The relationship between stress and deformation defines the rheological properties of a film. Most thin films encountered in vivo and in industrial applications are viscoelastic, where this relationship is intermediate between purely viscous and purely elastic.
The rheological properties are extremely important for defining product stability. Applications can be found in many industries. For example proteins, polymers, pigments, fluoroalkanes and other emulsifiers are strong stabilizers in dispersions and used in the pharmaceutical, cosmetic and food industries.
- Prediction of emulsion, froth and foam stability
Viscoelasticity of an interface can predict the stability of a complex fluid. Micelle/droplet fusion and fission are largely dependent on the interface viscoelasticity.
- Determination of thin film structure
The presence of networking, hydrogen bonding and other interactions can be detected from the viscoelastic behavior of films
- Examination of phase transitions
Phase transitions in a monolayer, thin film, can result in a change in the rheological properties of the layer.
- Real-time monitoring of surface reactions
Surface gelation, network formation and protein denaturation at interfaces are detected from the changes in the viscoelastic properties at the interface.
- Continuous monitoring of molecule adsorption into interfaces
Especially in biological systems the adsorption and desorption at interfaces and surfaces can change viscoelasticity. Many processes in cells such as mitosis are highly dependent on membrane rheology.
| The method marks a quantum leap in technology from the traditional rotational rheometers that lack the sensitivity to probe many of the phenomena occurring within a thickness range of a few nanometers. A magnetized probe, positioned at the air/liquid or liquid/liquid interface, is moved using a magnetic field. The movement of the probe is recorded with a camera from above. By measuring any changes in movement of the probe the surface modulus can be calculated and divided into the elastic and viscous properties of the film. Read more |
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Dynamic measurement
In a dynamic test, the instrument provides both the elastic (storage) and viscous (loss) moduli, G’(ω) and G”(ω) respectively. The relative magnitudes of these two properties immediately provide information whether the film behaves more like an elastic membrane or a viscous fluid film. These quantities can be converted to the dynamic, interfacial viscosity, μs*. The measurements can be performed as a function of frequency, time, strain, temperature or surface pressure.
Allows measurements of:
- Elastic (storage) modulus, G’
- Viscous (loss) modulus, G’’
- Dynamic interfacial viscosity, μs*
Static measurement
In creep compliance test mode, the instrument provides information to obtain whether the system behaves more like an ideal Newtonian liquid (dashpot model) or ideal elastic (spring model). Viscoelastic systems are more complex as they combine both elements. These can be modeled with Maxwell and Voigt-Kelvin models. From the models the film interfacial surface viscosity, η, storage modulus, G’, and relaxation time, τ, can be calculated.
Allows measurements of:
- Surface / interfacial viscosity, η
- Elastic moduli, G’
- Relaxation times, τ
The KSV NIMA ISR can be equipped with either a KSV NIMA Langmuir Trough (or Liquid-Liquid Trough) for simultaneous control of the film packing density or a Low Volume Measurement cell to work with small interfacial areas and reduced suphase volumes.
Both systems enable surface pressure measurement thanks to the integrated highly sensitive Wilhelmy balance. The Langmuir Trough and the Low Volume Measurement Cell are divided into an upper and lower compartment which can be used to study film viscoelasticity at the liquid-air or liquid-liquid interface.
KSV NIMA ISR with KSV NIMA Langmuir Trough
Combining the KSV NIMA ISR with a Langmuir Trough or Liquid-Liquid Trough allows controlling the compression of both soluble and insoluble films during the measurements. Like with any KSV NIMA Langmuir Trough, measurements of Isotherms, Isobars and interfacial dilational rheology are possible. Please ask for the KSV NIMA Langmuir and Langmuir-Blodgett brochure for additional information on Langmuir Troughs.
KSV NIMA ISR with Low Volume Measurement Cell
When working with valuable compounds and subphases, the KSV NIMA ISR can be used with the Low Volume Measurement Cell which require as little as a 4.7 ml of subphase. It is ideal to study material adsorption and reaction at interfaces. A quartz glass cover minimises liquid evaporation and reduces the influence of airflows. An integrated water circulator enables temperature control from 10 to 60°C. Two injection ports on each end of the Cell enable easy injection of materials (e.g. proteins, enzymes) in the subphase and allow gradual subphase exchange while measuring.
