Crossover from Two- to Three-Dimensional Contraction of Polymer Chains in Semidilute Solutions Confined to a Narrow Slit

2000 ◽  
Vol 33 (18) ◽  
pp. 6901-6903 ◽  
Author(s):  
Iwao Teraoka ◽  
Yongmei Wang
Keyword(s):  
Three Dimensional ◽  
Polymer Chains ◽  
Narrow Slit ◽  
Semidilute Solutions

Novel three-dimensional long-term bone marrow culture system using polymer particles with grafted epoxy-polymer-chains supports the proliferation and differentiation of hematopoietic stem cells

2011 ◽  
Vol 236 (11) ◽  
pp. 1342-1350 ◽  
Author(s):  
Yukio Hirabayashi ◽  
Yoshihiro Hatta ◽  
Jin Takeuchi ◽  
Isao Tsuboi ◽  
Tomonori Harada ◽  
...  
Keyword(s):  
Stromal Cells ◽  
Culture System ◽  
3D Structure ◽  
Three Dimensional ◽  
Hematopoietic Cells ◽  
3D Culture ◽  
Polymer Chains ◽  
Polymer Particles ◽  
Hematopoietic Stem ◽  
3D Culture System

Hematopoiesis occurs in the bone marrow, where primitive hematopoietic cells proliferate and differentiate in close association with a three-dimensional (3D) hematopoietic microenvironment composed of stromal cells. We examined the hematopoietic supportive ability of stromal cells in a 3D culture system using polymer particles with grafted epoxy polymer chains. Umbilical cord blood-derived CD34+ cells were co-cultivated with MS-5 stromal cells. They formed a 3D structure in the culture dish in the presence of particles, and the total numbers of cells and the numbers of hematopoietic progenitor cells, including colony-forming unit (CFU)-Mix, CFU-granulocyte-macrophage, CFU-megakaryocyte and burst-forming unit-erythroid, were measured every seven days. The hematopoietic supportive activity of the 3D culture containing polymer particles and stromal cells was superior to that of 2D culture, and allowed the expansion and maintenance of hematopoietic progenitor cells for more than 12 weeks. Various types of hematopoietic cells, including granulocytes, macrophages and megakaryocytes at different maturation stages, appeared in the 3D culture, suggesting that the CD34+ cells were able to differentiate into a range of blood cell types. Morphological examination showed that MS-5 stromal cells grew on the surface of the particles and bridged the gaps between them to form a 3D structure. Hematopoietic cells slipped into the 3D layer and proliferated within it, relying on the presence of the MS-5 cells. These results suggest that this 3D culture system using polymer particles reproduced the hematopoietic phenomenon in vitro, and might thus provide a new tool for investigating hematopoietic stem cell–stromal cell interactions.

Chemical Stress Relaxation of NR Networks Prepared in the Swollen State

1986 ◽  
Vol 59 (4) ◽  
pp. 541-550 ◽  
Author(s):  
Kyung-Do Suh ◽  
Hidetoshi Oikawa ◽  
Kenkichi Murakami
Keyword(s):  
Stress Relaxation ◽  
Network Structure ◽  
Three Dimensional ◽  
Polymer Chains ◽  
Chemical Stress ◽  
Network Chain ◽  
Crosslinking Process ◽  
Dimensional Network ◽  
Chemical Relaxation ◽  
The Difference

Abstract From the experimental results of the present investigation, it is apparent that two kinds of networks which have a different three-dimensional network structure give quite different behavior of chemical stress relaxation, even if both networks have the same network chain density. The difference in three-dimensional network structure for the two kinds of rubber arises from the degree of entanglement, which changes with the concentration of the polymer chains prior to the crosslinking process. The direct cause of chemical relaxation is due to the scission of network chains by degradation, whereas the total relaxation is caused by the change of geometrical conformation of network chains. This then casts doubt on the basic concept of chemorheology which is represented by Equation 2.

