Search results for "force"

The Influence of Intramolecular Coordination and Ring Strain on the Polymerization Potential of Cyclic Stannasiloxanes

2008

Single-chain conformations in symmetric binary polymer blends: Quantitative comparison between self-consistent field calculations and Monte Carlo sim…

1998

Single-chain properties in a symmetric binary polymer blend are studied by self-consistent field calculations and Monte Carlo simulations. Within the self-consistent field scheme, the statistical mechanics of a cluster of neighboring polymers is solved. Interactions among the polymers of a cluster and composition fluctuations within a cluster are incorporated exactly, a mean field approximation is invoked for intercluster interactions and long-range fluctuations. The results are compared to large scale Monte Carlo simulations for a broad range of chain lengths. While we find nearly quantitative agreement for single chain propertiese.g., the reduction of the chain dimensions of the minority …

1997

We have determined by forced Rayleigh scattering the diffusion coefficients of photo-labeled polystyrene micronetwork spheres (radii ≤ 10 nm) in melts of linear polyvinylmethylether (M W ≤ 40000 g/mol) at temperatures of 20-80°C. An expected slippage of the spheres through the meshes of the entanglement network appears possible but is still within the experimental uncertainty of our results.

Probing Poly(n-butyl-methacrylate) Latex Film via Diffusion of Hydrophilic and Hydrophobic Dye Molecules

2003

In the study of holographic grating relaxation (forced Rayleigh scattering, FRS) in nascent latex films we examined poly(n-butyl methacrylate) films using two complementary diffusing probes:  a hyd...

Rotaxanes and Catenanes Derived from Tetra-Urea Calix[4]arenes

2010

Calix[ 4] arenes, substituted by four urea groups at their wide rim, form dimeric capsules in apolar solvents, which are held together by a seam of intermolecular hydrogen bonds. The heterodimerisation of tetra-aryl and tetratosyl ureas was used to synthesize various derivatives, in which adjacent urea residues are connected to form two, three or four loops. The aliphatic connections were tied by olefin metathesis between adjacent alkenyl residues followed by hydrogenation. Heterodimers of tetra-alkenyl substituted tetra-ureas and bis- or tetraloop derivatives were converted analogously to multiple catenanes. Tetra[2]rotaxanes were obtained in a similar manner. In addition to the spectrosco…

Surface-relief gratings in halogen-bonded polymer-azobenzene complexes A concentration-dependence study

2017

In recent years, supramolecular complexes comprising a poly(4-vinylpyridine) backbone and azobenzene-based halogen bond donors have emerged as a promising class of materials for the inscription of light-induced surface-relief gratings (SRGs). The studies up to date have focused on building supramolecular hierarchies, i.e., optimizing the polymer–azobenzene noncovalent interaction for efficient surface patterning. They have been conducted using systems with relatively low azobenzene content, and little is known about the concentration dependence of SRG formation in halogen-bonded polymer–azobenzene complexes. Herein, we bridge this gap, and study the concentration dependence of SRG formation…

Temperature-controlled poly(propylene) glycol hydrophobicity on the formation of inclusion complexes with modified cyclodextrins. A DSC and ITC study.

2011

The study highlighted the main forces driving the formation of hydroxypropyl-cyclodextrins (HP-CDs) + poly(propylene) glycol 725 g mol(-1) inclusion complexes. The temperature parameter was chosen as the variable to modulate the hydrophobicity of the polymer, and consequently ITC experiments as functions of temperature as well as DSC measurements were done in a systematic way. The polymer is not included into HP-α-CD, it is strongly bound to HP-β-CD and it is floating in HP-γ-CD. The stability of the inclusion complexes is entropy controlled. The gain of the entropy is a unique result compared to the opposite literature findings for inclusion complexes based on polymers and CDs. This peculi…

Learning from nature: beta-sheet-mimicking copolymers get organized.

2007

The solution structures formed by coil-coil copolymers arise from the selective solvation of one of the two blocks and have been well described. In most cases in such relatively simple synthetic structures there are no specific attractive forces that can aid the aggregation process. Nature, however, provides plenty of inspiring polymeric architectures that are shaped and ordered hierarchically by noncovalent forces. The high level of structural definition displayed by proteins, for example, is unmatched by synthetic polymers. An emerging area of interest in polymer science tries to combine the best of both worlds, the natural and the synthetic, by conjugating synthetic polymers and beta-she…

Langmuir−Blodgett Films of Fluorinated Glycolipids and Polymerizable Lipids and Their Phase Separating Behavior

2010

This paper describes the phase separating behavior of Langmuir monolayers from mixtures of different lipids that (i) either carry already a glycopeptide recognition site or can be easily modified to carry one and (ii) polymerizable lipids. To ensure demixing during compression, we used fluorinated lipids for the biological headgroups and hydrocarbon based lipids as polymerizable lipids. As a representative for a lipid monomer, which can be polymerized in the hydrophilic headgroup, a methacrylic monomer was used. As a monomer, which can be polymerized in the hydrophobic tail, a lipid with a diacetylene unit was used (pentacosadiynoic acid, PDA). The fluorinated lipids were on the one hand a …

A study of spalling behaviour of PAN fibre-reinforced concrete by thermal analysis

1993

Comparisons are made between polypropylene (PP) fibres and polyacrylonitrile (PAN) fibres in order to relate the thermal properties of fibres with the respective fibre mortar behaviour under thermal exposure. Thermogravimetry (TG), differential scanning calorimetry (DSC) and thermochromatography (ThGC) are utilized. When a cementitious fibre mortar is being heated, several physical phenomena occur in the temperature range between 100°C and 200°C. There is a significant difference in the thermal behaviour between PP and PAN fibres. PP fibres melt at 160–170°C. The non‐melting behaviour of PAN fibre together with its rapid exothermic degradation reactions at around 300°C may add risk to the s…