Small-angle neutron scattering from typical synthetic and biopolymer solutions

Small-angle neutron scattering (SANS) has been used to investigate the solution properties of four model polymers, two poly-amino acids [poly(lysine) and poly(proline)], and two water-soluble synthetic polymers [poly(acrylic acid) and poly(ethylene oxide)]. In each case, one of the two polymers is charged, while the other is neutral. SANS measurements were made in the semi-dilute concentration regime in two different solvents [d-water and d-ethylene glycol]. The scattering signals were decomposed into low-Q clustering and high-Q solvation contributions. The temperature dependence of the scattering parameters was determined for poly(lysine) and poly(ethylene oxide) solutions over the temperature range of 13 to 82 °C. Analysis of the SANS spectra revealed that with increasing temperature, the solvation intensity increased in both solvents, while the clustering intensity increased in d-water and decreased in d-ethylene glycol. Significant differences were observed between the SANS spectra of charged and neutral polymer solutions. However, biopolymers and synthetic polymers exhibited qualitatively similar behavior.     

乙二醇中铜胶体共振光散射光谱

在乙二醇中,以聚乙烯吡咯烷酮（PVP）为分散剂,抗坏血酸（VC）为还原剂和抗氧化剂,还原CuSO4制得铜胶体溶液。 通过XRD、UV-Vis与共振光散射（RLS）光谱对铜胶体进行表征。 结果表明,铜胶体为面心立方晶体结构的0价铜,在592~602 nm呈现典型的等离子共振吸收峰,体系具有明显的RLS特征,最大散射波长在468 nm。 考察了反应条件、体系的稳定性与共存离子对乙二醇中铜胶体RLS的影响。 结果表明,适宜的反应条件为：试剂按照VC、CuSO4和PVP的加入顺序,3种物质量的比按照n(VC)/n(Cu2+)=15、n(PVP-K30)/n(Cu2+)=1.4;反应温度60 ℃;反应时间1 h,反应得到的铜胶体可稳定放置1 d。 在适宜条件下,ρ(Cu2+)在5.12~12.8 mg/L范围内与散射光强度（ΔIRLS）成正比,回归方程为ΔI=7 420.2ρ-631.8（r=0.9962）,检出限（3σ）为0.63 μg/L。 0.64 mg/L MnSO4、CdSO4和ZnSO4,1.28 mg/L KI,64 mg/L Na2CO3和Ca(OH)2,960 mg/L CH3CH2OH,640 mg/L CH3OH和320 mg/L CH3CH2CH2OH均不干扰10 mg/L Cu2+溶液的测量。 由此建立一种利用RLS光谱测定乙二醇中铜离子的简便方法。     

疏水链段对两亲性三嵌段共聚物在水中聚集行为的影响

以结构明确的两端为短的聚苯乙烯(PS)或聚甲基丙烯酸甲酯(PMMA)链段,中间为长的聚乙二醇(PEG)链段的PS-b-PEG-b-PS和PMMA-b-PEG-b-PMMA两亲性三嵌段共聚物为对象,研究了PS和PMMA链段对其在水中形成胶束和凝胶的影响.两种三嵌段共聚物在水中形成以PS或PMMA链段为核、PEG链段为壳的球形胶束,流体力学半径Rh,app为15.3~24.3 nm,并随PEG链段长度增长而增大.临界胶束浓度CMC均小于0.01 mg/mL,随着PS和PMMA链段长度的增加而减小.PS-b-PEG-b-PS浓度高于4.5 wt%可形成较强的疏水缔合的物理凝胶,平衡模量Ge可达到103Pa;PMMA-b-PEG-b-PMMA浓度高于7.5 wt%可以形成弱的凝胶,Ge<10 Pa.凝胶的储存模量G′和损耗模量G″均随着PS或PMMA链段的增长而增大.     

