Light,Small Angle Neutron and X-Ray Scattering from Gels

This paper gives two examples of experiments that demonstrate the power of small angle scattering techniques in the study of swollen polymer networks. First, it is shown how the partly ergodic character of these systems is directly detected by neutron spin echo experiments. The observed total field correlation function of the intensity scattered from a neutral gel allows the ergodic contribution to be directly distinguished from the non ergodic part, at values of transfer wave vector q that lie well beyond the range of dynamic light scattering. The results can be compared with those obtained at much lower q from visible light scattering. Second, a recent application of small angle X-ray (SAXS) and neutron (SANS) scattering is described for a polyelectrolyte molecule, DNA, in semi-dilute solutions under near-physiological conditions. For these observations, the divalent ion normally present, calcium, is replaced by an equivalent ion, strontium. The comparison between SANS and SAXS yields a quantitative picture of the cloud of divalent counter-ions around the central DNA core. At physiological conditions, the cloud is thinner than that predicted on the basis of the Debye screening length but thicker than if the counter-ions were condensed on the DNA chain.     

Small‐Angle Neutron Scattering from Elastomeric Networks in which the Junctions Alternate Regularly in their Functionality

We compute scattering form factors for SANS from labeled paths in Gaussian phantom networks in which junctions alternate regularly in their functionality (the number of chains emanating from a junction). Our calculations are based on the James‐Guth model of rubber‐like elasticity, which assumes that fluctuations are strain independent, while mean vectors transform affinely with the applied strain. Kratky plots for scattering from isotropic and uniaxially stretched bifunctional networks are computed and compared with corresponding plots for the simpler unifunctional networks. The results show the effects of the length of the labeled path, extent of deformation, direction of scattering with respect to the principal axis of the deformation and the functionalities of the network junctions.

     

Counterion Association and Structural Conformation Change of Charged PAMAM Dendrimer in Aqueous Solutions Revealed by Small Angle Neutron Scattering

Our previous study of the structure change of poly(amidoamine) starburst dendrimers (PAMAM) dendrimer of generation 5 (G5) have demonstrated that although the overall molecular size is practically unaffected by increasing DCl concentration, a configurational transformation, from a diffusive density profile to a more uniform density distribution, is clearly observed. In the current paper, the focus is placed on understanding the effect of counterion identity on the inter-molecular structure and the conformational properties by studying the effect due to DBr using small angle neutron scattering (SANS) and integral equation theory. While the overall molecular size is found to be essentially unaffected by the change in the pD of solutions, it is surprising that the intra-molecular configurational transformation is not observed when DBr is used. The overall effective charge of a dendrimer is nearly the same for α < 1, independent of the type of acids. However, when α > 1, the effect of counterion identity becomes significant, the effective charge carried by a charged G5 PAPAM protonated by DBr becomes smaller than that of solutions with DCl. As a consequence, a counterion identity dependence of counterion association is revealed: Under the same level of molecular protonation, the specific counterion association, which is defined as the ratio of bound chloride anions to positively charged amines per molecule, is larger for the G5 PAMAM dendrimer charged by DBr than the one by DCl.     

SANS investigations of oxide gel formation in inverse micelle and lamellar surfactant systems

The mechanisms of oxide gel formation in inverse micelle and lamellar surfactant systems have been investigated by Small Angle Neutron Scattering (SANS). In the first of these processes colloidal particles and gels are formed by the controlled hydrolysis and condensation of metal alkoxides in a reversed microemulsion system (water in oil), where the water is confined in the microemulsion core. With this route the rate of formation and structure of the oxide gel can be controlled by appropriate choice of the surfactant molecule (e.g. chain length) and the volume fraction of the micelles dispersed in the continuous organic phase. Investigations have been made with the system cyclohexane/water/C₈E _x , where C₈E _x is the non-ionic surfactant octylphenyl polyoxyethylene. The influence of the size and structure of the microemulsion has been studied by contrast variation (using deuterated solvents) before and during the reaction to form zirconia gels, and the mechanism of gelation is analysed in terms of percolation of fractal cluster aggregates. The structure of gels formed in surfactant/water lamellar phase systems, using surfactants with greater chain length, has also been investigated by SANS. The application of contrast variation to study such anisotropic bilayer systems, in which oriented gel films can be formed, is illustrated.     

