Characterisation Methods
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X-Ray Photoelectron spectroscopy (XPS, formerly known as ESCA)
The elemental composition of surfaces is analysed by XPS (ThermoScientific Nexsa) with Al Kα radiation. The instrument is equipped with an Ar cluster ion gun allowing for low energy (e.g. polymer) or high energy (e.g. metals) etching to clean the surface and analyzing depth profiles.
XPS
Inverse Gas Chromatograph (iGC)
iGC (SMS Surface Measurement Systems) is an advanced gas phase instrumentation for the characterisation of particulates, fibres and thin-films. Opposed to conventional GC, the sample acts as column and known amounts of various gases are injected and from the chromatograms e.g. surface energies and its components as well as specific surface areas, acid/base/polar functionality of surfaces, diffusion kinetics, solubility parameters, etc. calculated.
iGC
Moisture Uptake Behaviour
Dynamic vapour sorption (DVS)
DVS Intrinsic (SMS Surface Measurement Systems) allows automated, rapid and accurate gravimetric measurements of moisture uptake in solid materials (e.g., polymers, paper, natural fibres, composites and porous materials) over a wide temperature range using dynamic environment control and ultra-sensitive recording microbalance with resolution of ~0.1 μg. The ability to work with very small sample sizes combined with dynamic vapour flows reduces the time to measure moisture sorption isotherms from weeks or months to hours or days.
DVS
Foam analyser
The Dynamic Foam Analyser (Krüss) is used to study foamability and foam stability of liquid foams. Furthermore, bubble size and bubble size distribution can be measured as function of time.
Dynamic Foam Analyser
Dynamic Contact Angle measurement
The contact angle is the angle at which a liquid/vapor interface meets the solid surface, specific for any given system and is determined by the interactions across the three interfaces. Using a Drop Shape Analyzer (DSA30 K, Krüss) surfaces can be probed with a variety of test liquids to obtain advancing and receding contact angles and subsequently calculate surface energies. Hot melts and their interaction with surfaces (such as powder beds) can also be studied up to temperatures of 400°C.
DSA
Contact angle of polymer melts
Polymers can be extruded/injected into an environmental, temperature controlled measurement chamber of a Krüss DSA 10. The chamber can also be used to assess contact angles between a polymer melt and a substrate (in an inert/chosen gas atmosphere). Imbibition measurements of polymer melts into powder compacts of the reinforcement phase can be made to allow assessment of the interface between the phases.
High pressure and temperature contact angle rig
Surface and interfacial tensions (i.e. contact angles, captive bubbles/drops, interfacial tensions) at elevated temperatures and pressures are required in the development of materials or the understanding of phenomena relevant to the oil and gas industry. The surface / interfacial tension and wettability of a substrate in contact with one or two equilibrium liquid phases can be measured in a thermostated high-pressure view cell in aggressive environments at pressures of up to 700 bar at temperatures up to 200°C.
Zeta Potential (streaming & electrophoresis) measurement
The zeta-potential of porous media, fibres, films, and powders can be studied using various measuring cells by the Streaming Potential method (Elekrokinetic Analyser SurPass, Anton Paar) as a function of time, pH and type and concentration of the electrolyte. The zeta-potential plateau region and the isoelectric point (point of zero charge) can be determined by pH dependent measurements to assess surface modification by (for example) plasma treatment or compound adsorption.
By Electrophoresis (Malvern Zetasizer) the surface charge, electrokinetic mobility and size of particles in suspension can be assessed based on the principle of light scattering.
Elekrokinetic Analyser SurPass
Malvern Zetasizer
Tensiometry and single fibre wettability measurement
The dynamic fluid sorption (capillary rise) technique is used to determine the wettability of porous systems, fibres, powders and membranes using an automated Tensiometer (Krüss K100). By applying the modified Washburn equation surface energies can be calculated. Determination of surface/interfacial tensions using the Ring- or Wilhelmy-plate methods is also possible.
A modified Ultramicrobalance (4504 MP8, Sartorius, Göttingen, Germany; accuracy = 0.1 μg) is used to measure contact angles on single (carbon) fibres with diameters as low as 5 μm by applying the modified Wilhelmy-technique.
Tensiometer
Viscoelastic and rheological properties
Rotational Rheometer
Rotational Rheometry (TA Discvoery HR2) is used for determination of viscosities of fluids with various geometries (capillary, plate-plate, cone-plate, Cup & Bob).
Rotational Rheometry
BET Surface Analysis
A Surface Area Analyser (Micromeritics TriStar II) is used to determine specific surface areas utilizing the BET isotherm method by nitrogen adsorption/desorption.
TriStar
Molecular Weight
Gel permeation chromatography (GPC)
GPC equipped with triple detection system (Viscotek TDA 302) is used for the characterisation of the molecular weight (distribution) of water-soluble polymers.
