A flexible polymer chain in a critical solvent: Coil or globule?

2017

Soft Matter

Self Cite

We present an application of Flory-type theory of a flexible polymer chain dissolved in a binary mixture of solvents to theoretical description of co-nonsolvency. We show that our theoretical predictions are in good quantitative agreement with the recently published MD simulation results for the conformational behavior of a Lennard-Jones flexible chain in a binary mixture of the Lennard-Jones fluids. We show that our theory is able to describe co-nonsolvency suppression through pressure enhancement to extremely high values recently discovered in experiments and reproduced by full atomistic MD simulations. By analysing the co-solvent concentration in the internal polymer volume at different pressure values, we speculate that this phenomenon is caused by the suppression of the co-solvent preferential solvation of the polymer backbone at the rather high pressure imposed. We show that when the co-solvent-induced coil-globule transition takes place, the entropy and enthalpy contributions to the solvation free energy abruptly decrease, while the solvation free energy remains continuous.

Section: Theoretical Backgroundmentioning

confidence: 99%

Statistical description of co-nonsolvency suppression at high pressures

2017

Soft Matter

Self Cite

“…, where x is a co-solvent mole fraction in the bulk. Like in recent works 26,27,29,30 we assume for convenience that the volume of system consists of two parts: the gyration volume…”

Section: Theorymentioning

confidence: 99%

“…As well as in our previous work 29 , we assume that σ ij = (σ ii + σ jj )/2, whereas each energetic parameter ij is considered as independent. Within the present study we do not introduce the second virial coefficients as the parameters of interaction [26][27][28] , but as in the work 29 we construct the total free energy by using different expressions which are straightforwardly related to repulsive and attractive parts of interaction potentials (1). Moreover, in contrast to the works 26,28 we take into account the both solvent species explicitly.…”

Section: Theorymentioning

confidence: 99%

A statistical theory of coil-to-globule-to-coil transition of a polymer chain in a mixture of good solvents

Kalikin

et al. 2016

EPL

Self Cite

We present an off-lattice statistical model of a single polymer chain in mixed solvent media. Taking into account a polymer conformational entropy, renormalization of solvent composition near the polymer backbone, the universal intermolecular excluded volume and Van-der-Waals interactions within the self-consistent field theory the reentrant coil-to-globule-to-coil transition (co-nonsolvency) has been described in this paper. For convenience we split the system volume in two parts: the volume occupied by the polymer chain and the volume of bulk solution. Considering the equilibrium between two sub-volumes, the polymer solvation free energy as a function of radius of gyration and co-solvent mole fraction within internal polymer volume has been obtained. Minimizing the free energy of solvation with respect to its arguments, we show two qulitatively different regimes of co-nonsolvency. Namely, at sufficiently high temperature a reentrant coil-to-globule-to-coil transition proceeds smoothly. On the contrary, when the temperature drops below a certain threshold value a coil-globule transition occurs in the regime of first-order phase transition, i.e., discontinuous changes of the radius of gyration and the local co-solvent mole fraction near the polymer backbone. We show that, when the collapse of polymer chain takes place, the entropy and enthalpy contributions to the solvation free energy of globule strongly grow. From the first principles of statistical thermodynamics we confirm earlier speculations based on the MD simulations results that the co-nonsolvency is the essentially enthalpic-entropic effect and caused by enthalpy-entropy compensation.We show that the temperature dependences of solution heat capacity change due to the solvation of polymer chain are in qualitative agreement with the Differential scanning calorimetry data for PNIPAM in aqueous methanol. a) urabudkov@rambler.ru 2

“…The coil-globule transition has been considered within a simple theory of self-consistent field as well as a sophisticated field-theoretic formalism. [22][23][24][25][26][27][28][29][30][31][32][33] Most of these studies are based on the simple idea that the polymer coil shrinks lead to a collapse, when the solvent becomes poorer. It should be noted that the coil-globule transition usually occurs as first-or second-order phase transitions.…”

Section: Introductionmentioning

confidence: 99%

Communication: Polarizable polymer chain under external electric field in a dilute polymer solution

The Journal of Chemical Physics

Киселев

2015

Self Cite

We study the conformational behavior of polarizable polymer chain under an external homogeneous electric field within the Flory type self-consistent field theory. We consider the influence of electric field on the polymer coil as well as on the polymer globule. We show that when the polymer chain conformation is a coil, application of external electric field leads to its additional swelling. However, when the polymer conformation is a globule, a sufficiently strong field can induce a globule-coil transition. We show that such "field-induced" globule-coil transition at the sufficiently small monomer polarizabilities goes quite smoothly. On the contrary, when the monomer polarizability exceeds a certain threshold value, the globule-coil transition occurs as a dramatic expansion in the regime of first-order phase transition. The developed theoretical model can be applied to predicting polymer globule density change under external electric field in order to provide more efficient processes of polymer functionalization, such as sorption, dyeing, and chemical modification C 2015 AIP Publishing LLC. [http://dx