左旋18—甲基炔诺酮—硅橡胶缓释体系小角激光散射法研究

以小角激光前向散射和背散射法研究了左旋１８－甲基炔诺酮－甲基乙烯基硅橡胶缓释体系的光散射时效行为，用紫外分光光度法测定释放过程，讨论药物释放过程中高分子链段运动和聚合物结构对药物释放的影响．     

Crystallization and chain conformation of semicrystalline and amorphous polymer blends studied by wide‐angle and small‐angle scattering

We examine the crystallization and chain conformation behavior of semicrystalline poly(ethylene oxide) (PEO) and amorphous poly(vinyl acetate) (PVAc) mixtures with wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and small‐angle neutron scattering (SANS) experiments. For blends with PEO weight fractions (wt_PEO) greater than or equal to 0.3, below the melting point of PEO, the WAXD patterns reveal that crystalline PEO belongs to the monoclinic system. The unit‐cell parameters are independent of wt_PEO. However, the bulk crystallinity determined from WAXD decreases as wt_PEO decreases. The scattered intensities from SAXS experiments show that the systems form an ordered crystalline/amorphous lamellar structure. In a combination of WAXD and SAXS analysis, the related morphological parameters are assigned correctly. With the addition of amorphous PVAc, both the average amorphous layer thickness and long spacing increase, whereas the average crystalline layer thickness decreases. We find that a two‐phase analysis of the correlation function from SAXS, in which the scattering invariant is linearly proportional to the volume fraction of lamellar stacks, describes quantitatively the crystallization behavior of PEO in the presence of PVAc. When wt_PEO is close to 1, the samples are fully spaced‐filled with lamellar stacks. As wt_PEO decreases from 1.0 to 0.3, more PVAc chains are excluded from the interlamellar region into the interfibrillar region. The fraction outside the lamellar stacks, which is completely occupied with PVAc chains, increases from 0 to 58%. Because the radius of gyration of PVAc with a random‐coil configuration determined from SANS is smaller than the average amorphous layer thickness from SAXS, we believe that the amorphous PVAc chains still persist with a random‐coil configuration even when the blends form an ordered structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2705–2715, 2001     

Stable DOPG/Glycyrrhizin Vesicles with a Wide Range of Mixing Ratios: Structure and Stability as Seen by Scattering Experiments and Cryo-TEM

Phosphatidylglycerols represent a large share of the lipids in the plasmamembrane of procaryotes. Therefore, this study investigates the role of charged lipids in the plasma membrane with respect to the interaction of the antiviral saponin glycyrrhizin with such membranes. Glycyrrhizin is a natural triterpenic-based surfactant found in licorice. Vesicles made of 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1’-glycerol) (DOPG)/glycyrrhizin are characterized by small-angle scattering with neutrons and X-rays (SANS and SAXS). Small-angle scattering data are first evaluated by the model-independent modified Kratky–Porod method and afterwards fitted by a model describing the shape of small unilamellar vesicles (SUV) with an internal head-tail contrast. Complete miscibility of DOPG and glycyrrhizin was revealed even at a ratio of lipid:saponin of 1:1. Additional information about the chain-chain correlation distance of the lipid/saponin mixtures in the SUV structures is obtained from wide-angle X-ray scattering (WAXS).     

Characteristics of AOT Microemulsion Structure: a Small Angle X-ray Scattering Study

The structure of micelles has attracted renewed attention during the past decade years due to the widespread use of microemulsions in technology1 and life science1,2. To obtain information of the micellar structure, using X-ray scattering (SAXS) whose wavelength is close to the size of the micellar aggregates is one of the most direct method3-5 and SAXS has been proved to be very sensitive for the change of micellar composition6,7. SAXS experiments have been carried out to compare the st…     

Characterization of Nano-Scale Parallel Lamellar Defects in RDX and HMX Single Crystals by Two-Dimension Small Angle X-ray Scattering

Nano-scale crystal defects extremely affect the security and reliability of explosive charges of weapons. In this work, the nano-scale crystal defects of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) single crystals were characterized by two-dimension SAXS. Deducing from the changes of SAXS pattern with sample stage rotating, we firstly found the parallel lamellar nano-scale defects in both RDX and HMX single crystals. Further analysis shows that the average diameter and thickness of nano-scale lamellar defects for RDX single crystal are 66.4 nm and 19.3 nm, respectively. The results of X-ray diffraction (XRD) indicate that the lamellar nano-scale defects distribute along the (001) in RDX and the (011) in HMX, which are verified to be the crystal planes with the lowest binding energy by the theoretical calculation.     

