Dipartimento di Fisica and CNR-ISC, Università di Roma La Sapienza, Piazzale A. Moro 2, I-00185 Rome, Italy.
J Chem Phys. 2011 Jul 21;135(3):034501. doi: 10.1063/1.3605703.
We study a model consisting of particles with dissimilar bonding sites ("patches"), which exhibits self-assembly into chains connected by Y-junctions, and investigate its phase behaviour by both simulations and theory. We show that, as the energy cost ε(j) of forming Y-junctions increases, the extent of the liquid-vapour coexistence region at lower temperatures and densities is reduced. The phase diagram thus acquires a characteristic "pinched" shape in which the liquid branch density decreases as the temperature is lowered. To our knowledge, this is the first model in which the predicted topological phase transition between a fluid composed of short chains and a fluid rich in Y-junctions is actually observed. Above a certain threshold for ε(j), condensation ceases to exist because the entropy gain of forming Y-junctions can no longer offset their energy cost. We also show that the properties of these phase diagrams can be understood in terms of a temperature-dependent effective valence of the patchy particles.
我们研究了一个由具有不同键合位置的粒子（“补丁”）组成的模型，该模型表现出自组装成通过 Y 型结连接的链，并通过模拟和理论研究了其相行为。我们表明，随着形成 Y 型结的能量成本 ε(j)的增加，在较低温度和密度下的液-气相共存区域的程度减小。因此，相图获得了特征性的“挤压”形状，其中液体分支密度随着温度降低而减小。据我们所知，这是第一个实际观察到由短链组成的流体和富含 Y 型结的流体之间预测的拓扑相变的模型。在 ε(j)的某个阈值以上，由于形成 Y 型结的熵增益不再能够抵消其能量成本，因此凝聚不再存在。我们还表明，这些相图的性质可以用温度相关的有缺陷粒子的有效价来理解。
