尼龙1012的Brill转变

作为一类重要的结晶性聚合物 ,尼龙在加热或冷却过程中的晶型转变 [1,2 ]一直为人们所关注 .其中对尼龙 66的晶型转变研究得最多 [3～ 6 ] .在加热过程中尼龙 66室温下三斜的α晶型转变为高温下的假六方晶型 ,尼龙 66的这一晶型转变称为 Brill转变 [3] .在变温 X射线衍射测试中可明显观察到 Brill转变 :室温下α晶型的两个强的衍射峰随温度升高逐渐靠近 ,并在某一温度下合并为一个峰 ,这一温度称为 Brill转变温度 .近年来研究表明 ,许多脂肪族的尼龙升温时均表现出 Brill转变 ,并且 Brill转变温度随尼龙结晶条件及其结构的不同而不同 [7…     

牵伸作用对尼龙6纤维晶型结构及力学性能的影响

利用广角X射线衍射仪(WAXD)、傅里叶变换红外光谱仪(FTIR)、示差扫描量热仪(DSC)、声速取向测量仪、扫描电镜(SEM)以及纱线强伸度仪研究了不同牵伸倍数尼龙6复丝的晶型结构、熔融行为、取向度、表面形貌以及力学性能.结果表明,随着牵伸倍数的增加,伴随着γ晶型片晶的生长以及非晶区链段重排诱导α晶型的生成,尼龙6复丝的结晶度不断的提高,在牵伸倍数达到3倍时,样品中出现了α晶型的特征衍射峰,导致了其熔融温度的提高以及多重熔融峰的出现.同时,牵伸作用也增加了分子链沿纤维轴向的取向程度,消除了纤维表面的残余应力,改善了纤维的表面缺陷.在这些因素的共同作用下,尼龙6复丝的力学性能得到了一定程度的提高,当牵伸倍数为3倍时,拉伸强度与拉伸模量分别达到了5.0 c N/dtex和28.9 c N/dtex,与较低牵伸倍数相比较均有所提高.     

水热处理对聚酰胺6纤维结构和性能的影响

在150℃下对聚酰胺6(PA6)纤维进行了水热处理,通过二维广角X射线衍射(2D-WAXD)、二维小角X射线散射(2D-SAXS)、示差扫描量热法(DSC)、场发射扫描电子显微镜(FE-SEM)和单丝强力测试等表征方法,研究了水热处理对纤维结构、热学和力学性能的影响.水热条件下,随温度的增加,水分子渗透作用增强,分子链的运动加剧,纤维的内部结构发生变化.纤维晶区结构由原来的γ晶型转变成为α晶型,结晶度和晶区完善程度提高,微晶尺寸增加,从而使纤维的热稳定性提高,熔融温度和熔融焓增加.水热处理使得纤维形成了折叠链片晶结构.在拉伸过程中,纤维的长周期不断增加,片晶有序性排列程度提高.水热处理后PA6纤维非晶区体积分数降低,并伴随有微孔和大的孔洞的形成,纤维的断裂强度和断裂伸长率都有所降低.     

β晶型聚丙烯的力学性能与结晶行为研究

研究了β晶型成核剂（酰胺化合物）用量对聚丙烯力学性能的影响,并对β晶型聚丙烯进行了偏光显微镜观察,DSC和广角X射线衍射分析。结果表明：添加β晶型成核剂后,聚丙烯的球晶细密化,α晶型向β晶型转变,韧性增强。     

偏氟乙烯-六氟丙烯共聚物纤维结构与性能表征

采用熔融纺丝技术制备偏氟乙烯-六氟丙烯共聚物[P(VDF-HFP)]初生纤维,在90°C下分别拉伸2、4、6倍,用X射线衍射(XRD)、傅里叶红外光谱(FTIR)、热重分析(TG)、示差扫描量热分析(DSC)、拉伸试验等研究了纤维结晶、热性能、力学性能、弹性回复性能等.结果表明:P(VDF-HFP)纤维晶区主要源于偏氟乙烯(VDF)链段,具有α和β2种晶型;随着拉伸倍数的增大,α晶型转变为β晶型并逐步增加,纤维结晶度提高;拉伸倍数为6倍时,P(VDF-HFP)纤维在氮气氛围下的热分解温度为452.3°C,熔融温度为126.9°C,断裂强度为502.6 MPa,定伸长为20%时,重复拉伸50次的弹性回复率为81%.     

