Membranes chemical sensitivity

The advantage of sol-gel technology is the ability to produce a highly pure y-alumina and zirconia membrane at medium temperatures, about 700 °C, with a uniform pore size distribution in a thin film. However, the membrane is sensitive to heat treatment, resulting in cracking on the film layer. A successful crack-free product was produced, but it needed special care and time for suitable heat curing. Only y-alumina membrane have the disadvantage of poor chemical and thermal stability. 

Figure 1. Stylised chemical sensor comprising a conducting cable or track to convey the electronic signal to the outside world, a transducer to sense the chemical signal and convert it into an electronic form, and a chemically sensitive film or membrane at which the molecular binding event occurs.

The rapid expansion of reverse osmosis technology during the past two decades has resulted in the development of a variety of new membranes. Unique polymer systems and fabrication methods have led to the production of membranes with significantly improved performance and reliability. In spite of these developments little is known about chemical sensitivity or life expectancy of reverse osmosis membranes used in desalting applications. Manufacturers are consequently reluctant to guarantee their products for long runs especially in unique chemical environments. 

Osada et al. [52] have also grafted PMAA to a porous substrate in order to achieve an environmentally sensitive membrane. This sensitivity was termed a chemical valve function because mechanochemical forces caused the pores to enlarge and contract. PMAA was grafted onto poly(vinyl alcohol) (PVA) films which had a mean pore radius of 4 pm. The water permeation of the membrane was strongly affected by the conformational state of the PMAA grafts. At low pH the chains were contracted and the water permeability was... 

The chemical sensitivity or life expectancy of reverse osmosis membranes is very important for manufacturing application. Thus chlorine is the most well known reagent for water disinfection. Glaster et al. 61 inspected the influence of halogens on the performance and durability of reverse osmosis membranes. Cellulose acetate was unresponsive to halogen agents but polyamide-type membranes deteriorated rapidly when exposed to halogens. 

The ion controlled diode was an initial attempt to isolate the active electronics from the chemical solution by producing a metallic-like via that allows the isolation of the chemically sensitive region from an area where electronic components could be deposited (41,42). However, the limited precision of the non-standard microfabrication techniques made this process difficult and costly. Since this device is still essentially a capacitive membrane-insulator-semiconductor structure like the chemfet, the same problems of hermetic isolation of the gate remain. 

Figure 3. Ionic leakage paths in chemfet structures a.Schematic illustration of ionic leakage paths around the chemically sensitive membrane. Leakage through the membrane also occurs but is not illustrated b. Schematic illustration of leakage at the surface of a standard ion sensitive field effect transistor.

The integration of chemically sensitive membranes with solid-state electronics has led to the evolution of miniaturized, mass-produced potentiometric probes known as ion-selective field effect transistors (ISFETs). The development of ISFETs is considered as a logical extension of coated-wire electrodes (described in Section 5.2.4). The construction of ISFETs is based on the tech-... 

SAFETY PROFILE Moderately toxic by ingestion and skin contact. Corrosive to the eyes, skin, and mucous membranes. A sensitizer. See also AMINES. Flammable liquid when exposed to heat or flame can react with oxidizing materials. To fight fire, use foam, CO2, dry chemical. When heated to decomposition it emits toxic fumes of NO,. 

Membranes can be used to separate molecules that differ in size, polarity, ionic character, hydrophilicity, and hy-drophobicity.100 Their use is less energy-intensive than distillation. They can often separate azeotropes and close-boiling mixtures. They can sometimes replace traditional methods, such as solvent extraction, precipitation, and chromatography, that can be inefficient, expensive, or may result in the loss of substantial amounts of product. Thermally and chemically sensitive molecules can be handled. Membranes can be porous or nonporous, solid or liquid, organic or inorganic. 

HEALTH SYMPTOMS inhalation (coughing, shortness of breath, build-up of fluid in lungs, wheezing, chest tightness, irritates eyes, skin and respiratory system) skin absorption (respiratory system sensitization, skin sensitization, narcotic effects) contact (destroys tissues of mucous membranes, chemical bums to the skin and eyes, scarring, skin allergies). 

Free chlorine (CI2) is an oxidant. Polyamide RO and NF membranes are sensitive to chlorine. Hence, water must be dechlorinated by passing it through an activated carbon filter or by the addition of a reducing chemical such as sodium sulphite, sodium bisulphite, or sodium metabisulphite to feed water. However, it is necessary for CA membranes to protect them from bacterial attack. 

The membrane potentials can also be measured indirectly, if the membrane is fixed on the surface of a field-effect transistor (FET) from which the metallic gate has been removed. The electric current passing between the source and drain of the EET is then controlled by the membrane potential. The first sensor of this type [ion-selective FET (ISFET) or chemically sensitive FET (CHEMFET, CSFET)] was described by Bergveld in 1970 and the field has been developed primarily by Janata and co-workers and Japanese researchers. 

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