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Water induced evolution of dielectric and micro-structural properties of rice starch

Starzyk F., Chrzanowska A., Łużny W., Śniechowski M.

Archives of Materials Science and Engineering

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2009

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Vol. 39, nr 2

111-115

EN

Purpose: The purpose of this paper was to record and correlate mass (m) changes of population of rice starch micro-granules and their effective dielectric permittivity(ε'), as well as X-ray diffraction (XRD) changes observed in this system during humidification. Design/methodology/approach: Changes of mass of bio-polymeric-granular sample occurring during its exposition on saturated water vapour at room temperature, was recorded in the time. The ε' evolution was recorded by means of fringe-field-interdigit-dielectric spectroscopy (FFIDS) method. The temperature and relative humidity (RH %) of ambient atmosphere were controlled. Microstructure changes induced by water absorption were recorded by means of XRD diffractometer. Findings: The FFIDS method turned out to be sensitive technique to follow details of humidification process. Correlation between changes of ε' with simultaneously occurring mass increase can be a way to describe the humidification and drying processes of micro-granular bio-polymeric sample. The changes observed by means of XRD should enable to point the regions within granules structures where water molecules effectively interact with internal granules physical organisation on macromolecular level. Research limitations/implications: The time length of m(t) record was limited to ~11000 s in case of humidification by the nature of the process. The whole range of measurements was limited to max ~23 % of water uptake in order to prevent the molecular structure irreversible changes. Practical implications: The ε' monitoring of humidification turned out to be much more selective than only gravitational measurement of mass change. The correlation of both is giving new possibilities of modelling approach. The XRD observed changes within physical structures of rice starch granules seems to be of great importance for modelling of water behaviour in starch. Originality/value: For the first time humidification process was monitored in statu nascendi, without disturbing geometry of granules starch by means of ε' evolution record. It was enabled by application of interdigit comb capacitor as sensing unit. The high quality of XRD records enables a new insight into details of reversible swelling process of rise starch granules. Keywords: Bio-polymers; Micro-granular matter; Water uptake; Interdigit dielectrometry; Biological water

2

Influence of electric field DC-component on AC-response of ferroelectric powder

Starzyk F., Bąk W., Kajtoch C., Gabryś M.

Archives of Materials Science and Engineering

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2008

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Vol. 29, nr 1

36-39

EN

Purpose: of this work was to establish whether ac-response of freely stocked micro-granular ferroelectric matter on fringe measuring electric field depends on constant component presence VDC (or DC-Bias). Design/methodology/approach: used involves measurements of effective dielectric permittivity (and other effective dielectric quantities) by means of interdigit dielectrometry. Fringe measuring electric field was applied to BaTiO3 micro-powder by interdigit comb sensor (ICS) Netzsch of Ms25 type. ICS was driven by measuring generator with sinusoidal voltage: v(t)= VDC+VACsin(�ωt), within frequency range 20Hz-100kHz and for DC-Bias values ranging as VDC=(0-20)V. Findings: The interdigit dielectrometry was applied to measure complex dielectric permittivity, complex dielectric modulus and others dielectric functions of ferroelectric BaTiO3 powder. The influence of constant component of electric stimulus was investigated in the frequency range 100 kHz to 20 Hz. It was established that in the low frequency range constant component of electric field enhances effective dielectric permittivity, and changes two weak relaxation processes occurring in the ferroelectric micro-granular net. It turned out that effective dielectric complex modulus of this net is most sensitive quantity for application of constant component of electric stimulus. Research limitations/implications: The density solution effect is a source of small effective dielectric permittivity of micro-granular ferroelectric powder (�ε'). �Epsilon' values are being enhanced by presence of non zero VDC value. The same effect was established for effective energy loss coefficient (�ε"). The two relaxational processes connected with VDC�𕟀 seems to be a key feature of freely stocked ferroelectric matter. Originality/value: of this work relays on the fact, that this is a first report of the VDC influence on effective dielectric properties of ferroelectric micro-granular matter. It is opening the way to a new approach in modelling of effective dielectric properties of granular matter in nature and powders technology.

3

Humidification and drying of granular matter - correlation of mass change and effective dielectrometry

Starzyk F.

Archives of Materials Science and Engineering

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2008

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Vol. 34, nr 1

19-22

EN

Purpose: The purpose of this paper was to record and mutualy correlate mass changes of population of micro-granules of rye starch and effective dielectric permittivity of this system taking places during humidification and drying processes. Design/methodology/approach: Mass changes of biopolymeric mirco-granular sample occuring during its exposition on saturated water vapour at room temperature, was recorded in the time by means of precise torsional balance equipped with special chamber. The same was done in case of drying. Monitoring of effective dielectric permittivity was performed by means of interdigit comb capacitor and precise RLC meter equipped with PC program. Specially designed and constructed measuring chamber was applied to control temperature and relative humidity (RH %) of ambient sample atmosphere. Findings: Interdigit dielectric spectroscopy method turned out to be more sensitive technique to follow details of humidification as well as drying processes. Correlation of changes of effectife dielectric permittivity with simultaneously occurring mass increase or decrease can be a way to describe the humidification and drying processes of micro-granular biopolymeric sample. Practical implications: Effective dielectric permittivity monitoring of humidification and drying processes turned out to be much more selective than only gravitational measurement of mass change. For modeling purpose correlation of both is giving new possibilities of modelling approach. Originality/value: For the first time practically important humidification and drying processes were monitored in statu nascendi, without disturbing geometry of granules starch by means of ε' values evolution record. It was enabled by application of interdigit comb capacitor as sensing unit.