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POLYMER SOLUTIONS AND GELS GROUP

Rheology Microrheology Viscosimetry Scattering Conductivity Osmometry Other Instruments

Our group uses rheological and vicosimetric techniques to understand the dynamics of polymeric systems, especially polylelectrolytes. Scattering techniques are used to probe the structure of these systems. For this purpose, we use in-house instruments, as those listed in this section and also carry out experiments at synchrotrons and nuetron sources. Here you can find some information about the various instruments available in our labs and the kind of data that these yield. For some of the techniques a brief outline of the principles underlying the measurements is given - this is still work in progress. In addition to the rheology and scattering equipment, we also have have some conductivity and osmometry equipment to study the thermodynamics of polyelectrolyte solutions. Our other equipment include a high precision density meter, a refractometer, a freeze dryer, phase mapping apparatus, a UV-curing source, a laser micrometer and an ultrasonicator.

RHEOLOGY

Kinexus Ultra

This is our main rheometer to study polymer solutions. It is a controlled-stress rheometer which combines high sensitivity, with a minimum torque in steady shear of 1 nNm with an efficient solvent trap, which prevents sample evaporation for moderately volatile solvents.

The following geometries and accessories are available:

With our current setup, the accessible temperature range is 0-150 °C - this can be extended to -25°C if connected to an external circulator. For samples requiring a broader temperature range, the MCR302e can be used.

The maximum shear rate for low viscosity solutions is a few hundred s-1, before Taylor instabilities set in. The specific value depends on the viscosity and elasticity of the sample and the geometry employed. For concentrated polymer solutions, a few thousand s-1 can be reached before viscous heating and/or sample expulsion become significant. Measurements at higher shear rates can be performed with the m-VROCii rheometer.

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Kinexus Ultra rheometer

MCR302e

This is our main rheometer to study poly(ionic liquid) gels, which usually have glass transition temperatures on the range of -80 to -50°C. As the Kinexus ultra, this is a controlled-stress rheometer. The minimum torque is ≈ 1 nNm in steady shear and 0.5 nNm in oscillatory. The normal force can be varied between -50 N to 50 N.

The following geometries and accessories are available:

With our current setup, the accessible temperature range is -80°C to 400 °C - this can be extended down to -150°C if connected to a liquid nitrogen tank.

As with the Kinexus rheometer, the maximum shear rates that can be applied are limited, and the m-VROCii can be used to extend the measuring range.

A UV lamp can be connected to the rheometer to study light induced polymerisation or cross-linking processes.

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MCR302 rheometer and electrically heated device used for temperature control.

m-VROCii

The m-VROCii is a microfluidic rheometer. TheThe test fluid is flown though a straight channel. The volumetric flow is set by the speed of the pump and the pressure is measured by four pressure sensors at different positions along the channel. The principle of operation is similar to that of capillary viscometers - the main difference being that in the m-VROCii the flow rate is imposed and the pressure measuered while in the capillary systems the pressure is imposed (gravimetrically) and the flow rate is measured. Overviews of microfluidic rheometers can be found here and here .

The shear-rate accesible with the mVROCii depends on the chip dimensions and on the viscosity of the samples and can be as high as 2×106 s-1 for low viscosity samples.

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TriPAV- High Frequency Rheometer (coming soon)

The TriVAP is a piezo-electric squeeze-flow rheometer. The accessible frequency range is from 1 to 10,000 Hz. A frequency sweep can be carried out over the entire frequency range in under 5 minutes.

The samples are contained in a hermetically sealed chamber which requires less than 0.1 ml of sample.

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Contraves LS-30 (under repair)

The Contraves LS-30 is a cup-and-bob creep rheometer which offers exceptional accuracy for low viscosity samples at low shear rates. This is useful to study non-entangled solutions of high molecular weight polymers, and especially polyelectrolytes in salt-free solvents, where the relaxation time increases upon dilution.