Syntheses and crystal structures of two magnesium–tetrazole compounds in salt and polymeric forms

2015 ◽  
Vol 71 (3) ◽  
pp. 222-228 ◽  
Author(s):  
Mohamed Abdellatif Bensegueni ◽  
Aouatef Cherouana ◽  
Slimane Dahaoui
Keyword(s):  
Alkaline Earth ◽  
Three Dimensional ◽  
Polymer Chains ◽  
Magnesium Ion ◽  
Water Molecules ◽  
Compound I ◽  
Hydrothermal Conditions ◽  
One Dimensional ◽  
Polymeric Chains ◽  
Hydrogen Bonded

Two alkaline earth–tetrazole compounds, namelycatena-poly[[[triaquamagnesium(II)]-μ-5,5′-(azanediyl)ditetrazolato-κ3N1,N1′:N5] hemi{bis[μ-5,5′-(azanediyl)ditetrazolato-κ3N1,N1′:N2]bis[triaquamagnesium(II)]} monohydrate], {[Mg(C2HN9)(H2O)3][Mg2(C2HN9)2(H2O)6]0.5·H2O}n, (I), and bis[5-(pyrazin-2-yl)tetrazolate] hexaaquamagnesium(II), (C5H3N6)[Mg(H2O)6], (II), have been prepared under hydrothermal conditions. Compound (I) is a mixed dimer–polymer based on magnesium ion centres and can be regarded as the first example of a magnesium–tetrazolate polymer in the crystalline form. The structure shows a complex three-dimensional hydrogen-bonded network that involves magnesium–tetrazolate dimers, solvent water molecules and one-dimensional magnesium–tetrazolate polymeric chains. The intrinsic cohesion in the polymer chains is ensured by N—H...N hydrogen bonds, which formR22(7) rings, thus reinforcing the propagation of the polymer chain along theaaxis. The crystal structure of magnesium tetrazole salt (II) reveals a mixed ribbon of hydrogen-bonded rings, of typesR22(7),R22(9) andR24(10), running along thecaxis, which are linked byR24(16) rings, generating a 4,8-cflunet.

scholarly journals Mechanical properties of magnetic gels containing rod-like composite particles

2019 ◽  
Vol 377 (2143) ◽  
pp. 20180218 ◽  
Author(s):  
Mariem M. Abrougui ◽  
Modesto T. Lopez-Lopez ◽  
Juan D. G. Duran
Keyword(s):  
Mechanical Properties ◽  
Magnetic Particles ◽  
Three Dimensional ◽  
Heterogeneous Systems ◽  
Soft Materials ◽  
Polymer Chains ◽  
Composite Particles ◽  
Magnetite Particles ◽  
Magneto Rheological ◽  
Mr Effect

Magnetic gels (ferrogels) are heterogeneous systems structured at the nanoscale that contains magnetic particles dispersed in three-dimensional networks of polymer chains. In the present work, the magnetic particles were synthesized with a core–shell structure, consisting of sepiolite particles covered by magnetite nanoparticles. These composite particles had a rod-like shape with a high aspect ratio. The obtained sepiolite–magnetite particles showed a high enough susceptibility and saturation magnetization. The magneto-rheological (MR) properties, and the intensity of the MR effect, of aqueous suspensions of the synthesized particles were studied. The particles, functionalized by adsorption of alginate molecules, were imbedded in alginate hydrogels to get homogeneous soft materials. The particles were linked to the polymer chains as the knots in a network and dominated in a great extent the mechanical properties of the materials. After determining the optimal compositions of the ferrogels, their viscoelastic properties were measured in the absence/presence of magnetic fields. The results pointed out that the MR effect provided by the clay–magnetite particles was considerably more intense than those achieved in ferrogels that contain spherical magnetic microparticles. Therefore, the imbedding of rod-shaped magnetic particles in hydrogels allows controlling the mechanical properties in a wider range than in conventional ferrogels. This article is part of the theme issue ‘Heterogeneous materials: metastable and non-ergodic internal structures’.

One-dimensional CuIIcoordination polymers containingC2h-symmetric 1,1′:4′,1′′-terphenyl-3,3′-dicarboxylate linkers

2015 ◽  
Vol 71 (10) ◽  
pp. 929-935 ◽  
Author(s):  
Hyun-Chul Kim ◽  
Ja-Min Gu ◽  
Seong Huh ◽  
Chul-Hyun Yo ◽  
Youngmee Kim
Keyword(s):  
Coordination Polymers ◽  
Three Dimensional ◽  
Polymer Chains ◽  
Water Molecules ◽  
Binding Modes ◽  
Bridging Ligands ◽  
One Dimensional ◽  
X Ray Crystallography ◽  
Dimensional Network ◽  
The One

