Phase Behavior of Spherical Polyelectrolyte Brush Solution in Compressed Carbon Dioxide

 Phase Behavior of Spherical Polyelectrolyte Brush Solution in Compressed Carbon Dioxide

 

Lixiao Liu, Rui Zhang*, Yu Cang, Jianchao Zhang, Tao Li, Xuhong Guo*

State Key Laboratory of Chemical Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China.

*Corresponding authors. Tel.: +86-21-64253491; E-mail: r.zhang@ecust.edu.cn guoxuhong@ecust.edu.cn

Abstract: Spherical polyelectrolyte brushes (SPB), consisting of polystyrene cores with linear macromolecules grafted onto their surfaces, were widely used as nano-reactors for synthesis of metal nanoparticles, adsorption of proteins and ideal carrier for high-efficiency catalyst, et. al. Phase equilibrium of polyelectrolyte brushes-solvent-carbon dioxide (CO₂) ternary systems were first investigated experimentally. Polystyrene-poly acrylic acid (PS-PAA) was selected as model solute, while ethanol was chosen as the organic solvent. The cloud-point pressure is the critical pressure which the one phase system changes to two-phases. It has been measured under different temperatures, the solid contents and the sizes of the brushes. The results were shown in Fig. 1. Compared with the cloud-point of different size of PS-PAA (135nm and 450nm), we know that the pressure for phase-separation of the system decreases with increasing size under same temperature. The reason maybe the bigger size of PS-PAA has longer brush chain with same core and that means it's more sensitive to the solvability of CO₂ because CO₂ is easier to enter the circle of brush chain. When the temperature increases from 273.15K to 333.15K, the pressure for cloud-point increases from 3.8MPa to 6.7MPa at PS-PAA(135nm) 1% in ethanol. It can be explained that the solubility of CO₂ in organic solvent decreases with increasing of temperature, so the higher pressure is needed to modulate the solvability of the mixed solvent. The cloud-point pressure exhibits an increasing trend with the increasing of PS-PAA solid content in ethanol. It indicates that the SPB play an important role in the phase equilibrium. It will provide us a potential method about separate and recover polyelectrolyte brush both scientific research and industry application.

Keywords: phase behavior, spherical polyelectrolyte brush, compressed CO₂;

Figure 1. Phase diagram in PS-PAA/ethanol /CO₂ system