Graph 1
Graph 1 illustrates the evolution of the interfacial viscosity of a protein monolayer (lysozyme) residing between water and decane plotted as a function of time. The surface pressure of the layer is also plotted. The change in surface pressure shows the evolution of the adsorption, interfacial viscosity and the crosslinking of the protein as a viscoelastic “skin” develops at the interface as a function of time. The surface pressure data complements the interfacial rheology data.
Graph 2
In a KSV NIMA ISR Low Volume Measurement Cell, a 20 mg/ml solution of Lysozyme was injected in the subphase and interfacial viscolelastic properties were monitored (single frequency mode, 0.1 Hz) at an air-water interface (AW) and at an oil-water interface (OW). Graph 2 gives the storage and loss moduli obtained during both experiments. The lyzozyme injection was done at time 0s. The adsorption to the AW interface had only a slight effect on the viscoelastic properties. There was no network formation, the adsorption ended to a plateau and the viscosity dominated during the whole experiment. In the OW experiment the interfacial elasticity clearly developed faster than the interfacial viscosity and a gel point was reached after approximately 11 600 s (3.2 hours).
Graph 3
Graph 3 demonstrates the capability to observe a phase transition in eicosanol by measuring changes in the viscoelastic behaviuor as a function of surface pressure. The purple crosses show the viscous modulus (surface loss, G’’) that reaches a maximum value at a surface pressure of 5mN/m while nothing is visible on the surface pressure isotherm.The blue crosses show the elastic modulus (surface storage, G’). Both G’ and G’’ reach a constant value when the surface pressure reaches approximately 15 mN/m. The value corresponds to a phase transition in the packing of the eicosanol monolayer from tilted liquid to a non-tilted liquid phase. After the phase transition value is reached the film retains some viscous properties while the elasticity is practically zero.
- KSV NIMA ISR is the most sensitive rheometer able to measure very weak elastic and viscous moduli of surfaces and interfaces.
· Innovative non-contact technology between the probe and the instrument for increased sensitivity: the magnetic field eliminates the need for mechanical connection. This is especially useful for liquid-liquid interfaces as no probe comes through the upper liquid phase.
· Low inertia hydrophobic probe for sensitivity and optimal floating at the interface.
- Static and dynamic rheological measurement options in equilibrium conditions.
- Measurements in constant surface area compared to dilational (area changing) methods.
- Easily integrated with KSV NIMA Langmuir Trough allowing precise control of monolayer packing density.
· The only rheometer enabling surface pressure measurements and monolayer compression/expansion.
- Possibility to work with volume as low as 4.7 ml when using the Low Volume Measurement Cell. It enables time and cost savings when working with valuable compounds and subphases.
- Built in data plotting option with capability of viewing multiple measurement results in one graph. Measured data can easily be exported to a data file which is readable from common plotting Software.
- Wide range of experimental parameters that can be controlled and measured in real-time:
· Frequency
· Strain
· Stress
· Temperature
· Surface pressure
· Packing density (with the KSV NIMA Langmuir Trough)
Technical specifications
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MEASUREMENT:
| Dynamic moduli resolution: |
0.001 mN/m |
| Frequency range: |
0.01 to 10 rad/s (0.0016 to 1.6Hz) |
| Strain range: |
3x10-4 to 1 |
INSTRUMENT DIMENSIONS:
| ISR with Langmuir Trough: |
L 908 mm x W 370 mm x H 700 mm |
| ISR with Low Volume Cell: |
L 190 mm x W 370 mm x H 700 mm |
(dimensions exclude the pressure sensor Interface Unit: 158 x 209 x 273 mm)
LOW VOLUME MEASUREMENT CELL (INNER DIMENSIONS):
| Lower compartment (heavy phase): |
L 120 x W 11 x H 6.5 mm (volume 4.7 ml) |
| Upper compartment (light phase): |
L 120 x W 19.6 x H 6 mm (volume 13.9 ml) |
INSTRUMENT WEIGHT:
| ISR with Langmuir Trough: |
35 Kg |
| ISR with Low Volume Cell: |
25 Kg |
Computer Operating system requirements:
Minimum system requirements: 1GHz processor, 512 MB RAM, 40 GB hard disk drive (20GB free), 1024x768 resolution, USB Port, RS-232 Port (for water bath option)
The software is compatible with Windows XP SP2 (32 bit), Windows Vista Home SP1, Windows Vista Home Premium SP1, Windows Vista Ultimate (32 bit) SP1, Vista Business SP1 (32 bit).
Specifications and appearance are subject to change without prior notice. Biolin Scientific shall not be liable for any errors in this document.