Surface-enhanced hyper-Raman scattering (SEHRS) on Ag film over Nanosphere (FON) electrodes: surface symmetry of centrosymmetric adsorbates

Electrochemical surface-enhanced hyper-Raman scattering (SEHRS) and surface-enhanced Raman scattering (SERS) of centrosymmetric molecules on Ag film over nanosphere (AgFON) electrodes are presented. The SEHR spectra of trans-1,2-bis(4-pyridyl)ethylene (BPE) at different potentials (vs Ag/AgCl) are presented for the first time, and a reversible potential tuning of the SEHR spectra of BPE is demonstrated. The SEHRS and SERS techniques were used to determine to what extent either site symmetry reduction or field gradient effects dictate the origin of the observed vibrational spectra. It is found that the SEHR and SER spectra for the molecules studied were distinctly different at all frequency regions at a fixed voltage, suggesting that centrosymmetry is largely retained upon adsorption to the AgFON surface and that field gradient effects are negligible. This work also shows that the SEHR spectra clearly depend on potential, whereas the SER spectra are essentially independent of potenial. It is determined that the combination of changes in deltaGads and the presence of coadsorbed counterions are responsible for altering the local symmetry of the adsorbate and only SEHRS has the sensitivity to detect these changes in the surface environment. Thus, SEHRS is a uniquely useful spectroscopic tool that is much more sensitive to the local adsorption environment than is SERS.     

Surface-enhanced Raman scattering from oleate-stabilized silver colloids at a liquid/liquid interface.

Oleate-stabilized silver colloids of 5-nm-diameter were adsorbed to a toluene/water interface, and surface enhanced Raman scattering (SERS) spectra from these colloids were measured under the total internal reflection (TIR) condition. From the observed spectra, we examined the states of oleate ions and toluene molecules on silver colloids at the liquid/liquid interfacial region. The TIR-SERS spectra of oleate ions showed stronger peaks of the carboxylate group and the ethylene group than those of alkyl chains. From these results, it was found that the oleate ions were adsorbed on the silver surface in two different ways at the liquid/liquid interface; the carboxylate group adsorbed in the organic phase side, while the ethylene group adsorbed in the aqueous phase side. The shifts of the toluene in the interfacial SERS spectra were identical to those of bulk toluene, though the relative intensities among the peaks were not same. This result suggested that the toluene was adsorbed with a weak interaction, but was significantly enhanced by the local electromagnetic field at the colloid surface.     

Quantitative analysis of functional groups in HDPE powder by DRIFT spectroscopy

FT-IR spectra of ethylene homopolymers and ethylene/1-hexene copolymers polymerized under different conditions were studied by transmission and diffuse reflection (DRIFT) spectroscopy. The absorbance spectra of film samples were compared with the DRIFT spectra of powders ground from the films. For determining the concentration of the methyl and unsaturated (vinyl, vinylidene and trans-vinylene) groups of polyethylene powders the DRIFT spectra were calibrated by comparing the IR intensities of the corresponding bands measured by the two methods. The results proved that the effect of differences in scattering of the polymer powder originating from the irregularity of the top surface, as well as the size and shape of the particles can be eliminated by the use of a proper internal standard. Linear correlation was established between the logarithms of the normalized intensities measured in absorbance and Kubelka-Munk units. In the case of polyethylene the selection of the internal reference band affects significantly the accuracy of the calibration due to the difference in the refractive indices of the crystalline and amorphous phases.     

Brillouin scattering from polymers and gels

We report results from Brillouin scattering on highly swollen and crosslinked polymeric gels, i.e. methyl methacrylate (MMA) gels crosslinked with ethylene dimethacrylate (EDMA). The study is performed varying the crosslink amount of the gels from 0 to 6%. The Brillouin spectra are measured at different scattering wavevectors in the angular ranges 90°–150°. Ve also measured the spectra at constant wavevector (90°) changing the scattering volume, in particular we select the size and the positions of the sample scattering volume. The wavevector dependence of the measured quantities confirms that in our system a micro—phase separation phenomenon takes place. In particular, for samples with crosslink contents higher than 3%, Brillouin data (studied in terms of the group velocity) give information about the existence of well defined solid- and liquid-like islands (heterogeneities in the gel structure) with an extent of several hundred Angstroms (as confirmed by elastic scattering data). Furthermore, selecting different spatial positions of the scattering volume (of micrometric sizes) and the overall sizes of the same, and performing the measurements at different times, we are able to observe (for the first time with Brillouin scattering) the non–ergodic behavior typical of this system. We report here preliminary results of such a study.     

Raman-Untersuchungen über die Kristallinität von Äthylen-Propylen-Kautschuk

Laser Raman spectroscopy was applied to the detection of cristallinity in ethylene-propylene rubber. The ethylene content of the products investigated varied from 35 to 80%. For copolymers containing more than 65% of ethylene a correlation has been found between the amount of cristallinity, determined by Raman spectroscopy and by X-ray diffraction, and mechanical properties like the green strength. On the other hand, cristallinity cannot be evaluated from infrared spectra of the polymers concerned.     

