KSV Sigma 70 surface tension/contact angle meter

KSV Sigma 70 is a fully computer controlled and automatic Tensiometer for the measurement of surface/interfacial tensions and contact angles of liquids. Sigma 70 uses Wilhelmy plate or Du Nouy ring method for force measurement and its super sensitive fiber range balance operates at 0.25 mN to 25 mN range. Standard programs include automatic determination of CMC, push and pull surface and interfacial tension measurements, podwer wettability and measurement of dynamic advancing and receding contact angles. Measuring parameters are displayed on-line in clear digits on the interface unit and graphical result presentation can be monitored at the computer screen. All experimental data is stored on the hard disk and the flexible multitasking Windows software allows customized application development.

Features:

• full computer control and automatic operation of all measuring modes
• expansive Windows software programs
• uses Wilhelmy plate or Du Nouy ring method
• super sensitive fiber-range balance - up to 0.05 µN
• software controlled sample thermostation and stirring
• direct reading of sample temperature
• fully automatic dispenser for CMC measurements
• on-line digital displays of measuring parameters
• automatic calculation of ring correction values
• automatic calibration, zeroing, tarring and reset to start point
• result and graphics presented on screen
• data export to Lotus 1-2-3 or equivalent, hard disk data storage
• computer requirements IBM PC/AT compatible computer required

Performance:

• surface and interfacial tension measurements, push and pull modes
• dynamic advancing and receding contact angle measurements (DCA)
• wettability characteristics of single fibers
• automatic critical micelle concentrations (CMC) determination
• adsorption behavior measurement
• surface recovery and dehydration rate measurement
• measurement of surface free energy
• density of liquids
• critical surface tension (Zisman plot)
• determination of wetted length of solids and fibers

Options:

• on-line measurement of sample pH
• special sample vessel for temperatures up to 300 C
• evaporation preventer, thermostated double wall lid made of glass

Specifications:

Sigma 70 is fully computer controlled and automatic tensiometer for the measurement and recording of receding and advancing dynamic contact angles (DCA), surface and interfacial tensions, determinations of critical micelle concentration (CMC), and for the measurement adsorption behavior of solids. Sigma 70 uses Du Nouy ring or Wilhelmy plate method and its ultra sensitive balance is capable of characterizing wetting properties of single fibers with thicknesses of only few microns.

The system consist of three units. An Interface Unit equipped with on-line digital displays,   the Measuring Unit and an optional  Dispenser Unit for CMC dilution Unit.

Electronic micro balance

The balance, the force measurement sensor, is the heart of a tensiometer and crucial to all measurements is its accurate and reproducible operation. Because the forces acting upon the surfaces and interfaces are extremely minute and dynamic the balance must be capable of swift response to the lowest of force changes. Sigma balance detects forces as low as approx. 0.05 µN. Such a small force measurements are typical in wettability studies of single fibres. Sigma's micro electro balance works on a moving coil principle where the arm of the balance is held at constant position by controlling and regulating the electric current fed to the coil.

The maximum load of the balance is 25 mN (2.5 g). There are three measuring ranges to select from. 0.25 mN, -2.5 mN and 25 mN and resolutions respectively 0.01 µN, 0.1 µN and 1 µN. Tarring and calibration is automatic. Balances with heavier load ranges and holders for fibres and other non ideal samples are available by special order. Du Nouy ring is of platinum/iridium and made to DIN 53914-80 and ASTM D 971.

Measuring cup and sample temperature control
Standard measuring cups are 50 or 70 mm in diameter and the sample temperature is regulated by a sensor interfaced to a computer controlled bath/circulator. If sample thermostation is not needed plates or vessels up to max. 120 mm in diameter can be placed on the stage. Standard features include temperature measurement from the water jacket or optionally the temperature is measured directly from the sample by a special needle-like sensor probe. To provide maximum insulation and to prevent heat loss the water jacket is made of solvent resistant plastic. Temperature range is from -10 to +100 C.
The built in magnetic stirrer operation is computer controlled. Snap-in, precision water connectors make tube removal from the water jacket easy. Wide opening transparent doors provide easy access to the measuring chamber and protect the sample and probe from air borne particles and draft.

Vertical moving of the sample
Pulling and lowering of the probe i.e. ring, plate, fiber etc. is arranged by moving the liquid sample vertically while the probe is stationary. The measuring cup is placed into the thermostated jacket fixed onto a stage. The vertical movement of the stage is powered by a high accuracy DC motor to ensure smoothest possible ride of the stage . The rotational power of the motor is converted into vertical movement via tooth belt which turns the precision screw. The screw moves the stage shaft up or down depending on the direction of the screw rotation. All the stage movements and speeds are software controlled and user programmable. The length of shaft movement is 140 mm and speed is adjusted in 0.1 mm increments within speed range from 0.1 to 40 mm/min *(1.7 to 667 m/sec). An optional manual control key pad may be used to move the cup without computer control.
Interface Unit
The Interface Unit is in fact a power supply which acts as an interface between the computer, Dispenser Unit and the Measuring Unit. It houses on-line digital display for the measuring parameters such as, temperature, dispensing volume, stage position and surface tension - all of them displayed simultaneously. Readings of the surface tension can be selected in mN, dyne/cm and temperature in Centigrade or Farenheit. Digital display card provides on-line visual status of selected measuring parameter. The card and is easily mounted into its slide-in slots by hand. Anti reflection panel in front of the digits makes the reading easy for the eyes.
Dispenser Unit
Sigma70 automates the Critical Micelle Concentrations (CMC) measurement without need for the user to interrupt with tedious manual dispensing and control procedures. The Dispenser Unit takes care of it all. Just select the CMC program from menu and enter the required dispensing data i.e. - delivery volume(s), sample delivery and stirrer activation sequences, concentration and surface tension values - after that everything is automatic.
The software
The Sigma 70 Windows software includes programs for most of the known and standardized surface and interfacial tension measurements by the Du Nouy ring or Wilhelmy plate method. The list of standard experiments is extensive including software for specialized experiments such as CMC, surface tension,contact angle powder wetting and fiber wetting. All these are included in your software package with out any extra charge. For more on software click here.

