Induced crystallization behavior of poly(ethylene adipate) by highly oriented polyethylene

The crystallization behavior of poly(ethylene adipate) (PEA) on highly oriented high-density polyethylene (PE) substrate both from solution and isotropic melt was studied by means of optical microscopy, differential scanning calorimetry, atomic force microscopy and electron diffraction. The results show that the PE influences the crystallization of PEA strongly, which results in an epitaxial growth of PEA with well ordered structure. At the boundary of the PE substrate, a transcrystalline PEA layer is observed. Fine structural observation illustrates that the PEA grows on the PE substrate in edge-on lamellae with fixed orientation. Electron diffraction demonstrates that the epitaxial organization of PEA on PE occurs with both polymer chains parallel, which leads to the (00l) PEA diffractions inclined ±23.5° to the chain direction of PE crystals. Combining the real space morphological observation and electron diffraction results, it is concluded that the epitaxial PEA edge-on lamellae are folded in the {00l} lattice planes.     

Morphology and Crystalline Structure of Inclusion Compounds Formed between Poly（ethylene glycol） and Urea

The poly（ethylene glycol） （PEG, with Mw 2000）-urea inclusion compound （IC） crystallized at high temperature region showed two typical orientations, flat-on and edge-on crystals. 2D-XRD and polarized FTIR spectroscopy revealed that the PEG chains within urea channels were perpendicular to the substrate in fiat-on oriented crystals, while PEG chain axes were parallel to the substrate and lay along the growth direction in the edge-on crystals. FT1R absorption bands of PEG in the ICs are sensitive to orientation of the crystals. A scheme of PEG chain packing in the urea IC channel was proposed, which could explain the orientation of the crystal nucleus causing the two types of morphologies. Furthermore, functioning of PEG2000 chain end with analine had significantly influence on the morphology and orientation of the inclusion compound crystals, due to the defects caused by large terminal groups included in the urea channel.     

Morphologies of long chain branched isotactic polypropylene crystallized from melt

The crystallization behavior and resulting crystalline morphologies of long chain branched isotactic polypropylene (LCBPP) under different conditions were studied by means of differential scanning calorimetry and transmission electron microscopy combined with electron diffraction. The results indicate that the crystallization of LCBPP during fast cooling process, or at lower crystallization temperature, leads to the formation of mainly edge-on lamellar structures. The LCBPP exhibits also the wide angle lamellar branching frequently observed for linear isotactic polypropylene. Crystallizing LCBPP in temperature range of 110∼140 °C results in the formation of both edge-on and flat-on crystals, which coexist side by side with the content of flat-on crystals increases with increasing crystallization temperature. At high crystallization temperature, e.g. 145 °C, flat-on crystals with chain axis aligned perpendicular to the film plane are the only observed morphology. Moreover, the crystals of LCBPP grow slower than its linear counterpart and the crystal growth rates of both linear and long branched PPs are temperature dependent.     

左旋聚乳酸/聚(ε-己内酯)共混物在取向聚乙烯基底上的附生结晶行为

利用电子显微镜结合电子衍射研究了左旋聚乳酸/聚(ε-己内酯)(PLLA/PCL)共混物在取向聚乙烯(PE)基底上的结晶行为.纯PLLA在取向PE基底上能够附生结晶,主要形成分子链相互垂直的片晶结构.PCL在PE基质上也能发生附生结晶,导致两者分子链平行.PLLA/PCL共混物在取向PE基底上结晶的形态结构依赖于共混组成.在PLLA含量大于95 wt%时,PCL不影响PLLA与PE的附生结晶行为.当PCL含量增加至10 wt%时,PLLA在PE上的附生结晶行为受到了一定程度的影响.当PCL含量超过40 wt%时,PLLA在PE上的附生结晶被抑制,取而代之是PCL在PE取向基质上附生结晶,产生两者分子链平行的取向片晶.另外,在PLLA含量在50 wt%~30 wt%之间时,体系产生明显的微相分离,微相分离并不影响PCL与PE的附生结晶,在PCL的富集区仍然发生平行链附生结晶,而PLLA的富集区结构变得模糊.当PLLA含量少于20 wt%时,微相分离不明显,少量PLLA应该分散在PCL片晶间的非晶区.     

