Guo Hongxia, Olvera de la Cruz Monica
Department of Material Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
J Chem Phys. 2005 Nov 1;123(17):174903. doi: 10.1063/1.2084947.
The bulk and interfacial properties of ternary mixtures with asymmetric amphiphiles (A2B8) in A2 and B2 matrices and in A2 and B10 matrices are investigated by the dissipative particle dynamics type of molecular-dynamics simulations. The monomer concentrations of A2B8(phiA2B8) studied are below the critical micelle concentration (phiA2B8(cmc)) for the formation of micelles in the presence of an adsorbed amphiphilic monolayer at the interface. Macrophase separation from the mixed phase to the segregated state with A-rich and B-rich coexisting phases and the segregation of A2B8 at the interface are thermodynamically gradual but are accompanied by a pronounced stretching and orientation of the constituent chains. The segregation of A2B8 at the interface broadens the interfacial region and reduces the interfacial tension. The chain conformation of the asymmetric amphiphilic molecules and the interfacial properties are dominated by the majority block in the amphiphilic chain and dependent on the composition of the matrix in contact with the majority block. In the A2 and B2 matrices, the B8 blocks in A2B8 chains at the interface resemble a wet brush swollen by short B2 chains. Swelling is responsible for the pronounced stretching and orienting of the amphiphilic chains and the reduced interfacial amphiphile enrichment. At the same interfacial amphiphile excess, however, swollen amphiphiles are more efficient in reducing the interfacial tension than nonswollen amphiphiles.
通过分子动力学模拟中的耗散粒子动力学类型，研究了在A2和B2基质以及A2和B10基质中含有不对称两亲物（A2B8）的三元混合物的体相和界面性质。所研究的A2B8的单体浓度（phiA2B8）低于在界面处存在吸附两亲单层时形成胶束的临界胶束浓度（phiA2B8(cmc)）。从混合相到富含A和富含B的共存相的分相状态的宏观相分离以及A2B8在界面处的偏析在热力学上是渐进的，但伴随着组成链的明显拉伸和取向。A2B8在界面处的偏析拓宽了界面区域并降低了界面张力。不对称两亲分子的链构象和界面性质由两亲链中的多数嵌段主导，并取决于与多数嵌段接触的基质的组成。在A2和B2基质中，界面处A2B8链中的B8嵌段类似于被短B2链溶胀的湿刷。溶胀导致两亲链的明显拉伸和取向以及界面两亲物富集的减少。然而，在相同的界面两亲物过量情况下，溶胀的两亲物比未溶胀的两亲物在降低界面张力方面更有效。
