Organic Vapour and Water Sorption

DYNAMIC VAPOR SORPTION

DVS Advantage

Automated multi-vapor sorption analyser

The DVS Advantage automatically records organic and water sorption isotherms quickly, dynamically and accurately. It also offers greatly expanded functionality with options of;

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The DVS Advantage uses a dry carrier gas, usually nitrogen, and either water or an organic vapor source. A precise ratio of carrier gas and vapor flows over a sample suspended from an ultra-microbalance. This measures the weight change caused by sorption or desorption of the vapor molecule. It is these dynamic flow conditions that enable the sorption/desorption process to be rapidly studied.

The sample may be pre-heated speeding up the analysis cycle of bulk absorption or the drying of inorganic hydrates. This heating can be as a single step, or at a selected temperature ramp rate. The temperature of the whole system is precisely controlled to ensure constant solute vapor pressure at the sample. Isolation valves at the solvent reservoirs ensure that a true p/pº zero is always obtained.

The DVS Advantage from Surface Measurement Systems features:

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Software

The DVS Advantage control software enables a full range of conditions to be defined for isothermal and isohumidity (or constant partial pressure) sorption experiments. Complex protocols for multiple experiments can be created and run fully automatically. The smart operator interface provides a high standard of data integrity and security.

Analysis functions include Isotherms, Kinetics, BET Surface area, Heat of sorption, Surface energetic,Vapor pressure and Amorphous content.

More than 20 different Isotherm models are available for prediction of shelf life/storage stability, and understanding solvent interactions, hysteresis and surface characterisation.

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Microscope option

The DVS microscope provides an integrated solution for the visualisation of samples during experiments. It consists of an optical fibre light source, a high resolution camera and image capture software. Captured images can be overlayed with graphics showing date/time/temperature/vapor pressure.

Effect of reducing humidity of PMMA (Poly(methyl methacrylate)).

2 hours at 98.5% RH 18 hours at 90.5% RH

Examples of DVS Applications

Moisture sorption behaviour of rice starch at 25ºC – 2-cycle experiment

DVS isotherm plot DVS change in mass plot

WATER SORPTION ANALYSIS

DVS Intrinsic

The DVS intrinsic is an economical research grade water sorption instrument. It is easy to use and provides fast high quality isotherms with minimal operator training. It’s compact small footprint requires very little bench space.

The DVS Intrinsic measures the uptake and loss of moisture by flowing a carrier gas at a specified relative humidity (RH) over a sample suspended from an ultra-microbalance. The sorption/desorption of water vapor is measured by the increase/decrease in the mass of the material. Sorption behaviour can be accurately determined on very small samples (1-20 mg) thus providing great savings in the time required to reach water sorption equilibrium. The system can perform isoactivity measurements in which materials are kept under constant RH conditions while linearly or stepwise varying the temperature.

The water sorption properties of solid materials have traditionally been evaluated by storing samples in sealed jars containing saturated salt solutions and then periodically weighing these until equilibrium is reached. However, the disadvantages of these manual jar methods include:

In contrast the DVS Intrinsic offers an extremely rapid, highly sensitive and accurate means for the determination of moisture sorption properties of solids.

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The DVS Intrinsic from Surface Measurement Systems features:

Materials studied

Pharmaceuticals Food Natural materials
powders, tablets, API’s and excipients powders, processed food, biscuits grains/seed, wood
Building materials Personal care Packaging materials
aggregates, cement, ceramics cosmetics, hair care, contact lenses paper, plastics

Applications

DYNAMIC VACUUM SORPTION

DVS vacuum- a unique system that provides both static and dynamic sorption experiments.

DVS Vacuum

Static mode –for higher sorbate pressures.

Once the vapour enters the sample chamber, the chamber is sealed and the experiment occurs under static conditions i.e.no gas flow

Dynamic mode – for low sorbate pressures.

The instrument controls both the upstream entry rate of vapour and the downstream exit rate of vapour.

Dynamic mode delivers two crucial advantages:

1. Sorbate compositional certainty
By the continuous removal of any leaked air and its replacement with sorbate the sorbate molecules constitute the total measured pressure in the sample chamber. This provides certainty of the experimental concentration for low sorbate pressures (The Henry region).

2. Residence time control
The system reaches steady-state over a wide range of flow rates. This provides sufficient sorbate/substrate contact with the sample to accurately measure data such as pore size distributions and sorption kinetics

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The principle of dynamic vacuum

Controlling the sorbate’s entry and exit flows in tandem achieves dynamic vacuum conditions

(1) Downstream vacuum pump evacuates the sample chamber (2) Sorbate molecules fill the sample chamber until reaching the required concentration (3) Downstream valve opens to create equal exit and entry sorbate flow rates. Different sorbate concentrations are achieved by adjusting the exit/entry flow rates

DVS Vacuum from Surface Measurement Systems - Key features;

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Vacuum drying

Some materials need extensive drying/outgassing which is not possible with traditional methods like dry gas flow and thermal convection heating. The DVS Vacuum can dry all sorts of materials such as:

Microporous solids Chemical absorbents Nano‐powders and fillers
Complex inorganic solids Some strong hydrates Bio‐materials

Software

DVS Vacuum Pirani software makes it easy to create and run a sophisticated sequence of different experiments. All parameters such as vapor flow, purge gas, valve and pump sequence are controlled from the computer. Analysis functions include Isotherm generation, dm/dt and Knudsen vapor pressure analysis and overlay of multiple data graphs.

The Isotherm analysis suites elucidate key physicochemical parameters including:

  • BET surface area
  • Heat of sorption analysis
  • Diffusion analysis
  • Activation energy analysis
  • Pore size distributions

Applications examples

DVS Vacuum multi-component experiments simulate the industrial separation of compounds using Zeolite substrates. The Zeolite is activated using the DVS Vacuum’s optional sample pre-heater.

DVS Vacuum multi-component experiments simulate the industrial separation of compounds using Zeolite substrates. The Zeolite is activated using the DVS Vacuum’s optional sample pre-heater.

BET measurements at ambient temperatures DVS Vacuum offers a number of benefits over traditional volumetric BET analyses, including the ability to use adsorbates with a range of molecular cross sections, sizes and shapes, and the ability to perform measurements at ambient temperatures rather than 77K (–196°C). This allows researchers to explore the more subtle physicochemical properties of complex microporous materials.

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