John S. Dahler

Bio: John S. Dahler is an academic researcher from University of Minnesota. The author has contributed to research in topics: Distribution function & Viscosity. The author has an hindex of 22, co-authored 142 publications receiving 1917 citations.

Fluid Mechanical Aspects of Antisymmetric Stress

Abstract: Basic fluid mechanical concepts are reformulated in order to account for some structural aspects of fluid flow. A continuous spin field is assigned to the rotation or spin of molecular subunits. The interaction of internal spin with fluid flow is described by antisymmetric stress while couple stress accounts for viscous transport of internal angular momentum. With constitutive relations appropriate to a linear, isotropic fluid we obtain generalized Navier‐Stokes equations for the velocity and spin fields. Physical arguments are advanced in support of several alternative boundary conditions for the spin field. From this mathematical apparatus we obtain formulas that explicitly exhibit the effects of molecular structure upon fluid flow. The interactions of polar fluids with electric fields are described by a body‐torque density. The special case of a rapidly rotating electric field is examined in detail and the induction of fluid flow discussed. The effect of a rotating electric field upon an ionic solution is analyzed in terms of microscopically orbiting ions. This model demonstrates how antisymmetric stress and body torque can arise in ``structureless'' fluids.

Brownian Motion of Polyatomic Molecules: The Coupling of Rotational and Translational Motions

Abstract: The coupling of rotational and translation Brownian motions is examined from several points of view The first is a phenomenological theory based upon generalized Langevin equations of motion and a Markoff integral equation Next, a more detailed statistical‐mechanical theory is fashioned after the pattern of Kirkwood's theory for nonequilibrium processes in monatomic liquids Both schemes lead to a generalized Fokker—Planck—Chandrasekhar equation for the singlet‐distribution function This equation includes terms that account for separate rotational and translational motions as well as two mutually symmetric contributions which are descriptive of their coupling The friction tensors associated with the uncoupled components of these motions are found to be proportional to the autocorrelations of the environmental force and torque which act upon a given molecule The frictional coupling is related to the cross correlation of force and torque From the principle of microreversibility it is possible to estab

Transport Properties of Polyatomic Fluids, a Dilute Gas of Perfectly Rough Spheres

Abstract: A detailed account is given of the kinetic theory for a fluid composed of perfectly rough spheres. When one applies the method of Chapman and Enskog to a dilute gas of these spheres he finds that the nonequilibrium distribution function satisfies a nonself‐adjoint integral equation. The solution of this equation is not an isotropic function of the molecular spin velocity. A study has been made of the bearing of this spin anisotropy upon the calculated values for the gas transport coefficients.

Transport Phenomena in a Fluid Composed of Diatomic Molecules

Abstract: It is illustrated that the formal theory of transport processes developed by Kirkwood, Irving, Zwanzig, and Ross can be extended to fluids composed of polyatomic molecules. In Secs. II and III the hydrodynamical equations are established for the case of classical mechanics and in IV these same relationships are shown to obtain in the quantum theory. Section VI is devoted primarily to the equations of change for the classical distribution functions, special attention being given to cases where the intermolecular forces are impulsive. In V and VI the quantum theory is formulated in terms of generalized Wigner functions, i.e., Fourier transforms of the density matrix. In terms of these functions the transport properties of a dilute polyatomic fluid may be represented as those of a mixture whose components are molecules with different internal quantum states. Finally, in VII we consider the equations of change for the Wigner functions and the quantum analog of the Boltzmann integro‐differential equation.

Hydrodynamic screening and particle dynamics in porous media, semidilute polymer solutions and polymer gels

Abstract: The dynamics of particle interactions in porous media are studied using a newly formulated mean field theory. Statistical correlations in the gel network are analyzed in detail and found to have a crucial influence on the results. Self‐diffusion and mutual diffusion coefficients of Brownian particles moving through a gel are determined. Preaveraged hydrodynamic interaction tensors are derived for two mobile Brownian particles a mobile particle and an obstacle.

The non-linear field theories of mechanics

Abstract: Matter is commonly found in the form of materials. Analytical mechanics turned its back upon this fact, creating the centrally useful but abstract concepts of the mass point and the rigid body, in which matter manifests itself only through its inertia, independent of its constitution; “modern” physics likewise turns its back, since it concerns solely the small particles of matter, declining to face the problem of how a specimen made up of such particles will behave in the typical circumstances in which we meet it. Materials, however, continue to furnish the masses of matter we see and use from day to day: air, water, earth, flesh, wood, stone, steel, concrete, glass, rubber, ... All are deformable. A theory aiming to describe their mechanical behavior must take heed of their deformability and represent the definite principles it obeys.

