UV crosslinked polysiloxanes as new coating materials for SAW devices with high longterm stability

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UV crosslinked polysiloxanes as new coating
materials for SAW devices with high long-term
stability
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Introduction

• An increasing interest in chemical monitoring of
  organic volatiles in the environment
• Conventional analytical techniques
• The fast, small, and low-cost sensors for
  continuous supervision polymer coated SAW
  devices
• Principles of SAW sensors

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• Polymers can be flexible modified towards
  different analytes
• UV curing after coating promises better adherence
  of the polymer film to the sensor surface and an
  improvement of long-term stability

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Experimental

• Substrate LiTaO3
• Device SH filter
• Operating frequency 380 MHz
• Analytical SAW sensor system 8 SAW oscillators
  one common reference sampling system
• UV light conditions

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• Spin coating
• UV crosslinking was performed in N2
• The exposure time was 30 min at a wavelength of
  365 nm
• Gas system
• Measuring temperature 25 ? 0.01oC

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Results and discussionInfluence of the layer
thickness

• The sensitivity of a SAW sensor is highly
  influenced by the thickness of the applied
  polymer film

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Influence of side group substitution

• The sensitivity increases with increasing side
  group substitution

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Ageing behaviour

• UV crosslinked polysiloxanes has a good ageing
  behaviour

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Calibration lines and detection limits
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• Good linear relationships are between ?f and
  analyte concentration
• The detection limits are well below the German
  MAK value
• The detection limits have been improved by SAW
  sensors

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Building up a silicon layer system

• Polymeric coating are only partly selective
  towards a particular class of analytes
• It has to use an array to achieve high
  selectivity and perform a qualitative or
  quantitative analysis of organic vapors

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• The pattern observed within a single group of
  analytes are more similar
• Single members of a group can be discriminated by
  slightly differing sensing signals
• The phenyl side groups show the highest
  sensitivity towards aromatic compounds
• The octylated polysiloxane coating is most
  sensitive to aliphatic compounds
• The polydimenthyle ethylene oxide copolymer is
  most sensitive to alcohol compounds