纳米硅粉/MC尼龙6复合材料的制备与性能

将纳米硅粉分散于熔融的己内酰胺中,以NaOH为催化剂,2,4-甲苯二异氰酸酯为助催化剂,原位制备了纳米硅粉/MC尼龙6复合材料.用红外光谱、X射线衍射、场发射扫描电镜、热重分析仪和差示扫描量热仪对复合材料的界面结构和性能进行了研究.结果表明,纳米硅粉在尼龙6基体中具有较好的分散性,而且其与基体有比较强的界面作用,纳米硅粉促进了尼龙6的结晶,但是其对尼龙6的晶型结构没有产生明显的影响.     

纳米晶钛酸钡的介电性能

采用硬脂酸凝胶法制备了纳米晶BaTiO3,用差热热重分析、红外光谱分析、X射线衍射分析等手段对产物的形成过程、晶型、粒径进行了分析.通过对材料介电性能的研究发现,纳米材料的静态介电常数远大于常规材料的介电常数,随着粒径的减小,纳米材料的介电常数先增大而后有所降低.随着环境湿度的升高,纳米晶材料的介电常数逐渐增大,在高湿度条件下,其介电常数与湿度成线性关系.     

纳米结构MnO2的水热合成、晶型及形貌演化

以水热合成方法制备了具有不同微观形貌的纳米结构MnO2, 并以X射线衍射(XRD), 扫描电镜(SEM)和X射线光电子能谱(XPS)等方法对其进行了表征. 跟踪考察了二氧化锰的晶型及微观形貌随水热反应时间的演变过程, 在Ostwald ripening机理作用下, MnO2晶型转化过程为γ-MnO2, α-MnO2和β-MnO2, 同时形貌由微米球转变为海胆结构、空心海胆结构和纳米线.     

立方晶型Sb2O3纳米晶的合成及光催化性能

采用沉淀法合成了立方晶型Sb2O3纳米晶,通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、紫外-可见漫反射光谱(UV-Vis DRS)和电子自旋共振谱(ESR)等对样品进行了详细的表征。以紫外光光催化降解甲基橙为反应模型评价了样品的光催化性能。结果表明:沉淀法合成的立方晶型Sb2O3纳米晶颗粒小,表现出良好的光催化性能。对立方晶型Sb2O3纳米晶光催化降解甲基橙的原因进行了探讨,并提出了降解甲基橙的反应机理。     

拉伸温度对α’-型聚乳酸结构与性能的影响

α’-晶型聚乳酸(PLA)膜被制备和单轴拉伸.通过凝胶渗透色谱仪(GPC)、全反射红外光谱(ATR-IR)、差示扫描量热仪(DSC),X射线衍射(XRD)及Raman光谱等测试技术研究了拉伸温度梯度变化对α’-晶型PLA膜的分子量及其分布、分子链构象、结晶度、晶型转变和取向行为的影响.在恒定拉伸速度与应变下,拉伸温度对PLA膜的应力-应变曲线,特别是屈服强度、拉伸模量产生了较大的影响,其值随拉伸温度的增加而降低.GPC测试结果表明,在不同的温度下拉伸后,PLA会发生一定程度的降解,分子量降低;ATR-IR,XRD,DSC和Raman光谱测试结果表明,在不同的温度下拉伸后α’-型PLA没有发生晶型的转变,即没有由α’-晶体转变为α-或β-晶体.结果表明PLA的结晶度、分子链取向程度强烈依赖于拉伸温度:当拉伸温度低于100℃时,α’-型PLA膜的结晶度与沿着拉伸方向的变形程度随拉伸温度的增加而增加,分子链的高度取向诱导了PLA结晶;当拉伸温度超过100℃后,PLA的分子链沿着拉伸方向上的有序度与结晶度将降低.     

Investigation on the Brill transition of polyamide 618

The Brill transition of even-even polyamide 618 was investigated using differential scanning calorimetry (DSC), temperature-dependent wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR). The X-ray diffraction results indicate that the melt-crystallized sample of polyamide 618 transforms from the triclinic unit cell to the pseudo-hexagonal phase in the range of 120–180°C. In this range, the thermograph of polyamide 618 presents a broad endothermal peak. From the FTIR spectra, it was found that during the transition process of polyamide 618, the intensity of the intra-sheet hydrogen bonds becomes weak. At the same time, the CH₂-amide bonds twist, and the all-trans conformation of methylene sequences is disordered by inserting the gauche conformation. The CH₂ segments are in a mobile state because of the enhanced stretching and twisting vibrations of the C-CO and C-N bonds. Translated from Chemical Journal of Chinese Universities, 2006, 27 (2) (in Chinese)     

