2022.ph.867.1- An instrument mounted on a thick square of acrylic (~1.7cm thick), above which is a square of aluminum (~1cm thick). The acrylic square is supported by two blocks of wood (pieces of 2×4 lumber) that were not part of the original instrument. At the centre of the aluminum square is mounted a commercial XY translation stage. Three tall metal knobs with knurled tips surround this stage. These are used to level the aluminum plate relative to the acrylic surface.
Mounted on the translation stage is an assembly consisting of a larger metal stage, made of a copper alloy, at the top of which are two concentric circular elements, an inner and an outer electrode. The purpose of the copper stage is temperature control. It is wrapped in a length of heater wire. The translation stage is used to centre the inner electrode relative to the outer.
This assembly is supported by a second aluminum plate. The inner electrode sits at the centre of a hole in the outer electrode with a small gap between the outer circumference of the inner electrode and the circumference of the hole. A shaft, oriented vertically through the apparatus with one end protruding below the acrylic base, rotates the inner electrode using a motor that was not acquired with this instrument. A commercial slip ring electrical connection, located below the inner electrode, permits voltage to be applied to the inner electrode.
On the top surface of the outer electrode is the edge of a straight razor blade that has been split in half along its long axis. This is held in an arm-like assembly that can be moved along a radial axis relative to the two electrodes using a servo motor that is attached to the upper aluminum plate.
2022.ph.867.2 – A grey metal electronic box labeled “wiper motor control” on one side. At the top is a series of wire connectors with two rocker switches. At the front is a toothed wheel (used as a knob) as well as a switch and two sockets. Three wires, braided together, emerge from a hole on the back face. These are attached to connectors at the top of the instrument.
2022.ph.867.3 – A Ziplock bag with a handwritten label reading “Outer electrodes for Electroconvection Exps.” contains the following:
– One round plastic box containing inner electrodes and related components such as wires and plastic screws. Three of the inner electrodes are plated in gold. This inside of the lid is marked in blue with hand-written notes, presumably listing the dimensions of the inner electrodes.
– Two shafts to which the outer and inner electrodes are attached. These differ slightly in profile and appearance, one being white, the other an off-white material.
– Nine circular metal outer electrodes of varying diameters. These are separated by tissue paper onto which the dimensions of each electrode are written. Two of the outer electrodes are plated with gold.
2022.ph.867.4 – A clear plastic box containing seven small glass sample containers with black lids. The lid of the box had a ruled sticker label marked with purple ink. The label indicates that the samples contain 8CB (liquid crystal) doped with TCNQ (tetracyanoquinodimethane) in five different concentrations. The first sample (bottle “A”) is not doped.
2022.ph.867.5– A clear plastic bag, sealed at the top with five staples, contains six small bottles of liquid crystal samples. Four of the bottles have a manufacturer’s label from BDH, Ltd.
2022.ph.867.6 – A clear plastic bag, sealed at the top with five staples, contains eleven small bottles of liquid crystal samples. Three of the bottles are in a smaller inner bag. One of the bottles has a manufacturer’s label from BDH, Ltd.
2022.ph.867.7 – A clear plastic bag, sealed at the top with five staples, contains fourteen small bottles of liquid crystal samples.
2022.ph.867.8 – A single brown-tinted glass bottle with a red plastic lid. It is larger than the sample containers and has a manufacturer’s label indicating that it contains Tetracyanoquino Dimethane.
Accession Number: 2022.ph.867.1-8
Aluminum Alloy, Iron Alloy, Acrylic, Wood.
Dimensions (cm): Height = 28, Width = 25, Length = 28.
This apparatus contains the core components of an experiment in fluid mechanics that was developed to study electrically driven convection currents in films of liquid crystal. This material has the property of creating very thin, stable, and electrically conductive films of uniform thickness. The properties of such films can be varied using chemical doping agents and changes in current. A flow of electricity through the film creates a pattern of vortices. These can be visualized optically; a swirling pattern of colors represents variations in thickness in the film. An example is shown in the image below. The film may also be analyzed electrically, with variations in current indicating changes in convection patterns.
This version of the experiment involves an annular (ring-shaped) film that is created by drawing the edge of a razor, wetted with a tiny amount of liquid crystal, across the gap between two nested circular electrodes. The inner electrode can be made to rotate, allowing the experimenter to study the effects of a shear flow on the convection currents. Using electrodes of different dimensions permits the experimenter to explore films of varying aspect ratios. The experiment can be mounted in a vacuum chamber in order to eliminate the effects of air drag.
This artifact consists of the inner workings of a larger experiment. These are in good condition. Missing components include an optional vacuum chamber, an electrical motor used to rotate the inner electrode, and various electrical connections between the motor controller and the linear motor, which moves the razor blade that creates the film. A camera stand with a partial mirror was originally positioned above the apparatus to observe reflected light. This was not acquired.
The vacuum chamber and the frame of the camera stand can be seen in the final two images in this entry.
University of Toronto, Department of Physics
Date of Manufacture: Mid-to-late 1990s
This artifact was acquired from the laboratory of Dr. Stephen Morris on April 23rd, 2022.
For a list of publications related to smectic film electroconvection, including those related to this instrument, see this archived version of a page hosted by the University of Toronto Department of Physics.
Several YouTube videos, including this one, that show convection patterns, can be found on the YouTube channel of Professor Stephen Morris.
This type of experiment was created by Dr. Stephen Morris for his PhD research in the early 1990s. The initial “finite” version of the experiment used a ribbon arrangement with four sides. This annular version with a rotating inner electrode was created to study the effects of a shear flow on the electrical convection currents. It also avoids leakage of the current produced by the ends of the earlier “finite” version.
Depending on the experiment, the film consists of liquid crystal, (typically K24, produced by BDH, Ltd) doped with TCNQ (tetracyanoquinodimethane). The term “smectic” refers to an arrangement of molecules within liquid crystal in which the molecules are parallel and arranged into discrete layers. This permits the formation of extremely thin and uniform films in which convection patterns may be observed.
The experiment was also done in a vacuum chamber in order to eliminate air drag, though the large majority of experiments were done in open air.
- Donated to UTSIC