Orientation control of ferroelectric polymer molecules using contact-mode AFM

We have developed an orientation control technique for polymer molecules utilizing contact-mode atomic force microscopy (AFM). In this technique, the molecular chains were directly modified by scanning an AFM cantilever tip in contact with the film surface at the temperature just below its melting point. We call this process “modification scan”. Here, we applied this technique to poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) thin films on graphite and glass. We prepared a 75-nm thick copolymer crystalline film on graphite whose lamellar plane was perpendicular to the substrate (edge-on), and also prepared a film of the same thickness on glass whose lamellar plane was parallel to the substrate (flat-on). After applying this technique on both films, molecular chains were stretched and aligned to the modification scan direction, and new edge-on crystals were obtained, whose lamellar planes were well-aligned perpendicular to the modification scan direction.     

聚(ε-己内酯)薄膜结晶形貌及分子取向研究

用匀胶机通过溶液铸膜方法在硅片和铝箔基板上分别制备具有不同厚度的聚(ε-己内酯)(PCL)薄膜. 通过原子力显微镜(AFM)和偏光衰减全反射傅里叶红外光谱(ATR-FTIR)对薄膜中PCL的结晶形貌、 片晶生长方式及分子链取向进行了研究. AFM结果表明, 在200 nm或更厚的薄膜中, PCL主要以侧立(edge-on)片晶的方式生长; 对于厚度小于200 nm的薄膜, PCL片晶更倾向于以平躺(flat-on)的方式生长. 这种片晶生长方式的改变在硅片和铝箔基板上都表现出同样的倾向. 此外, 在15 nm或更薄的薄膜中, PCL结晶由通常的球晶结构变为树枝状晶体. 偏光ATR-FTIR结果表明, 当膜厚小于200 nm时, 薄膜结晶中PCL分子链沿垂直于基板表面方向取向, 并且膜越薄, 取向程度越高, 与AFM的观测结果一致.     

Effect of Materials Parameters on the Shape of Face-On Lamellae in Semi-Conducting Polymers: Insights From Qualitative Theory

Polymer semiconductors frequently form crystals or mesophases with lamellae, that comprise alternating layers of stacked backbones and side chains. Controlling lamellar orientation in films is essential for obtaining efficient charge carrier transport. Herein, lamellar orientation is investigated in an application-relevant setup: lamellae assembled on a substrate that strongly favors face-on orientation, but exposed to a film surface that promotes orientation along an “easy” direction, other than face on. It is assumed that the face-on order propagates from the substrate, but the lamellae bend to reduce their surface energy. A qualitative free-energy model is developed. The deformation is investigated as a function of film thickness, effective Young modulus, anchoring coefficient, and easy direction at the free surface. The calculations highlight the importance of elastic constants – lamellae can substantially deform already when Young moduli are only an order of magnitude smaller than the values that are reported for crystals. Softer Young moduli are expected when lamellar assembly occurs in a non-solidified mesophase that can be an equilibrium or (more speculatively) a transient state prior to crystallization. The alternative scenario of a two-layered film is also evaluated, where edge-on and face-on grains form, respectively, at the free surface and substrate.     

嵌段共聚物PVCH-b-PE-b-PVCH的多重结晶行为

通过采用差示扫描量热仪(DSC)主要研究了结晶-非晶嵌段共聚物聚乙烯基环己烷-b-聚乙烯-聚乙烯基环己烷(PVCH-b-PE-b-PVCH)溶液结晶样品的熔融与非等温再结晶过程.探讨了溶液结晶样品中微相分离结构的形成对嵌段共聚物受限结晶的影响,并发现样品在熔融后的非等温结晶过程中出现了多重结晶峰.通过对嵌段共聚物有序、...     