Structure of Hydrogen and Hydrophobically Bonded Amphiphilic Copolymer with Poly(methacrylic acid) Complexes as Revealed by Small Angle Neutron Scattering

We study by SANS the structure of intermolecular complexes formed through hydrogen bonding and hydrophobic interactions between poly(methacrylic acid) (PMA) and a neutral copolymer surfactant (PEO-PPO-PEO). The contrast variation method enables us to probe the structure factor of each polymer in the complex and their cross structure factor. The number of copolymer chains, which results from the cooperative action of hydrogen bonding and hydrophobic interactions increases as the charge of the polyacid decreases. The aggregation preserves the micellar core-corona organization of the copolymer and shrinks the polyacid chains which adopt a similar compact structure. Finally, the structure of the aggregates is compared to that of PEO-PMA homopolymer complex observed by SANS.     

Correlations and Fluctuations of Charged Colloids as Determined by Anomalous Small‐Angle X‐Ray Scattering

Summary: We performed molecular dynamics simulation of a charged colloidal particle with explicit counterions. Our work provides a direct comparison between simulations and ASAXS‐experiments, offering insight into the counterion distribution of charged colloidal suspensions. We give a detailed constitution of the appearing scattering terms with their physical meaning. It is shown that the cross‐correlation between a macroion and its counterions gives the meanfield approximation of the counterion density even if the counterion system is highly fluctuating. Furthermore, it is shown that cross‐correlations can be negative due to oscillations of the density amplitudes of the macroion and counterions and, therefore, must be distinguished from other scattering contributions. These oscillations become more pronounced if the counterions exhibit a fixed shape and if the size of the macroion and that of the counterion system are different.

Simulation sanpshot of a charged colloid (big central sphere) with counterions (small spheres).     

小角X射线散射法研究CH2Cl2,CHCl3和CCl4对PE液晶结构的影响

采用小角X射线散射法研究了CH_2Cl_2、CHCl_3和CCl_4对磷脂酰乙醇胺(PE)液晶结构影响的机理.CH_3Cl_2、CHCl_3和CCl_4对PE液晶结构影响的差别主要是其空间旋转电子云密度分布形状不同所致.空间旋转电子云密度分布呈椭球状的物质有使PE液晶形成六角形H_1相的趋向;呈圆锥状的物质有诱发PE液晶形成立方六角相的趋向;呈球状的物质有使PE液晶形成片层立方相的趋向.     

Polycaprolactone-b-Poly(ethylene oxide) Biocompatible Micelles as Drug Delivery Nanocarriers: Dynamic Light Scattering and Fluorescence Experiments

Summary: Dynamic light scattering (DLS) and fluorescence experiments were carried out to study PCL₄₄-b-PEO₁₁₄ biocompatible micelles used as nanocarriers in drug delivery. Micelles prepared by a simple procedure (THF removal under nitrogen flow) exhibited a narrow size distribution with an average diameter of 100 nm. For micelles containing a hydrophobic model compound (pyrene) within the PCL core, a smaller average micellar size of 80 nm was observed, with a simultaneous broadening in the size distribution profile. In parallel to DLS results, fluorescence experiments showed evidence of pyrene encapsulation, and that the onset of the micellization process occurs at approximately 10/90 (v/v) THF/water mixtures in the case of PCL₄₄-b-PEO₁₁₄ polymer.     