Structure formation of hydrophobically end-capped poly(ethylene oxide) in the solid state

The conformational transition of hydrophobically end-capped poly(ethylene oxide), HP-PEO-HP [hydrophobic-poly(ethylene oxide)-hydrophobic], was studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) methods. Conformational transitions of HP-PEO-HP from a planar zigzag to a 7/2 helical conformation were observed as the molecular weight of the PEO main chain increased. HP-PEO-HP 1(18), with a PEO molecular weight of 1000 and 18 hydrocarbons on each end, has mainly an alpha-helical structure in poor solvents, whereas alpha and beta conformations coexist in good solvents. This means that the alpha-helical structure caused by the hydrogen bonds between the urethane linkages was broken by the high chain mobility caused by the melted adjacent chains of PEO, and instead, the beta-sheet was formed by the interaction of multiple hydrogen bonds. Another indication of hydrogen bonds breaking at increasing temperature is the transition of the N-H stretching peak in the FTIR data. HP-PEO-HP 2(18) and 4(18), which have 18 hydrocarbons on each end and PEO molecular weights of 2000 and 4000, respectively, and consist mostly of PEO, showed spherulites. This result also suggests that the PEO molecule has a 7/2 zigzag helical conformation. In contrast, HP-PEO-HP 1(18), which is composed of less PEO than HP-PEO-HP 2(18) and 4(18), did not show a spherulite structure.     

Brill transition of nylon-6 in electrospun nanofibers

Electrospun nylon-6 fibers were prepared from its polyelectrolyte solution in formic acid with different concentrtaions. In situ Fourier transform infrared (FTIR), wide-angle X-ray diffraction and small-angle X-ray scattering (SAXS) were performed on the nylon-6 fibers heated to various temperatures until melting. For comparison, stepwise annealing of the solution-cast film having exclusively the α-form was also carried out to elucidate the structural evolution. Our results showed that Brill transition in the electrospun fibers occurs at a lower temperature than that in the solution-cast film due to the crystal size difference. Differential scanning calorimetry heating traces on the as-spun fibers exhibited a unique crystalline phase with a melting temperature of ～235?°C, higher than the equilibrium melting temperature of nylon-6. The content of high melting temperature (HMT) phase increased with increasing nylon-6 concentration; a maximum of 30?% of the fiber crystallinity was reached for fibers obtained from the 22?wt.% solution regardless of the heating rates used. Based on the SAXS and FTIR results, we speculated that the HMT phase is associated with thick α-form crystals developed from the highly oriented nylon-6 chains that are preserved in the skin layer of the as-spun fibers. A plausible mechanism for the formation of the skin/core fiber morphology during electrospinning was proposed.     

脂肪族聚酰胺热膨胀行为的研究

通过热膨胀测试,示差扫描量热分析(DSC)、广角X射线衍射(WAXD)与傅里叶变换红外光谱(FTIR)等方法研究了4种脂肪族聚酰胺玻璃化转变温度(Tg)、结晶行为以及氢键强度对热膨胀行为的影响,探索了影响脂肪族聚酰胺热膨胀的本质.DSC和X射线衍射结果表明,聚酰胺中结晶部分的热膨胀系数要低于无定形部分,但聚酰胺的熔融温度和结晶度对热膨胀的影响不够明确.相比较其它脂肪族聚酰胺,聚酰胺56(PA56)具有较高的玻璃化转变温度和较低的亚甲基/酰胺基(CH2/CONH)比例,表现出较低的热膨胀系数.研究发现,在相同条件下制备的脂肪族聚酰胺体系中,CH2/CONH比例或Tg与热膨胀系数具有明显的线性关系,随着CH2/CONH比例的降低或Tg的升高,热膨胀系数显著减小.FTIR的结果表明,聚酰胺分子链间的氢键密度和氢键强度随温度升高衰减的程度是影响其热膨胀行为的关键因素.     

In-site observation of the crystallization of nylon-6 mediated by the interfacial hydrogen bonds

Hydrogen bonds exist in many polymer systems and play a large role in the physical and chemical properties. In this study, nylon-6, which consists of repeated amide groups and contains large number of hydrogen bonds, is chosen as an example. Meanwhile, the oxidized unzipped MWCNTs (μCNTs) with oxygenated species such as carboxyl and hydroxyl groups are used as mediator to regulate the crystallization process of nylon-6 thin films. In-site experimental techniques, including Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, and polarized optical microscopy were utilized to get more direct insights on the crystallization mechanism of nylon-6 and μCNTs systems.     

