Field of Technology
This invention in general relates to Chemical Engineering and Chemical technology. Further this invention relates to the area of rheology. More particularly this invention relates to a new process of carrying out simultaneously the visual analysis and rheological measurements of complex fluids and soft solids.
This new instrument is capable of studying the evolution of the structure and the rheological properties simultaneously in complex fluid and soft solid systems. This provides a method for determining the relationship between the structure and the rheological properties for these materials.
Prior Art Disclosure
At present, the visual analysis at the micron scale and rheological measurements are usually carried out separately.
The visual analysis is usually carried out under a microscope. Light microscopes are used for structured fluids and soft solids in which the structures have dimensions comparable to or larger than the wavelength of light. For birefringent systems like liquid crystals with structures of smaller dimensions, polarising microscopy is used to identify the defect structures and their conformational change under flow. Microscopy is also used to study the deformation of interfaces under stress. In order to study the effect of flow on the observable structure of the fluid or soft material, shear cells consisting of glass plates which can be fitted under a microscope have been built[l,2]
The rheological measurement is carried out using instruments such as the viscometer or rheometer, where the stress and deformation of the sample are measured. The common configurations used are the cone and plate, plate and plate and Couette cell geometry. In all of these, the sample is placed between a rotating element called the rotor and a static surface called the stator. The rotor is the surface of a wide-angled cone for the cone-and-plate

geometry, a disk for the plate-and-plate geometry, and a cylinder for the Couette cell geometry. The stator is flat for the cone-and-plate and plate-and-plate geometry, and cylindrical for the Couette geometry. The torque and the rate of rotation of the rotating part is measured, and the stress and strain on the sample are determined. From this, the rheological properties, both steady and oscillatory, of the sample are calculated.
There are also some examples of rheometry and visualisation being carried out simultaneously. However, in these cases, there are severe limitations on the kind of rheological measurements that can be performed. These methods and their limitations are summarised below:
Microscope used in conjunction with a shear cell [3]
In this shear cell the concentric cylinder geometry is used. The inner cylinder, which is also the rotor, has a transparent cone as the base. The outer cylinder has a transparent glass plate as the base. The optical studies (light microscopy and light scattering) are conducted in the cone and plate and parallel plate geometries in transmission mode. The viscosity can also be measured by measuring the torque on the rotor. Therefore, in this setup, simultaneous visualisation and viscosity measurements can be conducted.
Limitations: It is not possible to conduct oscillatory measurements in this set up, and the viscoelastic components of the shear modulus cannot be measured. The measurement is restricted to only the steady viscosity. Also visualisation is restricted to the cone and plate geometry. It is not possible to conduct optical measurements in the concentric cylinder geometry. Normal stress also cannot be measured.
Shear cell used in conjunction with a microscope
The sample is taken between two transparent glass plates. The bottom plate is connected to a piezoelectric actuator. The motion of the top plate is monitored by a piezoelectric accelerometer. A lock-in amplifier is used to measure the vibration of the top plate. This can

be used to measure the viscoelastic moduli (G' and G") in the frequency range 10 - 300 Hz[4].
This shear cell is placed on the microscope stage of a polarising microscope enabling simultaneous visualisation.
Limitations: This instrument cannot be used to measure the steady viscosity, or the viscoelastic moduli outside the frequency range specified above. Normal stress also cannot be measured.
Light Scattering microscope
In this setup, a transparent outer cylinder has been used with a conventional rheometer [5] for the concentric cylinder geometry. A laser sheet illuminates the sample and the images are recorded with a video camera.
Limitations: It can only be used in the concentric cylinder geometry and for light scattering, and it has not been extended to light microscopy or polarising microscopy.
Imaging in a Couette flow geometry on a conventional rheometer [6|
The Couette flow geometry is made of a transparent outer cylinder and a blackened inner cylinder. A portion of the outer cylinder is illuminated by an external light source. A stereo microscope is used for visualisation. The diffuse light scattered from the sample enters the microscope, and thereby the illuminated region is studied. Polarisers are used on the light source and the microscope to carry out polarising microscopy.
Limitations: This procedure gives some visual information along with rheometry, but the quality of images is limited due to the diffuse nature of the illumination. In addition, it is difficult to align the polariser and analyser correctly due to the uncertainty in the orientation of the light source and the microscope.