Kinetic theories for granular flow: inelastic particles in Couette flow and slightly inelastic particles in a general flowfield

Abstract: The flow of an idealized granular material consisting of uniform smooth, but nelastic, spherical particles is studied using statistical methods analogous to those used in the kinetic theory of gases. Two theories are developed: one for the Couette flow of particles having arbitrary coefficients of restitution (inelastic particles) and a second for the general flow of particles with coefficients of restitution near 1 (slightly inelastic particles). The study of inelastic particles in Couette flow follows the method of Savage & Jeffrey (1981) and uses an ad hoc distribution function to describe the collisions between particles. The results of this first analysis are compared with other theories of granular flow, with the Chapman-Enskog dense-gas theory, and with experiments. The theory agrees moderately well with experimental data and it is found that the asymptotic analysis of Jenkins & Savage (1983), which was developed for slightly inelastic particles, surprisingly gives results similar to the first theory even for highly inelastic particles. Therefore the ‘nearly elastic’ approximation is pursued as a second theory using an approach that is closer to the established methods of Chapman-Enskog gas theory. The new approach which determines the collisional distribution functions by a rational approximation scheme, is applicable to general flowfields, not just simple shear. It incorporates kinetic as well as collisional contributions to the constitutive equations for stress and energy flux and is thus appropriate for dilute as well as dense concentrations of solids. When the collisional contributions are dominant, it predicts stresses similar to the first analysis for the simple shear case.

The nature of the liquid-vapour interface and other topics in the statistical mechanics of non-uniform, classical fluids

Abstract: Recent theoretical work on the microscopic structure and surface tension of the liquid-vapour interface of simple (argon-like) fluids is critically reviewed. In particular, the form of pairwise intermolecular correlations in the liquid surface and the capillary wave treatment of the interface are examined in some detail. It is argued that conventional capillary wave theory, which leads to divergences in the width of the density profile, is unsatisfactory for describing all the equilibrium aspects of the interface. The density functional formalism which has been developed to study the liquid-vapour interface can also be profitably applied to other problems in the statistical mechanics of non-uniform fluids; here a new generalization of the ‘linear’ theory of spinodal decomposition is formulated and by considering a ‘nearly uniform’ fluid, some useful results for the long-wavelength behaviour of the liquid structure factor of various monatomic liquids are obtained. Some other topics of current inte...

Perturbation Theory and Equation of State for Fluids. II. A Successful Theory of Liquids

Abstract: The perturbation theory previously shown to give good results for the equation of state of a square‐well fluid at liquid densities and temperatures is applied to more realistic potentials with soft repulsion, in particular the 6:12 potential. For an arbitrary potential function a modified potential is defined involving three parameters, namely a hard‐sphere diameter, an inverse‐steepness parameter for the repulsive region, and a depth parameter for the attractive region. When the latter parameters are zero, the modified potential becomes the hard‐sphere potential; when they are one, it becomes the original potential. The configuration integral is expanded in a double‐power series in the inverse‐steepness and depth parameters, the hard‐sphere diameter being chosen so that the first‐order term in the inverse‐steepness parameter is zero. The first‐order term in the depth parameter is evaluated essentially exactly and the second‐order term approximately: other second‐order terms and all higher‐order terms are neglected. The resulting equation of state is in good agreement with molecular dynamics, Monte Carlo results, and experimental data for argon at all temperatures and densities relevant for fluids.

X-ray photoelectron spectroscopy sulfur 2p study of organic thiol and disulfide binding interactions with gold surfaces

Abstract: The presence of two sulfur species was detected in X-ray photoelectron spectroscopy (XPS) studies of thiol and disulfide molecules adsorbed onto gold surfaces. These species are assigned to bound thiolate (S2p3/2 binding energy of 162 eV) and unbound thiol/disulfide (S2p3/2 binding energy from 163.5 to 164 eV). These assignments are consistent with XPS data obtained from different thiols (C12, C16, C18, and C22 alkane thiols, a fluorinated thiol, and a cyclic polysiloxane thiol) and different adsorption conditions (solvent type, thiol concentration, temperature, and rinsing). In particular, the use of a poor solvent for thiol adsorption solutions (e.g., ethanol for long chain alkanethiols) and the lack of a rinsing step both resulted in unbound thiol molecules present at the surface of the bound thiolate monolayer. This has implications for recent studies asserting the presence of multiple binding sites for gold−thiolate species in organic monolayers.