Phase transition, kinetics

Polymeric micelles with selected chemistries and molecular architecture of block copolymers, such as PIPAAm-CigHgs, PIPAAm-PSt, PIPAAm-PBMA, and PIPAAm-PLA micelles, showed the same LCST and the same thermoreponsive phase transition kinetics as those for PIPAAm irrespective of the hydrophobic segment incorporation. This confirms two points (a) that hydroxyl groups or amino goups of PIPAAm termini completely react with the hydrophobic segment end groups and (b) that the block copolymers form core-shell micellar structures with hydrophobic iimer cores completely isolated from the aqueous phase. 

LIPID PHASE TRANSITION KINETICS LIPID PHASE TRANSITION KINETICS LIPID TRACER KINETICS Lipid transfer across membrane bilayers, PHOSPHOLIPID FLIP-FLOP Lipoamide,... 

LIPID PHASE TRANSITION KINETICS Membrane lipid asymmetry,... 

Most of the liquid crystalline main-chain polymers synthesized are polyesters. For the present study where isothermal phase transition kinetics studies should be performed, this was a less suitable alternative since they undergo thermally induced reactions, i. e. transesterifications, and for this reason instead polyethers were chosen. Polyethers also have other advantages like lower transition temperatures and higher solubilities. 

Experiments for investigating the lamellar-Hn transition kinetics have been performed, for example, on DOPE dispersions. The F,p-phase diagram of DOPE in excess water is depicted in Fig. 21. Figures 22, 23 show the diffraction patterns and lattice parameters at 20 °C after a pressure jump from 300 to 110 bar. Clearly, the (001) reflection of the L phase and the (10) reflection of the developing Hu phase can be identified. In this case, a two-state mechanism is observed. Interestingly, we find that successive pressure jumps lead to an acceleration of the phase transition kinetics. The half transit time decays from 8.5 s for the first pressure jump to... 

A review of these disparate but related investigations is presented beginning with a description of the use of time-resolved X-ray diffraction (TRXRD) to study lipid phase transition kinetics and mechanism in Sect. 1. It is the enormous intrinsic intensity of synchrotron radiation that enables TRXRD measurements to be made. However, this advantage brings with it the hazards of radiation damage. This critical issue is addressed in Sect. 2 along with recommendations for minimizing the effect. 

The first TRXRD study of phase transitions occurring in membranes and membrane lipid extracts was described in 1972 [45]. It is interesting to note that these time-resolved measurements were realized through a technological innovation in the form of a linear, position-sensitive proportional X-ray counter. In the past decade, considerable interest in lipid phase transition kinetics has developed in response to the emergence of new technologies, the most important of which include the synchrotron radiation source, and X-ray optics and detectors. The increased interest level is reflected in a growing literature. 

A summary of the results to date pertaining to lipid phase transition kinetics established by TRXRD is presented in Table 1. Included in the table are data obtained using synchrotron X-radiation and a sampling of data collected using conventional X-ray sources. Entries are arranged by the type of trigger used to effect the transition, which includes temperature, pressure and composition. The means by which T-jumps were implemented include fluid flow (air or liquid) around the sample or sample compartment, as well as Peltier, Joule (capacitance) and microwave heating. 

TRXRD represents an important recent innovation in the experimental study of bulk lipid phase transition kinetics. The method provides direct structural information continuously throughout the course of the transition and offers useful insights into the transition mechanism. Although several successful experiments have been performed, the full potential of the method has yet to be realized. As indicated above, many of the limitations are of a technical nature. Next, I address some of the factors which, in my opinion, warrant attention if these limitations are to be removed and the potential of the TRXRD method fully exploited. 

The formation of new phases is accompanied by the formation of new interfaces and for a complete understanding of the phase transitions kinetics, the dynamic properties of the related adsorption layers stabilising the system have to be known as well. 

Interfaces play a central role in phase transition kinetics of both models A and B. Figure A3. 3.8 shows the interfacial structure corresponding to Figure A3.3.7 (b). One can see the relationship between the interfacial width and the domain size for a late-stage configuration. The upper part of the figure demarks the interfacial... 

Expanding the knowledge of the role of phase transition kinetics in determining the existence of the different polymorphs. 

L. Chu, J. Y. K., R. Shah, and D. Weitz, Monodisperse thermoresponsive microgels with tunable volume-phase transition kinetics. Advanced Eunctional Materials, 17, 3499-3504, 2007. 

Wang, Q., Y. Zhao, et al. (2009). Thermosensitive phase transition kinetics of poly(N-isopropylacryl amide-co-acrylamide) microgel aqueous dispersions. Journal of... 

In Figure 3 the n, and nj data of SiCl and SiCN as function of temperature are presented. We observed that the transition from the smectic to the nematic state is continuous if the sample is heated slowly with about 12 K/h. If the heating rate is higher (10 K/min) the n curve shows a discontinuity at the phase transition smectic nematic.A satisfactory interpretation cannot be given at present time, but this behaviour is obviously dependent on phase transition kinetics. 

The large body of thermotropic liquid crystalline polymers is polyesters [14], some of which have been successfully commercialized. And very recently, quite a lot of thermotropic liquid crystalline polyimides have been reported [15]. In this chapter, the crystallization behavior and phase transition kinetics of thermotropic polyesters and polyimides will be discussed. 

The system evolution upon transfer of the configurative point from outside the binodal to inside its dome is considered in a special division of phase transition science, namely, phase transition kinetics. The mechanism of evolution will essentially depend on where the configurative point is in the metrtstable or in the absolutely unstable region of the state diagram (even under the same pressure when the final two-phase states will be equal). 

More realistic models for the initiation and growth of new-phase particles are considered in the literature on phase transition kinetics. 

In order to keep the size of the book within bounds a description of the interface between demixed phases has not been included and the discussion of phase transition kinetics is rather brief. Also we emphasize that the references quoted do not claim to be a complete list. If the reader prefers it, (s)he can read the book at three levels. For a general idea of depletion interactions and their implications not only in coUoid science but also in systems of biological and technological interest it is recommended to study Chap. 1. At the second level one can study 2.1, 2.2, Chap. 3, 4.1, 4.2, 4.5 and 6.1-6.3, 6.5. This material could be used for 6-8 hour senior undergraduate or junior graduate course in physical chemistry or soft matter physics. The third level covers the complete text of this monograph. 

Characterization of solution-mediated transformations in the amorphous state can give an insight into amorphous crystallization (Zhang et al. 2(X)9). The importance of the phase transition kinetics, molecular interpretations, and process implications has been emphasized in numerous studies (Cardew and Davey 1985 Davey et al. 1986, 1997a, 1997b Rodriguez-Homedo et al. 1992 Blagden et al. 1998). 

V. J. Anderson and H. N. W. Lekkekerker, Insights into phase transition kinetics from colloid science, TVatunsllO, 811-815 (2002). 

T.B. Brill, R.J. Karpowicz, "Solid Phase Transition Kinetics. The Role of... 

The general phase equilibrium diagram shown in Fig. 5 makes it possible to consider (due account being taken of the phase transition kinetics) many practical cases of separation of rigid chain polymers from solution when obtaining fibers and films. This is particularly important when studying the structural properties of the polymeric materials obtained, and in controlling their properties. 

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