NUCLEATION MECHANISM OF PEO BLOCK IN DOUBLE-CRYSTALLINE POLY（ETHYLENE-co-BUTENE）-b-POLY（ETHYLENE OXIDE） BLOCK COPOLYMERS

In this paper, we proposed a method to determine the nucleation effect of pre-existing crystals on crystallization of the second block in double crystalline block copolymers, which is usually covered by the suppression effect. The nucleation mechanism of poly（ethylene oxide） （PEO） block from the pre-crystallized polyethylene （PE） block in poly（ethylene-cobutene）-b-poly（ethylene glycol） （EmEOn） diblock copolymers was investigated under variable crystallization environments. The crystallization environment for the PEO block was altered by cooling at different cooling rates or successive selfnucleation （SSN） to the PE block. It was found that the presence of nucleation effect is strongly dependent on composition of the block copolymers. The crystallization temperature （Tc） of PEO block in E174EO90 increases as cooling rate applied to the PE block decreases, indicating that PE block can nucleate the crystallization of PEO block and more perfect PE crystals have stronger nucleation effect. In E182EO41 crystallization of the PEO block is confined, shown by the disappearance of selfnucleation domain, and the PE block has no nucleation effect on the crystallization of PEO block. Double crystallization peaks are observed for the PEO block in E182EO41 and the intensity of the crystallization peak at higher temperature increases as the PE crystals become more perfect. After exclusion of homogeneous nucleation mechanism, the higher temperature crystallization peak of the PEO block in E182EO41 is tentatively ascribed to surface nucleation.     

Polymer decoration: The orientation of polymer folds as revealed by the crystallization of polymer vapors

A new technique of decoration of the fold surface of polymer crystals is described. It is similar in methodology to gold decoration, but makes use of vapors of crystallizable polymers, principally polyethylene, as decorating material. Upon condensation and crystallization, the highly anisometric decorating molecules become oriented parallel to the fold direction. They build up small crystalline lamellae which, seen edge-on, appear as elongated rods and can be easily observed by conventional transmission electron microscopy. This decoration technique reveals the sectorization of polymer single crystals grown from solution. It can be used to determine the local fold orientation (with a resolution of ca. 10 nm) of polymers crystallized under a wide range of conditions, including crystallization from the bulk. The technique reveals that under all crystallization conditions so far investigated the outermost part of the polymer fold surface is relatively ordered, and the folds and/or loops are, as a rule, oriented nearly parallel to the macroscopic growth front.     

含磷脂酰胆碱的聚乳酸的诱导矿化研究

分别以甘油磷脂酰胆碱和1,4-丁二醇为引发剂开环丙交酯,制备了含磷脂酰胆碱的聚乳酸(PLA-PC)和聚乳酸(PLA),比较了两者在诱导矿化中的差异.用傅立叶红外光谱仪(FTIR)、X-射线衍射仪(XRD)和扫描电子显微镜(SEM)对PLA-PC膜表面形成的矿化物进行了表征.结果表明,形成的矿化物为羟基磷灰石(HAP),PLA-PC膜有利于成核和生长,晶体呈片状,并随矿化时间延长,HAP晶粒逐渐增大,晶片厚度也逐渐变大.     

Different enantioselectivity of two types of poly(lactic acid) depolymerases toward poly(l-lactic acid) and poly(d-lactic acid)

Poly(lactic acid) (PLA) depolymerases are categorized into protease-type and lipase-type. Protease-types can hydrolyze poly(l-lactic acid) (PLLA) but not poly(d-lactic acid) (PDLA). Lipase-types, including cutinase-like enzyme (CLE) from Cryptococcus sp. strain S-2 preferentially hydrolyze PDLA. Both enzymes degraded not only PLA emulsion but also PLA film, in which amorphous region is preferentially attacked, but crystalline region can be also attacked. Stereocomplex PLA (sc-PLA) formed by 50:50 blending of PLLA and PDLA included no homo crystals, but a tiny homo crystallization peak appeared and crystallinity increased by 5% when attacked by CLE, although no significant change of molecular weight and crystalline size was found. Enantioselective degradation must occur in amorphous region of PLLA/PDLA film and preferentially hydrolyzed PDLA, resulting in a slightly excess amount of PLLA remained, which must be crystallized.     

