在升温过程中发生熔融重结晶的结果     

A Detailed Comparison of First Order Transitions by DSC and TMC

Indium was analyzed with both, standard differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) using sinusoidal and saw-tooth modulation. Instrument and sample effects were separated during nucleated, reversible melting and crystallization transitions, and irreversible crystallization with supercooling. The changes in heat flow, time, and sample and reference temperatures were correlated as functions of heating rate, mass, and modulation parameters. The transitions involve three regions of steady state (an initial and a final region before and after melting/crystallization, a region while melting/crystallization is in progress) and one region of approach to steady state (melting peak to final steady state region). Analyses in the time domain show promise when instrument lags, known from DSC, are used for correction of TMDSC. A new method of integral analysis is introduced for quantitative analysis even when irreversible processes occur in addition to reversible transitions. The information was derived from heat-flux calorimeters with control at the heater block or at the reference temperature sensor. This revised version was published online in July 2006 with corrections to the Cover Date.     

吡啶基离子液体[C_6py][DCA]热力学性质及利用新E?tv?s方程预测其表面张力

制备了吡啶类离子液体N-己基吡啶二氰胺盐[C_6py][DCA],并用核磁共振氢谱(~1H NMR)、核磁共振碳谱(~(13)C NMR)、差热扫描量热(DSC)、傅里叶变换红外(FT-IR)光谱对其进行表征。在288.15–338.15 K温度范围内,采用标准加入法,测定其密度(ρ)、表面张力(γ)和折光率(n_D)。在测得的实验数据的基础上,得到了离子液体[C_6py][DCA]的分子体积(V_m)、表面能(E_a)、摩尔极化度(R_m)和极化率(α_p)。结果显示E_a、R_m和α_p几乎不随温度的变化而发生改变。本文还提出了摩尔表面Gibbs自由能(g_s)的概念,并改进了E?tv?s方程。同时还计算了gs、临界温度(T_c)和E?tv?s方程经验参数(kE),并预测了离子液体[C_6py][DCA]的表面张力,预测值与实验值具有较好的一致性。     

尼龙610的多重熔融行为及其平衡热力学参数

用DSC,WAXD等方法研究了尼龙610的多重熔融行为。在DSC热谱图上,观察到三个熔融峰并按照部分熔融及分级熔融的观点对各峰的来源作了讨论。根据程序升温及等温结晶和比容测定的结果,求得尼龙610的T°_m及ΔH_m的值分别为517.6K及211.7j/g。     

Nonisothermal crystallization kinetics and melting behavior of bimodal medium density polyethylene/low density polyethylene blends

Nonisothermal crystallization kinetics and melting behavior of bimodal-medium-density- polyethylene (BMDPE) and the blends of BMDPE/LDPE were studied using differential scanning calorimetry (DSC) at various scanning rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the nonisothermal crystallization process of BMDPE. The BMDPE DSC data were analyzed by the theory of Ozawa. Kinetic parameters such as the Avrami exponent (n), the kinetic crystallization rate constant (Z_c), the peak temperatures (T_p) and the half-time of crystallization (t_1/2) etc. were determined at various scanning rates. The appearance of double melting peaks and the double crystallization peaks in the heating and cooling DSC curves of BMDPE/LDPE blends indicated that the BMDPE and LDPE could crystallize respectively.     

窄分子量分布茂金属短链支化聚乙烯结晶动力学

本工作用DSC方法对三种不同支化度的茂金属短链支化聚乙烯的等温、非等温结晶行为进行了研究 .样品为乙烯和己烯 1的共聚物 ,短支链主要为正丁基 ,分子量Mw =2 0 ,0 0 0 ,Mw/Mn<1 15 ,支化度 (每10 0 0C中CH3 数目 )分别为 1 6、10 4、40 .实验结果表明 ,茂金属短链支化聚乙烯结晶方式Ⅰ Ⅱ转变温度随支化度增加而降低 ,分别为 119 8℃、115 9℃、113 3℃ ;同时支链的存在降低了二次成核速率 ,增大了方式Ⅰ的结晶范围 ,总的结晶速度随支化度增大而减小