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SAMPLE ENVIRONMENTS & ACCESSORIES FOR RHEOLOGY

The Kinexus and MCR rheometers can be used with various geometries, see the table below. In addition to these, we have several accesories that can be used on the Kinexus or in the DHR-30 and ARES-G2 rheometer from prof. Colby's lab. Generally, solution work is best carried out using cone-plate geometries as these ensure a constant shear stress is applied throughout the sample. Plate-plate geometries are better suited for samples containing large particles or for elastomer samples.
Geometry Instrument
Double Gap Kinexus
Cone-Plate Kinexus (\(\phi = \) 40 mm, 1\(^\circ\)), MCR302e (\(\phi\) = 50 mm, 1\(^\circ\))
Plate-Plate MCR302e (8-50 mm), DHR30 (25 mm)
Couette Kinexus, DHR30, Contraves
Disposable plates Kinexus
List of geometries available.
In addition to rheoloigcal characterisation with the geometries listed above, the following setups are available:
Equipment Rheometer
Orthogonal Superposition Rheology DHR30
Rheo-Dielectric Spectroscopy DHR30
UV-Curing Setup MCR502/MCR302e
Light Scattering MCR502/MCR302e
Environmental Test Chamber DHR30
DMA: Torsion and Tension ARES-G2

Orthogonal Superposition Rheology

Shear rheology measurements are conventionally carried out either in steady or in oscillatory mode. Steady shear experiments such as creep tests can be used to, for example, evaluate the dependece of the viscosity on shear rate. Oscillatory shear experiments are usually discussed in terms of the loss G\(^{''}\) and storage modulus G\(^{'}\). Orthogonal superposition rheology is a technique which allows for steady and oscillatory shear to be simulataneously applied to a sample. For this, a Couette geometry is used. The bob rotates around its vertical axis (see orange arrows on the figure), imparting steady shear on the sample in the azimuthal direction. Additionally, the bob oscillates in the axial direction (blue arrow), thereby imposing an oscillatory flow in a perpendicular direction to the steady shear.

This setup is available for use with the TA DHR30 rheometer, the temperature is controlled with the Environmental Test Chamber described below. Further details about this technique can be found on the TA website .

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Image courtesy of TA instruments

Rheo-Dielectric Spectrocopy

A parallel plate geometry, where both plates act as electrodes can be used with the DHR-30 rheometer, combined with the ETC for sample environment control. An oscillating voltage is applied to the plates using the Keysight LCR meter (see below for more details on this instrument). This setup allows us to study the dielectric properties of solutions and gels as a function of applied shear. The Keysight LCR meter has a frequency range of 2Hz-300kHz, which for aqueous polyelectrolyte solutions allows us to measure the conducitivty of solutions but not relaxation processes related to counterion polarisation.

UV-Curing setup

The MCR302 rheometer can be set up with a transparent bottom plate through which UV or visible light of different frequencies can be shone. For details on the Omnicure light source, see below. This setup is particularly useful to monitor cross-linking processes, where the storage modulus and the loss tangent can be related to the degree of cross-linking. For the top geometry, either disposable plates or disposable cones can be used.

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Image courtesy of Anton Paar

Rheo-light scattering

The MCR302e rheometer can be configured in a small angle light scattering (SALS) setup. The light scattered from a sample under flow is measured using a CCD camera.

Environmental Test Chamber

The Environmental Test Chamber (ETC), depicted with a DMA accesory on the image to the right, allows the temperature to be changed between -160 °C to 600 using radiant and convective heating. The specific lower temperature ranged is determined by the cooling system employed. Currently, it is set up with the TA Air Chiller System, which can take the ETC down to -80°C without using liquid nitrogen. For lower temperatures, it is necessary to hook up the ETC to a liquid nitrogen dewar. The maximum heating rate of 60 °C/min.

The ETC is used to control the sample enviroment with the orthogonal superposition rheology and dielectric spectroscopy accessories.

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Image courtesy of TA Instruments


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MICRORHEOLOGY

Broadly defined, microrheology refers to a series of techniques used to study the mechanical properties of materials at the nanoscale and mesoscale. An overview of the various methods which have been developed over the last two decades can be found here,. A major advantage of microrheological techniques over conventional rotational rheometers is that they can access much higher frequencies. The figure on the right gives a rough estimate of the capabilities of various techniques. Rotational rheometry cannot susuallya access frequencies larger than ≈100 rad/s. Within that range, it is possible to measure moduly of up to GPa. In DLS-microrheology, samples are loaded with spherical particles with dimaters of a few hundred nanometers. The autocorrelation of the sample is measured and assuming a negligible contribution from the sample, the mean-squared displacement of the particles as a functio of time is calculated. The generalised Stokes-Einstein equation then allows for the storage and loss modulus to be evaluated. Frequencies of up to a few kHz are typically attainable, depending on the sample characteristics. Diffusing wave spectroscopy (DWS) also works by loading the samples with tracer particles, but in this case the concentration is sufficiently high to cause light to be scattered multiple times before it reaches the detector. DWS is usually run in back-scattering geometry. Our lab is equipped with two microheology instruments:

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Image courtesy of LS Instruments AG
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VISCOSIMETRY

In addition to the rheometers and microrheology instruments discussed above, we have a range of intstruments to measure the viscosity of fluids. These include a spinning ball viscometer , an automated rolling ball viscometer, a Stabinger viscometer and a range of capillary viscometers. . Each of these has different adavantages in terms of accuracy, sample volume, measuring time, viscosity range, sample environment etc, which you can find at the end of this section.

EMS-1000S

Samples for the EMS-1000s viscometer contained in a sealed vial, with a metal ball (Aluminium or titanium) is submerged in the liquid. A pair of magnets rotates around the lower part of the vial, causing the ball to rotate. The speed of rotation is recorded and the viscosity of the fluid is calculated. The shear rate range can be varied by changing the speed of rotation of the magnets. The accessible shear rate range depends on the sample's viscosity and the metal ball used. The minimum sample volume required depends on the size of the metal sphere (0.7 mL for \(\phi = 4.7 mm\) and 0.3 mL for \(\phi = 2 mm\)). A low sample volume option is available, which requires only 90 \(\mu L\) of sample. This option works for samples with viscosities in the 0.1-1000mPas range.

A key advantage of this viscometer is that it offers the possibility of measuring samples in a sealed vial. This allows highly volatile solvents to be measured. Samples can also be prepared in a CO\(_2\)-free atmosphere with relative ease.

More information about the instrument can be found on this website.
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EMS viscometer

LOVIS

The LOVIS is rolling ball viscometer where the shear-rate can be controlled by varying the inclination angle. The sample is contained inside a glass capillary and a metal ball, which has a higher density than that of the solution, is allowed to fall down the capillary. The time it takes for the ball to travel through the capillary is measured and used to calculate the kinematic viscosity of the fluid. The inclination can be varied between 15° and 80°, which varies the speed at which the ball travels down the capillary, thereby varying the shear rate. Three capilaries with different internal diameters can be used for measuring samples with different viscosity ranges:

Capillary ID [mm] Full angle viscosity range [mPas] Limited angle viscosity range [mPas]
1.59 1-90 0.3-20
2 2.5-1700 13-300
2.5 70-1700 12-10000

with the smallest capillary, the shear rate applied can be varied between (200-800/η)s^-1, where η is the viscosity in mPas. Because the speed of the ball travelling down the capillary varies inversely with the solution viscosity, the applied shear rate decreases as the viscosity increases.

LOVIS
LOVIS viscometer

SVM 3001 Cold Properties (Anton Paar)

The SVM3001 instrument is a Stabinger Viscometer. The instrument can measure in the temperatuere range of -60 °C to 100 °C. In addition to the viscosity, the instrument measures the density (reproducibility 0.0001 g/mL), the cloud point (reproducibility ≈ 2.5 °C) and freeze point (reproducibility ≈ 1.3 °C) of fluids. The applied shear rate depends on the viscosity of the sample. As with the LOVIS instrument, the higher the sample viscosity, the lower the shear rate at which the measurement is performed.

Vapro
SVM3001 cold-properties

Capillary viscometers with automated flow time detection

Measuring principle

For a Newtonian fluid flowing through a capillary, the flow time is given by the Hagen–Poiseuille equation:

\[ Q = \frac{\pi \cdot r^4 \cdot \Delta P}{8 \cdot \eta \cdot L} \]

where the symbols have the following meanings:

In capillary viscometers, the time taken for a fixed volume of fluid to flow through a capillary of known diameter and length is measured. The flow time (\(t_{flow}\)) can be determined visually or with an automated sensor. The average flow rate is given by the product of the cross-section of the capillary (\(\pi r^2\)) and the average velocity of flow (\(L/t_{flow}\)). The pressure drop across the capillary is a function of the liquid density and viscometer geometry. It is common to express the kinematic viscosity (\(\nu\)) of a fluid as:

\[ \nu = Kt_c \]

If end-effects are neglected, \(t_c\) corresponds to the flow time through the capillary, i.e. \(t_c = t_{flow}\). This is a good approximation when flow times are long but becomes increasingly problematic for short flow times, where the 'Hagenbach-Couette' or kinetic energy correction need to be applied, so that \(t_c =t_{flow} - t_{HC} \), where \(t_{HC}\) is a function of \(t_{flow}\). The values of \(t_{HC}\) are provided by the manufacturer for each viscometer type.