Crystalline transition of polyamide‐10,20 investigated by in situ Fourier transform infrared spectroscopy

Real‐time Fourier transform infrared spectroscopy was used to investigate the crystalline transition of even–even polyamide‐10,20. During the crystalline transition, the intensity of the hydrogen bonds became weak, the twisting of the C? CO and C? N bonds improved, and the gauche conformation of the CH₂ sequences increased, along with the strengthening of the vibration of the methylene units. The ordered stacking of methylene segments with the trans‐zigzag conformation gradually became disordered by the insertion of the gauche conformation upon heating. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4017–4022, 2004     

高硼含量的SiC陶瓷先驱体的合成和表征

采用经典硼氢化反应, 通过硼烷二级硫醚(BH₃·SMe₂)与二甲基二乙烯基硅烷(DVS)反应, 合成了聚硼碳硅烷(PBCS)陶瓷先驱体, PBCS在氮气中经高温裂解得到了高硼含量的SiC陶瓷.利用红外光谱、核磁共振波谱和热重分析对聚合物的结构和性能进行了表征; 利用元素分析、X射线衍射和扫描电子显微镜对聚合物的裂解产物进行了分析.结果表明, 聚合物的结构中含有B—C, Si—C和C—H键, 在1000℃氮气气氛中, 其陶瓷产率在50%以上.陶瓷产物在1100℃以无定形态存在, 硼含量高达6.46%, 在1300℃时出现明显结晶, 形成B₂O₃, C和β-SiC三相组成的多元复相陶瓷, 在1500℃以下陶瓷产物表面光滑, 结构致密.     

Preparation, characterization and crystalline transitions of odd-even polyamides 11,12 and 11,10

The novel odd-even polyamides 11,12 (P11, 12) and 11,10 (P11, 10) were synthesized via step-heating melting-polycondensation of 1,11-diaminoundecane with dodecanedioic acid and decanedioic acid, respectively. Their chemical structures were confirmed by various spectroscopic techniques (FTIR, Raman, NMR). The thermal properties of the polyamides under consideration were measured by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The crystalline transitions of the prepared polyamides were studied by wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR). The variable temperature WXRD results indicated that P11,10 undergoes the Brill transition during the heating process before melt while P11,12 does not. From the real time FTIR spectra of P11,10, it was found that the intensity of hydrogen bond becomes weak, and the twisting of the C-CO and C-N bonds becomes enhanced. The vibration of the methylene units strengthens and the trans-zigzag conformation decreases. The ordered stacking of the methylene segments becomes gradually disordered by insertion of the gauche conformation during the crystalline transition process.     

In situ Characterization of Phase Transition of Amorphous Poly(9,9-di-n-octyl-2,7-fluorene) Thin Film During Thermal Annealing

Amorphous poly(9,9-di-n-octyl-2,7-fluorene)(PFO)thin films were characterized in situ via thermal an- nealing based on grazing incidence X-ray diffraction(GIXRD)profiles,UV-visible absorption spectrophotometry,and Fourier transform infrared spectroscopy(FTIR).The results of GIXRD indicated that the amorphous phase transformed into a crystalline phase when the annealing temperature was higher than 80 ℃.Different outcomes were elicited for the intensities and d-spacings of the diffraction peaks below and above 80 ℃,which were attributed to the formation of the κ-phase.The mechanism of phase transition was revealed by in situ UV-visible absorption and FTIR spectra,whereby the rearrangement of the side chains was dominant and the movement of the main chains was minimal,even when the annealing temperature was lower than 80 ℃.In contrast,the rearrangement of the main chains was dominant when the temperature was higher than 80 ℃.     

SYNTHESIS AND CHARACTERIZATION OF AZO TYPE SIDE CHAIN LIQUID CRYSTALLINE POLYSILOXANE

A novel side chain liquid crystalline polymer (SCLCP) combining the polysiloxane as main chain with azo-based mesogen moieties as side chain through a flexible spacer has been synthesized by the hydrosilylation reaction using Cp_2PtCl_2 as catalyst. The phase transition behavior of both side chain monomer (AZO-C_6C_(11))and polymer (P-AZO-C_6C_(11))has been characterized via combination of hot-stage polarized microscope, DSC and X-ray diffraction methods (including temperature-variation and quenching techniques). As normal, the transition process included K→S→N→I. Some pretransition features have been observed.