Two new one-dimensional CuIIcoordination polymers (CPs) containing theC2h-symmetric terphenyl-based dicarboxylate linker 1,1′:4′,1′′-terphenyl-3,3′-dicarboxylate (3,3′-TPDC), namelycatena-poly[[bis(dimethylamine-κN)copper(II)]-μ-1,1′:4′,1′′-terphenyl-3,3′-dicarboxylato-κ4O,O′:O′′:O′′′] monohydrate], {[Cu(C20H12O4)(C2H7N)2]·H2O}n, (I), andcatena-poly[[aquabis(dimethylamine-κN)copper(II)]-μ-1,1′:4′,1′′-terphenyl-3,3′-dicarboxylato-κ2O3:O3′] monohydrate], {[Cu(C20H12O4)(C2H7N)2(H2O)]·H2O}n, (II), were both obtained from two different methods of preparation: one reaction was performed in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) as a potential pillar ligand and the other was carried out in the absence of the DABCO pillar. Both reactions afforded crystals of different colours,i.e.violet plates for (I) and blue needles for (II), both of which were analysed by X-ray crystallography. The 3,3′-TPDC bridging ligands coordinate the CuIIions in asymmetric chelating modes in (I) and in monodenate binding modes in (II), forming one-dimensional chains in each case. Both coordination polymers contain two coordinated dimethylamine ligands in mutuallytranspositions, and there is an additional aqua ligand in (II). The solvent water molecules are involved in hydrogen bonds between the one-dimensional coordination polymer chains, forming a two-dimensional network in (I) and a three-dimensional network in (II).

Rheology of Adhesion

1972 ◽  
Vol 45 (6) ◽  
pp. 1604-1622 ◽  
Author(s):  
D. H. Kaelble
Keyword(s):  
Polymer Composites ◽  
Three Dimensional ◽  
Polymeric Materials ◽  
Intermolecular Forces ◽  
Adhesive Joints ◽  
Polymer Chains ◽  
System Response ◽  
Ample Evidence ◽  
Volume State ◽  
And Performance

Abstract This discussion has outlined a series of considerations which begin with engineering definitions of system response of adhesive joints and end with propositions involving molecular interactions at interfaces. Connecting these extreme aspects of the argument is the central subject of the micromechanics of bonding and fracture. Cavitation theory, as simply described by Equations (6a) and (7), illustrates the scale of microresponse in which both the thermodynamic and rheological aspects of adhesion phenomena achieve a parity when applied to cavities of radius r=0.1 to 10 μ. The discussion of the micromechanics of polymer fracture provides ample evidence that pure materials, polymer composites, and adhesive joints, need to be described in terms of their microdefects. The several mathematical models for crack propagation which are imposed upon fracture mechanics data tend to oversimplify the visualization of the true micromechanisms of fracture. The fuller development of micromechanics theory and experimental analysis promises to be an important area of current developments in the better understanding of macroscopic response of filled systems, fiber reinforced composites, and adhesively bonded structures. Recent developments in the several theories of intermolecular forces and the physical chemistry of bonding provide new impetus to the chemist to design optimized polymeric materials with finely adjusted balances of surface and bulk properties. The fuller visualization of adsorption-interdiffusion bonding as a process involving both the two-dimensional interface and the three-dimensional interphase defines bonding as both a thermodynamical and a rheological process. The microstages of bond formation are somewhat the reverse of the stages of microfracture listed earlier. The microdefects that commonly exist in polymeric materials and polymer composites tend to indicate that the viscoelastic constraints typical of polymer chains and networks play an important role in preventing equilibrium bonding in the simple thermodynamic sense as expressed by idealized liquid—liquid or liquid—solid interactions. The current development and application of a refined thermodynamical and rheological argument to both bonding and fracture processes stands as a central issue in directly correlating the molecular criteria of adhesion and performance of bonded systems. Any of the simple mathematical relations introduced in this discussion may be expressed with greater detail and precision by incorporating detailed statements concerning chemical composition, macromolecular structure, and free volume state of the polymeric adhesive.