The constant K for a given capillary can be determined by measuring a fluid of known viscosity.

For Newtonian liquid (viscosity is independent of the shear rate), the shear rate at the wall of a capillary viscometer can be shown to be:

\[ \dot{\gamma} = \frac{4Q}{\pi r^3} \] where the symbols have the same meaning as above. For typical viscometers, this turns out to be around ~1000 s\(^{-1}\).
Vapro
Ubbelohde viscometer. R1 and R2 marks correspond to the fluid position at t = 0 and t = \(t_{flow}\)

Water bath and automatic detection system

A water bath from Cannon Instrument, model CT-518, in combination with an immersion chiller, this allows the temperature of the capillary viscometers to be controlled between 20-100 °C, with a stability of ≈ 0.01 °C. The bath is 46 cm deep, so that long capillary viscometers can be submerged in it. Flow times can be recorded manually with the help of a chronometer or using the Lauda automatic iVisc detection system. The iVisc system is controlled with a computer. It can be programmed to draw the solution into the capillary tube, release it, and record the time taken for it to flow down the capillary using an IR sensor. This is typically repated 3-6 times to accurately determine \(t_{flow}\). The iVisc system works with single capillary Ubbelohde viscometers, as shown in the picture above. It cannot be used for other capillary vicometers such as the multiple bulb Ubbelohde or the Cannon-Fieske viscometers. We have a range od different capillary viscometers available in our lab which cover different viscosity ranges and volume requirements. These are listed on the tables below.

Automatic detection system for capillary viscometers
Automatic detection system.

Capillary viscometers

Ubbelohde Viscometers

These viscometers require a volume of ≈ 20 mL. They are compatible with the Lauda iVisc automatic detection system.
Type K [mm²/s²] viscosity min [mm²/s] viscosity max [mm²/s]
0 0.001 0.3 1
0C 0.003 0.6 3
0B 0.005 1 5
1 0.01 2 10
1C 0.03 6 30

Low volume Ubbelohde viscometers

This type of viscometer requires ≈ 1 mL per sample (Cannon viscometers) or ≈ 2 mL per sample (Lauda viscometers). Automatic detection is possible with the Lauda viscometers. We have the following types available in our lab.
Manufacturer Size K [mm²/s²] viscosity min [mm²/s] viscosity max [mm²/s] Automatic detection
Cannon 25 0.002 0.4 2 No
Lauda I 0.01 0.3 6 Yes
Lauda III 1 30 800 Yes

Cannon-Manning Semi-Micro Viscometer

This type of viscometer requires only ≈ 0.5 mL per sample. Automatic detection is not possible. We have the following types available in our lab.
Size K [mm²/s²] viscosity min [mm²/s] viscosity max [mm²/s]
25 0.002 0.4 2.0

Shear dilution Ubbelohde viscometers

One of the major drawbacks of capillary viscometers is that they apply relatively high shear rates. For high molecular weight polymers, this means that measurements do not always correspond to the zero-shear rate value. This problem can be partially overcome my using capillary viscometers with varying capillary diameters. For this purpose, we have the following viscometers available, which provide a range of ×10 in shear rate. They can be operated with the same viscometer bath as the other systems. Automatic detection is not possible.

Catalog no. Size K [mm2/s2] viscosity min [mm²/s] viscosity max [mm²/s] shear rate min [s-1] shear rate max [s-1]
9723-M50 (x10) 25 0.002 0.4 2 82 3300
9723-M53 (x10) 50 0.004 0.8 4 45 1800
9723-M50 (x5) 25 0.002 0.4 2 82 1650

A water bath from Cannon Instrument, model CT-518, in combination with an external water re-circulator allows the temperature of the capillary viscometers to be controlled between 20-100 °C, with a stability of ≈ 0.01 °C. The bath is 46 cm deep, so that long capillary viscometers can be submerged in it. Flow times can be recorded manually with the help of a chronometer.

