An overview is given of theory and experiments on liquid crystal phases which appear in solutions of elongated colloidal particles or stiff polymers. The Onsager (1949) virial thecry for the isotropionematic transition of thin rodlike particles is treated comprehensively along with extensions to polydisperse solutions and soft interactions. Computer simulations of liquid crystal phases in hard particle fluids are summarized and used to assess the quality of statistical mechanical thwries for stiff panicles at higher dume haion-like the inclusion of higher Virial coefficients, yexpansion, scaled particle theory and density functional theory. Both computer simulations and density functional theory indicate formation of more highly ordered smectic phases. The range of experimental applicability h strongly widened by the extension of the viriai theory to wormlike chains by Khokhlov and Semenov (1981, 1982). Fmally, experimental results for a number of carefully studied, charged and uncharged colloids and polymers are summarized and wmpared to theoretical results. IE many cases the agreement is semi-quantitative.

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Phase transitions in lyotropic colloidal and polymer liquid crystals

▪ Abstract Applications of state-of-the-art atomic force microscopy methods to the elucidation of the surface and near-surface structure of polymeric solids are described. Contact, tapping, force modulation, frictional force, and other modes of atomic force microscopy are described, and recent results are summarized. Conformational and chain order, crystalline order, polymer crystals, lamellar structures, lamellar surfaces, fold surfaces, and fibers and films with highly oriented molecules all yield important information. Controlled deformation of polymer surfaces, both reversible and irreversible, with the atomic force microscope, provides a wealth of information about mechanical properties on a nanometer scale. The observation of phase-separated regions and of polymer crystals lying below a smooth surface shows that not only topography but also elastic inhomogeneity can be observed in great detail with the atomic force microscope. This is a rapidly developing field, and some indications of future develo...

Characterization of polymer surfaces with atomic force microscopy

Understanding the microscopic structure and macroscopic properties of condensed matter from a molecular perspective is important for both traditional and modern chemical engineering. A cornerstone of such understanding is provided by statistical mechanics, which bridges the gap between molecular events and the structural and physiochemical properties of macro- and mesoscopic systems. With ever-increasing computer power, molecular simulations and ab initio quantum mechanics are promising to provide a nearly exact route to accomplishing the full potential of statistical mechanics. However, in light of their versatility for solving problems involving multiple length and timescales that are yet unreachable by direct simulations, phenomenological and semiempirical methods remain relevant for chemical engineering applications in the foreseeable future. Classical density functional theory offers a compromise: on the one hand, it is able to retain the theoretical rigor of statistical mechanics and, on the other hand, similar to a phenomenological method, it demands only modest computational cost for modeling the properties of uniform and inhomogeneous systems. Recent advances are summarized of classical density functional theory with emphasis on applications to quantitative modeling of the phase and interfacial behavior of condensed fluids and soft materials, including colloids, polymer solutions, nanocomposites, liquid crystals, and biological systems. Attention is also given to some potential applications of density functional theory to material fabrications and biomolecular engineering. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Density functional theory for chemical engineering: From capillarity to soft materials

Phase transitions in liquid crystals

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Hard convex body fluids

The Onsager theory for the isotropic–anisotropic phase separation in a solution of rodlike particles is extended to the case of mixtures of such particles with different lengths. The concentration, composition, order parameters, and orientation dependent thermodynamic quantities of the coexisting phases are calculated for the case of a mixture of rods of two different lengths for different length ratios. It is found that there is a significantly higher mole fraction of the longer rods in the anisotropic phase than in the isotropic phase. The order parameter of the longer rods is higher than in the one component case, whereas the order parameter of the shorter rods first increases and then decreases as the mole fraction of the longer rods is increased. All these features are accentuated as the length ratio of the two kinds of rods increases.

/pdf/on-the-isotropic-liquid-crystal-phase-separation-in-a-33hx3wp8bm.pdf

On the isotropic-liquid crystal phase separation in a solution of rodlike particles of different lengths

Failure mechanisms in polyolefines: The role of crazing, shear yielding and the entanglement network

Strain hardening modulus as a measure of environmental stress crack resistance of high density polyethylene

The convolution of tip shape on sample topography can introduce significant inaccuracy in an AFM image, when the tip radius is comparable to the typical dimension of the sample features to be observed. The blind estimation method allows one to obtain information on the AFM tip through an unknown characterizer sample and thus to perform the deconvolution of the tip shape from an image. When applying the blind estimation method to determine the AFM tip shape, some apparently trivial issues relating to the experimental operating parameters must be taken into account. In this paper, the effects of the operating parameters, e.g., sampling intervals (resolution) and instrumental noise, have been taken into account for the practical use of blind estimation and the result is that instrumental noise tends to provide a smaller estimation of the tip size, while larger sampling intervals provide a larger value of it. This paper presents guidelines to those effects in AFM and appropriate experimental conditions for applying the blind estimation method to obtain more reliable data on tip radius and therefore on sample topography.

https://iopscience.iop.org/article/10.1088/0957-0233/17/10/014/pdf

Some experimental issues of AFM tip blind estimation: the effect of noise and resolution

Gel-drawn ultrahigh molecular weight polyethylene was studied by atomic force microscopy (AFM). Three-dimensional surface profiles were recorded for tapes drawn to different extents. AFM images allowed the discrimination of different well-defined levels of the fibrillar morphology: (i) bundles of microfibrils with a diameter between 4 and 7 μm strongly depending on the elongation; (ii) microfibrils with a diameter between 0.2 and 1.2 nm which also decreased with increasing draw ratio; (iii) nanofibrils which form the elementary fibrillar building blocks; and (iv) regular chain patterns on the molecular level which correspond to the crystalline packing of polyethylene chains at the surface of the nanofibrils. The nanofibrils were formed during the initial conversion of lamellae to fibrillar crystallites and did not change considerably in diameter up to draw ratios of λ = 70.

R. Deblieck

Papers

On the isotropic-liquid crystal phase separation in a solution of rodlike particles of different lengths

Failure mechanisms in polyolefines: The role of crazing, shear yielding and the entanglement network

Strain hardening modulus as a measure of environmental stress crack resistance of high density polyethylene

Some experimental issues of AFM tip blind estimation: the effect of noise and resolution

Atomic-force microscopy of gel-drawn ultrahigh-molecular-weight polyethylene