Crystallographic and morphological characterization of thin pentacene films on polycrystalline copper surfaces

The degree of crystallinity, the structure and orientation of crystallites, and the morphology of thin pentacene films grown by vapor deposition in an ultrahigh vacuum environment on polycrystalline copper substrates have been investigated by x-ray diffraction and tapping-mode scanning force microscopy (TM-SFM). Depending on the substrate temperature during deposition, very different results are obtained: While at 77 K a long-range order is missing, the films become crystalline at elevated temperatures. From a high-resolution x-ray-diffraction profile analysis, the volume-weighted size of the crystallites perpendicular to the film surface could be determined. This size of the crystallites increases strongly upon changing temperature between room temperature and 333 K, at which point the size of individual crystallites typically exceeds 100 nm. In this temperature region, three different polymorphs are identified. The vast majority of crystallites have a fiber texture with the (001) net planes parallel to the substrate. In this geometry, the molecules are oriented standing up on the substrate (end-on arrangement). This alignment is remarkably different from that on single-crystalline metal surfaces, indicating that the growth is not epitaxial. Additionally, TM-SFM images show needlelike structures which suggest the presence of at least one additional orientation of crystallites (flat-on or edge-on). These results indicate that properties of thin crystalline pentacene films prepared on technologically relevant polycrystalline metal substrates for fast electronic applications may be compromised by the simultaneous presence of different local molecular aggregation states at all temperatures.     

Effects of polylactic acid and rPET minor components on phase evolution,tensile and thermal properties of polyethylene‐based composite fibers

High mechanical performance and partially biodegradable PE‐composite fibers modified with polylactic acid (PLA) and recycled polyethylene terephthalate (rPET) minor components were prepared using melt extrusion and hot drawing process. Rheological properties, morphology, tensile, and thermal properties were investigated. All blends exhibited shear thinning behavior except for starting PLA and rPET. PLA and rPET dispersed phases appeared as droplets in as‐extruded strand, and PLA droplets were mostly larger than those of rPET. The fibrillation of both PLA and rPET domains was achieved after further hot drawing as the fiber. The morphology and tensile properties of the fibers mainly depended on the types and contents of dispersed phases including draw ratios. The ultimate strength of the polymer fibers at draw ratio of 20 was more than 600 times higher than that of the as‐spun sample of the same composition. Remarkable improvement in secant modulus and ultimate strength was found for PE‐30PLA, but the drawing process of this composition encountered some difficulties and rough surface of the fiber was observed. The stiffness and tensile stress for PE‐10PLA‐10rPET fiber were clearly improved when compared with PE and PE‐10PLA. A decrease in thermal stability of PE/PLA composites was observed with increasing PLA content whereas additional presence of rPET significantly increased the stability of the composites both in nitrogen and in air. PE/PLA/rPET fiber possessing high stiffness with good thermal stability prepared in this work has high potential for being utilized as structural parts for load‐bearing applications.     

Morphological behaviour of poly(lactic acid) during hydrolytic degradation

The hydrolytic degradation and the morphological behaviour of a packaging grade of poly(lactic acid) (PLA) were characterized by a series of techniques. During the initial degradation process (stage 1) at a temperature near the glass transition temperature (T_g), the molecular weight of PLA decreased as degradation time increased following a bulk erosion mechanism while the crystallinity increased simultaneously, but no observable weight loss occurred at stage 1. Mainly α-form PLA crystal structure was formed for the crystalline PLA with a low content of d stereo-isomers, but the material displayed a lower regularity, smaller domain size, lower melting temperatures T_m and different motional dynamics as compared to the original PLA with a similar level of crystallinity achieved by annealing. The amorphous PLA with a higher amount of d stereo-isomers also yielded the α crystalline phase as well as stereo-complex crystals at stage 1. When the molecular weight and the crystallinity reached a stable level, PLA started erosion into the degrading aqueous medium. During this stage of degradation (stage 2), the crystalline structure in PLA residues was further modified and both pH and temperature influenced the modification. The degradation at stage 2 was likely to follow a surface erosion mechanism with lactic acid as the major product of the weight loss. Besides the crystallinity effect on the degradation, temperature also played a key role in determining the rate of PLA degradation in both stages. The process was very slow at temperatures below the T_g of PLA but the rate was greatly enhanced at temperatures above the T_g.     