GPC
Particle Size
Nano-/Microparticles
The size of nanoparticles from 0.5 nm to 10 µm is analyzed using Dynamic Light Scattering with a Nanophox (Sympatec). For larger particles (0.1 µm to 8.75 mm) Helos KR (Sympatec) is used.
Nanophox
Helos KR
Mechanical Characterisation of Materials
Mechanical Testing
Two universal testframes (Instron 3345 & 5969) are used for the mechanical characterization of polymer and composite sample in tensile, compression or bending mode.
Single Fibre-Pull-Out Testing Machine
Our single fibre pull-out device was designed by BAM Berlin. The device uses a piezo-actuator (with a displacement resolution of a few nanometres) and a piezo force transducer (with a resolution of 0.1 mN). A microscope is fitted to allow optical observations during testing. We use this instrument to determine strength and modulus of thin reinforcing fibres, incl. strength dependence of fibres at short gauge lengths as well as adhesion and friction properties of single fibre composites.
Gas Permeability
Gas permeability of porous media and polymer films (LabThink VAC VBS & W3 031), e.g. oxygen or water vapour, is an important feature, in particular of (food) packaging materials. Both, O2 and H2O vapour are detrimental for the expiration date of food, but usually (polymer or paper) materials employed constitute either a barrier for O2 or H2O vapour.
Characterisation of Porous Media
Mercury porosimetry
Mercury porosimetry allows for simultaneous measurement of pore volume distribution, limiting pore throat diameter, permeability distribution and electrical conductivity of porous materials following the penetration of pores with mercury. Porous samples are placed in the sample cell and mercury is forced into pores. Mercury is non-wetting and thus the pressure applied to the mercury can be used to determine the diameter of the pores being filled. Incremental increases in the applied pressure result in the determination of the pore volume distribution. Application of a pressure gradient across the sample induces mercury flow through pores of a specific diameter and a permeability distribution can be developed. The applied pressure corresponding to the onset of mercury flow indicates the limiting pore throat size.
Surface modification by Atmospheric Pressure Plasma treatment
We use an atmospheric plasma spray device (Openair-Plasma-Technology system with a single rotating FLUME Jet RD1004, Plasmatreat, Steinhagen, Germany) to modify a variety of surfaces using air or other gases to introduce various functional groups (which depends on the feed gas (composition) used) onto the surface of fibres (natural and carbon) and polymers. This atmospheric plasma system is ideal to tailor adhesion between (carbon, natural) fibres and a polymer matrix in composite systems. We can modify fibre surfaces continuously as well as films and 3D porous polymer scaffolds using our plasma system. Plasma treated modified (porous) polymers may be used in tissue engineering applications.
Injection and compression moulding
Using our (mini)injection moulding machine we can process polymers as well as short-fibre or nanomaterial reinforced polymer composites (injection moulder). A variety of shaped specimens can be formed for tensile, compression, flexural or DMTA testing to assess the effect of the reinforcement on the material properties.
We use compression moulding (via a hot pressing) combined with specially designed moulds to produce long fibre reinforced specimens (in various fibre orientations).
Extrusion, mixing and compounding
To ensure adequate blending of the matrix and reinforcement (often carbon nanotubes or bacterial cellulose) we use several pieces of equipment (shown below) that enables melt extrusion and compounding of composites prior to further processing. Our facilities include a small twin screw extruder, a micro-twin-screw extruder (DSM, The Netherlands) and a Brabender mixer.
Hot press facilities
We have four hot presses for the production of compression moulded specimens (moulded often in dog-bone shapes for tensile testing) and for the production of flat specimens for composite testing.
Three-dimensional printing
A desired design (e.g. in the form of a CAD drawing) can be converted to a set of instructions for the AutoDrop printing system in terms of required locations for the deposition of droplets of the material in each layer of the final 3D structure. The AutoDrop system (Microdrop Technologies GmbH, Norderstedt, Germany) has a printing head that contains 4 printing nozzles, each supplied from an independent reservoir. Droplets down to 30 µm diameter can be deposited onto a substrate in multiple layers with a spatial accuracy of ±5 µm. The AutoDrop System is able to process a wide range of liquids including solutions, suspensions, or melts. At present, our set-up allows for two of the reservoirs and nozzles to be heated up to 120°C. We are successfully applying the printing of melts for the fabricatio n of templates for poro us media and electroactive structures. There is an upper limit on the viscosity of the fluid that can be printed, as the device only permits to deposit liquids with a viscosity not higher than 10,000 mPas. The system is able to eject single droplets or it can be operated in a quasi-continuous mode, up to a maximum possible ejection rate of 2000 droplets/s.
Large volume centrifuge
Our group purchased a centrifuge that can process up to 1.5 litres. This unit is able to exert up to 15,000g (10,000 rpm) at temperatures ranging from -10 to 40 degree celsius to room temperature and accomodate up to six 250 mL centrifuge tubes at a time. We also have adaptors to spin smaller volumes (50 mL or 15 mL of centrifuge tubes).
