**8. References**

122 Recent Advances in Plasticizers

The plasticizer showed an effect on the dielectric constant of a memebrane. **Kumar and Sekhon,** *European Polymer Journal*, **2002**, studied such effect by addition of plasticizer to the polyethylene oxide (PEO)–ammonium fluoride (NH4F) polymer electrolytes. They found to result in an increase in conductivity value and the magnitude of increase has been found to depend upon the dielectric constant of the plasticizer. The addition of dimethylacetamide as a plasticizer with dielectric constant (*ϵ* =37.8) higher than that of PEO (*ϵ* =5) results in an increase of conductivity by more than three orders of magnitude whereas the addition of diethylcarbonate as a plasticizer with dielectric constant (*ϵ* =2.82) lower than that of PEO does not enhance the conductivity of PEO–NH4F polymer electrolytes. The increase in conductivity has further been found to depend upon the concentration of plasticizer, the concentration of salt in the polymer electrolyte as well as on the dielectric constant value of the plasticizer used. The conductivity modification with the addition of plasticizer has been explained on the basis of dissociation of ion aggregates formed in PEO–NH4F polymer

Similar study was applied earlier by **William Robert**, *Ploymer* **1998**. They studied the influence of plasticizer on the dielectric characteristics of highly plasticized PVC.Three citrate-related compounds [Citroflex A-4 (CFA4), Citroflex A-6 (CFA6), and Citroflex B-6 (CFB6)] and six sebacate-related compounds [dimethyl sebacate (DMS), diethyl sebacate (DES), dibutyl sebacate (DBS), dioctyl sebacate (DOS), dioctyl azelate (DOZ), and dioctyl adipate (DOA)] were used to evaluate the effects of configurational changes in plasticizer on the dielectric properties of ion-selective poly(vinyl chloride) membranes. Tridodecylamine (TDDA) and potassium tetrakis-4-chlorophenyl borate (KTpCIPB) were used as neutral charge carriers and negative sites, respectively. Using parallel plate sensors, the dielectric properties [ionic conductivity (σ) and tan δ] of the plasticized PVC membranes were determined at temperatures from − 100 to + 100°C and seven log frequencies (− 1, 0, 1, 2, 3, 4, and 5 Hz). Generally, increasing the amount of plasticizer in the membrane improved the σ and lowered the temperature of the tan δ peak. A positive linear correlation existed between the log σ and the log phr ratio for a given temperature and frequency, when no data was included for membranes below the melting temperature of the plasticizer. When plotted *versus* temperature, the slopes of all these lines passed through a maximum between 0 and 60°C. The intercepts of all these lines increased monotonically with increasing temperature. These intercepts were highly dependent on the frequency at low temperatures, becoming less frequency dependent as the temperature increased. Having established that configurational changes of the plasticizers had no effect above the melting point of each plasticizer, global nomograms were only required for the citrate- and sebacate-related plasticizers, respectively. Using the appropriate nomogram for a selected plasticizer, the σ

could be predicted at a given phr ratio, temperature, and frequency.

**6. Plasticizers and the physical properties of membrane** 

Puncture tests quantified five mechanical properties for at least eight levels of seven plasticizers were applied (**Gibbons et al**, *Polymer*, **1997)**. Using Citroflex B-6 at a phr ratio of 0.31, the strength and secant stiffness peaked at 9.63 N and 1250 N m−1, respectively. At a phr ratio of 0.6 the toughness peaked at 48 N mm. These three properties decreased at

**5. Plasticizer and di-electric constant** 

electrolytes at higher salt concentrations.

Buck R.P. and Lindner E., Pure & App. Chem. 1994, 66, 2527–2536.


Zareh M., Ismail I., and Abd El-Aziz M., *Electroanalysis* 2010, 22, 1369-1375.


**7** 

*Romania* 

Cristina Mihali and Nora Vaum

*North University of Baia Mare* 

**Use of Plasticizers for Electrochemical Sensors** 

Plasticizers represent a category of organic substances that can be added to polymers in order to improve some of their characteristics like elasticity and mechanical properties. Plasticizers are very important for the design of the selective polymeric membrane for potentiometric sensors, an important class of the electrochemical sensors. They fix the dielectric constant of the membrane and improve the selectivity of those devices. Ion – selective electrodes are instruments used in the potentiometric analysis. They have analytical applications in fields such as environment analysis, pharmaceutical analysis and, quality assurance in different fabrications. Choosing an appropriate plasticizer as well as an adequate electrode component and sometimes an additive is essential for the construction of an ion- selective electrode with high analytical performances such as

**2. Plasticizers used for the polymeric membranes of ion-selective electrodes**  The development of plasticized polymeric membrane sensors was a big step forward. It led to the advance and diversification of ion-selective electrode analysis. The liquid membranes of the electrodes were difficult to handle and did not allow the use of ion-selective electrodes (ISEs) in any position because the liquid membrane would leak. The polymeric membrane has properties similar to those of liquid membranes, but the range of applications is much larger. Plasticized polymers are in fact highly viscous liquids and they are known in the literature as liquid membranes due to high values of diffusion coefficients of ionophores and their complexes. This membrane can still be considered as a liquid phase, because diffusion coefficients for a dissolved low-molecular-mass component (e.g., an ionophore) are on the order of 10-7 to 10-8 cm2 s-1 (Moody & Thomas, 1979 as cited in Oesch et al., 1986). Typically, such a solvent polymeric membrane contains about 66 g of plasticizer and only 33 g of PVC per 100 g. Only at very low plasticizer contents (<20 g/100 g), diffusion coefficients may be l0-11 cm2 s-1 and smaller, approaching values that are found for

The plasticizers used in the preparation of the polymeric membrane of ion –selective electrodes must be compatible with the polymer and electrodic component and also must be solved in tetrahydrofuran or cyclohexanone, the solvent used in the membrane preparation. The plasticizers with high lipophilicity are preferred. The most used plasticizers are: *ortho*-nitrophenyloctyl ether (NPOE), dibutyl phthalate (DBP),

sensibility, selectivity, fast response, and long lifetime.

**1. Introduction** 

solids.