H型(PS)2PEG(PS)2嵌段共聚物在旋涂过程中的结晶行为

采用原子力显微镜和X射线衍射等手段研究了H型(PS)₂PEG(PS)2嵌段共聚物在不同溶剂和不同浓度的溶液中旋涂所得薄膜的形貌, 并与聚乙二醇(PEG)均聚物进行了比较. 虽然(PS)₂PEG(PS)₂中PS的链长很短, 但对形貌有很大影响, PS链段的存在改变了聚合物在基底上的稳定性, 使用四氢呋喃为溶剂, 当溶液浓度较小时, 在旋涂过程中发生去润湿, 然后再发生结晶, 膜厚较大时去润湿被抑止, 所得形貌与PEG均聚物类似. 以甲苯为溶剂时, 由于PEG和PS与溶剂的相互作用不同, 共聚物在溶液中形成胶束, 从而改变了聚合物的结晶形貌.     

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.     

Molecular packing of high-mobility diketo pyrrolo-pyrrole polymer semiconductors with branched alkyl side chains

We describe a series of highly soluble diketo pyrrolo-pyrrole (DPP)-bithiophene copolymers exhibiting field effect hole mobilities up to 0.74 cm(2) V(-1) s(-1), with a common synthetic motif of bulky 2-octyldodecyl side groups on the conjugated backbone. Spectroscopy, diffraction, and microscopy measurements reveal a transition in molecular packing behavior from a preferentially edge-on orientation of the conjugated plane to a preferentially face-on orientation as the attachment density of the side chains increases. Thermal annealing generally reduces both the face-on population and the misoriented edge-on domains. The highest hole mobilities of this series were obtained from edge-on molecular packing and in-plane liquid-crystalline texture, but films with a bimodal orientation distribution and no discernible in-plane texture exhibited surprisingly comparable mobilities. The high hole mobility may therefore arise from the molecular packing feature common to the entire polymer series: backbones that are strictly oriented parallel to the substrate plane and coplanar with other backbones in the same layer.     

Epitaxial crystallization of polyoxymethylene on NaCl single crystal in dilute solution

The epitaxial crystallization of polyoxymethylene (POM) is observed from 0.01% cyclohexanol solution on the (001) cleavage face of NaCl. High-resolution electron microscopy reveals that the crystals are definitely triangular, rather than rectangular prisms, although the crystals have previously been interpreted as “edge-on” arrangements of lamellar crystals. An electron diffraction pattern obtained from films, which were piled up with a maximum of nine sheets per grid, shows that plane spacing of the epitaxial crystals is 3.87 Å and almost the same as the \[ \left\{ {10\bar 10} \right\} \] spacing (3.86 Å) of hexagonal single crystal of POM: the axes of POM fold chains in the crystals are parallel to the (001) plane. A possible mechanism for the epitaxial crystallization of POM is proposed.     

Thickness-dependent Orientation Structure in Poly（ethylene oxide） Multi-layer Crystals

Poly(ethylene oxide) multi-layer crystals were obtained and the re-crystallization behavior was studied to give insight into how melt thickness and temperature affect the lamellar orientation. For a special re-crystallization temperature, there exists a critical transition thickness range for the occurrence of edge-on lamellar orientation. Below the critical thickness, only flat-on lamellae were observed. While above the critical thickness, both flat-on and edge-on lamellae were found and the proportion of the edge-on lamellae increases with thickness. At low re-crystallization temperatures(below 30 °C), the critical transition thickness gradually increases from about 15 nm to 35 nm when the re-crystallization temperature was increased from 20 °C to 30 °C. However, when the re-crystallization temperature is above 30 °C, the critical transition thickness becomes constant. Our results demonstrated that the lamellar orientation could be specially modified by changing the melt thickness and re-crystallization temperature.