Low Pressure Plasma Treatment System
Plasma treatments of materials are one of the most important physical-chemical methods to modify the surface properties and characteristics of all types of solid surfaces of myriad shapes. Surface modifications are for instance necessary, if it is attempted:
- to produce composites, which require good interfacial adhesion between the individual components
- to deposit functional coatings
- to tailor the wettability of surfaces
- to glue different materials together, to dye or print on them, or to coat their surfaces or
- to achieve material compatibility, which is necessary i.e. for biomedical materials to tailor cell-materials interaction.
Plasma treatments have gained increasingly more industrial interest for several important surface treatments replacing existing wet-chemical procedures that involve chemicals and solvents (which might be hazardous for humans and the environment). This equipment enables us to modify the chemical- and/or physical surface properties of materials and to deposit thin, highly adhered coatings or protective layers onto nearly all types of materials having nearly all shapes without affecting the intrinsic bulk properties of the material itself.
The Plasma facility offers the unique possibility to clean, etch (or ablate) and chemically modify (introducing different surface groups or depositing a wide possible of plasma polymer-coatings or graft copolymers) any solid materials surfaces, so that only the topmost material surface (from 10 nm to 2 mm) is affected. Polymers can also be crosslinked or branched during plasma treatment. The plasma reactor would allow control over the surface chemistry by controlling the plasma process parameters, such as feed gas and feed gas composition, chamber pressure, temperature, power and frequency. It is also possible to modify the interior surfaces of porous polymers most effectively using low pressure plasma treatments, which will enable other contributors to modify porous solids. Our system allows also for plasma enhanced CVD growth of CNTs.
Freeze-dryers
We have extensive experience in manufacturing highly porous foams with tailored pore structures via thermally induced phase separation (TIPS). Our freeze dryers are able to operate at -110 and -40 degrees Celsius, respectively. With the temperature of the freezer at 110 degree Celsius, samples can be freeze dried from organic solvents.
Cryomill
The cryomill performs cryogenic grinding of virtually any material. It is ideal for particle size reduction and, generally, grinding tough materials. The integrated cooling system continously circulates liquid nitrogen before and during the grinding process without directly contacting the sample or exposing the operator. The sample is held in a stainless steel ar and crushed by a stainless steel ball. Maximum batch size is around 15 mL.
Microscopic analysis
We have a wide array of optical microscopes (e.g. Leica DM 2700), are interfaced with digital cameras and image analysis software for measuring e.g. pore sizes. Linkham hot plate and cold stage accessories are used for studying the development of crystallinity of polymers over time, this is also used to identify the site of nucleation (i.e. from the surface of carbon fibres).
We also have a table top SEM (JEOL NeoScope JCM-6000) and access to high-res Scanning Electron and Transmission Elcetron Microscopy at the Faculty Center for Nano Structure Research.
Surface and interface analysis
- Drop Shape Analysis for the determination of dynamic contact angles (on hydrated and dry surfaces), sliding angles, surface and interfacial tensions (one instrument with high temparture cell (up to 400°C) and one istrument with high pressure cell (700 bar at 200°C) equipped with high pressure CO2 pump)
- Wilhelmy Balance for the determination of fibre perimeters (diameters) and dynamic contact angles
- Spinning Drop Tensiometer
- Zeta potential streaming potential (Anton Paar SurPass) and electropheresis instruments (Malvern zetasizer)
- Tensiometry for surface and interfacial tension, sedimentation, and contact angle measurements on porous media and fibres
- mini Langmuir-Blodgett Trough
- Pycnometer skeleton and envelope density (Micromeritics AccuPyc II 1340 and GeoPyc 1360)
- BET surface analysis (Micromeritics TriStar II)
- Inverse Gas Chromatography (iGC, SMS)
- Adhesion (single fibre pull-out testing)
- Table top SEM (JEOL NeoScope JCM-6000)
- Optical Micro- and Macroscopes equipped with hot stages (Leica DM 2700)
- Gas Permeability testers for porous media and polymer films (Lab Think VAC VBS & W3 031)
- Dead end filtration cells (Sterlitech Hp 4301)
- Water vapour transmission rate (SMS DVS Intrinsic)
- Dielectric spectroscopy
- QCM
- FTIR spectrometer (Bruker Tensor II)
- XPS/ESCA spectrometer (ThermoScientific Nexsa)
- Dynamic Foam Analyzer (Krüss)
Thermal Analysis
- DSC Differential scanning calorimetry (TA Discovery)
- DMTA Dynamic mechanical thermal analysis (TA G2 RSA)
- TGA Thermogravimetric analysis (TA Discovery)
Mechanical Testing
- Universal Test Frames Instron 3345 & 5969
- Single Fibre-Pull-Out Testing Device
Rheological Testing
- Rheometer couette, plate-to-plate, capillary (TA Discovery HR2)
Vienna Experiment for Drag Reducing Agents (ViEDRA)
- Pressure driven pipe flow facility for characterization of drag reducing agents in turbulent flow