Pelaez-Fernandez M, Souslov Anton, Lyon L A, Goldbart P M, Fernandez-Nieves A
School of Physics, Georgia Institute of Technology, 837 State Street, Atlanta, Georgia 30332, USA.
School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive, Atlanta, Georgia 30332, USA.
Phys Rev Lett. 2015 Mar 6;114(9):098303. doi: 10.1103/PhysRevLett.114.098303.
We study ionic microgel suspensions composed of swollen particles for various single-particle stiffnesses. We measure the osmotic pressure π of these suspensions and show that it is dominated by the contribution of free ions in solution. As this ionic osmotic pressure depends on the volume fraction of the suspension ϕ, we can determine ϕ from π, even at volume fractions so high that the microgel particles are compressed. We find that the width of the fluid-solid phase coexistence, measured using ϕ, is larger than its hard-sphere value for the stiffer microgels that we study and progressively decreases for softer microgels. For sufficiently soft microgels, the suspensions are fluidlike, irrespective of volume fraction. By calculating the dependence on ϕ of the mean volume of a microgel particle, we show that the behavior of the phase-coexistence width correlates with whether or not the microgel particles are compressed at the volume fractions corresponding to fluid-solid phase coexistence.
我们研究了由具有各种单颗粒刚度的溶胀颗粒组成的离子微凝胶悬浮液。我们测量了这些悬浮液的渗透压π，并表明它主要由溶液中自由离子的贡献主导。由于这种离子渗透压取决于悬浮液的体积分数ϕ，我们甚至可以在微凝胶颗粒被压缩的高体积分数下，根据π来确定ϕ。我们发现，使用ϕ测量的液-固共存相的宽度，对于我们研究的较硬微凝胶来说，大于其硬球值，而对于较软微凝胶则逐渐减小。对于足够软的微凝胶，悬浮液呈流体状，与体积分数无关。通过计算微凝胶颗粒平均体积对ϕ的依赖性，我们表明相共存宽度的行为与微凝胶颗粒在对应于液-固相共存的体积分数下是否被压缩相关。