Surface and interfacial tension measurements

Du Nouy ring method

In this method the force required to detach a ring from a liquid surface or interface is measured. The detachment force is proportional to the surface or interfacial tension ,s, by the expression s=kf, where F is the force pulling the ring out of the liquid and k is the factor for certain complex mathematical corrections values deriving from a physics of curved interfaces and for geometrical dimensions of the ring.

Wilhelmy Plate method

The Wilhelmy plate method can be applied for measurement of surface and interfacial tensions liquids. The method incorporates a micro roughened platinum plate suspended from the Sigma 70 balance. The plate is withdrawn from the liquid and the weight of the liquid lifted by the plate is measured. The weight of the liquid held up above the bulk of the liquid surface increases to some maximum value which equals the surface tension times the length of the contact line in between plate and the liquid while the lower edge of the plate is kept stationary at level of the surface of the bulk of the liquid.

Static measurement
The sample surface is lifted until it comers into contact and "jumps" onto the plate. Plate is wetted by a capillary force which is directly proportional to the surface tension.

Dynamic measurement
The sample is completely immersed into the sample and then lifted through the surface until the maximum force is reached. The plate is not detached from the surface but, as in the repetitive ring method, lowered a bit and then again pulled to the maximum.

Dynamic Contact Angle measurement
Measurement of dynamic contact angles provides information on the properties of surfaces such as porosity and homogeneity, surface topography and reactivity. The method is based on the Wilhelmy plate principle where the solid sample is held by the electro balance and then dipped or pulled from the substance. Therefore the weight of the sample alternates depending on direction of the movement. The force changes obtained are directly proportional to the contact angle. The contact angle is the angle formed by the tangent to the point of contact at the solid/liquid interfaces. As the solid sample penetrates the surface and dips into the liquid a advancing contact angle is determined and the pull of the sample from the substance provides receding contact angle information.
  The progress of the experiment is expressed in form of graphical buoyancy slope where the x axis represent the immersion depth and the y-axis the force. The contact angles is calculated from the force versus depth information.


CMC measurement
Surface active molecules, surfactants, concentrates at the surfaces or interfaces of liquids. Surfactant molecules have polar and non-polar ends. At the interface the end of the molecule least compatible with the molecules in the bulk of the liquid orients itself to the next phase.
    By adding surfactant molecules into the solvent they at some certain concentration form a monolayer at the interface. If concentration is increased beyond this point the surfactant molecules are forced into the bulk of the solvent where they start forming molecule groups called micelles.
     After the formation of the monolayer the surface tension stabilises. This stabilising point is called critical micelle concentration, CMC, and it is characteristics to a given surfactant.

CMC software
CMC software is included in the KSV Sigma 70 software package. The whole measuring process is fully automatic and you can use either plate or ring method. The programming of all dispenser operations, stirring activation, balance adjustments, stage movement and temperature data are entered into program by filling out the pull down experimental set up window.

Adsorption measurements
Adsorption measurements are used to study wetting behaviour of porous solids like medicine tablets, paper and pulp products etc. The sample is hooked to the balance and the liquid is raised until it slightly touches the sample resulting in a significant increase of force. After the contact of the solid and the liquid the weight of the sample increases as the liquid climbs up its surface. The focus of the interest of this specific measurement is in how long it takes until a constant contact angle is formed in between the solid sample and the liquid.

Adsorption software

• measurement of advancing and receding contact angle
• linear or logarithmic graph presentation
• weight progression vs. time
• data acquisition in linear or logarithmic time intervals

• Accessories:
  

  Code	Description
  T101	Dispenser computer controlled and software operated peristaltic dispenser for automatic measurements of CMC. Complete with all accessories for serial or single sample dilution.
  T102	Bath/circulator constant temperature bath/circulator, for sample liquid temperature regulation. Software controlled, fully automatic operation. Temperature range -30 to +130 C°. Stability 0.01 C°. Digital readout.
  T104	Sample Vessel fireproof, diameter 70 mm, 5 pcs/box
  T105	Sample Vessel fireproof, diameter 50 mm, 5 pcs/box
  T106	Du Nouy ring Pt-Ir-ring made to DIN 53914-80 and ASTM D 971 specifications. Packed in wooden box.
  T107	Wilhelmy Plate, platinum plate with micro roughened surface
  T108	Ring re-form tool for straightening of disformed Du Nouy ring.
  T109	Sample holder for plates. For rigid plate like samples. Max. sample thickness 3 mm.
  T110	Sample holder for plates. For flexible plate like samples. Max. sample thickness 3 mm.
  T111	Sample holder for fibres. Single use aluminium tube hanged from balance hook. 10 pcs/bag

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