Vapro

The table below summarises the various advandtagres of the viscometers, considering different performance metrics. Capillary viscometers offer the best accuracy, but this comes at the expense of measuring time and sample volume.
Instrument Sample Volume Viscosity Range Accuracy Temperature Range Measurement Time Shear Rate Range Sample Environment
EMS-1000S ≈ 0.3-0.7 mL, (\(90\ \mu L\) with low volume option) 0.1-100000 mPas ≈ 3% 0-200°C, 0-50°C (small sample volume) < 1 min Variable Sealed Environment
SVM-3001 Cold properties ≈ 3 mL 0.2-30000 mPas ≈ 1% 0-60°C (lower T can be extended with external chiller) ≈ 1 min 1-1000s\(^{-1}\), depends on sample viscosity Capillary tube
LOVIS ≈ 2 mL 0.5-90 mPas (upper range can be extended with wider capillaries) ≈ 1% ≈ 5-90\(^{\circ}\)C ≈ 5-30 min, depending on solvent viscosity 200-800\(^{-1}/\eta\), with \(\eta\) in mPas Capillary tube
Capillary viscometer with automated detection ≈ 2-20 mL, depending on viscometer ≲ 10 mPas ≈ 0.35% ≈ 20-60\(^{\circ}\)C ≈ 10-30 min ≈ 90-2000s\(^{-1}\), depending on viscosity Open capillary
Shear dilution Ubbelohde ≈ 20 mL ≲ 10 mPas ≈ 0.35% ≈ 20-60\(^{\circ}\)C ≈ 5-20 min ≈ 800s\(^{-1}\) Open capillary


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OSMOMETRY

MEMBRANE OSMOMETERS

Donnan equlibrium of polyelectrolytes

BMT 923 (coming soon)

The BMT 923 'onkometer' is a membrane osmometer designed to measure the properties of physiological fluids. The maximum measurable osmotic pressure is 99.9 mmHg or around 13 kPa. For higher osmotic pressures, the osmomanometer can be used. More information about this instrument can be found here.

Osmomanometer (under construction)

Membrane osmometers are extremely useful to study the thermodynamic properties of polyelectrolyte solutions. Dialysis membranes are typically permeable to solvent and salt molecules but not to polyelectrolytes. If a polyelectrolyte solution is dialyzed against a salt solution and the osmotic pressure is measured, the polymer contribution to the osmotic pressure can be calculated. This differs from vapor pressure and freeze point depression osmometers, where the oncotic osmotic pressure, which contains contribution from both the polyelectrolyte and salt molecules is measured. Although membrane osmometry was standard characterisation technique in polymer science for several decades, its use has declined. Today, membrane osmometers are not commercially available. Raspaud suggested the construction of a simple osmometer, named the osmomanometer, see this article for details. We are in the process of setting up this instrument.


VAPOUR PRESSURE OSMOMETERS

Vapro 5600 osmometer

Our lab is equiped with the Elitech VAPRO 5600 and Wescor 5500 osmometers. Some of the main characteristics are listed on the table below. Literature studies on the osmotic coefficient of polyelectrolytes in salt-free solution using vapour osmometry can be found here , here and here .

Sample Volume <0.1 mL.
Osmolality range 0 - 3200 mmol/kg
Measurement Time 90 seconds.
Resolution 1 mmol/kg.
Repeatability 2 mmol/kg Standard Deviation.
Linearity ± 1% of reading over calibrated range (100 mmol/kg - 1000 mmol/kg) ± 5% < 100 mmol/kg and > 1000 mmol/kg up to 3200 mmol/kg ± 10% > 3200 mmol/kg.
Vapro
Vapro 5600 Osmometer

Wescor 5500

This instrument was designed to analyse biological samples. It operates at 37C and works best for high osmolarities (\(\gtrsim 100\) Osm).
Temperature 37 °C
Sample Volume 10 μL.
Osmolality range 0 - 2000 mmol/kg
Measurement Time 60-90 seconds.
Resolution 1 mmol/kg.
Repeatability 2 mmol/kg Standard Deviation.
Linearity ± 1% of reading over calibrated range (100 mmol/kg - 1000 mmol/kg) ± 5% < 100 mmol/kg
Vapro
Wescor 5500 Osmometer

Knauer K7000 (under repair)

