scholarly journals Effect of Elastomeric Nanoparticles on Polystyrene/Organic Nanocomposites

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Sungwon Ma ◽  
Yonathan Thio
Keyword(s):  
Percolation Threshold ◽  
Self Assembly ◽  
Structural Changes ◽  
Volume Concentration ◽  
Filler Loading ◽  
Cross Linking ◽  
Zero Shear Viscosity ◽  
Threshold Theory ◽  
Vulcanization Process ◽  
Nanosized Filler

The rheological behavior of nanosheet composites and the effect of morphology between elastomeric nanofiber and nanosheet composites were studied using a Cross-Williamson model and critical volume concentration was investigated by percolation threshold theory for fiber and sheet morphologies. Nanofiber and nanosheet particles were synthesized by a cold vulcanization process using a S2Cl2cross-linking reagent resulting from self-assembly of a PS-PI block copolymer. Nanofiber and nanosheet characterization was done by SEM. Rheological properties were measured and analyzed in terms of varying nanofiller and nanosheet loading from 0.5 to 10 wt%. For the nanofiber and nanosheet composites, the moduli were increased with increasing filler loading, whereas moduli of SI23 and SI43 composite decreased with increasing content. Both nanofiber and nanosheet composites showed a nanosized filler effect and their structural changes were between 5 and 10 wt%. Cross-Williamson three-parameter model was used to find zero-shear viscosity and relaxation time. Percolation threshold theory was used to study structural changes and calculate values.

Embedding Procedure for Water Swollen Samples

1970 ◽  
Vol 28 ◽  
pp. 504-505
Author(s):  
Ann M. Thomas ◽  
Virginia Shemeley
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Ion Exchange ◽  
Structural Changes ◽  
Cross Linking ◽  
Ion Exchange Resins ◽  
Transmission Electron ◽  
First Pass ◽  
Exchange Resins

Those samples which swell rapidly when exposed to water are, at best, difficult to section for transmission electron microscopy. Some materials literally burst out of the embedding block with the first pass by the knife, and even the most rapid cutting cycle produces sections of limited value. Many ion exchange resins swell in water; some undergo irreversible structural changes when dried. We developed our embedding procedure to handle this type of sample, but it should be applicable to many materials that present similar sectioning difficulties.The purpose of our embedding procedure is to build up a cross-linking network throughout the sample, while it is in a water swollen state. Our procedure was suggested to us by the work of Rosenberg, where he mentioned the formation of a tridimensional structure by the polymerization of the GMA biproduct, triglycol dimethacrylate.

Folding-Controlled Assembly of Ortho-Phenylene-Based Macrocycles

2020 ◽  
Author(s):  
Viraj kirinda ◽  
Scott Hartley
Keyword(s):  
Self Assembly ◽  
Structural Control ◽  
Structural Changes ◽  
Condensation Product ◽  
Gel Permeation Chromatography ◽  
Emergent Behavior ◽  
Order Structure ◽  
High Level ◽  
Alkoxy Groups ◽  
Energy Surfaces

The self-assembly of foldamers into macrocycles is a simple approach to non-biological higher-order structure. Previous work on the co-assembly of ortho-phenylene foldamers with rod-shaped linkers has shown that folding and self-assembly affect each other; that is, the combination leads to new emergent behavior, such as access to otherwise unfavorable folding states. To this point this relationship has been passive. Here, we demonstrate control of self-assembly by manipulating the foldamers’ conformational energy surfaces. A series of o-phenylene decamers and octamers have been assembled into macrocycles using imine condensation. Product distributions were analyzed by gel-permeation chromatography and molecular geometries extracted from a combination of NMR spectroscopy and computational chemistry. The assembly of o-phenylene decamers functionalized with alkoxy groups or hydrogens gives both [2+2] and [3+3] macrocycles. The mixture results from a subtle balance of entropic and enthalpic effects in these systems: the smaller [2+2] macrocycles are entropically favored but require the oligomer to misfold, whereas a perfectly folded decamer fits well within the larger [3+3] macrocycle that is entropically disfavored. Changing the substituents to fluoro groups, however, shifts assembly quantitatively to the [3+3] macrocycle products, even though the structural changes are well-removed from the functional groups directly participating in bond formation. The electron-withdrawing groups favor folding in these systems by strengthening arene–arene stacking interactions, increasing the enthalpic penalty to misfolding. The architectural changes are substantial even though the chemical perturbation is small: analogous o-phenylene octamers do not fit within macrocycles when perfectly folded, and quantitatively misfold to give small macrocycles regardless of substitution. Taken together, these results represent both a high level of structural control in structurally complex foldamer systems and the demonstration of large-amplitude structural changes as a consequence of a small structural effects.