Effect of solvent additives on bulk heterojunction morphology of organic photovoltaics and their impact on device performance

Morphology of the active layer in an organic photovoltaic (OPV) device is known to have a significant impact on the device performance. It is, however, difficult to characterize nanoscale morphologies in detail, especially at the ensemble level. Herein, we report the utilization of small angle neutron scattering (SANS) to investigate variations in the nanoscale morphologies of the active layer of poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction OPV depending on the composition of casting solvent. Both the power law and the poly hard sphere model were utilized to characterize the state of the donor and acceptor components, respectively, from the obtained SANS data. Furthermore, the relationship between the nanoscale morphology and device performance is outlined. It was found that the use of 2-chlorophenol, a poor solvent for P3HT and, at the same time, a very good solvent for PCBM, leads to nanomorphology featuring ordered, highly crystalline P3HT and small (15.2 nm) PCBM domains. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 128–134     

Structural Phase Behavior of High-Concentration,Alignable Biomimetic Bicelle Mixtures

The structures of bicelle mixtures composed of dimyristoyl and dihexanoyl phosphatidylcholines (DMPC and DHPC) with DMPC/DHPC molar ratios of 3.2 and 5 are characterized using polarized optical microscopy (POM) and small angle neutron scattering (SANS). Three phases, isotropic (I), chiral nematic (N^*) and smectic (S) are observed as temperature (T) varies from 10 to 70 °C. The structure of the magnetically alignable N^* phase, which was previously considered to be made up of discoidal micelles, is found to be composed of “ribbons”. Doping with the charged lipid, dimyristoyl phosphatidylglycerol (DMPG), which has the same 14:0 hydrocarbon chains as DMPC, results in a structural change of the aggregates where only the isotropic and smectic phases are observed. The smectic phase for the mixtures doped with DMPG is shear-alignable and follows one-dimensional swelling. However, at high-T zwitterionic DMPC/DHPC mixtures form multi-lamellar vesicles (MLV) with a relatively constant lamellar spacing of 66 Å, independent of water content.     

Synthesis and Characterization of Poly(ethylene glycol) Dimethacrylate Hydrogels

Facile synthesis and detailed characterization of photo-polymerizable and biocompatible poly(ethylene glycol) dimethacrylates (PEGDM) and their hydrogels are described. Combined analyses of ¹H NMR and MALDI-TOF MS confirmed the formation of prepolymers of high purity and narrow mass distribution (PD < 1.02). A systematic investigation into the structure and mechanical properties of PEGDM hydrogels was performed to characterize the relationships between the network structure and gel properties. Small-angle neutron scattering was used to characterize the structural features of hydrogels with respect to their semidilute solution precursors. A well-defined structural length scale (correlation length) manifested as a maximum in the scattering intensity was observed for hydrogels derived from high molecular mass PEGDMs and/or high oligomer mass fractions. Hydrogels derived from lower molecular mass PEGDMs and/or low oligomer mass fractions exhibited multiple correlation lengths suggesting the formation of inhomogeneous gel structures. The shear moduli, determined from uniaxial compression measurement, showed that the gel structures correlate well with the gel mechanical properties.     

聚二烯丙基二甲基氯化铵与核酸相互作用的共振光散射光谱及分析应用

实验基于核酸与聚阳离子聚二烯丙基二甲基氯化铵(PDDA)的相互作用导致共振光散射(RLS)增强的现象来测定核酸。考察了pH值、PDDA浓度和离子强度对体系共振光散射强度的影响。在优化条件下,建立了用RLS光谱测定微量核酸的新方法。方法的抗干扰能力较强,可允许大部分的常见金属离子、核苷酸、氨基酸、糖、蛋白质等干扰物质的存在。同时用于合成样品的分析,结果令人满意。     

Real‐time SAXS and WAXS study of the multiple melting behavior of poly(ε‐caprolactone)

The multiple melting behavior of poly(ε‐caprolactone) (PCL) was investigated by real‐time small angle X‐ray scattering (SAXS) and wide angle X‐ray scattering (WAXS) measurements coupling with differential scanning calorimetry (DSC). Semicrystalline specimens prepared by a continuous cooling process showed lengthening of the Bragg period during the progress of double melting. A model of variable thickness of lamella was proposed to fit to the SAXS patterns and revealed that both the crystalline lamella and the amorphous layer contributed to the increase in Bragg period while the later dominated the contribution. The model of variable thickness although satisfied the SAXS data was unable to compromise the data from other probing tools. A modification of the model proposed that each lamella piling up to construct the stacks in the crystallites was itself nonuniform in thickness. The modification with the parallel occurrence of the mechanism of surface melting and crystallization successfully compromised the observations from SAXS, DSC, and optical microscopy and provided a new perspective for the explanation to lengthening of the Bragg period related to multiple melting behavior. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1777–1785, 2010