We report measurements of the mechanical \(Q\) of a 32.7 kHz quartz tuning fork as a function of pressure for helium and argon at T \(=\) 300 K and for helium in the temperature range 7.0–0.7 K. In the low pressure ballistic regime, the damping due to the surrounding gas is inversely proportional to \(P\), while for higher pressures, a hydrodynamic treatment accounts for most of the variation of \(Q\) with \(P\). We have combined the ballistic and hydrodynamic models together with calculations of the thermal transpiration correction to correlate the tuning fork \(Q\) at low temperature with the pressure measured with a room temperature pressure gauge. The fork was found to be useful as an in situ pressure gauge for pressures above \(\sim \)0.1 mTorr. A dissipation peak and frequency drop associated with the superfluid transition in the adsorbed helium film is also observed for \(T<1.4\) K.

The break up of a non-Newtonian yield stress fluid bridge (acrylic paint, mayonnaise, hair gel, foam, and bentonite) was investigated. The minimum neck radius, h(min), was measured as a function of time and fit to a power law with exponent n(1). A rotational rheometer was used to measure the shear stress-rate of strain curve which was fit to a Herschel-Bulkley model with exponent n(2). For the pure, as purchased fluids, the exponent from the time dependence of h(min) (n(1)) and the rheology power law index (n(2)) were quantitatively the same. These results provide the first experimental confirmation of this relationship predicted by Suryo and Basaran. In the pure fluids, the pinch-off did not produce a satellite drop. In contrast, when the non-Newtonian fluids were diluted with a Newtonian fluid, the relationship between n(1) and n(2) was more complicated even though the diluted fluids were still Herschel-Bulkley, and the pinch-off produced satellite drops whose size was a continuous function of dilution.

The equilibrium configuration of a nonwetted three fluid system takes the form of a floating liquid lens, where the lens resides between an upper and lower phase. The axisymmetric profiles of the three interfaces can be computed by solving the nonlinear Young-Laplace differential equation for each interface with coupled boundary conditions at the contact line. Here we describe a numerical method applicable to sessile or pendant lenses and provide a free, downloadable Mathematica Player file which uses a graphical interface for analyzing and plotting lens profiles. The results of the calculations were compared to optical photographs of various liquid lens systems which were analyzed using basic ray-tracing and Moiré imaging. The lens profile calculator, together with a measurement of the lens radius for a known volume, provides a simple and convenient method of determining the spreading coefficient (S) of a liquid lens system if all other fluid parameters are known. If surfactants are present, the subphase surface tension must also be self-consistently determined. A procedure is described for extracting characteristic features in the optical images to uniquely determine both parameters. The method gave good agreement with literature values for pure fluids such as alkanes on water and also for systems with a surfactant (hexadecane/DTAB), which show a transition from partial wetting to the pseudopartial wetting regime. Our technique is the analog of axisymmetric drop shape analysis, applied to a three fluid system.