Consequently, with the present procedures it is not possible to conduct light microscopy and the range of rheological measurements of interest in all the geometries for the study of complex fluids and soft solids. Due to this limitation, it is not possible to correlate the evolution of the structure of the sample with the variation of the rheological properties. This is a severe limitation, because structure — rheology relationships are very important to facilitate the design of new materials with carefully controlled properties.
Objects of Invention:
It is the primary object of the invention to design a novel process/procedure to do simultaneously the visualisation and rheometry.
It is another object of the invention to correlate the rheological properties with the visually observed structures, in order to infer structure-property correlation.
It is another object of the invention to conduct optical measurements in the concentric cylinder geometry and to measure the normal stress.
It is another object of the invention to measure the steady viscosity, and the visco-elastic moduli outside the frequency range 10 to 300 Hz.
Further objects of the inventions will be clear from the following description.
Now the invention will be described in detail. The description of the invention will refer to the accompanying drawings of the complete specification. The descriptions will extensively deal with the nature of the invention and the manner in which it is to be performed.
The statements of the drawings, which accompany this complete specification, are as follows:

1. Figure 1 of the drawings shows the Schematic diagram of the microscope in conjunction with the rheometer, parallel plate geometry.
2. Figure 2 of the drawings shows the Schematic diagram indicating the optics involved in the parallel plate geometry.
3. Figure 3 of the drawings shows the Schematic diagram of the microscope in conjunction with the rheometer, concentric cylinder geometry.
4. Figure 4 of the drawings shows the Schematic diagram indicating the optics involved in the concentric cylinder geometry.
The invention is to carry out simultaneous visualisation and rheology of a sample in a modified viscometer, rheometer or rheogoniometer. Examples of the modification of the commonly used plate and plate and cylindrical Couette geometry are shown in figures 1 and 3.
In the modified plate and plate rheometer, a glass plate is stuck to the center of the metal top plate of the rotating parallel plate geometry of a smaller diameter. Thus the sample can be observed through the transparent glass between the edge of the metal top plate and the edge of the glass plate. To enhance the illumination of the sample, the bottom plate is modified by a plane reflecting material such as a front-coated mirror or a polished metal sheet.
A modified reflection microscope is configured as shown in figure 1. The light initially passes through a polariser and is reflected by a mirror. This incident light is again reflected onto the objective lens with the aid of a prism (figure 2). The light passes through the sample, and is reflected from the bottom-reflecting surface. The reflected light passes through the objective, is reflected by the prism, passes through the analyser and then forms the image on the eye or on a CCD camera for recording and further processing. Micrometers attached to the microscope are used to measure the distance from the edge of the glass plate, and also the height at which the microscope is focussed. This permits the analysis of the

visual features of the sample as a function of the distance from the top and bottom plates.
In the modified cylindrical Couette geometry, the outer stationary cylinder is made of a transparent material such as glass or quartz. The inner cylinder is coated with a reflecting material such as a polished metal coating. A modified microscope is integrated with the rheometer in the configuration shown in figure 3. The light is focussed on the sample through the objective lens (figure 4). It is reflected from the inner cylinder, and the reflected light passes through the objective and eyepiece and forms an image on the eye of an observer or on a CCD camera for recording and further processing. Micrometer screws can be used to measure the distance at which the microscope is focussed relative to the inner and outer cylinders, in order to study the variation of the visual structures as a function of the distance from the inner and outer cvlinders.

Claim
1. A system for simultaneous visual analysis and rheological measurements of complex
fluids and soft solids comprising a modified parallel plate rheometer; a glass plate
is stuck to the centre of the metal top plate of the rotating parallel plate geometry of
smaller diameter, allowing the sample to be observed between the edge of the metal top plate and the edge of the glass plate. To enhance the illumination of the sample, the bottom plate is modified by a plane reflecting material such as a front coated mirror or a polished metal sheet.
2. A system for simulteneous visual analysis and rheological measurements of complex
fluids and soft solids as claimed in claim 1, wherein rheometry instrument being
capable of studying the evolution of the visual structure and the rheological
properties simultaneously in complex fluid and soft solid systems.
3. A system for simulteneous visvual analysis and rheological measurements of complex fluids and soft solids as claimed in claim 1, wherein the system provides a method for determining the relationship between the structure and the rheological properties for these materials.
4. A system for simultaneous visual analysis and rheological measurements of complex fluids and soft solids as claimed in claim 1 wherein micrometers attached to the microscope are used to measure the distance from the edge of the glass plate, and also the height at which the microscope is focussed and this permits the analysis of the visual features of the sample as a function of the distance from the top and bottom plates.
5. A system for simultaneous visual analysis and rheological measurements of complex fluids and soft solids as claimed in claim 1 wherein in the modified cylindrical Couette geometry, the outer stationary cylinder is made of a transparent material such as glass or quartz and the inner cylinder is coated with a reflecting material

such as a polished metal coating.
6. A system for simultaneous visual analysis and rheological measurements of complex
fluids and soft solids as claimed in claim 1 wherein a modified microscope is integrated with rheometer.
7. A system for simultaneous visual analysis and rheological measurement of complex
fluids and soft solids as claimed in claim 1 wherein micrometer screw can be used
to measure the distance at which the microscope is focussed relative to the inner and
outer cylinders, in order to study the variations of the visual structure as a function
of the distance from the inner and outer cylinders.
8. A system for simultaneous visual analysis and rheological measurements of complex
fluids and soft solids as described in the complete specification and as illustrated by
way of drawings.
Dated this 18th day of February 2002