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Multi-Phase Systems
Published in Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will, Commonly Asked Questions in Thermodynamics, 2022
Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will
Liquid mixtures can separate into two liquid phases. The two phases appear at a temperature below what is called an upper critical solution temperature (UCST) or above a lower critical solution temperature (LCST). Mixtures with a LCST can also have a USCT at higher temperature and exhibit what is called closed loop miscibility. It is possible to have a LCST at a temperature greater than the UCST so that at temperature between the liquids are miscible. An example of such a circumstance is provided by the system water and 2-butoxy-ethanol, CH2(OH)CH2OC4H9. Figure 4.15 shows examples of UCST and LCST.
Smart Polymeric Biomaterials in Tissue Engineering
Published in Rajesh K. Kesharwani, Raj K. Keservani, Anil K. Sharma, Tissue Engineering, 2022
Akhilesh Kumar Maurya, Nidhi Mishra
The polymeric biomaterials are responsive or sensitive to change in temperature. These are most used and safest biomaterials in drug administration systems. Thermosensitive biomaterials have very sensitive balance between the hydrophilic and hydrophobic groups and can create new adjustment of structure with small change in temperature (Park and Bae, 1999) and have unique property of sol–gel transition above certain temperature. Some polymeric biomaterials show phase transition near the physiological temperature of human body. On the basis of response of polymer to change in temperature, polymers are categorized in two classes; first, upper critical solution temperature (UCST)—polymers which precipitate and undergo phase change below a critical temperature and second, LCST—polymers which become insoluble above a critical temperature (Bajpai et al., 2008). UCST-type polymer solutions are heterogeneously cloudy and opaque below the UCST, “positive temperature-sensitive polymers,” i.e., polyacrylic acid (PAA), PAM, and poly(acrylamide-co-butyl methacrylate), while LCST-type polymer solutions are homogeneously clear and transparent below the LCST, “negative temperature-sensitive polymers,” that is, PNIPAM (Teotia et al., 2015; Aoki et al., 1999). UCSTs of interpenetrating networks (IPNs) of PAM and PAA are at 25 ºC. Poly(allylurea-co-allylamine) (PU-Am)-based polymers have 8–65 oC UCST (Glatzel et al., 2011; Owens et al., 2007). LCST of PNIPAM is at 32 oC in aqueous media; below the LSCT, it shows extended, swelling chain conformation and above the LCST, it shows
Application of Bioresponsive Polymers in Gene Delivery
Published in Deepa H. Patel, Bioresponsive Polymers, 2020
Tamgue Serges William, Drashti Pathak, Deepa H. Patel
Body temperature variation in some pathological conditions or diseases, especially in the tumor microenvironment (TME) (increase by 1–2°C), has been widely exploited as physical stimuli to serve as a trigger for the delivery of therapeutic agents in bioresponsive drug delivery system. Temperature-sensitive polymers have a specific critical solution temperature which can be set by upper critical solution temperature (UCST) that becomes soluble after heating or lower critical solution temperature (LCST) that becomes insoluble after heating. With small temperature changes around this temperature, there is a change in the hydrophilic and hydro-phobic interactions between the polymer and the aqueous medium. That interaction changing leads to an architectural or structural modification of the polymer, which can be manifested by an expansion (swollen networks), or a collapse (collapsed network) [33].
Variable reactivity and phase separation in patchy particle systems
Published in Molecular Physics, 2019
R. E. Ryltsev, L. D. Son, K. Yu. Shunyaev, M. G. Vasin
Now consider the case of U>0 that means DSI is effectively repulsive. Such situation might seem physically incorrect but it can in fact be realized if U is treated as effective bonding enthalpy in the systems with concurrent thermoreversible bonds [3]. Typical miscibility curves for this case are shown in Figure 5. At low χ values, we see two separate miscibility gaps (Figure 5(a,c)). The low-temperature one is usual regular solution cupola caused by van der Waals interaction. The high-temperature part of the diagram, caused by DSI, has lower critical solution temperature and immiscibility region extended up to arbitrary high temperatures. At an increase of χ, upper critical solution temperature rises that lads eventually to confluence of two parts of the diagram with the formation of critical-points-free miscibility gaps (Figure 5(b,d)). The (a,b) and (b,c) panels in Figure 5 demonstrate clearly the difference between constant and variable particle reactivity. In the latter case, miscibility gaps are strongly asymmetric; high-χ diagram has reentrant separation area (panel d). Similar phase diagrams have been predicted for molecular solutions with DSI within the framework of Flory-like model [3, 4] as well as for binary mixtures of patchy colloids with distinct types of patches [25].