Poly volume phase transition temperature

Such behavior can be explained as follows when batch adsorption is performed above the volume phase transition temperature (1) the mechanical entrapment of protein molecules in the interfacial shell layer due to the poly(NlPAM) tentacles (octopus-like adsorption process) and... 

Zhou SQ, Wu C (1996) In-situ interferometry studies of the drying and swelling kinetics of an ultrathin poly(W-isopropylacrylamide) gel film below and above its volume phase transition temperature. Macromolecules 29 4998-5001... 

Furthermore, it is desirable that the self-oscillation can be induced around body temperature. Typically, the volume phase transition temperature of the poly(NIPAAm-co-Ru(bpy)3) gel is around 25 °C, and above that temperature the gel shrinks for both the reduced and oxidized states. As a result, it is difficult to induce self-oscillation... 

The normalized optical density variation as a function of the temperature of linear and microgel poly(NIPAM) is illustrated in Figure 9.23. The optical density increases with increasing the temperature for both linear thermally sensitive polymer and microgel particles. Such behavior is related to change in the refractive index of the polymer (ep. In fact, below the volume phase transition temperature, the polymer is highly hydrated (i.e., e + (1 4>)6p, O is the water fraction in... 

The effect of ionic strength on the adsorption of protein onto poly[NIPAM] is more complex than was expected. In fact, salinity affects not only electrostatic interactions but also the colloidal properties of such thermally sensitive particles (1) the increase in ionic strength leads to a reduction in particle size induced by lowering the volume phase transition temperature (i.e., the LCST of linear thermally sensitive polymer decreases as the salinity of the medium increases) and (2) salinity affects the degree of attractive and repulsive electrostatic interactions. As a result, the adsorption of proteins onto thermally sensitive microgel particles is generally and dramatically reduced as salinity increases, irrespective of temperature (as illustrated for P24 [Figure 9.26] adsorption onto poly(NIPAM) particles). 

SI-IMP has been used for synthesis of different types of stimuli-responsive polymer brushes that are responsive to several external stimuli, such as pFI, temperature, and ionic strength [28,58-65]. Because materials interact with their surroundings via their interfaces, the ability to fashion soft interfacial layers and tune the range, extent, and type of physicochemical interactions across interfaces is central to a variety of applications. Rahane et al. carried out sequential SI-IMP of two monomers to create bilevel poly(methacrylic acid)-Woc/c-poly(N-isopropylacrylamide) (PMAA-b-PNIPAM) block copolymer brushes that can respond to multiple stimuli [28]. They observed that each strata in the bilevel PMAA-b-PNIPAM brush retained its customary responsive characteristics PMAA being a "weak" polyelectrolyte swells as pH is increased and the thermoresponsive PNIPAM block collapses as temperature is raised through the volume phase transition temperature due to its lower critical solution temperature (LCST) behavior. As a result of ions added to make buffer solutions of various pH and because of the effect of surface confinement, the swollen-collapse transition of the PNIPAM layer occurs at a... 

The sample used to study the relationship between the volume phase transition and the frictional property is poly( /V-isopropylacrylamide) gel which shows a small discontinuous volume phase transition at 33.6 °C. The sample gel is prepared by free radical polymerization 7.8 g of re-crystallized N-iso-propylacrylamide (main constituent, Kodak), 0.133 g lV,iV -methylenebis-acrylamide (cross-linker, Bio-Rad), 240 ml tetramethylenediamine (accelerator, Bio-Rad), and 40 mg ammonium persulfate (initiator, Mallinckrodt) are dissolved in distilled water (100 ml) at 0°C. The gel mold is immersed in the pre-gel solution and then degassed for 40 min at 0°C. The temperature is raised to 20.0 °C after this treatment to initiate the gelation reaction. The sample gel thus obtained is homogeneous and transparent, at least by visual inspection. 

In spite of the constant density of the gel, the friction of the poly(N-isopropylacrylamide) gel reversibly decreases by three orders of magnitude and appears to diminish as the gel approaches a certain temperature. This phenomenon should be universal and may be observed in any gel under optimal experimental conditions of the solvent composition and the temperature because the unique parameter describing the friction is the correlation length which tends to diverge in the vicinity of the volume phase transition point of gels. The exponent v for the correlation length obtained from the frictional experiment is far from the theoretical value. It will, therefore, be important to study a poly(N-isopropylacrylamide) gel prepared at the critical isochore where the frictional property of gel may be governed by the critical density fluctuations of the gel. 

Among stimuli-responsive or thermoresponsive polymer microspheres, poly(N-isopropylacrylamidc) (PNIPA) was investigated most intensively. Cross-linked PNIPA is a thermosensitive hydrogel which undergoes a volume phase transition at its lower critical solution temperature (LCST) of around 34 °C. Several authors reported the synthesis of PNIPA microspheres [68-73]. 

D. Patterson in 1968 based on an analysis of Flory-Rehner theory. It took ten years for the phenomenon to be experimentally observed after prediction. It was found by T. Tanaka that, when a critical amount of an organic solvent was added to a water-swollen poly(acrylamide) gel, the gel collapses. Many gels of synthetic and natural polymers have been studied. Subsequent experiments showed that a volume phase transition (swelling/collapse) could also be brought about by changes in other environmental parameters such as pH, ionic strength, and temperature. 

More recently we utilized the well-known temperature-induced volume phase transition properties of poly(N-isopropylacrylamide) (PNIPAM) (73-75) to create novel CCA materials with variable sphere size and variable array periodicity (76). In water below 30°C, PNIPAM is hydrated and swollen, but when heated above its lower critical solution temperature ( 32 C) it undergoes a reversible volume phase transition to a collapsed, dehydrated state. The temperature increase causes the polymer to expel water and shrink into a more hydrophobic polymer state. 

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