Adhesion phenomena in ferrofluids

Abstract

One efficient way of determining the bond strength of adhesives is to measure the force or the work required to separate two surfaces bonded by a thin adhesive film. We consider the case in which the thin film is not a conventional adhesive material but a high viscosity ferrofluid confined between two narrowly spaced parallel flat plates subjected to an external magnetic field. Our theoretical results demonstrate that both the peak adhesive force and the separation energy are significantly influenced by the action and symmetry properties of the applied field. Specifically, we show that the adhesive strength of a ferrofluid is reduced if the applied magnetic field is perpendicular to the plates or if the applied field is in plane and exhibits azimuthal symmetry. Conversely, the adhesive strength can be either enhanced or reduced if the applied field is in plane and is directed radially outward. This establishes an interesting connection between adhesion and ferrohydrodynamic phenomena, allowing the control of important adhesive properties by magnetic means.

Magnetic fluid in a time-dependent gap Hele–Shaw cell

“…Eqs. (3)-(6) agree with the results obtained in Ref [8]. if normal stresses are not taken into account (d ¼ 0).…”

“…2 we plot CðnÞ as a function of time for two values of n. As in Refs. [2,8] we assume an exponentially increasing gap spacing bðtÞ ¼ e t : The solid (dashed) curves describe the behavior of CðnÞ in the absence (presence) of the magnetic field. The black (gray) curves assume that the normal stress parameter d ¼ 0 ðd ¼ 1Þ: Light (dark) gray curves refer to q ¼ 125 ð175Þ: It is evident from Fig.…”

Adhesion force in fluids: Effects of fingering, wetting, and viscous normal stresses

“…One interesting aspect that connects the research performed in Refs [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] (evaluation of the adhesion force) and that of Refs. [19][20][21][22][23][24][25][26][27][28][29][30][31][32] (study of the emerging pattern-forming structures) is the influence of fingering formation on the determination of the adhesion force itself.…”

“…In addition to the assessment of the lifting adhesion force, another aspect of the problem has also been intensively investigated, both experimentally and theoretically [19][20][21][22][23][24][25][26][27][28][29][30][31][32], It refers to the study of the appealing pattern formation phenomenon that takes place at the interface separating the lifted, more viscous fluid (e.g., oil), and the surrounding fluid (for instance, air) during the lifting procedure. As the plates separate, the outer less-viscous fluid enters the system, and the more-viscous inner fluid moves inward.…”

“…The study of the adhesion properties of viscous fluids has been the object of a lot of research in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In all these investigations a key factor is the precise evaluation and characterization of the bond strength of spatially confined, liquid thin films.…”