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Dogic Z Zhang J Lau AW Aranda-Espinoza H Dalhaimer P Discher DE Janmey PA Kamien RD Lubensky TC Yodh AG 《Physical review letters》2004,92(12):125503
We directly visualize single polymers with persistence lengths l(p), ranging from 0.05 to 16 microm, dissolved in the nematic phase of rodlike fd virus. Polymers with a sufficiently large persistence length undergo a coil-rod transition at the isotropic-nematic transition of the background solvent. We quantitatively analyze the transverse fluctuations of the semiflexible polymers and show that at long wavelengths they are driven by the fluctuating nematic background. We extract the Odijk deflection length and the elastic constant of the background nematic phase from the data. 相似文献
74.
We report the creation of nematic nanotube gels containing large domains of isolated, oriented, half-micron-long, single-wall carbon nanotubes (SWNTs). We make them by homogeneously dispersing surfactant coated SWNTs at low concentration in an N-isopropyl acrylamide gel and then inducing a volume-compression transition. These gels exhibit hallmark properties of a nematic: birefrigence, anisotropy in optical absorption, and disclination defects. We also investigate the isotropic-to-nematic transition of these gels, and we describe the physical properties of their ensuing nematic state, including a novel buckling of sample walls. Finally, we provide a simple model to explain our observations. 相似文献
75.
We have observed angular anisotropy in weak localization of light from highly scattering, orientationally ordered, nematic liquid crystals. This demonstration of angular anisotropy in a multiple-scattering interference phenomenon was facilitated by a light scattering instrument with extraordinary angular resolution. The measured anisotropies were consistent with a simple model of coherent backscattering generalized for propagation-direction dependent mean free paths. 相似文献
76.
Direct measurement of the polarized optical absorption cross section of single-wall carbon nanotubes
We determine optical absorption cross sections of single-wall carbon nanotubes for visible light copolarized and cross polarized with respect to the nanotube axis. The need for perfectly aligned ensembles in absorbance measurements is eliminated by using Raman scattering to measure the nematic order parameter in magnetically aligned nanotube suspensions. The absorbance data allow the first quantitative, spectral comparisons with theories of local field depolarization, and provide benchmark spectra for simple, rapid, and quantitative measurements of alignment within nanotube dispersions. 相似文献
77.
Lin Kh Crocker JC Prasad V Schofield A Weitz DA Lubensky TC Yodh AG 《Physical review letters》2000,85(8):1770-1773
We investigate the self-assembly of colloidal spheres on periodically patterned templates. The surface potentials and the surface phases are induced entropically by the presence of dissolved, nonadsorbing polymers. A rich variety of two-dimensional fluidlike and solidlike phases was observed to form on template potentials with both one- and two-dimensional symmetry. The same methodology was then used to nucleate an oriented single fcc crystal more than 30 layers thick. The general approach provides a new route for directed self-assembly of novel mesoscopic structures. 相似文献
78.
Crocker JC Valentine MT Weeks ER Gisler T Kaplan PD Yodh AG Weitz DA 《Physical review letters》2000,85(4):888-891
We demonstrate a novel method for measuring the microrheology of soft viscoelastic media, based on cross correlating the thermal motion of pairs of embedded tracer particles. The method does not depend on the exact nature of the coupling between the tracers and the medium, and yields accurate rheological data for highly inhomogeneous materials. We demonstrate the accuracy of this method with a guar solution, for which other microscopic methods fail due to the polymer's mesoscopic inhomogeneity. Measurements in an F-actin solution suggest conventional microrheology measurements may not reflect the true bulk behavior. 相似文献
79.
We investigate the influence of morphology and size on the vibrational properties of disordered clusters of colloidal particles with attractive interactions. Spectral features of the vibrational modes are found to depend strongly on the average number of nearest neighbors, NN, but only weakly on the number of particles in each glassy cluster. In particular, the median phonon frequency, ω(med), is constant for NN<2 and then grows linearly with NN for NN>2. This behavior parallels concurrent observations about local isostatic structures, which are absent in clusters with NN<2 and then grow linearly in number for NN>2. Thus, cluster vibrational properties appear to be strongly connected to cluster mechanical stability, and the scaling of ω(med) with NN is reminiscent of the jamming transition. Simulations of random networks of springs corroborate observations. 相似文献
80.
Water-lutidine mixtures permit the interparticle potentials of colloidal particles suspended therein to be tuned, in situ, from repulsive to attractive. We employ these systems to directly elucidate the effects of interparticle potential on glass dynamics in experimental samples composed of the same particles at the same packing fractions. Cooperative rearrangement regions (CRRs) and heterogeneous dynamics are observed in both types of glasses. Compared to repulsive glasses, the attractive glass dynamics are found to be heterogeneous over a wider range of time and length scales, and its CRRs involve more particles. Additionally, the CRRs are observed to be stringlike structures in repulsive glasses and compact structures in attractive glasses. Thus, the experiments demonstrate explicitly that glassy dynamics can depend on the sign of the interparticle interaction. 相似文献