Polymer collapse

The nature of the solvent influences both the structure of the polymer in solution and its dynamics. In good solvents the polymer adopts an expanded configuration and in poor solvents it takes on a compact form. If the polymer solution is suddenly changed from good to poor solvent conditions, polymer collapse from the expanded to compact forms will occur [78], A number of models have been suggested for the mechanism of the collapse [79-82], Hydrodynamic interactions are expected to play an important part in the dynamics of the collapse and we show how MPC simulations have been used to investigate this problem. Hybrid MD-MPC simulations of the collapse dynamics have been carried out for systems where bead-solvent interactions are either explicitly included [83] or accounted for implicitly in the multiparticle collision events [84, 85]. 

The effect of hydrodynamic interactions on polymer collapse has also been studied using MPC dynamics, where the polymer beads are included in the multiparticle collision step [28, 84]. Hydrodynamic interactions can be turned off by replacing multiparticle collisions in the cells by sampling of the particle velocities from a Boltzmann distribution. Collapse occurs more rapidly in the... 

N. Kikuchi, A. Gent, and J. M. Yeomans, Polymer collapse in the presence of hydrodynamic... 

Therefore, the ring polymer collapses into a single point Ri. This is the classical limit (p=l). In this case, the classical description is reasonable. Light nuclei, such as protons have relatively longer thermal wave lengths than those for heavier nuclei. Therefore, it is desirable to describe them quantum mechanically, especially at low temperatures. Usually, a large but limited p is enough to describe such systems. [9,78,80]... 

Solvent quality decreases as temperature is lowered, leading to polymer collapse and possible phase separation (the lower part of Fig. 5.1). In... 

The overall conformation of the chain is determined by the relative value of Ni and N. If N the repulsive polyelectrolyte interaction dominates and the chain behaves more like a usual polyelectrolyte. The necessary net charge to swell, and thus redissolve the polyampholyte, is therefore ... 

Lastly, we have determined that in addition to polymer structure, the addition order of materials, such as polymer, surfactant and salt, to a formulation affects the compositional range of coacervate formation and the coacervation mechanism. Depending on the flexibility of the polymer structure, the mechanisms of coacervation in the presence of added electrolyte can vary. Poly (4-vinyl pyridine)-LAS-NaCl systems show a polymer collapse mechanism with the formation of a super-salt when salt and polymer are pre-mbced. However, for the stiff cellulosic polymers, the pre-mixing of salt and polymer before surfactant addition enhances micelle-bridging without complete polymer collapse. Also, the addition... 

As mentioned earlier, a beautiful theory of polymer collapse in a solvent was provided long ago by Paul Flory in a theoiy currently known as the Flory-Huggins theory. The present understanding of this phenomenon (including that of protein folding) has been developed around this theory by modifying the same. We now discuss the theory. 

Furthermore, polymers such as PDMAEMA combine a weak polybase character with thermoresponsive properties at high pH and low temperatures PDMAEMA is not ionized, but, nevertheless, is soluble in water. An increase in temperature, however, leads to an increase in the hydrophobicity of the monomers and, at T > LCST, the unionized polymers collapse, lose solubility, and precipitate from aqueous solution [47]. 

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