Influence of programming strain rates on the shape‐memory performance of semicrystalline multiblock copolymers

Multiblock copolymers named PCL‐PIBMD consisting of crystallizable poly(ε‐caprolactone) segments and crystallizable poly[oligo(3S‐iso‐butylmorpholine‐2,5‐dione)] segments coupled by trimethyl hexamethylene diisocyanate provide a versatile molecular architecture for achieving shape‐memory effects (SMEs) in polymers. The mechanical properties as well as the SME performance of PCL‐PIBMD can be tailored by the variation of physical parameters during programming such as deformation strain or applied temperature protocols. In this study, we explored the influence of applying different strain rates during programming on the resulting nanostructure of PCL‐PIBMD. Programming was conducted at 50 °C by elongation to ε_m = 50% with strain rates of 1 or 10 or 50 mm min^?1. The nanostructural changes were visualized by atomic force microscopy (AFM) measurements and investigated by in situ wide and small angle X‐ray scattering experiments. With increasing the strain rate, a higher degree of orientation was observed in the amorphous domains. Simultaneously the strain‐induced formation of new PIBMD crystals as well as the fragmentation of existing large PIBMD crystals occurred. The observed differences in shape fixity ratio and recovery stress of samples deformed with various strain rates can be attributed to their different nanostructures. The achieved findings can be relevant parameters for programming the shape‐memory polymers with designed recovery forces. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1935–1943     

Molecular mechanism leading to memory effect of mesomorphic isotactic polypropylene

In this study, memory effect of mesomorphic isotactic polypropylene (iPP) was investigated using polarized optical microscope and small‐angle X‐ray scattering. Differing from classical memory effect, mesomorphic iPP melt had a higher growth rate and a higher memory temperature. The relative growth rate increased with increasing crystallization temperature. Lauritzen–Hoffman plots indicated that the increased growth rate arose from reduced surface nucleation barrier. The highest memory temperature was estimated to be 185 °C, which was close to the equilibrium melting point of iPP crystal. Additionally, Small‐angle X‐ray scattering measurements showed that a liquid crystal layer might exist between lamellar and amorphous layers. Based on above results, a crystallization model was proposed. In the mesomorphic iPP melt, there exist aggregates structurally similar to β phase except α‐phase crystal residuals, which cannot act as nucleation sites or transform to β crystal through surface nucleation. The only way for the aggregate is to transform to α crystal during crystal growth. The aggregate decreases the surface nucleation barrier and promotes the helical growth, leading to higher growth rate. Only when the aggregate relaxes to polymer coils through thickening at a higher temperature, can the memory effect be erased. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1573–1580     

Lyotropic Liquid Crystals Formed by Brij 97/PEO‐PPO‐PEO Mixtures

The phase diagrams of Brij 97/(PEO)_m(PPO)_n(PEO)_m/water/IPM quaternary systems (A L‐64: m=13, n=30; A L‐62: m=7, n=32; A L‐61: m=3.5, n=31) were determined at 25°C. The liquid crystalline phases (lamellar L_αand hexagonal H₁) were investigated by means of small angle x‐ray scattering (SAXS) and rheological techniques, with comparison of composition and component effects. The lamellar phases formed in Brij 97/A L‐64 and Brij 97/A L‐62 systems array more orderly than that of Brij 97/A L‐61 system, indicated by the stronger intensity of the second reflection peak in the SAXS patterns and the higher moduli (G′ and G″) in the dynamic rheograms. In Brij 97/A L‐64/water/IPM system, all L_α phases exhibit elastic rheograms, moreover the viscous property get increased with increase in water content. On the other hand, with this change, the H₁ phases show Maxwell and gel‐like rheograms in order, in which the latter shows mechanical and relaxation spectra typical of highly structured materials.     

Grazing-incidence transmission small angle X-ray scattering from thin films of block copolymers

Thin films of lamellar and cylindrical block copolymers are popular systems for low-cost nanolithography. To be useful as nanoscale templates, the lamellae or cylinders must be oriented perpendicular to the substrate. Domain orientations are usually characterized by microscopy measurements of the film surface, but these techniques cannot detect tilted, bent, or tortuous domains in the film interior. We report a simple method to quantify out-of-plane disorder in thin films of block copolymers based on a variant of grazing-incidence small angle X-ray scattering (GI-SAXS). A typical GI-SAXS experiment illuminates the center of a substrate-supported film at a grazing angle of incidence (near the film/substrate critical angle), and the strong reflected signal is interpreted with the distorted-wave Born approximation. In a new approach, the beam footprint is moved to the far edge of the sample, allowing the acquisition of a transmission pattern. The grazing-incidence transmission data are interpreted with the simple Born approximation, and out-of-plane defects are quantified through analysis of crystal truncation rods and partial Debye-Scherrer rings. Significantly, this study demonstrates that grazing-incidence transmission small angle X-ray scattering can detect and quantify the buried defect structure in thin films of block copolymers. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Analysis of spherical polyelectrolyte brushes by small angle X-ray scattering