Surface-enhanced hyper-Raman spectroscopy with a picosecond laser: gold and copper colloids

We have obtained surface-enhanced hyper-Raman scattering (SEHRS) spectra of crystal violet, rhodamine 6G and Ru(trpy) (BPE)₃²⁺ adsorbed on gold and copper colloidal surfaces (where TRPY=2,2′,2″-terpyridine, BPE=trans-bis(4-pyridyl)ethylene). Our results demonstrate that the SEHRS effect is not intrinsically restricted to a Ag substrate and that surface enhancements at the emitted hyper-Raman photon frequencies are not required for observing SEHRS signals.     

Transition metal-coated nanoparticle films: vibrational characterization with surface-enhanced Raman scattering

The utilization of surface-attached gold nanoparticles as templates for generating Pt-group particles displaying near-optimal surface-enhanced Raman scattering (SERS) characteristics is described. Essentially epitaxial transition metal coatings down to the monolayer level can be prepared, most readily by the spontaneous replacement of an electrochemically deposited copper layer by the desired Pt-group metal. The and essentially pinhole-free nature of the coated nanoparticles is demonstrated from the form of the SER spectra for chemisorbed carbon monoxide and ethylene. The potential of the present strategy for synthesizing relatively monodispersed "core-shell" nanoparticles using a myriad of coating materials, also displaying SERS activity, is pointed out.     

Quasielastic electron scattering from methane, methane-d4, methane-d2, ethylene, and 2-methylpropane

Quasielastic electron scattering from gaseous species at high momentum transfer was recently reported for the first time [Cooper et al., J. Electron Spectrosc. Relat. Phenom. 155, 28 (2007)]. The first results for CH(4) and CD(4) were well explained by a classical electron Compton scattering picture in which the electron scatters independently from each atom rather than the molecule as a whole. However, an alternative possible interpretation in terms of nondipole molecular vibrational excitation is suggested by previously published quantum mechanical calculations on high momentum transfer electron scattering from diatomic molecules [Bonham and de Souza, J. Chem. Phys. 79, 134 (1983)]. In order to determine which of these two interpretations best fits the experimental results, we have measured the quasielastic spectra of gaseous 2-methylpropane, ethylene, methane, and two isotopically substituted methanes, CH(2)D(2) and CD(4), at a momentum transfer of approximately 20 a.u. (2.25 keV impact energy and 100 degrees scattering angle). The experimental spectra are found to be composed of as many peaks as there are different atomic isotopes in the molecule (two for CH(4), C(2)H(4), 2-methylpropane, and CD(4) and three for CH(2)D(2)). The peak positions are predicted accurately by the independent atom electron Compton scattering model, and the relative intensities are in reasonable agreement. The experimental results thus support classical electron Compton scattering as the origin of the signal.     

锌-硫氰酸盐-结晶紫体系共振散射法测定痕量锌

在pH 5.0 NaAc-HAc介质和吐温80溶液中,研究了zn(SCN)42-与结晶紫形成的离子缔合微粒的共振散射光谱,考察了其各种影响因素和适宜的反应条件,确定了共振散射强度与Zn2+浓度的关系,建立了测定痕量zn(Ⅱ)的共振散射新方法.研究表明,在0.020～0.80μg/mL范围内,体系的共振散射强度△I与Zn...     

Vibrations of dispersed silicas: A comparative

Four families of disperse amorphous silica representing different solid species modifications have been studied by inelastic neutron scattering at 10, 80 and 290 K. Doubly amplitude-weighted density of vibrational states (AWDS) have been obtained from the experimental time-of-flight spectra.     

Synthesis of Pt, Pd, Pt/Ag and Pd/Ag nanoparticles by microwave-polyol method

Pt, Pd, Pt-Ag and Pd-Ag bimetallic nanoparticles were synthesized in ethylene glycol and glycerol using the microwave technique in the presence of a stabilizer poly(N-vinylpyrrolidone) (PVP). It has been observed that PVP is capable of complexing and stabilizing nanoparticles. Mixed clusters were formed by simultaneous reduction of the metal ions. The clusters were characterized using UV-Vis spectra, XRD and dynamic light scattering. To understand the mechanism of formation of mixed nanoparticles, several experimental parameters such asin situ irradiation of mixed metal salts and mixing of individual sols were attempted.     

