The relationship between stresses and deformation defines the rheological properties of a film. Most systems encountered in industry and in biology are viscoelastic films where these relationships are nonlinear and intermediate between purely viscous and purely elastic responses. The rheological properties are extremely important for defining product stability in different industries such as food, petrochemical, cosmetics, and pharmaceuticals. For example protein layers and polymers are strong stabilizers in dispersion and typically used in the food industry for foams and emulsions. In the petrochemical industry oil extraction is performed in multiple steps where oil-water and water-oil emulsions are formed to recover oil and later on destabilized to separate the two phases. Many different kinds of emulsifiers, pigments and stabilizers are widely used in cosmetic and pharmaceutical industries such as lotions, creams and hair sprays.
- 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. |
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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 graph below shows two curves of compliance that are plotted as functions of time. The straight, gray line is the linear response of a Newtonian phase of arachidyl alcohol. The inverse of the slope of the curve is the surface viscosity of the layer. The blue line is the nonlinear response of a monolayer of the amphiphilic polymer Poly(octadecyl methacrylate), which shows a highly viscoelastic and non-Newtonian response.
The second graph illustrates the evolution of the interfacial viscosity of a monolayer of the protein lysozyme residing between water and decane plotted as a function of time. Also plotted is the surface pressure of the layer. This data shows the evolution of the adsorption and crosslinking of the protein as a viscoelastic “skin” develops at the interface as a function of time.
The third graph demonstrates the capability to observe phase transition as function of surface pressure. The viscoelastic properties of eicasanol is shown to have interesting behavior as a function of surface pressure. The red dots show the Viscotic modulus (surface loss, G’’) which reaches a maximum value at a surface pressure of 5mN/m and the black crosses show 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 liquid untilted phase. After the phase transition value is reached the film retains some viscous properties while the elasticity is practically zero.
- ISR can measure very weak elastic and viscous moduli of surfaces and interfaces.
- Low inertia hydrophobic probe for sensitivity and optimal floating at the interface
- Innovative non-contact connection between the probe and the instrument. Magnetic field eliminates the need for mechanical connection, increasing sensitivity.
- 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
- 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
Technical specifications
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| Dynamic moduli resolution: |
0.001 mN/m |
| Frequency range: |
0.01 to 10 rad/s (0.0016 to 1.6Hz) |
Strain range:
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3x10-4 to 1 |
Dimensions:
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908mm x 370mm x 600mm (L x W x H) |
| Weight: |
40kg |
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).
Compatibility
The KSV NIMA ISR software is fully compatible with the KSV NIMA Langmuir Blodgett instrument andsoftware. The real time surface pressure can be recorded with surface dynamic modulus data allowing easy observation of rheological changes as a function of surface pressure.
Specifications and appearance are subject to change without prior notice. Biolin Scientific shall not be liable for any errors in this document.