Spherical polyelectrolyte brushes （SPBs） with PS core and poly（acrylic acid） （PAA） brushes were prepared and analyzed by SAXS in this article. A radial electron density profile of SPB was brought up, which fits well with the SAXS result and shows a core-shell structure. The effect of pH on SPB form was represented by SAXS and it proves that the chains of SPB will stretch in response to increased pH owning to the increased electrostatic repulsion. SPBs immobilized with magnetic nanoparticles or bovine serum albumin （BSA） were prepared and analyzed by SAXS as well. SAXS could characterize the changes of electron density inside brushes of SPBs due to the immobilization of magnetic nanoparticles or BSA. This provides significant supports for further application of immobilized metal nanoparticles or proteins.     

Long-Term Colloidally Stable Aqueous Dispersions of ≤5 nm Spinel Ferrite Nanoparticles

Applications in biomedicine and ferrofluids, for instance, require long-term colloidally stable, concentrated aqueous dispersions of magnetic, biocompatible nanoparticles. Iron oxide and related spinel ferrite nanoparticles stabilized with organic molecules allow fine-tuning of magnetic properties via cation substitution and water-dispersibility. Here, we synthesize≤5 nm iron oxide and spinel ferrite nanoparticles, capped with citrate, betaine and phosphocholine, in a one-pot strategy. We present a robust approach combining elemental (CHN) and thermal gravimetric analysis (TGA) to quantify the ratio of residual solvent molecules and organic stabilizers on the particle surface, being of particular accuracy for ligands with heteroatoms compared to the solvent. SAXS experiments demonstrate the long-term colloidal stability of our aqueous iron oxide and spinel ferrite nanoparticle dispersions for at least 3 months. By the use of SAXS we approved directly the colloidal stability of the nanoparticle dispersions for high concentrations up to 100 g L⁻¹.     

Fully exfoliated layered silicate epoxy nanocomposites

Fully exfoliated layered silicate epoxy nanocomposites are reported in this article. The processing route that resulted in these fully exfoliated layered silicate epoxies is based on a combination of high‐shear mixing in the presence of acetone and ultrasonication. Homomogeneous and random dispersion of the individual silicate nanolayers in the epoxy is confirmed through transmission electron microscopy images spanning low to high magnification as well as by X‐ray diffraction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3981–3986, 2004     

小角x射线散射法研究甲基改性氧化硅凝胶的双分形结构

以正硅酸乙酯［Si(OC2H5)4,TEOS］和甲基三乙氧基硅烷［CH3Si(OC2H5)3,MTES］为前驱体，通过共水解法和两步法制备出两种不同的甲基改性氧化硅凝胶，在北京同步辐射光源(BSRF)小角x射线散射(SAXS)站测量了凝胶的散射强度，计算了凝胶的平均粒径、两相间比表面积等参数，在此基础上分析了凝胶的分形特征，发现存在两个尺度上的分形结构，分别对应于从SiO2原生颗粒到一次团聚体和从一次团聚体到簇团两种尺度.辅以透射电子显微镜(TEM)观测，证实由两种方法获得的凝胶具有非常不同的微观结构.实验证明，利用SAXS技术研究甲基改性凝胶的分形特征是获得凝胶微观结构的有力工具. 关键词： 甲基改性凝胶 氧化硅 小角x射线散射(SAXS) 分形结构     

Effect of selected structural parameters of styrene–butadiene block copolymers on their compatibilization efficiency in polystyrene/polybutadiene blends

The effects of the block length and block number of linear styrene–butadiene (S–B) block copolymers on their compatibilization efficiency in blending polystyrene with polybutadiene were studied. For this purpose, two sets of model S–B copolymers and both homopolymers were prepared by anionic polymerization. Diblocks, triblocks, or pentablocks of S–B copolymers were blended with these homopolymers, and the structures and some end‐use properties of the blends were determined. The supramolecular structure (determined by small‐angle X‐ray scattering), morphology (determined by transmission and scanning electron microscopy), and stress‐transfer characteristics (impact and tensile strengths) of the blends were chosen as criteria for the compatibilization efficiency of the copolymers used. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2612–2623, 2002