Effect of adding glycols to the micellar properties of Tween: small-angle neutron scattering and turbidity measurements

Small-angle neutron scattering (SANS) and turbidity measurements have been carried out on the nonionic surfactants Tween 20 and Tween 80, in the presence of diethyleneglycol (DEG), triethyleneglycol (TEG), ethylene glycol monoethyl ether (EGMEE), and ethyleneglycol mono butyl ether (EGMBE). SANS measurements show that the shapes of the Tween 20 and Tween 80 micelles are oblate ellipsoidal, which do not change predominantly in the presence of DEG and TEG. However, the presence of EGMBE and EGMEE reduces the aggregation number of Tween. This has been attributed to the solubilization of EGMBE and EGMEE in the Tween micelles, providing them with additional hydrophobicity.     

Synthesis of novel biscrown ethers with rigid cis/trans ethylene bridge

Two novel biscrown ethers with rigid cis/trans ethylene linker were synthesized via Wittig reaction in high yield （about 80%）. Their pure cisltrans-isomers were obtained by column chromatography separation. And their structure/configuration was confirmed by ^1H NMR,^ 13C NMR, ESI mass spectrum, elemental analysis and UV-vis speca＇a.     

Crystallinity of ethylene oxide oligomers

Nonaethylene glycol and pentadecaethylene glycol and their dimethyl ethers have been prepared and characterized, with respect to crystallinity by wide- and small-angle X-ray scattering, Raman scattering, i.r. spectroscopy and differential scanning calorimetry. Wide-angle X-ray scattering is similar to that from high molecular weight poly(ethylene oxide). The crystal habit is lamella. The lamellae are highly crystalline and the surface layers are ordered. Comparison with crystalline poly(ethylene oxide) prepared conventionally, and having a distribution of chain lengths, shows that such samples crystallize into lamellae with disordered surface layers.     

液相卤化银纳米微粒的界面荧光和共振散射光谱特性

液相卤化银纳米微粒的共振散射光谱和发射光谱表明,AgCl和AgBr纳米微粒均在330,400,470和680nm处产生4个共振散射峰,在340,400和470nm处产生三个荧光峰．Ad纳米微粒在340,400,437,470和680nm处产生5个共振散射峰;除在340,400和470nm处产生3个荧光峰外,在434nm处有一最强的荧光峰．卤化银纳米微粒体系的浓度对共振散射信号的影响与浓度对荧光强度的影响一致,Aga,AgBr和AgI体系的共振散射光信号强度分别约为荧光信号的110,130和80倍,即荧光与共振散射之间存在相关性．提出了液相AgX纳米微粒荧光产生机理,解释了荧光与共振散射之间存在相关性的原因．     

An endogenous multiple scattering method for the calculation of the elastic scattering cross sections of electron shape resonances in polyatomic molecu

A procedure is described for obtaining the scattering potential for elastic electron—molecule scattering within the one-electron overlapping sphere multiple scattering Xα method. The method has been used to calculate the total elastic electron scattering cross sections for the nitrogen, ethylene and 1,3,5-trifluorobenzene molecules, which compare well with experimental data.     

Effect of the ionic aggregation on the crystallisation behavior of poly(ethylene) part of ionomer

The influence of ionic interaction on the melt-crystallization behavior of the ethylene ionomer was studied using modulated DSC (MDSC^TM), wide angle X-ray scattering (XRD) and hot stage microscopy. The kinetics of the crystallization process of the ionomer was evaluated using isothermal differential scanning calorimetry (iso-DSC). Wide-angle X-ray scattering was used to examine the d spacing of poly(ethylene) part. The crystallinity of the poly(ethylene) part of ionomer measured from XRD is found to be 24%, which is comparable to that obtained from MDSC^TM. Small-angle X-ray scattering (SAXS) results show that the clusters and multiplets exist in the ionomer, and the cluster is about 127Ĺ. The kinetics of crystallization process obtained using Avrami equation shows that the crystallization process is fundamentally similar to poly(ethylene) as it goes through nucleation and propagation stages of the crystals. However, the morphology of the crystal appears to be different and influenced by clusters (platelike and/or needle-shaped) as evident from Avrami constant. This is different from the poly(ethylene) (which is spherulitic in nature) due to polar cluster and hydrophobic PE melt interaction. This revised version was published online in July 2006 with corrections to the Cover Date.