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Sun G Kappl M Pakula T Kremer K Butt HJ 《Langmuir : the ACS journal of surfaces and colloids》2004,20(19):8030-8034
Forces across polymer melts are poorly understood despite their importance for adhesion and fabricating composite materials. Using an atomic force microscope (AFM), this interaction was measured for poly(dimethyl siloxane) (PDMS). The structure of the polymer at the surface changed during the first approximately 10 h. Afterward, short-range attractive forces were observed with short-chain PDMS (M(w) = 4200 g/mol). Using PDMS with a molecular weight (M(w) = 18 000 g/mol) above the entanglement limit, we measured a monotonically decaying repulsive force, which indicates that a quasi-immobilized layer had formed at the solid surface. Due to the small radius of curvature of the tip, forces could be measured in equilibrium. 相似文献
15.
Ben Yahia H Gaudin E Darriet J Banks M Kremer RK Villesuzanne A Whangbo MH 《Inorganic chemistry》2005,44(9):3087-3093
A new magnetic oxide, CuMnVO4, was prepared, and its crystal structure was determined by single-crystal X-ray diffraction. The magnetic properties of CuMnVO4 were characterized by magnetic susceptibility and specific heat measurements, and the spin exchange interactions of CuMnVO4 were analyzed on the basis of spin-polarized electronic band structure calculations. CuMnVO4 contains MnO4 chains made up of edge-sharing MnO6 octahedra containing high-spin Mn2+ cations. Our work shows that CuMnVO4 undergoes a three-dimensional antiferromagnetic transition at approximately 20 K. Both the intrachain and interchain spin exchanges are antiferromagnetic, and the interchain spin exchange is not negligible compared to the intrachain spin exchange. 相似文献
16.
A renormalization group for polymer chains with hard-core interaction is considered, where a chain ofN
0 links of lengthl
0 and hard-core diameterh
0 is mapped onto a chain ofN
1=N
0/s links of lengthl
1 and hard-core diameterh
1. The lengthl
1 is defined in terms of suitable interior distances of the original chain, andh
1 is found from the condition that the end-to-end distance is left invariant. This renormalization group procedure is carried through by various Monte-Carlo methods (simple sampling is found advantageous for short enough chains or high dimensionalities, while dynamic methods involving kinkjumps or reptation are used else). Particular attention is paid to investigate systematic errors of the method by checking the dependence of the results on bothN
0 ands. It is found that for dimensionalitiesd=2, 3 only the nontrivial fixed-point is stable, where upon iteration the ratio
k
=h
k
/l
k
tends to nonzero fixed-point value *, while ford=4,5 the method converges to the gaussian fixed point with *=0. Taking both statistical and systematic errors into account, we estimate the exponentv asv=0.74±0.01 (d=2) andv =0.59±0.01 (d=3). The results are consistent with the expected crossover exponents =1/2 (d=3) and =1 (d=2), respectively. 相似文献
17.
Three ion pair complexes, [4-R-benzylpyridinium][bis(maleodinitriledithiolato)platinum(III)] (abbreviated as [RBzPy][Pt(mnt)(2)]; R = Cl (1), Br (2), or NO(2) (3)), have been synthesized. The cations and anions stack into well-separated columns in the solid state, and the Pt(III) ions form a 1-D zigzag chain within a [Pt(mnt)(2)](-) column through Pt...S, S...S, and Pt...S...Pt interactions. The chain is uniform in 1 and 2, while it alternates in 3. Unusual magnetic phase transitions from paramagnetism to diamagnetism were observed in these three complexes at approximately 275 K for 1, approximately 269 K for 2, and approximately 184 K for 3. These phase transitions were also found in DSC measurements for 1 and 2. The overall magnetic behaviors for 1-3 indicate the presence of antiferromagnetic exchange interactions in the high-temperature phase and spin-gapped systems in the low-temperature phase. Below 50 K, 2 exhibits weak ferromagnetism. The spontaneous moments are nearly repressed by a field of 1.0 T. The crystal structure of 2 at 173 K reveals that there are two crystallographically independent [Pt(mnt)(2)](-) entries in an asymmetric unit. These two crystallographically independent [Pt(mnt)(2)](-) entries satisfy the spin-canting condition, and the EPR spectra measured at room temperature exhibit anisotropic character. Therefore, the weak ferromagnetic behavior in the low-temperature region for 2 can be attributed to the spin-canting phenomenon. 相似文献
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Dieter Naumann Prof. Dr. Wieland Tyrra Dr. Hendrik T. M. Fischer Silke Kremer 《无机化学与普通化学杂志》2007,633(4):527-528
Tetrakis(pentafluorophenyl)tellurium(IV), Te(C6F5)4, was prepared from the reaction of TeCl4 and Mg(C6F5)Br. Crystallization of the crude product from n‐pentane at ?25 °C gave suitable single crystals. The title compound crystallizes in the monoclinic space group P21/c (Z = 8) with two independent molecules per unit cell. 相似文献
20.
Xiaoming Ren Jingli Xie Youcun Chen Reinhard Karl Kremer 《Journal of Molecular Structure》2003,660(1-3):139-146
The two ion-pair complexes, [pyH]2[Zn(mnt)2] (1) and [4,4′-bipyH2]-[Zn(mnt)2] (2), were synthesized, where mnt2− denotes maleonitriledithiolate, and [pyH]+, [4,4′-bipyH2]2+ represent pyridinium and diprotonated 4,4′-bipyridinium, respectively. Their single crystal structures show that there are strong bifurcated H-bonding interactions between the cations of the pyridinium derivative and the [Zn(mnt)2]2− anions in both 1 and 2. The bifurcated H-bonding interactions between the N–H of the pyridiniums and the CN groups of the mnt2− ligands give rise to a 2D layered H-bonding network, the adjacent layers come together in such way as mutual embrace to give a tight pack, thus 2D hydrogen-bonding sheets further develop into 3D H-bonding networks through weak C–HS and ππ stacking interactions in 1. As for 2, the cations and anions connect into several types of H-bonding macrorings ([2+2], [3+3] and [4+4]), these H-bonding macrorings fuse to extend into 2D layered structure, the interpenetration between [3+3] and [4+4] type H-bonding macrorings in the adjacent layers give further rise to novel 3D extended H-bonding networks, in which there are clearly parallel stacks of cations and the chelate rings of anions. 相似文献