Electroelasticity of dielectric elastomers based on molecular chain statistics

2018 ◽  
Vol 24 (3) ◽  
pp. 862-873 ◽  
Author(s):  
Mikhail Itskov ◽  
Vu Ngoc Khiêm ◽  
Sugeng Waluyo
Keyword(s):  
Constitutive Model ◽  
Polymer Chain ◽  
Mechanical Response ◽  
Three Dimensional ◽  
Polymer Chains ◽  
Molecular Chain ◽  
Dielectric Elastomers ◽  
Finite Extensibility ◽  
Single Polymer Chain ◽  
Non Gaussian

The mechanical response of dielectric elastomers can be influenced or even controlled by an imposed electric field. It can, for example, cause mechanical stress or strain without any applied load; this phenomenon is referred to as electrostriction. There are many purely phenomenological hyperelastic models describing this electroactive response of dielectric elastomers. In this contribution, we propose an electromechanical constitutive model based on molecular chain statistics. The model considers polarization of single polymer chain segments and takes into account their directional distribution. The latter results from non-Gaussian chain statistics, taking finite extensibility of polymer chains into account. The resulting (one-dimensional) electric potential of a single polymer chain is further generalized to the (three-dimensional) network potential. To this end, we apply directional averaging on the basis of numerical integration over a unit sphere. In a special case of the eight-direction (Arruda–Boyce) model, directional averaging is obtained analytically. This results in an invariant-based electroelastic constitutive model of dielectric elastomers. The model includes a small number of physically interpretable material constants and demonstrates good agreement with experimental data, with respect to the electroactive response and electrostriction of dielectric elastomers.

scholarly journals Polymer gel with a flexible and highly ordered three-dimensional network synthesized via bond percolation

2019 ◽  
Vol 5 (12) ◽  
pp. eaax8647 ◽  
Author(s):  
X. Li ◽  
S. Nakagawa ◽  
Y. Tsuji ◽  
N. Watanabe ◽  
M. Shibayama
Keyword(s):  
Network Formation ◽  
General Scheme ◽  
Polymer Network ◽  
Three Dimensional ◽  
Geometric Constraints ◽  
Polymer Chains ◽  
Bond Percolation ◽  
Polymer Gel ◽  
Temporal Correlations ◽  
Before And After

Gels are a soft elastic material consisting of a three-dimensional polymer network with nanometer-sized pores and are used in a variety of applications. However, gel networks typically have a substantial level of defects because the network formation reaction proceeds stochastically. In this study, we present a general scheme to fabricate gels with extremely low levels of defects by applying geometric constraints into pregel solution based on the “bond percolation” concept. In the formed gel, stationary laser speckles, which are an indicator of spatial defects, were not observed at all. In addition, we found that the concentration fluctuations of the polymer chains were ergodic across the whole gel network. In such a homogeneous gel, both the spatial and temporal correlations of polymer chains are the same before and after gelation.

Liquid Crystal Elastomers with Piezoelectric Properties

MRS Bulletin ◽  
1991 ◽  
Vol 16 (1) ◽  
pp. 29-31 ◽  
Author(s):  
Wolfgang Meier ◽  
Heino Finkelmann
Keyword(s):  
Liquid Crystals ◽  
Liquid Crystalline ◽  
Three Dimensional ◽  
Polymer Chains ◽  
Side Chain ◽  
Shape Stability ◽  
Technical Application ◽  
Mechanical Field ◽  
Dimensional Network ◽  
Liquid Crystal Elastomers

During the last few years, liquid crystalline elastomers (LCEs) have been systematically produced by cross-linking liquid crystalline side-chain polymers. In these networks, a liquid crystalline molecule is fixed at each monomeric unit. LCEs exhibit a novel combination of properties. Due to liquid crystalline groups, they show anisotropic liquid crystalline properties similar to conventional liquid crystals (LCs); but due to the three-dimensional network-structure of the polymer chains, they show typical elastomer properties, such as rubber elasticity or shape stability. One exceptional property of this combination is demonstrated when a mechanical deformation to the LCE causes macroscopically uniform orientation of the long molecular axis of the LC units (the so-called “director”).This response of the LC-phase structure to an applied mechanical field is similar to the effect of electric or magnetic fields on low molecular weight liquid crystals (LMLC), as illustrated in Figure 1. Figure la shows an undeformed LCE. Because of the non-uniform orientation of the director, the sample scatters light strongly so the elastomer is translucent like frosted glass. On the other hand, applying a mechanical field the director becomes uniformly aligned and the sample is transparent (Figure 1b). Such a macroscopically ordered rubber exhibits optical properties very similar to single crystals. These propertie s of LCEs offer new prospects for technical application, e.g., in nonlinear and integrated optics.

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