The K-7000 instrument can be used for osmometry of solutions organic solvents. A manual of the instrument can be found here. .
Concentration range 1 x 10-3–15 molal
Sensitivity 3.3 x 10-5 mol/kg in toluene and 1.7 x 10-4 mol/kg in H2O
Sample volume approx. 10 µl (one drop)
Number of samples up to 4 samples
Test time 1.5–5 Minutes per measurement
Working temperature 20–130 °C
ΔT head thermostat 0–6 °C
K7000
Knauer K-7000

FREEZE POINT DEPRESSION OSMOMETERS

Freeze point osmometers work by super-cooling a solution several degrees below the freezing point. A mechanical disturbance is then applied to induce ice formation, which is accompanied by the release of heat of fusion. This increases the temperature of the solution until its freezing point. The decrease in freezing/melting point of water (\(\Delta T\)) can be related to the osmotic coefficient of the solution. Specifically, using the crysocopic constant of water of K = 1.858 mK/osmomol, the osmotic coefficient of a solution is: \(\phi = \Delta T/(1.858c) \), where c is the concentration in moles per liter. For an overview of the principles and limitations of freeze-point depression osmometer, see this article.

OsmoTECH XT

The OsmoTECH XT is a freeze point depresion osmometer. An advandtage of the OsmoTECH XT over conventional freezeing point osmometers is its ability to handle viscous samples. Details of the instrument performance and sample requirements are listed on the table below.

Parameter Value
Sample Volume 20 μL
Test Time (Low Range) ≤150 seconds
Test Time (High Range) ≤190 seconds
Resolution 1 mOsm/kg H₂O
Osmolality Range 0 to 4000 mOsm/kg H₂O
Accuracy (0-400 mOsm/kg H₂O) ±2 mOsm/kg H₂O from nominal value
Accuracy (400-1500 mOsm/kg H₂O) ±0.5% from nominal value
Accuracy (1500-4000 mOsm/kg H₂O) ±1% from nominal value
Within-Run Repeatability (0-400 mOsm/kg H₂O) Standard deviation ≤2 mOsm/kg H₂O
Within-Run Repeatability (400-1500 mOsm/kg H₂O) Coefficient of variation ≤0.5%
Within-Run Repeatability (1500-4000 mOsm/kg H₂O) Coefficient of variation ≤1%
Vapro
Osmotech-XT

Knauer K-7400S Semi-Micro Osmometer (coming soon)

The Knauer K-7400S Semi-Micro is a freeze point depresion osmometer. Details of the instrument performance and sample requirements are listed on the table below. For this osmometer, the time-temperature curve can be seen using the EuroOsmo software.

Parameter Value
Sample Volume 150 μL
Test Time 2 minutes
Resolution 1 mOsm/kg H₂O
Osmolality Range 0 to 2000 mOsm/kg H₂O
Precision (0-400 mOsm/kg H₂O) ±4 mOsm/kg H₂O
Precision (400-2000 mOsm/kg H₂O) ±1%
Knauer
K-7400S

Hygro-osmometer (under construction)

Zhan et al proposed a simple idea to measure the osmotic pressure of aqueous solutions using a relative humidity sensor.



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SCATTERING

Multi-angle SLS/DLS

We use a Brookhaven 2000-BI instrument from Prof. Gomez's lab to study the structure and dynamics of polymers in solution. Some characteristics of this instrument are listed below.

Click on the subheadings below to see how the static and dynamic light scattering techniques can be applied to study polymers and polyelectrolytes in solution.

Static light scattering

Dynamic light scattering

Combined Static and Dynamic light scattering

BeNano Zeta-pro 180

The BeNano Zeta-pro 180 perfoms three light scattering techniques: static light scattering, dynamic light scattering and electrophoretic light scattering. For samples such as protein solutions, this allows the particle size, zeta potential and molecular weight, to be determined. Additionally, samples are loaded and the DLS measurement can be used to perform microrheology experiments.

The instrument is equiped with a solid-state 50 mW red laser (λ = 671 nm) and avalanche photodiode detectors. SLS and DLS can be performed at angles of 90° and 173° (backscattering). For small particles such as proteins, for which the scattering intensity is q-independent in the light scattering range, the weigth average molar mass and second virial coefficient can be obtained from SLS and the hydrodynamic radius and diffusion virial coefficient can be obtained from DLS.* Electrophoretic light scattering is performed at 12°. In the back-scattering mode, the instrument can perform non-invasive back-scattering, which is useful to prevent multiple scattering in concentrated samples.

