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Light-Driven Microfluidic Systems
Published in George K. Knopf, Kenji Uchino, Light Driven Micromachines, 2018
One type of pH-sensitive hydrogel that has incorporated in a variety of microsystems contains hydroxyethyl methacrylate-acrylic acid (HEMA-AA). This environmentally sensitive hydrogel undergoes abrupt volumetric changes when the pH of the surrounding medium increases slightly above the phase transition point pKa. Note that pKa is the negative of the base-10 logarithm of the acid dissociation constant (Ka) of a solution. If the networked gel is immersed in an ionic aqueous solution, then the polymer chains will absorb water and the association, dissociation, and binding of the various ions to the chains will cause the hydrogel material to swell producing a usable micro-force. The expansion and contraction of the hydrogel (Section 5.2) under environmental stimuli has been used to regulate the flow of liquids in a variety of microfluidic systems (Baldi et al. 2003; Liu et al. 2002a). The advantages of hydrogel over other smart material microactuator are relatively simple fabrication, no external power requirements, no integrated electronics, significant displacements (up to 185 μm), and relatively large force generation (~22 mN) (Al-Aribe and Knopf 2010).
Hydrothermal Processes in Subcritical Water
Published in Yatish T. Shah, Water for Energy and Fuel Production, 2014
Figure 5.1 illustrates the variations in dissociation constant, dielectric constant, and density as a function of temperature at ~30 MPa pressure. The figure shows that the density, the dissociation constant, and the static dielectric constant all vary significantly between the room temperature and the critical temperature. These changes cause enormous changes in the solvation behavior of water; it is changed from the polar, highly hydrogen-bonded solvent to the behavior of nonpolar solvent such as hexane. The dielectric constant changes from 80 to <2 in the temperature range of 25°C–450°C. While the dissociation constant goes through a maximum with changes in temperature, it is also changed by about 5 orders of magnitude in nearly the same temperature range.
Instrumentation and Test Methods
Published in Paul N. Cheremisinoff, Handbook of Water and Wastewater Treatment Technology, 2019
The dissociation constant is a way of expressing the equilibrium between a chemical substance and its dissociation into fragments in aqueous solution. The value obtained is obviously related to the compound’s solubility in water. This property is required in order to evaluate the environmental fate of chemicals and treatment processes for their removal from water. Knowledge of the distribution of the undissociated chemical and ionic species with pH (predominantly under acidic conditions) can be useful in ascertaining the availability of the substance to enter into biologically mediated oxidation reduction reactions, dissolution, ion exchange, coagulation, or adsorption.
Effect of brine type and pH on the interfacial tension behavior of carbonated brine/crude oil
Published in Journal of Dispersion Science and Technology, 2021
Saeed Zaker, Roohollah Parvizi, Ebrahim Ghaseminejad, Amin Moradi
In the second stage of this investigation, the effect of pH on IFT values is investigated since pH can affect the IFT values of binary solutions either acidic crude oil or non-acidic crude oil by synergistic or antagonistic effects. In more detail, it has been well proven that the composition of the aqueous phase is one of the most important and effective parameters on IFT modification greatly affected by pH value. For the cases with low pH values and using Le Chatelier’s principle, the net interface charge will be positive while at higher pH values it would be negative.[27,28] In detail, Equation (2) indicates a weak acid/base reaction in water for acid groups like carboxylic acids . where AH represents the nonionic form of the acid groups and A- is the ionized form of the acid groups. The degree of dissociation of acids and bases is expressed in terms of dissociation constant also known as ionization constant (Ka). This constant expresses the concentration ratio of the molecules in ionic form to nonionic form at the state of equilibrium, and is given as follows for Equation (2):[29] where square brackets represent the concentration of each species,
Determination of acid dissociation constants and reaction kinetics of dimethylamine-based PPCPs with O3, NaClO, ClO2 and KMnO4
Published in Journal of Environmental Science and Health, Part A, 2019
Xiaofeng Wang, Beihai Zhou, Xia Shao
All DMA-based PPCPs have one or more tertiary amine functional groups. Their ionisation state is controlled by both the acidic dissociation constant (pKa) and the pH value of the solution. These different chemical species (cationic, neutral, or anionic) often have vastly different properties with respect to water solubility, volatility, absorption and reactivity with chemical oxidants.[12] However, the pKa values of these DMA-based PPCPs are not accurately known. Potentiometric titration is the most frequently used method for pKa determination in aqueous solution[13] due to its time saving, accuracy and good reproducibility.
Design of an effective piezoelectric microcantilever biosensor for rapid detection of COVID-19
Published in Journal of Medical Engineering & Technology, 2021
Hannaneh Kabir, Mohsen Merati, Mohammad J. Abdekhodaie
When a specific agent reactivity stimulates reactions outside the main supposed reaction, cross-reactivity happens. In immunology, this event can be observed between the immune system and antigens when an antibody conjugates with antigens of two different pathogens [47]. The designed biosensor in this study should possess a good functionality in response to cross-reactivity and must be selective enough to differentiate antigens binding to the same antibody. Co-occurrence of COVID-19 pandemics and influenza viruses (flu) which become widespread in fall and winter, might affect a lot of people and must be considered seriously. Influenza viruses are divided into four types of A, B, C, and D. Influenza A and B are the flu seasons causing seasonal epidemic disease. Among these types, only influenza A leads to a flu pandemic. H1N1 is one of the main subtypes of influenza A spreading between people, routinely [48]. Although COVID-19 and H1N1 are originated from different viruses, they cause respiratory disease with a wide range of analogous symptoms from mild to severe disease and death. As they have similar presentations, discriminating between them is difficult which makes testing inevitable. Since COVID-19 has a high speed of transmission, the patients must be distinguished and isolated rapidly in order to control the rate of spreading. In the following, by assessing the H1N1 experimental data, it will be approved that the designed biosensor has the capability to diagnose appropriately if both of the viruses’ antigens tend to pair the same antibody immobilised to the top surface of the microcantilever. Lee and co-workers introduced 32D6 as a human H1N1 neutralising antibody through an Eptein-Barr virus – immobilised B cell-based technology. According to their experimental data, 0.036 µg/ml of 32D6 was needed to neutralise H1N1. Table 3 also displayed the binding kinetics of 32D6 towards HA of H1N1. As it is shown, the dissociation constant (KD) was reported 3.528* 10−10 M. KD is the ratio of Koff/Kon. Kon means how quickly the antibody binds to the antigen and Koff is used to determine how quickly an antibody dissociates from its target. A low KD value discloses a high speed reaction, while a high KD value relates to a low speed interaction. In this research, Kon and Koff were measured as 2.585*105 M−1S−1 and 9.121*10−5S−1, respectively. The low KD value represents a high affinity interaction in this research [49].