Multilayer composite beads constructed via layer-by-layer self-assembly for lysozyme controlled release

RSC Advances ◽  
2014 ◽  
Vol 4 (46) ◽  
pp. 24369-24376 ◽  
Author(s):  
Jiemin Zhao ◽  
Xiaoping Wang ◽  
Yanshen Kuang ◽  
Yufeng Zhang ◽  
Xiaowen Shi ◽  
...  
Keyword(s):  
Controlled Release ◽  
Self Assembly ◽  
Cross Linking ◽  
Layer By Layer ◽  
Multilayer Composite ◽  
Composite Beads ◽  
Assembly Technique ◽  
Positively Charged

Alginate (ALG)–lysozyme (LZ) beads were fabricated by a cross-linking process. Negatively charged ALG and positively charged LZ were alternately deposited on the positively charged ALG–LZ beads via a layer-by-layer (LBL) self-assembly technique.

scholarly journals Preparation and Cross-Linking of All-Acrylamide Diblock Copolymer Nano-Objects via Polymerization-Induced Self-Assembly in Aqueous Solution

2017 ◽  
Vol 50 (4) ◽  
pp. 1482-1493 ◽  
Author(s):  
Sarah J. Byard ◽  
Mark Williams ◽  
Beulah E. McKenzie ◽  
Adam Blanazs ◽  
Steven P. Armes
Keyword(s):  
Aqueous Solution ◽  
Diblock Copolymer ◽  
Self Assembly ◽  
Cross Linking

Radical Mechanisms in Saturated and Olefinic Systems. II. Disubstitutive Carbon-Carbon Cross-Linking by Tertiary Alkoxy Radicals in Isoprenic Olefins and Rubber

1951 ◽  
Vol 24 (4) ◽  
pp. 777-786
Author(s):  
E. H. Farmer ◽  
C. G. Moore
Keyword(s):  
Natural Rubber ◽  
Cross Linking ◽  
Chain Molecules ◽  
Alkoxy Radicals ◽  
Full Extent ◽  
Carbon Chains ◽  
Butyl Peroxide ◽  
High Degree ◽  
Vulcanization Process

Abstract The high degree of dehydrogenation effected by tert.-butoxy radicals at the α-methylenic groups of olefins enables these radicals to be used for the carbon-to-carbon cross-linking of unsaturated carbon chains, and especially of the polyisoprenic chains of natural rubber. Such cross-linking amounts to a vulcanization process in which the connecting links between chain molecules are just C—C bonds, which may be expected to have appropriate attributes. An examination has first been made of the cross-linking produced by tert.- butoxy radicals (from di-tert.-butyl peroxide) at 140° between the short iso-prenic chains in 1-methylcyclohexene, 4-methylhept-3-ene, 2,6-dimethylocta-2, 6-diene, and digeranyl. Cross-linking proceeds efficiently in each case, and the points of union in these isoprene units which become directly joined are not confined to original α-methylenic carbon atoms. Where the reagent radicals are in considerable deficit, e.g., one per two or three of the isoprene units present, those olefin molecules which are attacked become linked together mostly by single unions to form aggregates containing two, three or four molecules; but in the tetraisoprenic olefins the extent to which more than one union is formed between some of the directly linked molecules becomes appreciable. In natural rubber, cross-linking occurs smoothly and to nearly the full extent corresponding to the (in practice restricted) proportion of peroxidic reagent employed. Good vulcanizates can be so obtained in which the tensile stength is found to increase towards a maximum and then to decline rapidly as the degree of cross-linking steadily increases. Thus to obtain vulcanizates of the optimum physical characteristics, the degree of cross-linking must be suitably chosen. The role of the peroxidic reagent is almost entirely non-additive and non-degradative.

scholarly journals Chemically Cross-Linked Graphene Oxide as a Selective Layer on Electrospun Polyvinyl Alcohol Nanofiber Membrane for Nanofiltration Application

Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2867
Author(s):  
Myoung Jun Park ◽  
Grace M. Nisola ◽  
Dong Han Seo ◽  
Chen Wang ◽  
Sherub Phuntsho ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Polyvinyl Alcohol ◽  
Self Assembly ◽  
Water Flux ◽  
Composite Membranes ◽  
Cross Linking ◽  
Support Surface ◽  
Eosin Y ◽  
Selective Layer ◽  
Assembly Technique

Graphene oxide (GO) nanosheets were utilized as a selective layer on a highly porous polyvinyl alcohol (PVA) nanofiber support via a pressure-assisted self-assembly technique to synthesize composite nanofiltration membranes. The GO layer was rendered stable by cross-linking the nanosheets (GO-to-GO) and by linking them onto the support surface (GO-to-PVA) using glutaraldehyde (GA). The amounts of GO and GA deposited on the PVA substrate were varied to determine the optimum nanofiltration membrane both in terms of water flux and salt rejection performances. The successful GA cross-linking of GO interlayers and GO-PVA via acetalization was confirmed by FTIR and XPS analyses, which corroborated with other characterization results from contact angle and zeta potential measurements. Morphologies of the most effective membrane (CGOPVA-50) featured a defect-free GA cross-linked GO layer with a thickness of ~67 nm. The best solute rejections of the CGOPVA-50 membrane were 91.01% for Na2SO4 (20 mM), 98.12% for Eosin Y (10 mg/L), 76.92% for Methylene blue (10 mg/L), and 49.62% for NaCl (20 mM). These findings may provide one of the promising approaches in synthesizing mechanically stable GO-based thin-film composite membranes that are effective for solute separation via nanofiltration.

A Disulfide Cross-linking Strategy Useful for Studying Ligand-induced Structural Changes in GPCRs

2010 ◽  
pp. 147-167
Author(s):  
Jian Hua Li ◽  
Stuart D. C. Ward ◽  
Sung-Jun Han ◽  
Fadi F. Hamdan ◽  
Jrgen Wess
Keyword(s):  
Structural Changes ◽  
Cross Linking

Structural Changes in Cotton: Effect of Premercerization Conditions on Subsequent Cross-Linking

1969 ◽  
Vol 39 (2) ◽  
pp. 148-154 ◽  
Author(s):  
Ricardo H. Wade ◽  
Tyrone L. Vigo
Keyword(s):  
Structural Changes ◽  
Cotton Effect ◽  
Cross Linking ◽  
Fragmentation Pattern ◽  
Cellulose I ◽  
Metal Hydroxides ◽  
Normal Length ◽  
Expansion Pattern ◽  
The Cross ◽  
Fiber Fragmentation

Structural changes due to tension applied to caustic-swollen yarns were studied. It was found that the cross-linking of yarns which had been mercerized slack, at normal length, or slack and then restretched to normal length produced differences in tenacity and X-ray orientation. It was concluded that this was due to structural rearrangements induced by the application of load to fiber systems. Differences in wet pickup of the cross-linking resin were shown to produce differences in the fiber fragmentation pattern but not in the layer-expansion pattern. Only a fraction of the added cross-linking resin was considered to have contributed to the properties usually attributed to cross-linked yarns. The regions believed responsible for the effect of cross-linking are the less ordered lattices close to the crystalline structures. The strength retained after cross-linking was dependent on the tension and the method of its application. Differences in the degree of conversion of cellulose I to cellulose II were noted in the slack-mercerized yarns treated with different alkali metal hydroxides. These differences, with the exception of lithium hydroxide, correlated with swelling effectiveness of the alkalis used.

Self-assembly of g-C3N4-based 3D aerogel induced by N-modified carbon dots for enhanced photocatalytic hydrogen production

2021 ◽  
Author(s):  
Pu Xiao-Long ◽  
yang xuechun ◽  
Shan-Shan Liang ◽  
Wenzhong Wang ◽  
Jing-Tai Zhao ◽  
...  
Keyword(s):  
Hydrogen Production ◽  
Self Assembly ◽  
Carbon Dots ◽  
Carbon Nitride ◽  
Graphitic Carbon ◽  
Graphitic Carbon Nitride ◽  
Cross Linking ◽  
Photocatalytic Hydrogen Production

The N-modified carbon dots/graphitic carbon nitride (NCDs/g-C3N4) aerogel was successfully prepared by simple electrostatic self-assembly of NCDs and g-C3N4 nanosheets without any harmful solvents or cross-linking agents. The prepared aerogel...

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