*Light scattering at single angle

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Electrophoretic light scattering

Xenocs 2.0 (Materials Characteirsation Lab)

In addition to the Xenocs instrument at the Materials Characterisation Lab, we use the BL40XU beamline at the Spring-8 synchrotron.


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CONDUCTIVITY & POTENTIOMETRY

SevenExcellence S475 pH/mV/ION and Conductivity Meter

The SevenExcellence instrument can be used to measure the electrical conductivity and pH of solutions. Additionally, it is possible to use ion-selective electrodes to determine the concentration of different ions. A list of the various probes available can be found in the table below:

Model number  Type  Notes  Range 
INLAB 720 ELECTRODE  Conductivity  2 platinum poles conductivity cell  0.1 – 500 µS/cm 
PROBE CONDUCTIVITY 741  Conductivity  2 steel poles  0.001 – 500 µS/cm 
INLAB 710 ELECTRODE  Conductivity  4 platinum poles  10 – 5×105 µS/cm 
PROBE CONDUCTIVITY 731  Conductivity  4 graphite poles  10 – 106 µS/cm 
SODIUM ELECTRODE W/S7 HEAD  Ion Selective electrode  Na+  1×10-7 – 1 mol/L 
POTASSIUM ELECTRODE WITH BNC  Ion Selective electrode  K+  1×10-6 – 1 mol/L 
PH ELECTRODE INLAB ROUTINE PRO  pH Electrode  12 mm shaft  0-14 
INLAB MICRO PRO-ISM ELECTRODE  pH Electrode  5 mm shaft  0-14 
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2-electrode cells typically display greater sensitivity and are hence more suited for low conductivity samples, such as solutions in apolar organic solvents. 4-electrode probes are better suited for solutions with higher conductivity and are less affected by electrode polarisation. For salt-containing solutions, the LCR Meter from Keysight should be used to make sure that the conductivity is measured over a frequency range over which electrode polarisation effects are not important.

BeNano Zeta pro 180

In electrophoretic light scattering mode, the BeNano measures the conductivity of samples by applying an oscillating electric field with a frequency of ≈ 200 Hz. The electrodes are 1 cm appart magnitude of the field can be tuned between 1 and 200 V. Working at low electric fields helps mitigate electrode polarisation. While less precise than the conducitivty meter, conductivity measurements on the BeNano instrument require less sample volume (≈ 1-1.5 mL), and the sample is contained in a sealed environment, thus preventing evaporation. Measurements can be run over a temperature range of 10-70 °C. U-shaped capillary cells are available for aqueous samples and a dip cell is available for organics.

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Keysight E4980Al LCR Meter (coming soon)

As mentioned above, electrode polarization can be a problem when studying the conductivity of salt-containing solutions, see this this document, written by Prof. Ralph Colby for a detailed explanation of the phenomenon. The Keysight E4980AL LCR Meter can be used to measure the electrical impedance of solutions to be measured in the range of 20Hz to 300 kHz, which allows the conductivity of solutions to be obtained without electrode polarization effects.

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Co-axial liquid cell

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For liquid samples, we have a co-axial cylinder cell from Novocontrol, as shown on the figure to the right. This can be connected to the Keysight LCR meter or the Novocontrol dielectric spectrometer instrument from prof. Colby's lab. The sample volume required using this cell is ≈ 3 mL.



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OTHER INSTRUMENTS

Ultrasonicators

Our lab is equipped with several ultrasonic homogenizers and baths. Ultrasound can produce cavitation in a fluid, generating large local stresses. These can be used to disperse nanoparticles in a fluid or to reduce the molar mass of polymers in solution. The efficiency of ultrasound to break up aggregates or single polymer chains in solution depends on the properties of the ultrasonic tip and the viscosity of the solution.

Model name  Frequency  Power  Type 
1800 W 2-in-1 Ultrasonic Homogenizer Ultrasonicator Cell Disruptor Mixer - Integrated Type  20 kHz  1800 W  Homogeniser 
3L Ultrasonic cleaner from US solid 40 kHz  120 W  Ultrasonic bath 
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Freeze dryer

For freeze drying of aqueous solutions, a Scientific Pro Freeze Dryer from HarvestRight with an Oil-Free Pump is available. Samples are frozen to - 40 °C in a vacuum of 500 mTorr. The instrument has a capacity of ≈ 7 liters of sublimated ice. You can find more information about the instrument here.

