Preparation, characterization and dielectric properties of sodium alginate/titanium dioxide composite membranes
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Sodium alginate/titanium dioxide solid polymer composite membranes were prepared by solution casting method. The electrical, optical and thermal properties of these composite membranes are in great demand for advanced electronic device applications. The present study is aimed at the preparation of dioxide membranes to enhance the conductivity of sodium alginate. The diffraction pattern confirmed the change of sodium alginate polymer matrix structure from amorphous to polycrystalline upon dispersing TiO2 powder particles into sodium alginate solution. The surface morphology also evidenced the non-crystalline and polycrystalline (containing grains and grain boundaries) nature of formed films. The infrared spectra showed the presence of various functional groups such as –OH, C=O, O–H, C–H and Na–O. The differential scanning calorimeter (DSC) investigation revealed the existence of exothermic/endothermic peaks, melting and crystallization temperatures. Furthermore, the weight loss of all the films was described as a function of temperature. The dielectric properties highlighted the 5 wt% of TiO2 dispersed in the sodium alginate solution due to its high dielectric constant (ε′), dielectric loss (ε″) and ac-electrical conductivity (σac).
KeywordsAmorphous materials Polymer composites Microstructure Electrical properties X-ray techniques
Polymer composite membranes continue to receive tremendous attention for their potential advanced material applications . Polymer composite membranes are the polymer membranes in which small amount of powder particles are dispersed. The physical, chemical, and electrostatic interactions between the polymer and filler result in improvements of electrical, optical, mechanical, thermal properties of polymer membranes [1, 2, 3, 4]. These are needed to meet the demand in emerging technological applications for such advanced materials. More recently, the significant development occurred in the area of flexible electronic devices.
Sodium alginate (SA) is an environmentally safe, inexpensive, nontoxic, weak acidic, anionic, and linear chained natural polysaccharide material . Recently, the SA acquired more significance because of its diverse properties as well as gel forming capability with metal oxides . Thus, the usage of SA revealed distinct applications in controlled drug delivery, dehydration of organic solvents, removal of metal ions from aqueous solutions, textile industries, food industries etc., . In addition, the SA based polymeric specimen exhibited high ε′ which in turn responsible for potential applications in actuators, artificial muscles, and charge stored capacitors . The polymers containing high ε′ can also adopt high ε″. Therefore, it promotes the electrical conductivity to larger extent. Moreover, the polymer composite membranes possessing high σac value showed extensive applications in molecular electronics . In order to increase the electrical conductivity and dielectric constant in polymers, one has to disperse the ceramic powder particles with high dielectric constant into the polymer solution. In this concern, many scientists used to disperse the inorganic powder particles into the polymer solution such as SA and polyaniline [4, 5, 6, 7, 8, 9, 10, 11]. Subsequently, biomedical, electronic device and environmental cleaning applications were obtained. Hence, the polymer composite membranes can be synthesized. In the literature  TiO2 fillers were added to the polyaniline for further increase of dielectric constant and electrical conductivity. At this juncture, the authors got an idea to introduce the TiO2 fillers into the SA polymer solution in order to achieve the good dielectric constant and electrical conductivity. However, in the literature very limited studies were found on SA/TiO2 polymer composite membranes [12, 13, 14, 15].
2 Experimental procedure
Sodium Alginate (viscosity > 2000 CP) (SDFC, 99.4% purity) and TiO2 (Merck, 99.2% purity) were used as the starting materials. Double distilled water was used throughout the experiment for film casting.
2.2 Membrane preparation
The polymer composite membranes of sodium alginate dispersed with TiO2 were prepared by solution casting method. At first, 4 wt% of sodium alginate solution was prepared by continuous magnetic stirring of 4 g amount of NaAlg in 90 ml of water for 48 h. The required amount of TiO2 (5, 10, 15 wt% based on weight of NaAlg) for each sample was first dispersed in 10 ml of distilled water under ultrasonication for 2 h at room temperature. The well dispersed TiO2 then added to an aqueous of 4 wt% of NaAlg solution. Furthermore, it was magnetically stirred until completely dissolved in order to obtain a homogeneous NaAlg–TiO2 viscous solution. This solution was poured into a polypropylene petri dish and left to dry at room temperature in order to obtain free standing polymer composite membranes. The thickness of NaAlg–TiO2 films for 0, 5 10, 15 wt% concentrations of TiO2 were 0.12, 0.12, 0.13 and 0.13 mm respectively. These are indicated by SA, SA1, SA2 and SA3 respectively. These films were initially dried in vacuum. Further, the films were subjected for different characterization techniques like X-ray diffractometer (Bruker X-Ray Powder Diffractometer, CuKα, λ = 0.15406 nm), Scanning Electron Microscope (Ultra 55 SEM Carl Zeiss), FT-IR spectrophotometer (IR affinity-1, Shimadzu), Differential Scanning Calorimeter (DSC 131, Setaram), Thermo gravimetric Analyzer (TGA, Linseis STA PT 1750) and LCR HiTESTER (HIOKI 3532-50, Japan) for structural, morphological, functional group, thermal and dielectric properties respectively.
3 Results and discussion
3.1 X-ray diffraction (XRD) analysis
3.2 SEM analysis
3.3 FTIR analysis
3.4 DSC analysis
3.5 TGA analysis
3.6 Dielectric properties
The dielectric behaviour of polymer composite materials is a powerful technique for studying relaxation and conduction mechanisms in polymer material. Dielectric permittivity is complex quantity given by: ε* = ε′ − iε″, where ε′ and ε″ are the real and imaginary parts permittivities. The real part generally is referred as dielectric constant while the imaginary part is associated to the dielectric loss. The dielectric constant is calculated by using the relation: ε′ = Cd/Aεo, where ‘C’ is the capacitance, ‘A’ is area of cross section of material, ‘d’ is the thickness and permittivity of free space . The dielectric loss (ε″ = ε′ tanδ) is computed using the product of dielectric constant and loss tangent . Both ε′ and ε″ parameters of SA, SA1, SA2, and SA3 mainly depend on two factors such as applied temperature and frequency. These are described as follows.
3.7 Temperature dependence of ε′ and ε″
3.8 Frequency dependence of ε′ and ε″
3.9 Temperature and frequency dependence of AC-conductivity
The SA/TiO2 polymer composite membranes were prepared by solution casting method.
The diffraction pattern confirmed the change of sodium alginate polymer matrix structure from amorphous to polycrystalline on dispersing the TiO2 powder particles into sodium alginate solution.
The SEM micrographs evidenced the non-crystalline and polycrystalline nature of formed films.
The FTIR spectra showed the existence of functional groups like –OH, C=O, O–H, C–H and Na–O.
The DSC curve of SA showed sharp endothermic peak at 185.76° and is associated to melting temperature. This peak was shifted to higher temperature region of 218.71°, 218.9°, 219.22° for SA1, SA2 and SA3 respectively.
The TGA analysis showed the major weight loss above 180 °C due moisture and residual solvent in sodium alginate.
The high dielectric constant and loss observed at 5 wt% of TiO2 dispersed in the sodium alginate solution.
The high σac ~ 2.3 × 10−7 noticed for SA3 at 4 MHz may be well suited for molecular electronics applications.
The authors express thankful to Prof. T. Subba Rao, S. K. University, Anantapur, A.P., for helping in sample preparation.
The work is contributed by the all authors according to the priority given in the name section. In addition, these samples are not creating any problems to the nature or living organic matter.
Compliance with ethical standards
Conflict of interest
The authors declare that we have no conflicts of interest.
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