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Density Meter

Our lab is equipped with a KEM DA-860 Density Meter. Some of the instrument parameters are listed below.

Measurement Range 0 to 3 g/cm³
Temperature Range 0 to 100°C
Accuracy Density: 0.000003 g/cm³
Temperature: ±0.02℃
Repeatability 0.000001 g/cm³
Reproducibility 0.000002 g/cm³
Sample volume ≈ 1 mL
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If the density of a solution (\(\rho\)) of concentration C and that of the solvent (\(\rho_s\)) are known, the partial specific volume (\(\nu\)) can be calculated:

\[\rho = \rho_s + (1-\nu\rho_s)C\]

Knowing \(\nu\) accurately is important to determine the contrast in SANS and SAXS experiments. As the partial specific volume may not be C-independent, it is usually best to perform density measurements at several concentrations. For polyelectrolytes, which usually have relatively high density due to the presence of metallic counterions, density measurements for concentrations as low as ≈ 1 g/L typically yield sufficiently accurate data for \(\nu\) to be estimated.

Refractometer

Knowing the refractive index increment of polymer solutions is essential for accurate molar mass determination using static light scattering. Our Lab is equipped with a RA-620 refractometer by KYOTO ELECTRONICS MANUFACTURING (KEM). Some of the model characteristics are listed below. The instrument also provides the refractive index in terms of the Brix scale, which can be used to estimate the concentration of dissolved sugars in an aqueous solution.
Measuring Method Detection of Critical Angle of Optical Refraction
Light Source LED Na-D Line (589.3nm)
Measuring Range Refractive Index (n): 1.32000 - 1.58000
Accuracy Refractive Index (n): ±0.00002
Repeatability & Resolution Refractive Index (n): ±0.00001
Temperature Range 5 - 75 °C
Temperature Indication Resolution 0.01°C
Minimum Amount of Sample 0.2 mL
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More information: consult the manufacturer's website.

The refractive index increment varies with laser wavelength according to the Cauchy equation:

\[ \frac{dn}{dc} = A + B \lambda^{-2} \]

where A and B are coefficients which depends on the polymer-solvent pair. The molar mass of the may sometimes have an influence on these coefficients.

In order to obtain the refractive index increment matching the SLS/DLS instrument, we combine measurements on the KEM refractometer at \(\lambda = 589\) nm with measurements for \(\lambda = 620\) using the Brookhaven BI-DNDC instrument from prof. Colby's lab and extrapolate to \(\lambda = 641\) nm.

UV lamp

An OmniCure S2000 Elite system with a High Pressure 200 Watt Mercury Vapor Short Arc lamp (irradiance up to 10W/cm2) is available on our lab. The wavelength can be set using one of the available filters, which are listed on the table below. The OmniCure R2000 radiometer can be used to monitor the UV intensity. The UV system can be connected to the MCR302e instrument to perform monitor the rheological properties of UV-curing proecesses.
Filter Type Specification
S2000 Elite Filter 400-500 nm
S2000 Elite Filter 365 mm
S2000 Elite Filter 320-390 mm
S2000 Elite Filter 250-450 nm
S2000 Elite Filter 320-500 nm
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Centrifuges

The following centrifuges available in our lab:

Model name  Max rmp  Max g  Sample volume 
Labnet Mini Centrifuge C1301 6000 2000 1.5/2mL vials
Hettich Hand centrifuge ≈ 1000 ≈ 3000 15mL tubes1
1 The Hettich centrifuge is primarily used to load viscous samples into SAXS capillary tubes.
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Phase mapping

SVM3001 Cold Properties

The SVM3001 instrument can measure the cloud point of solutions with an accuracy of 2 °C.

BeNano

The 90° SLS detector on the Benano instrument can be used to measure the turbidity of samples over a temperature range of -10°C - 110°C. The temperature is set with an accuracy of ≈ 0.1 °C. Measurements can be carried out on a standard cell, whhich requires ≈ 1 mL of sample or on a micro-cuvette, requiring ≈ 50 microliters.

Shaking water bath (coming soon)

Sample preparation equipment

The following equipment is available to aid with preparation of solutions:
Roller mixer
Thermoshaker
Mass balance
Vortexer

Coming soon

Laser Micrometer

Constant volume dialysis cells